How to set a breakpoint in GDB where the function returns?

Question

I have a C++ function which has many return statements at various places. How to set a breakpoint at the return statement where the function actually returns ?

And

Answer 1

rr reverse debugging

Similar to GDB record mentioned at https://stackoverflow.com/a/3649698/895245 , but much more functional as of GDB 7.11 vs rr 4.1.0 in Ubuntu 16.04.

Notably, it deals with AVX correctly:

• gdb reverse debugging fails with "Process record does not support instruction 0xf0d at address"
• "target record-full" in gdb makes "n" command fail on printf with "Process record does not support instruction 0xc5 at address 0x7ffff7dee6e7"?

which prevents it from working with the default standard library calls.

Install Ubuntu 16.04:

sudo apt-get install rr linux-tools-common linux-tools-generic linux-cloud-tools-generic
sudo cpupower frequency-set -g performance

But also consider compiling from source to get the latest updates, it was not hard.

Test program:

int where_return(int i) {
    if (i)
        return 1;
    else
        return 0;
}

int main(void) {
    where_return(0);
    where_return(1);
}

compile and run:

gcc -O0 -ggdb3 -o reverse.out -std=c89 -Wextra reverse.c
rr record ./reverse.out
rr replay

Now you are left inside a GDB session, and you can properly reverse debug:

(rr) break main
Breakpoint 1 at 0x56057c458619: file a.c, line 9.
(rr) continue
Continuing.

Breakpoint 1, main () at a.c:9
9           where_return(0);
(rr) step
where_return (i=0) at a.c:2
2           if (i)
(rr) finish
Run till exit from #0  where_return (i=0) at a.c:2
main () at a.c:10
10          where_return(1);
Value returned is $1 = 0
(rr) reverse-step
where_return (i=0) at a.c:6
6       }
(rr) reverse-step
5               return 0;

We are now on the correct return line.