On Fri, 7 Oct 2005, Horst von Brand wrote:
> PaweÅ' Sikora <[email protected]> wrote:
>> I've a simple program called empty.c.
>>
>> $ cat empty.c
>>
>> int main(int argc, char* argv[])
>> {
>> return 0;
>> }
>>
>> $ cat empty410.s
>>
>> .file "empty.c"
>> .text
>> .p2align 4,,15
>> .globl main
>> .type main, @function
>> main:
>> xorl %eax, %eax
>> ret
>> .size main, .-main
>> .ident "GCC: (GNU) 4.1.0 20050922 (experimental)"
>> .section .note.GNU-stack,"", at progbits
>
With this compilation, the 'C' compiler looked and said; "you
are just going to return 0..." So that's the code it generated.
This compiler probably defaults to "-fomit-frame-pointer".
> I get a substantially different empty.s (gcc-4.0.2, Fedora rawhide on i686):
>
> .file "empty.c"
> .text
> .p2align 2,,3
> .globl main
> .type main, @function
> main:
> pushl %ebp
> movl %esp, %ebp
> subl $8, %esp
> andl $-16, %esp
> subl $16, %esp
> xorl %eax, %eax
> leave
> ret
> .size main, .-main
> .ident "GCC: (GNU) 4.0.2 20050928 (Red Hat 4.0.2-1)"
> .section .note.GNU-stack,"",@progbits
With this compiler, it assumed that you were going to do something
useful so it set up a stack-frame. It also aligned the stack after
it saved the intitial value in EBP. Then it cleared the return-
value, reset the stack, and returned.
This compiler did not default to "-fomit-frame-pointer" so it
set up a stack-frame.
>
>> binutils-2.15.94.0.2.2 produces for this code empty .data and .bss
>> sections:
>
There is nothing wrong here at all.
> binutils-2.16.91.0.2-4 doesn't. It looks like you are using broken tools.
> --
> Dr. Horst H. von Brand User #22616 counter.li.org
> Departamento de Informatica Fono: +56 32 654431
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Cheers,
Dick Johnson
Penguin : Linux version 2.6.13 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction.
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