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Message-ID: <16212.28592.322946.64754@gargle.gargle.HOWL>
Date: Tue, 2 Sep 2003 12:23:44 +0200
From: Mikael Pettersson <mikpe@csd.uu.se>
To: =?iso-8859-1?Q?J=F6rn?= Engel <joern@wohnheim.fh-wedel.de>
Cc: Dave Olien <dmo@osdl.org>, Petri Koistinen <petri.koistinen@iki.fi>,
       linux-kernel@vger.kernel.org
Subject: Re: Sparse warning: bitmap.h: bad constant expression
In-Reply-To: <20030902095628.GB7616@wohnheim.fh-wedel.de>
References: <Pine.LNX.4.56.0309012249230.14789@dsl-hkigw4a35.dial.inet.fi>
	<20030902015702.GA10265@osdl.org>
	<20030902095628.GB7616@wohnheim.fh-wedel.de>
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=?iso-8859-1?Q?J=F6rn?= Engel writes:
 > On Mon, 1 September 2003 18:57:02 -0700, Dave Olien wrote:
 > > 
 > > The problem seems to be that sparse currently will only accept array
 > > declarations with a size that can be evaluated at compile time to
 > > a fixed value.  So an array declaration of the form:
 > > 
 > > int asize;
 > > int data[asize];
 > > 
 > > will fail.  sparse needs to be modified to recognize this type of 
 > > declaration with a variable array size.  That'll take a few hours of
 > > someone's time to fix.
 > 
 > Not quite true.  The above is an implicit call to alloca and should
 > not exist in the kernel.  No need to hack support into sparse.

If data is a local variable then this is perfectly valid example of a
C99 variable-length array (VLA). This works at least with gcc-2.95.3
and newer, and gcc handles it by itself w/o calling alloca().

Of course, VLAs should be bounded in size to avoid overflowing the
kernel stack, but that doesn't make them illegal per se.

/Mikael
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