[libvirt] [PATCH] Improve compiler flag checking

[Daniel P. Berrange]

On Sat, Dec 20, 2008 at 08:49:01AM -0800, john.levon at sun.com wrote:
> # HG changeset patch
> # User john.levon at sun.com
> # Date 1229789393 28800
> # Node ID a158bbc6df6fb8b15af875d08e73cfd3ca75f907
> # Parent  34706075e6c801cd9532490c11b20b64dfcf464b
> Improve compiler flag checking
> 
> Some compilers (including GCC) don't set the return value consistently
> if an erroneous option is passed on the command line. Account for that.
> 
> Signed-off-by: John Levon <john.levon at sun.com>

ACK to this patch.

> diff --git a/acinclude.m4 b/acinclude.m4
> --- a/acinclude.m4
> +++ b/acinclude.m4
> @@ -45,21 +45,9 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
>  	;;
>      esac
>  
> -    compiler_flags=
> +    COMPILER_FLAGS=
>      for option in $try_compiler_flags; do
> -	SAVE_CFLAGS="$CFLAGS"
> -	CFLAGS="$CFLAGS $option"
> -	AC_MSG_CHECKING([whether gcc understands $option])
> -	AC_TRY_LINK([], [],
> -		has_option=yes,
> -		has_option=no,)
> -	CFLAGS="$SAVE_CFLAGS"
> -	AC_MSG_RESULT($has_option)
> -	if test $has_option = yes; then
> -	  compiler_flags="$compiler_flags $option"
> -	fi
> -	unset has_option
> -	unset SAVE_CFLAGS
> +        gl_COMPILER_FLAGS($option)
>      done
>      unset option
>      unset try_compiler_flags
> @@ -85,7 +73,7 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
>      fi
>      AC_MSG_RESULT($complCFLAGS)
>  
> -    WARN_CFLAGS="$compiler_flags $complCFLAGS"
> +    WARN_CFLAGS="$COMPILER_FLAGS $complCFLAGS"
>      AC_SUBST(WARN_CFLAGS)
>  
>      dnl Needed to keep compile quiet on python 2.4
> diff --git a/m4/compiler-flags.m4 b/m4/compiler-flags.m4
> --- a/m4/compiler-flags.m4
> +++ b/m4/compiler-flags.m4
> @@ -25,10 +25,16 @@ AC_DEFUN([gl_COMPILER_FLAGS],
>     AC_SUBST(COMPILER_FLAGS)
>     ac_save_CFLAGS="$CFLAGS"
>     CFLAGS="$CFLAGS $1"
> -   AC_TRY_COMPILE(,
> -    [int x;],
> -    COMPILER_FLAGS="$COMPILER_FLAGS $1"
> -    AC_MSG_RESULT(yes),
> -    AC_MSG_RESULT(no))
> -  CFLAGS="$ac_save_CFLAGS"
> +   AC_TRY_LINK([], [], has_option=yes, has_option=no,)
> +   echo 'int x;' >conftest.c
> +   $CC $CFLAGS -c conftest.c 2>conftest.err
> +   ret=$?
> +   if test $ret != 0 -o -s conftest.err -o $has_option = "no"; then
> +       AC_MSG_RESULT(no)
> +   else
> +       AC_MSG_RESULT(yes)
> +       COMPILER_FLAGS="$COMPILER_FLAGS $1"
> +   fi
> +   CFLAGS="$ac_save_CFLAGS"
> +   rm -f conftest*
>   ])


Daniel
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