lkml.org 
[lkml]   [2006]   [Jan]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: set_bit() is broken on i386?
Andreas Schwab <schwab@suse.de> wrote:
>
> Trond Myklebust <trond.myklebust@fys.uio.no> writes:
>
> > On Fri, 2006-01-20 at 19:53 -0500, Chuck Ebbert wrote:
> >
> >> #define ADDR (*(volatile long *) addr)
> >> static inline void set_bit(int nr, volatile unsigned long * addr)
> >> {
> >> __asm__ __volatile__( "lock ; "
> >> "btsl %1,%0"
> >> :"=m" (ADDR)
> >> :"Ir" (nr));
> >> }
> >
> > The asm needs a memory clobber in order to avoid reordering with the
> > assignment to b[1]:
>
> Check out 2.6.16-rc1, this has already been fixed.
>

No, that doesn't fix this testcase.

We need to somehow tell the compiler "this assembly statement altered
memory and you can't cache memory contents across it". That's what
"memory" (ie: barrier()) does. I don't think there's a way of telling gcc
_what_ memory was clobbered - just "all of memory".
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-01-21 03:42    [W:0.511 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site