What is the proper way to break on failed asserts in gdb? - c++

Question

I am attempting to capture failed asserts in my program. I’m using a library that makes direct calls to assert(), rather than a custom function or macro, and it is within this library I am currently trying to trace several porting-related bugs. Everything involved has been compiled with debug symbols in g++.
The best solution I have found is breaking at the file:line of the assert, with the condition of the assert expression. This allows stopping on the assert before it fails, but is a horrible solution. It requires special setup for each possibly-failing assert, won’t work from my IDE, and is far too much effort in general.
How can I break on any failed assert using gdb & gcc in such a way that allows examination of the callstack and variables within the scope of the assert call?
It would be even better if the solution allowed me to discard the assert's failure and continue running.

Answer 1

Setting a breakpoint on abort() seems to be the best answer.
break abort in gdb's CLI.

Answer 2

No break is needed on Linux, just type bt on the prompt
abort() causes the SIGABRT signal to be raised in Linux, and GDB already breaks on signals by default. E.g.:
a.c
#include <assert.h>
void g(int i) {
assert(0);
}
void f(int i) {
g(i);
}
int main(void) {
f(1);
}
Then:
gcc -std=c99 -O0 -ggdb3 -o a a.c
gdb -ex run ./a
Then just type bt in the shell:
(gdb) bt
#0 __GI_raise (sig=sig#entry=6) at ../sysdeps/unix/sysv/linux/raise.c:58
#1 0x00007ffff7a483ea in __GI_abort () at abort.c:89
#2 0x00007ffff7a3ebb7 in __assert_fail_base (fmt=<optimized out>, assertion=assertion#entry=0x555555554788 "0", file=file#entry=0x555555554784 "a.c", line=line#entry=4,
function=function#entry=0x55555555478a <__PRETTY_FUNCTION__.1772> "g") at assert.c:92
#3 0x00007ffff7a3ec62 in __GI___assert_fail (assertion=0x555555554788 "0", file=0x555555554784 "a.c", line=4, function=0x55555555478a <__PRETTY_FUNCTION__.1772> "g")
at assert.c:101
#4 0x00005555555546ca in g (i=1) at a.c:4
#5 0x00005555555546df in f (i=1) at a.c:8
#6 0x00005555555546f0 in main () at a.c:12
Which already shows the function values (f (i=1)).
And you can also do as usual:
(gdb) f 4
#4 0x00005555555546ca in g (i=1) at a.c:4
4 assert(0);
(gdb) p i
$1 = 1
The setting that controls if GDB breaks on signals by default or not is: handle all nostop as shown at: How to handle all signals in GDB
Tested in Ubuntu 16.10, gdb 7.11.

Answer 3

If suggested above answers doesn't work for you, you may try to break on __assert_fail function.
break __assert_fail
Name is most probably implementation - dependent, but it's easy to find if you look at definition of assert macro on your platform. This will allow you to break before SIGABRT.

Answer 4

Another option in code:
#include <windows.h>
#include <signal.h>
static void abortHandler(int signalNumber)
{
DebugBreak();
}
int main()
{
signal(SIGABRT, &abortHandler);
}