linux-kernel - Re: [PATCH v2] compiler: prevent dead store elimination

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Message-ID: <20100302121701.GA19208@basil.fritz.box>
Date:	Tue, 2 Mar 2010 13:17:02 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	Roel Kluin <roel.kluin@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	"David S. Miller" <davem@...emloft.net>, penberg@...helsinki.fi,
	Brian Gerst <brgerst@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, Herbert@...dor.apana.org.au
Subject: Re: [PATCH v2] compiler: prevent dead store elimination

>  > +	do {						\
>  > +		struct __scrub { typeof(*p) c[n]; };	\
> 
> The typeof(*p) suggestion doesn't work. It would require p to always be
> a pointer type with an accurate (for memset) sizeof(*p). In general however
> we'll memset some array described by a void*/size_t pair, and typeof in
> that case is useless. The original'struct __scrub { char c[n]; };' was Ok.

I just suggested it because of the original array name of the macro
and without it it would have only worked for char arrays. With the new
naming it's ok I guess.

It could be made to work with macros and builtin_type_match I guess,
but it would be fairly ugly and not worth it.

-Andi

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