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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug tdep/30019] New: [gdb/tdep, i386] frame address at first insn
 in main is zero
Date: Wed, 18 Jan 2023 10:39:57 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gdb
X-Bugzilla-Component: tdep
X-Bugzilla-Version: HEAD
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: vries at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D30019

            Bug ID: 30019
           Summary: [gdb/tdep, i386] frame address at first insn in main
                    is zero
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Test-case:
...
$ cat test.c
void
foo (const char *s)
{
}

int
main (void)
{
  foo ("foo");
  return 0;
}
...

Compile for x86_64/-m32:
...
$ gcc test.c -m32
...

Note how we have "frame at 0x0" for the two first insns:
...
$ gdb -q -batch a.out \
    -ex "set trace-commands on" \
    -ex "maint set dwarf unwinders off" \
    -ex "b *main" \
    -ex "display /i \$pc" \
    -ex "display /x \$esp" \
    -ex "display /x \$ebp" \
    -ex run \
    -ex "info frame" \
    -ex stepi \
    -ex "info frame" \
    -ex stepi \
    -ex "info frame"
+maint set dwarf unwinders off
+b *main
Breakpoint 1 at 0x80483fc
+display /i $pc
+display /x $esp
+display /x $ebp
+run

Breakpoint 1, 0x080483fc in main ()
1: x/i $pc
=3D> 0x80483fc <main>:    push   %ebp
2: /x $esp =3D 0xffffce0c
3: /x $ebp =3D 0x0
+info frame
Stack level 0, frame at 0x0:
 eip =3D 0x80483fc in main; saved eip =3D <not saved>
 Outermost frame: outermost
 Arglist at unknown address.
 Locals at unknown address, Previous frame's sp in esp
+stepi
0x080483fd in main ()
1: x/i $pc
=3D> 0x80483fd <main+1>:  mov    %esp,%ebp
2: /x $esp =3D 0xffffce08
3: /x $ebp =3D 0x0
+info frame
Stack level 0, frame at 0x0:
 eip =3D 0x80483fd in main; saved eip =3D <not saved>
 Outermost frame: outermost
 Arglist at unknown address.
 Locals at unknown address, Previous frame's sp in esp
+stepi
0x080483ff in main ()
1: x/i $pc
=3D> 0x80483ff <main+3>:  push   $0x80484a0
2: /x $esp =3D 0xffffce08
3: /x $ebp =3D 0xffffce08
+info frame
Stack level 0, frame at 0xffffce10:
 eip =3D 0x80483ff in main; saved eip =3D 0xf7dceaa6
 Arglist at 0xffffce08, args:=20
 Locals at 0xffffce08, Previous frame's sp is 0xffffce10
 Saved registers:
  ebp at 0xffffce08, eip at 0xffffce0c
...

--=20
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