linux-kernel - Re: Memory corruption due to word sharing

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Message-ID: <xnbopg8lex.fsf@greed.delorie.com>
Date:	Fri, 03 Feb 2012 01:45:42 -0500
From:	DJ Delorie <dj@...hat.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	linux-ia64@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	dsterba@...e.cz, ptesarik@...e.cz, rguenther@...e.de,
	gcc@....gnu.org
Subject: Re: Memory corruption due to word sharing


Jan Kara <jack@...e.cz> writes:
>   we've spotted the following mismatch between what kernel folks expect
> from a compiler and what GCC really does, resulting in memory corruption on
> some architectures. Consider the following structure:
> struct x {
>     long a;
>     unsigned int b1;
>     unsigned int b2:1;
> };

If this structure were volatile, you could try
-fstrict-volatile-bitfields, which forces GCC to use the C type to
define the access width, instead of doing whatever it thinks is optimal.

Note: that flag is enabled by default for some targets already, most
notably ARM.
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