[Bug debug/49382] New: -O2 -g: DW_AT_location at the very first PC is already modified

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49382

           Summary: -O2 -g: DW_AT_location at the very first PC is already
                    modified
           Product: gcc
           Version: 4.5.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: jan.kratoch...@redhat.com
                CC: ja...@gcc.gnu.org
            Target: x86_64-unknown-linux-gnu


int i;
void __attribute__((noinline, noclone))
clobber (int x)
{
  i = x;
}
void __attribute__((noinline, noclone))
func (int x)
{
  clobber (x++);
  i = 1;    /* line 11 */
}
int main (void) { func (5); return 0; }

gcc -c -Wall -g -O2

PASS gcc (GCC) 4.4.7 20110611 (prerelease)
FAIL gcc (GCC) 4.5.4 20110612 (prerelease)
FAIL gcc (GCC) 4.6.1 20110612 (prerelease)
FAIL gcc (GCC) 4.7.0 20110612 (experimental)

 <1><5c>: Abbrev Number: 2 (DW_TAG_subprogram)
    <5e>   DW_AT_name        : (indirect string, offset: 0x3d): func
    <65>   DW_AT_low_pc      : 0x10
    <6d>   DW_AT_high_pc     : 0x20
 <2><7c>: Abbrev Number: 5 (DW_TAG_formal_parameter)
    <7d>   DW_AT_name        : x
    <85>   DW_AT_location    : 0x0      (location list)

FAIL:
Offset Begin          End              Expression
000000 00000000000010 0000000000000014 (DW_OP_breg5 (rdi): 1;
DW_OP_stack_value)
000000 <End of list>
+
0000000000000010 <func>:
void __attribute__((noinline, noclone))
func (int x)
{
  clobber (x++);
  10:   e8 00 00 00 00          callq  15 <func+0x5>
                        11: R_X86_64_PC32       clobber-0x4

PASS:
Offset Begin          End              Expression
000000 00000000000010 0000000000000015 (DW_OP_reg5 (rdi))
000000 <End of list>

One should see X and not X + 1.
(gdb) break *func
Breakpoint 1 at 0x400480: file /home/jkratoch/t/entrypc.c, line 10.
(gdb) run
FAIL:
Breakpoint 1, func (x=6) at /home/jkratoch/t/entrypc.c:10
PASS:
Breakpoint 1, func (x=5) at /home/jkratoch/t/entrypc.c:10

Also at the very first PC one needs to know the register to match it
DW_TAG_GNU_call_site_parameter->DW_AT_location in the caller.