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    Subject[PATCH 5.13 183/266] powerpc/barrier: Avoid collision with clangs __lwsync macro
    Date
    From: Nathan Chancellor <nathan@kernel.org>

    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@vger.kernel.org
    Signed-off-by: Nathan Chancellor <nathan@kernel.org>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    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@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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
    @@ -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")

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