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From:   Nathan Chancellor <nathan@kernel.org>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Nathan Chancellor <nathan@kernel.org>, stable@vger.kernel.org
Subject: [PATCH] powerpc/barrier: Avoid collision with clang's __lwsync macro
Date:   Fri, 28 May 2021 11:27:52 -0700
Message-Id: <20210528182752.1852002-1-nathan@kernel.org>
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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.

Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/1386
Link: https://github.com/llvm/llvm-project/commit/62b5df7fe2b3fda1772befeda15598fbef96a614
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 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
 #endif
 
+/* 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
-- 
2.32.0.rc0