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Some versions of GCC suboptimally generate calls to the __multi3()
intrinsic for MIPS64r6 builds, resulting in link failures due to the
missing function:
LD vmlinux.o
MODPOST vmlinux.o
kernel/bpf/verifier.o: In function `kmalloc_array':
include/linux/slab.h:631: undefined reference to `__multi3'
fs/select.o: In function `kmalloc_array':
include/linux/slab.h:631: undefined reference to `__multi3'
...
We already have a workaround for this in which we provide the
instrinsic, but we do so selectively for GCC 7 only. Unfortunately the
issue occurs with older GCC versions too - it has been observed with
both GCC 5.4.0 & GCC 6.4.0.
MIPSr6 support was introduced in GCC 5, so all major GCC versions prior
to GCC 8 are affected and we extend our workaround accordingly to all
MIPS64r6 builds using GCC versions older than GCC 8.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Reported-by: Vladimir Kondratiev <vladimir.kondratiev@intel.com>
Fixes: ebabcf17bc ("MIPS: Implement __multi3 for GCC7 MIPS64r6 builds")
Patchwork: https://patchwork.linux-mips.org/patch/20297/
Cc: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org # 4.15+
55 lines
1.3 KiB
C
55 lines
1.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/export.h>
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#include "libgcc.h"
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/*
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* GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for
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* that specific case only we implement that intrinsic 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__ < 8)
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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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/* 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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/* 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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aa.ti = a;
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bb.ti = b;
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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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return res.ti;
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}
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EXPORT_SYMBOL(__multi3);
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#endif /* 64BIT && CPU_MIPSR6 && GCC7 */
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