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@@ -0,0 +1,107 @@
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+MIPS: Implement __multi3 for GCC7 MIPS64r6 builds
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+
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+Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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+Signed-off-by: James Hogan <jhogan@kernel.org>
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+
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+diff -Nur linux-4.14.8.orig/arch/mips/lib/libgcc.h linux-4.14.8/arch/mips/lib/libgcc.h
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+--- linux-4.14.8.orig/arch/mips/lib/libgcc.h 2017-12-20 10:10:38.000000000 +0100
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++++ linux-4.14.8/arch/mips/lib/libgcc.h 2017-12-25 16:58:38.258470502 +0100
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+@@ -10,10 +10,18 @@
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+ struct DWstruct {
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+ int high, low;
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+ };
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++
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++struct TWstruct {
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++ long long high, low;
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++};
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+ #elif defined(__LITTLE_ENDIAN)
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+ struct DWstruct {
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+ int low, high;
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+ };
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++
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++struct TWstruct {
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++ long long low, high;
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++};
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+ #else
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+ #error I feel sick.
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+ #endif
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+@@ -23,4 +31,13 @@
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+ long long ll;
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+ } DWunion;
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+
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++#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6)
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++typedef int ti_type __attribute__((mode(TI)));
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++
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++typedef union {
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++ struct TWstruct s;
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++ ti_type ti;
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++} TWunion;
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++#endif
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++
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+ #endif /* __ASM_LIBGCC_H */
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+diff -Nur linux-4.14.8.orig/arch/mips/lib/Makefile linux-4.14.8/arch/mips/lib/Makefile
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+--- linux-4.14.8.orig/arch/mips/lib/Makefile 2017-12-20 10:10:38.000000000 +0100
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++++ linux-4.14.8/arch/mips/lib/Makefile 2017-12-25 16:58:38.258470502 +0100
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+@@ -16,4 +16,5 @@
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+ obj-$(CONFIG_CPU_TX39XX) += r3k_dump_tlb.o
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+
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+ # libgcc-style stuff needed in the kernel
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+-obj-y += ashldi3.o ashrdi3.o bswapsi.o bswapdi.o cmpdi2.o lshrdi3.o ucmpdi2.o
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++obj-y += ashldi3.o ashrdi3.o bswapsi.o bswapdi.o cmpdi2.o lshrdi3.o multi3.o \
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++ ucmpdi2.o
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+diff -Nur linux-4.14.8.orig/arch/mips/lib/multi3.c linux-4.14.8/arch/mips/lib/multi3.c
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+--- linux-4.14.8.orig/arch/mips/lib/multi3.c 1970-01-01 01:00:00.000000000 +0100
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++++ linux-4.14.8/arch/mips/lib/multi3.c 2017-12-25 16:58:38.258470502 +0100
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+@@ -0,0 +1,52 @@
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++// SPDX-License-Identifier: GPL-2.0
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++#include <linux/export.h>
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++
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++#include "libgcc.h"
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++
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++/*
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++ * GCC 7 suboptimally generates __multi3 calls for mips64r6, so for that
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++ * specific case only we'll implement it here.
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++ *
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++ * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
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++ */
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++#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ == 7)
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++
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++/* multiply 64-bit values, low 64-bits returned */
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++static inline long long notrace dmulu(long long a, long long b)
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++{
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++ long long res;
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++ asm ("dmulu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
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++ return res;
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++}
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++
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++/* multiply 64-bit unsigned values, high 64-bits of 128-bit result returned */
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++static inline long long notrace dmuhu(long long a, long long b)
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++{
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++ long long res;
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++ asm ("dmuhu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
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++ return res;
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++}
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++
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++/* multiply 128-bit values, low 128-bits returned */
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++ti_type notrace __multi3(ti_type a, ti_type b)
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++{
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++ TWunion res, aa, bb;
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++
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++ aa.ti = a;
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++ bb.ti = b;
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++
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++ /*
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++ * a * b = (a.lo * b.lo)
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++ * + 2^64 * (a.hi * b.lo + a.lo * b.hi)
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++ * [+ 2^128 * (a.hi * b.hi)]
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++ */
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++ res.s.low = dmulu(aa.s.low, bb.s.low);
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++ res.s.high = dmuhu(aa.s.low, bb.s.low);
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++ res.s.high += dmulu(aa.s.high, bb.s.low);
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++ res.s.high += dmulu(aa.s.low, bb.s.high);
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++
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++ return res.ti;
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++}
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++EXPORT_SYMBOL(__multi3);
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++
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++#endif /* 64BIT && CPU_MIPSR6 && GCC7 */
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Waldemar Brodkorb