From: Andrew Morton <akpm@osdl.org>
To: Andreas Schwab <schwab@suse.de>
Cc: trond.myklebust@fys.uio.no, 76306.1226@compuserve.com,
linux-kernel@vger.kernel.org, ak@suse.de, mingo@redhat.com,
torvalds@osdl.org
Subject: Re: set_bit() is broken on i386?
Date: Fri, 20 Jan 2006 18:38:57 -0800 [thread overview]
Message-ID: <20060120183857.188ef516.akpm@osdl.org> (raw)
In-Reply-To: <jek6cu73jy.fsf@sykes.suse.de>
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".
next prev parent reply other threads:[~2006-01-21 2:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-21 0:53 set_bit() is broken on i386? Chuck Ebbert
2006-01-21 1:15 ` Trond Myklebust
2006-01-21 1:49 ` Andreas Schwab
2006-01-21 2:38 ` Andrew Morton [this message]
2006-01-21 19:26 ` Trond Myklebust
2006-01-21 1:32 ` Valdis.Kletnieks
2006-01-21 2:01 ` Grzegorz Kulewski
2006-01-21 1:48 ` Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2006-01-21 1:38 Kenny Simpson
2006-01-21 1:46 Kenny Simpson
2006-01-21 2:07 Kenny Simpson
2006-01-21 7:43 Chuck Ebbert
2006-01-21 20:49 Chuck Ebbert
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