linux-kernel - Re: [PATCH v2] lib/mpi: Eliminate unused umul

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Date:   Mon, 12 Aug 2019 12:37:48 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-mips@...r.kernel.org,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] lib/mpi: Eliminate unused umul_ppmm definitions for MIPS

On Mon, Aug 12, 2019 at 12:36 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang errors out when building this macro:
>
> 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:652:20: note: expanded from macro 'umul_ppmm'
>         : "=l" ((USItype)(w0)), \
>                 ~~~~~~~~~~^~~
> lib/mpi/generic_mpih-mul1.c:37:3: error: invalid output constraint '=h'
> in asm
>                 umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
>                 ^
> lib/mpi/longlong.h:653:7: note: expanded from macro 'umul_ppmm'
>              "=h" ((USItype)(w1)) \
>              ^
> 2 errors generated.
>
> The C version that is used for GCC 4.4 and up works well with clang;
> however, it is not currently being used because Clang masks itself
> as GCC 4.2.1 for compatibility reasons. As Nick points out, we require
> GCC 4.6 and newer in the kernel so we can eliminate all of the
> versioning checks and just use the C version of umul_ppmm for all
> supported compilers.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/605
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

LGTM thanks Nathan.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
> This supersedes the following two patches:
>
> https://lore.kernel.org/lkml/20190812033120.43013-4-natechancellor@gmail.com/
>
> https://lore.kernel.org/lkml/20190812033120.43013-5-natechancellor@gmail.com/
>
> I labelled this as a v2 so those don't get applied.
>
>  lib/mpi/longlong.h | 36 +-----------------------------------
>  1 file changed, 1 insertion(+), 35 deletions(-)
>
> diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
> index 3bb6260d8f42..2dceaca27489 100644
> --- a/lib/mpi/longlong.h
> +++ b/lib/mpi/longlong.h
> @@ -639,30 +639,12 @@ do { \
>         **************  MIPS  *****************
>         ***************************************/
>  #if defined(__mips__) && W_TYPE_SIZE == 32
> -#if (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
>  #define umul_ppmm(w1, w0, u, v)                        \
>  do {                                           \
>         UDItype __ll = (UDItype)(u) * (v);      \
>         w1 = __ll >> 32;                        \
>         w0 = __ll;                              \
>  } while (0)
> -#elif __GNUC__ > 2 || __GNUC_MINOR__ >= 7
> -#define umul_ppmm(w1, w0, u, v) \
> -       __asm__ ("multu %2,%3" \
> -       : "=l" ((USItype)(w0)), \
> -            "=h" ((USItype)(w1)) \
> -       : "d" ((USItype)(u)), \
> -            "d" ((USItype)(v)))
> -#else
> -#define umul_ppmm(w1, w0, u, v) \
> -       __asm__ ("multu %2,%3\n" \
> -          "mflo %0\n" \
> -          "mfhi %1" \
> -       : "=d" ((USItype)(w0)), \
> -            "=d" ((USItype)(w1)) \
> -       : "d" ((USItype)(u)), \
> -            "d" ((USItype)(v)))
> -#endif
>  #define UMUL_TIME 10
>  #define UDIV_TIME 100
>  #endif /* __mips__ */
> @@ -687,7 +669,7 @@ do {                                                                        \
>                  : "d" ((UDItype)(u)),                                  \
>                    "d" ((UDItype)(v)));                                 \
>  } while (0)
> -#elif (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
> +#else
>  #define umul_ppmm(w1, w0, u, v) \
>  do {                                                                   \
>         typedef unsigned int __ll_UTItype __attribute__((mode(TI)));    \
> @@ -695,22 +677,6 @@ do {                                                                       \
>         w1 = __ll >> 64;                                                \
>         w0 = __ll;                                                      \
>  } while (0)
> -#elif __GNUC__ > 2 || __GNUC_MINOR__ >= 7
> -#define umul_ppmm(w1, w0, u, v) \
> -       __asm__ ("dmultu %2,%3" \
> -       : "=l" ((UDItype)(w0)), \
> -            "=h" ((UDItype)(w1)) \
> -       : "d" ((UDItype)(u)), \
> -            "d" ((UDItype)(v)))
> -#else
> -#define umul_ppmm(w1, w0, u, v) \
> -       __asm__ ("dmultu %2,%3\n" \
> -          "mflo %0\n" \
> -          "mfhi %1" \
> -       : "=d" ((UDItype)(w0)), \
> -            "=d" ((UDItype)(w1)) \
> -       : "d" ((UDItype)(u)), \
> -            "d" ((UDItype)(v)))
>  #endif
>  #define UMUL_TIME 20
>  #define UDIV_TIME 140
> --
> 2.23.0.rc2
>


-- 
Thanks,
~Nick Desaulniers