optimization/3323: gcc -O2 -fomit-frame-pointer -fPIC references unitialized %ebp on x86

[mitr at volny dot cz]

>Number:         3323
>Category:       optimization
>Synopsis:       gcc -O2 -fomit-frame-pointer -fPIC references unitialized %ebp on x86
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 21 03:36:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Miloslav Trmac
>Release:        3.0
>Organization:
NA
>Environment:
System: Linux linux.localdomain 2.4.2-2 #1 Sun Apr 8 19:37:14 EDT 2001 i586 unknown
Architecture: i586

host: i586-pc-linux-gnu
build: i586-pc-linux-gnu
target: i586-pc-linux-gnu
configured with: ../gcc-3.0/configure 
>Description:
The enclosed file, when compiled with -g -O2 -fomit-frame-pointer -fPIC,
results in fillgrent starting with
        pushl   %ebp
        leal    8(%ebp), %eax
It seems the compiler can't "decide" whether it uses %ebp as frame pointer or
as a general register. Omitting either -fomit-frame-pointer or -fPIC
seems to make the problem go away.

The called function do_field () must be static, so that fillgrent doesn't
need %ebx pointing to the GOT. The example has been simplified as much as
possible, so don't try to figure what it should actually do :-)
Nevertheless I'm sure at the function calls should be generated correctly,
AFAICS the code is strictly conforming C.
	
>How-To-Repeat:
------------------------File grp.i
struct group
{
  const char *gr_name;
  int gr_gid;
  const char *src;
  const char **gr_mem;
};
static void
do_field (const char **_FIELD, void **_MEM)
{
}
void
fillgrent (struct group *_GROUP, void *_MEM)
{
  const char *tmp;
  const char **cm;
  do_field (&_GROUP->gr_name, &_MEM);
  cm = _MEM;
  tmp = _GROUP->src;
  _GROUP->gr_mem = cm;
  for (;;)
    {
      *cm = tmp;
      do_field (cm, &_MEM);
    }
}
-----------------------Result of gcc -g -O2 -fomit-frame-pointer -fPIC grp.i -S
	.file	"grp.i"
	.stabs	"/home/mirek/",100,0,0,.Ltext0
	.stabs	"grp.i",100,0,0,.Ltext0
	.text
.Ltext0:
	.stabs	"gcc2_compiled.",60,0,0,0
	.stabs	"int:t(0,1)=r(0,1);-2147483648;2147483647;",128,0,0,0
	.stabs	"char:t(0,2)=r(0,2);0;127;",128,0,0,0
	.stabs	"long int:t(0,3)=r(0,3);-2147483648;2147483647;",128,0,0,0
	.stabs	"unsigned int:t(0,4)=r(0,4);0000000000000;0037777777777;",128,0,0,0
	.stabs	"long unsigned int:t(0,5)=r(0,5);0000000000000;0037777777777;",128,0,0,0
	.stabs	"long long int:t(0,6)=@s64;r(0,6);01000000000000000000000;0777777777777777777777;",128,0,0,0
	.stabs	"long long unsigned int:t(0,7)=@s64;r(0,7);0000000000000;01777777777777777777777;",128,0,0,0
	.stabs	"short int:t(0,8)=@s16;r(0,8);-32768;32767;",128,0,0,0
	.stabs	"short unsigned int:t(0,9)=@s16;r(0,9);0;65535;",128,0,0,0
	.stabs	"signed char:t(0,10)=@s8;r(0,10);-128;127;",128,0,0,0
	.stabs	"unsigned char:t(0,11)=@s8;r(0,11);0;255;",128,0,0,0
	.stabs	"float:t(0,12)=r(0,1);4;0;",128,0,0,0
	.stabs	"double:t(0,13)=r(0,1);8;0;",128,0,0,0
	.stabs	"long double:t(0,14)=r(0,1);12;0;",128,0,0,0
	.stabs	"complex int:t(0,15)=s8real:(0,1),0,32;imag:(0,1),32,32;;",128,0,0,0
	.stabs	"complex float:t(0,16)=r(0,16);8;0;",128,0,0,0
	.stabs	"complex double:t(0,17)=r(0,17);16;0;",128,0,0,0
	.stabs	"complex long double:t(0,18)=r(0,18);24;0;",128,0,0,0
	.stabs	"__builtin_va_list:t(0,19)=*(0,20)=(0,20)",128,0,0,0
	.stabs	"_Bool:t(0,21)=@s8;-16;",128,0,0,0
	.stabs	"group:T(0,22)=s16gr_name:(0,23)=*(0,2),0,32;gr_gid:(0,1),32,32;src:(0,23),64,32;gr_mem:(0,24)=*(0,23),96,32;;",128,0,0,0
	.align 16
	.stabs	"do_field:f(0,20)",36,0,10,do_field
	.stabs	"_FIELD:p(0,24)",160,0,9,4
	.stabs	"_MEM:p(0,25)=*(0,26)=*(0,20)",160,0,9,8
	.type	do_field,@function
do_field:
	.stabn 68,0,10,.LM1-do_field
.LM1:
	.stabn 68,0,11,.LM2-do_field
.LM2:
	ret
.Lfe1:
	.size	do_field,.Lfe1-do_field
.Lscope0:
	.stabs	"",36,0,0,.Lscope0-do_field
	.align 16
	.stabs	"fillgrent:F(0,20)",36,0,14,fillgrent
	.stabs	"_GROUP:p(0,27)=*(0,22)",160,0,13,4
	.stabs	"_MEM:p(0,26)",160,0,13,8
.globl fillgrent
	.type	fillgrent,@function
fillgrent:
	.stabn 68,0,14,.LM3-fillgrent
.LM3:
.LBB2:
	pushl	%ebp
	.stabn 68,0,17,.LM4-fillgrent
.LM4:
	leal	8(%ebp), %eax
	.stabn 68,0,14,.LM5-fillgrent
.LM5:
	pushl	%edi
	pushl	%esi
	movl	4(%ebp), %esi
	movl	8(%ebp), %edi
	.stabn 68,0,17,.LM6-fillgrent
.LM6:
	pushl	%edx
	pushl	%edx
	pushl	%eax
	pushl	%esi
	call	do_field
	addl	$16, %esp
	.stabn 68,0,19,.LM7-fillgrent
.LM7:
	movl	8(%esi), %ebp
	.stabn 68,0,20,.LM8-fillgrent
.LM8:
	movl	%edi, 12(%esi)
	.p2align 4,,7
.L3:
	.stabn 68,0,23,.LM9-fillgrent
.LM9:
	movl	%ebp, (%edi)
	.stabn 68,0,24,.LM10-fillgrent
.LM10:
	pushl	%eax
	pushl	%eax
	leal	8(%ebp), %eax
	pushl	%eax
	pushl	%edi
	call	do_field
	addl	$16, %esp
	.stabn 68,0,21,.LM11-fillgrent
.LM11:
	jmp	.L3
.LBE2:
.Lfe2:
	.size	fillgrent,.Lfe2-fillgrent
	.stabs	"_GROUP:r(0,27)",64,0,13,6
	.stabs	"tmp:r(0,23)",64,0,15,5
	.stabs	"cm:r(0,24)",64,0,16,7
	.stabn	192,0,0,.LBB2-fillgrent
	.stabn	224,0,0,.LBE2-fillgrent
.Lscope1:
	.stabs	"",36,0,0,.Lscope1-fillgrent
	.text
	.stabs "",100,0,0,.Letext
.Letext:
	.ident	"GCC: (GNU) 3.0"
-------------------------------------------------------------------------------
>Fix:
	Omitting -fomit-frame-pointer seems to sidestep the problem.
>Release-Note:
>Audit-Trail:
>Unformatted: