Re: gcc-3.0 20010314: Miscompiled C source with -O3 -fomit-frame-pointer

[pavenis at lanet dot lv]

On 17 Mar 2001, at 9:20, Mike Harrold wrote:

> The assembly output is fine. 16(%ebp) is the third parameter passed to
> the function (the string you're trying to pass to strlen). The reason
> you're getting a SIGSEGV is because that string is NULL.
> 
> You can use gdb to verify this.
> 

I can agree if I saw something like

 	pushl	%ebp
	mov	%esp, %ebp         This line is not present in assembler output
 	pushl	%edi
 	pushl	%esi
 	pushl	%ebx
	
but as I used -fomit-frame-pointer, %ebp is undefined at entry of procedure and 
nothing is put into this register after begin of procedure
before use. I think we should have something like 
	movl  something(%esp) , %ech
when -fomit-frame-pointer is being used

Andris

> > 
> > --Message-Boundary-28126
> > Content-type: text/plain; charset=US-ASCII
> > Content-transfer-encoding: 7BIT
> > Content-description: Mail message body
> > 
> > I got following C source (see preprocessed source in attachment and
> > assembler output in attachment) miscompiled with gcc-3.0 20010314 
> > (targets i586-pc-msdosdjgpp and i686-pc-linux-gnu):
> > 
> > Compiler command line:
> > 	gcc -O3 -fomit-frame-pointer -S text7.i
> > 
> > Bad asembler output: 
> > 	In procedure _outtextxy contents of register %ebp used but is 
> > 	undefined. As result I'm getting SIGSEGV when running
> > 	applications that uses this procedure.
> > 
> > This output is for target i586-pc-msdosdjgpp but I got practically the 
> > same problem also for i686-pc-linux-gnu
> > 
> > Andris
> > 
> > 	.p2align 4
> > .globl _outtextxy
> > _outtextxy:
> > 	pushl	%ebp
> > 	pushl	%edi
> > 	pushl	%esi
> > 	pushl	%ebx
> > 	subl	$56, %esp
> > 	movl	16(%ebp), %ecx
> > 	pushl	%ecx
> > 	call	_strlen
> > 	movl	%eax, %edi
> > 	movl	___gr_vpt, %ebx
> >