powerpc/barrier: Avoid collision with clang's __lwsync macro

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 [email protected]

Link https://github.com/ClangBuiltLinux/linux/issues/1386

Link https://github.com/llvm/llvm-project/commit/62b5df7fe2b3fda1772befeda15598fbef96a614

Signed-off-by Nathan Chancellor <[email protected]>

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

arch/powerpc/include/asm/barrier.h +2 -0

index 7ae29cfb06c0..f0e687236484 100644
@@ -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

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.

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