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Info file gdb.info, produced by Makeinfo, -*- Text -*- from input file gdb-all.texi. This file documents the GNU debugger GDB. Copyright (C) 1988, 1989, 1990, 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: gdb.info, Node: Files, Next: Symbol Errors, Prev: GDB Files, Up: GDB Files Commands to Specify Files ========================= GDB needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start the program. To debug a core dump of a previous run, GDB must be told the file name of the core dump. The usual way to specify the executable and core dump file names is with the command arguments given when you start GDB, as discussed in *note Invocation::.. Occasionally it is necessary to change to a different file during a GDB session. Or you may run GDB and forget to specify the files you want to use. In these situations the GDB commands to specify new files are useful. `file FILENAME' Use FILENAME as the program to be debugged. It is read for its symbols and for the contents of pure memory. It is also the program executed when you use the `run' command. If you do not specify a directory and the file is not found in GDB's working directory, GDB uses the environment variable `PATH' as a list of directories to search, just as the shell does when looking for a program to run. You can change the value of this variable, for both GDB and your program, using the `path' command. `file' `file' with no argument makes GDB discard any information it has on both executable file and the symbol table. `exec-file [ FILENAME ]' Specify that the program to be run (but not the symbol table) is found in FILENAME. GDB will search the environment variable `PATH' if necessary to locate the program. Omitting FILENAME means to discard information on the executable file. `symbol-file [ FILENAME ]' Read symbol table information from file FILENAME. `PATH' is searched when necessary. Use the `file' command to get both symbol table and program to run from the same file. `symbol-file' with no argument clears out GDB's information on your program's symbol table. The `symbol-file' command causes GDB to forget the contents of its convenience variables, the value history, and all breakpoints and auto-display expressions. This is because they may contain pointers to the internal data recording symbols and data types, which are part of the old symbol table data being discarded inside GDB. `symbol-file' will not repeat if you press RET again after executing it once. On some kinds of object files, the `symbol-file' command does not actually read the symbol table in full right away. Instead, it scans the symbol table quickly to find which source files and which symbols are present. The details are read later, one source file at a time, when they are needed. The purpose of this two-stage reading strategy is to make GDB start up faster. For the most part, it is invisible except for occasional pauses while the symbol table details for a particular source file are being read. (The `set verbose' command can turn these pauses into messages if desired. *Note Messages/Warnings::). When the symbol table is stored in COFF format, `symbol-file' does read the symbol table data in full right away. We haven't implemented the two-stage strategy for COFF yet. When GDB is configured for a particular environment, it will understand debugging information in whatever format is the standard generated for that environment; you may use either a GNU compiler, or other compilers that adhere to the local conventions. Best results are usually obtained from GNU compilers; for example, using `gcc' you can generate debugging information for optimized code. `core-file [ FILENAME ]' Specify the whereabouts of a core dump file to be used as the "contents of memory". Traditionally, core files contain only some parts of the address space of the process that generated them; GDB can access the executable file itself for other parts. `core-file' with no argument specifies that no core file is to be used. Note that the core file is ignored when your program is actually running under GDB. So, if you have been running the program and you wish to debug a core file instead, you must kill the subprocess in which the program is running. To do this, use the `kill' command (*note Kill Process::.). `load FILENAME' Depending on what remote debugging facilities are configured into GDB, the `load' command may be available. Where it exists, it is meant to make FILENAME (an executable) available for debugging on the remote system--by downloading, or dynamic linking, for example. `load' also records FILENAME's symbol table in GDB, like the `add-symbol-file' command. If `load' is not available on your GDB, attempting to execute it gets the error message "`You can't do that when your target is ...'" On VxWorks, `load' will dynamically link FILENAME on the current target system as well as adding its symbols in GDB. With the Nindy interface to an Intel 960 board, `load' will download FILENAME to the 960 as well as adding its symbols in GDB. `load' will not repeat if you press RET again after using it. `add-symbol-file FILENAME ADDRESS' The `add-symbol-file' command reads additional symbol table information from the file FILENAME. You would use this command when FILENAME has been dynamically loaded (by some other means) into the program that is running. ADDRESS should be the memory address at which the file has been loaded; GDB cannot figure this out for itself. The symbol table of the file FILENAME is added to the symbol table originally read with the `symbol-file' command. You can use the `add-symbol-file' command any number of times; the new symbol data thus read keeps adding to the old. To discard all old symbol data instead, use the `symbol-file' command. `add-symbol-file' will not repeat if you press RET after using it. `info files' `info target' `info files' and `info target' are synonymous; both print the current targets (*note Targets::.), including the names of the executable and core dump files currently in use by GDB, and the files from which symbols were loaded. The command `help targets' lists all possible targets rather than current ones. All file-specifying commands allow both absolute and relative file names as arguments. GDB always converts the file name to an absolute path name and remembers it that way. GDB supports the SunOS shared library format. GDB automatically loads symbol definitions from shared libraries when you use the `run' command, or when you examine a core file. (Before you issue the `run' command, GDB won't understand references to a function in a shared library, however--unless you're debugging a core file). `info share' `info sharedlibrary' Print the names of the shared libraries which are currently loaded. `sharedlibrary REGEX' `share REGEX' This is an obsolescent command; you can use it to explicitly load shared object library symbols for files matching a UNIX regular expression, but as with files loaded automatically, it will only load shared libraries required by your program for a core file or after typing `run'. If REGEX is omitted all shared libraries required by your program are loaded. File: gdb.info, Node: Symbol Errors, Prev: Files, Up: GDB Files Errors Reading Symbol Files =========================== While reading a symbol file, GDB will occasionally encounter problems, such as symbol types it does not recognize, or known bugs in compiler output. By default, GDB does not notify you of such problems, since they're relatively common and primarily of interest to people debugging compilers. If you are interested in seeing information about ill-constructed symbol tables, you can either ask GDB to print only one message about each such type of problem, no matter how many times the problem occurs; or you can ask GDB to print more messages, to see how many times the problems occur, with the `set complaints' command (*Note Messages/Warnings::). The messages currently printed, and their meanings, are: `inner block not inside outer block in SYMBOL' The symbol information shows where symbol scopes begin and end (such as at the start of a function or a block of statements). This error indicates that an inner scope block is not fully contained in its outer scope blocks. GDB circumvents the problem by treating the inner block as if it had the same scope as the outer block. In the error message, SYMBOL may be shown as "`(don't know)'" if the outer block is not a function. `block at ADDRESS out of order' The symbol information for symbol scope blocks should occur in order of increasing addresses. This error indicates that it does not do so. GDB does not circumvent this problem, and will have trouble locating symbols in the source file whose symbols being read. (You can often determine what source file is affected by specifying `set verbose on'. *Note Messages/Warnings::.) `bad block start address patched' The symbol information for a symbol scope block has a start address smaller than the address of the preceding source line. This is known to occur in the SunOS 4.1.1 (and earlier) C compiler. GDB circumvents the problem by treating the symbol scope block as starting on the previous source line. `bad string table offset in symbol N' Symbol number N contains a pointer into the string table which is larger than the size of the string table. GDB circumvents the problem by considering the symbol to have the name `foo', which may cause other problems if many symbols end up with this name. `unknown symbol type `0xNN'' The symbol information contains new data types that GDB does not yet know how to read. `0xNN' is the symbol type of the misunderstood information, in hexadecimal. GDB circumvents the error by ignoring this symbol information. This will usually allow the program to be debugged, though certain symbols will not be accessible. If you encounter such a problem and feel like debugging it, you can debug `gdb' with itself, breakpoint on `complain', then go up to the function `read_dbx_symtab' and examine `*bufp' to see the symbol. `stub type has NULL name' GDB could not find the full definition for a struct or class. `const/volatile indicator missing (ok if using g++ v1.x), got...' The symbol information for a C++ member function is missing some information that recent versions of the compiler should have output for it. `info mismatch between compiler and debugger' GDB could not parse a type specification output by the compiler. File: gdb.info, Node: Targets, Next: Controlling GDB, Prev: GDB Files, Up: Top Specifying a Debugging Target ***************************** A "target" is the execution environment occupied by your program. Often, GDB runs in the same host environment as the program you are debugging; in that case, the debugging target is specified as a side effect when you use the `file' or `core' commands. When you need more flexibility--for example, running GDB on a physically separate host, or controlling a standalone system over a serial port or a realtime system over a TCP/IP connection--you can use the `target' command to specify one of the target types configured for GDB (*note Target Commands::.). * Menu: * Active Targets:: Active Targets * Target Commands:: Commands for Managing Targets * Remote:: Remote Debugging File: gdb.info, Node: Active Targets, Next: Target Commands, Prev: Targets, Up: Targets Active Targets ============== There are three classes of targets: processes, core files, and executable files. GDB can work concurrently on up to three active targets, one in each class. This allows you to (for example) start a process and inspect its activity without abandoning your work on a core file. If, for example, you execute `gdb a.out', then the executable file `a.out' is the only active target. If you designate a core file as well--presumably from a prior run that crashed and coredumped--then GDB has two active targets and will use them in tandem, looking first in the corefile target, then in the executable file, to satisfy requests for memory addresses. (Typically, these two classes of target are complementary, since core files contain only the program's read-write memory--variables and so on--plus machine status, while executable files contain only the program text and initialized data.) When you type `run', your executable file becomes an active process target as well. When a process target is active, all GDB commands requesting memory addresses refer to that target; addresses in an active core file or executable file target are obscured while the process target is active. Use the `core-file', and `exec-file' commands to select a new core file or executable target (*note Files::.). To specify as a target a process that's already running, use the `attach' command (*note Attach::.). File: gdb.info, Node: Target Commands, Next: Remote, Prev: Active Targets, Up: Targets Commands for Managing Targets ============================= `target TYPE PARAMETERS' Connects the GDB host environment to a target machine or process. A target is typically a protocol for talking to debugging facilities. You use the argument TYPE to specify the type or protocol of the target machine. Further PARAMETERS are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates. The `target' command will not repeat if you press RET again after executing the command. `help target' Displays the names of all targets available. To display targets currently selected, use either `info target' or `info files' (*note Files::.). `help target NAME' Describe a particular target, including any parameters necessary to select it. Here are some common targets (available, or not, depending on the GDB configuration): `target exec PROG' An executable file. `target exec PROG' is the same as `exec-file PROG'. `target core FILENAME' A core dump file. `target core FILENAME' is the same as `core-file FILENAME'. `target remote DEV' Remote serial target in GDB-specific protocol. The argument DEV specifies what serial device to use for the connection (e.g. `/dev/ttya'). *Note Remote::. `target amd-eb DEV SPEED PROG' Remote PC-resident AMD EB29K board, attached over serial lines. DEV is the serial device, as for `target remote'; SPEED allows you to specify the linespeed; and PROG is the name of the program to be debugged, as it appears to DOS on the PC. *Note EB29K Remote::. `target nindy DEVICENAME' An Intel 960 board controlled by a Nindy Monitor. DEVICENAME is the name of the serial device to use for the connection, e.g. `/dev/ttya'. *Note i960-Nindy Remote::. `target vxworks MACHINENAME' A VxWorks system, attached via TCP/IP. The argument MACHINENAME is the target system's machine name or IP address. *Note VxWorks Remote::. Different targets are available on different configurations of GDB; your configuration may have more or fewer targets. File: gdb.info, Node: Remote, Prev: Target Commands, Up: Targets Remote Debugging ================ * Menu: * i960-Nindy Remote:: GDB with a Remote i960 (Nindy) * EB29K Remote:: GDB with a Remote EB29K * VxWorks Remote:: GDB and VxWorks If you are trying to debug a program running on a machine that can't run GDB in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger. Some configurations of GDB have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, GDB comes with a generic serial protocol (specific to GDB, but not specific to any particular target system) which you can use if you write the remote stubs--the code that will run on the remote system to communicate with GDB. To use the GDB remote serial protocol, the program to be debugged on the remote machine needs to contain a debugging stub which talks to GDB over the serial line. Several working remote stubs are distributed with GDB; see the `README' file in the GDB distribution for more information. For details of this communication protocol, see the comments in the GDB source file `remote.c'. To start remote debugging, first run GDB and specify as an executable file the program that is running in the remote machine. This tells GDB how to find the program's symbols and the contents of its pure text. Then establish communication using the `target remote' command with a device name as an argument. For example: target remote /dev/ttyb if the serial line is connected to the device named `/dev/ttyb'. This will stop the remote machine if it is not already stopped. Now you can use all the usual commands to examine and change data and to step and continue the remote program. To resume the remote program and stop debugging it, use the `detach' command. Other remote targets may be available in your configuration of GDB; use `help targets' to list them. File: gdb.info, Node: i960-Nindy Remote, Next: EB29K Remote, Prev: Remote, Up: Remote GDB with a Remote i960 (Nindy) ------------------------------ "Nindy" is a ROM Monitor program for Intel 960 target systems. When GDB is configured to control a remote Intel 960 using Nindy, you can tell GDB how to connect to the 960 in several ways: * Through command line options specifying serial port, version of the Nindy protocol, and communications speed; * By responding to a prompt on startup; * By using the `target' command at any point during your GDB session. *Note Target Commands::. * Menu: * Nindy Startup:: Startup with Nindy * Nindy Options:: Options for Nindy * Nindy reset:: Nindy Reset Command File: gdb.info, Node: Nindy Startup, Next: Nindy Options, Prev: i960-Nindy Remote, Up: i960-Nindy Remote Startup with Nindy .................. If you simply start `GDB' without using any command-line options, you are prompted for what serial port to use, *before* you reach the ordinary GDB prompt: Attach /dev/ttyNN -- specify NN, or "quit" to quit: Respond to the prompt with whatever suffix (after `/dev/tty') identifies the serial port you want to use. You can, if you choose, simply start up with no Nindy connection by responding to the prompt with an empty line. If you do this, and later wish to attach to Nindy, use `target' (*note Target Commands::.). File: gdb.info, Node: Nindy Options, Next: Nindy reset, Prev: Nindy Startup, Up: i960-Nindy Remote Options for Nindy ................. These are the startup options for beginning your GDB session with a Nindy-960 board attached: `-r PORT' Specify the serial port name of a serial interface to be used to connect to the target system. This option is only available when GDB is configured for the Intel 960 target architecture. You may specify PORT as any of: a full pathname (e.g. `-r /dev/ttya'), a device name in `/dev' (e.g. `-r ttya'), or simply the unique suffix for a specific `tty' (e.g. `-r a'). `-O' (An uppercase letter "O", not a zero.) Specify that GDB should use the "old" Nindy monitor protocol to connect to the target system. This option is only available when GDB is configured for the Intel 960 target architecture. *Warning:* if you specify `-O', but are actually trying to connect to a target system that expects the newer protocol, the connection will fail, appearing to be a speed mismatch. GDB will repeatedly attempt to reconnect at several different line speeds. You can abort this process with an interrupt. `-brk' Specify that GDB should first send a `BREAK' signal to the target system, in an attempt to reset it, before connecting to a Nindy target. *Warning:* Many target systems do not have the hardware that this requires; it only works with a few boards. The standard `-b' option controls the line speed used on the serial port. File: gdb.info, Node: Nindy reset, Prev: Nindy Options, Up: i960-Nindy Remote Nindy Reset Command ................... `reset' For a Nindy target, this command sends a "break" to the remote target system; this is only useful if the target has been equipped with a circuit to perform a hard reset (or some other interesting action) when a break is detected. File: gdb.info, Node: EB29K Remote, Next: VxWorks Remote, Prev: i960-Nindy Remote, Up: Remote GDB with a Remote EB29K ----------------------- To use GDB from a Unix system to run programs on AMD's EB29K board in a PC, you must first connect a serial cable between the PC and a serial port on the Unix system. In the following, we assume you've hooked the cable between the PC's `COM1' port and `/dev/ttya' on the Unix system. * Menu: * Comms (EB29K):: Communications Setup * gdb-EB29K:: EB29K cross-debugging * Remote Log:: Remote Log File: gdb.info, Node: Comms (EB29K), Next: gdb-EB29K, Prev: EB29K Remote, Up: EB29K Remote Communications Setup .................... The next step is to set up the PC's port, by doing something like the following in DOS on the PC: C:\> MODE com1:9600,n,8,1,none This example--run on an MS DOS 4.0 system--sets the PC port to 9600 bps, no parity, eight data bits, one stop bit, and no "retry" action; you must match the communications parameters when establishing the Unix end of the connection as well. To give control of the PC to the Unix side of the serial line, type the following at the DOS console: C:\> CTTY com1 (Later, if you wish to return control to the DOS console, you can use the command `CTTY con'--but you must send it over the device that had control, in our example over the `COM1' serial line). From the Unix host, use a communications program such as `tip' or `cu' to communicate with the PC; for example, cu -s 9600 -l /dev/ttya The `cu' options shown specify, respectively, the linespeed and the serial port to use. If you use `tip' instead, your command line may look something like the following: tip -9600 /dev/ttya Your system may define a different name where our example uses `/dev/ttya' as the argument to `tip'. The communications parameters, including what port to use, are associated with the `tip' argument in the "remote" descriptions file--normally the system table `/etc/remote'. Using the `tip' or `cu' connection, change the DOS working directory to the directory containing a copy of your 29K program, then start the PC program `EBMON' (an EB29K control program supplied with your board by AMD). You should see an initial display from `EBMON' similar to the one that follows, ending with the `EBMON' prompt `#'-- C:\> G: G:\> CD \usr\joe\work29k G:\USR\JOE\WORK29K> EBMON Am29000 PC Coprocessor Board Monitor, version 3.0-18 Copyright 1990 Advanced Micro Devices, Inc. Written by Gibbons and Associates, Inc. Enter '?' or 'H' for help PC Coprocessor Type = EB29K I/O Base = 0x208 Memory Base = 0xd0000 Data Memory Size = 2048KB Available I-RAM Range = 0x8000 to 0x1fffff Available D-RAM Range = 0x80002000 to 0x801fffff PageSize = 0x400 Register Stack Size = 0x800 Memory Stack Size = 0x1800 CPU PRL = 0x3 Am29027 Available = No Byte Write Available = Yes # ~. Then exit the `cu' or `tip' program (done in the example by typing `~.' at the `EBMON' prompt). `EBMON' will keep running, ready for GDB to take over. For this example, we've assumed what is probably the most convenient way to make sure the same 29K program is on both the PC and the Unix system: a PC/NFS connection that establishes "drive `G:'" on the PC as a file system on the Unix host. If you don't have PC/NFS or something similar connecting the two systems, you must arrange some other way--perhaps floppy-disk transfer--of getting the 29K program from the Unix system to the PC; GDB will *not* download it over the serial line. File: gdb.info, Node: gdb-EB29K, Next: Remote Log, Prev: Comms (EB29K), Up: EB29K Remote EB29K cross-debugging ..................... Finally, `cd' to the directory containing an image of your 29K program on the Unix system, and start GDB--specifying as argument the name of your 29K program: cd /usr/joe/work29k gdb myfoo Now you can use the `target' command: target amd-eb /dev/ttya 9600 MYFOO In this example, we've assumed your program is in a file called `myfoo'. Note that the filename given as the last argument to `target amd-eb' should be the name of the program as it appears to DOS. In our example this is simply `MYFOO', but in general it can include a DOS path, and depending on your transfer mechanism may not resemble the name on the Unix side. At this point, you can set any breakpoints you wish; when you're ready to see your program run on the 29K board, use the GDB command `run'. To stop debugging the remote program, use the GDB `detach' command. To return control of the PC to its console, use `tip' or `cu' once again, after your GDB session has concluded, to attach to `EBMON'. You can then type the command `q' to shut down `EBMON', returning control to the DOS command-line interpreter. Type `CTTY con' to return command input to the main DOS console, and type `~.' to leave `tip' or `cu'. File: gdb.info, Node: Remote Log, Prev: gdb-EB29K, Up: EB29K Remote Remote Log .......... The `target amd-eb' command creates a file `eb.log' in the current working directory, to help debug problems with the connection. `eb.log' records all the output from `EBMON', including echoes of the commands sent to it. Running `tail -f' on this file in another window often helps to understand trouble with `EBMON', or unexpected events on the PC side of the connection. File: gdb.info, Node: VxWorks Remote, Prev: EB29K Remote, Up: Remote GDB and VxWorks --------------- GDB enables developers to spawn and debug tasks running on networked VxWorks targets from a Unix host. Already-running tasks spawned from the VxWorks shell can also be debugged. GDB uses code that runs on both the UNIX host and on the VxWorks target. The program `gdb' is installed and executed on the UNIX host. The remote debugging interface (RDB) routines are installed and executed on the VxWorks target. These routines are included in the VxWorks library `rdb.a' and are incorporated into the system image when source-level debugging is enabled in the VxWorks configuration. Defining `INCLUDE_RDB' in the VxWorks configuration file `configAll.h' includes the RDB interface routines and spawns the source debugging task `tRdbTask' when VxWorks is booted. For more information on configuring and remaking VxWorks, see the `VxWorks Programmer's Guide'. Once you have included the RDB interface in your VxWorks system image and set your Unix execution search path to find GDB, you are ready to run GDB. From your UNIX host, type: % gdb GDB will come up showing the prompt: (gdb) * Menu: * VxWorks connection:: Connecting to VxWorks * VxWorks download:: VxWorks Download * VxWorks attach:: Running Tasks File: gdb.info, Node: VxWorks connection, Next: VxWorks download, Prev: VxWorks Remote, Up: VxWorks Remote Connecting to VxWorks ..................... The GDB command `target' lets you connect to a VxWorks target on the network. To connect to a target whose host name is "`tt'", type: (gdb) target vxworks tt GDB will display a message similar to the following: Attaching remote machine across net... Success! GDB will then attempt to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted. GDB locates these files by searching the directories listed in the command search path (*note Environment::.); if it fails to find an object file, it will display a message such as: prog.o: No such file or directory. This will cause the `target' command to abort. When this happens, you should add the appropriate directory to the search path, with the GDB command `path', and execute the `target' command again. File: gdb.info, Node: VxWorks download, Next: VxWorks attach, Prev: VxWorks connection, Up: VxWorks Remote VxWorks Download ................ If you have connected to the VxWorks target and you want to debug an object that has not yet been loaded, you can use the GDB `load' command to download a file from UNIX to VxWorks incrementally. The object file given as an argument to the `load' command is actually opened twice: first by the VxWorks target in order to download the code, then by GDB in order to read the symbol table. This can lead to problems if the current working directories on the two systems differ. It is simplest to set the working directory on both systems to the directory in which the object file resides, and then to reference the file by its name, without any path. Thus, to load a program `prog.o', residing in `wherever/vw/demo/rdb', on VxWorks type: -> cd "wherever/vw/demo/rdb" On GDB type: (gdb) cd wherever/vw/demo/rdb (gdb) load prog.o GDB will display a response similar to the following: Reading symbol data from wherever/vw/demo/rdb/prog.o... done. You can also use the `load' command to reload an object module after editing and recompiling the corresponding source file. Note that this will cause GDB to delete all currently-defined breakpoints, auto-displays, and convenience variables, and to clear the value history. (This is necessary in order to preserve the integrity of debugger data structures that reference the target system's symbol table.) File: gdb.info, Node: VxWorks attach, Prev: VxWorks download, Up: VxWorks Remote Running Tasks ............. You can also attach to an existing task using the `attach' command as follows: (gdb) attach TASK where TASK is the VxWorks hexadecimal task ID. The task can be running or suspended when you attach to it. If running, it will be suspended at the time of attachment. File: gdb.info, Node: Controlling GDB, Next: Sequences, Prev: Targets, Up: Top Controlling GDB *************** You can alter many aspects of GDB's interaction with you by using the `set' command. For commands controlling how GDB displays data, *note Print Settings::.; other settings are described here. * Menu: * Prompt:: Prompt * Editing:: Command Editing * History:: Command History * Screen Size:: Screen Size * Numbers:: Numbers * Messages/Warnings:: Optional Warnings and Messages File: gdb.info, Node: Prompt, Next: Editing, Prev: Controlling GDB, Up: Controlling GDB 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 GDBs so that you can always tell which one you are talking to. `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' File: gdb.info, Node: Editing, Next: History, Prev: Prompt, Up: Controlling GDB 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 `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. File: gdb.info, Node: History, Next: Screen Size, Prev: Editing, Up: Controlling GDB Command History =============== `set history filename FNAME' Set the name of the GDB command history file to FNAME. This is the file from which GDB will read an initial command history list or to which it will write this list when it exits. This list is accessed 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' if this variable is not set. `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. `set history save off' Stop recording command history in a file. `set history size SIZE' Set the number of commands which GDB will keep in its history list. This defaults to the value of the environment variable `HISTSIZE', or to 256 if this variable is not set. History expansion assigns special meaning to the character `!'. 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 will 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. The readline code comes with more complete documentation of editing and history expansion features. Users unfamiliar with `emacs' or `vi' may wish to read it. `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: Numbers, Prev: History, Up: Controlling GDB 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 RET when you want to continue the output. GDB also uses the screen width setting to determine when to wrap lines of output. Depending on what is being printed, it 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 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' `show height' `set width CPL' `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 zero lines, GDB will 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. File: gdb.info, Node: Numbers, Next: Messages/Warnings, Prev: Screen Size, Up: Controlling GDB 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 begin with none of these 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 `set radix' command. `set radix BASE' Set the default base for numeric input and display. Supported choices for BASE are decimal 2, 8, 10, 16. BASE must itself be specified either unambiguously or using the current default radix; for example, any of set radix 1010 set radix 012 set radix 10. set radix 0xa will set the base to decimal. On the other hand, `set radix 10' will leave the radix unchanged no matter what it was. `show radix' Display the current default base for numeric input and display. File: gdb.info, Node: Messages/Warnings, Prev: Numbers, Up: Controlling GDB 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. It will make GDB tell you when it does a lengthy internal operation, so you won't 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 (*note Files::., in the description of the command `symbol-file'). `set verbose on' Enables GDB's output of certain informational messages. `set verbose off' Disables GDB's 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 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 seem 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're willing to unflinchingly face the consequences of your own commands, you can disable this "feature": `set confirm off' Disables confirmation requests. `set confirm on' Enables confirmation requests (the default). `show confirm' Displays state of confirmation requests. Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you're running on one of these systems, you can allow GDB to reload the symbols for automatically relinked modules: `set symbol-reloading on' Replace symbol definitions for the corresponding source file when an object file with a particular name is seen again. `set symbol-reloading off' Don't replace symbol definitions when re-encountering object files of the same name. This is the default state; if you're not running on a system that permits automatically relinking modules, you should leave `symbol-reloading' off, since otherwise GDB may discard symbols when linking large programs, that may contain several modules (from different directories or libraries) with the same name. `show symbol-reloading' Show the current `on' or `off' setting. File: gdb.info, Node: Sequences, Next: Emacs, Prev: Controlling GDB, Up: Top Canned Sequences of Commands **************************** Aside from breakpoint commands (*note Break Commands::.), GDB provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files. * Menu: * Define:: User-Defined Commands * Command Files:: Command Files * Output:: Commands for Controlled Output File: gdb.info, Node: Define, Next: Command Files, Prev: Sequences, Up: Sequences 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. `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 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' Give documentation to the user-defined command COMMANDNAME. 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 will print the documentation you have specified. You may use the `document' command again to change the documentation of a command. Redefining the command with `define' does not change the documentation. `help user-defined' List all user-defined commands, with the first line of the documentation (if any) for each. `info user' `info 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. User-defined commands do not take arguments. When they are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command. Commands that would ask for confirmation if used interactively 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: Command Files, Next: Output, Prev: Define, Up: Sequences Command Files ============= A command file for GDB is a file 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. When you start GDB, it automatically executes commands from its "init files". These are files named `.gdbinit'. GDB reads the init file (if any) in your home directory and then the init file (if any) in the current working directory. (The init files are not executed if you use the `-nx' option; *note Mode Options::..) You can also request the execution of a command file with the `source' command: `source FILENAME' Execute the command file FILENAME. The lines in a command file are executed sequentially. They are not printed as they are executed. An error in any command terminates execution of the command file. 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. File: gdb.info, Node: Output, Prev: Command Files, Up: Sequences 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 will be 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 outputting a string with spaces at the beginning or the end, since leading and trailing spaces are otherwise trimmed from all arguments. Thus, 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:: 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::., for more information. `printf STRING, EXPRESSIONS...' Print the values of the EXPRESSIONS under the control of STRING. The EXPRESSIONS are separated by commas and may be either numbers or pointers. Their values are printed as specified by STRING, exactly as if the program were to execute printf (STRING, EXPRESSIONS...); For example, you can print two values in hex like this: printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo The only backslash-escape sequences that you can use in the format string are the simple ones that consist of backslash followed by a letter.