From: Andreas Schwab <schwab@suse.de>
To: Peter Lund <firefly@vax64.dk>
Cc: Christoph Lameter <clameter@sgi.com>,
Christoph Hellwig <hch@infradead.org>,
trivial@kernel.org, linux-kernel@vger.kernel.org,
Momchil Velikov <velco@fadata.bg>,
"Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [PATCH] avoid negative shifts in radix-tree.c, take 2
Date: Wed, 29 Aug 2007 14:47:17 +0200 [thread overview]
Message-ID: <jeodgq1p9m.fsf@sykes.suse.de> (raw)
In-Reply-To: <1188390865.7216.5.camel@localhost.localdomain> (Peter Lund's message of "Wed\, 29 Aug 2007 14\:34\:25 +0200")
Peter Lund <firefly@vax64.dk> writes:
> Shifting by more than the width of the value on the left is also not allowed.
Shifting by the width of the value is not allowed as well.
> --- linux-2.6.22/lib/radix-tree.c.orig 2007-08-27 15:42:37.000000000 +0200
> +++ linux-2.6.22/lib/radix-tree.c 2007-08-29 13:19:19.000000000 +0200
> @@ -980,12 +980,13 @@
>
> static __init unsigned long __maxindex(unsigned int height)
> {
> - unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
> - unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
> + unsigned int width = height * RADIX_TREE_MAP_SHIFT;
> + int shift = RADIX_TREE_INDEX_BITS - width;
>
> - if (tmp >= RADIX_TREE_INDEX_BITS)
> - index = ~0UL;
> - return index;
> + if (shift < 0)
> + return ~0UL;
> + else
> + return ~0UL >> shift;
Since height can be zero, you still have undefined behaviour.
Andreas.
--
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
prev parent reply other threads:[~2007-08-29 12:47 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-29 12:34 Peter Lund
2007-08-29 12:47 ` Andreas Schwab [this message]
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