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Date:   Fri, 9 Aug 2019 17:10:52 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
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>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH] powerpc: fix inline asm constraints for dcbz
Message-ID: <20190809221052.GP31406@gate.crashing.org>
References: <87h873zs88.fsf@concordia.ellerman.id.au> <20190809182106.62130-1-ndesaulniers@google.com> <CAK8P3a3LynWTbpV8=VPm2TqgNM2MnoEyCPJd0PL2D+tcZqJgHg@mail.gmail.com> <20190809220301.Horde.AR6y4Bx4WGIq58V9K0En9g4@messagerie.si.c-s.fr> <CAK8P3a1AwmAe+PpHTRmN153fhG4ZkF_pb+240rj1ZAg-S6SKeg@mail.gmail.com>
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On Fri, Aug 09, 2019 at 10:12:56PM +0200, Arnd Bergmann wrote:
> @@ -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;                                                     \
>  }

That will no longer compile something like
  u8 *p;
  u16 x = in_le16(p + 12);
(you'll get something like "invalid %y value, try using the 'Z' constraint").

So then you remove the %y, but that makes you get something like
  sync;lhbrx 3,12(3);twi 0,3,0;isync
which is completely wrong.


Segher