From: Stefan Hajnoczi <stefanha@gmail.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Raghavendra D Prabhu <rprabhu@wnohang.net>,
qemu-devel@nongnu.org,
Raghavendra D Prabhu <raghu.prabhu13@gmail.com>,
kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [PATCH 2/3] Add fno-strict-overflow
Date: Tue, 5 Jul 2011 06:41:36 +0100 [thread overview]
Message-ID: <CAJSP0QWS7ouVekY2-b4Y5dr-tmDX0_k_-FJLcA-X8FUsNE6XvA@mail.gmail.com> (raw)
In-Reply-To: <CAFEAcA_mDcMgBzyaXwO_qAdmAA4GagQoah7TFbSdGZbMiEa8cw@mail.gmail.com>
On Mon, Jul 4, 2011 at 11:38 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 4 July 2011 23:00, Raghavendra D Prabhu <raghu.prabhu13@gmail.com> wrote:
>> This is to avoid gcc optimizating out the comparison in assert,
>> due to assumption of signed overflow being undefined by default (-Werror=strict-overflow).
>
>>--- a/Makefile.hw
>>+++ b/Makefile.hw
>>@@ -9,7 +9,7 @@ include $(SRC_PATH)/rules.mak
>>
>> $(call set-vpath, $(SRC_PATH):$(SRC_PATH)/hw)
>>
>> -QEMU_CFLAGS+=-I.. -I$(SRC_PATH)/fpu
>> +QEMU_CFLAGS+=-I.. -I$(SRC_PATH)/fpu -fno-strict-overflow
>
> Can you give a more detailed description of the problem this is trying
> to solve? I think it would be nicer if we could remove the assumptions
> about signed overflows instead, if that's practical.
>
> (Also, if we do want to add this compiler flag then it ought to be
> done in configure I think, as we do for -fno-strict-aliasing.)
"a correct C/C++ program must never generate signed overflow when
computing an expression. It also means that a compiler may assume that
a program will never generated signed overflow."
http://www.airs.com/blog/archives/120
Stefan
next prev parent reply other threads:[~2011-07-05 5:41 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-04 21:59 [Qemu-devel] [PATCH 0/3] Build fixes Raghavendra D Prabhu
2011-07-04 22:00 ` [Qemu-devel] [PATCH 1/3] Avoid the use of deprecated gnutls gnutls_*_set_priority functions Raghavendra D Prabhu
2011-08-22 8:26 ` Stefan Hajnoczi
2011-08-22 10:13 ` Gerd Hoffmann
2011-08-25 10:54 ` Stefan Hajnoczi
2011-08-25 11:02 ` Daniel P. Berrange
2011-07-04 22:00 ` [Qemu-devel] [PATCH 2/3] Add fno-strict-overflow Raghavendra D Prabhu
2011-07-04 22:38 ` Peter Maydell
2011-07-05 5:41 ` Stefan Hajnoczi [this message]
2011-07-05 9:34 ` Stefan Hajnoczi
2011-07-05 15:36 ` Raghavendra D Prabhu
2011-07-05 20:30 ` Stefan Hajnoczi
2011-07-07 21:51 ` Raghavendra D Prabhu
2011-07-04 22:00 ` [Qemu-devel] [PATCH 3/3] Avoid Wunsed-but-set warnings (or errors in case of Werror) Raghavendra D Prabhu
2011-07-05 6:15 ` Markus Armbruster
2011-07-05 7:02 ` Peter Maydell
2011-07-05 7:49 ` Markus Armbruster
2011-07-05 8:05 ` Paolo Bonzini
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