From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Paul Mackerras <paulus@samba.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
kbuild test robot <lkp@intel.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Segher Boessenkool <segher@kernel.crashing.org>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] powerpc: fix inline asm constraints for dcbz
Date: Fri, 9 Aug 2019 15:03:30 -0700 [thread overview]
Message-ID: <CAKwvOdmhUPTUPa3=_AQ04zEDTsScduqOM29TfK656riAb_t=rQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1AwmAe+PpHTRmN153fhG4ZkF_pb+240rj1ZAg-S6SKeg@mail.gmail.com>
On Fri, Aug 9, 2019 at 1:13 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Aug 9, 2019 at 10:02 PM Christophe Leroy
> <christophe.leroy@c-s.fr> wrote:
> >
> > Arnd Bergmann <arnd@arndb.de> a écrit :
> > > On Fri, Aug 9, 2019 at 8:21 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-linux@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
next prev parent reply other threads:[~2019-08-09 22:03 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 20:25 [PATCH] powerpc: workaround clang codegen bug in dcbz Nick Desaulniers
2019-07-29 20:32 ` Nathan Chancellor
2019-07-29 20:45 ` Nick Desaulniers
2019-07-29 20:47 ` Nathan Chancellor
2019-07-29 20:49 ` Nick Desaulniers
2019-07-29 21:52 ` Segher Boessenkool
2019-07-30 7:34 ` Arnd Bergmann
2019-07-30 11:17 ` Michael Ellerman
2019-08-09 18:21 ` [PATCH] powerpc: fix inline asm constraints for dcbz Nick Desaulniers
2019-08-09 18:28 ` Arnd Bergmann
2019-08-09 20:03 ` Christophe Leroy
2019-08-09 20:12 ` Arnd Bergmann
2019-08-09 22:03 ` Nick Desaulniers [this message]
2019-08-09 22:10 ` Segher Boessenkool
2019-08-09 22:00 ` Segher Boessenkool
2019-08-09 22:03 ` [PATCH v3] Revert "powerpc: slightly improve cache helpers" Nick Desaulniers
2019-08-10 9:09 ` Michael Ellerman
2019-08-09 21:55 ` [PATCH] powerpc: fix inline asm constraints for dcbz Segher Boessenkool
2019-08-09 20:36 ` Nathan Chancellor
2019-07-30 13:48 ` [PATCH] powerpc: workaround clang codegen bug in dcbz Segher Boessenkool
2019-07-30 14:30 ` Arnd Bergmann
2019-07-30 16:16 ` Segher Boessenkool
2019-07-30 17:07 ` Segher Boessenkool
2019-07-30 18:24 ` Arnd Bergmann
2019-07-30 18:24 ` Arnd Bergmann
2019-07-30 19:35 ` Segher Boessenkool
2019-07-30 5:31 ` Christophe Leroy
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