Re: [PATCH 4/4] configure: ignore preexisting QEMU_*FLAGS envvars

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 11/8/21 09:43, Paolo Bonzini wrote:
> User flags should be passed via CFLAGS/CXXFLAGS/LDFLAGS,
> or --extra-cflags/extra-cxxflags/--extra-ldflags on the
> command line.
> 
> QEMU_CFLAGS, QEMU_CXXFLAGS and QEMU_LDFLAGS are reserved
> for flags detected by configure, so do not add to them
> and clear them at the beginning of the script.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  configure | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/configure b/configure
> index 1ea26c67e5..2048a52b20 100755
> --- a/configure
> +++ b/configure
> @@ -158,7 +158,7 @@ update_cxxflags() {
>      # Set QEMU_CXXFLAGS from QEMU_CFLAGS by filtering out those
>      # options which some versions of GCC's C++ compiler complain about
>      # because they only make sense for C programs.
> -    QEMU_CXXFLAGS="$QEMU_CXXFLAGS -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS"
> +    QEMU_CXXFLAGS="-D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS"
>      CONFIGURE_CXXFLAGS=$(echo "$CONFIGURE_CFLAGS" | sed s/-std=gnu11/-std=gnu++11/)
>      for arg in $QEMU_CFLAGS; do
>          case $arg in

update_cxxflags() should keep previous QEMU_CXXFLAGS. But since
we call it only once, we don't use it to update. IMHO we should
inline this code where it is called, then overwriting QEMU_CXXFLAGS
makes sense.