Re: [Qemu-devel] [PATCH] build: disable -Wmissing-braces on older compilers

[Laszlo Ersek <lersek@redhat.com>]

On 10/20/17 12:12, Paolo Bonzini wrote:
> GCC 4.9 and newer stopped warning for missing braces around the
> "universal" C zero initializer {0}.  One such initializer sneaked

s/sneaked/snuck/

Hmmm, no, wait, both forms are valid!

https://en.wiktionary.org/wiki/sneaked
https://en.wiktionary.org/wiki/snuck

    The irregular form snuck originated by analogy with struck for the
    past of strike. Snuck was originally limited to a few dialects, but
    is now very widespread (especially in American English) and is
    recognized by most dictionaries. The word is now one of the best
    examples of irregularization of a regular verb, along with dove.

> into scsi/qemu-pr-helper.c and is breaking the build with such
> older GCC versions.
> 
> Detect the lack of support for the idiom, and disable the warning
> in that case.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>         Of course it's always possible to use "memset", but {0}
>         is neater in my opinion.

Strongly agree.

> 
>  configure | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/configure b/configure
> index 7766e74125..0b2d595c6e 100755
> --- a/configure
> +++ b/configure
> @@ -1651,6 +1651,19 @@ EOF
>    fi
>  fi
>  
> +# Disable -Wmissing-braces on older compilers that warn even for
> +# the "universal" C zero initializer {0}.
> +cat > $TMPC << EOF
> +struct {
> +  int a[2];
> +} x = {0};
> +EOF
> +if compile_object "-Werror" "" ; then
> +  :
> +else

Is this an established idiom for the configure script, in place of:

  if ! compile_object "-Werror" "" ; then

?

Looks good to me otherwise.

Thanks!
Laszlo

> +  QEMU_CFLAGS="$QEMU_CFLAGS -Wno-missing-braces"
> +fi
> +
>  # Workaround for http://gcc.gnu.org/PR55489.  Happens with -fPIE/-fPIC and
>  # large functions that use global variables.  The bug is in all releases of
>  # GCC, but it became particularly acute in 4.6.x and 4.7.x.  It is fixed in
>