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From: Stefan Weil <sw@weilnetz.de>
Message-ID: <57667FD0.6020106@weilnetz.de>
Date: Sun, 19 Jun 2016 13:19:44 +0200
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Subject: Re: [Qemu-devel] [PATCH 2/2] configure: Make AVX2 test robust to
 non-ELF systems
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Peter Maydell <pmaydell@chiark.greenend.org.uk>, QEMU Developers <qemu-devel@nongnu.org>, Patch Tracking <patches@linaro.org>

Am 19.06.2016 um 11:41 schrieb Peter Maydell:
> On 19 June 2016 at 06:53, Stefan Weil <sw@weilnetz.de> wrote:
>> Am 19.06.2016 um 00:05 schrieb Peter Maydell:
>>> From: Peter Maydell <peter.maydell@linaro.org>
>>>
>>> The AVX2 optimization test assumes that the object format
>>> is ELF and the system has the readelf utility. If this isn't
>>> true then configure might fail or emit a warning (since in
>>> a pipe "foo | bar >/dev/null 2>&1" does not redirect the
>>> stderr of foo, only of bar). Adjust the check so that if
>>> we don't have readelf or don't have an ELF object then we
>>> just don't enable the AVX2 optimization.
>>>
>>> Reported-by: Stefan Weil <sw@weilnetz.de>
>>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>>> ---
>>>  configure | 6 ++++--
>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/configure b/configure
>>> index 7beefcd..30bca55 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -1792,8 +1792,10 @@ int foo(void *a) __attribute__((ifunc("bar_ifunc")));
>>>  int main(int argc, char *argv[]) { return foo(argv[0]);}
>>>  EOF
>>>  if compile_object "" ; then
>>> -    if readelf --syms $TMPO |grep "IFUNC.*foo" >/dev/null 2>&1; then
>>> -        avx2_opt="yes"
>>> +    if has readelf; then
>>> +        if readelf --syms $TMPO 2>/dev/null |grep -q "IFUNC.*foo"; then
>>> +            avx2_opt="yes"
>>> +        fi
>>>      fi
>>>  fi
>>>
>>>
>>
>> You could check "has readelf" earlier and avoid the compile test
>> if there is no readelf (saves a little time).
> 
> I guess so, though there's not much in it.
> 
>> The final I/O redirection is still needed (otherwise Linux users will
>> see the grep output).
> 
> I added -q which should suppress that, no ?
> 
> thanks
> -- PMM
> 

Sorry, I missed that detail.

Reviewed-by: Stefan Weil <sw@weilnetz.de>