linux-kernel - Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

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Message-ID: <AANLkTikeYLrqXhvTP_uuKnKhy=k7pAQCbONJdKBc838O@mail.gmail.com>
Date:	Mon, 15 Nov 2010 11:21:30 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jakub Jelinek <jakub@...hat.com>
Cc:	Jim Bos <jim876@...all.nl>, Andi Kleen <andi@...stfloor.org>,
	James Cloos <cloos@...loos.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andreas Schwab <schwab@...hat.com>,
	Michael Matz <matz@...e.de>,
	Dave Korn <dave.korn.cygwin@...il.com>,
	Richard Guenther <richard.guenther@...il.com>, gcc@....gnu.org
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

On Mon, Nov 15, 2010 at 11:12 AM, Jakub Jelinek <jakub@...hat.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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