[Bug gdb/27613] New: finish from sigreturn trampoline sometimes doesn't stop

[Bug gdb/27613] New: finish from sigreturn trampoline sometimes doesn't stop

[ismith at undo dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=27613

            Bug ID: 27613
           Summary: finish from sigreturn trampoline sometimes doesn't
                    stop
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: ismith at undo dot io
  Target Milestone: ---

It seems that if a signal is delivered when the program is about to execute a
'ret' instruction in an assembly function, using 'finish' in the signal handler
goes to the trampoline (fine) but 'finish' from there doesn't stop until the
next breakpoint (or end of program).

Test files:

asm.S

 .global asm_func
asm_func:
    mov $0xdeadbeefdeadbeef, %rdi
    ret



test.c

#include <assert.h>
#include <inttypes.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>

static void
sig_handler(int sig)
{
    (void)sig;
}

void asm_func(void);

int
main(void)
{
    struct sigaction act;
    act.sa_sigaction = (void *)sig_handler;
    act.sa_flags = 0;
    sigemptyset(&act.sa_mask);
    int r = sigaction(SIGVTALRM, &act, NULL);
    assert(r == 0);

    asm_func();
    return 0;
}

Compiled with:
gcc (Ubuntu 10.1.0-2ubuntu1~18.04) 10.1.0

gcc -g asm.S test.c -o test

$ gdb -q ./test
Reading symbols from ./test...done.
(gdb) b asm_func
Breakpoint 1 at 0x7d8: file asm.S, line 3.
(gdb) r
Starting program: /home/ismith/work/overnight_failures/gdb_bug/test 

Breakpoint 1, asm_func () at asm.S:3
3           mov $0xdeadbeefdeadbeef, %rdi
(gdb) si
asm_func () at asm.S:4
4           ret
(gdb) b sig_handler
Breakpoint 2 at 0x55555555472c: file test.c, line 13.
(gdb) signal SIGVTALRM
Continuing with signal SIGVTALRM.

Breakpoint 2, sig_handler (sig=26) at test.c:13
13      }
(gdb) fin
Run till exit from #0  sig_handler (sig=26) at test.c:13
<signal handler called>
(gdb) 
Run till exit from #0  <signal handler called>
[Inferior 1 (process 29158) exited normally]
(gdb) 


I think the second finish should have taken me to the ret instruction at the
end of asm_func.

The test originally had "proper" signals in it -- so this isn't a bug in the
way 'signal' delivers signals.

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[Bug gdb/27613] finish from sigreturn trampoline sometimes doesn't stop

[ismith at undo dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=27613

--- Comment #1 from Isa Smith <ismith at undo dot io> ---
The transcript there is from gdb 8.1 but I tested this on
7b9f985957798ba4dacc454f22c9e426c6897cb8 from master and saw the same
behaviour.

Other info:
This GDB was configured as "x86_64-pc-linux-gnu".

$ uname -a
Linux brunost-thinkpad 5.4.0-67-generic #75~18.04.1-Ubuntu SMP Tue Feb 23
19:17:50 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

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