On Fri, Aug 9, 2019 at 1:13 PM Arnd Bergmann <a...@arndb.de> wrote:
>
> On Fri, Aug 9, 2019 at 10:02 PM Christophe Leroy
> <christophe.le...@c-s.fr> wrote:
> >
> > Arnd Bergmann <a...@arndb.de> a écrit :
> > > On Fri, Aug 9, 2019 at 8:21 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-li...@googlegroups.com> wrote:
> > >
> > >> static inline void dcbz(void *addr)
> > >> {
> > >> - __asm__ __volatile__ ("dcbz %y0" : : "Z"(*(u8 *)addr) :
> > >> "memory");
> > >> + __asm__ __volatile__ ("dcbz %y0" : "=Z"(*(u8 *)addr) ::
> > >> "memory");
> > >> }
> > >>
> > >> static inline void dcbi(void *addr)
> > >> {
> > >> - __asm__ __volatile__ ("dcbi %y0" : : "Z"(*(u8 *)addr) :
> > >> "memory");
> > >> + __asm__ __volatile__ ("dcbi %y0" : "=Z"(*(u8 *)addr) ::
> > >> "memory");
> > >> }
> > >
> > > I think the result of the discussion was that an output argument only
> > > kind-of
> > > makes sense for dcbz, but for the others it's really an input, and clang
> > > is
> > > wrong in the way it handles the "Z" constraint by making a copy, which it
> > > doesn't do for "m".
> > >
> > > I'm not sure whether it's correct to use "m" instead of "Z" here, which
> > > would be a better workaround if that works. More importantly though,
> > > clang really needs to be fixed to handle "Z" correctly.
> >
> > As the benefit is null, I think the best is probably to reverse my
> > original commit until at least CLang is fixed, as initialy suggested
> > by mpe
>
> Yes, makes sense.
>
> There is one other use of the "Z" constraint, so on top of the revert, I
> think it might be helpful if Nick could check if the patch below makes
> any difference with clang and, if it does, whether the current version
> is broken.
>
> Arnd
>
> diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h
> index 23e5d5d16c7e..28b467779328 100644
> --- a/arch/powerpc/include/asm/io.h
> +++ b/arch/powerpc/include/asm/io.h
> @@ -106,7 +106,7 @@ static inline u##size name(const volatile u##size
> __iomem *addr) \
> { \
> u##size ret; \
> __asm__ __volatile__("sync;"#insn" %0,%y1;twi 0,%0,0;isync" \
> - : "=r" (ret) : "Z" (*addr) : "memory"); \
> + : "=r" (ret) : "m" (*addr) : "memory"); \
> return ret; \
> }
>
> @@ -114,7 +114,7 @@ static inline u##size name(const volatile u##size
> __iomem *addr) \
> static inline void name(volatile u##size __iomem *addr, u##size val) \
> { \
> __asm__ __volatile__("sync;"#insn" %1,%y0" \
> - : "=Z" (*addr) : "r" (val) : "memory"); \
> + : "=m" (*addr) : "r" (val) : "memory"); \
> mmiowb_set_pending(); \
> }
Does not work:
https://travis-ci.com/ClangBuiltLinux/continuous-integration/builds/122654899
https://github.com/ClangBuiltLinux/continuous-integration/pull/197/files#diff-40bd16e3188587e4d648c30e0c2d6d37
--
Thanks,
~Nick Desaulniers
