Re: [Qemu-devel] [PATCH] configure: Force the C standard to gnu11

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

On Mon, Jan 07, 2019 at 11:45:26AM +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 are
> GCC v4.8 and Clang v3.4 now, and both basically support "gnu11" already,
> this seems to be a good choice.

In 4.x   gnu11 is marked as experimental. I'm not really comfortable
using experimental features - even if its warning free there's a risk
it would silently mis-compile something.

gnu99 is ok with 4.x - it is merely "incomplete".

> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  configure | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index 79375af..07f8105 100755
> --- a/configure
> +++ b/configure
> @@ -107,6 +107,9 @@ update_cxxflags() {
>              -Wstrict-prototypes|-Wmissing-prototypes|-Wnested-externs|\
>              -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls)
>                  ;;
> +            -std=gnu11)
> +                QEMU_CXXFLAGS=${QEMU_CXXFLAGS:+$QEMU_CXXFLAGS }-std=gnu++11
> +                ;;
>              *)
>                  QEMU_CXXFLAGS=${QEMU_CXXFLAGS:+$QEMU_CXXFLAGS }$arg
>                  ;;
> @@ -585,7 +588,7 @@ ARFLAGS="${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=gnu11 $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"
> -- 
> 1.8.3.1
> 

Regards,
Daniel
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