From: Avi Kivity <avi@cloudius-systems.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>,
Patch Tracking <patches@linaro.org>,
Michael Tokarev <mjt@tls.msk.ru>,
QEMU Developers <qemu-devel@nongnu.org>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [Qemu-trivial] [PATCH 2/3] int128.h: Avoid undefined behaviours involving signed arithmetic
Date: Mon, 07 Apr 2014 18:22:38 +0300 [thread overview]
Message-ID: <5342C2BE.4020805@cloudius-systems.com> (raw)
In-Reply-To: <CAFEAcA-dCJ+i+g7F+hxgPr3AZjwOgrWj4X+9dXLvpj56JYQ07A@mail.gmail.com>
On 04/07/2014 06:17 PM, Peter Maydell wrote:
> On 7 April 2014 15:56, Avi Kivity <avi@cloudius-systems.com> wrote:
>> On 04/06/2014 01:18 PM, Peter Maydell wrote:
>>> The alternative would be to say that Int128 should have
>>> undefined behaviour on underflow/overflow and the test
>>> code is wrong, but that doesn't seem very useful to me.
>> Isn't the test broken here? It is trying to add (or shift) -2^127 and
>> something else, and the result truly overflows.
> Well, the test code is assuming "semantics as per 2s
> complement arithmetic" and checking various corner cases.
> As I say, we could define that this is invalid and
> rewrite the test cases.
It is invalid. The test thinks that -2^127 * 2 == 0, but if a guest
could trigger it, it would probably be a security issue.
next prev parent reply other threads:[~2014-04-07 15:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-28 15:12 [Qemu-devel] [PATCH 0/3] More fixes for undefined behaviour Peter Maydell
2014-03-28 15:12 ` [Qemu-devel] [PATCH 1/3] hw/ide/ahci.c: Avoid shift left into sign bit Peter Maydell
2014-04-06 7:10 ` [Qemu-devel] [Qemu-trivial] " Michael Tokarev
2014-03-28 15:12 ` [Qemu-devel] [PATCH 2/3] int128.h: Avoid undefined behaviours involving signed arithmetic Peter Maydell
2014-04-06 7:09 ` [Qemu-devel] [Qemu-trivial] " Michael Tokarev
2014-04-06 10:18 ` Peter Maydell
2014-04-06 14:13 ` Michael Tokarev
2014-04-06 14:58 ` Peter Maydell
2014-04-06 15:27 ` Peter Maydell
2014-04-07 14:25 ` Richard Henderson
2014-04-07 14:47 ` Peter Maydell
2014-04-07 15:49 ` Markus Armbruster
2014-04-07 14:56 ` Avi Kivity
2014-04-07 15:17 ` Peter Maydell
2014-04-07 15:22 ` Avi Kivity [this message]
2014-03-28 15:12 ` [Qemu-devel] [PATCH 3/3] xbzrle.c: Avoid undefined behaviour with " Peter Maydell
2014-04-06 14:15 ` [Qemu-devel] [Qemu-trivial] " Michael Tokarev
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