From: Nathan Chancellor <natechancellor@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: arnd@arndb.de, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org, kbuild test robot <lkp@intel.com>
Subject: Re: [PATCH] powerpc: workaround clang codegen bug in dcbz
Date: Mon, 29 Jul 2019 13:32:46 -0700 [thread overview]
Message-ID: <20190729203246.GA117371@archlinux-threadripper> (raw)
In-Reply-To: <20190729202542.205309-1-ndesaulniers@google.com>
On Mon, Jul 29, 2019 at 01:25:41PM -0700, Nick Desaulniers wrote:
> Commit 6c5875843b87 ("powerpc: slightly improve cache helpers") exposed
> what looks like a codegen bug in Clang's handling of `%y` output
> template with `Z` constraint. This is resulting in panics during boot
> for 32b powerpc builds w/ Clang, as reported by our CI.
>
> Add back the original code that worked behind a preprocessor check for
> __clang__ until we can fix LLVM.
>
> Further, it seems that clang allnoconfig builds are unhappy with `Z`, as
> reported by 0day bot. This is likely because Clang warns about inline
> asm constraints when the constraint requires inlining to be semantically
> valid.
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=42762
> Link: https://github.com/ClangBuiltLinux/linux/issues/593
> Link: https://lore.kernel.org/lkml/20190721075846.GA97701@archlinux-threadripper/
> Debugged-by: Nathan Chancellor <natechancellor@gmail.com>
> Reported-by: Nathan Chancellor <natechancellor@gmail.com>
> Reported-by: kbuild test robot <lkp@intel.com>
> Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Alternatively, we could just revert 6c5875843b87. It seems that GCC
> generates the same code for these functions for out of line versions.
> But I'm not sure how the inlined code generated would be affected.
For the record:
https://godbolt.org/z/z57VU7
This seems consistent with what Michael found so I don't think a revert
is entirely unreasonable.
Either way:
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
next prev parent reply other threads:[~2019-07-29 20:39 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 [this message]
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
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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