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From: Nathan Chancellor <>
To: Michael Ellerman <>
Cc: Benjamin Herrenschmidt <>,
	Paul Mackerras <>,
	Nick Desaulniers <>,,,,
	Nathan Chancellor <>,
Subject: [PATCH] powerpc/barrier: Avoid collision with clang's __lwsync macro
Date: Fri, 28 May 2021 11:27:52 -0700	[thread overview]
Message-ID: <> (raw)

A change in clang 13 results in the __lwsync macro being defined as
__builtin_ppc_lwsync, which emits 'lwsync' or 'msync' depending on what
the target supports. This breaks the build because of -Werror in
arch/powerpc, along with thousands of warnings:

 In file included from arch/powerpc/kernel/pmc.c:12:
 In file included from include/linux/bug.h:5:
 In file included from arch/powerpc/include/asm/bug.h:109:
 In file included from include/asm-generic/bug.h:20:
 In file included from include/linux/kernel.h:12:
 In file included from include/linux/bitops.h:32:
 In file included from arch/powerpc/include/asm/bitops.h:62:
 arch/powerpc/include/asm/barrier.h:49:9: error: '__lwsync' macro redefined [-Werror,-Wmacro-redefined]
 #define __lwsync()      __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
 <built-in>:308:9: note: previous definition is here
 #define __lwsync __builtin_ppc_lwsync
 1 error generated.

Undefine this macro so that the runtime patching introduced by
commit 2d1b2027626d ("powerpc: Fixup lwsync at runtime") continues to
work properly with clang and the build no longer breaks.

Signed-off-by: Nathan Chancellor <>
 arch/powerpc/include/asm/barrier.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index 7ae29cfb06c0..f0e687236484 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -46,6 +46,8 @@
 #    define SMPWMB      eieio
+/* clang defines this macro for a builtin, which will not work with runtime patching */
+#undef __lwsync
 #define __lwsync()	__asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
 #define dma_rmb()	__lwsync()
 #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")

base-commit: 97e5bf604b7a0d6e1b3e00fe31d5fd4b9bffeaae

             reply	other threads:[~2021-05-28 18:29 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-28 18:27 Nathan Chancellor [this message]
2021-06-01 18:23 ` Nick Desaulniers
2021-06-18  3:51 ` Michael Ellerman

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