Most tricky/useful commands for gdb debugger

Question

Can you post your most tricky and useful commands while you run a debugger like gdb or dbx.

I found this documentation is good. https://scc.ustc.edu.cn/zlsc/sugon/intel/debugger/cl/index.htm#commandref/gdb_mode/cmd_condition.htm — Rick, Mar 31 '20 at 04:50

score 140 · Accepted Answer · edited May 01 '13 at 16:43

140

backtrace full: Complete backtrace with local variables
up, down, frame: Move through frames
watch: Suspend the process when a certain condition is met
set print pretty on: Prints out prettily formatted C source code
set logging on: Log debugging session to show to others for support
set print array on: Pretty array printing
finish: Continue till end of function
enable and disable: Enable/disable breakpoints
tbreak: Break once, and then remove the breakpoint
where: Line number currently being executed
info locals: View all local variables
info args: View all function arguments
list: view source
rbreak: break on function matching regular expression

edited May 01 '13 at 16:43

grokus

18,046
9
29
35

answered Sep 24 '09 at 12:20

artagnon

3,609
3
23
26

7

`info locals` -- View all local variables; list -- view source; rbreak -- break on function matching regular expression. – Paul Biggar Sep 27 '09 at 10:53
source /path/to/macro/file And all of my nifty macros are there to help me debug in seconds. – Sudhanshu Jan 13 '10 at 05:19
1

`set print object on` for polymorphic elements and `set print elements 0` are two commands I use very often. Pretty useful. – Kiril Kirov Jul 17 '14 at 09:04
1

Also, `t a a bt` (meaning `thread apply all backtrace`). Could be used with (almost) all other commands. Especially useful with `bt full`. – Kiril Kirov Jul 17 '14 at 09:10
Very useful information received in this thread , thank you all. – user28186 Jun 14 '22 at 22:26

score 103 · Answer 2 · answered Sep 27 '09 at 10:30

103

Start gdb with a textual user interface

gdb -tui

answered Sep 27 '09 at 10:30

Amro

123,847
25
243
454

22

I cannot believe this feature escaped me for all these years. Thank you, thank you, thank you! – DevSolar Dec 15 '09 at 13:55
Thanks You saved lot of my time.. Wonderfull.... – sujin Jun 20 '14 at 12:53
2

And another: RET – SullX Oct 28 '15 at 22:38
1

or use [cgdb](https://cgdb.github.io/) – Patryk Jun 03 '16 at 08:12
very nice features. Missed this so far... – PraveenMax May 04 '17 at 10:43

score 45 · Answer 3 · edited Aug 29 '14 at 01:18

Starting in gdb 7.0, there is reversible debugging, so your new favourite commands are:

* reverse-continue ('rc') -- Continue program being debugged but run it in reverse
* reverse-finish -- Execute backward until just before the selected stack frame is called
* reverse-next ('rn') -- Step program backward, proceeding through subroutine calls.
* reverse-nexti ('rni') -- Step backward one instruction, but proceed through called subroutines.
* reverse-step ('rs') -- Step program backward until it reaches the beginning of a previous source line
* reverse-stepi -- Step backward exactly one instruction
* set exec-direction (forward/reverse) -- Set direction of execution.

score 21 · Answer 4 · answered Oct 09 '09 at 07:53

21

Instead of launching GDB with "-tui" param you can also switch to text mode after a while using by typing "wh".

answered Oct 09 '09 at 07:53

martin

1,106
2
9
11

3

Ctrl-a a to switch back to 'normal' command line view ! – Kevin Feb 16 '11 at 21:26
2

"-' can be used instaed of 'wh'. shorter the better..:) – raj_gt1 May 05 '15 at 13:55
6

`Ctrl-a a`? Is it a joke? Looks more like `tmux`/`screen` command. And doesn't work for me. It must be one of [as](http://stackoverflow.com/questions/8409540/how-to-close-layout-src-windows-in-gdb) per [docs](https://sourceware.org/gdb/onlinedocs/gdb/TUI-Keys.html#TUI-Keys): `C-x C-a`, `C-x a`, `C-x A`. – x-yuri Oct 08 '15 at 21:49
It's actually `C-x a`. You can also switch views with `C-x 1` and `C-x 2` when in tui mode to see assembly as well (if need be). – Sam Oct 16 '17 at 13:06

score 16 · Answer 5 · edited Jun 01 '10 at 00:04

16

thread apply all bt or thread apply all print $pc: For finding out quickly what all threads are doing.

edited Jun 01 '10 at 00:04

Earlz

62,085
98
303
499

answered Sep 27 '09 at 09:50

Olof

533
3
12

That was the command I was looking for a long-long time! It is really nasty to check all 30 threads one by one! – tothphu Apr 28 '13 at 23:57
Very useful reply – user28186 Jun 14 '22 at 22:27

score 6 · Answer 6 · answered Sep 24 '09 at 12:06

6

For example the macros defined in stl-views.gdb

answered Sep 24 '09 at 12:06

grigy

6,696
12
49
76

score 6 · Answer 7 · answered Oct 10 '09 at 08:28

6

scripting gdb is a good trick, other than that I like set scheduler locking on / off to prevent the running of other threads when you are stepping in one.

answered Oct 10 '09 at 08:28

Ben

7,372
8
38
46

1

How do you set scheduler locking? – deft_code Jun 01 '10 at 00:09
4

`set scheduler-locking on` inside gdb – Ben Jun 01 '10 at 07:54
how do you make this the default? I tried it .gdbinit but gdb prints /home/omry/.gdbinit:1: Error in sourced command file: Target 'None' cannot support this command. – Omry Yadan Nov 26 '14 at 01:44

score 6 · Answer 8 · edited May 05 '14 at 10:22

6

Using the -command=<file with gdb commands> option while firing up gdb. Same as -x <command file>. This command file can contain gdb commands like breakpoints, options, etc. Useful in case a particular executable needs to be put through successive debug runs using gdb.

edited May 05 '14 at 10:22

toasted_flakes

2,502
1
23
38

answered Dec 15 '09 at 13:47

raghava

236
4
12

You can also use the `-iex` option to add individual commands on the gdb command line. – doug65536 Apr 30 '17 at 10:21

score 4 · Answer 9 · answered Oct 13 '09 at 16:42

Using .gdbinit (start up file where you can write macros and call from gdb). Place .gdbinit in your home directory so that it is picked up every time gdb is loaded
info threads to list all the active threads, and f(#) -> # thread number you want to switch to
sometime i use gdb to convert from hex to decimal or binary, its very handy instead of opening up a calculator
- p/d 0x10 -> gives decimal equivalent of 0x10
- p/t 0x10 -> binary equivalent of 0x10
- p/x 256 -> hex equivalent of 256

Rose Perrone · Answer 10 · 2011-12-02T02:50:08.467

4

Instead of starting gdb with the option -tui to see a child process that contains a screen that highlights where the executing line of code is in your program, jump in and out of this feature with C-x o and C-x a. This is useful if you're using the feature and what to temporarily not use it so you can use the up-arrow to get a previous command.

edited Dec 02 '11 at 02:50

answered Dec 02 '11 at 02:44

Rose Perrone

61,572
58
208
243

3

you can change the focus to the command window using `focus cmd` so that the up/down arrows work. You switch back using `focus src`. – Nathan Fellman Aug 11 '14 at 11:14

score 3 · Answer 11 · answered Jan 20 '10 at 16:10

3

This can be useful, I am sure it could be improved though, help welcome:

define mallocinfo
  set $__f = fopen("/dev/tty", "w")
  call malloc_info(0, $__f)
  call fclose($__f)

answered Jan 20 '10 at 16:10

elmarco

31,633
21
64
68

score 2 · Answer 12 · answered Nov 29 '10 at 11:00

2

To debug STL, add content to .gdbinit, follow these instructions:

http://www.yolinux.com/TUTORIALS/GDB-Commands.html#STLDEREF

answered Nov 29 '10 at 11:00

Bob Yoplait

2,421
1
23
35

Most tricky/useful commands for gdb debugger

12 Answers12