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    Subject[PATCH 4.4 12/34] lib/mpi: Fix umul_ppmm() for MIPS64r6
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: James Hogan <jhogan@kernel.org>


    [ Upstream commit bbc25bee37d2b32cf3a1fab9195b6da3a185614a ]

    Current MIPS64r6 toolchains aren't able to generate efficient
    DMULU/DMUHU based code for the C implementation of umul_ppmm(), which
    performs an unsigned 64 x 64 bit multiply and returns the upper and
    lower 64-bit halves of the 128-bit result. Instead it widens the 64-bit
    inputs to 128-bits and emits a __multi3 intrinsic call to perform a 128
    x 128 multiply. This is both inefficient, and it results in a link error
    since we don't include __multi3 in MIPS linux.

    For example commit 90a53e4432b1 ("cfg80211: implement regdb signature
    checking") merged in v4.15-rc1 recently broke the 64r6_defconfig and
    64r6el_defconfig builds by indirectly selecting MPILIB. The same build
    errors can be reproduced on older kernels by enabling e.g. CRYPTO_RSA:

    lib/mpi/generic_mpih-mul1.o: In function `mpihelp_mul_1':
    lib/mpi/generic_mpih-mul1.c:50: undefined reference to `__multi3'
    lib/mpi/generic_mpih-mul2.o: In function `mpihelp_addmul_1':
    lib/mpi/generic_mpih-mul2.c:49: undefined reference to `__multi3'
    lib/mpi/generic_mpih-mul3.o: In function `mpihelp_submul_1':
    lib/mpi/generic_mpih-mul3.c:49: undefined reference to `__multi3'
    lib/mpi/mpih-div.o In function `mpihelp_divrem':
    lib/mpi/mpih-div.c:205: undefined reference to `__multi3'
    lib/mpi/mpih-div.c:142: undefined reference to `__multi3'

    Therefore add an efficient MIPS64r6 implementation of umul_ppmm() using
    inline assembly and the DMULU/DMUHU instructions, to prevent __multi3
    calls being emitted.

    Fixes: 7fd08ca58ae6 ("MIPS: Add build support for the MIPS R6 ISA")
    Signed-off-by: James Hogan <jhogan@kernel.org>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Herbert Xu <herbert@gondor.apana.org.au>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: linux-mips@linux-mips.org
    Cc: linux-crypto@vger.kernel.org
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    lib/mpi/longlong.h | 18 +++++++++++++++++-
    1 file changed, 17 insertions(+), 1 deletion(-)

    --- a/lib/mpi/longlong.h
    +++ b/lib/mpi/longlong.h
    @@ -671,7 +671,23 @@ do { \
    ************** MIPS/64 **************
    ***************************************/
    #if (defined(__mips) && __mips >= 3) && W_TYPE_SIZE == 64
    -#if (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
    +#if defined(__mips_isa_rev) && __mips_isa_rev >= 6
    +/*
    + * 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.
    + */
    +#define umul_ppmm(w1, w0, u, v) \
    +do { \
    + __asm__ ("dmulu %0,%1,%2" \
    + : "=d" ((UDItype)(w0)) \
    + : "d" ((UDItype)(u)), \
    + "d" ((UDItype)(v))); \
    + __asm__ ("dmuhu %0,%1,%2" \
    + : "=d" ((UDItype)(w1)) \
    + : "d" ((UDItype)(u)), \
    + "d" ((UDItype)(v))); \
    +} while (0)
    +#elif (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
    #define umul_ppmm(w1, w0, u, v) \
    do { \
    typedef unsigned int __ll_UTItype __attribute__((mode(TI))); \

    \
     
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