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Re: [PATCH v2] xfs: Silence bounds checking compiler warning

To: Andi Kleen <andi@xxxxxxxxxxxxxx>
Subject: Re: [PATCH v2] xfs: Silence bounds checking compiler warning
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Thu, 23 Jun 2011 18:55:33 +0100
Cc: Maarten Lankhorst <m.b.lankhorst@xxxxxxxxx>, Alex Elder <aelder@xxxxxxx>, xfs-masters@xxxxxxxxxxx, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <m2boxocvb5.fsf@xxxxxxxxxxxxxx>
References: <4E037001.8090306__42924.0493024283$1308849791$gmane$org@xxxxxxxxx> <m2boxocvb5.fsf@xxxxxxxxxxxxxx>
Sender: Al Viro <viro@xxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Jun 23, 2011 at 10:27:26AM -0700, Andi Kleen wrote:
> Maarten Lankhorst <m.b.lankhorst@xxxxxxxxx> 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, 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...

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