Re: [Qemu-devel] [PATCH 2/2] configure: Make AVX2 test robust to non-ELF systems

[Peter Maydell]

On 19 June 2016 at 06:53, Stefan Weil <address@hidden> wrote:
> Am 19.06.2016 um 00:05 schrieb Peter Maydell:
>> From: Peter Maydell <address@hidden>
>>
>> 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 <address@hidden>
>> Signed-off-by: Peter Maydell <address@hidden>
>> ---
>>  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