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Re: [PATCH] lib/mpi: Fix umul_ppmm() for MIPS64r6

To: James Hogan <>
Subject: Re: [PATCH] lib/mpi: Fix umul_ppmm() for MIPS64r6
From: Herbert Xu <>
Date: Fri, 22 Dec 2017 19:41:19 +1100
Cc: Ralf Baechle <>, "David S. Miller" <>, James Hogan <>,,
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On Tue, Dec 05, 2017 at 11:31:35PM +0000, James Hogan wrote:
> From: James Hogan <>
> 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 <>
> Cc: Ralf Baechle <>
> Cc: Herbert Xu <>
> Cc: "David S. Miller" <>
> Cc:
> Cc:

Patch applied.  Thanks.
Email: Herbert Xu <>
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