[Bug debug/95432] New: inconsistent behaviors at -O2

[Bug debug/95432] New: inconsistent behaviors at -O2

[yangyibiao at hust dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95432

            Bug ID: 95432
           Summary: inconsistent behaviors at -O2
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yangyibiao at hust dot edu.cn
  Target Milestone: ---

Consider test case:
...
$ cat small.c
__attribute__ ((noinline, noclone)) 
int foo (char *c)
{
  asm volatile ("" : : "r" (c) : "memory");
  return 1;
}

int main ()
{
  char tpl1[20] = "/tmp/test.XXX";
  char tpl2[20] = "/tmp/test.XXX";
  int fd1 = foo (tpl1);
  int fd2 = foo (tpl2);
  if (fd1 == -1) {
    return 1;
  }

  return 0;
}
...



When stepping with step, line 13 is not hit by gdb.
...
$ gcc -O2 -g small.c; gdb -q a.out
Reading symbols from a.out...
(gdb) b main
Breakpoint 1 at 0x401020: file small.c, line 10.
(gdb) r
Starting program: /home/yibiao/Debugger/a.out 

Breakpoint 1, main () at small.c:10
10        char tpl1[20] = "/tmp/test.XXX";
(gdb) step
11        char tpl2[20] = "/tmp/test.XXX";
(gdb) 
12        int fd1 = foo (tpl1);
(gdb) 
foo (c=c@entry=0x7fffffffdea0 "/tmp/test.XXX") at small.c:5
5         return 1;
(gdb) 
foo (c=c@entry=0x7fffffffdec0 "/tmp/test.XXX") at small.c:5
5         return 1;
(gdb) 
main () at small.c:14
14        if (fd1 == -1) {
(gdb) 
0x00007ffff7df4023 in __libc_start_main () from /usr/lib/libc.so.6
(gdb) 
Single stepping until exit from function __libc_start_main,
which has no line number information.
[Inferior 1 (process 1852557) exited normally]
...



When stepping with stepi, line 13 is hit by gdb as follow.
...
$ gcc -O2 -g small.c; gdb -q a.out
Reading symbols from a.out...
(gdb) b main
Breakpoint 1 at 0x401020: file small.c, line 10.
(gdb) r
Starting program: /home/yibiao/Debugger/a.out 

Breakpoint 1, main () at small.c:10
10        char tpl1[20] = "/tmp/test.XXX";
(gdb) stepi
0x0000000000401024      10        char tpl1[20] = "/tmp/test.XXX";
(gdb) 
0x000000000040102c      12        int fd1 = foo (tpl1);
(gdb) 
0x000000000040102f      10        char tpl1[20] = "/tmp/test.XXX";
(gdb) 
11        char tpl2[20] = "/tmp/test.XXX";
(gdb) 
12        int fd1 = foo (tpl1);
(gdb) 
0x0000000000401043      11        char tpl2[20] = "/tmp/test.XXX";
(gdb) 
0x0000000000401048      12        int fd1 = foo (tpl1);
(gdb) 
foo (c=c@entry=0x7fffffffdea0 "/tmp/test.XXX") at small.c:5
5         return 1;
(gdb) 
0x0000000000401165      5         return 1;
(gdb) 
0x000000000040104d in main () at small.c:13
13        int fd2 = foo (tpl2);
(gdb) 
...


$ gcc --version
gcc (GCC) 10.0.1 20200419 (experimental)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gdb --version
GNU gdb (GDB) 10.0.50.20200517-git
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

[Bug debug/95432] inconsistent behaviors at -O2

[yangyibiao at hust dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95432

Yibiao Yang <yangyibiao at hust dot edu.cn> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yangyibiao at hust dot edu.cn

--- Comment #1 from Yibiao Yang <yangyibiao at hust dot edu.cn> ---
Created attachment 48639
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48639&action=edit
a.out

[Bug debug/95432] inconsistent behaviors at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95432

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Assembly:
        .loc 1 12 3 is_stmt 1 view .LVU12
        .loc 1 10 8 is_stmt 0 view .LVU13
        movaps  %xmm0, (%rsp)
        .loc 1 11 8 view .LVU14
        movaps  %xmm0, 32(%rsp)
        .loc 1 12 13 view .LVU15
        call    foo
.LVL1:
        .loc 1 13 13 view .LVU16
        leaq    32(%rsp), %rdi
        .loc 1 12 13 view .LVU17
        movl    %eax, %edx
.LVL2:
        .loc 1 13 3 is_stmt 1 view .LVU18
        .loc 1 13 13 is_stmt 0 view .LVU19
        call    foo
.LVL3:
        .loc 1 14 3 is_stmt 1 view .LVU20
        .loc 1 14 6 is_stmt 0 view .LVU21

Looks correct to me, both call foo have the correct line on them.  I think this
is another GDB issue, most likely how dwarf3 and is_stmt is handled just like
95431 even.

[Bug debug/95432] inconsistent behaviors at -O2

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95432

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Assembly:
>         .loc 1 12 3 is_stmt 1 view .LVU12
>         .loc 1 10 8 is_stmt 0 view .LVU13
>         movaps  %xmm0, (%rsp)
>         .loc 1 11 8 view .LVU14
>         movaps  %xmm0, 32(%rsp)
>         .loc 1 12 13 view .LVU15
>         call    foo
> .LVL1:
>         .loc 1 13 13 view .LVU16
>         leaq    32(%rsp), %rdi
>         .loc 1 12 13 view .LVU17
>         movl    %eax, %edx
> .LVL2:
>         .loc 1 13 3 is_stmt 1 view .LVU18
>         .loc 1 13 13 is_stmt 0 view .LVU19
>         call    foo
> .LVL3:
>         .loc 1 14 3 is_stmt 1 view .LVU20
>         .loc 1 14 6 is_stmt 0 view .LVU21
> 
> Looks correct to me, both call foo have the correct line on them.  I think
> this is another GDB issue, most likely how dwarf3 and is_stmt is handled
> just like 95431 even.

Ack, this is gdb PR breakpoints/26063 (
https://sourceware.org/bugzilla/show_bug.cgi?id=26063 ).

Fixed by
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ebde6f2ddc987e7e2d5a218ee8cf0126ec189424
.

[Bug debug/95432] inconsistent behaviors at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95432

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |MOVED

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Closing as moved as it was reported and fixed in gdb already.