[PATCH 4.19 284/421] powerpc/barrier: Avoid collision with clangs __lwsync macro

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 12:27:25 EST

From: Nathan Chancellor <nathan@xxxxxxxxxx>

commit 015d98149b326e0f1f02e44413112ca8b4330543 upstream.

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@xxxxxxxxxxxxxxx
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/1386
Link: https://github.com/llvm/llvm-project/commit/62b5df7fe2b3fda1772befeda15598fbef96a614
Link: https://lore.kernel.org/r/20210528182752.1852002-1-nathan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/powerpc/include/asm/barrier.h | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -44,6 +44,8 @@
# 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")