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References: <1453280742-20718-1-git-send-email-liang.z.li@intel.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <569F5883.2090608@redhat.com>
Date: Wed, 20 Jan 2016 10:50:59 +0100
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Subject: Re: [Qemu-devel] [PATCH v4 1/2] configure: detect ifunc and avx2
	attribute
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To: Liang Li <liang.z.li@intel.com>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, mst@redhat.com, rth7680@gmail.com, dgilbert@redhat.com, quintela@redhat.com, stefanha@redhat.com, amit.shah@redhat.com, rth@twiddle.net



On 20/01/2016 10:05, Liang Li wrote:
> Detect if the compiler can support the ifun and avx2, if so, set
> CONFIG_AVX2_OPT which will be used to turn on the avx2 instruction
> optimization.
> 
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> ---
>  configure | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/configure b/configure
> index 44ac9ab..b7f4661 100755
> --- a/configure
> +++ b/configure
> @@ -310,6 +310,7 @@ smartcard=""
>  libusb=""
>  usb_redir=""
>  opengl=""
> +avx2_opt=""
>  zlib="yes"
>  lzo=""
>  snappy=""
> @@ -1827,6 +1828,20 @@ EOF
>  fi
>  
>  ##########################################
> +# avx2 optimization requirement check
> +
> +cat > $TMPC << EOF
> +static void bar(void) {}

Might be nicer to use "void *" and return an actual function name:

static void bar(void) {}
static void *bar_ifunc(void) { return (void *)bar; }
void foo(void) __attribute__((ifunc("bar_ifunc")));

And also you probably should use "readelf --syms ... | grep IFUNC.*foo"
to check that the attribute was not ignored.

Paolo


> +static void foo(void) __attribute__((ifunc("bar")));
> +int main(void) { foo(); return 0; }
> +EOF
> +if compile_prog "" "-mavx2" ; then
> +    avx2_opt="yes"
> +else
> +    avx2_opt="no"
> +fi
> +
> +#########################################
>  # zlib check
>  
>  if test "$zlib" != "no" ; then
> @@ -4855,6 +4870,7 @@ echo "bzip2 support     $bzip2"
>  echo "NUMA host support $numa"
>  echo "tcmalloc support  $tcmalloc"
>  echo "jemalloc support  $jemalloc"
> +echo "avx2 optimization $avx2_opt"
>  
>  if test "$sdl_too_old" = "yes"; then
>  echo "-> Your SDL version is too old - please upgrade to have SDL support"
> @@ -5236,6 +5252,10 @@ if test "$opengl" = "yes" ; then
>    echo "OPENGL_LIBS=$opengl_libs" >> $config_host_mak
>  fi
>  
> +if test "$avx2_opt" = "yes" ; then
> +  echo "CONFIG_AVX2_OPT=y" >> $config_host_mak
> +fi
> +
>  if test "$lzo" = "yes" ; then
>    echo "CONFIG_LZO=y" >> $config_host_mak
>  fi
>