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Date: Tue, 5 Jul 2011 06:41:36 +0100
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From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] Add fno-strict-overflow
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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

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