Re: [E-devel] Re: libast from Eterm CVS fails to build with gcc4 on x86_64

[Tres M. <tr...@mi...>]

On Mon, 2005-06-06 at 19:26 -0400, Mike Frysinger wrote:
> i use asm label tricks:
> $ cat test.c
> int main(int argc, char *argv[])
> {
>         int a;
>         asm("startit:");
>         a = 10;
>         asm("stopit:");
>         return 0;
> }
> 
> $ gcc -c test.c && objdump -d test.o
> test.o:     file format elf64-x86-64
> 
> Disassembly of section .text:
> 
> 0000000000000000 <main>:
>    0:   55                      push   %rbp
>    1:   48 89 e5                mov    %rsp,%rbp
>    4:   89 7d fc                mov    %edi,0xfffffffffffffffc(%rbp)
>    7:   48 89 75 f0             mov    %rsi,0xfffffffffffffff0(%rbp)
> 
> 000000000000000b <startit>:
>    b:   c7 45 ec 0a 00 00 00    movl   $0xa,0xffffffffffffffec(%rbp)
> 
> 0000000000000012 <stopit>:
>   12:   b8 00 00 00 00          mov    $0x0,%eax
>   17:   c9                      leaveq 
>   18:   c3                      retq   
> -mike

Well, the pages I was reading used the nop trick but it looks like a
better solution has been presented.  I almost forgot that integers are
still 32 bit on x86-64 so explaining the movl instead of movq.  For
those interested the "gcc -S" is (the #APP/#NO_APP is gcc's way of
marking inline asm):

--------- 8< ----------
#APP
        startit:
#NO_APP
        movl    $10, -20(%rbp)
#APP
        stopit:
#NO_APP
--------- >8 ----------


Thanks Vapier,
-- 
Tres