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From: Stefan Weil <sw@weilnetz.de>
Message-ID: <57663351.50802@weilnetz.de>
Date: Sun, 19 Jun 2016 07:53:21 +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 <pmaydell@chiark.greenend.org.uk>, qemu-devel@nongnu.org
Cc: patches@linaro.org

Am 19.06.2016 um 00:05 schrieb Peter Maydell:
> From: Peter Maydell <peter.maydell@linaro.org>
>=20
> 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.
>=20
> 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(-)
>=20
> 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=3D"yes"
> +    if has readelf; then
> +        if readelf --syms $TMPO 2>/dev/null |grep -q "IFUNC.*foo"; the=
n
> +            avx2_opt=3D"yes"
> +        fi
>      fi
>  fi
> =20
>=20

You could check "has readelf" earlier and avoid the compile test
if there is no readelf (saves a little time).

The final I/O redirection is still needed (otherwise Linux users will
see the grep output).

Regards
Stefan