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MIPS: lib: Provide MIPS64r6 __multi3() for GCC < 7

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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+
This commit is contained in:
Paul Burton 2018-08-21 12:12:59 -07:00
parent 906d441feb
commit 690d9163bf
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1 changed files with 3 additions and 3 deletions
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6
arch/mips/lib/multi3.c
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@ -4,12 +4,12 @@
#include "libgcc.h"
/*
* GCC 7 suboptimally generates __multi3 calls for mips64r6, so for that
* specific case only we'll implement it here.
* GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for
* that specific case only we implement that intrinsic here.
*
* See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
*/
#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ == 7)
#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8)
/* multiply 64-bit values, low 64-bits returned */
static inline long long notrace dmulu(long long a, long long b)