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    Subject[PATCH AUTOSEL 4.9 24/50] lib/mpi: Fix 64-bit MIPS build with Clang
    Date
    From: Nathan Chancellor <natechancellor@gmail.com>

    [ Upstream commit 18f1ca46858eac22437819937ae44aa9a8f9f2fa ]

    When building 64r6_defconfig with CONFIG_MIPS32_O32 disabled and
    CONFIG_CRYPTO_RSA enabled:

    lib/mpi/generic_mpih-mul1.c:37:24: error: invalid use of a cast in a
    inline asm context requiring an l-value: remove the cast
    or build with -fheinous-gnu-extensions
    umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
    ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    lib/mpi/longlong.h:664:22: note: expanded from macro 'umul_ppmm'
    : "=d" ((UDItype)(w0))
    ~~~~~~~~~~^~~
    lib/mpi/generic_mpih-mul1.c:37:13: error: invalid use of a cast in a
    inline asm context requiring an l-value: remove the cast
    or build with -fheinous-gnu-extensions
    umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
    ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    lib/mpi/longlong.h:668:22: note: expanded from macro 'umul_ppmm'
    : "=d" ((UDItype)(w1))
    ~~~~~~~~~~^~~
    2 errors generated.

    This special case for umul_ppmm for MIPS64r6 was added in
    commit bbc25bee37d2b ("lib/mpi: Fix umul_ppmm() for MIPS64r6"), due to
    GCC being inefficient and emitting a __multi3 intrinsic.

    There is no such issue with clang; with this patch applied, I can build
    this configuration without any problems and there are no link errors
    like mentioned in the commit above (which I can still reproduce with
    GCC 9.3.0 when that commit is reverted). Only use this definition when
    GCC is being used.

    This really should have been caught by commit b0c091ae04f67 ("lib/mpi:
    Eliminate unused umul_ppmm definitions for MIPS") when I was messing
    around in this area but I was not testing 64-bit MIPS at the time.

    Link: https://github.com/ClangBuiltLinux/linux/issues/885
    Reported-by: Dmitry Golovin <dima@golovin.in>
    Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    lib/mpi/longlong.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
    index 8f383cca6bb1..623440d3d365 100644
    --- a/lib/mpi/longlong.h
    +++ b/lib/mpi/longlong.h
    @@ -671,7 +671,7 @@ do { \
    ************** MIPS/64 **************
    ***************************************/
    #if (defined(__mips) && __mips >= 3) && W_TYPE_SIZE == 64
    -#if defined(__mips_isa_rev) && __mips_isa_rev >= 6
    +#if defined(__mips_isa_rev) && __mips_isa_rev >= 6 && defined(CONFIG_CC_IS_GCC)
    /*
    * GCC ends up emitting a __multi3 intrinsic call for MIPS64r6 with the plain C
    * code below, so we special case MIPS64r6 until the compiler can do better.
    --
    2.25.1
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