linux-kernel - Re: 2.4.x: i386/x86

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Message-ID: <20061008224440.GA30172@1wt.eu>
Date:	Mon, 9 Oct 2006 00:44:40 +0200
From:	Willy Tarreau <w@....eu>
To:	Jan Kiszka <jan.kiszka@....de>
Cc:	linux-kernel@...r.kernel.org,
	Willy Tarreau <wtarreau@...a.kernel.org>
Subject: Re: 2.4.x: i386/x86_64 bitops clobberings

Hi Jan,

On Sun, Oct 08, 2006 at 11:42:07PM +0200, Jan Kiszka wrote:
> Hi,
> 
> after going through debugging hell with some out-of-tree code, I
> realised that this patch
> 
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=92934bcbf96bc9dc931c40ca5f1a57685b7b813b
> 
> makes a difference: current 2.6 works with the following code sequence
> as expected (printk is executed), 2.4 fails.
> 
> 
> #include <asm/bitops.h>
> #include <linux/module.h>
> 
> unsigned long a = 1;
> 
> int module_init(void)
> {
> 	unsigned long b = 0;
> 	int x;
> 
> 	x = __test_and_set_bit(0, &b);
> 	if (__test_and_set_bit(0, &a))
> 		printk("x = %d\n", x);
> 
> 	return -1;
> }
> 
> 
> There will likely be a way to work around my issue. Nevertheless, I
> wondered if that patch was already considered for 2.4 inclusion. Or is
> there no risk that in-tree code is affected?

While I remember some discussion on the subject for 2.6, I don't
recall anything similiar in 2.4. Wouldn't you happen to build with
gcc-3.4 ? IIRC, the clobbering changed around this version. Could
you confirm that the patch you pointed above fixes the problem for
your case ?

Thanks in advance,
Willy

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