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Re: [Qemu-ppc] [Qemu-devel] [PULL 16/20] target/arm: Use vector infrastr

From: Thomas Huth
Subject: Re: [Qemu-ppc] [Qemu-devel] [PULL 16/20] target/arm: Use vector infrastructure for aa64 compares
Date: Thu, 5 Apr 2018 07:06:08 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 05.04.2018 02:54, Richard Henderson wrote:
> On 04/05/2018 10:07 AM, Richard Henderson wrote:
>> On 04/05/2018 02:49 AM, Emilio G. Cota wrote:
>>> 1. grab this binary:
>>>   http://cs.columbia.edu/~cota/qemu/nbench-aarch64
>>> 2. run it on a PowerPC host with:
>>>   $ aarch64-linux-user/qemu-aarch64 nbench-aarch64 -V
>>> Note: the "-V" (or "-v") flag is important! Without it, there's no segfault.
>> How quickly?  I did not see one up until it exited for lack of NNET.DAT.
>> I will note that I am using gcc 7.2 on gcc112 
>> (/opt/cfarm/gcc-latest/bin/gcc).
>> Are you using gcc 4.8.5, and is commit 74912f6dad in your tree?
>> That commit might have made a difference...
> Bah.  I confirm that it doesn't, and that the test still fails.
> Since qemu does work on the same host when built with gcc 7.2, I can only 
> blame
> this failure on a compiler bug wrt gcc 4.8 on ppc64.
> I have not tracked down exactly what's going wrong, and probably won't unless
> someone feels that it's worthwhile.  This only begs the question of whether we
> should blacklist this compiler entirely.  Certainly it's old enough that it's
> probably not worth fixing.

GCC 4.8 is still used in enterprise distros like RHEL7 and AFAIK also in
SLES 12 ... so blacklisting this compiler does not sound like a good
idea to me.


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