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Date: Thu, 23 Jun 2011 18:55:33 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Andi Kleen <andi@firstfloor.org>
Cc: Maarten Lankhorst <m.b.lankhorst@gmail.com>, Alex Elder <aelder@sgi.com>,
        xfs-masters@oss.sgi.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        xfs@oss.sgi.com
Subject: Re: [PATCH v2] xfs: Silence bounds checking compiler warning
Message-ID: <20110623175533.GK11521@ZenIV.linux.org.uk>
References: <4E037001.8090306__42924.0493024283$1308849791$gmane$org@gmail.com>
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On Thu, Jun 23, 2011 at 10:27:26AM -0700, Andi Kleen wrote:
> Maarten Lankhorst <m.b.lankhorst@gmail.com> writes:
> 
> > gcc with -Warray-bounds generates a false positive on this
> > since xfs defines the struct with u8 name[1]; to be able to
> > add a tag at the end.
> 
> A better way would be to define it as name[0]. Then the compiler
> would know it's a VLA. You may need to check noone relies on
> the one byte though.

... and even better is to write in real C and have u8 name[]; in the
end of your structure.  That's the standard C99 for this kind of thing
(see 6.7.2.1p2, p16).  Zero-sized array is a gccism predating standard
flexible array members and since the standard syntax is accepted by
any gcc version that might be recent enough to build the kernel...