* [Qemu-devel] possible qemu miscompilation by latest gcc
@ 2010-01-21 6:15 John Regehr
2010-01-21 16:57 ` Richard Henderson
0 siblings, 1 reply; 2+ messages in thread
From: John Regehr @ 2010-01-21 6:15 UTC (permalink / raw)
To: qemu-devel
Hi folks-
Just wanted to let you know that perhaps the function
helper_neon_rshl_s8() is being miscompiled by the latest gcc.
I'm using qemu 0.12.2 and gcc rev 156103, which is a pre-version of gcc
4.5. This is on an x86 machine running Ubuntu 9.10.
At -O2 or higher this is the resulting object code:
00002060 <helper_neon_rshl_s8>:
2060: 31 c0 xor %eax,%eax
2062: c3 ret
If this is not the intended result, then either the function has a
latent bug or else the compiler is doing something bad.
Hope this is helpful,
John Regehr
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Qemu-devel] possible qemu miscompilation by latest gcc
2010-01-21 6:15 [Qemu-devel] possible qemu miscompilation by latest gcc John Regehr
@ 2010-01-21 16:57 ` Richard Henderson
0 siblings, 0 replies; 2+ messages in thread
From: Richard Henderson @ 2010-01-21 16:57 UTC (permalink / raw)
To: John Regehr; +Cc: qemu-devel
On 01/20/2010 10:15 PM, John Regehr wrote:
> Hi folks-
>
> Just wanted to let you know that perhaps the function
> helper_neon_rshl_s8() is being miscompiled by the latest gcc.
>
> I'm using qemu 0.12.2 and gcc rev 156103, which is a pre-version of gcc
> 4.5. This is on an x86 machine running Ubuntu 9.10.
>
> At -O2 or higher this is the resulting object code:
>
> 00002060 <helper_neon_rshl_s8>:
> 2060: 31 c0 xor %eax,%eax
> 2062: c3 ret
>
> If this is not the intended result, then either the function has a
> latent bug or else the compiler is doing something bad.
Confirmed. The compiler is at fault.
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42833
r~
^ permalink raw reply [flat|nested] 2+ messages in thread
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