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Date: Tue, 19 Jul 2016 20:12:53 +0100
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Message-ID: <20160719191253.GI2087@work-vm>
References: <20160714193657.GC28687@codeaurora.org>
	<1468525094-11959-1-git-send-email-alindsay@codeaurora.org>
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Subject: Re: [Qemu-devel] [PATCH] avx2 configure: Disable if static build
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To: Aaron Lindsay <alindsay@codeaurora.org>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org

* Aaron Lindsay (alindsay@codeaurora.org) wrote:
> This avoids a segfault like the following for at least some 4.8 versions
> of gcc when configured with --static if avx2 instructions are also
> enabled:
> 
> 	Program received signal SIGSEGV, Segmentation fault.
> 	buffer_find_nonzero_offset_ifunc () at ./util/cutils.c:333
> 	333     {
> 	(gdb) bt
> 	#0  buffer_find_nonzero_offset_ifunc () at ./util/cutils.c:333
> 	#1  0x0000000000939c58 in __libc_start_main ()
> 	#2  0x0000000000419337 in _start ()
> 
> Signed-off-by: Aaron Lindsay <alindsay@codeaurora.org>

It does look like the simplest solution to the problem;

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Dave

> ---
>  configure | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/configure b/configure
> index 5ada56d..169aa88 100755
> --- a/configure
> +++ b/configure
> @@ -1788,7 +1788,9 @@ fi
>  ##########################################
>  # avx2 optimization requirement check
>  
> -cat > $TMPC << EOF
> +
> +if test "$static" = "no" ; then
> +  cat > $TMPC << EOF
>  #pragma GCC push_options
>  #pragma GCC target("avx2")
>  #include <cpuid.h>
> @@ -1801,12 +1803,13 @@ static void *bar_ifunc(void) {return (void*) bar;}
>  int foo(void *a) __attribute__((ifunc("bar_ifunc")));
>  int main(int argc, char *argv[]) { return foo(argv[0]);}
>  EOF
> -if compile_object "" ; then
> -    if has readelf; then
> -        if readelf --syms $TMPO 2>/dev/null |grep -q "IFUNC.*foo"; then
> -            avx2_opt="yes"
> -        fi
> -    fi
> +  if compile_object "" ; then
> +      if has readelf; then
> +          if readelf --syms $TMPO 2>/dev/null |grep -q "IFUNC.*foo"; then
> +              avx2_opt="yes"
> +          fi
> +      fi
> +  fi
>  fi
>  
>  #########################################
> -- 
> Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the
> Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK