Re: [Qemu-devel] [PATCH v2] configure: Force the C standard to gnu99

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jan 09, 2019 at 03:24:29PM +0100, Thomas Huth wrote:
> Different versions of GCC and Clang use different versions of the C standard.
> This repeatedly caused problems already, e.g. with duplicated typedefs:
> 
>  https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg05829.html
> 
> or with for-loop variable initializers:
> 
>  https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg00237.html
> 
> To avoid these problems, we should enforce the C language version to the
> same level for all compilers. Since our minimum compiler versions is
> GCC v4.8, our best option is "gnu99" right now ("gnu17" is not available
> there yet, and "gnu11" is marked as "experimental").
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2: Use gnu99 instead of gnu11
> 
>  configure | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


> 
> diff --git a/configure b/configure
> index b9f34af..721ade7 100755
> --- a/configure
> +++ b/configure
> @@ -105,7 +105,8 @@ update_cxxflags() {
>      for arg in $QEMU_CFLAGS; do
>          case $arg in
>              -Wstrict-prototypes|-Wmissing-prototypes|-Wnested-externs|\
> -            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls)
> +            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls|\
> +            -std=gnu99)

IIUC this is to  drop  -std=gnu99 from CXXFLAGS, so C++ code (only the
guest-agent on Win32 IIUC) will use the compiler default still. No worse
than what we have today.

We could consider also setting a suitable -std for CXXFLAGS too in future
though...

>                  ;;
>              *)
>                  QEMU_CXXFLAGS=${QEMU_CXXFLAGS:+$QEMU_CXXFLAGS }$arg
> @@ -585,7 +586,7 @@ ARFLAGS="${ARFLAGS-rv}"
>  # left shift of signed integers is well defined and has the expected
>  # 2s-complement style results. (Both clang and gcc agree that it
>  # provides these semantics.)
> -QEMU_CFLAGS="-fno-strict-aliasing -fno-common -fwrapv $QEMU_CFLAGS"
> +QEMU_CFLAGS="-fno-strict-aliasing -fno-common -fwrapv -std=gnu99 $QEMU_CFLAGS"
>  QEMU_CFLAGS="-Wall -Wundef -Wwrite-strings -Wmissing-prototypes $QEMU_CFLAGS"
>  QEMU_CFLAGS="-Wstrict-prototypes -Wredundant-decls $QEMU_CFLAGS"
>  QEMU_CFLAGS="-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE $QEMU_CFLAGS"

Regards,
Daniel
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