Re: Opteron bug

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Jun 21, 2004 at 02:54:53AM +0300, Denis Vlasenko wrote:
> On Sunday 20 June 2004 15:02, Jakub Jelinek wrote:
> > On Sun, Jun 20, 2004 at 01:47:17PM +0200, R. J. Wysocki wrote:
> > > Well, is there any case in which the gcc can produce such stuff?
> >
> > GCC doesn't ever generate std instruction (only cld), though users
> > can use it in inline assembly or assembly source file.
> > AFAIK x86_64 glibc doesn't use it at all either.
> 
> glibc-2.3/sysdeps/i386/memcopy.h:
> 
> #define BYTE_COPY_BWD(dst_ep, src_ep, nbytes)                                 \
>   do                                                                          \
>     {                                                                         \
>       int __d0;                                                               \
>       asm volatile(/* Set the direction flag, so copying goes backwards.  */  \
>                    "std\n"                                                    \
>                    /* Copy bytes.  */                                         \
>                    "rep\n"                                                    \
>                    "movsb\n"                                                  \
>                    /* Clear the dir flag.  Convention says it should be 0. */ \
>                    "cld" :                                                    \
>                    "=D" (dst_ep), "=S" (src_ep), "=c" (__d0) :                \
>                    "0" (dst_ep - 1), "1" (src_ep - 1), "2" (nbytes) :         \
>                    "memory");                                                 \
>       dst_ep += 1;                                                            \
>       src_ep += 1;                                                            \
>     } while (0)
> 
> WORD_COPY_BWD also does this

I know, but I said x86_64 glibc, which doesn't do this.

	Jakub