gdb(1) GNU Tools gdb(1) NNAAMMEE gdb - The GNU Debugger SSYYNNOOPPSSIISS ggddbb [--hheellpp] [--nnxx] [--qq] [--bbaattcchh] [--ccdd==_d_i_r] [--ff] [--bb _b_p_s] [--ttttyy==_d_e_v] [--ss _s_y_m_f_i_l_e] [--ee _p_r_o_g] [--ssee _p_r_o_g] [--cc _c_o_r_e] [--xx _c_m_d_s] [--dd _d_i_r] [_p_r_o_g[_c_o_r_e|_p_r_o_c_I_D_]_] DDEESSCCRRIIPPTTIIOONN The purpose of a debugger such as GDB is to allow you to see what is going on ``inside'' another program while it executes--or what another program was doing at the moment it crashed. GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: +o Start your program, specifying anything that might affect its behavior. +o Make your program stop on specified conditions. +o Examine what has happened, when your program has stopped. +o Change things in your program, so you can experi- ment with correcting the effects of one bug and go on to learn about another. You can use GDB to debug programs written in C, C++, and Modula-2. Fortran support will be added when a GNU For- tran compiler is ready. GDB is invoked with the shell command ggddbb. Once started, it reads commands from the terminal until you tell it to exit with the GDB command qquuiitt. You can get online help from ggddbb itself by using the command hheellpp. You can run ggddbb with no arguments or options; but the most usual way to start GDB is with one argument or two, speci- fying an executable program as the argument: gdb program You can also start with both an executable program and a core file specified: gdb program core You can, instead, specify a process ID as a second argu- ment, if you want to debug a running process: gdb program 1234 would attach GDB to process 11223344 (unless you also have a file named `11223344'; GDB does check for a core file first). Here are some of the most frequently needed GDB commands: bbrreeaakk [_f_i_l_e::]_f_u_n_c_t_i_o_n Set a breakpoint at _f_u_n_c_t_i_o_n (in _f_i_l_e). rruunn [_a_r_g_l_i_s_t] Start your program (with _a_r_g_l_i_s_t, if specified). bbtt Backtrace: display the program stack. pprriinntt _e_x_p_r Display the value of an expression. cc Continue running your program (after stopping, e.g. at a breakpoint). nneexxtt Execute next program line (after stopping); step _o_v_e_r any function calls in the line. sstteepp Execute next program line (after stopping); step _i_n_t_o any function calls in the line. hheellpp [_n_a_m_e] Show information about GDB command _n_a_m_e, or general information about using GDB. qquuiitt Exit from GDB. For full details on GDB, see _U_s_i_n_g _G_D_B_: _A _G_u_i_d_e _t_o _t_h_e _G_N_U _S_o_u_r_c_e_-_L_e_v_e_l _D_e_b_u_g_g_e_r, by Richard M. Stallman and Roland H. Pesch. The same text is available online as the ggddbb entry in the iinnffoo program. OOPPTTIIOONNSS Any arguments other than options specify an executable file and core file (or process ID); that is, the first argument encountered with no associated option flag is equivalent to a `--ssee' option, and the second, if any, is equivalent to a `--cc' option if it's the name of a file. Many options have both long and short forms; both are shown here. The long forms are also recognized if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with `++' rather than `--', though we illustrate the more usual convention.) All the options and command line arguments you give are processed in sequential order. The order makes a differ- ence when the `--xx' option is used. --hheellpp --hh List all options, with brief explanations. --ssyymmbboollss==_f_i_l_e --ss _f_i_l_e Read symbol table from file _f_i_l_e. --wwrriittee Enable writing into executable and core files. --eexxeecc==_f_i_l_e --ee _f_i_l_e Use file _f_i_l_e as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. --ssee==_f_i_l_e Read symbol table from file _f_i_l_e and use it as the executable file. --ccoorree==_f_i_l_e --cc _f_i_l_e Use file _f_i_l_e as a core dump to examine. --ccoommmmaanndd==_f_i_l_e --xx _f_i_l_e Execute GDB commands from file _f_i_l_e. --ddiirreeccttoorryy==_d_i_r_e_c_t_o_r_y --dd _d_i_r_e_c_t_o_r_y Add _d_i_r_e_c_t_o_r_y to the path to search for source files. --nnxx --nn Do not execute commands from any `..ggddbbiinniitt' ini- tialization files. Normally, the commands in these files are executed after all the command options and arguments have been processed. --qquuiieett --qq ``Quiet''. Do not print the introductory and copy- right messages. These messages are also suppressed in batch mode. --bbaattcchh Run in batch mode. Exit with status 00 after pro- cessing all the command files specified with `--xx' (and `..ggddbbiinniitt', if not inhibited). Exit with nonzero status if an error occurs in executing the GDB commands in the command files. Batch mode may be useful for running GDB as a fil- ter, for example to download and run a program on another computer; in order to make this more use- ful, the message Program exited normally. (which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode. --ccdd==_d_i_r_e_c_t_o_r_y Run GDB using _d_i_r_e_c_t_o_r_y as its working directory, instead of the current directory. --ffuullllnnaammee --ff Emacs sets this option when it runs GDB as a sub- process. It tells GDB to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time the program stops). This recog- nizable format looks like two ` 3322' characters, followed by the file name, line number and charac- ter position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two ` 3322' characters as a signal to display the source code for the frame. --bb _b_p_s Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging. --ttttyy==_d_e_v_i_c_e Run using _d_e_v_i_c_e for your program's standard input and output. SSEEEE AALLSSOO `ggddbb' entry in iinnffoo; _U_s_i_n_g _G_D_B_: _A _G_u_i_d_e _t_o _t_h_e _G_N_U _S_o_u_r_c_e_- _L_e_v_e_l _D_e_b_u_g_g_e_r, Richard M. Stallman and Roland H. Pesch, July 1991. CCOOPPYYIINNGG Copyright (c) 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 ver- sions of this manual under the conditions for verbatim copying, 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 con- ditions for modified versions, except that this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English. GNU Tools 4nov1991 gdb(1)