Re: [Qemu-devel] [PATCH] qemu-barrier: Fix compiler version check for future gcc versions

[Stefan Weil]

Am 08.10.2012 22:01, schrieb Michael S. Tsirkin:
> On Wed, Oct 03, 2012 at 11:11:02PM +0200, Stefan Weil wrote:
> > The current check will give a wrong result for gcc-5.x with x < 4.
> > Using QEMU_GNUC_PREREQ is simpler and fixes that issue.
> >
> > Signed-off-by: Stefan Weil <address@hidden>
> > ---
> >
> > With current gcc versions (gcc-4.x) there is no problem.
> > Nevertheless, I suggest to fix this in stable versions, too.
> >
> > Regards
> >
> > Stefan Weil
> ACK for stable tree.
>
> >   qemu-barrier.h |    2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/qemu-barrier.h b/qemu-barrier.h
> > index 7e11197..16f0942 100644
> > --- a/qemu-barrier.h
> > +++ b/qemu-barrier.h
> > @@ -19,7 +19,7 @@
> >    * mfence on 32 bit as well, e.g. if built with -march=pentium-m.
> >    * However, on i386, there seem to be known bugs as recently as 4.3.
> >    * */
> > -#if defined(__GNUC__) && __GNUC__ >= 4 && __GNUC_MINOR__ >= 4
> > +#if QEMU_GNUC_PREREQ(4, 4)
> >   #define smp_mb() __sync_synchronize()
> >   #else
> >   #define smp_mb() asm volatile("lock; addl $0,0(%%esp) " ::: "memory")
> > --
> > 1.7.10

My patch was incomplete: an include statement for compiler.h
is needed (see the patches which were applied to the same file in
git master.

Regards

Stefan Weil