From: Christophe Leroy <christophe.leroy@c-s.fr> To: Nathan Chancellor <natechancellor@gmail.com>, Nick Desaulniers <ndesaulniers@google.com> Cc: mpe@ellerman.id.au, segher@kernel.crashing.org, arnd@arndb.de, kbuild test robot <lkp@intel.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH] powerpc: workaround clang codegen bug in dcbz Date: Tue, 30 Jul 2019 07:31:23 +0200 [thread overview] Message-ID: <8f2331db-151f-a481-23e0-ec6dd9ba6f1c@c-s.fr> (raw) In-Reply-To: <20190729203246.GA117371@archlinux-threadripper> Le 29/07/2019 à 22:32, Nathan Chancellor a écrit : > 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. Your example functions are too simple to show anything. The functions takes only one parameter so of course GCC won't use two registers allthough given the opportunity. Christophe > > Either way: > > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> >
WARNING: multiple messages have this Message-ID (diff)
From: Christophe Leroy <christophe.leroy@c-s.fr> To: Nathan Chancellor <natechancellor@gmail.com>, 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: Tue, 30 Jul 2019 07:31:23 +0200 [thread overview] Message-ID: <8f2331db-151f-a481-23e0-ec6dd9ba6f1c@c-s.fr> (raw) In-Reply-To: <20190729203246.GA117371@archlinux-threadripper> Le 29/07/2019 à 22:32, Nathan Chancellor a écrit : > 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. Your example functions are too simple to show anything. The functions takes only one parameter so of course GCC won't use two registers allthough given the opportunity. Christophe > > Either way: > > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> >
next prev parent reply other threads:[~2019-07-30 5:31 UTC|newest] Thread overview: 52+ 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 20:25 ` Nick Desaulniers 2019-07-29 20:32 ` Nathan Chancellor 2019-07-29 20:32 ` Nathan Chancellor 2019-07-29 20:45 ` Nick Desaulniers 2019-07-29 20:45 ` Nick Desaulniers 2019-07-29 20:47 ` Nathan Chancellor 2019-07-29 20:47 ` Nathan Chancellor 2019-07-29 20:49 ` Nick Desaulniers 2019-07-29 20:49 ` Nick Desaulniers 2019-07-29 21:52 ` Segher Boessenkool 2019-07-29 21:52 ` Segher Boessenkool 2019-07-30 7:34 ` Arnd Bergmann 2019-07-30 7:34 ` Arnd Bergmann 2019-07-30 11:17 ` Michael Ellerman 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 18:21 ` Nick Desaulniers 2019-08-09 18:28 ` Arnd Bergmann 2019-08-09 18:28 ` Arnd Bergmann 2019-08-09 20:03 ` Christophe Leroy 2019-08-09 20:03 ` Christophe Leroy 2019-08-09 20:12 ` Arnd Bergmann 2019-08-09 20:12 ` Arnd Bergmann 2019-08-09 22:03 ` Nick Desaulniers 2019-08-09 22:03 ` Nick Desaulniers 2019-08-09 22:10 ` Segher Boessenkool 2019-08-09 22:10 ` Segher Boessenkool 2019-08-09 22:00 ` Segher Boessenkool 2019-08-09 22:00 ` Segher Boessenkool 2019-08-09 22:03 ` [PATCH v3] Revert "powerpc: slightly improve cache helpers" Nick Desaulniers 2019-08-09 22:03 ` Nick Desaulniers 2019-08-10 9:09 ` Michael Ellerman 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 21:55 ` Segher Boessenkool 2019-08-09 20:36 ` Nathan Chancellor 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 13:48 ` Segher Boessenkool 2019-07-30 14:30 ` Arnd Bergmann 2019-07-30 14:30 ` Arnd Bergmann 2019-07-30 16:16 ` Segher Boessenkool 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 18:24 ` Arnd Bergmann 2019-07-30 19:35 ` Segher Boessenkool 2019-07-30 19:35 ` Segher Boessenkool 2019-07-30 5:31 ` Christophe Leroy [this message] 2019-07-30 5:31 ` Christophe Leroy
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