Re: [PATCH 3/4] configure: propagate --extra-cflags and --extra-ldflags to meson compile tests

[Thomas Huth <thuth@redhat.com>]

On 08/11/2021 09.43, Paolo Bonzini wrote:
> Meson (intentionally) does not add QEMU_CFLAGS to cc.compiles/cc.links
> tests, as they are supposed to be independent of the specific sets of
> compilation flags used to build the programs.  However, the user can
> still use CFLAGS or the toolchain file's LANG_args/LANG_link_args option
> to specify -I or -L options that apply to cc.compiles/cc.links as well.
> 
> This is also the intended use of configure's --extra-cflags,
> --extra-cxxflags and --extra-ldflags options.  For example, if
> one has netmap's header in a nonstandard directory, up to commit
> 837b84b1c078bf3e909 it used to work fine to do:
> 
> .../configure --enable-netmap \
>       --extra-cflags=-I/path/to/netmap/sys
> 
> but since the test was converted to meson, this does not work anymore.
> 
> Pass these options to meson via the toolchain file instead of via
> config-host.mak, since the toolchain file's variables have the
> same purpose as configure's --extra-*flags arguments.
> 
> Reported-by: Owen LaGarde
> Reported-by: Thomas Huth <thuth@redhat.com>
> Fixes: 47b30835e4 ("configure: consistently pass CFLAGS/CXXFLAGS/LDFLAGS to meson", 2020-10-06)
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   configure | 36 ++++++++++++++++++++----------------
>   1 file changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/configure b/configure
> index d268f59246..1ea26c67e5 100755
> --- a/configure
> +++ b/configure
> @@ -174,14 +174,14 @@ update_cxxflags() {
>   
>   compile_object() {
>     local_cflags="$1"
> -  do_cc $CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -c -o $TMPO $TMPC
> +  do_cc $CFLAGS $EXTRA_CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -c -o $TMPO $TMPC
>   }
>   
>   compile_prog() {
>     local_cflags="$1"
>     local_ldflags="$2"
> -  do_cc $CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC \
> -      $LDFLAGS $CONFIGURE_LDFLAGS $QEMU_LDFLAGS $local_ldflags
> +  do_cc $CFLAGS $EXTRA_CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC \
> +      $LDFLAGS $EXTRA_LDFLAGS $CONFIGURE_LDFLAGS $QEMU_LDFLAGS $local_ldflags
>   }
>   
>   # symbolically link $1 to $2.  Portable version of "ln -sf".
> @@ -286,6 +286,10 @@ for opt do
>     esac
>   done
>   
> +EXTRA_CFLAGS=""
> +EXTRA_CXXFLAGS=""
> +EXTRA_LDFLAGS=""
> +
>   xen_ctrl_version="$default_feature"
>   xfs="$default_feature"
>   membarrier="$default_feature"
> @@ -394,13 +398,13 @@ for opt do
>     ;;
>     --cpu=*) cpu="$optarg"
>     ;;
> -  --extra-cflags=*) QEMU_CFLAGS="$QEMU_CFLAGS $optarg"
> -                    QEMU_LDFLAGS="$QEMU_LDFLAGS $optarg"
> +  --extra-cflags=*)
> +    EXTRA_CFLAGS="$EXTRA_CFLAGS $optarg"
> +    EXTRA_CXXFLAGS="$EXTRA_CXXFLAGS $optarg"

I'd rather drop that EXTRA_CXXFLAGS line here - I think that calls for 
trouble otherwise if a user is trying to add a C compiler option that is not 
supported in C++ mode.
If the users have some options that need to be passed to both, C and C++, 
they should simply use --extra-cxxflags in addition instead.

  Thomas

> +    ;;
> +  --extra-cxxflags=*) EXTRA_CXXFLAGS="$EXTRA_CXXFLAGS $optarg"
>     ;;
> -  --extra-cxxflags=*) QEMU_CXXFLAGS="$QEMU_CXXFLAGS $optarg"
> -  ;;
> -  --extra-ldflags=*) QEMU_LDFLAGS="$QEMU_LDFLAGS $optarg"
> -                     EXTRA_LDFLAGS="$optarg"
> +  --extra-ldflags=*) EXTRA_LDFLAGS="$EXTRA_LDFLAGS $optarg"
>     ;;
>     --enable-debug-info) debug_info="yes"
>     ;;