This is gdb.info, produced by makeinfo version 6.7 from gdb.texinfo. Copyright (C) 1988-2022 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software" and "Free Software Needs Free Documentation", with the Front-Cover Texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: "You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom." INFO-DIR-SECTION Software development START-INFO-DIR-ENTRY * Gdb: (gdb). The GNU debugger. * gdbserver: (gdb) Server. The GNU debugging server. END-INFO-DIR-ENTRY This file documents the GNU debugger GDB. This is the Tenth Edition, of 'Debugging with GDB: the GNU Source-Level Debugger' for GDB (GDB) Version 12.1. Copyright (C) 1988-2022 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software" and "Free Software Needs Free Documentation", with the Front-Cover Texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: "You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom."  File: gdb.info, Node: AVR, Next: CRIS, Prev: PowerPC Embedded, Up: Embedded Processors 21.3.9 Atmel AVR ---------------- When configured for debugging the Atmel AVR, GDB supports the following AVR-specific commands: 'info io_registers' This command displays information about the AVR I/O registers. For each register, GDB prints its number and value.  File: gdb.info, Node: CRIS, Next: Super-H, Prev: AVR, Up: Embedded Processors 21.3.10 CRIS ------------ When configured for debugging CRIS, GDB provides the following CRIS-specific commands: 'set cris-version VER' Set the current CRIS version to VER, either '10' or '32'. The CRIS version affects register names and sizes. This command is useful in case autodetection of the CRIS version fails. 'show cris-version' Show the current CRIS version. 'set cris-dwarf2-cfi' Set the usage of DWARF-2 CFI for CRIS debugging. The default is 'on'. Change to 'off' when using 'gcc-cris' whose version is below 'R59'. 'show cris-dwarf2-cfi' Show the current state of using DWARF-2 CFI. 'set cris-mode MODE' Set the current CRIS mode to MODE. It should only be changed when debugging in guru mode, in which case it should be set to 'guru' (the default is 'normal'). 'show cris-mode' Show the current CRIS mode.  File: gdb.info, Node: Super-H, Prev: CRIS, Up: Embedded Processors 21.3.11 Renesas Super-H ----------------------- For the Renesas Super-H processor, GDB provides these commands: 'set sh calling-convention CONVENTION' Set the calling-convention used when calling functions from GDB. Allowed values are 'gcc', which is the default setting, and 'renesas'. With the 'gcc' setting, functions are called using the GCC calling convention. If the DWARF-2 information of the called function specifies that the function follows the Renesas calling convention, the function is called using the Renesas calling convention. If the calling convention is set to 'renesas', the Renesas calling convention is always used, regardless of the DWARF-2 information. This can be used to override the default of 'gcc' if debug information is missing, or the compiler does not emit the DWARF-2 calling convention entry for a function. 'show sh calling-convention' Show the current calling convention setting.  File: gdb.info, Node: Architectures, Prev: Embedded Processors, Up: Configurations 21.4 Architectures ================== This section describes characteristics of architectures that affect all uses of GDB with the architecture, both native and cross. * Menu: * AArch64:: * i386:: * Alpha:: * MIPS:: * HPPA:: HP PA architecture * PowerPC:: * Nios II:: * Sparc64:: * S12Z::  File: gdb.info, Node: AArch64, Next: i386, Up: Architectures 21.4.1 AArch64 -------------- When GDB is debugging the AArch64 architecture, it provides the following special commands: 'set debug aarch64' This command determines whether AArch64 architecture-specific debugging messages are to be displayed. 'show debug aarch64' Show whether AArch64 debugging messages are displayed. 21.4.1.1 AArch64 SVE. ..................... When GDB is debugging the AArch64 architecture, if the Scalable Vector Extension (SVE) is present, then GDB will provide the vector registers '$z0' through '$z31', vector predicate registers '$p0' through '$p15', and the '$ffr' register. In addition, the pseudo register '$vg' will be provided. This is the vector granule for the current thread and represents the number of 64-bit chunks in an SVE 'z' register. If the vector length changes, then the '$vg' register will be updated, but the lengths of the 'z' and 'p' registers will not change. This is a known limitation of GDB and does not affect the execution of the target process. 21.4.1.2 AArch64 Pointer Authentication. ........................................ When GDB is debugging the AArch64 architecture, and the program is using the v8.3-A feature Pointer Authentication (PAC), then whenever the link register '$lr' is pointing to an PAC function its value will be masked. When GDB prints a backtrace, any addresses that required unmasking will be postfixed with the marker [PAC]. When using the MI, this is printed as part of the 'addr_flags' field. 21.4.1.3 AArch64 Memory Tagging Extension. .......................................... When GDB is debugging the AArch64 architecture, the program is using the v8.5-A feature Memory Tagging Extension (MTE) and there is support in the kernel for MTE, GDB will make memory tagging functionality available for inspection and editing of logical and allocation tags. *Note Memory Tagging::. To aid debugging, GDB will output additional information when SIGSEGV signals are generated as a result of memory tag failures. If the tag violation is synchronous, the following will be shown: Program received signal SIGSEGV, Segmentation fault Memory tag violation while accessing address 0x0500fffff7ff8000 Allocation tag 0x1 Logical tag 0x5. If the tag violation is asynchronous, the fault address is not available. In this case GDB will show the following: Program received signal SIGSEGV, Segmentation fault Memory tag violation Fault address unavailable. A special register, 'tag_ctl', is made available through the 'org.gnu.gdb.aarch64.mte' feature. This register exposes some options that can be controlled at runtime and emulates the 'prctl' option 'PR_SET_TAGGED_ADDR_CTRL'. For further information, see the documentation in the Linux kernel.  File: gdb.info, Node: i386, Next: Alpha, Prev: AArch64, Up: Architectures 21.4.2 x86 Architecture-specific Issues --------------------------------------- 'set struct-convention MODE' Set the convention used by the inferior to return 'struct's and 'union's from functions to MODE. Possible values of MODE are '"pcc"', '"reg"', and '"default"' (the default). '"default"' or '"pcc"' means that 'struct's are returned on the stack, while '"reg"' means that a 'struct' or a 'union' whose size is 1, 2, 4, or 8 bytes will be returned in a register. 'show struct-convention' Show the current setting of the convention to return 'struct's from functions. 21.4.2.1 Intel "Memory Protection Extensions" (MPX). .................................................... Memory Protection Extension (MPX) adds the bound registers 'BND0' (1) through 'BND3'. Bound registers store a pair of 64-bit values which are the lower bound and upper bound. Bounds are effective addresses or memory locations. The upper bounds are architecturally represented in 1's complement form. A bound having lower bound = 0, and upper bound = 0 (1's complement of all bits set) will allow access to the entire address space. 'BND0' through 'BND3' are represented in GDB as 'bnd0raw' through 'bnd3raw'. Pseudo registers 'bnd0' through 'bnd3' display the upper bound performing the complement of one operation on the upper bound value, i.e. when upper bound in 'bnd0raw' is 0 in the GDB 'bnd0' it will be '0xfff...'. In this sense it can also be noted that the upper bounds are inclusive. As an example, assume that the register BND0 holds bounds for a pointer having access allowed for the range between 0x32 and 0x71. The values present on bnd0raw and bnd registers are presented as follows: bnd0raw = {0x32, 0xffffffff8e} bnd0 = {lbound = 0x32, ubound = 0x71} : size 64 This way the raw value can be accessed via bnd0raw...bnd3raw. Any change on bnd0...bnd3 or bnd0raw...bnd3raw is reflect on its counterpart. When the bnd0...bnd3 registers are displayed via Python, the display includes the memory size, in bits, accessible to the pointer. Bounds can also be stored in bounds tables, which are stored in application memory. These tables store bounds for pointers by specifying the bounds pointer's value along with its bounds. Evaluating and changing bounds located in bound tables is therefore interesting while investigating bugs on MPX context. GDB provides commands for this purpose: 'show mpx bound POINTER' Display bounds of the given POINTER. 'set mpx bound POINTER, LBOUND, UBOUND' Set the bounds of a pointer in the bound table. This command takes three parameters: POINTER is the pointers whose bounds are to be changed, LBOUND and UBOUND are new values for lower and upper bounds respectively. When you call an inferior function on an Intel MPX enabled program, GDB sets the inferior's bound registers to the init (disabled) state before calling the function. As a consequence, bounds checks for the pointer arguments passed to the function will always pass. This is necessary because when you call an inferior function, the program is usually in the middle of the execution of other function. Since at that point bound registers are in an arbitrary state, not clearing them would lead to random bound violations in the called function. You can still examine the influence of the bound registers on the execution of the called function by stopping the execution of the called function at its prologue, setting bound registers, and continuing the execution. For example: $ break *upper Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47. $ print upper (a, b, c, d, 1) Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48).... $ print $bnd0 {lbound = 0x0, ubound = ffffffff} : size -1 At this last step the value of bnd0 can be changed for investigation of bound violations caused along the execution of the call. In order to know how to set the bound registers or bound table for the call consult the ABI. ---------- Footnotes ---------- (1) The register named with capital letters represent the architecture registers.  File: gdb.info, Node: Alpha, Next: MIPS, Prev: i386, Up: Architectures 21.4.3 Alpha ------------ See the following section.  File: gdb.info, Node: MIPS, Next: HPPA, Prev: Alpha, Up: Architectures 21.4.4 MIPS ----------- Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires GDB to search backward in the object code to find the beginning of a function. To improve response time (especially for embedded applications, where GDB may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands: 'set heuristic-fence-post LIMIT' Restrict GDB to examining at most LIMIT bytes in its search for the beginning of a function. A value of 0 (the default) means there is no limit. However, except for 0, the larger the limit the more bytes 'heuristic-fence-post' must search and therefore the longer it takes to run. You should only need to use this command when debugging a stripped executable. 'show heuristic-fence-post' Display the current limit. These commands are available _only_ when GDB is configured for debugging programs on Alpha or MIPS processors. Several MIPS-specific commands are available when debugging MIPS programs: 'set mips abi ARG' Tell GDB which MIPS ABI is used by the inferior. Possible values of ARG are: 'auto' The default ABI associated with the current binary (this is the default). 'o32' 'o64' 'n32' 'n64' 'eabi32' 'eabi64' 'show mips abi' Show the MIPS ABI used by GDB to debug the inferior. 'set mips compression ARG' Tell GDB which MIPS compressed ISA (Instruction Set Architecture) encoding is used by the inferior. GDB uses this for code disassembly and other internal interpretation purposes. This setting is only referred to when no executable has been associated with the debugging session or the executable does not provide information about the encoding it uses. Otherwise this setting is automatically updated from information provided by the executable. Possible values of ARG are 'mips16' and 'micromips'. The default compressed ISA encoding is 'mips16', as executables containing MIPS16 code frequently are not identified as such. This setting is "sticky"; that is, it retains its value across debugging sessions until reset either explicitly with this command or implicitly from an executable. The compiler and/or assembler typically add symbol table annotations to identify functions compiled for the MIPS16 or microMIPS ISAs. If these function-scope annotations are present, GDB uses them in preference to the global compressed ISA encoding setting. 'show mips compression' Show the MIPS compressed ISA encoding used by GDB to debug the inferior. 'set mipsfpu' 'show mipsfpu' *Note set mipsfpu: MIPS Embedded. 'set mips mask-address ARG' This command determines whether the most-significant 32 bits of 64-bit MIPS addresses are masked off. The argument ARG can be 'on', 'off', or 'auto'. The latter is the default setting, which lets GDB determine the correct value. 'show mips mask-address' Show whether the upper 32 bits of MIPS addresses are masked off or not. 'set remote-mips64-transfers-32bit-regs' This command controls compatibility with 64-bit MIPS targets that transfer data in 32-bit quantities. If you have an old MIPS 64 target that transfers 32 bits for some registers, like SR and FSR, and 64 bits for other registers, set this option to 'on'. 'show remote-mips64-transfers-32bit-regs' Show the current setting of compatibility with older MIPS 64 targets. 'set debug mips' This command turns on and off debugging messages for the MIPS-specific target code in GDB. 'show debug mips' Show the current setting of MIPS debugging messages.  File: gdb.info, Node: HPPA, Next: PowerPC, Prev: MIPS, Up: Architectures 21.4.5 HPPA ----------- When GDB is debugging the HP PA architecture, it provides the following special commands: 'set debug hppa' This command determines whether HPPA architecture-specific debugging messages are to be displayed. 'show debug hppa' Show whether HPPA debugging messages are displayed. 'maint print unwind ADDRESS' This command displays the contents of the unwind table entry at the given ADDRESS.  File: gdb.info, Node: PowerPC, Next: Nios II, Prev: HPPA, Up: Architectures 21.4.6 PowerPC -------------- When GDB is debugging the PowerPC architecture, it provides a set of pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point numbers stored in the floating point registers. These values must be stored in two consecutive registers, always starting at an even register like 'f0' or 'f2'. The pseudo-registers go from '$dl0' through '$dl15', and are formed by joining the even/odd register pairs 'f0' and 'f1' for '$dl0', 'f2' and 'f3' for '$dl1' and so on. For POWER7 processors, GDB provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers ('f32' through 'f63').  File: gdb.info, Node: Nios II, Next: Sparc64, Prev: PowerPC, Up: Architectures 21.4.7 Nios II -------------- When GDB is debugging the Nios II architecture, it provides the following special commands: 'set debug nios2' This command turns on and off debugging messages for the Nios II target code in GDB. 'show debug nios2' Show the current setting of Nios II debugging messages.  File: gdb.info, Node: Sparc64, Next: S12Z, Prev: Nios II, Up: Architectures 21.4.8 Sparc64 -------------- 21.4.8.1 ADI Support .................... The M7 processor supports an Application Data Integrity (ADI) feature that detects invalid data accesses. When software allocates memory and enables ADI on the allocated memory, it chooses a 4-bit version number, sets the version in the upper 4 bits of the 64-bit pointer to that data, and stores the 4-bit version in every cacheline of that data. Hardware saves the latter in spare bits in the cache and memory hierarchy. On each load and store, the processor compares the upper 4 VA (virtual address) bits to the cacheline's version. If there is a mismatch, the processor generates a version mismatch trap which can be either precise or disrupting. The trap is an error condition which the kernel delivers to the process as a SIGSEGV signal. Note that only 64-bit applications can use ADI and need to be built with ADI-enabled. Values of the ADI version tags, which are in granularity of a cacheline (64 bytes), can be viewed or modified. 'adi (examine | x) [ / N ] ADDR' The 'adi examine' command displays the value of one ADI version tag per cacheline. N is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to display. ADDR is the address in user address space where you want GDB to begin displaying the ADI version tags. Below is an example of displaying ADI versions of variable "shmaddr". (gdb) adi x/100 shmaddr 0xfff800010002c000: 0 0 'adi (assign | a) [ / N ] ADDR = TAG' The 'adi assign' command is used to assign new ADI version tag to an address. N is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to modify. ADDR is the address in user address space where you want GDB to begin modifying the ADI version tags. TAG is the new ADI version tag. For example, do the following to modify then verify ADI versions of variable "shmaddr": (gdb) adi a/100 shmaddr = 7 (gdb) adi x/100 shmaddr 0xfff800010002c000: 7 7  File: gdb.info, Node: S12Z, Prev: Sparc64, Up: Architectures 21.4.9 S12Z ----------- When GDB is debugging the S12Z architecture, it provides the following special command: 'maint info bdccsr' This command displays the current value of the microprocessor's BDCCSR register.  File: gdb.info, Node: Controlling GDB, Next: Extending GDB, Prev: Configurations, Up: Top 22 Controlling GDB ****************** You can alter the way GDB interacts with you by using the 'set' command. For commands controlling how GDB displays data, see *note Print Settings: Print Settings. Other settings are described here. * Menu: * Prompt:: Prompt * Editing:: Command editing * Command History:: Command history * Screen Size:: Screen size * Output Styling:: Output styling * Numbers:: Numbers * ABI:: Configuring the current ABI * Auto-loading:: Automatically loading associated files * Messages/Warnings:: Optional warnings and messages * Debugging Output:: Optional messages about internal happenings * Other Misc Settings:: Other Miscellaneous Settings  File: gdb.info, Node: Prompt, Next: Editing, Up: Controlling GDB 22.1 Prompt =========== GDB indicates its readiness to read a command by printing a string called the "prompt". This string is normally '(gdb)'. You can change the prompt string with the 'set prompt' command. For instance, when debugging GDB with GDB, it is useful to change the prompt in one of the GDB sessions so that you can always tell which one you are talking to. _Note:_ 'set prompt' does not add a space for you after the prompt you set. This allows you to set a prompt which ends in a space or a prompt that does not. 'set prompt NEWPROMPT' Directs GDB to use NEWPROMPT as its prompt string henceforth. 'show prompt' Prints a line of the form: 'Gdb's prompt is: YOUR-PROMPT' Versions of GDB that ship with Python scripting enabled have prompt extensions. The commands for interacting with these extensions are: 'set extended-prompt PROMPT' Set an extended prompt that allows for substitutions. *Note gdb.prompt::, for a list of escape sequences that can be used for substitution. Any escape sequences specified as part of the prompt string are replaced with the corresponding strings each time the prompt is displayed. For example: set extended-prompt Current working directory: \w (gdb) Note that when an extended-prompt is set, it takes control of the PROMPT_HOOK hook. *Note prompt_hook::, for further information. 'show extended-prompt' Prints the extended prompt. Any escape sequences specified as part of the prompt string with 'set extended-prompt', are replaced with the corresponding strings each time the prompt is displayed.  File: gdb.info, Node: Editing, Next: Command History, Prev: Prompt, Up: Controlling GDB 22.2 Command Editing ==================== GDB reads its input commands via the "Readline" interface. This GNU library provides consistent behavior for programs which provide a command line interface to the user. Advantages are GNU Emacs-style or "vi"-style inline editing of commands, 'csh'-like history substitution, and a storage and recall of command history across debugging sessions. You may control the behavior of command line editing in GDB with the command 'set'. 'set editing' 'set editing on' Enable command line editing (enabled by default). 'set editing off' Disable command line editing. 'show editing' Show whether command line editing is enabled. *Note Command Line Editing::, for more details about the Readline interface. Users unfamiliar with GNU Emacs or 'vi' are encouraged to read that chapter. GDB sets the Readline application name to 'gdb'. This is useful for conditions in '.inputrc'. GDB defines a bindable Readline command, 'operate-and-get-next'. This is bound to 'C-o' by default. This command accepts the current line for execution and fetches the next line relative to the current line from the history for editing. Any argument is ignored.  File: gdb.info, Node: Command History, Next: Screen Size, Prev: Editing, Up: Controlling GDB 22.3 Command History ==================== GDB can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the GDB command history facility. GDB uses the GNU History library, a part of the Readline package, to provide the history facility. *Note Using History Interactively::, for the detailed description of the History library. To issue a command to GDB without affecting certain aspects of the state which is seen by users, prefix it with 'server ' (*note Server Prefix::). This means that this command will not affect the command history, nor will it affect GDB's notion of which command to repeat if is pressed on a line by itself. The server prefix does not affect the recording of values into the value history; to print a value without recording it into the value history, use the 'output' command instead of the 'print' command. Here is the description of GDB commands related to command history. 'set history filename [FNAME]' Set the name of the GDB command history file to FNAME. This is the file where GDB reads an initial command history list, and where it writes the command history from this session when it exits. You can access this list through history expansion or through the history command editing characters listed below. This file defaults to the value of the environment variable 'GDBHISTFILE', or to './.gdb_history' ('./_gdb_history' on MS-DOS) if this variable is not set. The 'GDBHISTFILE' environment variable is read after processing any GDB initialization files (*note Startup::) and after processing any commands passed using command line options (for example, '-ex'). If the FNAME argument is not given, or if the 'GDBHISTFILE' is the empty string then GDB will neither try to load an existing history file, nor will it try to save the history on exit. 'set history save' 'set history save on' Record command history in a file, whose name may be specified with the 'set history filename' command. By default, this option is disabled. The command history will be recorded when GDB exits. If 'set history filename' is set to the empty string then history saving is disabled, even when 'set history save' is 'on'. 'set history save off' Don't record the command history into the file specified by 'set history filename' when GDB exits. 'set history size SIZE' 'set history size unlimited' Set the number of commands which GDB keeps in its history list. This defaults to the value of the environment variable 'GDBHISTSIZE', or to 256 if this variable is not set. Non-numeric values of 'GDBHISTSIZE' are ignored. If SIZE is 'unlimited' or if 'GDBHISTSIZE' is either a negative number or the empty string, then the number of commands GDB keeps in the history list is unlimited. The 'GDBHISTSIZE' environment variable is read after processing any GDB initialization files (*note Startup::) and after processing any commands passed using command line options (for example, '-ex'). 'set history remove-duplicates COUNT' 'set history remove-duplicates unlimited' Control the removal of duplicate history entries in the command history list. If COUNT is non-zero, GDB will look back at the last COUNT history entries and remove the first entry that is a duplicate of the current entry being added to the command history list. If COUNT is 'unlimited' then this lookbehind is unbounded. If COUNT is 0, then removal of duplicate history entries is disabled. Only history entries added during the current session are considered for removal. This option is set to 0 by default. History expansion assigns special meaning to the character '!'. *Note Event Designators::, for more details. Since '!' is also the logical not operator in C, history expansion is off by default. If you decide to enable history expansion with the 'set history expansion on' command, you may sometimes need to follow '!' (when it is used as logical not, in an expression) with a space or a tab to prevent it from being expanded. The readline history facilities do not attempt substitution on the strings '!=' and '!(', even when history expansion is enabled. The commands to control history expansion are: 'set history expansion on' 'set history expansion' Enable history expansion. History expansion is off by default. 'set history expansion off' Disable history expansion. 'show history' 'show history filename' 'show history save' 'show history size' 'show history expansion' These commands display the state of the GDB history parameters. 'show history' by itself displays all four states. 'show commands' Display the last ten commands in the command history. 'show commands N' Print ten commands centered on command number N. 'show commands +' Print ten commands just after the commands last printed.  File: gdb.info, Node: Screen Size, Next: Output Styling, Prev: Command History, Up: Controlling GDB 22.4 Screen Size ================ Certain commands to GDB may produce large amounts of information output to the screen. To help you read all of it, GDB pauses and asks you for input at the end of each page of output. Type when you want to see one more page of output, 'q' to discard the remaining output, or 'c' to continue without paging for the rest of the current command. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, GDB tries to break the line at a readable place, rather than simply letting it overflow onto the following line. Normally GDB knows the size of the screen from the terminal driver software. For example, on Unix GDB uses the termcap data base together with the value of the 'TERM' environment variable and the 'stty rows' and 'stty cols' settings. If this is not correct, you can override it with the 'set height' and 'set width' commands: 'set height LPP' 'set height unlimited' 'show height' 'set width CPL' 'set width unlimited' 'show width' These 'set' commands specify a screen height of LPP lines and a screen width of CPL characters. The associated 'show' commands display the current settings. If you specify a height of either 'unlimited' or zero lines, GDB does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer. Likewise, you can specify 'set width unlimited' or 'set width 0' to prevent GDB from wrapping its output. 'set pagination on' 'set pagination off' Turn the output pagination on or off; the default is on. Turning pagination off is the alternative to 'set height unlimited'. Note that running GDB with the '--batch' option (*note -batch: Mode Options.) also automatically disables pagination. 'show pagination' Show the current pagination mode.  File: gdb.info, Node: Output Styling, Next: Numbers, Prev: Screen Size, Up: Controlling GDB 22.5 Output Styling =================== GDB can style its output on a capable terminal. This is enabled by default on most systems, but disabled by default when in batch mode (*note Mode Options::). Various style settings are available; and styles can also be disabled entirely. 'set style enabled 'on|off'' Enable or disable all styling. The default is host-dependent, with most hosts defaulting to 'on'. 'show style enabled' Show the current state of styling. 'set style sources 'on|off'' Enable or disable source code styling. This affects whether source code, such as the output of the 'list' command, is styled. The default is 'on'. Note that source styling only works if styling in general is enabled, and if a source highlighting library is available to GDB. There are two ways that highlighting can be done. First, if GDB was linked with the GNU Source Highlight library, then it is used. Otherwise, if GDB was configured with Python scripting support, and if the Python Pygments package is available, then it will be used. 'show style sources' Show the current state of source code styling. 'set style disassembler enabled 'on|off'' Enable or disable disassembler styling. This affects whether disassembler output, such as the output of the 'disassemble' command, is styled. Disassembler styling only works if styling in general is enabled (with 'set style enabled on'), and if a source highlighting library is available to GDB. To highlight disassembler output, GDB must be compiled with Python support, and the Python Pygments package must be available. If these requirements are not met then GDB will not highlight disassembler output, even when this option is 'on'. 'show style disassembler enabled' Show the current state of disassembler styling. Subcommands of 'set style' control specific forms of styling. These subcommands all follow the same pattern: each style-able object can be styled with a foreground color, a background color, and an intensity. For example, the style of file names can be controlled using the 'set style filename' group of commands: 'set style filename background COLOR' Set the background to COLOR. Valid colors are 'none' (meaning the terminal's default color), 'black', 'red', 'green', 'yellow', 'blue', 'magenta', 'cyan', and'white'. 'set style filename foreground COLOR' Set the foreground to COLOR. Valid colors are 'none' (meaning the terminal's default color), 'black', 'red', 'green', 'yellow', 'blue', 'magenta', 'cyan', and'white'. 'set style filename intensity VALUE' Set the intensity to VALUE. Valid intensities are 'normal' (the default), 'bold', and 'dim'. The 'show style' command and its subcommands are styling a style name in their output using its own style. So, use 'show style' to see the complete list of styles, their characteristics and the visual aspect of each style. The style-able objects are: 'filename' Control the styling of file names. By default, this style's foreground color is green. 'function' Control the styling of function names. These are managed with the 'set style function' family of commands. By default, this style's foreground color is yellow. 'variable' Control the styling of variable names. These are managed with the 'set style variable' family of commands. By default, this style's foreground color is cyan. 'address' Control the styling of addresses. These are managed with the 'set style address' family of commands. By default, this style's foreground color is blue. 'version' Control the styling of GDB's version number text. By default, this style's foreground color is magenta and it has bold intensity. The version number is displayed in two places, the output of 'show version', and when GDB starts up. In order to control how GDB styles the version number at startup, add the 'set style version' family of commands to the early initialization command file (*note Initialization Files::). 'title' Control the styling of titles. These are managed with the 'set style title' family of commands. By default, this style's intensity is bold. Commands are using the title style to improve the readability of large output. For example, the commands 'apropos' and 'help' are using the title style for the command names. 'highlight' Control the styling of highlightings. These are managed with the 'set style highlight' family of commands. By default, this style's foreground color is red. Commands are using the highlight style to draw the user attention to some specific parts of their output. For example, the command 'apropos -v REGEXP' uses the highlight style to mark the documentation parts matching REGEXP. 'tui-border' Control the styling of the TUI border. Note that, unlike other styling options, only the color of the border can be controlled via 'set style'. This was done for compatibility reasons, as TUI controls to set the border's intensity predated the addition of general styling to GDB. *Note TUI Configuration::. 'tui-active-border' Control the styling of the active TUI border; that is, the TUI window that has the focus.  File: gdb.info, Node: Numbers, Next: ABI, Prev: Output Styling, Up: Controlling GDB 22.6 Numbers ============ You can always enter numbers in octal, decimal, or hexadecimal in GDB by the usual conventions: octal numbers begin with '0', decimal numbers end with '.', and hexadecimal numbers begin with '0x'. Numbers that neither begin with '0' or '0x', nor end with a '.' are, by default, entered in base 10; likewise, the default display for numbers--when no particular format is specified--is base 10. You can change the default base for both input and output with the commands described below. 'set input-radix BASE' Set the default base for numeric input. Supported choices for BASE are decimal 8, 10, or 16. The base must itself be specified either unambiguously or using the current input radix; for example, any of set input-radix 012 set input-radix 10. set input-radix 0xa sets the input base to decimal. On the other hand, 'set input-radix 10' leaves the input radix unchanged, no matter what it was, since '10', being without any leading or trailing signs of its base, is interpreted in the current radix. Thus, if the current radix is 16, '10' is interpreted in hex, i.e. as 16 decimal, which doesn't change the radix. 'set output-radix BASE' Set the default base for numeric display. Supported choices for BASE are decimal 8, 10, or 16. The base must itself be specified either unambiguously or using the current input radix. 'show input-radix' Display the current default base for numeric input. 'show output-radix' Display the current default base for numeric display. 'set radix [BASE]' 'show radix' These commands set and show the default base for both input and output of numbers. 'set radix' sets the radix of input and output to the same base; without an argument, it resets the radix back to its default value of 10.  File: gdb.info, Node: ABI, Next: Auto-loading, Prev: Numbers, Up: Controlling GDB 22.7 Configuring the Current ABI ================================ GDB can determine the "ABI" (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage GDB's view of the current ABI. One GDB configuration can debug binaries for multiple operating system targets, either via remote debugging or native emulation. GDB will autodetect the "OS ABI" (Operating System ABI) in use, but you can override its conclusion using the 'set osabi' command. One example where this is useful is in debugging of binaries which use an alternate C library (e.g. UCLIBC for GNU/Linux) which does not have the same identifying marks that the standard C library for your platform provides. When GDB is debugging the AArch64 architecture, it provides a "Newlib" OS ABI. This is useful for handling 'setjmp' and 'longjmp' when debugging binaries that use the NEWLIB C library. The "Newlib" OS ABI can be selected by 'set osabi Newlib'. 'show osabi' Show the OS ABI currently in use. 'set osabi' With no argument, show the list of registered available OS ABI's. 'set osabi ABI' Set the current OS ABI to ABI. Generally, the way that an argument of type 'float' is passed to a function depends on whether the function is prototyped. For a prototyped (i.e. ANSI/ISO style) function, 'float' arguments are passed unchanged, according to the architecture's convention for 'float'. For unprototyped (i.e. K&R style) functions, 'float' arguments are first promoted to type 'double' and then passed. Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If GDB calls a function that is not marked as prototyped, it consults 'set coerce-float-to-double'. 'set coerce-float-to-double' 'set coerce-float-to-double on' Arguments of type 'float' will be promoted to 'double' when passed to an unprototyped function. This is the default setting. 'set coerce-float-to-double off' Arguments of type 'float' will be passed directly to unprototyped functions. 'show coerce-float-to-double' Show the current setting of promoting 'float' to 'double'. GDB needs to know the ABI used for your program's C++ objects. The correct C++ ABI depends on which C++ compiler was used to build your application. GDB only fully supports programs with a single C++ ABI; if your program contains code using multiple C++ ABI's or if GDB can not identify your program's ABI correctly, you can tell GDB which ABI to use. Currently supported ABI's include "gnu-v2", for 'g++' versions before 3.0, "gnu-v3", for 'g++' versions 3.0 and later, and "hpaCC" for the HP ANSI C++ compiler. Other C++ compilers may use the "gnu-v2" or "gnu-v3" ABI's as well. The default setting is "auto". 'show cp-abi' Show the C++ ABI currently in use. 'set cp-abi' With no argument, show the list of supported C++ ABI's. 'set cp-abi ABI' 'set cp-abi auto' Set the current C++ ABI to ABI, or return to automatic detection.  File: gdb.info, Node: Auto-loading, Next: Messages/Warnings, Prev: ABI, Up: Controlling GDB 22.8 Automatically loading associated files =========================================== GDB sometimes reads files with commands and settings automatically, without being explicitly told so by the user. We call this feature "auto-loading". While auto-loading is useful for automatically adapting GDB to the needs of your project, it can sometimes produce unexpected results or introduce security risks (e.g., if the file comes from untrusted sources). There are various kinds of files GDB can automatically load. In addition to these files, GDB supports auto-loading code written in various extension languages. *Note Auto-loading extensions::. Note that loading of these associated files (including the local '.gdbinit' file) requires accordingly configured 'auto-load safe-path' (*note Auto-loading safe path::). For these reasons, GDB includes commands and options to let you control when to auto-load files and which files should be auto-loaded. 'set auto-load off' Globally disable loading of all auto-loaded files. You may want to use this command with the '-iex' option (*note Option -init-eval-command::) such as: $ gdb -iex "set auto-load off" untrusted-executable corefile Be aware that system init file (*note System-wide configuration::) and init files from your home directory (*note Home Directory Init File::) still get read (as they come from generally trusted directories). To prevent GDB from auto-loading even those init files, use the '-nx' option (*note Mode Options::), in addition to 'set auto-load no'. 'show auto-load' Show whether auto-loading of each specific 'auto-load' file(s) is enabled or disabled. (gdb) show auto-load gdb-scripts: Auto-loading of canned sequences of commands scripts is on. libthread-db: Auto-loading of inferior specific libthread_db is on. local-gdbinit: Auto-loading of .gdbinit script from current directory is on. python-scripts: Auto-loading of Python scripts is on. safe-path: List of directories from which it is safe to auto-load files is $debugdir:$datadir/auto-load. scripts-directory: List of directories from which to load auto-loaded scripts is $debugdir:$datadir/auto-load. 'info auto-load' Print whether each specific 'auto-load' file(s) have been auto-loaded or not. (gdb) info auto-load gdb-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.gdb libthread-db: No auto-loaded libthread-db. local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been loaded. python-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.py These are GDB control commands for the auto-loading: *Note set auto-load off::. Disable auto-loading globally. *Note show auto-load::. Show setting of all kinds of files. *Note info auto-load::. Show state of all kinds of files. *Note set auto-load gdb-scripts::. Control for GDB command scripts. *Note show auto-load gdb-scripts::. Show setting of GDB command scripts. *Note info auto-load gdb-scripts::. Show state of GDB command scripts. *Note set auto-load python-scripts::.Control for GDB Python scripts. *Note show auto-load python-scripts::.Show setting of GDB Python scripts. *Note info auto-load python-scripts::.Show state of GDB Python scripts. *Note set auto-load guile-scripts::. Control for GDB Guile scripts. *Note show auto-load guile-scripts::.Show setting of GDB Guile scripts. *Note info auto-load guile-scripts::.Show state of GDB Guile scripts. *Note set auto-load scripts-directory::.Control for GDB auto-loaded scripts location. *Note show auto-load scripts-directory::.Show GDB auto-loaded scripts location. *Note add-auto-load-scripts-directory::.Add directory for auto-loaded scripts location list. *Note set auto-load local-gdbinit::. Control for init file in the current directory. *Note show auto-load local-gdbinit::.Show setting of init file in the current directory. *Note info auto-load local-gdbinit::.Show state of init file in the current directory. *Note set auto-load libthread-db::. Control for thread debugging library. *Note show auto-load libthread-db::. Show setting of thread debugging library. *Note info auto-load libthread-db::. Show state of thread debugging library. *Note set auto-load safe-path::. Control directories trusted for automatic loading. *Note show auto-load safe-path::. Show directories trusted for automatic loading. *Note add-auto-load-safe-path::. Add directory trusted for automatic loading. * Menu: * Init File in the Current Directory:: 'set/show/info auto-load local-gdbinit' * libthread_db.so.1 file:: 'set/show/info auto-load libthread-db' * Auto-loading safe path:: 'set/show/info auto-load safe-path' * Auto-loading verbose mode:: 'set/show debug auto-load'  File: gdb.info, Node: Init File in the Current Directory, Next: libthread_db.so.1 file, Up: Auto-loading 22.8.1 Automatically loading init file in the current directory --------------------------------------------------------------- By default, GDB reads and executes the canned sequences of commands from init file (if any) in the current working directory, see *note Init File in the Current Directory during Startup::. Note that loading of this local '.gdbinit' file also requires accordingly configured 'auto-load safe-path' (*note Auto-loading safe path::). 'set auto-load local-gdbinit [on|off]' Enable or disable the auto-loading of canned sequences of commands (*note Sequences::) found in init file in the current directory. 'show auto-load local-gdbinit' Show whether auto-loading of canned sequences of commands from init file in the current directory is enabled or disabled. 'info auto-load local-gdbinit' Print whether canned sequences of commands from init file in the current directory have been auto-loaded.  File: gdb.info, Node: libthread_db.so.1 file, Next: Auto-loading safe path, Prev: Init File in the Current Directory, Up: Auto-loading 22.8.2 Automatically loading thread debugging library ----------------------------------------------------- This feature is currently present only on GNU/Linux native hosts. GDB reads in some cases thread debugging library from places specific to the inferior (*note set libthread-db-search-path::). The special 'libthread-db-search-path' entry '$sdir' is processed without checking this 'set auto-load libthread-db' switch as system libraries have to be trusted in general. In all other cases of 'libthread-db-search-path' entries GDB checks first if 'set auto-load libthread-db' is enabled before trying to open such thread debugging library. Note that loading of this debugging library also requires accordingly configured 'auto-load safe-path' (*note Auto-loading safe path::). 'set auto-load libthread-db [on|off]' Enable or disable the auto-loading of inferior specific thread debugging library. 'show auto-load libthread-db' Show whether auto-loading of inferior specific thread debugging library is enabled or disabled. 'info auto-load libthread-db' Print the list of all loaded inferior specific thread debugging libraries and for each such library print list of inferior PIDs using it.  File: gdb.info, Node: Auto-loading safe path, Next: Auto-loading verbose mode, Prev: libthread_db.so.1 file, Up: Auto-loading 22.8.3 Security restriction for auto-loading -------------------------------------------- As the files of inferior can come from untrusted source (such as submitted by an application user) GDB does not always load any files automatically. GDB provides the 'set auto-load safe-path' setting to list directories trusted for loading files not explicitly requested by user. Each directory can also be a shell wildcard pattern. If the path is not set properly you will see a warning and the file will not get loaded: $ ./gdb -q ./gdb Reading symbols from /home/user/gdb/gdb... warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". To instruct GDB to go ahead and use the init files anyway, invoke GDB like this: $ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb The list of trusted directories is controlled by the following commands: 'set auto-load safe-path [DIRECTORIES]' Set the list of directories (and their subdirectories) trusted for automatic loading and execution of scripts. You can also enter a specific trusted file. Each directory can also be a shell wildcard pattern; wildcards do not match directory separator - see 'FNM_PATHNAME' for system function 'fnmatch' (*note fnmatch: (libc)Wildcard Matching.). If you omit DIRECTORIES, 'auto-load safe-path' will be reset to its default value as specified during GDB compilation. The list of directories uses path separator (':' on GNU and Unix systems, ';' on MS-Windows and MS-DOS) to separate directories, similarly to the 'PATH' environment variable. 'show auto-load safe-path' Show the list of directories trusted for automatic loading and execution of scripts. 'add-auto-load-safe-path' Add an entry (or list of entries) to the list of directories trusted for automatic loading and execution of scripts. Multiple entries may be delimited by the host platform path separator in use. This variable defaults to what '--with-auto-load-dir' has been configured to (*note with-auto-load-dir::). '$debugdir' and '$datadir' substitution applies the same as for *note set auto-load scripts-directory::. The default 'set auto-load safe-path' value can be also overriden by GDB configuration option '--with-auto-load-safe-path'. Setting this variable to '/' disables this security protection, corresponding GDB configuration option is '--without-auto-load-safe-path'. This variable is supposed to be set to the system directories writable by the system superuser only. Users can add their source directories in init files in their home directories (*note Home Directory Init File::). See also deprecated init file in the current directory (*note Init File in the Current Directory during Startup::). To force GDB to load the files it declined to load in the previous example, you could use one of the following ways: '~/.gdbinit': 'add-auto-load-safe-path ~/src/gdb' Specify this trusted directory (or a file) as additional component of the list. You have to specify also any existing directories displayed by by 'show auto-load safe-path' (such as '/usr:/bin' in this example). 'gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" ...' Specify this directory as in the previous case but just for a single GDB session. 'gdb -iex "set auto-load safe-path /" ...' Disable auto-loading safety for a single GDB session. This assumes all the files you debug during this GDB session will come from trusted sources. './configure --without-auto-load-safe-path' During compilation of GDB you may disable any auto-loading safety. This assumes all the files you will ever debug with this GDB come from trusted sources. On the other hand you can also explicitly forbid automatic files loading which also suppresses any such warning messages: 'gdb -iex "set auto-load no" ...' You can use GDB command-line option for a single GDB session. '~/.gdbinit': 'set auto-load no' Disable auto-loading globally for the user (*note Home Directory Init File::). While it is improbable, you could also use system init file instead (*note System-wide configuration::). This setting applies to the file names as entered by user. If no entry matches GDB tries as a last resort to also resolve all the file names into their canonical form (typically resolving symbolic links) and compare the entries again. GDB already canonicalizes most of the filenames on its own before starting the comparison so a canonical form of directories is recommended to be entered.  File: gdb.info, Node: Auto-loading verbose mode, Prev: Auto-loading safe path, Up: Auto-loading 22.8.4 Displaying files tried for auto-load ------------------------------------------- For better visibility of all the file locations where you can place scripts to be auto-loaded with inferior -- or to protect yourself against accidental execution of untrusted scripts -- GDB provides a feature for printing all the files attempted to be loaded. Both existing and non-existing files may be printed. For example the list of directories from which it is safe to auto-load files (*note Auto-loading safe path::) applies also to canonicalized filenames which may not be too obvious while setting it up. (gdb) set debug auto-load on (gdb) file ~/src/t/true auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb" for objfile "/tmp/true". auto-load: Updating directories of "/usr:/opt". auto-load: Using directory "/usr". auto-load: Using directory "/opt". warning: File "/tmp/true-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "/usr:/opt". 'set debug auto-load [on|off]' Set whether to print the filenames attempted to be auto-loaded. 'show debug auto-load' Show whether printing of the filenames attempted to be auto-loaded is turned on or off.  File: gdb.info, Node: Messages/Warnings, Next: Debugging Output, Prev: Auto-loading, Up: Controlling GDB 22.9 Optional Warnings and Messages =================================== By default, GDB is silent about its inner workings. If you are running on a slow machine, you may want to use the 'set verbose' command. This makes GDB tell you when it does a lengthy internal operation, so you will not think it has crashed. Currently, the messages controlled by 'set verbose' are those which announce that the symbol table for a source file is being read; see 'symbol-file' in *note Commands to Specify Files: Files. 'set verbose on' Enables GDB output of certain informational messages. 'set verbose off' Disables GDB output of certain informational messages. 'show verbose' Displays whether 'set verbose' is on or off. By default, if GDB encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (*note Errors Reading Symbol Files: Symbol Errors.). 'set complaints LIMIT' Permits GDB to output LIMIT complaints about each type of unusual symbols before becoming silent about the problem. Set LIMIT to zero to suppress all complaints; set it to a large number to prevent complaints from being suppressed. 'show complaints' Displays how many symbol complaints GDB is permitted to produce. By default, GDB is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running: (gdb) run The program being debugged has been started already. Start it from the beginning? (y or n) If you are willing to unflinchingly face the consequences of your own commands, you can disable this "feature": 'set confirm off' Disables confirmation requests. Note that running GDB with the '--batch' option (*note -batch: Mode Options.) also automatically disables confirmation requests. 'set confirm on' Enables confirmation requests (the default). 'show confirm' Displays state of confirmation requests. If you need to debug user-defined commands or sourced files you may find it useful to enable "command tracing". In this mode each command will be printed as it is executed, prefixed with one or more '+' symbols, the quantity denoting the call depth of each command. 'set trace-commands on' Enable command tracing. 'set trace-commands off' Disable command tracing. 'show trace-commands' Display the current state of command tracing.  File: gdb.info, Node: Debugging Output, Next: Other Misc Settings, Prev: Messages/Warnings, Up: Controlling GDB 22.10 Optional Messages about Internal Happenings ================================================= GDB has commands that enable optional debugging messages from various GDB subsystems; normally these commands are of interest to GDB maintainers, or when reporting a bug. This section documents those commands. 'set exec-done-display' Turns on or off the notification of asynchronous commands' completion. When on, GDB will print a message when an asynchronous command finishes its execution. The default is off. 'show exec-done-display' Displays the current setting of asynchronous command completion notification. 'set debug aarch64' Turns on or off display of debugging messages related to ARM AArch64. The default is off. 'show debug aarch64' Displays the current state of displaying debugging messages related to ARM AArch64. 'set debug arch' Turns on or off display of gdbarch debugging info. The default is off 'show debug arch' Displays the current state of displaying gdbarch debugging info. 'set debug aix-solib' Control display of debugging messages from the AIX shared library support module. The default is off. 'show debug aix-solib' Show the current state of displaying AIX shared library debugging messages. 'set debug aix-thread' Display debugging messages about inner workings of the AIX thread module. 'show debug aix-thread' Show the current state of AIX thread debugging info display. 'set debug check-physname' Check the results of the "physname" computation. When reading DWARF debugging information for C++, GDB attempts to compute each entity's name. GDB can do this computation in two different ways, depending on exactly what information is present. When enabled, this setting causes GDB to compute the names both ways and display any discrepancies. 'show debug check-physname' Show the current state of "physname" checking. 'set debug coff-pe-read' Control display of debugging messages related to reading of COFF/PE exported symbols. The default is off. 'show debug coff-pe-read' Displays the current state of displaying debugging messages related to reading of COFF/PE exported symbols. 'set debug dwarf-die' Dump DWARF DIEs after they are read in. The value is the number of nesting levels to print. A value of zero turns off the display. 'show debug dwarf-die' Show the current state of DWARF DIE debugging. 'set debug dwarf-line' Turns on or off display of debugging messages related to reading DWARF line tables. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. 'show debug dwarf-line' Show the current state of DWARF line table debugging. 'set debug dwarf-read' Turns on or off display of debugging messages related to reading DWARF debug info. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. 'show debug dwarf-read' Show the current state of DWARF reader debugging. 'set debug displaced' Turns on or off display of GDB debugging info for the displaced stepping support. The default is off. 'show debug displaced' Displays the current state of displaying GDB debugging info related to displaced stepping. 'set debug event' Turns on or off display of GDB event debugging info. The default is off. 'show debug event' Displays the current state of displaying GDB event debugging info. 'set debug event-loop' Controls output of debugging info about the event loop. The possible values are 'off', 'all' (shows all debugging info) and 'all-except-ui' (shows all debugging info except those about UI-related events). 'show debug event-loop' Shows the current state of displaying debugging info about the event loop. 'set debug expression' Turns on or off display of debugging info about GDB expression parsing. The default is off. 'show debug expression' Displays the current state of displaying debugging info about GDB expression parsing. 'set debug fbsd-lwp' Turns on or off debugging messages from the FreeBSD LWP debug support. 'show debug fbsd-lwp' Show the current state of FreeBSD LWP debugging messages. 'set debug fbsd-nat' Turns on or off debugging messages from the FreeBSD native target. 'show debug fbsd-nat' Show the current state of FreeBSD native target debugging messages. 'set debug fortran-array-slicing' Turns on or off display of GDB Fortran array slicing debugging info. The default is off. 'show debug fortran-array-slicing' Displays the current state of displaying GDB Fortran array slicing debugging info. 'set debug frame' Turns on or off display of GDB frame debugging info. The default is off. 'show debug frame' Displays the current state of displaying GDB frame debugging info. 'set debug gnu-nat' Turn on or off debugging messages from the GNU/Hurd debug support. 'show debug gnu-nat' Show the current state of GNU/Hurd debugging messages. 'set debug infrun' Turns on or off display of GDB debugging info for running the inferior. The default is off. 'infrun.c' contains GDB's runtime state machine used for implementing operations such as single-stepping the inferior. 'show debug infrun' Displays the current state of GDB inferior debugging. 'set debug jit' Turn on or off debugging messages from JIT debug support. 'show debug jit' Displays the current state of GDB JIT debugging. 'set debug linux-nat [on|off]' Turn on or off debugging messages from the Linux native target debug support. 'show debug linux-nat' Show the current state of Linux native target debugging messages. 'set debug linux-namespaces' Turn on or off debugging messages from the Linux namespaces debug support. 'show debug linux-namespaces' Show the current state of Linux namespaces debugging messages. 'set debug mach-o' Control display of debugging messages related to Mach-O symbols processing. The default is off. 'show debug mach-o' Displays the current state of displaying debugging messages related to reading of COFF/PE exported symbols. 'set debug notification' Turn on or off debugging messages about remote async notification. The default is off. 'show debug notification' Displays the current state of remote async notification debugging messages. 'set debug observer' Turns on or off display of GDB observer debugging. This includes info such as the notification of observable events. 'show debug observer' Displays the current state of observer debugging. 'set debug overload' Turns on or off display of GDB C++ overload debugging info. This includes info such as ranking of functions, etc. The default is off. 'show debug overload' Displays the current state of displaying GDB C++ overload debugging info. 'set debug parser' Turns on or off the display of expression parser debugging output. Internally, this sets the 'yydebug' variable in the expression parser. *Note Tracing Your Parser: (bison)Tracing, for details. The default is off. 'show debug parser' Show the current state of expression parser debugging. 'set debug remote' Turns on or off display of reports on all packets sent back and forth across the serial line to the remote machine. The info is printed on the GDB standard output stream. The default is off. 'show debug remote' Displays the state of display of remote packets. 'set debug remote-packet-max-chars' Sets the maximum number of characters to display for each remote packet when 'set debug remote' is on. This is useful to prevent GDB from displaying lengthy remote packets and polluting the console. The default value is '512', which means GDB will truncate each remote packet after 512 bytes. Setting this option to 'unlimited' will disable truncation and will output the full length of the remote packets. 'show debug remote-packet-max-chars' Displays the number of bytes to output for remote packet debugging. 'set debug separate-debug-file' Turns on or off display of debug output about separate debug file search. 'show debug separate-debug-file' Displays the state of separate debug file search debug output. 'set debug serial' Turns on or off display of GDB serial debugging info. The default is off. 'show debug serial' Displays the current state of displaying GDB serial debugging info. 'set debug solib-frv' Turn on or off debugging messages for FR-V shared-library code. 'show debug solib-frv' Display the current state of FR-V shared-library code debugging messages. 'set debug symbol-lookup' Turns on or off display of debugging messages related to symbol lookup. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. 'show debug symbol-lookup' Show the current state of symbol lookup debugging messages. 'set debug symfile' Turns on or off display of debugging messages related to symbol file functions. The default is off. *Note Files::. 'show debug symfile' Show the current state of symbol file debugging messages. 'set debug symtab-create' Turns on or off display of debugging messages related to symbol table creation. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. 'show debug symtab-create' Show the current state of symbol table creation debugging. 'set debug target' Turns on or off display of GDB target debugging info. This info includes what is going on at the target level of GDB, as it happens. The default is 0. Set it to 1 to track events, and to 2 to also track the value of large memory transfers. 'show debug target' Displays the current state of displaying GDB target debugging info. 'set debug timestamp' Turns on or off display of timestamps with GDB debugging info. When enabled, seconds and microseconds are displayed before each debugging message. 'show debug timestamp' Displays the current state of displaying timestamps with GDB debugging info. 'set debug varobj' Turns on or off display of GDB variable object debugging info. The default is off. 'show debug varobj' Displays the current state of displaying GDB variable object debugging info. 'set debug xml' Turn on or off debugging messages for built-in XML parsers. 'show debug xml' Displays the current state of XML debugging messages.  File: gdb.info, Node: Other Misc Settings, Prev: Debugging Output, Up: Controlling GDB 22.11 Other Miscellaneous Settings ================================== 'set interactive-mode' If 'on', forces GDB to assume that GDB was started in a terminal. In practice, this means that GDB should wait for the user to answer queries generated by commands entered at the command prompt. If 'off', forces GDB to operate in the opposite mode, and it uses the default answers to all queries. If 'auto' (the default), GDB tries to determine whether its standard input is a terminal, and works in interactive-mode if it is, non-interactively otherwise. In the vast majority of cases, the debugger should be able to guess correctly which mode should be used. But this setting can be useful in certain specific cases, such as running a MinGW GDB inside a cygwin window. 'show interactive-mode' Displays whether the debugger is operating in interactive mode or not. 'set suppress-cli-notifications' If 'on', command-line-interface (CLI) notifications that are printed by GDB are suppressed. If 'off', the notifications are printed as usual. The default value is 'off'. CLI notifications occur when you change the selected context or when the program being debugged stops, as detailed below. _User-selected context changes:_ When you change the selected context (i.e. the current inferior, thread and/or the frame), GDB prints information about the new context. For example, the default behavior is below: (gdb) inferior 1 [Switching to inferior 1 [process 634] (/tmp/test)] [Switching to thread 1 (process 634)] #0 main () at test.c:3 3 return 0; (gdb) When the notifications are suppressed, the new context is not printed: (gdb) set suppress-cli-notifications on (gdb) inferior 1 (gdb) _The program being debugged stops:_ When the program you are debugging stops (e.g. because of hitting a breakpoint, completing source-stepping, an interrupt, etc.), GDB prints information about the stop event. For example, below is a breakpoint hit: (gdb) break test.c:3 Breakpoint 2 at 0x555555555155: file test.c, line 3. (gdb) continue Continuing. Breakpoint 2, main () at test.c:3 3 return 0; (gdb) When the notifications are suppressed, the output becomes: (gdb) break test.c:3 Breakpoint 2 at 0x555555555155: file test.c, line 3. (gdb) set suppress-cli-notifications on (gdb) continue Continuing. (gdb) Suppressing CLI notifications may be useful in scripts to obtain a reduced output from a list of commands. 'show suppress-cli-notifications' Displays whether printing CLI notifications is suppressed or not.  File: gdb.info, Node: Extending GDB, Next: Interpreters, Prev: Controlling GDB, Up: Top 23 Extending GDB **************** GDB provides several mechanisms for extension. GDB also provides the ability to automatically load extensions when it reads a file for debugging. This allows the user to automatically customize GDB for the program being debugged. To facilitate the use of extension languages, GDB is capable of evaluating the contents of a file. When doing so, GDB can recognize which extension language is being used by looking at the filename extension. Files with an unrecognized filename extension are always treated as a GDB Command Files. *Note Command files: Command Files. You can control how GDB evaluates these files with the following setting: 'set script-extension off' All scripts are always evaluated as GDB Command Files. 'set script-extension soft' The debugger determines the scripting language based on filename extension. If this scripting language is supported, GDB evaluates the script using that language. Otherwise, it evaluates the file as a GDB Command File. 'set script-extension strict' The debugger determines the scripting language based on filename extension, and evaluates the script using that language. If the language is not supported, then the evaluation fails. 'show script-extension' Display the current value of the 'script-extension' option. * Menu: * Sequences:: Canned Sequences of GDB Commands * Aliases:: Command Aliases * Python:: Extending GDB using Python * Guile:: Extending GDB using Guile * Auto-loading extensions:: Automatically loading extensions * Multiple Extension Languages:: Working with multiple extension languages  File: gdb.info, Node: Sequences, Next: Aliases, Up: Extending GDB 23.1 Canned Sequences of Commands ================================= Aside from breakpoint commands (*note Breakpoint Command Lists: Break Commands.), GDB provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files. * Menu: * Define:: How to define your own commands * Hooks:: Hooks for user-defined commands * Command Files:: How to write scripts of commands to be stored in a file * Output:: Commands for controlled output * Auto-loading sequences:: Controlling auto-loaded command files  File: gdb.info, Node: Define, Next: Hooks, Up: Sequences 23.1.1 User-defined Commands ---------------------------- A "user-defined command" is a sequence of GDB commands to which you assign a new name as a command. This is done with the 'define' command. User commands may accept an unlimited number of arguments separated by whitespace. Arguments are accessed within the user command via '$arg0...$argN'. A trivial example: define adder print $arg0 + $arg1 + $arg2 end To execute the command use: adder 1 2 3 This defines the command 'adder', which prints the sum of its three arguments. Note the arguments are text substitutions, so they may reference variables, use complex expressions, or even perform inferior functions calls. In addition, '$argc' may be used to find out how many arguments have been passed. define adder if $argc == 2 print $arg0 + $arg1 end if $argc == 3 print $arg0 + $arg1 + $arg2 end end Combining with the 'eval' command (*note eval::) makes it easier to process a variable number of arguments: define adder set $i = 0 set $sum = 0 while $i < $argc eval "set $sum = $sum + $arg%d", $i set $i = $i + 1 end print $sum end 'define COMMANDNAME' Define a command named COMMANDNAME. If there is already a command by that name, you are asked to confirm that you want to redefine it. The argument COMMANDNAME may be a bare command name consisting of letters, numbers, dashes, dots, and underscores. It may also start with any predefined or user-defined prefix command. For example, 'define target my-target' creates a user-defined 'target my-target' command. The definition of the command is made up of other GDB command lines, which are given following the 'define' command. The end of these commands is marked by a line containing 'end'. 'document COMMANDNAME' Document the user-defined command COMMANDNAME, so that it can be accessed by 'help'. The command COMMANDNAME must already be defined. This command reads lines of documentation just as 'define' reads the lines of the command definition, ending with 'end'. After the 'document' command is finished, 'help' on command COMMANDNAME displays the documentation you have written. You may use the 'document' command again to change the documentation of a command. Redefining the command with 'define' does not change the documentation. 'define-prefix COMMANDNAME' Define or mark the command COMMANDNAME as a user-defined prefix command. Once marked, COMMANDNAME can be used as prefix command by the 'define' command. Note that 'define-prefix' can be used with a not yet defined COMMANDNAME. In such a case, COMMANDNAME is defined as an empty user-defined command. In case you redefine a command that was marked as a user-defined prefix command, the subcommands of the redefined command are kept (and GDB indicates so to the user). Example: (gdb) define-prefix abc (gdb) define-prefix abc def (gdb) define abc def Type commands for definition of "abc def". End with a line saying just "end". >echo command initial def\n >end (gdb) define abc def ghi Type commands for definition of "abc def ghi". End with a line saying just "end". >echo command ghi\n >end (gdb) define abc def Keeping subcommands of prefix command "def". Redefine command "def"? (y or n) y Type commands for definition of "abc def". End with a line saying just "end". >echo command def\n >end (gdb) abc def ghi command ghi (gdb) abc def command def (gdb) 'dont-repeat' Used inside a user-defined command, this tells GDB that this command should not be repeated when the user hits (*note repeat last command: Command Syntax.). 'help user-defined' List all user-defined commands and all python commands defined in class COMMAND_USER. The first line of the documentation or docstring is included (if any). 'show user' 'show user COMMANDNAME' Display the GDB commands used to define COMMANDNAME (but not its documentation). If no COMMANDNAME is given, display the definitions for all user-defined commands. This does not work for user-defined python commands. 'show max-user-call-depth' 'set max-user-call-depth' The value of 'max-user-call-depth' controls how many recursion levels are allowed in user-defined commands before GDB suspects an infinite recursion and aborts the command. This does not apply to user-defined python commands. In addition to the above commands, user-defined commands frequently use control flow commands, described in *note Command Files::. When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command. If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many GDB commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.  File: gdb.info, Node: Hooks, Next: Command Files, Prev: Define, Up: Sequences 23.1.2 User-defined Command Hooks --------------------------------- You may define "hooks", which are a special kind of user-defined command. Whenever you run the command 'foo', if the user-defined command 'hook-foo' exists, it is executed (with no arguments) before that command. A hook may also be defined which is run after the command you executed. Whenever you run the command 'foo', if the user-defined command 'hookpost-foo' exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command. It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinite recursion. In addition, a pseudo-command, 'stop' exists. Defining ('hook-stop') makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed. For example, to ignore 'SIGALRM' signals while single-stepping, but treat them normally during normal execution, you could define: define hook-stop handle SIGALRM nopass end define hook-run handle SIGALRM pass end define hook-continue handle SIGALRM pass end As a further example, to hook at the beginning and end of the 'echo' command, and to add extra text to the beginning and end of the message, you could define: define hook-echo echo <<<--- end define hookpost-echo echo --->>>\n end (gdb) echo Hello World <<<---Hello World--->>> (gdb) You can define a hook for any single-word command in GDB, but not for command aliases; you should define a hook for the basic command name, e.g. 'backtrace' rather than 'bt'. You can hook a multi-word command by adding 'hook-' or 'hookpost-' to the last word of the command, e.g. 'define target hook-remote' to add a hook to 'target remote'. If an error occurs during the execution of your hook, execution of GDB commands stops and GDB issues a prompt (before the command that you actually typed had a chance to run). If you try to define a hook which does not match any known command, you get a warning from the 'define' command.  File: gdb.info, Node: Command Files, Next: Output, Prev: Hooks, Up: Sequences 23.1.3 Command Files -------------------- A command file for GDB is a text file made of lines that are GDB commands. Comments (lines starting with '#') may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal. You can request the execution of a command file with the 'source' command. Note that the 'source' command is also used to evaluate scripts that are not Command Files. The exact behavior can be configured using the 'script-extension' setting. *Note Extending GDB: Extending GDB. 'source [-s] [-v] FILENAME' Execute the command file FILENAME. The lines in a command file are generally executed sequentially, unless the order of execution is changed by one of the _flow-control commands_ described below. The commands are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console. GDB first searches for FILENAME in the current directory. If the file is not found there, and FILENAME does not specify a directory, then GDB also looks for the file on the source search path (specified with the 'directory' command); except that '$cdir' is not searched because the compilation directory is not relevant to scripts. If '-s' is specified, then GDB searches for FILENAME on the search path even if FILENAME specifies a directory. The search is done by appending FILENAME to each element of the search path. So, for example, if FILENAME is 'mylib/myscript' and the search path contains '/home/user' then GDB will look for the script '/home/user/mylib/myscript'. The search is also done if FILENAME is an absolute path. For example, if FILENAME is '/tmp/myscript' and the search path contains '/home/user' then GDB will look for the script '/home/user/tmp/myscript'. For DOS-like systems, if FILENAME contains a drive specification, it is stripped before concatenation. For example, if FILENAME is 'd:myscript' and the search path contains 'c:/tmp' then GDB will look for the script 'c:/tmp/myscript'. If '-v', for verbose mode, is given then GDB displays each command as it is executed. The option must be given before FILENAME, and is interpreted as part of the filename anywhere else. Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many GDB commands that normally print messages to say what they are doing omit the messages when called from command files. GDB also accepts command input from standard input. In this mode, normal output goes to standard output and error output goes to standard error. Errors in a command file supplied on standard input do not terminate execution of the command file--execution continues with the next command. gdb < cmds > log 2>&1 (The syntax above will vary depending on the shell used.) This example will execute commands from the file 'cmds'. All output and errors would be directed to 'log'. Since commands stored on command files tend to be more general than commands typed interactively, they frequently need to deal with complicated situations, such as different or unexpected values of variables and symbols, changes in how the program being debugged is built, etc. GDB provides a set of flow-control commands to deal with these complexities. Using these commands, you can write complex scripts that loop over data structures, execute commands conditionally, etc. 'if' 'else' This command allows to include in your script conditionally executed commands. The 'if' command takes a single argument, which is an expression to evaluate. It is followed by a series of commands that are executed only if the expression is true (its value is nonzero). There can then optionally be an 'else' line, followed by a series of commands that are only executed if the expression was false. The end of the list is marked by a line containing 'end'. 'while' This command allows to write loops. Its syntax is similar to 'if': the command takes a single argument, which is an expression to evaluate, and must be followed by the commands to execute, one per line, terminated by an 'end'. These commands are called the "body" of the loop. The commands in the body of 'while' are executed repeatedly as long as the expression evaluates to true. 'loop_break' This command exits the 'while' loop in whose body it is included. Execution of the script continues after that 'while's 'end' line. 'loop_continue' This command skips the execution of the rest of the body of commands in the 'while' loop in whose body it is included. Execution branches to the beginning of the 'while' loop, where it evaluates the controlling expression. 'end' Terminate the block of commands that are the body of 'if', 'else', or 'while' flow-control commands.  File: gdb.info, Node: Output, Next: Auto-loading sequences, Prev: Command Files, Up: Sequences 23.1.4 Commands for Controlled Output ------------------------------------- During the execution of a command file or a user-defined command, normal GDB output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want. 'echo TEXT' Print TEXT. Nonprinting characters can be included in TEXT using C escape sequences, such as '\n' to print a newline. *No newline is printed unless you specify one.* In addition to the standard C escape sequences, a backslash followed by a space stands for a space. This is useful for displaying a string with spaces at the beginning or the end, since leading and trailing spaces are otherwise trimmed from all arguments. To print ' and foo = ', use the command 'echo \ and foo = \ '. A backslash at the end of TEXT can be used, as in C, to continue the command onto subsequent lines. For example, echo This is some text\n\ which is continued\n\ onto several lines.\n produces the same output as echo This is some text\n echo which is continued\n echo onto several lines.\n 'output EXPRESSION' Print the value of EXPRESSION and nothing but that value: no newlines, no '$NN = '. The value is not entered in the value history either. *Note Expressions: Expressions, for more information on expressions. 'output/FMT EXPRESSION' Print the value of EXPRESSION in format FMT. You can use the same formats as for 'print'. *Note Output Formats: Output Formats, for more information. 'printf TEMPLATE, EXPRESSIONS...' Print the values of one or more EXPRESSIONS under the control of the string TEMPLATE. To print several values, make EXPRESSIONS be a comma-separated list of individual expressions, which may be either numbers or pointers. Their values are printed as specified by TEMPLATE, exactly as a C program would do by executing the code below: printf (TEMPLATE, EXPRESSIONS...); As in 'C' 'printf', ordinary characters in TEMPLATE are printed verbatim, while "conversion specification" introduced by the '%' character cause subsequent EXPRESSIONS to be evaluated, their values converted and formatted according to type and style information encoded in the conversion specifications, and then printed. For example, you can print two values in hex like this: printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo 'printf' supports all the standard 'C' conversion specifications, including the flags and modifiers between the '%' character and the conversion letter, with the following exceptions: * The argument-ordering modifiers, such as '2$', are not supported. * The modifier '*' is not supported for specifying precision or width. * The ''' flag (for separation of digits into groups according to 'LC_NUMERIC'') is not supported. * The type modifiers 'hh', 'j', 't', and 'z' are not supported. * The conversion letter 'n' (as in '%n') is not supported. * The conversion letters 'a' and 'A' are not supported. Note that the 'll' type modifier is supported only if the underlying 'C' implementation used to build GDB supports the 'long long int' type, and the 'L' type modifier is supported only if 'long double' type is available. As in 'C', 'printf' supports simple backslash-escape sequences, such as '\n', '\t', '\\', '\"', '\a', and '\f', that consist of backslash followed by a single character. Octal and hexadecimal escape sequences are not supported. Additionally, 'printf' supports conversion specifications for DFP ("Decimal Floating Point") types using the following length modifiers together with a floating point specifier. letters: * 'H' for printing 'Decimal32' types. * 'D' for printing 'Decimal64' types. * 'DD' for printing 'Decimal128' types. If the underlying 'C' implementation used to build GDB has support for the three length modifiers for DFP types, other modifiers such as width and precision will also be available for GDB to use. In case there is no such 'C' support, no additional modifiers will be available and the value will be printed in the standard way. Here's an example of printing DFP types using the above conversion letters: printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl 'eval TEMPLATE, EXPRESSIONS...' Convert the values of one or more EXPRESSIONS under the control of the string TEMPLATE to a command line, and call it.  File: gdb.info, Node: Auto-loading sequences, Prev: Output, Up: Sequences 23.1.5 Controlling auto-loading native GDB scripts -------------------------------------------------- When a new object file is read (for example, due to the 'file' command, or because the inferior has loaded a shared library), GDB will look for the command file 'OBJFILE-gdb.gdb'. *Note Auto-loading extensions::. Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed. 'set auto-load gdb-scripts [on|off]' Enable or disable the auto-loading of canned sequences of commands scripts. 'show auto-load gdb-scripts' Show whether auto-loading of canned sequences of commands scripts is enabled or disabled. 'info auto-load gdb-scripts [REGEXP]' Print the list of all canned sequences of commands scripts that GDB auto-loaded. If REGEXP is supplied only canned sequences of commands scripts with matching names are printed.  File: gdb.info, Node: Aliases, Next: Python, Prev: Sequences, Up: Extending GDB 23.2 Command Aliases ==================== Aliases allow you to define alternate spellings for existing commands. For example, if a new GDB command defined in Python (*note Python::) has a long name, it is handy to have an abbreviated version of it that involves less typing. GDB itself uses aliases. For example 's' is an alias of the 'step' command even though it is otherwise an ambiguous abbreviation of other commands like 'set' and 'show'. Aliases are also used to provide shortened or more common versions of multi-word commands. For example, GDB provides the 'tty' alias of the 'set inferior-tty' command. You can define a new alias with the 'alias' command. 'alias [-a] [--] ALIAS = COMMAND [DEFAULT-ARGS]' ALIAS specifies the name of the new alias. Each word of ALIAS must consist of letters, numbers, dashes and underscores. COMMAND specifies the name of an existing command that is being aliased. COMMAND can also be the name of an existing alias. In this case, COMMAND cannot be an alias that has default arguments. The '-a' option specifies that the new alias is an abbreviation of the command. Abbreviations are not used in command completion. The '--' option specifies the end of options, and is useful when ALIAS begins with a dash. You can specify DEFAULT-ARGS for your alias. These DEFAULT-ARGS will be automatically added before the alias arguments typed explicitly on the command line. For example, the below defines an alias 'btfullall' that shows all local variables and all frame arguments: (gdb) alias btfullall = backtrace -full -frame-arguments all For more information about DEFAULT-ARGS, see *note Default Arguments: Command aliases default args. Here is a simple example showing how to make an abbreviation of a command so that there is less to type. Suppose you were tired of typing 'disas', the current shortest unambiguous abbreviation of the 'disassemble' command and you wanted an even shorter version named 'di'. The following will accomplish this. (gdb) alias -a di = disas Note that aliases are different from user-defined commands. With a user-defined command, you also need to write documentation for it with the 'document' command. An alias automatically picks up the documentation of the existing command. Here is an example where we make 'elms' an abbreviation of 'elements' in the 'set print elements' command. This is to show that you can make an abbreviation of any part of a command. (gdb) alias -a set print elms = set print elements (gdb) alias -a show print elms = show print elements (gdb) set p elms 200 (gdb) show p elms Limit on string chars or array elements to print is 200. Note that if you are defining an alias of a 'set' command, and you want to have an alias for the corresponding 'show' command, then you need to define the latter separately. Unambiguously abbreviated commands are allowed in COMMAND and ALIAS, just as they are normally. (gdb) alias -a set pr elms = set p ele Finally, here is an example showing the creation of a one word alias for a more complex command. This creates alias 'spe' of the command 'set print elements'. (gdb) alias spe = set print elements (gdb) spe 20 * Menu: * Command aliases default args:: Default arguments for aliases  File: gdb.info, Node: Command aliases default args, Up: Aliases 23.2.1 Default Arguments ------------------------ You can tell GDB to always prepend some default arguments to the list of arguments provided explicitly by the user when using a user-defined alias. If you repeatedly use the same arguments or options for a command, you can define an alias for this command and tell GDB to automatically prepend these arguments or options to the list of arguments you type explicitly when using the alias(1). For example, if you often use the command 'thread apply all' specifying to work on the threads in ascending order and to continue in case it encounters an error, you can tell GDB to automatically preprend the '-ascending' and '-c' options by using: (gdb) alias thread apply asc-all = thread apply all -ascending -c Once you have defined this alias with its default args, any time you type the 'thread apply asc-all' followed by 'some arguments', GDB will execute 'thread apply all -ascending -c some arguments'. To have even less to type, you can also define a one word alias: (gdb) alias t_a_c = thread apply all -ascending -c As usual, unambiguous abbreviations can be used for ALIAS and DEFAULT-ARGS. The different aliases of a command do not share their default args. For example, you define a new alias 'bt_ALL' showing all possible information and another alias 'bt_SMALL' showing very limited information using: (gdb) alias bt_ALL = backtrace -entry-values both -frame-arg all \ -past-main -past-entry -full (gdb) alias bt_SMALL = backtrace -entry-values no -frame-arg none \ -past-main off -past-entry off (For more on using the 'alias' command, see *note Aliases::.) Default args are not limited to the arguments and options of COMMAND, but can specify nested commands if COMMAND accepts such a nested command as argument. For example, the below defines 'faalocalsoftype' that lists the frames having locals of a certain type, together with the matching local vars: (gdb) alias faalocalsoftype = frame apply all info locals -q -t (gdb) faalocalsoftype int #1 0x55554f5e in sleeper_or_burner (v=0xdf50) at sleepers.c:86 i = 0 ret = 21845 This is also very useful to define an alias for a set of nested 'with' commands to have a particular combination of temporary settings. For example, the below defines the alias 'pp10' that pretty prints an expression argument, with a maximum of 10 elements if the expression is a string or an array: (gdb) alias pp10 = with print pretty -- with print elements 10 -- print This defines the alias 'pp10' as being a sequence of 3 commands. The first part 'with print pretty --' temporarily activates the setting 'set print pretty', then launches the command that follows the separator '--'. The command following the first part is also a 'with' command that temporarily changes the setting 'set print elements' to 10, then launches the command that follows the second separator '--'. The third part 'print' is the command the 'pp10' alias will launch, using the temporary values of the settings and the arguments explicitly given by the user. For more information about the 'with' command usage, see *note Command Settings::. ---------- Footnotes ---------- (1) GDB could easily accept default arguments for pre-defined commands and aliases, but it was deemed this would be confusing, and so is not allowed.  File: gdb.info, Node: Python, Next: Guile, Prev: Aliases, Up: Extending GDB 23.3 Extending GDB using Python =============================== You can extend GDB using the Python programming language (http://www.python.org/). This feature is available only if GDB was configured using '--with-python'. GDB can be built against either Python 2 or Python 3; which one you have depends on this configure-time option. Python scripts used by GDB should be installed in 'DATA-DIRECTORY/python', where DATA-DIRECTORY is the data directory as determined at GDB startup (*note Data Files::). This directory, known as the "python directory", is automatically added to the Python Search Path in order to allow the Python interpreter to locate all scripts installed at this location. Additionally, GDB commands and convenience functions which are written in Python and are located in the 'DATA-DIRECTORY/python/gdb/command' or 'DATA-DIRECTORY/python/gdb/function' directories are automatically imported when GDB starts. * Menu: * Python Commands:: Accessing Python from GDB. * Python API:: Accessing GDB from Python. * Python Auto-loading:: Automatically loading Python code. * Python modules:: Python modules provided by GDB.  File: gdb.info, Node: Python Commands, Next: Python API, Up: Python 23.3.1 Python Commands ---------------------- GDB provides two commands for accessing the Python interpreter, and one related setting: 'python-interactive [COMMAND]' 'pi [COMMAND]' Without an argument, the 'python-interactive' command can be used to start an interactive Python prompt. To return to GDB, type the 'EOF' character (e.g., 'Ctrl-D' on an empty prompt). Alternatively, a single-line Python command can be given as an argument and evaluated. If the command is an expression, the result will be printed; otherwise, nothing will be printed. For example: (gdb) python-interactive 2 + 3 5 'python [COMMAND]' 'py [COMMAND]' The 'python' command can be used to evaluate Python code. If given an argument, the 'python' command will evaluate the argument as a Python command. For example: (gdb) python print 23 23 If you do not provide an argument to 'python', it will act as a multi-line command, like 'define'. In this case, the Python script is made up of subsequent command lines, given after the 'python' command. This command list is terminated using a line containing 'end'. For example: (gdb) python >print 23 >end 23 'set python print-stack' By default, GDB will print only the message component of a Python exception when an error occurs in a Python script. This can be controlled using 'set python print-stack': if 'full', then full Python stack printing is enabled; if 'none', then Python stack and message printing is disabled; if 'message', the default, only the message component of the error is printed. 'set python ignore-environment [on|off]' By default this option is 'off', and, when GDB initializes its internal Python interpreter, the Python interpreter will check the environment for variables that will effect how it behaves, for example 'PYTHONHOME', and 'PYTHONPATH'(1). If this option is set to 'on' before Python is initialized then Python will ignore all such environment variables. As Python is initialized early during GDB's startup process, then this option must be placed into the early initialization file (*note Initialization Files::) to have the desired effect. This option is equivalent to passing '-E' to the real 'python' executable. 'set python dont-write-bytecode [auto|on|off]' When this option is 'off', then, once GDB has initialized the Python interpreter, the interpreter will byte-compile any Python modules that it imports and write the byte code to disk in '.pyc' files. If this option is set to 'on' before Python is initialized then Python will no longer write the byte code to disk. As Python is initialized early during GDB's startup process, then this option must be placed into the early initialization file (*note Initialization Files::) to have the desired effect. By default this option is set to 'auto', in this mode Python will check the environment variable 'PYTHONDONTWRITEBYTECODE' to see if it should write out byte-code or not. This option is equivalent to passing '-B' to the real 'python' executable. It is also possible to execute a Python script from the GDB interpreter: 'source script-name' The script name must end with '.py' and GDB must be configured to recognize the script language based on filename extension using the 'script-extension' setting. *Note Extending GDB: Extending GDB. The following commands are intended to help debug GDB itself: 'set debug py-breakpoint on|off' 'show debug py-breakpoint' When 'on', GDB prints debug messages related to the Python breakpoint API. This is 'off' by default. 'set debug py-unwind on|off' 'show debug py-unwind' When 'on', GDB prints debug messages related to the Python unwinder API. This is 'off' by default. ---------- Footnotes ---------- (1) See the ENVIRONMENT VARIABLES section of 'man 1 python' for a comprehensive list.  File: gdb.info, Node: Python API, Next: Python Auto-loading, Prev: Python Commands, Up: Python 23.3.2 Python API ----------------- You can get quick online help for GDB's Python API by issuing the command 'python help (gdb)'. Functions and methods which have two or more optional arguments allow them to be specified using keyword syntax. This allows passing some optional arguments while skipping others. Example: 'gdb.some_function ('foo', bar = 1, baz = 2)'. * Menu: * Basic Python:: Basic Python Functions. * Exception Handling:: How Python exceptions are translated. * Values From Inferior:: Python representation of values. * Types In Python:: Python representation of types. * Pretty Printing API:: Pretty-printing values. * Selecting Pretty-Printers:: How GDB chooses a pretty-printer. * Writing a Pretty-Printer:: Writing a Pretty-Printer. * Type Printing API:: Pretty-printing types. * Frame Filter API:: Filtering Frames. * Frame Decorator API:: Decorating Frames. * Writing a Frame Filter:: Writing a Frame Filter. * Unwinding Frames in Python:: Writing frame unwinder. * Xmethods In Python:: Adding and replacing methods of C++ classes. * Xmethod API:: Xmethod types. * Writing an Xmethod:: Writing an xmethod. * Inferiors In Python:: Python representation of inferiors (processes) * Events In Python:: Listening for events from GDB. * Threads In Python:: Accessing inferior threads from Python. * Recordings In Python:: Accessing recordings from Python. * CLI Commands In Python:: Implementing new CLI commands in Python. * GDB/MI Commands In Python:: Implementing new GDB/MI commands in Python. * Parameters In Python:: Adding new GDB parameters. * Functions In Python:: Writing new convenience functions. * Progspaces In Python:: Program spaces. * Objfiles In Python:: Object files. * Frames In Python:: Accessing inferior stack frames from Python. * Blocks In Python:: Accessing blocks from Python. * Symbols In Python:: Python representation of symbols. * Symbol Tables In Python:: Python representation of symbol tables. * Line Tables In Python:: Python representation of line tables. * Breakpoints In Python:: Manipulating breakpoints using Python. * Finish Breakpoints in Python:: Setting Breakpoints on function return using Python. * Lazy Strings In Python:: Python representation of lazy strings. * Architectures In Python:: Python representation of architectures. * Registers In Python:: Python representation of registers. * Connections In Python:: Python representation of connections. * TUI Windows In Python:: Implementing new TUI windows.  File: gdb.info, Node: Basic Python, Next: Exception Handling, Up: Python API 23.3.2.1 Basic Python ..................... At startup, GDB overrides Python's 'sys.stdout' and 'sys.stderr' to print using GDB's output-paging streams. A Python program which outputs to one of these streams may have its output interrupted by the user (*note Screen Size::). In this situation, a Python 'KeyboardInterrupt' exception is thrown. Some care must be taken when writing Python code to run in GDB. Two things worth noting in particular: * GDB install handlers for 'SIGCHLD' and 'SIGINT'. Python code must not override these, or even change the options using 'sigaction'. If your program changes the handling of these signals, GDB will most likely stop working correctly. Note that it is unfortunately common for GUI toolkits to install a 'SIGCHLD' handler. * GDB takes care to mark its internal file descriptors as close-on-exec. However, this cannot be done in a thread-safe way on all platforms. Your Python programs should be aware of this and should both create new file descriptors with the close-on-exec flag set and arrange to close unneeded file descriptors before starting a child process. GDB introduces a new Python module, named 'gdb'. All methods and classes added by GDB are placed in this module. GDB automatically 'import's the 'gdb' module for use in all scripts evaluated by the 'python' command. Some types of the 'gdb' module come with a textual representation (accessible through the 'repr' or 'str' functions). These are offered for debugging purposes only, expect them to change over time. -- Variable: gdb.PYTHONDIR A string containing the python directory (*note Python::). -- Function: gdb.execute (command [, from_tty [, to_string]]) Evaluate COMMAND, a string, as a GDB CLI command. If a GDB exception happens while COMMAND runs, it is translated as described in *note Exception Handling: Exception Handling. The FROM_TTY flag specifies whether GDB ought to consider this command as having originated from the user invoking it interactively. It must be a boolean value. If omitted, it defaults to 'False'. By default, any output produced by COMMAND is sent to GDB's standard output (and to the log output if logging is turned on). If the TO_STRING parameter is 'True', then output will be collected by 'gdb.execute' and returned as a string. The default is 'False', in which case the return value is 'None'. If TO_STRING is 'True', the GDB virtual terminal will be temporarily set to unlimited width and height, and its pagination will be disabled; *note Screen Size::. -- Function: gdb.breakpoints () Return a sequence holding all of GDB's breakpoints. *Note Breakpoints In Python::, for more information. In GDB version 7.11 and earlier, this function returned 'None' if there were no breakpoints. This peculiarity was subsequently fixed, and now 'gdb.breakpoints' returns an empty sequence in this case. -- Function: gdb.rbreak (regex [, minsyms [, throttle, [, symtabs ]]]) Return a Python list holding a collection of newly set 'gdb.Breakpoint' objects matching function names defined by the REGEX pattern. If the MINSYMS keyword is 'True', all system functions (those not explicitly defined in the inferior) will also be included in the match. The THROTTLE keyword takes an integer that defines the maximum number of pattern matches for functions matched by the REGEX pattern. If the number of matches exceeds the integer value of THROTTLE, a 'RuntimeError' will be raised and no breakpoints will be created. If THROTTLE is not defined then there is no imposed limit on the maximum number of matches and breakpoints to be created. The SYMTABS keyword takes a Python iterable that yields a collection of 'gdb.Symtab' objects and will restrict the search to those functions only contained within the 'gdb.Symtab' objects. -- Function: gdb.parameter (parameter) Return the value of a GDB PARAMETER given by its name, a string; the parameter name string may contain spaces if the parameter has a multi-part name. For example, 'print object' is a valid parameter name. If the named parameter does not exist, this function throws a 'gdb.error' (*note Exception Handling::). Otherwise, the parameter's value is converted to a Python value of the appropriate type, and returned. -- Function: gdb.set_parameter (name, value) Sets the gdb parameter NAME to VALUE. As with 'gdb.parameter', the parameter name string may contain spaces if the parameter has a multi-part name. -- Function: gdb.with_parameter (name, value) Create a Python context manager (for use with the Python 'with' statement) that temporarily sets the gdb parameter NAME to VALUE. On exit from the context, the previous value will be restored. This uses 'gdb.parameter' in its implementation, so it can throw the same exceptions as that function. For example, it's sometimes useful to evaluate some Python code with a particular gdb language: with gdb.with_parameter('language', 'pascal'): ... language-specific operations -- Function: gdb.history (number) Return a value from GDB's value history (*note Value History::). The NUMBER argument indicates which history element to return. If NUMBER is negative, then GDB will take its absolute value and count backward from the last element (i.e., the most recent element) to find the value to return. If NUMBER is zero, then GDB will return the most recent element. If the element specified by NUMBER doesn't exist in the value history, a 'gdb.error' exception will be raised. If no exception is raised, the return value is always an instance of 'gdb.Value' (*note Values From Inferior::). -- Function: gdb.add_history (value) Takes VALUE, an instance of 'gdb.Value' (*note Values From Inferior::), and appends the value this object represents to GDB's value history (*note Value History::), and return an integer, its history number. If VALUE is not a 'gdb.Value', it is is converted using the 'gdb.Value' constructor. If VALUE can't be converted to a 'gdb.Value' then a 'TypeError' is raised. When a command implemented in Python prints a single 'gdb.Value' as its result, then placing the value into the history will allow the user convenient access to those values via CLI history facilities. -- Function: gdb.history_count () Return an integer indicating the number of values in GDB's value history (*note Value History::). -- Function: gdb.convenience_variable (name) Return the value of the convenience variable (*note Convenience Vars::) named NAME. NAME must be a string. The name should not include the '$' that is used to mark a convenience variable in an expression. If the convenience variable does not exist, then 'None' is returned. -- Function: gdb.set_convenience_variable (name, value) Set the value of the convenience variable (*note Convenience Vars::) named NAME. NAME must be a string. The name should not include the '$' that is used to mark a convenience variable in an expression. If VALUE is 'None', then the convenience variable is removed. Otherwise, if VALUE is not a 'gdb.Value' (*note Values From Inferior::), it is is converted using the 'gdb.Value' constructor. -- Function: gdb.parse_and_eval (expression) Parse EXPRESSION, which must be a string, as an expression in the current language, evaluate it, and return the result as a 'gdb.Value'. This function can be useful when implementing a new command (*note CLI Commands In Python::, *note GDB/MI Commands In Python::), as it provides a way to parse the command's argument as an expression. It is also useful simply to compute values. -- Function: gdb.find_pc_line (pc) Return the 'gdb.Symtab_and_line' object corresponding to the PC value. *Note Symbol Tables In Python::. If an invalid value of PC is passed as an argument, then the 'symtab' and 'line' attributes of the returned 'gdb.Symtab_and_line' object will be 'None' and 0 respectively. This is identical to 'gdb.current_progspace().find_pc_line(pc)' and is included for historical compatibility. -- Function: gdb.post_event (event) Put EVENT, a callable object taking no arguments, into GDB's internal event queue. This callable will be invoked at some later point, during GDB's event processing. Events posted using 'post_event' will be run in the order in which they were posted; however, there is no way to know when they will be processed relative to other events inside GDB. GDB is not thread-safe. If your Python program uses multiple threads, you must be careful to only call GDB-specific functions in the GDB thread. 'post_event' ensures this. For example: (gdb) python >import threading > >class Writer(): > def __init__(self, message): > self.message = message; > def __call__(self): > gdb.write(self.message) > >class MyThread1 (threading.Thread): > def run (self): > gdb.post_event(Writer("Hello ")) > >class MyThread2 (threading.Thread): > def run (self): > gdb.post_event(Writer("World\n")) > >MyThread1().start() >MyThread2().start() >end (gdb) Hello World -- Function: gdb.write (string [, stream]) Print a string to GDB's paginated output stream. The optional STREAM determines the stream to print to. The default stream is GDB's standard output stream. Possible stream values are: 'gdb.STDOUT' GDB's standard output stream. 'gdb.STDERR' GDB's standard error stream. 'gdb.STDLOG' GDB's log stream (*note Logging Output::). Writing to 'sys.stdout' or 'sys.stderr' will automatically call this function and will automatically direct the output to the relevant stream. -- Function: gdb.flush () Flush the buffer of a GDB paginated stream so that the contents are displayed immediately. GDB will flush the contents of a stream automatically when it encounters a newline in the buffer. The optional STREAM determines the stream to flush. The default stream is GDB's standard output stream. Possible stream values are: 'gdb.STDOUT' GDB's standard output stream. 'gdb.STDERR' GDB's standard error stream. 'gdb.STDLOG' GDB's log stream (*note Logging Output::). Flushing 'sys.stdout' or 'sys.stderr' will automatically call this function for the relevant stream. -- Function: gdb.target_charset () Return the name of the current target character set (*note Character Sets::). This differs from 'gdb.parameter('target-charset')' in that 'auto' is never returned. -- Function: gdb.target_wide_charset () Return the name of the current target wide character set (*note Character Sets::). This differs from 'gdb.parameter('target-wide-charset')' in that 'auto' is never returned. -- Function: gdb.host_charset () Return a string, the name of the current host character set (*note Character Sets::). This differs from 'gdb.parameter('host-charset')' in that 'auto' is never returned. -- Function: gdb.solib_name (address) Return the name of the shared library holding the given ADDRESS as a string, or 'None'. This is identical to 'gdb.current_progspace().solib_name(address)' and is included for historical compatibility. -- Function: gdb.decode_line ([expression]) Return locations of the line specified by EXPRESSION, or of the current line if no argument was given. This function returns a Python tuple containing two elements. The first element contains a string holding any unparsed section of EXPRESSION (or 'None' if the expression has been fully parsed). The second element contains either 'None' or another tuple that contains all the locations that match the expression represented as 'gdb.Symtab_and_line' objects (*note Symbol Tables In Python::). If EXPRESSION is provided, it is decoded the way that GDB's inbuilt 'break' or 'edit' commands do (*note Specify Location::). -- Function: gdb.prompt_hook (current_prompt) If PROMPT_HOOK is callable, GDB will call the method assigned to this operation before a prompt is displayed by GDB. The parameter 'current_prompt' contains the current GDB prompt. This method must return a Python string, or 'None'. If a string is returned, the GDB prompt will be set to that string. If 'None' is returned, GDB will continue to use the current prompt. Some prompts cannot be substituted in GDB. Secondary prompts such as those used by readline for command input, and annotation related prompts are prohibited from being changed. -- Function: gdb.architecture_names () Return a list containing all of the architecture names that the current build of GDB supports. Each architecture name is a string. The names returned in this list are the same names as are returned from 'gdb.Architecture.name' (*note Architecture.name: gdbpy_architecture_name.). -- Function: gdb.connections Return a list of 'gdb.TargetConnection' objects, one for each currently active connection (*note Connections In Python::). The connection objects are in no particular order in the returned list.  File: gdb.info, Node: Exception Handling, Next: Values From Inferior, Prev: Basic Python, Up: Python API 23.3.2.2 Exception Handling ........................... When executing the 'python' command, Python exceptions uncaught within the Python code are translated to calls to GDB error-reporting mechanism. If the command that called 'python' does not handle the error, GDB will terminate it and print an error message containing the Python exception name, the associated value, and the Python call stack backtrace at the point where the exception was raised. Example: (gdb) python print foo Traceback (most recent call last): File "", line 1, in NameError: name 'foo' is not defined GDB errors that happen in GDB commands invoked by Python code are converted to Python exceptions. The type of the Python exception depends on the error. 'gdb.error' This is the base class for most exceptions generated by GDB. It is derived from 'RuntimeError', for compatibility with earlier versions of GDB. If an error occurring in GDB does not fit into some more specific category, then the generated exception will have this type. 'gdb.MemoryError' This is a subclass of 'gdb.error' which is thrown when an operation tried to access invalid memory in the inferior. 'KeyboardInterrupt' User interrupt (via 'C-c' or by typing 'q' at a pagination prompt) is translated to a Python 'KeyboardInterrupt' exception. In all cases, your exception handler will see the GDB error message as its value and the Python call stack backtrace at the Python statement closest to where the GDB error occured as the traceback. When implementing GDB commands in Python via 'gdb.Command', or functions via 'gdb.Function', it is useful to be able to throw an exception that doesn't cause a traceback to be printed. For example, the user may have invoked the command incorrectly. GDB provides a special exception class that can be used for this purpose. 'gdb.GdbError' When thrown from a command or function, this exception will cause the command or function to fail, but the Python stack will not be displayed. GDB does not throw this exception itself, but rather recognizes it when thrown from user Python code. Example: (gdb) python >class HelloWorld (gdb.Command): > """Greet the whole world.""" > def __init__ (self): > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) > def invoke (self, args, from_tty): > argv = gdb.string_to_argv (args) > if len (argv) != 0: > raise gdb.GdbError ("hello-world takes no arguments") > print ("Hello, World!") >HelloWorld () >end (gdb) hello-world 42 hello-world takes no arguments  File: gdb.info, Node: Values From Inferior, Next: Types In Python, Prev: Exception Handling, Up: Python API 23.3.2.3 Values From Inferior ............................. GDB provides values it obtains from the inferior program in an object of type 'gdb.Value'. GDB uses this object for its internal bookkeeping of the inferior's values, and for fetching values when necessary. Inferior values that are simple scalars can be used directly in Python expressions that are valid for the value's data type. Here's an example for an integer or floating-point value 'some_val': bar = some_val + 2 As result of this, 'bar' will also be a 'gdb.Value' object whose values are of the same type as those of 'some_val'. Valid Python operations can also be performed on 'gdb.Value' objects representing a 'struct' or 'class' object. For such cases, the overloaded operator (if present), is used to perform the operation. For example, if 'val1' and 'val2' are 'gdb.Value' objects representing instances of a 'class' which overloads the '+' operator, then one can use the '+' operator in their Python script as follows: val3 = val1 + val2 The result of the operation 'val3' is also a 'gdb.Value' object corresponding to the value returned by the overloaded '+' operator. In general, overloaded operators are invoked for the following operations: '+' (binary addition), '-' (binary subtraction), '*' (multiplication), '/', '%', '<<', '>>', '|', '&', '^'. Inferior values that are structures or instances of some class can be accessed using the Python "dictionary syntax". For example, if 'some_val' is a 'gdb.Value' instance holding a structure, you can access its 'foo' element with: bar = some_val['foo'] Again, 'bar' will also be a 'gdb.Value' object. Structure elements can also be accessed by using 'gdb.Field' objects as subscripts (*note Types In Python::, for more information on 'gdb.Field' objects). For example, if 'foo_field' is a 'gdb.Field' object corresponding to element 'foo' of the above structure, then 'bar' can also be accessed as follows: bar = some_val[foo_field] A 'gdb.Value' that represents a function can be executed via inferior function call. Any arguments provided to the call must match the function's prototype, and must be provided in the order specified by that prototype. For example, 'some_val' is a 'gdb.Value' instance representing a function that takes two integers as arguments. To execute this function, call it like so: result = some_val (10,20) Any values returned from a function call will be stored as a 'gdb.Value'. The following attributes are provided: -- Variable: Value.address If this object is addressable, this read-only attribute holds a 'gdb.Value' object representing the address. Otherwise, this attribute holds 'None'. -- Variable: Value.is_optimized_out This read-only boolean attribute is true if the compiler optimized out this value, thus it is not available for fetching from the inferior. -- Variable: Value.type The type of this 'gdb.Value'. The value of this attribute is a 'gdb.Type' object (*note Types In Python::). -- Variable: Value.dynamic_type The dynamic type of this 'gdb.Value'. This uses the object's virtual table and the C++ run-time type information (RTTI) to determine the dynamic type of the value. If this value is of class type, it will return the class in which the value is embedded, if any. If this value is of pointer or reference to a class type, it will compute the dynamic type of the referenced object, and return a pointer or reference to that type, respectively. In all other cases, it will return the value's static type. Note that this feature will only work when debugging a C++ program that includes RTTI for the object in question. Otherwise, it will just return the static type of the value as in 'ptype foo' (*note ptype: Symbols.). -- Variable: Value.is_lazy The value of this read-only boolean attribute is 'True' if this 'gdb.Value' has not yet been fetched from the inferior. GDB does not fetch values until necessary, for efficiency. For example: myval = gdb.parse_and_eval ('somevar') The value of 'somevar' is not fetched at this time. It will be fetched when the value is needed, or when the 'fetch_lazy' method is invoked. The following methods are provided: -- Function: Value.__init__ (VAL) Many Python values can be converted directly to a 'gdb.Value' via this object initializer. Specifically: Python boolean A Python boolean is converted to the boolean type from the current language. Python integer A Python integer is converted to the C 'long' type for the current architecture. Python long A Python long is converted to the C 'long long' type for the current architecture. Python float A Python float is converted to the C 'double' type for the current architecture. Python string A Python string is converted to a target string in the current target language using the current target encoding. If a character cannot be represented in the current target encoding, then an exception is thrown. 'gdb.Value' If 'val' is a 'gdb.Value', then a copy of the value is made. 'gdb.LazyString' If 'val' is a 'gdb.LazyString' (*note Lazy Strings In Python::), then the lazy string's 'value' method is called, and its result is used. -- Function: Value.__init__ (VAL, TYPE) This second form of the 'gdb.Value' constructor returns a 'gdb.Value' of type TYPE where the value contents are taken from the Python buffer object specified by VAL. The number of bytes in the Python buffer object must be greater than or equal to the size of TYPE. If TYPE is 'None' then this version of '__init__' behaves as though TYPE was not passed at all. -- Function: Value.cast (type) Return a new instance of 'gdb.Value' that is the result of casting this instance to the type described by TYPE, which must be a 'gdb.Type' object. If the cast cannot be performed for some reason, this method throws an exception. -- Function: Value.dereference () For pointer data types, this method returns a new 'gdb.Value' object whose contents is the object pointed to by the pointer. For example, if 'foo' is a C pointer to an 'int', declared in your C program as int *foo; then you can use the corresponding 'gdb.Value' to access what 'foo' points to like this: bar = foo.dereference () The result 'bar' will be a 'gdb.Value' object holding the value pointed to by 'foo'. A similar function 'Value.referenced_value' exists which also returns 'gdb.Value' objects corresponding to the values pointed to by pointer values (and additionally, values referenced by reference values). However, the behavior of 'Value.dereference' differs from 'Value.referenced_value' by the fact that the behavior of 'Value.dereference' is identical to applying the C unary operator '*' on a given value. For example, consider a reference to a pointer 'ptrref', declared in your C++ program as typedef int *intptr; ... int val = 10; intptr ptr = &val; intptr &ptrref = ptr; Though 'ptrref' is a reference value, one can apply the method 'Value.dereference' to the 'gdb.Value' object corresponding to it and obtain a 'gdb.Value' which is identical to that corresponding to 'val'. However, if you apply the method 'Value.referenced_value', the result would be a 'gdb.Value' object identical to that corresponding to 'ptr'. py_ptrref = gdb.parse_and_eval ("ptrref") py_val = py_ptrref.dereference () py_ptr = py_ptrref.referenced_value () The 'gdb.Value' object 'py_val' is identical to that corresponding to 'val', and 'py_ptr' is identical to that corresponding to 'ptr'. In general, 'Value.dereference' can be applied whenever the C unary operator '*' can be applied to the corresponding C value. For those cases where applying both 'Value.dereference' and 'Value.referenced_value' is allowed, the results obtained need not be identical (as we have seen in the above example). The results are however identical when applied on 'gdb.Value' objects corresponding to pointers ('gdb.Value' objects with type code 'TYPE_CODE_PTR') in a C/C++ program. -- Function: Value.referenced_value () For pointer or reference data types, this method returns a new 'gdb.Value' object corresponding to the value referenced by the pointer/reference value. For pointer data types, 'Value.dereference' and 'Value.referenced_value' produce identical results. The difference between these methods is that 'Value.dereference' cannot get the values referenced by reference values. For example, consider a reference to an 'int', declared in your C++ program as int val = 10; int &ref = val; then applying 'Value.dereference' to the 'gdb.Value' object corresponding to 'ref' will result in an error, while applying 'Value.referenced_value' will result in a 'gdb.Value' object identical to that corresponding to 'val'. py_ref = gdb.parse_and_eval ("ref") er_ref = py_ref.dereference () # Results in error py_val = py_ref.referenced_value () # Returns the referenced value The 'gdb.Value' object 'py_val' is identical to that corresponding to 'val'. -- Function: Value.reference_value () Return a 'gdb.Value' object which is a reference to the value encapsulated by this instance. -- Function: Value.const_value () Return a 'gdb.Value' object which is a 'const' version of the value encapsulated by this instance. -- Function: Value.dynamic_cast (type) Like 'Value.cast', but works as if the C++ 'dynamic_cast' operator were used. Consult a C++ reference for details. -- Function: Value.reinterpret_cast (type) Like 'Value.cast', but works as if the C++ 'reinterpret_cast' operator were used. Consult a C++ reference for details. -- Function: Value.format_string (...) Convert a 'gdb.Value' to a string, similarly to what the 'print' command does. Invoked with no arguments, this is equivalent to calling the 'str' function on the 'gdb.Value'. The representation of the same value may change across different versions of GDB, so you shouldn't, for instance, parse the strings returned by this method. All the arguments are keyword only. If an argument is not specified, the current global default setting is used. 'raw' 'True' if pretty-printers (*note Pretty Printing::) should not be used to format the value. 'False' if enabled pretty-printers matching the type represented by the 'gdb.Value' should be used to format it. 'pretty_arrays' 'True' if arrays should be pretty printed to be more convenient to read, 'False' if they shouldn't (see 'set print array' in *note Print Settings::). 'pretty_structs' 'True' if structs should be pretty printed to be more convenient to read, 'False' if they shouldn't (see 'set print pretty' in *note Print Settings::). 'array_indexes' 'True' if array indexes should be included in the string representation of arrays, 'False' if they shouldn't (see 'set print array-indexes' in *note Print Settings::). 'symbols' 'True' if the string representation of a pointer should include the corresponding symbol name (if one exists), 'False' if it shouldn't (see 'set print symbol' in *note Print Settings::). 'unions' 'True' if unions which are contained in other structures or unions should be expanded, 'False' if they shouldn't (see 'set print union' in *note Print Settings::). 'address' 'True' if the string representation of a pointer should include the address, 'False' if it shouldn't (see 'set print address' in *note Print Settings::). 'deref_refs' 'True' if C++ references should be resolved to the value they refer to, 'False' (the default) if they shouldn't. Note that, unlike for the 'print' command, references are not automatically expanded when using the 'format_string' method or the 'str' function. There is no global 'print' setting to change the default behaviour. 'actual_objects' 'True' if the representation of a pointer to an object should identify the _actual_ (derived) type of the object rather than the _declared_ type, using the virtual function table. 'False' if the _declared_ type should be used. (See 'set print object' in *note Print Settings::). 'static_members' 'True' if static members should be included in the string representation of a C++ object, 'False' if they shouldn't (see 'set print static-members' in *note Print Settings::). 'max_elements' Number of array elements to print, or '0' to print an unlimited number of elements (see 'set print elements' in *note Print Settings::). 'max_depth' The maximum depth to print for nested structs and unions, or '-1' to print an unlimited number of elements (see 'set print max-depth' in *note Print Settings::). 'repeat_threshold' Set the threshold for suppressing display of repeated array elements, or '0' to represent all elements, even if repeated. (See 'set print repeats' in *note Print Settings::). 'format' A string containing a single character representing the format to use for the returned string. For instance, ''x'' is equivalent to using the GDB command 'print' with the '/x' option and formats the value as a hexadecimal number. 'styling' 'True' if GDB should apply styling to the returned string. When styling is applied, the returned string might contain ANSI terminal escape sequences. Escape sequences will only be included if styling is turned on, see *note Output Styling::. Additionally, GDB only styles some value contents, so not every output string will contain escape sequences. When 'False', which is the default, no output styling is applied. -- Function: Value.string ([encoding[, errors[, length]]]) If this 'gdb.Value' represents a string, then this method converts the contents to a Python string. Otherwise, this method will throw an exception. Values are interpreted as strings according to the rules of the current language. If the optional length argument is given, the string will be converted to that length, and will include any embedded zeroes that the string may contain. Otherwise, for languages where the string is zero-terminated, the entire string will be converted. For example, in C-like languages, a value is a string if it is a pointer to or an array of characters or ints of type 'wchar_t', 'char16_t', or 'char32_t'. If the optional ENCODING argument is given, it must be a string naming the encoding of the string in the 'gdb.Value', such as '"ascii"', '"iso-8859-6"' or '"utf-8"'. It accepts the same encodings as the corresponding argument to Python's 'string.decode' method, and the Python codec machinery will be used to convert the string. If ENCODING is not given, or if ENCODING is the empty string, then either the 'target-charset' (*note Character Sets::) will be used, or a language-specific encoding will be used, if the current language is able to supply one. The optional ERRORS argument is the same as the corresponding argument to Python's 'string.decode' method. If the optional LENGTH argument is given, the string will be fetched and converted to the given length. -- Function: Value.lazy_string ([encoding [, length]]) If this 'gdb.Value' represents a string, then this method converts the contents to a 'gdb.LazyString' (*note Lazy Strings In Python::). Otherwise, this method will throw an exception. If the optional ENCODING argument is given, it must be a string naming the encoding of the 'gdb.LazyString'. Some examples are: 'ascii', 'iso-8859-6' or 'utf-8'. If the ENCODING argument is an encoding that GDB does recognize, GDB will raise an error. When a lazy string is printed, the GDB encoding machinery is used to convert the string during printing. If the optional ENCODING argument is not provided, or is an empty string, GDB will automatically select the encoding most suitable for the string type. For further information on encoding in GDB please see *note Character Sets::. If the optional LENGTH argument is given, the string will be fetched and encoded to the length of characters specified. If the LENGTH argument is not provided, the string will be fetched and encoded until a null of appropriate width is found. -- Function: Value.fetch_lazy () If the 'gdb.Value' object is currently a lazy value ('gdb.Value.is_lazy' is 'True'), then the value is fetched from the inferior. Any errors that occur in the process will produce a Python exception. If the 'gdb.Value' object is not a lazy value, this method has no effect. This method does not return a value.  File: gdb.info, Node: Types In Python, Next: Pretty Printing API, Prev: Values From Inferior, Up: Python API 23.3.2.4 Types In Python ........................ GDB represents types from the inferior using the class 'gdb.Type'. The following type-related functions are available in the 'gdb' module: -- Function: gdb.lookup_type (name [, block]) This function looks up a type by its NAME, which must be a string. If BLOCK is given, then NAME is looked up in that scope. Otherwise, it is searched for globally. Ordinarily, this function will return an instance of 'gdb.Type'. If the named type cannot be found, it will throw an exception. Integer types can be found without looking them up by name. *Note Architectures In Python::, for the 'integer_type' method. If the type is a structure or class type, or an enum type, the fields of that type can be accessed using the Python "dictionary syntax". For example, if 'some_type' is a 'gdb.Type' instance holding a structure type, you can access its 'foo' field with: bar = some_type['foo'] 'bar' will be a 'gdb.Field' object; see below under the description of the 'Type.fields' method for a description of the 'gdb.Field' class. An instance of 'Type' has the following attributes: -- Variable: Type.alignof The alignment of this type, in bytes. Type alignment comes from the debugging information; if it was not specified, then GDB will use the relevant ABI to try to determine the alignment. In some cases, even this is not possible, and zero will be returned. -- Variable: Type.code The type code for this type. The type code will be one of the 'TYPE_CODE_' constants defined below. -- Variable: Type.dynamic A boolean indicating whether this type is dynamic. In some situations, such as Rust 'enum' types or Ada variant records, the concrete type of a value may vary depending on its contents. That is, the declared type of a variable, or the type returned by 'gdb.lookup_type' may be dynamic; while the type of the variable's value will be a concrete instance of that dynamic type. For example, consider this code: int n; int array[n]; Here, at least conceptually (whether your compiler actually does this is a separate issue), examining 'gdb.lookup_symbol("array", ...).type' could yield a 'gdb.Type' which reports a size of 'None'. This is the dynamic type. However, examining 'gdb.parse_and_eval("array").type' would yield a concrete type, whose length would be known. -- Variable: Type.name The name of this type. If this type has no name, then 'None' is returned. -- Variable: Type.sizeof The size of this type, in target 'char' units. Usually, a target's 'char' type will be an 8-bit byte. However, on some unusual platforms, this type may have a different size. A dynamic type may not have a fixed size; in this case, this attribute's value will be 'None'. -- Variable: Type.tag The tag name for this type. The tag name is the name after 'struct', 'union', or 'enum' in C and C++; not all languages have this concept. If this type has no tag name, then 'None' is returned. -- Variable: Type.objfile The 'gdb.Objfile' that this type was defined in, or 'None' if there is no associated objfile. -- Variable: Type.is_scalar This property is 'True' if the type is a scalar type, otherwise, this property is 'False'. Examples of non-scalar types include structures, unions, and classes. -- Variable: Type.is_signed For scalar types (those for which 'Type.is_scalar' is 'True'), this property is 'True' if the type is signed, otherwise this property is 'False'. Attempting to read this property for a non-scalar type (a type for which 'Type.is_scalar' is 'False'), will raise a 'ValueError'. The following methods are provided: -- Function: Type.fields () Return the fields of this type. The behavior depends on the type code: * For structure and union types, this method returns the fields. * Range types have two fields, the minimum and maximum values. * Enum types have one field per enum constant. * Function and method types have one field per parameter. The base types of C++ classes are also represented as fields. * Array types have one field representing the array's range. * If the type does not fit into one of these categories, a 'TypeError' is raised. Each field is a 'gdb.Field' object, with some pre-defined attributes: 'bitpos' This attribute is not available for 'enum' or 'static' (as in C++) fields. The value is the position, counting in bits, from the start of the containing type. Note that, in a dynamic type, the position of a field may not be constant. In this case, the value will be 'None'. Also, a dynamic type may have fields that do not appear in a corresponding concrete type. 'enumval' This attribute is only available for 'enum' fields, and its value is the enumeration member's integer representation. 'name' The name of the field, or 'None' for anonymous fields. 'artificial' This is 'True' if the field is artificial, usually meaning that it was provided by the compiler and not the user. This attribute is always provided, and is 'False' if the field is not artificial. 'is_base_class' This is 'True' if the field represents a base class of a C++ structure. This attribute is always provided, and is 'False' if the field is not a base class of the type that is the argument of 'fields', or if that type was not a C++ class. 'bitsize' If the field is packed, or is a bitfield, then this will have a non-zero value, which is the size of the field in bits. Otherwise, this will be zero; in this case the field's size is given by its type. 'type' The type of the field. This is usually an instance of 'Type', but it can be 'None' in some situations. 'parent_type' The type which contains this field. This is an instance of 'gdb.Type'. -- Function: Type.array (N1 [, N2]) Return a new 'gdb.Type' object which represents an array of this type. If one argument is given, it is the inclusive upper bound of the array; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the array, and the second argument is the upper bound of the array. An array's length must not be negative, but the bounds can be. -- Function: Type.vector (N1 [, N2]) Return a new 'gdb.Type' object which represents a vector of this type. If one argument is given, it is the inclusive upper bound of the vector; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the vector, and the second argument is the upper bound of the vector. A vector's length must not be negative, but the bounds can be. The difference between an 'array' and a 'vector' is that arrays behave like in C: when used in expressions they decay to a pointer to the first element whereas vectors are treated as first class values. -- Function: Type.const () Return a new 'gdb.Type' object which represents a 'const'-qualified variant of this type. -- Function: Type.volatile () Return a new 'gdb.Type' object which represents a 'volatile'-qualified variant of this type. -- Function: Type.unqualified () Return a new 'gdb.Type' object which represents an unqualified variant of this type. That is, the result is neither 'const' nor 'volatile'. -- Function: Type.range () Return a Python 'Tuple' object that contains two elements: the low bound of the argument type and the high bound of that type. If the type does not have a range, GDB will raise a 'gdb.error' exception (*note Exception Handling::). -- Function: Type.reference () Return a new 'gdb.Type' object which represents a reference to this type. -- Function: Type.pointer () Return a new 'gdb.Type' object which represents a pointer to this type. -- Function: Type.strip_typedefs () Return a new 'gdb.Type' that represents the real type, after removing all layers of typedefs. -- Function: Type.target () Return a new 'gdb.Type' object which represents the target type of this type. For a pointer type, the target type is the type of the pointed-to object. For an array type (meaning C-like arrays), the target type is the type of the elements of the array. For a function or method type, the target type is the type of the return value. For a complex type, the target type is the type of the elements. For a typedef, the target type is the aliased type. If the type does not have a target, this method will throw an exception. -- Function: Type.template_argument (n [, block]) If this 'gdb.Type' is an instantiation of a template, this will return a new 'gdb.Value' or 'gdb.Type' which represents the value of the Nth template argument (indexed starting at 0). If this 'gdb.Type' is not a template type, or if the type has fewer than N template arguments, this will throw an exception. Ordinarily, only C++ code will have template types. If BLOCK is given, then NAME is looked up in that scope. Otherwise, it is searched for globally. -- Function: Type.optimized_out () Return 'gdb.Value' instance of this type whose value is optimized out. This allows a frame decorator to indicate that the value of an argument or a local variable is not known. Each type has a code, which indicates what category this type falls into. The available type categories are represented by constants defined in the 'gdb' module: 'gdb.TYPE_CODE_PTR' The type is a pointer. 'gdb.TYPE_CODE_ARRAY' The type is an array. 'gdb.TYPE_CODE_STRUCT' The type is a structure. 'gdb.TYPE_CODE_UNION' The type is a union. 'gdb.TYPE_CODE_ENUM' The type is an enum. 'gdb.TYPE_CODE_FLAGS' A bit flags type, used for things such as status registers. 'gdb.TYPE_CODE_FUNC' The type is a function. 'gdb.TYPE_CODE_INT' The type is an integer type. 'gdb.TYPE_CODE_FLT' A floating point type. 'gdb.TYPE_CODE_VOID' The special type 'void'. 'gdb.TYPE_CODE_SET' A Pascal set type. 'gdb.TYPE_CODE_RANGE' A range type, that is, an integer type with bounds. 'gdb.TYPE_CODE_STRING' A string type. Note that this is only used for certain languages with language-defined string types; C strings are not represented this way. 'gdb.TYPE_CODE_BITSTRING' A string of bits. It is deprecated. 'gdb.TYPE_CODE_ERROR' An unknown or erroneous type. 'gdb.TYPE_CODE_METHOD' A method type, as found in C++. 'gdb.TYPE_CODE_METHODPTR' A pointer-to-member-function. 'gdb.TYPE_CODE_MEMBERPTR' A pointer-to-member. 'gdb.TYPE_CODE_REF' A reference type. 'gdb.TYPE_CODE_RVALUE_REF' A C++11 rvalue reference type. 'gdb.TYPE_CODE_CHAR' A character type. 'gdb.TYPE_CODE_BOOL' A boolean type. 'gdb.TYPE_CODE_COMPLEX' A complex float type. 'gdb.TYPE_CODE_TYPEDEF' A typedef to some other type. 'gdb.TYPE_CODE_NAMESPACE' A C++ namespace. 'gdb.TYPE_CODE_DECFLOAT' A decimal floating point type. 'gdb.TYPE_CODE_INTERNAL_FUNCTION' A function internal to GDB. This is the type used to represent convenience functions. Further support for types is provided in the 'gdb.types' Python module (*note gdb.types::).  File: gdb.info, Node: Pretty Printing API, Next: Selecting Pretty-Printers, Prev: Types In Python, Up: Python API 23.3.2.5 Pretty Printing API ............................ A pretty-printer is just an object that holds a value and implements a specific interface, defined here. An example output is provided (*note Pretty Printing::). -- Function: pretty_printer.children (self) GDB will call this method on a pretty-printer to compute the children of the pretty-printer's value. This method must return an object conforming to the Python iterator protocol. Each item returned by the iterator must be a tuple holding two elements. The first element is the "name" of the child; the second element is the child's value. The value can be any Python object which is convertible to a GDB value. This method is optional. If it does not exist, GDB will act as though the value has no children. For efficiency, the 'children' method should lazily compute its results. This will let GDB read as few elements as necessary, for example when various print settings (*note Print Settings::) or '-var-list-children' (*note GDB/MI Variable Objects::) limit the number of elements to be displayed. Children may be hidden from display based on the value of 'set print max-depth' (*note Print Settings::). -- Function: pretty_printer.display_hint (self) The CLI may call this method and use its result to change the formatting of a value. The result will also be supplied to an MI consumer as a 'displayhint' attribute of the variable being printed. This method is optional. If it does exist, this method must return a string or the special value 'None'. Some display hints are predefined by GDB: 'array' Indicate that the object being printed is "array-like". The CLI uses this to respect parameters such as 'set print elements' and 'set print array'. 'map' Indicate that the object being printed is "map-like", and that the children of this value can be assumed to alternate between keys and values. 'string' Indicate that the object being printed is "string-like". If the printer's 'to_string' method returns a Python string of some kind, then GDB will call its internal language-specific string-printing function to format the string. For the CLI this means adding quotation marks, possibly escaping some characters, respecting 'set print elements', and the like. The special value 'None' causes GDB to apply the default display rules. -- Function: pretty_printer.to_string (self) GDB will call this method to display the string representation of the value passed to the object's constructor. When printing from the CLI, if the 'to_string' method exists, then GDB will prepend its result to the values returned by 'children'. Exactly how this formatting is done is dependent on the display hint, and may change as more hints are added. Also, depending on the print settings (*note Print Settings::), the CLI may print just the result of 'to_string' in a stack trace, omitting the result of 'children'. If this method returns a string, it is printed verbatim. Otherwise, if this method returns an instance of 'gdb.Value', then GDB prints this value. This may result in a call to another pretty-printer. If instead the method returns a Python value which is convertible to a 'gdb.Value', then GDB performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer. Python scalars (integers, floats, and booleans) and strings are convertible to 'gdb.Value'; other types are not. Finally, if this method returns 'None' then no further operations are peformed in this method and nothing is printed. If the result is not one of these types, an exception is raised. GDB provides a function which can be used to look up the default pretty-printer for a 'gdb.Value': -- Function: gdb.default_visualizer (value) This function takes a 'gdb.Value' object as an argument. If a pretty-printer for this value exists, then it is returned. If no such printer exists, then this returns 'None'.  File: gdb.info, Node: Selecting Pretty-Printers, Next: Writing a Pretty-Printer, Prev: Pretty Printing API, Up: Python API 23.3.2.6 Selecting Pretty-Printers .................................. GDB provides several ways to register a pretty-printer: globally, per program space, and per objfile. When choosing how to register your pretty-printer, a good rule is to register it with the smallest scope possible: that is prefer a specific objfile first, then a program space, and only register a printer globally as a last resort. -- Variable: gdb.pretty_printers The Python list 'gdb.pretty_printers' contains an array of functions or callable objects that have been registered via addition as a pretty-printer. Printers in this list are called 'global' printers, they're available when debugging all inferiors. Each 'gdb.Progspace' contains a 'pretty_printers' attribute. Each 'gdb.Objfile' also contains a 'pretty_printers' attribute. Each function on these lists is passed a single 'gdb.Value' argument and should return a pretty-printer object conforming to the interface definition above (*note Pretty Printing API::). If a function cannot create a pretty-printer for the value, it should return 'None'. GDB first checks the 'pretty_printers' attribute of each 'gdb.Objfile' in the current program space and iteratively calls each enabled lookup routine in the list for that 'gdb.Objfile' until it receives a pretty-printer object. If no pretty-printer is found in the objfile lists, GDB then searches the pretty-printer list of the current program space, calling each enabled function until an object is returned. After these lists have been exhausted, it tries the global 'gdb.pretty_printers' list, again calling each enabled function until an object is returned. The order in which the objfiles are searched is not specified. For a given list, functions are always invoked from the head of the list, and iterated over sequentially until the end of the list, or a printer object is returned. For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date. The consequences of a broken pretty-printer are severe enough that GDB provides support for enabling and disabling individual printers. For example, if 'print frame-arguments' is on, a backtrace can become highly illegible if any argument is printed with a broken printer. Pretty-printers are enabled and disabled by attaching an 'enabled' attribute to the registered function or callable object. If this attribute is present and its value is 'False', the printer is disabled, otherwise the printer is enabled.  File: gdb.info, Node: Writing a Pretty-Printer, Next: Type Printing API, Prev: Selecting Pretty-Printers, Up: Python API 23.3.2.7 Writing a Pretty-Printer ................................. A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself. Here is an example showing how a 'std::string' printer might be written. *Note Pretty Printing API::, for details on the API this class must provide. class StdStringPrinter(object): "Print a std::string" def __init__(self, val): self.val = val def to_string(self): return self.val['_M_dataplus']['_M_p'] def display_hint(self): return 'string' And here is an example showing how a lookup function for the printer example above might be written. def str_lookup_function(val): lookup_tag = val.type.tag if lookup_tag is None: return None regex = re.compile("^std::basic_string$") if regex.match(lookup_tag): return StdStringPrinter(val) return None The example lookup function extracts the value's type, and attempts to match it to a type that it can pretty-print. If it is a type the printer can pretty-print, it will return a printer object. If not, it returns 'None'. We recommend that you put your core pretty-printers into a Python package. If your pretty-printers are for use with a library, we further recommend embedding a version number into the package name. This practice will enable GDB to load multiple versions of your pretty-printers at the same time, because they will have different names. You should write auto-loaded code (*note Python Auto-loading::) such that it can be evaluated multiple times without changing its meaning. An ideal auto-load file will consist solely of 'import's of your printer modules, followed by a call to a register pretty-printers with the current objfile. Taken as a whole, this approach will scale nicely to multiple inferiors, each potentially using a different library version. Embedding a version number in the Python package name will ensure that GDB is able to load both sets of printers simultaneously. Then, because the search for pretty-printers is done by objfile, and because your auto-loaded code took care to register your library's printers with a specific objfile, GDB will find the correct printers for the specific version of the library used by each inferior. To continue the 'std::string' example (*note Pretty Printing API::), this code might appear in 'gdb.libstdcxx.v6': def register_printers(objfile): objfile.pretty_printers.append(str_lookup_function) And then the corresponding contents of the auto-load file would be: import gdb.libstdcxx.v6 gdb.libstdcxx.v6.register_printers(gdb.current_objfile()) The previous example illustrates a basic pretty-printer. There are a few things that can be improved on. The printer doesn't have a name, making it hard to identify in a list of installed printers. The lookup function has a name, but lookup functions can have arbitrary, even identical, names. Second, the printer only handles one type, whereas a library typically has several types. One could install a lookup function for each desired type in the library, but one could also have a single lookup function recognize several types. The latter is the conventional way this is handled. If a pretty-printer can handle multiple data types, then its "subprinters" are the printers for the individual data types. The 'gdb.printing' module provides a formal way of solving these problems (*note gdb.printing::). Here is another example that handles multiple types. These are the types we are going to pretty-print: struct foo { int a, b; }; struct bar { struct foo x, y; }; Here are the printers: class fooPrinter: """Print a foo object.""" def __init__(self, val): self.val = val def to_string(self): return ("a=<" + str(self.val["a"]) + "> b=<" + str(self.val["b"]) + ">") class barPrinter: """Print a bar object.""" def __init__(self, val): self.val = val def to_string(self): return ("x=<" + str(self.val["x"]) + "> y=<" + str(self.val["y"]) + ">") This example doesn't need a lookup function, that is handled by the 'gdb.printing' module. Instead a function is provided to build up the object that handles the lookup. import gdb.printing def build_pretty_printer(): pp = gdb.printing.RegexpCollectionPrettyPrinter( "my_library") pp.add_printer('foo', '^foo$', fooPrinter) pp.add_printer('bar', '^bar$', barPrinter) return pp And here is the autoload support: import gdb.printing import my_library gdb.printing.register_pretty_printer( gdb.current_objfile(), my_library.build_pretty_printer()) Finally, when this printer is loaded into GDB, here is the corresponding output of 'info pretty-printer': (gdb) info pretty-printer my_library.so: my_library foo bar  File: gdb.info, Node: Type Printing API, Next: Frame Filter API, Prev: Writing a Pretty-Printer, Up: Python API 23.3.2.8 Type Printing API .......................... GDB provides a way for Python code to customize type display. This is mainly useful for substituting canonical typedef names for types. A "type printer" is just a Python object conforming to a certain protocol. A simple base class implementing the protocol is provided; see *note gdb.types::. A type printer must supply at least: -- Instance Variable of type_printer: enabled A boolean which is True if the printer is enabled, and False otherwise. This is manipulated by the 'enable type-printer' and 'disable type-printer' commands. -- Instance Variable of type_printer: name The name of the type printer. This must be a string. This is used by the 'enable type-printer' and 'disable type-printer' commands. -- Method on type_printer: instantiate (self) This is called by GDB at the start of type-printing. It is only called if the type printer is enabled. This method must return a new object that supplies a 'recognize' method, as described below. When displaying a type, say via the 'ptype' command, GDB will compute a list of type recognizers. This is done by iterating first over the per-objfile type printers (*note Objfiles In Python::), followed by the per-progspace type printers (*note Progspaces In Python::), and finally the global type printers. GDB will call the 'instantiate' method of each enabled type printer. If this method returns 'None', then the result is ignored; otherwise, it is appended to the list of recognizers. Then, when GDB is going to display a type name, it iterates over the list of recognizers. For each one, it calls the recognition function, stopping if the function returns a non-'None' value. The recognition function is defined as: -- Method on type_recognizer: recognize (self, type) If TYPE is not recognized, return 'None'. Otherwise, return a string which is to be printed as the name of TYPE. The TYPE argument will be an instance of 'gdb.Type' (*note Types In Python::). GDB uses this two-pass approach so that type printers can efficiently cache information without holding on to it too long. For example, it can be convenient to look up type information in a type printer and hold it for a recognizer's lifetime; if a single pass were done then type printers would have to make use of the event system in order to avoid holding information that could become stale as the inferior changed.  File: gdb.info, Node: Frame Filter API, Next: Frame Decorator API, Prev: Type Printing API, Up: Python API 23.3.2.9 Filtering Frames ......................... Frame filters are Python objects that manipulate the visibility of a frame or frames when a backtrace (*note Backtrace::) is printed by GDB. Only commands that print a backtrace, or, in the case of GDB/MI commands (*note GDB/MI::), those that return a collection of frames are affected. The commands that work with frame filters are: 'backtrace' (*note The backtrace command: backtrace-command.), '-stack-list-frames' (*note The -stack-list-frames command: -stack-list-frames.), '-stack-list-variables' (*note The -stack-list-variables command: -stack-list-variables.), '-stack-list-arguments' *note The -stack-list-arguments command: -stack-list-arguments.) and '-stack-list-locals' (*note The -stack-list-locals command: -stack-list-locals.). A frame filter works by taking an iterator as an argument, applying actions to the contents of that iterator, and returning another iterator (or, possibly, the same iterator it was provided in the case where the filter does not perform any operations). Typically, frame filters utilize tools such as the Python's 'itertools' module to work with and create new iterators from the source iterator. Regardless of how a filter chooses to apply actions, it must not alter the underlying GDB frame or frames, or attempt to alter the call-stack within GDB. This preserves data integrity within GDB. Frame filters are executed on a priority basis and care should be taken that some frame filters may have been executed before, and that some frame filters will be executed after. An important consideration when designing frame filters, and well worth reflecting upon, is that frame filters should avoid unwinding the call stack if possible. Some stacks can run very deep, into the tens of thousands in some cases. To search every frame when a frame filter executes may be too expensive at that step. The frame filter cannot know how many frames it has to iterate over, and it may have to iterate through them all. This ends up duplicating effort as GDB performs this iteration when it prints the frames. If the filter can defer unwinding frames until frame decorators are executed, after the last filter has executed, it should. *Note Frame Decorator API::, for more information on decorators. Also, there are examples for both frame decorators and filters in later chapters. *Note Writing a Frame Filter::, for more information. The Python dictionary 'gdb.frame_filters' contains key/object pairings that comprise a frame filter. Frame filters in this dictionary are called 'global' frame filters, and they are available when debugging all inferiors. These frame filters must register with the dictionary directly. In addition to the 'global' dictionary, there are other dictionaries that are loaded with different inferiors via auto-loading (*note Python Auto-loading::). The two other areas where frame filter dictionaries can be found are: 'gdb.Progspace' which contains a 'frame_filters' dictionary attribute, and each 'gdb.Objfile' object which also contains a 'frame_filters' dictionary attribute. When a command is executed from GDB that is compatible with frame filters, GDB combines the 'global', 'gdb.Progspace' and all 'gdb.Objfile' dictionaries currently loaded. All of the 'gdb.Objfile' dictionaries are combined, as several frames, and thus several object files, might be in use. GDB then prunes any frame filter whose 'enabled' attribute is 'False'. This pruned list is then sorted according to the 'priority' attribute in each filter. Once the dictionaries are combined, pruned and sorted, GDB creates an iterator which wraps each frame in the call stack in a 'FrameDecorator' object, and calls each filter in order. The output from the previous filter will always be the input to the next filter, and so on. Frame filters have a mandatory interface which each frame filter must implement, defined here: -- Function: FrameFilter.filter (iterator) GDB will call this method on a frame filter when it has reached the order in the priority list for that filter. For example, if there are four frame filters: Name Priority Filter1 5 Filter2 10 Filter3 100 Filter4 1 The order that the frame filters will be called is: Filter3 -> Filter2 -> Filter1 -> Filter4 Note that the output from 'Filter3' is passed to the input of 'Filter2', and so on. This 'filter' method is passed a Python iterator. This iterator contains a sequence of frame decorators that wrap each 'gdb.Frame', or a frame decorator that wraps another frame decorator. The first filter that is executed in the sequence of frame filters will receive an iterator entirely comprised of default 'FrameDecorator' objects. However, after each frame filter is executed, the previous frame filter may have wrapped some or all of the frame decorators with their own frame decorator. As frame decorators must also conform to a mandatory interface, these decorators can be assumed to act in a uniform manner (*note Frame Decorator API::). This method must return an object conforming to the Python iterator protocol. Each item in the iterator must be an object conforming to the frame decorator interface. If a frame filter does not wish to perform any operations on this iterator, it should return that iterator untouched. This method is not optional. If it does not exist, GDB will raise and print an error. -- Variable: FrameFilter.name The 'name' attribute must be Python string which contains the name of the filter displayed by GDB (*note Frame Filter Management::). This attribute may contain any combination of letters or numbers. Care should be taken to ensure that it is unique. This attribute is mandatory. -- Variable: FrameFilter.enabled The 'enabled' attribute must be Python boolean. This attribute indicates to GDB whether the frame filter is enabled, and should be considered when frame filters are executed. If 'enabled' is 'True', then the frame filter will be executed when any of the backtrace commands detailed earlier in this chapter are executed. If 'enabled' is 'False', then the frame filter will not be executed. This attribute is mandatory. -- Variable: FrameFilter.priority The 'priority' attribute must be Python integer. This attribute controls the order of execution in relation to other frame filters. There are no imposed limits on the range of 'priority' other than it must be a valid integer. The higher the 'priority' attribute, the sooner the frame filter will be executed in relation to other frame filters. Although 'priority' can be negative, it is recommended practice to assume zero is the lowest priority that a frame filter can be assigned. Frame filters that have the same priority are executed in unsorted order in that priority slot. This attribute is mandatory. 100 is a good default priority.  File: gdb.info, Node: Frame Decorator API, Next: Writing a Frame Filter, Prev: Frame Filter API, Up: Python API 23.3.2.10 Decorating Frames ........................... Frame decorators are sister objects to frame filters (*note Frame Filter API::). Frame decorators are applied by a frame filter and can only be used in conjunction with frame filters. The purpose of a frame decorator is to customize the printed content of each 'gdb.Frame' in commands where frame filters are executed. This concept is called decorating a frame. Frame decorators decorate a 'gdb.Frame' with Python code contained within each API call. This separates the actual data contained in a 'gdb.Frame' from the decorated data produced by a frame decorator. This abstraction is necessary to maintain integrity of the data contained in each 'gdb.Frame'. Frame decorators have a mandatory interface, defined below. GDB already contains a frame decorator called 'FrameDecorator'. This contains substantial amounts of boilerplate code to decorate the content of a 'gdb.Frame'. It is recommended that other frame decorators inherit and extend this object, and only to override the methods needed. 'FrameDecorator' is defined in the Python module 'gdb.FrameDecorator', so your code can import it like: from gdb.FrameDecorator import FrameDecorator -- Function: FrameDecorator.elided (self) The 'elided' method groups frames together in a hierarchical system. An example would be an interpreter, where multiple low-level frames make up a single call in the interpreted language. In this example, the frame filter would elide the low-level frames and present a single high-level frame, representing the call in the interpreted language, to the user. The 'elided' function must return an iterable and this iterable must contain the frames that are being elided wrapped in a suitable frame decorator. If no frames are being elided this function may return an empty iterable, or 'None'. Elided frames are indented from normal frames in a 'CLI' backtrace, or in the case of GDB/MI, are placed in the 'children' field of the eliding frame. It is the frame filter's task to also filter out the elided frames from the source iterator. This will avoid printing the frame twice. -- Function: FrameDecorator.function (self) This method returns the name of the function in the frame that is to be printed. This method must return a Python string describing the function, or 'None'. If this function returns 'None', GDB will not print any data for this field. -- Function: FrameDecorator.address (self) This method returns the address of the frame that is to be printed. This method must return a Python numeric integer type of sufficient size to describe the address of the frame, or 'None'. If this function returns a 'None', GDB will not print any data for this field. -- Function: FrameDecorator.filename (self) This method returns the filename and path associated with this frame. This method must return a Python string containing the filename and the path to the object file backing the frame, or 'None'. If this function returns a 'None', GDB will not print any data for this field. -- Function: FrameDecorator.line (self): This method returns the line number associated with the current position within the function addressed by this frame. This method must return a Python integer type, or 'None'. If this function returns a 'None', GDB will not print any data for this field. -- Function: FrameDecorator.frame_args (self) This method must return an iterable, or 'None'. Returning an empty iterable, or 'None' means frame arguments will not be printed for this frame. This iterable must contain objects that implement two methods, described here. This object must implement a 'symbol' method which takes a single 'self' parameter and must return a 'gdb.Symbol' (*note Symbols In Python::), or a Python string. The object must also implement a 'value' method which takes a single 'self' parameter and must return a 'gdb.Value' (*note Values From Inferior::), a Python value, or 'None'. If the 'value' method returns 'None', and the 'argument' method returns a 'gdb.Symbol', GDB will look-up and print the value of the 'gdb.Symbol' automatically. A brief example: class SymValueWrapper(): def __init__(self, symbol, value): self.sym = symbol self.val = value def value(self): return self.val def symbol(self): return self.sym class SomeFrameDecorator() ... ... def frame_args(self): args = [] try: block = self.inferior_frame.block() except: return None # Iterate over all symbols in a block. Only add # symbols that are arguments. for sym in block: if not sym.is_argument: continue args.append(SymValueWrapper(sym,None)) # Add example synthetic argument. args.append(SymValueWrapper(``foo'', 42)) return args -- Function: FrameDecorator.frame_locals (self) This method must return an iterable or 'None'. Returning an empty iterable, or 'None' means frame local arguments will not be printed for this frame. The object interface, the description of the various strategies for reading frame locals, and the example are largely similar to those described in the 'frame_args' function, (*note The frame filter frame_args function: frame_args.). Below is a modified example: class SomeFrameDecorator() ... ... def frame_locals(self): vars = [] try: block = self.inferior_frame.block() except: return None # Iterate over all symbols in a block. Add all # symbols, except arguments. for sym in block: if sym.is_argument: continue vars.append(SymValueWrapper(sym,None)) # Add an example of a synthetic local variable. vars.append(SymValueWrapper(``bar'', 99)) return vars -- Function: FrameDecorator.inferior_frame (self): This method must return the underlying 'gdb.Frame' that this frame decorator is decorating. GDB requires the underlying frame for internal frame information to determine how to print certain values when printing a frame.  File: gdb.info, Node: Writing a Frame Filter, Next: Unwinding Frames in Python, Prev: Frame Decorator API, Up: Python API 23.3.2.11 Writing a Frame Filter ................................ There are three basic elements that a frame filter must implement: it must correctly implement the documented interface (*note Frame Filter API::), it must register itself with GDB, and finally, it must decide if it is to work on the data provided by GDB. In all cases, whether it works on the iterator or not, each frame filter must return an iterator. A bare-bones frame filter follows the pattern in the following example. import gdb class FrameFilter(): def __init__(self): # Frame filter attribute creation. # # 'name' is the name of the filter that GDB will display. # # 'priority' is the priority of the filter relative to other # filters. # # 'enabled' is a boolean that indicates whether this filter is # enabled and should be executed. self.name = "Foo" self.priority = 100 self.enabled = True # Register this frame filter with the global frame_filters # dictionary. gdb.frame_filters[self.name] = self def filter(self, frame_iter): # Just return the iterator. return frame_iter The frame filter in the example above implements the three requirements for all frame filters. It implements the API, self registers, and makes a decision on the iterator (in this case, it just returns the iterator untouched). The first step is attribute creation and assignment, and as shown in the comments the filter assigns the following attributes: 'name', 'priority' and whether the filter should be enabled with the 'enabled' attribute. The second step is registering the frame filter with the dictionary or dictionaries that the frame filter has interest in. As shown in the comments, this filter just registers itself with the global dictionary 'gdb.frame_filters'. As noted earlier, 'gdb.frame_filters' is a dictionary that is initialized in the 'gdb' module when GDB starts. What dictionary a filter registers with is an important consideration. Generally, if a filter is specific to a set of code, it should be registered either in the 'objfile' or 'progspace' dictionaries as they are specific to the program currently loaded in GDB. The global dictionary is always present in GDB and is never unloaded. Any filters registered with the global dictionary will exist until GDB exits. To avoid filters that may conflict, it is generally better to register frame filters against the dictionaries that more closely align with the usage of the filter currently in question. *Note Python Auto-loading::, for further information on auto-loading Python scripts. GDB takes a hands-off approach to frame filter registration, therefore it is the frame filter's responsibility to ensure registration has occurred, and that any exceptions are handled appropriately. In particular, you may wish to handle exceptions relating to Python dictionary key uniqueness. It is mandatory that the dictionary key is the same as frame filter's 'name' attribute. When a user manages frame filters (*note Frame Filter Management::), the names GDB will display are those contained in the 'name' attribute. The final step of this example is the implementation of the 'filter' method. As shown in the example comments, we define the 'filter' method and note that the method must take an iterator, and also must return an iterator. In this bare-bones example, the frame filter is not very useful as it just returns the iterator untouched. However this is a valid operation for frame filters that have the 'enabled' attribute set, but decide not to operate on any frames. In the next example, the frame filter operates on all frames and utilizes a frame decorator to perform some work on the frames. *Note Frame Decorator API::, for further information on the frame decorator interface. This example works on inlined frames. It highlights frames which are inlined by tagging them with an "[inlined]" tag. By applying a frame decorator to all frames with the Python 'itertools imap' method, the example defers actions to the frame decorator. Frame decorators are only processed when GDB prints the backtrace. This introduces a new decision making topic: whether to perform decision making operations at the filtering step, or at the printing step. In this example's approach, it does not perform any filtering decisions at the filtering step beyond mapping a frame decorator to each frame. This allows the actual decision making to be performed when each frame is printed. This is an important consideration, and well worth reflecting upon when designing a frame filter. An issue that frame filters should avoid is unwinding the stack if possible. Some stacks can run very deep, into the tens of thousands in some cases. To search every frame to determine if it is inlined ahead of time may be too expensive at the filtering step. The frame filter cannot know how many frames it has to iterate over, and it would have to iterate through them all. This ends up duplicating effort as GDB performs this iteration when it prints the frames. In this example decision making can be deferred to the printing step. As each frame is printed, the frame decorator can examine each frame in turn when GDB iterates. From a performance viewpoint, this is the most appropriate decision to make as it avoids duplicating the effort that the printing step would undertake anyway. Also, if there are many frame filters unwinding the stack during filtering, it can substantially delay the printing of the backtrace which will result in large memory usage, and a poor user experience. class InlineFilter(): def __init__(self): self.name = "InlinedFrameFilter" self.priority = 100 self.enabled = True gdb.frame_filters[self.name] = self def filter(self, frame_iter): frame_iter = itertools.imap(InlinedFrameDecorator, frame_iter) return frame_iter This frame filter is somewhat similar to the earlier example, except that the 'filter' method applies a frame decorator object called 'InlinedFrameDecorator' to each element in the iterator. The 'imap' Python method is light-weight. It does not proactively iterate over the iterator, but rather creates a new iterator which wraps the existing one. Below is the frame decorator for this example. class InlinedFrameDecorator(FrameDecorator): def __init__(self, fobj): super(InlinedFrameDecorator, self).__init__(fobj) def function(self): frame = self.inferior_frame() name = str(frame.name()) if frame.type() == gdb.INLINE_FRAME: name = name + " [inlined]" return name This frame decorator only defines and overrides the 'function' method. It lets the supplied 'FrameDecorator', which is shipped with GDB, perform the other work associated with printing this frame. The combination of these two objects create this output from a backtrace: #0 0x004004e0 in bar () at inline.c:11 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21 #2 0x00400566 in main () at inline.c:31 So in the case of this example, a frame decorator is applied to all frames, regardless of whether they may be inlined or not. As GDB iterates over the iterator produced by the frame filters, GDB executes each frame decorator which then makes a decision on what to print in the 'function' callback. Using a strategy like this is a way to defer decisions on the frame content to printing time. Eliding Frames -------------- It might be that the above example is not desirable for representing inlined frames, and a hierarchical approach may be preferred. If we want to hierarchically represent frames, the 'elided' frame decorator interface might be preferable. This example approaches the issue with the 'elided' method. This example is quite long, but very simplistic. It is out-of-scope for this section to write a complete example that comprehensively covers all approaches of finding and printing inlined frames. However, this example illustrates the approach an author might use. This example comprises of three sections. class InlineFrameFilter(): def __init__(self): self.name = "InlinedFrameFilter" self.priority = 100 self.enabled = True gdb.frame_filters[self.name] = self def filter(self, frame_iter): return ElidingInlineIterator(frame_iter) This frame filter is very similar to the other examples. The only difference is this frame filter is wrapping the iterator provided to it ('frame_iter') with a custom iterator called 'ElidingInlineIterator'. This again defers actions to when GDB prints the backtrace, as the iterator is not traversed until printing. The iterator for this example is as follows. It is in this section of the example where decisions are made on the content of the backtrace. class ElidingInlineIterator: def __init__(self, ii): self.input_iterator = ii def __iter__(self): return self def next(self): frame = next(self.input_iterator) if frame.inferior_frame().type() != gdb.INLINE_FRAME: return frame try: eliding_frame = next(self.input_iterator) except StopIteration: return frame return ElidingFrameDecorator(eliding_frame, [frame]) This iterator implements the Python iterator protocol. When the 'next' function is called (when GDB prints each frame), the iterator checks if this frame decorator, 'frame', is wrapping an inlined frame. If it is not, it returns the existing frame decorator untouched. If it is wrapping an inlined frame, it assumes that the inlined frame was contained within the next oldest frame, 'eliding_frame', which it fetches. It then creates and returns a frame decorator, 'ElidingFrameDecorator', which contains both the elided frame, and the eliding frame. class ElidingInlineDecorator(FrameDecorator): def __init__(self, frame, elided_frames): super(ElidingInlineDecorator, self).__init__(frame) self.frame = frame self.elided_frames = elided_frames def elided(self): return iter(self.elided_frames) This frame decorator overrides one function and returns the inlined frame in the 'elided' method. As before it lets 'FrameDecorator' do the rest of the work involved in printing this frame. This produces the following output. #0 0x004004e0 in bar () at inline.c:11 #2 0x00400529 in main () at inline.c:25 #1 0x00400529 in max (b=6, a=12) at inline.c:15 In that output, 'max' which has been inlined into 'main' is printed hierarchically. Another approach would be to combine the 'function' method, and the 'elided' method to both print a marker in the inlined frame, and also show the hierarchical relationship.  File: gdb.info, Node: Unwinding Frames in Python, Next: Xmethods In Python, Prev: Writing a Frame Filter, Up: Python API 23.3.2.12 Unwinding Frames in Python .................................... In GDB terminology "unwinding" is the process of finding the previous frame (that is, caller's) from the current one. An unwinder has three methods. The first one checks if it can handle given frame ("sniff" it). For the frames it can sniff an unwinder provides two additional methods: it can return frame's ID, and it can fetch registers from the previous frame. A running GDB mantains a list of the unwinders and calls each unwinder's sniffer in turn until it finds the one that recognizes the current frame. There is an API to register an unwinder. The unwinders that come with GDB handle standard frames. However, mixed language applications (for example, an application running Java Virtual Machine) sometimes use frame layouts that cannot be handled by the GDB unwinders. You can write Python code that can handle such custom frames. You implement a frame unwinder in Python as a class with which has two attributes, 'name' and 'enabled', with obvious meanings, and a single method '__call__', which examines a given frame and returns an object (an instance of 'gdb.UnwindInfo class)' describing it. If an unwinder does not recognize a frame, it should return 'None'. The code in GDB that enables writing unwinders in Python uses this object to return frame's ID and previous frame registers when GDB core asks for them. An unwinder should do as little work as possible. Some otherwise innocuous operations can cause problems (even crashes, as this code is not not well-hardened yet). For example, making an inferior call from an unwinder is unadvisable, as an inferior call will reset GDB's stack unwinding process, potentially causing re-entrant unwinding. Unwinder Input -------------- An object passed to an unwinder (a 'gdb.PendingFrame' instance) provides a method to read frame's registers: -- Function: PendingFrame.read_register (reg) This method returns the contents of the register REG in the frame as a 'gdb.Value' object. For a description of the acceptable values of REG see *note Frame.read_register: gdbpy_frame_read_register. If REG does not name a register for the current architecture, this method will throw an exception. Note that this method will always return a 'gdb.Value' for a valid register name. This does not mean that the value will be valid. For example, you may request a register that an earlier unwinder could not unwind--the value will be unavailable. Instead, the 'gdb.Value' returned from this method will be lazy; that is, its underlying bits will not be fetched until it is first used. So, attempting to use such a value will cause an exception at the point of use. The type of the returned 'gdb.Value' depends on the register and the architecture. It is common for registers to have a scalar type, like 'long long'; but many other types are possible, such as pointer, pointer-to-function, floating point or vector types. It also provides a factory method to create a 'gdb.UnwindInfo' instance to be returned to GDB: -- Function: PendingFrame.create_unwind_info (frame_id) Returns a new 'gdb.UnwindInfo' instance identified by given FRAME_ID. The argument is used to build GDB's frame ID using one of functions provided by GDB. FRAME_ID's attributes determine which function will be used, as follows: 'sp, pc' The frame is identified by the given stack address and PC. The stack address must be chosen so that it is constant throughout the lifetime of the frame, so a typical choice is the value of the stack pointer at the start of the function--in the DWARF standard, this would be the "Call Frame Address". This is the most common case by far. The other cases are documented for completeness but are only useful in specialized situations. 'sp, pc, special' The frame is identified by the stack address, the PC, and a "special" address. The special address is used on architectures that can have frames that do not change the stack, but which are still distinct, for example the IA-64, which has a second stack for registers. Both SP and SPECIAL must be constant throughout the lifetime of the frame. 'sp' The frame is identified by the stack address only. Any other stack frame with a matching SP will be considered to match this frame. Inside gdb, this is called a "wild frame". You will never need this. Each attribute value should be an instance of 'gdb.Value'. -- Function: PendingFrame.architecture () Return the 'gdb.Architecture' (*note Architectures In Python::) for this 'gdb.PendingFrame'. This represents the architecture of the particular frame being unwound. -- Function: PendingFrame.level () Return an integer, the stack frame level for this frame. *Note Stack Frames: Frames. Unwinder Output: UnwindInfo --------------------------- Use 'PendingFrame.create_unwind_info' method described above to create a 'gdb.UnwindInfo' instance. Use the following method to specify caller registers that have been saved in this frame: -- Function: gdb.UnwindInfo.add_saved_register (reg, value) REG identifies the register, for a description of the acceptable values see *note Frame.read_register: gdbpy_frame_read_register. VALUE is a register value (a 'gdb.Value' object). Unwinder Skeleton Code ---------------------- GDB comes with the module containing the base 'Unwinder' class. Derive your unwinder class from it and structure the code as follows: from gdb.unwinders import Unwinder class FrameId(object): def __init__(self, sp, pc): self.sp = sp self.pc = pc class MyUnwinder(Unwinder): def __init__(....): super(MyUnwinder, self).__init___() def __call__(pending_frame): if not : return None # Create UnwindInfo. Usually the frame is identified by the stack # pointer and the program counter. sp = pending_frame.read_register() pc = pending_frame.read_register() unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc)) # Find the values of the registers in the caller's frame and # save them in the result: unwind_info.add_saved_register(, ) .... # Return the result: return unwind_info Registering a Unwinder ---------------------- An object file, a program space, and the GDB proper can have unwinders registered with it. The 'gdb.unwinders' module provides the function to register a unwinder: -- Function: gdb.unwinder.register_unwinder (locus, unwinder, replace=False) LOCUS is specifies an object file or a program space to which UNWINDER is added. Passing 'None' or 'gdb' adds UNWINDER to the GDB's global unwinder list. The newly added UNWINDER will be called before any other unwinder from the same locus. Two unwinders in the same locus cannot have the same name. An attempt to add a unwinder with already existing name raises an exception unless REPLACE is 'True', in which case the old unwinder is deleted. Unwinder Precedence ------------------- GDB first calls the unwinders from all the object files in no particular order, then the unwinders from the current program space, and finally the unwinders from GDB.  File: gdb.info, Node: Xmethods In Python, Next: Xmethod API, Prev: Unwinding Frames in Python, Up: Python API 23.3.2.13 Xmethods In Python ............................ "Xmethods" are additional methods or replacements for existing methods of a C++ class. This feature is useful for those cases where a method defined in C++ source code could be inlined or optimized out by the compiler, making it unavailable to GDB. For such cases, one can define an xmethod to serve as a replacement for the method defined in the C++ source code. GDB will then invoke the xmethod, instead of the C++ method, to evaluate expressions. One can also use xmethods when debugging with core files. Moreover, when debugging live programs, invoking an xmethod need not involve running the inferior (which can potentially perturb its state). Hence, even if the C++ method is available, it is better to use its replacement xmethod if one is defined. The xmethods feature in Python is available via the concepts of an "xmethod matcher" and an "xmethod worker". To implement an xmethod, one has to implement a matcher and a corresponding worker for it (more than one worker can be implemented, each catering to a different overloaded instance of the method). Internally, GDB invokes the 'match' method of a matcher to match the class type and method name. On a match, the 'match' method returns a list of matching _worker_ objects. Each worker object typically corresponds to an overloaded instance of the xmethod. They implement a 'get_arg_types' method which returns a sequence of types corresponding to the arguments the xmethod requires. GDB uses this sequence of types to perform overload resolution and picks a winning xmethod worker. A winner is also selected from among the methods GDB finds in the C++ source code. Next, the winning xmethod worker and the winning C++ method are compared to select an overall winner. In case of a tie between a xmethod worker and a C++ method, the xmethod worker is selected as the winner. That is, if a winning xmethod worker is found to be equivalent to the winning C++ method, then the xmethod worker is treated as a replacement for the C++ method. GDB uses the overall winner to invoke the method. If the winning xmethod worker is the overall winner, then the corresponding xmethod is invoked via the '__call__' method of the worker object. If one wants to implement an xmethod as a replacement for an existing C++ method, then they have to implement an equivalent xmethod which has exactly the same name and takes arguments of exactly the same type as the C++ method. If the user wants to invoke the C++ method even though a replacement xmethod is available for that method, then they can disable the xmethod. *Note Xmethod API::, for API to implement xmethods in Python. *Note Writing an Xmethod::, for implementing xmethods in Python.  File: gdb.info, Node: Xmethod API, Next: Writing an Xmethod, Prev: Xmethods In Python, Up: Python API 23.3.2.14 Xmethod API ..................... The GDB Python API provides classes, interfaces and functions to implement, register and manipulate xmethods. *Note Xmethods In Python::. An xmethod matcher should be an instance of a class derived from 'XMethodMatcher' defined in the module 'gdb.xmethod', or an object with similar interface and attributes. An instance of 'XMethodMatcher' has the following attributes: -- Variable: name The name of the matcher. -- Variable: enabled A boolean value indicating whether the matcher is enabled or disabled. -- Variable: methods A list of named methods managed by the matcher. Each object in the list is an instance of the class 'XMethod' defined in the module 'gdb.xmethod', or any object with the following attributes: 'name' Name of the xmethod which should be unique for each xmethod managed by the matcher. 'enabled' A boolean value indicating whether the xmethod is enabled or disabled. The class 'XMethod' is a convenience class with same attributes as above along with the following constructor: -- Function: XMethod.__init__ (self, name) Constructs an enabled xmethod with name NAME. The 'XMethodMatcher' class has the following methods: -- Function: XMethodMatcher.__init__ (self, name) Constructs an enabled xmethod matcher with name NAME. The 'methods' attribute is initialized to 'None'. -- Function: XMethodMatcher.match (self, class_type, method_name) Derived classes should override this method. It should return a xmethod worker object (or a sequence of xmethod worker objects) matching the CLASS_TYPE and METHOD_NAME. CLASS_TYPE is a 'gdb.Type' object, and METHOD_NAME is a string value. If the matcher manages named methods as listed in its 'methods' attribute, then only those worker objects whose corresponding entries in the 'methods' list are enabled should be returned. An xmethod worker should be an instance of a class derived from 'XMethodWorker' defined in the module 'gdb.xmethod', or support the following interface: -- Function: XMethodWorker.get_arg_types (self) This method returns a sequence of 'gdb.Type' objects corresponding to the arguments that the xmethod takes. It can return an empty sequence or 'None' if the xmethod does not take any arguments. If the xmethod takes a single argument, then a single 'gdb.Type' object corresponding to it can be returned. -- Function: XMethodWorker.get_result_type (self, *args) This method returns a 'gdb.Type' object representing the type of the result of invoking this xmethod. The ARGS argument is the same tuple of arguments that would be passed to the '__call__' method of this worker. -- Function: XMethodWorker.__call__ (self, *args) This is the method which does the _work_ of the xmethod. The ARGS arguments is the tuple of arguments to the xmethod. Each element in this tuple is a gdb.Value object. The first element is always the 'this' pointer value. For GDB to lookup xmethods, the xmethod matchers should be registered using the following function defined in the module 'gdb.xmethod': -- Function: register_xmethod_matcher (locus, matcher, replace=False) The 'matcher' is registered with 'locus', replacing an existing matcher with the same name as 'matcher' if 'replace' is 'True'. 'locus' can be a 'gdb.Objfile' object (*note Objfiles In Python::), or a 'gdb.Progspace' object (*note Progspaces In Python::), or 'None'. If it is 'None', then 'matcher' is registered globally.  File: gdb.info, Node: Writing an Xmethod, Next: Inferiors In Python, Prev: Xmethod API, Up: Python API 23.3.2.15 Writing an Xmethod ............................ Implementing xmethods in Python will require implementing xmethod matchers and xmethod workers (*note Xmethods In Python::). Consider the following C++ class: class MyClass { public: MyClass (int a) : a_(a) { } int geta (void) { return a_; } int operator+ (int b); private: int a_; }; int MyClass::operator+ (int b) { return a_ + b; } Let us define two xmethods for the class 'MyClass', one replacing the method 'geta', and another adding an overloaded flavor of 'operator+' which takes a 'MyClass' argument (the C++ code above already has an overloaded 'operator+' which takes an 'int' argument). The xmethod matcher can be defined as follows: class MyClass_geta(gdb.xmethod.XMethod): def __init__(self): gdb.xmethod.XMethod.__init__(self, 'geta') def get_worker(self, method_name): if method_name == 'geta': return MyClassWorker_geta() class MyClass_sum(gdb.xmethod.XMethod): def __init__(self): gdb.xmethod.XMethod.__init__(self, 'sum') def get_worker(self, method_name): if method_name == 'operator+': return MyClassWorker_plus() class MyClassMatcher(gdb.xmethod.XMethodMatcher): def __init__(self): gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher') # List of methods 'managed' by this matcher self.methods = [MyClass_geta(), MyClass_sum()] def match(self, class_type, method_name): if class_type.tag != 'MyClass': return None workers = [] for method in self.methods: if method.enabled: worker = method.get_worker(method_name) if worker: workers.append(worker) return workers Notice that the 'match' method of 'MyClassMatcher' returns a worker object of type 'MyClassWorker_geta' for the 'geta' method, and a worker object of type 'MyClassWorker_plus' for the 'operator+' method. This is done indirectly via helper classes derived from 'gdb.xmethod.XMethod'. One does not need to use the 'methods' attribute in a matcher as it is optional. However, if a matcher manages more than one xmethod, it is a good practice to list the xmethods in the 'methods' attribute of the matcher. This will then facilitate enabling and disabling individual xmethods via the 'enable/disable' commands. Notice also that a worker object is returned only if the corresponding entry in the 'methods' attribute of the matcher is enabled. The implementation of the worker classes returned by the matcher setup above is as follows: class MyClassWorker_geta(gdb.xmethod.XMethodWorker): def get_arg_types(self): return None def get_result_type(self, obj): return gdb.lookup_type('int') def __call__(self, obj): return obj['a_'] class MyClassWorker_plus(gdb.xmethod.XMethodWorker): def get_arg_types(self): return gdb.lookup_type('MyClass') def get_result_type(self, obj): return gdb.lookup_type('int') def __call__(self, obj, other): return obj['a_'] + other['a_'] For GDB to actually lookup a xmethod, it has to be registered with it. The matcher defined above is registered with GDB globally as follows: gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher()) If an object 'obj' of type 'MyClass' is initialized in C++ code as follows: MyClass obj(5); then, after loading the Python script defining the xmethod matchers and workers into 'GDBN', invoking the method 'geta' or using the operator '+' on 'obj' will invoke the xmethods defined above: (gdb) p obj.geta() $1 = 5 (gdb) p obj + obj $2 = 10 Consider another example with a C++ template class: template class MyTemplate { public: MyTemplate () : dsize_(10), data_ (new T [10]) { } ~MyTemplate () { delete [] data_; } int footprint (void) { return sizeof (T) * dsize_ + sizeof (MyTemplate); } private: int dsize_; T *data_; }; Let us implement an xmethod for the above class which serves as a replacement for the 'footprint' method. The full code listing of the xmethod workers and xmethod matchers is as follows: class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker): def __init__(self, class_type): self.class_type = class_type def get_arg_types(self): return None def get_result_type(self): return gdb.lookup_type('int') def __call__(self, obj): return (self.class_type.sizeof + obj['dsize_'] * self.class_type.template_argument(0).sizeof) class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher): def __init__(self): gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher') def match(self, class_type, method_name): if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>', class_type.tag) and method_name == 'footprint'): return MyTemplateWorker_footprint(class_type) Notice that, in this example, we have not used the 'methods' attribute of the matcher as the matcher manages only one xmethod. The user can enable/disable this xmethod by enabling/disabling the matcher itself.  File: gdb.info, Node: Inferiors In Python, Next: Events In Python, Prev: Writing an Xmethod, Up: Python API 23.3.2.16 Inferiors In Python ............................. Programs which are being run under GDB are called inferiors (*note Inferiors Connections and Programs::). Python scripts can access information about and manipulate inferiors controlled by GDB via objects of the 'gdb.Inferior' class. The following inferior-related functions are available in the 'gdb' module: -- Function: gdb.inferiors () Return a tuple containing all inferior objects. -- Function: gdb.selected_inferior () Return an object representing the current inferior. A 'gdb.Inferior' object has the following attributes: -- Variable: Inferior.num ID of inferior, as assigned by GDB. -- Variable: Inferior.connection The 'gdb.TargetConnection' for this inferior (*note Connections In Python::), or 'None' if this inferior has no connection. -- Variable: Inferior.connection_num ID of inferior's connection as assigned by GDB, or None if the inferior is not connected to a target. *Note Inferiors Connections and Programs::. This is equivalent to 'gdb.Inferior.connection.num' in the case where 'gdb.Inferior.connection' is not 'None'. -- Variable: Inferior.pid Process ID of the inferior, as assigned by the underlying operating system. -- Variable: Inferior.was_attached Boolean signaling whether the inferior was created using 'attach', or started by GDB itself. -- Variable: Inferior.progspace The inferior's program space. *Note Progspaces In Python::. A 'gdb.Inferior' object has the following methods: -- Function: Inferior.is_valid () Returns 'True' if the 'gdb.Inferior' object is valid, 'False' if not. A 'gdb.Inferior' object will become invalid if the inferior no longer exists within GDB. All other 'gdb.Inferior' methods will throw an exception if it is invalid at the time the method is called. -- Function: Inferior.threads () This method returns a tuple holding all the threads which are valid when it is called. If there are no valid threads, the method will return an empty tuple. -- Function: Inferior.architecture () Return the 'gdb.Architecture' (*note Architectures In Python::) for this inferior. This represents the architecture of the inferior as a whole. Some platforms can have multiple architectures in a single address space, so this may not match the architecture of a particular frame (*note Frames In Python::). -- Function: Inferior.read_memory (address, length) Read LENGTH addressable memory units from the inferior, starting at ADDRESS. Returns a buffer object, which behaves much like an array or a string. It can be modified and given to the 'Inferior.write_memory' function. In Python 3, the return value is a 'memoryview' object. -- Function: Inferior.write_memory (address, buffer [, length]) Write the contents of BUFFER to the inferior, starting at ADDRESS. The BUFFER parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from 'Inferior.read_memory'. If given, LENGTH determines the number of addressable memory units from BUFFER to be written. -- Function: Inferior.search_memory (address, length, pattern) Search a region of the inferior memory starting at ADDRESS with the given LENGTH using the search pattern supplied in PATTERN. The PATTERN parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from 'gdb.read_memory'. Returns a Python 'Long' containing the address where the pattern was found, or 'None' if the pattern could not be found. -- Function: Inferior.thread_from_handle (handle) Return the thread object corresponding to HANDLE, a thread library specific data structure such as 'pthread_t' for pthreads library implementations. The function 'Inferior.thread_from_thread_handle' provides the same functionality, but use of 'Inferior.thread_from_thread_handle' is deprecated.  File: gdb.info, Node: Events In Python, Next: Threads In Python, Prev: Inferiors In Python, Up: Python API 23.3.2.17 Events In Python .......................... GDB provides a general event facility so that Python code can be notified of various state changes, particularly changes that occur in the inferior. An "event" is just an object that describes some state change. The type of the object and its attributes will vary depending on the details of the change. All the existing events are described below. In order to be notified of an event, you must register an event handler with an "event registry". An event registry is an object in the 'gdb.events' module which dispatches particular events. A registry provides methods to register and unregister event handlers: -- Function: EventRegistry.connect (object) Add the given callable OBJECT to the registry. This object will be called when an event corresponding to this registry occurs. -- Function: EventRegistry.disconnect (object) Remove the given OBJECT from the registry. Once removed, the object will no longer receive notifications of events. Here is an example: def exit_handler (event): print ("event type: exit") if hasattr (event, 'exit_code'): print ("exit code: %d" % (event.exit_code)) else: print ("exit code not available") gdb.events.exited.connect (exit_handler) In the above example we connect our handler 'exit_handler' to the registry 'events.exited'. Once connected, 'exit_handler' gets called when the inferior exits. The argument "event" in this example is of type 'gdb.ExitedEvent'. As you can see in the example the 'ExitedEvent' object has an attribute which indicates the exit code of the inferior. The following is a listing of the event registries that are available and details of the events they emit: 'events.cont' Emits 'gdb.ThreadEvent'. Some events can be thread specific when GDB is running in non-stop mode. When represented in Python, these events all extend 'gdb.ThreadEvent'. Note, this event is not emitted directly; instead, events which are emitted by this or other modules might extend this event. Examples of these events are 'gdb.BreakpointEvent' and 'gdb.ContinueEvent'. -- Variable: ThreadEvent.inferior_thread In non-stop mode this attribute will be set to the specific thread which was involved in the emitted event. Otherwise, it will be set to 'None'. Emits 'gdb.ContinueEvent' which extends 'gdb.ThreadEvent'. This event indicates that the inferior has been continued after a stop. For inherited attribute refer to 'gdb.ThreadEvent' above. 'events.exited' Emits 'events.ExitedEvent' which indicates that the inferior has exited. 'events.ExitedEvent' has two attributes: -- Variable: ExitedEvent.exit_code An integer representing the exit code, if available, which the inferior has returned. (The exit code could be unavailable if, for example, GDB detaches from the inferior.) If the exit code is unavailable, the attribute does not exist. -- Variable: ExitedEvent.inferior A reference to the inferior which triggered the 'exited' event. 'events.stop' Emits 'gdb.StopEvent' which extends 'gdb.ThreadEvent'. Indicates that the inferior has stopped. All events emitted by this registry extend StopEvent. As a child of 'gdb.ThreadEvent', 'gdb.StopEvent' will indicate the stopped thread when GDB is running in non-stop mode. Refer to 'gdb.ThreadEvent' above for more details. Emits 'gdb.SignalEvent' which extends 'gdb.StopEvent'. This event indicates that the inferior or one of its threads has received as signal. 'gdb.SignalEvent' has the following attributes: -- Variable: SignalEvent.stop_signal A string representing the signal received by the inferior. A list of possible signal values can be obtained by running the command 'info signals' in the GDB command prompt. Also emits 'gdb.BreakpointEvent' which extends 'gdb.StopEvent'. 'gdb.BreakpointEvent' event indicates that one or more breakpoints have been hit, and has the following attributes: -- Variable: BreakpointEvent.breakpoints A sequence containing references to all the breakpoints (type 'gdb.Breakpoint') that were hit. *Note Breakpoints In Python::, for details of the 'gdb.Breakpoint' object. -- Variable: BreakpointEvent.breakpoint A reference to the first breakpoint that was hit. This function is maintained for backward compatibility and is now deprecated in favor of the 'gdb.BreakpointEvent.breakpoints' attribute. 'events.new_objfile' Emits 'gdb.NewObjFileEvent' which indicates that a new object file has been loaded by GDB. 'gdb.NewObjFileEvent' has one attribute: -- Variable: NewObjFileEvent.new_objfile A reference to the object file ('gdb.Objfile') which has been loaded. *Note Objfiles In Python::, for details of the 'gdb.Objfile' object. 'events.clear_objfiles' Emits 'gdb.ClearObjFilesEvent' which indicates that the list of object files for a program space has been reset. 'gdb.ClearObjFilesEvent' has one attribute: -- Variable: ClearObjFilesEvent.progspace A reference to the program space ('gdb.Progspace') whose objfile list has been cleared. *Note Progspaces In Python::. 'events.inferior_call' Emits events just before and after a function in the inferior is called by GDB. Before an inferior call, this emits an event of type 'gdb.InferiorCallPreEvent', and after an inferior call, this emits an event of type 'gdb.InferiorCallPostEvent'. 'gdb.InferiorCallPreEvent' Indicates that a function in the inferior is about to be called. -- Variable: InferiorCallPreEvent.ptid The thread in which the call will be run. -- Variable: InferiorCallPreEvent.address The location of the function to be called. 'gdb.InferiorCallPostEvent' Indicates that a function in the inferior has just been called. -- Variable: InferiorCallPostEvent.ptid The thread in which the call was run. -- Variable: InferiorCallPostEvent.address The location of the function that was called. 'events.memory_changed' Emits 'gdb.MemoryChangedEvent' which indicates that the memory of the inferior has been modified by the GDB user, for instance via a command like 'set *addr = value'. The event has the following attributes: -- Variable: MemoryChangedEvent.address The start address of the changed region. -- Variable: MemoryChangedEvent.length Length in bytes of the changed region. 'events.register_changed' Emits 'gdb.RegisterChangedEvent' which indicates that a register in the inferior has been modified by the GDB user. -- Variable: RegisterChangedEvent.frame A gdb.Frame object representing the frame in which the register was modified. -- Variable: RegisterChangedEvent.regnum Denotes which register was modified. 'events.breakpoint_created' This is emitted when a new breakpoint has been created. The argument that is passed is the new 'gdb.Breakpoint' object. 'events.breakpoint_modified' This is emitted when a breakpoint has been modified in some way. The argument that is passed is the new 'gdb.Breakpoint' object. 'events.breakpoint_deleted' This is emitted when a breakpoint has been deleted. The argument that is passed is the 'gdb.Breakpoint' object. When this event is emitted, the 'gdb.Breakpoint' object will already be in its invalid state; that is, the 'is_valid' method will return 'False'. 'events.before_prompt' This event carries no payload. It is emitted each time GDB presents a prompt to the user. 'events.new_inferior' This is emitted when a new inferior is created. Note that the inferior is not necessarily running; in fact, it may not even have an associated executable. The event is of type 'gdb.NewInferiorEvent'. This has a single attribute: -- Variable: NewInferiorEvent.inferior The new inferior, a 'gdb.Inferior' object. 'events.inferior_deleted' This is emitted when an inferior has been deleted. Note that this is not the same as process exit; it is notified when the inferior itself is removed, say via 'remove-inferiors'. The event is of type 'gdb.InferiorDeletedEvent'. This has a single attribute: -- Variable: NewInferiorEvent.inferior The inferior that is being removed, a 'gdb.Inferior' object. 'events.new_thread' This is emitted when GDB notices a new thread. The event is of type 'gdb.NewThreadEvent', which extends 'gdb.ThreadEvent'. This has a single attribute: -- Variable: NewThreadEvent.inferior_thread The new thread. 'events.gdb_exiting' This is emitted when GDB exits. This event is not emitted if GDB exits as a result of an internal error, or after an unexpected signal. The event is of type 'gdb.GdbExitingEvent', which has a single attribute: -- Variable: GdbExitingEvent.exit_code An integer, the value of the exit code GDB will return. 'events.connection_removed' This is emitted when GDB removes a connection (*note Connections In Python::). The event is of type 'gdb.ConnectionEvent'. This has a single read-only attribute: -- Variable: ConnectionEvent.connection The 'gdb.TargetConnection' that is being removed.  File: gdb.info, Node: Threads In Python, Next: Recordings In Python, Prev: Events In Python, Up: Python API 23.3.2.18 Threads In Python ........................... Python scripts can access information about, and manipulate inferior threads controlled by GDB, via objects of the 'gdb.InferiorThread' class. The following thread-related functions are available in the 'gdb' module: -- Function: gdb.selected_thread () This function returns the thread object for the selected thread. If there is no selected thread, this will return 'None'. To get the list of threads for an inferior, use the 'Inferior.threads()' method. *Note Inferiors In Python::. A 'gdb.InferiorThread' object has the following attributes: -- Variable: InferiorThread.name The name of the thread. If the user specified a name using 'thread name', then this returns that name. Otherwise, if an OS-supplied name is available, then it is returned. Otherwise, this returns 'None'. This attribute can be assigned to. The new value must be a string object, which sets the new name, or 'None', which removes any user-specified thread name. -- Variable: InferiorThread.num The per-inferior number of the thread, as assigned by GDB. -- Variable: InferiorThread.global_num The global ID of the thread, as assigned by GDB. You can use this to make Python breakpoints thread-specific, for example (*note The Breakpoint.thread attribute: python_breakpoint_thread.). -- Variable: InferiorThread.ptid ID of the thread, as assigned by the operating system. This attribute is a tuple containing three integers. The first is the Process ID (PID); the second is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID). Either the LWPID or TID may be 0, which indicates that the operating system does not use that identifier. -- Variable: InferiorThread.inferior The inferior this thread belongs to. This attribute is represented as a 'gdb.Inferior' object. This attribute is not writable. -- Variable: InferiorThread.details A string containing target specific thread state information. The format of this string varies by target. If there is no additional state information for this thread, then this attribute contains 'None'. For example, on a GNU/Linux system, a thread that is in the process of exiting will return the string 'Exiting'. For remote targets the 'details' string will be obtained with the 'qThreadExtraInfo' remote packet, if the target supports it (*note 'qThreadExtraInfo': qThreadExtraInfo.). GDB displays the 'details' string as part of the 'Target Id' column, in the 'info threads' output (*note 'info threads': info_threads.). A 'gdb.InferiorThread' object has the following methods: -- Function: InferiorThread.is_valid () Returns 'True' if the 'gdb.InferiorThread' object is valid, 'False' if not. A 'gdb.InferiorThread' object will become invalid if the thread exits, or the inferior that the thread belongs is deleted. All other 'gdb.InferiorThread' methods will throw an exception if it is invalid at the time the method is called. -- Function: InferiorThread.switch () This changes GDB's currently selected thread to the one represented by this object. -- Function: InferiorThread.is_stopped () Return a Boolean indicating whether the thread is stopped. -- Function: InferiorThread.is_running () Return a Boolean indicating whether the thread is running. -- Function: InferiorThread.is_exited () Return a Boolean indicating whether the thread is exited. -- Function: InferiorThread.handle () Return the thread object's handle, represented as a Python 'bytes' object. A 'gdb.Value' representation of the handle may be constructed via 'gdb.Value(bufobj, type)' where BUFOBJ is the Python 'bytes' representation of the handle and TYPE is a 'gdb.Type' for the handle type.  File: gdb.info, Node: Recordings In Python, Next: CLI Commands In Python, Prev: Threads In Python, Up: Python API 23.3.2.19 Recordings In Python .............................. The following recordings-related functions (*note Process Record and Replay::) are available in the 'gdb' module: -- Function: gdb.start_recording ([method], [format]) Start a recording using the given METHOD and FORMAT. If no FORMAT is given, the default format for the recording method is used. If no METHOD is given, the default method will be used. Returns a 'gdb.Record' object on success. Throw an exception on failure. The following strings can be passed as METHOD: * '"full"' * '"btrace"': Possible values for FORMAT: '"pt"', '"bts"' or leave out for default format. -- Function: gdb.current_recording () Access a currently running recording. Return a 'gdb.Record' object on success. Return 'None' if no recording is currently active. -- Function: gdb.stop_recording () Stop the current recording. Throw an exception if no recording is currently active. All record objects become invalid after this call. A 'gdb.Record' object has the following attributes: -- Variable: Record.method A string with the current recording method, e.g. 'full' or 'btrace'. -- Variable: Record.format A string with the current recording format, e.g. 'bt', 'pts' or 'None'. -- Variable: Record.begin A method specific instruction object representing the first instruction in this recording. -- Variable: Record.end A method specific instruction object representing the current instruction, that is not actually part of the recording. -- Variable: Record.replay_position The instruction representing the current replay position. If there is no replay active, this will be 'None'. -- Variable: Record.instruction_history A list with all recorded instructions. -- Variable: Record.function_call_history A list with all recorded function call segments. A 'gdb.Record' object has the following methods: -- Function: Record.goto (instruction) Move the replay position to the given INSTRUCTION. The common 'gdb.Instruction' class that recording method specific instruction objects inherit from, has the following attributes: -- Variable: Instruction.pc An integer representing this instruction's address. -- Variable: Instruction.data A buffer with the raw instruction data. In Python 3, the return value is a 'memoryview' object. -- Variable: Instruction.decoded A human readable string with the disassembled instruction. -- Variable: Instruction.size The size of the instruction in bytes. Additionally 'gdb.RecordInstruction' has the following attributes: -- Variable: RecordInstruction.number An integer identifying this instruction. 'number' corresponds to the numbers seen in 'record instruction-history' (*note Process Record and Replay::). -- Variable: RecordInstruction.sal A 'gdb.Symtab_and_line' object representing the associated symtab and line of this instruction. May be 'None' if no debug information is available. -- Variable: RecordInstruction.is_speculative A boolean indicating whether the instruction was executed speculatively. If an error occured during recording or decoding a recording, this error is represented by a 'gdb.RecordGap' object in the instruction list. It has the following attributes: -- Variable: RecordGap.number An integer identifying this gap. 'number' corresponds to the numbers seen in 'record instruction-history' (*note Process Record and Replay::). -- Variable: RecordGap.error_code A numerical representation of the reason for the gap. The value is specific to the current recording method. -- Variable: RecordGap.error_string A human readable string with the reason for the gap. A 'gdb.RecordFunctionSegment' object has the following attributes: -- Variable: RecordFunctionSegment.number An integer identifying this function segment. 'number' corresponds to the numbers seen in 'record function-call-history' (*note Process Record and Replay::). -- Variable: RecordFunctionSegment.symbol A 'gdb.Symbol' object representing the associated symbol. May be 'None' if no debug information is available. -- Variable: RecordFunctionSegment.level An integer representing the function call's stack level. May be 'None' if the function call is a gap. -- Variable: RecordFunctionSegment.instructions A list of 'gdb.RecordInstruction' or 'gdb.RecordGap' objects associated with this function call. -- Variable: RecordFunctionSegment.up A 'gdb.RecordFunctionSegment' object representing the caller's function segment. If the call has not been recorded, this will be the function segment to which control returns. If neither the call nor the return have been recorded, this will be 'None'. -- Variable: RecordFunctionSegment.prev A 'gdb.RecordFunctionSegment' object representing the previous segment of this function call. May be 'None'. -- Variable: RecordFunctionSegment.next A 'gdb.RecordFunctionSegment' object representing the next segment of this function call. May be 'None'. The following example demonstrates the usage of these objects and functions to create a function that will rewind a record to the last time a function in a different file was executed. This would typically be used to track the execution of user provided callback functions in a library which typically are not visible in a back trace. def bringback (): rec = gdb.current_recording () if not rec: return insn = rec.instruction_history if len (insn) == 0: return try: position = insn.index (rec.replay_position) except: position = -1 try: filename = insn[position].sal.symtab.fullname () except: filename = None for i in reversed (insn[:position]): try: current = i.sal.symtab.fullname () except: current = None if filename == current: continue rec.goto (i) return Another possible application is to write a function that counts the number of code executions in a given line range. This line range can contain parts of functions or span across several functions and is not limited to be contiguous. def countrange (filename, linerange): count = 0 def filter_only (file_name): for call in gdb.current_recording ().function_call_history: try: if file_name in call.symbol.symtab.fullname (): yield call except: pass for c in filter_only (filename): for i in c.instructions: try: if i.sal.line in linerange: count += 1 break; except: pass return count  File: gdb.info, Node: CLI Commands In Python, Next: GDB/MI Commands In Python, Prev: Recordings In Python, Up: Python API 23.3.2.20 CLI Commands In Python ................................ You can implement new GDB CLI commands in Python. A CLI command is implemented using an instance of the 'gdb.Command' class, most commonly using a subclass. -- Function: Command.__init__ (name, COMMAND_CLASS [, COMPLETER_CLASS [, PREFIX]]) The object initializer for 'Command' registers the new command with GDB. This initializer is normally invoked from the subclass' own '__init__' method. NAME is the name of the command. If NAME consists of multiple words, then the initial words are looked for as prefix commands. In this case, if one of the prefix commands does not exist, an exception is raised. There is no support for multi-line commands. COMMAND_CLASS should be one of the 'COMMAND_' constants defined below. This argument tells GDB how to categorize the new command in the help system. COMPLETER_CLASS is an optional argument. If given, it should be one of the 'COMPLETE_' constants defined below. This argument tells GDB how to perform completion for this command. If not given, GDB will attempt to complete using the object's 'complete' method (see below); if no such method is found, an error will occur when completion is attempted. PREFIX is an optional argument. If 'True', then the new command is a prefix command; sub-commands of this command may be registered. The help text for the new command is taken from the Python documentation string for the command's class, if there is one. If no documentation string is provided, the default value "This command is not documented." is used. -- Function: Command.dont_repeat () By default, a GDB command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the 'dont_repeat' method. This is similar to the user command 'dont-repeat', see *note dont-repeat: Define. -- Function: Command.invoke (argument, from_tty) This method is called by GDB when this command is invoked. ARGUMENT is a string. It is the argument to the command, after leading and trailing whitespace has been stripped. FROM_TTY is a boolean argument. When true, this means that the command was entered by the user at the terminal; when false it means that the command came from elsewhere. If this method throws an exception, it is turned into a GDB 'error' call. Otherwise, the return value is ignored. To break ARGUMENT up into an argv-like string use 'gdb.string_to_argv'. This function behaves identically to GDB's internal argument lexer 'buildargv'. It is recommended to use this for consistency. Arguments are separated by spaces and may be quoted. Example: print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"") ['1', '2 "3', '4 "5', "6 '7"] -- Function: Command.complete (text, word) This method is called by GDB when the user attempts completion on this command. All forms of completion are handled by this method, that is, the and key bindings (*note Completion::), and the 'complete' command (*note complete: Help.). The arguments TEXT and WORD are both strings; TEXT holds the complete command line up to the cursor's location, while WORD holds the last word of the command line; this is computed using a word-breaking heuristic. The 'complete' method can return several values: * If the return value is a sequence, the contents of the sequence are used as the completions. It is up to 'complete' to ensure that the contents actually do complete the word. A zero-length sequence is allowed, it means that there were no completions available. Only string elements of the sequence are used; other elements in the sequence are ignored. * If the return value is one of the 'COMPLETE_' constants defined below, then the corresponding GDB-internal completion function is invoked, and its result is used. * All other results are treated as though there were no available completions. When a new command is registered, it must be declared as a member of some general class of commands. This is used to classify top-level commands in the on-line help system; note that prefix commands are not listed under their own category but rather that of their top-level command. The available classifications are represented by constants defined in the 'gdb' module: 'gdb.COMMAND_NONE' The command does not belong to any particular class. A command in this category will not be displayed in any of the help categories. 'gdb.COMMAND_RUNNING' The command is related to running the inferior. For example, 'start', 'step', and 'continue' are in this category. Type 'help running' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_DATA' The command is related to data or variables. For example, 'call', 'find', and 'print' are in this category. Type 'help data' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_STACK' The command has to do with manipulation of the stack. For example, 'backtrace', 'frame', and 'return' are in this category. Type 'help stack' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_FILES' This class is used for file-related commands. For example, 'file', 'list' and 'section' are in this category. Type 'help files' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_SUPPORT' This should be used for "support facilities", generally meaning things that are useful to the user when interacting with GDB, but not related to the state of the inferior. For example, 'help', 'make', and 'shell' are in this category. Type 'help support' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_STATUS' The command is an 'info'-related command, that is, related to the state of GDB itself. For example, 'info', 'macro', and 'show' are in this category. Type 'help status' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_BREAKPOINTS' The command has to do with breakpoints. For example, 'break', 'clear', and 'delete' are in this category. Type 'help breakpoints' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_TRACEPOINTS' The command has to do with tracepoints. For example, 'trace', 'actions', and 'tfind' are in this category. Type 'help tracepoints' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_TUI' The command has to do with the text user interface (*note TUI::). Type 'help tui' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_USER' The command is a general purpose command for the user, and typically does not fit in one of the other categories. Type 'help user-defined' at the GDB prompt to see a list of commands in this category, as well as the list of gdb macros (*note Sequences::). 'gdb.COMMAND_OBSCURE' The command is only used in unusual circumstances, or is not of general interest to users. For example, 'checkpoint', 'fork', and 'stop' are in this category. Type 'help obscure' at the GDB prompt to see a list of commands in this category. 'gdb.COMMAND_MAINTENANCE' The command is only useful to GDB maintainers. The 'maintenance' and 'flushregs' commands are in this category. Type 'help internals' at the GDB prompt to see a list of commands in this category. A new command can use a predefined completion function, either by specifying it via an argument at initialization, or by returning it from the 'complete' method. These predefined completion constants are all defined in the 'gdb' module: 'gdb.COMPLETE_NONE' This constant means that no completion should be done. 'gdb.COMPLETE_FILENAME' This constant means that filename completion should be performed. 'gdb.COMPLETE_LOCATION' This constant means that location completion should be done. *Note Specify Location::. 'gdb.COMPLETE_COMMAND' This constant means that completion should examine GDB command names. 'gdb.COMPLETE_SYMBOL' This constant means that completion should be done using symbol names as the source. 'gdb.COMPLETE_EXPRESSION' This constant means that completion should be done on expressions. Often this means completing on symbol names, but some language parsers also have support for completing on field names. The following code snippet shows how a trivial CLI command can be implemented in Python: class HelloWorld (gdb.Command): """Greet the whole world.""" def __init__ (self): super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) def invoke (self, arg, from_tty): print ("Hello, World!") HelloWorld () The last line instantiates the class, and is necessary to trigger the registration of the command with GDB. Depending on how the Python code is read into GDB, you may need to import the 'gdb' module explicitly.  File: gdb.info, Node: GDB/MI Commands In Python, Next: Parameters In Python, Prev: CLI Commands In Python, Up: Python API 23.3.2.21 GDB/MI Commands In Python ................................... It is possible to add GDB/MI (*note GDB/MI::) commands implemented in Python. A GDB/MI command is implemented using an instance of the 'gdb.MICommand' class, most commonly using a subclass. -- Function: MICommand.__init__ (name) The object initializer for 'MICommand' registers the new command with GDB. This initializer is normally invoked from the subclass' own '__init__' method. NAME is the name of the command. It must be a valid name of a GDB/MI command, and in particular must start with a hyphen ('-'). Reusing the name of a built-in GDB/MI is not allowed, and a 'RuntimeError' will be raised. Using the name of an GDB/MI command previously defined in Python is allowed, the previous command will be replaced with the new command. -- Function: MICommand.invoke (arguments) This method is called by GDB when the new MI command is invoked. ARGUMENTS is a list of strings. Note, that '--thread' and '--frame' arguments are handled by GDB itself therefore they do not show up in 'arguments'. If this method raises an exception, then it is turned into a GDB/MI '^error' response. Only 'gdb.GdbError' exceptions (or its sub-classes) should be used for reporting errors to users, any other exception type is treated as a failure of the 'invoke' method, and the exception will be printed to the error stream according to the 'set python print-stack' setting (*note 'set python print-stack': set_python_print_stack.). If this method returns 'None', then the GDB/MI command will return a '^done' response with no additional values. Otherwise, the return value must be a dictionary, which is converted to a GDB/MI RESULT-RECORD (*note GDB/MI Output Syntax::). The keys of this dictionary must be strings, and are used as VARIABLE names in the RESULT-RECORD, these strings must comply with the naming rules detailed below. The values of this dictionary are recursively handled as follows: * If the value is Python sequence or iterator, it is converted to GDB/MI LIST with elements converted recursively. * If the value is Python dictionary, it is converted to GDB/MI TUPLE. Keys in that dictionary must be strings, which comply with the VARIABLE naming rules detailed below. Values are converted recursively. * Otherwise, value is first converted to a Python string using 'str ()' and then converted to GDB/MI CONST. The strings used for VARIABLE names in the GDB/MI output must follow the following rules; the string must be at least one character long, the first character must be in the set '[a-zA-Z]', while every subsequent character must be in the set '[-_a-zA-Z0-9]'. An instance of 'MICommand' has the following attributes: -- Variable: MICommand.name A string, the name of this GDB/MI command, as was passed to the '__init__' method. This attribute is read-only. -- Variable: MICommand.installed A boolean value indicating if this command is installed ready for a user to call from the command line. Commands are automatically installed when they are instantiated, after which this attribute will be 'True'. If later, a new command is created with the same name, then the original command will become uninstalled, and this attribute will be 'False'. This attribute is read-write, setting this attribute to 'False' will uninstall the command, removing it from the set of available commands. Setting this attribute to 'True' will install the command for use. If there is already a Python command with this name installed, the currently installed command will be uninstalled, and this command installed in its place. The following code snippet shows how a two trivial MI command can be implemented in Python: class MIEcho(gdb.MICommand): """Echo arguments passed to the command.""" def __init__(self, name, mode): self._mode = mode super(MIEcho, self).__init__(name) def invoke(self, argv): if self._mode == 'dict': return { 'dict': { 'argv' : argv } } elif self._mode == 'list': return { 'list': argv } else: return { 'string': ", ".join(argv) } MIEcho("-echo-dict", "dict") MIEcho("-echo-list", "list") MIEcho("-echo-string", "string") The last three lines instantiate the class three times, creating three new GDB/MI commands '-echo-dict', '-echo-list', and '-echo-string'. Each time a subclass of 'gdb.MICommand' is instantiated, the new command is automatically registered with GDB. Depending on how the Python code is read into GDB, you may need to import the 'gdb' module explicitly. The following example shows a GDB session in which the above commands have been added: (gdb) -echo-dict abc def ghi ^done,dict={argv=["abc","def","ghi"]} (gdb) -echo-list abc def ghi ^done,list=["abc","def","ghi"] (gdb) -echo-string abc def ghi ^done,string="abc, def, ghi" (gdb)  File: gdb.info, Node: Parameters In Python, Next: Functions In Python, Prev: GDB/MI Commands In Python, Up: Python API 23.3.2.22 Parameters In Python .............................. You can implement new GDB parameters using Python. A new parameter is implemented as an instance of the 'gdb.Parameter' class. Parameters are exposed to the user via the 'set' and 'show' commands. *Note Help::. There are many parameters that already exist and can be set in GDB. Two examples are: 'set follow fork' and 'set charset'. Setting these parameters influences certain behavior in GDB. Similarly, you can define parameters that can be used to influence behavior in custom Python scripts and commands. -- Function: Parameter.__init__ (name, COMMAND-CLASS, PARAMETER-CLASS [, ENUM-SEQUENCE]) The object initializer for 'Parameter' registers the new parameter with GDB. This initializer is normally invoked from the subclass' own '__init__' method. NAME is the name of the new parameter. If NAME consists of multiple words, then the initial words are looked for as prefix parameters. An example of this can be illustrated with the 'set print' set of parameters. If NAME is 'print foo', then 'print' will be searched as the prefix parameter. In this case the parameter can subsequently be accessed in GDB as 'set print foo'. If NAME consists of multiple words, and no prefix parameter group can be found, an exception is raised. COMMAND-CLASS should be one of the 'COMMAND_' constants (*note CLI Commands In Python::). This argument tells GDB how to categorize the new parameter in the help system. PARAMETER-CLASS should be one of the 'PARAM_' constants defined below. This argument tells GDB the type of the new parameter; this information is used for input validation and completion. If PARAMETER-CLASS is 'PARAM_ENUM', then ENUM-SEQUENCE must be a sequence of strings. These strings represent the possible values for the parameter. If PARAMETER-CLASS is not 'PARAM_ENUM', then the presence of a fourth argument will cause an exception to be thrown. The help text for the new parameter includes the Python documentation string from the parameter's class, if there is one. If there is no documentation string, a default value is used. The documentation string is included in the output of the parameters 'help set' and 'help show' commands, and should be written taking this into account. -- Variable: Parameter.set_doc If this attribute exists, and is a string, then its value is used as the first part of the help text for this parameter's 'set' command. The second part of the help text is taken from the documentation string for the parameter's class, if there is one. The value of 'set_doc' should give a brief summary specific to the set action, this text is only displayed when the user runs the 'help set' command for this parameter. The class documentation should be used to give a fuller description of what the parameter does, this text is displayed for both the 'help set' and 'help show' commands. The 'set_doc' value is examined when 'Parameter.__init__' is invoked; subsequent changes have no effect. -- Variable: Parameter.show_doc If this attribute exists, and is a string, then its value is used as the first part of the help text for this parameter's 'show' command. The second part of the help text is taken from the documentation string for the parameter's class, if there is one. The value of 'show_doc' should give a brief summary specific to the show action, this text is only displayed when the user runs the 'help show' command for this parameter. The class documentation should be used to give a fuller description of what the parameter does, this text is displayed for both the 'help set' and 'help show' commands. The 'show_doc' value is examined when 'Parameter.__init__' is invoked; subsequent changes have no effect. -- Variable: Parameter.value The 'value' attribute holds the underlying value of the parameter. It can be read and assigned to just as any other attribute. GDB does validation when assignments are made. There are two methods that may be implemented in any 'Parameter' class. These are: -- Function: Parameter.get_set_string (self) If this method exists, GDB will call it when a PARAMETER's value has been changed via the 'set' API (for example, 'set foo off'). The 'value' attribute has already been populated with the new value and may be used in output. This method must return a string. If the returned string is not empty, GDB will present it to the user. If this method raises the 'gdb.GdbError' exception (*note Exception Handling::), then GDB will print the exception's string and the 'set' command will fail. Note, however, that the 'value' attribute will not be reset in this case. So, if your parameter must validate values, it should store the old value internally and reset the exposed value, like so: class ExampleParam (gdb.Parameter): def __init__ (self, name): super (ExampleParam, self).__init__ (name, gdb.COMMAND_DATA, gdb.PARAM_BOOLEAN) self.value = True self.saved_value = True def validate(self): return False def get_set_string (self): if not self.validate(): self.value = self.saved_value raise gdb.GdbError('Failed to validate') self.saved_value = self.value return "" -- Function: Parameter.get_show_string (self, svalue) GDB will call this method when a PARAMETER's 'show' API has been invoked (for example, 'show foo'). The argument 'svalue' receives the string representation of the current value. This method must return a string. When a new parameter is defined, its type must be specified. The available types are represented by constants defined in the 'gdb' module: 'gdb.PARAM_BOOLEAN' The value is a plain boolean. The Python boolean values, 'True' and 'False' are the only valid values. 'gdb.PARAM_AUTO_BOOLEAN' The value has three possible states: true, false, and 'auto'. In Python, true and false are represented using boolean constants, and 'auto' is represented using 'None'. 'gdb.PARAM_UINTEGER' The value is an unsigned integer. The value of 0 should be interpreted to mean "unlimited". 'gdb.PARAM_INTEGER' The value is a signed integer. The value of 0 should be interpreted to mean "unlimited". 'gdb.PARAM_STRING' The value is a string. When the user modifies the string, any escape sequences, such as '\t', '\f', and octal escapes, are translated into corresponding characters and encoded into the current host charset. 'gdb.PARAM_STRING_NOESCAPE' The value is a string. When the user modifies the string, escapes are passed through untranslated. 'gdb.PARAM_OPTIONAL_FILENAME' The value is a either a filename (a string), or 'None'. 'gdb.PARAM_FILENAME' The value is a filename. This is just like 'PARAM_STRING_NOESCAPE', but uses file names for completion. 'gdb.PARAM_ZINTEGER' The value is an integer. This is like 'PARAM_INTEGER', except 0 is interpreted as itself. 'gdb.PARAM_ZUINTEGER' The value is an unsigned integer. This is like 'PARAM_INTEGER', except 0 is interpreted as itself, and the value cannot be negative. 'gdb.PARAM_ZUINTEGER_UNLIMITED' The value is a signed integer. This is like 'PARAM_ZUINTEGER', except the special value -1 should be interpreted to mean "unlimited". Other negative values are not allowed. 'gdb.PARAM_ENUM' The value is a string, which must be one of a collection string constants provided when the parameter is created.  File: gdb.info, Node: Functions In Python, Next: Progspaces In Python, Prev: Parameters In Python, Up: Python API 23.3.2.23 Writing new convenience functions ........................................... You can implement new convenience functions (*note Convenience Vars::) in Python. A convenience function is an instance of a subclass of the class 'gdb.Function'. -- Function: Function.__init__ (name) The initializer for 'Function' registers the new function with GDB. The argument NAME is the name of the function, a string. The function will be visible to the user as a convenience variable of type 'internal function', whose name is the same as the given NAME. The documentation for the new function is taken from the documentation string for the new class. -- Function: Function.invoke (*ARGS) When a convenience function is evaluated, its arguments are converted to instances of 'gdb.Value', and then the function's 'invoke' method is called. Note that GDB does not predetermine the arity of convenience functions. Instead, all available arguments are passed to 'invoke', following the standard Python calling convention. In particular, a convenience function can have default values for parameters without ill effect. The return value of this method is used as its value in the enclosing expression. If an ordinary Python value is returned, it is converted to a 'gdb.Value' following the usual rules. The following code snippet shows how a trivial convenience function can be implemented in Python: class Greet (gdb.Function): """Return string to greet someone. Takes a name as argument.""" def __init__ (self): super (Greet, self).__init__ ("greet") def invoke (self, name): return "Hello, %s!" % name.string () Greet () The last line instantiates the class, and is necessary to trigger the registration of the function with GDB. Depending on how the Python code is read into GDB, you may need to import the 'gdb' module explicitly. Now you can use the function in an expression: (gdb) print $greet("Bob") $1 = "Hello, Bob!"  File: gdb.info, Node: Progspaces In Python, Next: Objfiles In Python, Prev: Functions In Python, Up: Python API 23.3.2.24 Program Spaces In Python .................................. A program space, or "progspace", represents a symbolic view of an address space. It consists of all of the objfiles of the program. *Note Objfiles In Python::. *Note program spaces: Inferiors Connections and Programs, for more details about program spaces. The following progspace-related functions are available in the 'gdb' module: -- Function: gdb.current_progspace () This function returns the program space of the currently selected inferior. *Note Inferiors Connections and Programs::. This is identical to 'gdb.selected_inferior().progspace' (*note Inferiors In Python::) and is included for historical compatibility. -- Function: gdb.progspaces () Return a sequence of all the progspaces currently known to GDB. Each progspace is represented by an instance of the 'gdb.Progspace' class. -- Variable: Progspace.filename The file name of the progspace as a string. -- Variable: Progspace.pretty_printers The 'pretty_printers' attribute is a list of functions. It is used to look up pretty-printers. A 'Value' is passed to each function in order; if the function returns 'None', then the search continues. Otherwise, the return value should be an object which is used to format the value. *Note Pretty Printing API::, for more information. -- Variable: Progspace.type_printers The 'type_printers' attribute is a list of type printer objects. *Note Type Printing API::, for more information. -- Variable: Progspace.frame_filters The 'frame_filters' attribute is a dictionary of frame filter objects. *Note Frame Filter API::, for more information. A program space has the following methods: -- Function: Progspace.block_for_pc (pc) Return the innermost 'gdb.Block' containing the given PC value. If the block cannot be found for the PC value specified, the function will return 'None'. -- Function: Progspace.find_pc_line (pc) Return the 'gdb.Symtab_and_line' object corresponding to the PC value. *Note Symbol Tables In Python::. If an invalid value of PC is passed as an argument, then the 'symtab' and 'line' attributes of the returned 'gdb.Symtab_and_line' object will be 'None' and 0 respectively. -- Function: Progspace.is_valid () Returns 'True' if the 'gdb.Progspace' object is valid, 'False' if not. A 'gdb.Progspace' object can become invalid if the program space file it refers to is not referenced by any inferior. All other 'gdb.Progspace' methods will throw an exception if it is invalid at the time the method is called. -- Function: Progspace.objfiles () Return a sequence of all the objfiles referenced by this program space. *Note Objfiles In Python::. -- Function: Progspace.solib_name (address) Return the name of the shared library holding the given ADDRESS as a string, or 'None'. One may add arbitrary attributes to 'gdb.Progspace' objects in the usual Python way. This is useful if, for example, one needs to do some extra record keeping associated with the program space. In this contrived example, we want to perform some processing when an objfile with a certain symbol is loaded, but we only want to do this once because it is expensive. To achieve this we record the results with the program space because we can't predict when the desired objfile will be loaded. (gdb) python def clear_objfiles_handler(event): event.progspace.expensive_computation = None def expensive(symbol): """A mock routine to perform an "expensive" computation on symbol.""" print ("Computing the answer to the ultimate question ...") return 42 def new_objfile_handler(event): objfile = event.new_objfile progspace = objfile.progspace if not hasattr(progspace, 'expensive_computation') or \ progspace.expensive_computation is None: # We use 'main' for the symbol to keep the example simple. # Note: There's no current way to constrain the lookup # to one objfile. symbol = gdb.lookup_global_symbol('main') if symbol is not None: progspace.expensive_computation = expensive(symbol) gdb.events.clear_objfiles.connect(clear_objfiles_handler) gdb.events.new_objfile.connect(new_objfile_handler) end (gdb) file /tmp/hello Reading symbols from /tmp/hello... Computing the answer to the ultimate question ... (gdb) python print gdb.current_progspace().expensive_computation 42 (gdb) run Starting program: /tmp/hello Hello. [Inferior 1 (process 4242) exited normally]  File: gdb.info, Node: Objfiles In Python, Next: Frames In Python, Prev: Progspaces In Python, Up: Python API 23.3.2.25 Objfiles In Python ............................ GDB loads symbols for an inferior from various symbol-containing files (*note Files::). These include the primary executable file, any shared libraries used by the inferior, and any separate debug info files (*note Separate Debug Files::). GDB calls these symbol-containing files "objfiles". The following objfile-related functions are available in the 'gdb' module: -- Function: gdb.current_objfile () When auto-loading a Python script (*note Python Auto-loading::), GDB sets the "current objfile" to the corresponding objfile. This function returns the current objfile. If there is no current objfile, this function returns 'None'. -- Function: gdb.objfiles () Return a sequence of objfiles referenced by the current program space. *Note Objfiles In Python::, and *note Progspaces In Python::. This is identical to 'gdb.selected_inferior().progspace.objfiles()' and is included for historical compatibility. -- Function: gdb.lookup_objfile (name [, by_build_id]) Look up NAME, a file name or build ID, in the list of objfiles for the current program space (*note Progspaces In Python::). If the objfile is not found throw the Python 'ValueError' exception. If NAME is a relative file name, then it will match any source file name with the same trailing components. For example, if NAME is 'gcc/expr.c', then it will match source file name of '/build/trunk/gcc/expr.c', but not '/build/trunk/libcpp/expr.c' or '/build/trunk/gcc/x-expr.c'. If BY_BUILD_ID is provided and is 'True' then NAME is the build ID of the objfile. Otherwise, NAME is a file name. This is supported only on some operating systems, notably those which use the ELF format for binary files and the GNU Binutils. For more details about this feature, see the description of the '--build-id' command-line option in *note Command Line Options: (ld)Options. Each objfile is represented by an instance of the 'gdb.Objfile' class. -- Variable: Objfile.filename The file name of the objfile as a string, with symbolic links resolved. The value is 'None' if the objfile is no longer valid. See the 'gdb.Objfile.is_valid' method, described below. -- Variable: Objfile.username The file name of the objfile as specified by the user as a string. The value is 'None' if the objfile is no longer valid. See the 'gdb.Objfile.is_valid' method, described below. -- Variable: Objfile.owner For separate debug info objfiles this is the corresponding 'gdb.Objfile' object that debug info is being provided for. Otherwise this is 'None'. Separate debug info objfiles are added with the 'gdb.Objfile.add_separate_debug_file' method, described below. -- Variable: Objfile.build_id The build ID of the objfile as a string. If the objfile does not have a build ID then the value is 'None'. This is supported only on some operating systems, notably those which use the ELF format for binary files and the GNU Binutils. For more details about this feature, see the description of the '--build-id' command-line option in *note Command Line Options: (ld)Options. -- Variable: Objfile.progspace The containing program space of the objfile as a 'gdb.Progspace' object. *Note Progspaces In Python::. -- Variable: Objfile.pretty_printers The 'pretty_printers' attribute is a list of functions. It is used to look up pretty-printers. A 'Value' is passed to each function in order; if the function returns 'None', then the search continues. Otherwise, the return value should be an object which is used to format the value. *Note Pretty Printing API::, for more information. -- Variable: Objfile.type_printers The 'type_printers' attribute is a list of type printer objects. *Note Type Printing API::, for more information. -- Variable: Objfile.frame_filters The 'frame_filters' attribute is a dictionary of frame filter objects. *Note Frame Filter API::, for more information. One may add arbitrary attributes to 'gdb.Objfile' objects in the usual Python way. This is useful if, for example, one needs to do some extra record keeping associated with the objfile. In this contrived example we record the time when GDB loaded the objfile. (gdb) python import datetime def new_objfile_handler(event): # Set the time_loaded attribute of the new objfile. event.new_objfile.time_loaded = datetime.datetime.today() gdb.events.new_objfile.connect(new_objfile_handler) end (gdb) file ./hello Reading symbols from ./hello... (gdb) python print gdb.objfiles()[0].time_loaded 2014-10-09 11:41:36.770345 A 'gdb.Objfile' object has the following methods: -- Function: Objfile.is_valid () Returns 'True' if the 'gdb.Objfile' object is valid, 'False' if not. A 'gdb.Objfile' object can become invalid if the object file it refers to is not loaded in GDB any longer. All other 'gdb.Objfile' methods will throw an exception if it is invalid at the time the method is called. -- Function: Objfile.add_separate_debug_file (file) Add FILE to the list of files that GDB will search for debug information for the objfile. This is useful when the debug info has been removed from the program and stored in a separate file. GDB has built-in support for finding separate debug info files (*note Separate Debug Files::), but if the file doesn't live in one of the standard places that GDB searches then this function can be used to add a debug info file from a different place. -- Function: Objfile.lookup_global_symbol (name [, domain]) Search for a global symbol named NAME in this objfile. Optionally, the search scope can be restricted with the DOMAIN argument. The DOMAIN argument must be a domain constant defined in the 'gdb' module and described in *note Symbols In Python::. This function is similar to 'gdb.lookup_global_symbol', except that the search is limited to this objfile. The result is a 'gdb.Symbol' object or 'None' if the symbol is not found. -- Function: Objfile.lookup_static_symbol (name [, domain]) Like 'Objfile.lookup_global_symbol', but searches for a global symbol with static linkage named NAME in this objfile.  File: gdb.info, Node: Frames In Python, Next: Blocks In Python, Prev: Objfiles In Python, Up: Python API 23.3.2.26 Accessing inferior stack frames from Python ..................................................... When the debugged program stops, GDB is able to analyze its call stack (*note Stack frames: Frames.). The 'gdb.Frame' class represents a frame in the stack. A 'gdb.Frame' object is only valid while its corresponding frame exists in the inferior's stack. If you try to use an invalid frame object, GDB will throw a 'gdb.error' exception (*note Exception Handling::). Two 'gdb.Frame' objects can be compared for equality with the '==' operator, like: (gdb) python print gdb.newest_frame() == gdb.selected_frame () True The following frame-related functions are available in the 'gdb' module: -- Function: gdb.selected_frame () Return the selected frame object. (*note Selecting a Frame: Selection.). -- Function: gdb.newest_frame () Return the newest frame object for the selected thread. -- Function: gdb.frame_stop_reason_string (reason) Return a string explaining the reason why GDB stopped unwinding frames, as expressed by the given REASON code (an integer, see the 'unwind_stop_reason' method further down in this section). -- Function: gdb.invalidate_cached_frames GDB internally keeps a cache of the frames that have been unwound. This function invalidates this cache. This function should not generally be called by ordinary Python code. It is documented for the sake of completeness. A 'gdb.Frame' object has the following methods: -- Function: Frame.is_valid () Returns true if the 'gdb.Frame' object is valid, false if not. A frame object can become invalid if the frame it refers to doesn't exist anymore in the inferior. All 'gdb.Frame' methods will throw an exception if it is invalid at the time the method is called. -- Function: Frame.name () Returns the function name of the frame, or 'None' if it can't be obtained. -- Function: Frame.architecture () Returns the 'gdb.Architecture' object corresponding to the frame's architecture. *Note Architectures In Python::. -- Function: Frame.type () Returns the type of the frame. The value can be one of: 'gdb.NORMAL_FRAME' An ordinary stack frame. 'gdb.DUMMY_FRAME' A fake stack frame that was created by GDB when performing an inferior function call. 'gdb.INLINE_FRAME' A frame representing an inlined function. The function was inlined into a 'gdb.NORMAL_FRAME' that is older than this one. 'gdb.TAILCALL_FRAME' A frame representing a tail call. *Note Tail Call Frames::. 'gdb.SIGTRAMP_FRAME' A signal trampoline frame. This is the frame created by the OS when it calls into a signal handler. 'gdb.ARCH_FRAME' A fake stack frame representing a cross-architecture call. 'gdb.SENTINEL_FRAME' This is like 'gdb.NORMAL_FRAME', but it is only used for the newest frame. -- Function: Frame.unwind_stop_reason () Return an integer representing the reason why it's not possible to find more frames toward the outermost frame. Use 'gdb.frame_stop_reason_string' to convert the value returned by this function to a string. The value can be one of: 'gdb.FRAME_UNWIND_NO_REASON' No particular reason (older frames should be available). 'gdb.FRAME_UNWIND_NULL_ID' The previous frame's analyzer returns an invalid result. This is no longer used by GDB, and is kept only for backward compatibility. 'gdb.FRAME_UNWIND_OUTERMOST' This frame is the outermost. 'gdb.FRAME_UNWIND_UNAVAILABLE' Cannot unwind further, because that would require knowing the values of registers or memory that have not been collected. 'gdb.FRAME_UNWIND_INNER_ID' This frame ID looks like it ought to belong to a NEXT frame, but we got it for a PREV frame. Normally, this is a sign of unwinder failure. It could also indicate stack corruption. 'gdb.FRAME_UNWIND_SAME_ID' This frame has the same ID as the previous one. That means that unwinding further would almost certainly give us another frame with exactly the same ID, so break the chain. Normally, this is a sign of unwinder failure. It could also indicate stack corruption. 'gdb.FRAME_UNWIND_NO_SAVED_PC' The frame unwinder did not find any saved PC, but we needed one to unwind further. 'gdb.FRAME_UNWIND_MEMORY_ERROR' The frame unwinder caused an error while trying to access memory. 'gdb.FRAME_UNWIND_FIRST_ERROR' Any stop reason greater or equal to this value indicates some kind of error. This special value facilitates writing code that tests for errors in unwinding in a way that will work correctly even if the list of the other values is modified in future GDB versions. Using it, you could write: reason = gdb.selected_frame().unwind_stop_reason () reason_str = gdb.frame_stop_reason_string (reason) if reason >= gdb.FRAME_UNWIND_FIRST_ERROR: print ("An error occured: %s" % reason_str) -- Function: Frame.pc () Returns the frame's resume address. -- Function: Frame.block () Return the frame's code block. *Note Blocks In Python::. If the frame does not have a block - for example, if there is no debugging information for the code in question - then this will throw an exception. -- Function: Frame.function () Return the symbol for the function corresponding to this frame. *Note Symbols In Python::. -- Function: Frame.older () Return the frame that called this frame. -- Function: Frame.newer () Return the frame called by this frame. -- Function: Frame.find_sal () Return the frame's symtab and line object. *Note Symbol Tables In Python::. -- Function: Frame.read_register (register) Return the value of REGISTER in this frame. Returns a 'Gdb.Value' object. Throws an exception if REGISTER does not exist. The REGISTER argument must be one of the following: 1. A string that is the name of a valid register (e.g., ''sp'' or ''rax''). 2. A 'gdb.RegisterDescriptor' object (*note Registers In Python::). 3. A GDB internal, platform specific number. Using these numbers is supported for historic reasons, but is not recommended as future changes to GDB could change the mapping between numbers and the registers they represent, breaking any Python code that uses the platform-specific numbers. The numbers are usually found in the corresponding 'PLATFORM-tdep.h' file in the GDB source tree. Using a string to access registers will be slightly slower than the other two methods as GDB must look up the mapping between name and internal register number. If performance is critical consider looking up and caching a 'gdb.RegisterDescriptor' object. -- Function: Frame.read_var (variable [, block]) Return the value of VARIABLE in this frame. If the optional argument BLOCK is provided, search for the variable from that block; otherwise start at the frame's current block (which is determined by the frame's current program counter). The VARIABLE argument must be a string or a 'gdb.Symbol' object; BLOCK must be a 'gdb.Block' object. -- Function: Frame.select () Set this frame to be the selected frame. *Note Examining the Stack: Stack. -- Function: Frame.level () Return an integer, the stack frame level for this frame. *Note Stack Frames: Frames.  File: gdb.info, Node: Blocks In Python, Next: Symbols In Python, Prev: Frames In Python, Up: Python API 23.3.2.27 Accessing blocks from Python ...................................... In GDB, symbols are stored in blocks. A block corresponds roughly to a scope in the source code. Blocks are organized hierarchically, and are represented individually in Python as a 'gdb.Block'. Blocks rely on debugging information being available. A frame has a block. Please see *note Frames In Python::, for a more in-depth discussion of frames. The outermost block is known as the "global block". The global block typically holds public global variables and functions. The block nested just inside the global block is the "static block". The static block typically holds file-scoped variables and functions. GDB provides a method to get a block's superblock, but there is currently no way to examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (*note Symbol Tables In Python::). Here is a short example that should help explain blocks: /* This is in the global block. */ int global; /* This is in the static block. */ static int file_scope; /* 'function' is in the global block, and 'argument' is in a block nested inside of 'function'. */ int function (int argument) { /* 'local' is in a block inside 'function'. It may or may not be in the same block as 'argument'. */ int local; { /* 'inner' is in a block whose superblock is the one holding 'local'. */ int inner; /* If this call is expanded by the compiler, you may see a nested block here whose function is 'inline_function' and whose superblock is the one holding 'inner'. */ inline_function (); } } A 'gdb.Block' is iterable. The iterator returns the symbols (*note Symbols In Python::) local to the block. Python programs should not assume that a specific block object will always contain a given symbol, since changes in GDB features and infrastructure may cause symbols move across blocks in a symbol table. You can also use Python's "dictionary syntax" to access variables in this block, e.g.: symbol = some_block['variable'] # symbol is of type gdb.Symbol The following block-related functions are available in the 'gdb' module: -- Function: gdb.block_for_pc (pc) Return the innermost 'gdb.Block' containing the given PC value. If the block cannot be found for the PC value specified, the function will return 'None'. This is identical to 'gdb.current_progspace().block_for_pc(pc)' and is included for historical compatibility. A 'gdb.Block' object has the following methods: -- Function: Block.is_valid () Returns 'True' if the 'gdb.Block' object is valid, 'False' if not. A block object can become invalid if the block it refers to doesn't exist anymore in the inferior. All other 'gdb.Block' methods will throw an exception if it is invalid at the time the method is called. The block's validity is also checked during iteration over symbols of the block. A 'gdb.Block' object has the following attributes: -- Variable: Block.start The start address of the block. This attribute is not writable. -- Variable: Block.end One past the last address that appears in the block. This attribute is not writable. -- Variable: Block.function The name of the block represented as a 'gdb.Symbol'. If the block is not named, then this attribute holds 'None'. This attribute is not writable. For ordinary function blocks, the superblock is the static block. However, you should note that it is possible for a function block to have a superblock that is not the static block - for instance this happens for an inlined function. -- Variable: Block.superblock The block containing this block. If this parent block does not exist, this attribute holds 'None'. This attribute is not writable. -- Variable: Block.global_block The global block associated with this block. This attribute is not writable. -- Variable: Block.static_block The static block associated with this block. This attribute is not writable. -- Variable: Block.is_global 'True' if the 'gdb.Block' object is a global block, 'False' if not. This attribute is not writable. -- Variable: Block.is_static 'True' if the 'gdb.Block' object is a static block, 'False' if not. This attribute is not writable.  File: gdb.info, Node: Symbols In Python, Next: Symbol Tables In Python, Prev: Blocks In Python, Up: Python API 23.3.2.28 Python representation of Symbols .......................................... GDB represents every variable, function and type as an entry in a symbol table. *Note Examining the Symbol Table: Symbols. Similarly, Python represents these symbols in GDB with the 'gdb.Symbol' object. The following symbol-related functions are available in the 'gdb' module: -- Function: gdb.lookup_symbol (name [, block [, domain]]) This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments. NAME is the name of the symbol. It must be a string. The optional BLOCK argument restricts the search to symbols visible in that BLOCK. The BLOCK argument must be a 'gdb.Block' object. If omitted, the block for the current frame is used. The optional DOMAIN argument restricts the search to the domain type. The DOMAIN argument must be a domain constant defined in the 'gdb' module and described later in this chapter. The result is a tuple of two elements. The first element is a 'gdb.Symbol' object or 'None' if the symbol is not found. If the symbol is found, the second element is 'True' if the symbol is a field of a method's object (e.g., 'this' in C++), otherwise it is 'False'. If the symbol is not found, the second element is 'False'. -- Function: gdb.lookup_global_symbol (name [, domain]) This function searches for a global symbol by name. The search scope can be restricted to by the domain argument. NAME is the name of the symbol. It must be a string. The optional DOMAIN argument restricts the search to the domain type. The DOMAIN argument must be a domain constant defined in the 'gdb' module and described later in this chapter. The result is a 'gdb.Symbol' object or 'None' if the symbol is not found. -- Function: gdb.lookup_static_symbol (name [, domain]) This function searches for a global symbol with static linkage by name. The search scope can be restricted to by the domain argument. NAME is the name of the symbol. It must be a string. The optional DOMAIN argument restricts the search to the domain type. The DOMAIN argument must be a domain constant defined in the 'gdb' module and described later in this chapter. The result is a 'gdb.Symbol' object or 'None' if the symbol is not found. Note that this function will not find function-scoped static variables. To look up such variables, iterate over the variables of the function's 'gdb.Block' and check that 'block.addr_class' is 'gdb.SYMBOL_LOC_STATIC'. There can be multiple global symbols with static linkage with the same name. This function will only return the first matching symbol that it finds. Which symbol is found depends on where GDB is currently stopped, as GDB will first search for matching symbols in the current object file, and then search all other object files. If the application is not yet running then GDB will search all object files in the order they appear in the debug information. -- Function: gdb.lookup_static_symbols (name [, domain]) Similar to 'gdb.lookup_static_symbol', this function searches for global symbols with static linkage by name, and optionally restricted by the domain argument. However, this function returns a list of all matching symbols found, not just the first one. NAME is the name of the symbol. It must be a string. The optional DOMAIN argument restricts the search to the domain type. The DOMAIN argument must be a domain constant defined in the 'gdb' module and described later in this chapter. The result is a list of 'gdb.Symbol' objects which could be empty if no matching symbols were found. Note that this function will not find function-scoped static variables. To look up such variables, iterate over the variables of the function's 'gdb.Block' and check that 'block.addr_class' is 'gdb.SYMBOL_LOC_STATIC'. A 'gdb.Symbol' object has the following attributes: -- Variable: Symbol.type The type of the symbol or 'None' if no type is recorded. This attribute is represented as a 'gdb.Type' object. *Note Types In Python::. This attribute is not writable. -- Variable: Symbol.symtab The symbol table in which the symbol appears. This attribute is represented as a 'gdb.Symtab' object. *Note Symbol Tables In Python::. This attribute is not writable. -- Variable: Symbol.line The line number in the source code at which the symbol was defined. This is an integer. -- Variable: Symbol.name The name of the symbol as a string. This attribute is not writable. -- Variable: Symbol.linkage_name The name of the symbol, as used by the linker (i.e., may be mangled). This attribute is not writable. -- Variable: Symbol.print_name The name of the symbol in a form suitable for output. This is either 'name' or 'linkage_name', depending on whether the user asked GDB to display demangled or mangled names. -- Variable: Symbol.addr_class The address class of the symbol. This classifies how to find the value of a symbol. Each address class is a constant defined in the 'gdb' module and described later in this chapter. -- Variable: Symbol.needs_frame This is 'True' if evaluating this symbol's value requires a frame (*note Frames In Python::) and 'False' otherwise. Typically, local variables will require a frame, but other symbols will not. -- Variable: Symbol.is_argument 'True' if the symbol is an argument of a function. -- Variable: Symbol.is_constant 'True' if the symbol is a constant. -- Variable: Symbol.is_function 'True' if the symbol is a function or a method. -- Variable: Symbol.is_variable 'True' if the symbol is a variable. A 'gdb.Symbol' object has the following methods: -- Function: Symbol.is_valid () Returns 'True' if the 'gdb.Symbol' object is valid, 'False' if not. A 'gdb.Symbol' object can become invalid if the symbol it refers to does not exist in GDB any longer. All other 'gdb.Symbol' methods will throw an exception if it is invalid at the time the method is called. -- Function: Symbol.value ([frame]) Compute the value of the symbol, as a 'gdb.Value'. For functions, this computes the address of the function, cast to the appropriate type. If the symbol requires a frame in order to compute its value, then FRAME must be given. If FRAME is not given, or if FRAME is invalid, then this method will throw an exception. The available domain categories in 'gdb.Symbol' are represented as constants in the 'gdb' module: 'gdb.SYMBOL_UNDEF_DOMAIN' This is used when a domain has not been discovered or none of the following domains apply. This usually indicates an error either in the symbol information or in GDB's handling of symbols. 'gdb.SYMBOL_VAR_DOMAIN' This domain contains variables, function names, typedef names and enum type values. 'gdb.SYMBOL_STRUCT_DOMAIN' This domain holds struct, union and enum type names. 'gdb.SYMBOL_LABEL_DOMAIN' This domain contains names of labels (for gotos). 'gdb.SYMBOL_MODULE_DOMAIN' This domain contains names of Fortran module types. 'gdb.SYMBOL_COMMON_BLOCK_DOMAIN' This domain contains names of Fortran common blocks. The available address class categories in 'gdb.Symbol' are represented as constants in the 'gdb' module: 'gdb.SYMBOL_LOC_UNDEF' If this is returned by address class, it indicates an error either in the symbol information or in GDB's handling of symbols. 'gdb.SYMBOL_LOC_CONST' Value is constant int. 'gdb.SYMBOL_LOC_STATIC' Value is at a fixed address. 'gdb.SYMBOL_LOC_REGISTER' Value is in a register. 'gdb.SYMBOL_LOC_ARG' Value is an argument. This value is at the offset stored within the symbol inside the frame's argument list. 'gdb.SYMBOL_LOC_REF_ARG' Value address is stored in the frame's argument list. Just like 'LOC_ARG' except that the value's address is stored at the offset, not the value itself. 'gdb.SYMBOL_LOC_REGPARM_ADDR' Value is a specified register. Just like 'LOC_REGISTER' except the register holds the address of the argument instead of the argument itself. 'gdb.SYMBOL_LOC_LOCAL' Value is a local variable. 'gdb.SYMBOL_LOC_TYPEDEF' Value not used. Symbols in the domain 'SYMBOL_STRUCT_DOMAIN' all have this class. 'gdb.SYMBOL_LOC_LABEL' Value is a label. 'gdb.SYMBOL_LOC_BLOCK' Value is a block. 'gdb.SYMBOL_LOC_CONST_BYTES' Value is a byte-sequence. 'gdb.SYMBOL_LOC_UNRESOLVED' Value is at a fixed address, but the address of the variable has to be determined from the minimal symbol table whenever the variable is referenced. 'gdb.SYMBOL_LOC_OPTIMIZED_OUT' The value does not actually exist in the program. 'gdb.SYMBOL_LOC_COMPUTED' The value's address is a computed location. 'gdb.SYMBOL_LOC_COMMON_BLOCK' The value's address is a symbol. This is only used for Fortran common blocks.