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arm64: support __int128 on gcc 5+

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Versions of gcc prior to gcc 5 emitted a __multi3 function call when
dealing with TI types, resulting in failures when trying to link to
libgcc, and more generally, bad performance. However, since gcc 5,
the compiler supports actually emitting fast instructions, which means
we can at long last enable this option and receive the speedups.

The gcc commit that added proper Aarch64 support is:
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=d1ae7bb994f49316f6f63e6173f2931e837a351d
This commit appears to be part of the gcc 5 release.

There are still a few instructions, __ashlti3 and __ashrti3, which
require libgcc, which is fine. Rather than linking to libgcc, we
simply provide them ourselves, since they're not that complicated.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Jason A. Donenfeld 2017-11-03 15:18:58 +01:00 committed by Will Deacon
parent ce6990813f
commit fb8722735f
3 changed files with 62 additions and 1 deletions
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2
arch/arm64/Makefile
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@ -57,6 +57,8 @@ KBUILD_AFLAGS += $(lseinstr) $(brokengasinst)
KBUILD_CFLAGS += $(call cc-option,-mabi=lp64)
KBUILD_AFLAGS += $(call cc-option,-mabi=lp64)
KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
CHECKFLAGS += -D__AARCH64EB__

2
arch/arm64/lib/Makefile
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@ -2,7 +2,7 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \
copy_to_user.o copy_in_user.o copy_page.o \
clear_page.o memchr.o memcpy.o memmove.o memset.o \
memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \
strchr.o strrchr.o
strchr.o strrchr.o tishift.o
# Tell the compiler to treat all general purpose registers (with the
# exception of the IP registers, which are already handled by the caller

59
arch/arm64/lib/tishift.S Normal file
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@ -0,0 +1,59 @@
/*
* Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <linux/linkage.h>
ENTRY(__ashlti3)
cbz x2, 1f
mov x3, #64
sub x3, x3, x2
cmp x3, #0
b.le 2f
lsl x1, x1, x2
lsr x3, x0, x3
lsl x2, x0, x2
orr x1, x1, x3
mov x0, x2
1:
ret
2:
neg w1, w3
mov x2, #0
lsl x1, x0, x1
mov x0, x2
ret
ENDPROC(__ashlti3)
ENTRY(__ashrti3)
cbz x2, 3f
mov x3, #64
sub x3, x3, x2
cmp x3, #0
b.le 4f
lsr x0, x0, x2
lsl x3, x1, x3
asr x2, x1, x2
orr x0, x0, x3
mov x1, x2
3:
ret
4:
neg w0, w3
asr x2, x1, #63
asr x0, x1, x0
mov x1, x2
ret
ENDPROC(__ashrti3)