linux-kernel - [PATCH] powerpc: fix inline asm constraints for dcbz

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Message-Id: <20190809182106.62130-1-ndesaulniers@google.com>
Date:   Fri,  9 Aug 2019 11:21:05 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     mpe@...erman.id.au
Cc:     christophe.leroy@....fr, segher@...nel.crashing.org, arnd@...db.de,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        kbuild test robot <lkp@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH] powerpc: fix inline asm constraints for dcbz

The input parameter is modified, so it should be an output parameter
with "=" to make it so that a copy of the input is not made by Clang.

Link: https://bugs.llvm.org/show_bug.cgi?id=42762
Link: https://gcc.gnu.org/onlinedocs/gcc/Modifiers.html#Modifiers
Link: https://github.com/ClangBuiltLinux/linux/issues/593
Link: https://godbolt.org/z/QwhZXi
Link: https://lore.kernel.org/lkml/20190721075846.GA97701@archlinux-threadripper/
Fixes: 6c5875843b87 ("powerpc: slightly improve cache helpers")
Debugged-by: Nathan Chancellor <natechancellor@...il.com>
Reported-by: Nathan Chancellor <natechancellor@...il.com>
Reported-by: kbuild test robot <lkp@...el.com>
Suggested-by: Arnd Bergmann <arnd@...db.de>
Suggested-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Green CI run:
https://travis-ci.com/ClangBuiltLinux/continuous-integration/builds/122521976
https://github.com/ClangBuiltLinux/continuous-integration/pull/197/files#diff-40bd16e3188587e4d648c30e0c2d6d37

 arch/powerpc/include/asm/cache.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
index b3388d95f451..5a0df6a1b9dc 100644
--- a/arch/powerpc/include/asm/cache.h
+++ b/arch/powerpc/include/asm/cache.h
@@ -107,22 +107,22 @@ extern void _set_L3CR(unsigned long);
 
 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");
 }
 
 static inline void dcbf(void *addr)
 {
-	__asm__ __volatile__ ("dcbf %y0" : : "Z"(*(u8 *)addr) : "memory");
+	__asm__ __volatile__ ("dcbf %y0" : "=Z"(*(u8 *)addr) :: "memory");
 }
 
 static inline void dcbst(void *addr)
 {
-	__asm__ __volatile__ ("dcbst %y0" : : "Z"(*(u8 *)addr) : "memory");
+	__asm__ __volatile__ ("dcbst %y0" : "=Z"(*(u8 *)addr) :: "memory");
 }
 #endif /* !__ASSEMBLY__ */
 #endif /* __KERNEL__ */
-- 
2.23.0.rc1.153.gdeed80330f-goog