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GDB

Tips

TL;DR:
    s(tep) - Execute the current line, stop at the first possible occasion.
    n(ext) - Continue execution until the next line in the current function is reached or it returns.
    finish - Execute until selected stack frame returns.    
    stepi - Execute one machine instruction, then stop and return to the debugger.   
    l(ist) - Displays 11 lines around the current line or continue the previous listing.
    b(reak) - Set a breakpoint (depending on the argument provided).
    p(rint) - Evaluate the expression in the current context and print its value. There’s also pp to display using pprint instead.
    r(eturn) - Continue execution until the current function returns.
    q(uit) - Quit the debugger.
    info - info about thread, stack, frame, args, locals, variables, breakpoints
Full backtrace

thread apply all bt or bt full

GDB CFLAGS

CFLAGS='-O0 -ggdb3'

Breakpoints:
g_assert_not_reached();
G_BREAKPOINT();
#define G_BRAKPOINT() __asm__ __volatile__ ("int $03");       // https://github.com/GNOME/glib/blob/2.68.1/glib/gbacktrace.h#L46
__builtin_trap();     // https://clang.llvm.org/docs/LanguageExtensions.html#builtin-trap

https://github.com/chromium/chromium/blob/d9d917c05c2a781d58ec15e3182e1dbd24c6530c/base/debug/debugger_posix.cc

or

break do_quert
break fields.c:172
Printfs:
__builtin_printf
__builtin_dump_struct      // https://clang.llvm.org/docs/LanguageExtensions.html#builtin-dump-struct
Args
gdb --args gst-launch-1.0 videotestsrc num-buffers=200 pattern=1 ! video/x-raw, framerate=25/1 ! autovideoconvert  !  fakesink
Batch
gdb -batch -n -ex 'set pagination off' -ex run -ex bt -ex 'bt full' -ex 'thread apply all bt full' --args hello
Logging
(gdb) set logging on
(gdb) set logging file my_god_object.log
(gdb) show logging

https://stackoverflow.com/questions/5941158/gdb-print-to-file-instead-of-stdout

Function
(gdb) define fn
> finish
> next
> end

https://stackoverflow.com/questions/1262639/multiple-commands-in-gdb-separated-by-some-sort-of-delimiter

Script
$ cat gdb.script
file /usr/bin/gst-launch-1.0
set args filesrc location= MPEG2_1080i_sample.mkv ! matroskademux ! fakesink
break file.c:59 if j == 1615
commands
silent
printf "GDB DEBUG i == %d\n", i
cont
end
run
$ gdb -x gdb.script

set debuginfod enabled on is useful

Reload shares
info shared
shared .
# set auto-solib-add off # to disable outload
Set source code directories
function (void) at  file.c:66
file.c: No such file or directory.
(gdb) dir /tmp/pr/PK_4.4.6211.0/source/modules/stub
Source directories searched: /tmp/pr/PK_4.4.6211.0/source/modules/stub:$cdir:$cwd
Install Debug Symbol Packages

Ubuntu:

apt install debian-goodies
find-dbgsym-packages [core_path|running_pid|binary_path]

from https://wiki.ubuntu.com/Debug%20Symbol%20Packages

Centos:

dnf debuginfo-install xxxx
Inspect memory mappings
(gdb) catch syscall exit exit_group
(gdb) run
(gdb) info proc map

from https://fasterthanli.me/articles/whats-in-the-box

Print instead of stopping inside a bp
break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end

from https://stackoverflow.com/questions/6517423/how-to-do-an-specific-action-when-a-certain-breakpoint-is-hit-in-gdb

Override system symbol
// File getenv.c
// To compile: gcc -shared -Wall -fPIC -o getenv.so getenv.c -ldl
// To use: export LD_PRELOAD="./getenv.so", then run any program you want
// See http://www.catonmat.net/blog/simple-ld-preload-tutorial-part-2/
#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>
// This function will take the place of the original getenv() in libc
char *getenv(const char *name) {
  printf("Calling getenv(\"%s\")\n", name);
  char *(*original_getenv)(const char*);
  original_getenv = dlsym(RTLD_NEXT, "getenv");
  return (*original_getenv)(name);
}

From https://github.com/zdobersek/libpine or https://frida.re (similar to https://blog.jhm.dev/posts/papers-please/)

coredumpctl

Ubuntu package systemd-coredump

break _start
run
record
reverse-step reverse-continue reverse-next reverse-finish

vs rr from https://www.sourceware.org/gdb/wiki/ProcessRecord/Tutorial

gdbinit

https://github.com/rubenrua/dotfiles/blob/master/.gdbinit

Links