Re: [2.6] binfmt_elf bug (exposed by klibc).

[linux-os (Dick Johnson)]

On Fri, 7 Oct 2005, Horst von Brand wrote:

> PaweÅ' Sikora <pluto@xxxxxxxx> 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
> Universidad Tecnica Federico Santa Maria              +56 32 654239
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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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