[Bug debug/107909] New: [powerpc64le, debug] Incorrect call site location due to nop after call insn

[Bug debug/107909] New: [powerpc64le, debug] Incorrect call site location due to nop after call insn

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107909

            Bug ID: 107909
           Summary: [powerpc64le, debug] Incorrect call site location due
                    to nop after call insn
           Product: gcc
           Version: 7.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Consider test-case vla-optimized-out.c:
...
int
__attribute__((noinline,weak)) __attribute__((noclone))
f1 (int i)
{
  char a[i + 1];
  a[0] = 5;
  return a[0];
}

int
main (void)
{
  volatile int j;
  int i = 5;
  asm volatile ("" : "=r" (i) : "0" (i));
  j = f1 (i);
  return 0;
}
...
compiled with -O1 -g.

We generate a nop after the bl insn:
...
        bl f1    # 11   *call_value_nonlocal_aixdi      [length = 8]
        nop
.LVL4:
...
and the label after the nop is a call site location:
...
        .uleb128 0x5     # (DIE (0x67) DW_TAG_GNU_call_site)
        .8byte  .LVL4    # DW_AT_low_pc
        .4byte  0x81     # DW_AT_abstract_origin
...

Consequently we can't actually find the call site:
...
$ gdb -q -batch ./a.out -ex "break f1" -ex run -ex "set debug entry-values 1"
-ex "print sizeof (a)"
Breakpoint 1 at 0x1000065c: file vla-optimized-out.c, line 8.

Breakpoint 1, f1 (i=5) at vla-optimized-out.c:8
8       }
DW_OP_entry_value resolving cannot find DW_TAG_call_site 0x10000690 in main
$1 = <optimized out>
...

If we manually fix this in the .s file, we get a bit further:
...
$ gdb -q -batch ./a.out -ex "break f1" -ex run -ex "set debug entry-values 1"
-ex "print sizeof (a)"
Breakpoint 1 at 0x1000065c: file vla-optimized-out.c, line 8.

Breakpoint 1, f1 (i=5) at vla-optimized-out.c:8
8       }
Cannot find matching parameter at DW_TAG_call_site 0x10000690 at main
$1 = <optimized out>
...

The problem now is that the DW_AT_abstract_origin in the DW_TAG_GNU_call_site
is not properly handled by gdb. 

I reproduced this with gcc 7.5.0, but after looking at the pattern for
call_value_nonlocal_aixdi I think this should be reproducible with trunk.

[Bug target/107909] [powerpc64le, debug] Incorrect call site location due to nop after call insn

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107909

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://gcc.gnu.org/legacy-ml/gcc-patches/2010-08/txt00153.txt for the
description of the call site dwarf.

[Bug target/107909] [powerpc64le, debug] Incorrect call site location due to nop after call insn

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107909

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Hmm, the nop is required by the ABI because the TOC might be different and
replaced with a load during linking ...
I am not 100% sure this is not just a definition of DW_TAG_GNU_call_site for
powerpc64 ABIs really. Since DW_TAG_GNU_call_site is an GNU extension I would
assume we can still define it for PowerPC64 (and powerpc-aix) any way we want
to define it. That is define it to be the instruction after the TOC update.

[Bug target/107909] [powerpc64le, debug] Incorrect call site location due to nop after call insn

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107909

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Oh wait DW_TAG_call_site is now part of dwarf5. maybe the powerpc ABI can
define it that way then ...