Re: [PATCH for-8.0 15/29] include/qemu/int128: Add vector type to Int128Alias

[Philippe Mathieu-Daudé]

On 22/11/22 19:21, Philippe Mathieu-Daudé wrote:
> On 18/11/22 10:47, Richard Henderson wrote:
> > Adding a vector type will make it easier to handle i386
> > have_atomic16 via AVX.
> >
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> >   include/qemu/int128.h | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/qemu/int128.h b/include/qemu/int128.h
> > index f62a46b48c..f29f90e6f4 100644
> > --- a/include/qemu/int128.h
> > +++ b/include/qemu/int128.h
> > @@ -479,16 +479,16 @@ static inline void bswap128s(Int128 *s)
> >   /*
> >    * When compiler supports a 128-bit type, define a combination of
> >    * a possible structure and the native types.  Ease parameter passing
> > - * via use of the transparent union extension.
> > + * via use of the transparent union extension.  Provide a vector type
> > + * for use in atomicity on some hosts.
> >    */
> > -#ifdef CONFIG_INT128
> >   typedef union {
> >       Int128 s;
> > +    uint64_t v __attribute__((vector_size(16)));
> > +#ifdef CONFIG_INT128
> >       __int128_t i;
> >       __uint128_t u;
> > -} Int128Alias __attribute__((transparent_union));
> > -#else
> > -typedef Int128 Int128Alias;
> >   #endif /* CONFIG_INT128 */
> > +} Int128Alias __attribute__((transparent_union));
> >   #endif /* INT128_H */
>
> This triggers a warning with GCC:

Ah no, looking closer, even configured as ''--cc=gcc-12 --host-cc=gcc-12
--cxx=/bin/false', Clang got selected for ObjC, and this warning comes
from it:

Compiling Objective-C object libcommon.fa.p/ui_cocoa.m.o
In file included from ../../ui/cocoa.m:36:
In file included from include/sysemu/sysemu.h:5:
In file included from include/qemu/timer.h:4:
In file included from include/qemu/bitops.h:16:
In file included from include/qemu/host-utils.h:35:

> include/qemu/int128.h:487:14: warning: alignment of field 'v' (128 bits) 
> does not match the alignment of the first field in transparent union; 
> transparent_union attribute ignored [-Wignored-attributes]
>      uint64_t v __attribute__((vector_size(16)));
>               ^
> include/qemu/int128.h:486:12: note: alignment of first field is 64 bits
>      Int128 s;
>             ^
> Meson:
>
> Project version: 7.1.91
> C compiler for the host machine: gcc-12 (gcc 12.2.0 "gcc-12 (Homebrew 
> GCC 12.2.0) 12.2.0")
> C linker for the host machine: gcc-12 ld64 819.6
> Host machine cpu family: aarch64
> Host machine cpu: arm64

Objective-C compiler for the host machine: clang (clang 14.0.0)
Objective-C linker for the host machine: clang ld64 819.6

Regards,

Phil.