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SubjectRe: spin_lock forgets to clobber memory and other smp fixes [was Re: [patch] waitqueue optimization, 2.4.0-test7]
On Thu, 7 Sep 2000, Jamie Lokier wrote:

>I tried it with two compilers, one older than yours and one newer:

So maybe I'm just been unlucky/lucky (depends on the point of view :) or
maybe we patched something I'm not aware of to make the kernel to compile
right.

> .ident "GCC: (GNU) egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)"
> .ident "GCC: (GNU) 2.96 20000724 (experimental)"
>
>The command lines were:
>
> gcc -S -O2 test4.c
> kgcc -S -O2 test4.c
>
>In both cases, the memory read occurs before "zzz".

andrea@inspiron:~ > cat p.c
int *p;
int func()
{
int x;
x = *p;
__asm__ __volatile__ ("" : : );
x = *p;
return x;
}
andrea@inspiron:~ > gcc -O2 -S p.c
andrea@inspiron:~ > cat p.s
.file "p.c"
.version "01.01"
gcc2_compiled.:
.text
.align 16
.globl func
.type func,@function
func:
pushl %ebp
movl %esp,%ebp
#APP
#NO_APP
^^^^^^^
movl p,%eax
movl %ebp,%esp
popl %ebp
movl (%eax),%eax
^^^^^^^^^^^^^^^^
ret
.Lfe1:
.size func,.Lfe1-func
.comm p,4,4
.ident "GCC: (GNU) 2.95.2 19991024 (release)"
Andrea

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