Re: [Qemu-devel] [PATCH v2] configure: disable FORTIFY_SOURCE under clang

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/11/2015 21:43, John Snow wrote:
> Some versions of clang may have difficulty compiling glibc headers when
> -D_FORTIFY_SOURCE is used. For example, Clang++ 3.5.0-9.fc22 cannot
> compile glibc's stdio headers when -D_FORTIFY_SOURCE=2 is used. This
> manifests currently as build failures with clang and any arm target.
> 
> According to LLVM dev Richard Smith, clang does not target or support
> FORTIFY_SOURCE + glibc, and it should not be relied on.
> "It's still an unsupported combination, and while it might compile, some
> of the checks are unlikely to work because they require a frontend
> inliner to be useful"
> 
> See: http://lists.llvm.org/pipermail/cfe-dev/2015-November/045846.html
> 
> Conclusion: disable fortify-source if we appear to be using clang instead
> of testing for compile success or failure, which may be incidental or not
> indicative of proper support of the feature.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  configure | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index 7a1d08d..4d74fcc 100755
> --- a/configure
> +++ b/configure
> @@ -261,6 +261,7 @@ rdma=""
>  gprof="no"
>  debug_tcg="no"
>  debug="no"
> +fortify_source=""
>  strip_opt="yes"
>  tcg_interpreter="no"
>  bigendian="no"
> @@ -876,6 +877,7 @@ for opt do
>        debug_tcg="yes"
>        debug="yes"
>        strip_opt="no"
> +      fortify_source="no"
>    ;;
>    --enable-sparse) sparse="yes"
>    ;;
> @@ -4435,6 +4437,19 @@ if ! compile_object "-Werror"; then
>      ccache_cpp2=yes
>  fi
>  
> +#################################################
> +# clang does not support glibc + FORTIFY_SOURCE.
> +
> +if test "$fortify_source" != "no"; then
> +  if echo | $cc -dM -E - | grep __clang__ > /dev/null 2>&1 ; then
> +    fortify_source="no";
> +  elif echo | $cxx -dM -E - | grep __clang__ > /dev/null 2>&1 ; then
> +    fortify_source="no";
> +  else
> +    fortify_source="yes"
> +  fi
> +fi
> +
>  ##########################################
>  # End of CC checks
>  # After here, no more $cc or $ld runs
> @@ -4442,7 +4457,7 @@ fi
>  if test "$gcov" = "yes" ; then
>    CFLAGS="-fprofile-arcs -ftest-coverage -g $CFLAGS"
>    LDFLAGS="-fprofile-arcs -ftest-coverage $LDFLAGS"
> -elif test "$debug" = "no" ; then
> +elif test "$fortify_source" = "yes" ; then
>    CFLAGS="-O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 $CFLAGS"
>  fi
>  
> 

Queued, thanks!

Paolo