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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 15 Nov 2010 11:21:30 -0800
Message-ID: <AANLkTikeYLrqXhvTP_uuKnKhy=k7pAQCbONJdKBc838O@mail.gmail.com>
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?
To: Jakub Jelinek <jakub@redhat.com>
Cc: Jim Bos <jim876@xs4all.nl>, Andi Kleen <andi@firstfloor.org>,
        James Cloos <cloos@jhcloos.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andreas Schwab <schwab@redhat.com>, Michael Matz <matz@suse.de>,
        Dave Korn <dave.korn.cygwin@gmail.com>,
        Richard Guenther <richard.guenther@gmail.com>, gcc@gcc.gnu.org
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On Mon, Nov 15, 2010 at 11:12 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>
> Ah, the problem is that memory_identifier_string is only initialized in
> ipa-reference.c's initialization, so it can be (and is in this case) NULL in
> ipa-pure-const.c.

Ok. And I guess you can verify that all versions of gcc do this
correctly for "asm volatile"?

Because since we'll have to work around this problem in the kernel, I
suspect the simplest solution is to remove the "+m" that causes
register pressure problems, and then use "asm volatile" to work around
the const-function bug.

And add a large comment about why "asm volatile" is probably always a
good idea when you have a memory clobber and don't have any other
visible memory modifications.

I do wonder if this explains some of the problems we had with the
bitop asms too.

Hmm?

                       Linus
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