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Date: Sun, 6 Dec 2009 18:31:57 +0000
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] [PATCH] Permit zero-sized qemu_malloc() & friends
Message-ID: <20091206183157.GA1021@shareable.org>
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To: Ian Molton <ian.molton@collabora.co.uk>
Cc: Blue Swirl <blauwirbel@gmail.com>, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>, Paul Brook <paul@codesourcery.com>

Ian Molton wrote:
> > Read the beginning of the thread.  Basically it's for arrays, malloc(n *
> > sizeof(x)).
> 
> well, make sure n is not 0. Its not that hard. I dont think I've *ever*
> had a situation where I wanted to pass 0 to malloc.

I would like to remind everyone that sizeof(x) can be 0 too.  For
example, on Linux sizeof(spinlock_t) == 0 on UP.  Anything where you
have a bunch of structure fields which depend on compile time
configuration, or where a type might be replaced by a stub empty
structure, is a possible sizeof(x) == 0.

> Its not that hard.

The fact is there are a number of bugs in qemu where n == 0 is not
checked prior to calling qemu_malloc() at the moment.  None of them
are "hard" to fix - they are rare cases that nobody noticed when
writing them.

Until we have code analysis tools checking for that, bugs of that kind
will probably keep arising.

-- Jamie