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MIPS: Support binutils configured with --enable-mips-fix-loongson3-llsc=yes

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From version 2.35, binutils can be configured with
--enable-mips-fix-loongson3-llsc=yes, which means it defaults to
-mfix-loongson3-llsc. This breaks labels which might then point at the
wrong instruction.

The workaround to explicitly pass -mno-fix-loongson3-llsc has been
added in Linux version 5.1, but is only enabled when building a Loongson
64 kernel. As vendors might use a common toolchain for building Loongson
and non-Loongson kernels, just move that workaround to
arch/mips/Makefile. At the same time update the comments to reflect the
current status.

Cc: stable@vger.kernel.org # 5.1+
Cc: YunQiang Su <syq@debian.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
This commit is contained in:
Aurelien Jarno 2021-01-09 20:30:47 +01:00 committed by Thomas Bogendoerfer
parent 8790ccf8da
commit 5373ae67c3
2 changed files with 19 additions and 22 deletions
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19
arch/mips/Makefile
View File

@ -136,6 +136,25 @@ cflags-$(CONFIG_SB1XXX_CORELIS) += $(call cc-option,-mno-sched-prolog) \
# #
cflags-y += -fno-stack-check cflags-y += -fno-stack-check
# binutils from v2.35 when built with --enable-mips-fix-loongson3-llsc=yes,
# supports an -mfix-loongson3-llsc flag which emits a sync prior to each ll
# instruction to work around a CPU bug (see __SYNC_loongson3_war in asm/sync.h
# for a description).
#
# We disable this in order to prevent the assembler meddling with the
# instruction that labels refer to, ie. if we label an ll instruction:
#
# 1: ll v0, 0(a0)
#
# ...then with the assembler fix applied the label may actually point at a sync
# instruction inserted by the assembler, and if we were using the label in an
# exception table the table would no longer contain the address of the ll
# instruction.
#
# Avoid this by explicitly disabling that assembler behaviour.
#
cflags-y += $(call as-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
# #
# CPU-dependent compiler/assembler options for optimization. # CPU-dependent compiler/assembler options for optimization.
# #

22
arch/mips/loongson64/Platform
View File

@ -5,28 +5,6 @@
cflags-$(CONFIG_CPU_LOONGSON64) += -Wa,--trap cflags-$(CONFIG_CPU_LOONGSON64) += -Wa,--trap
#
# Some versions of binutils, not currently mainline as of 2019/02/04, support
# an -mfix-loongson3-llsc flag which emits a sync prior to each ll instruction
# to work around a CPU bug (see __SYNC_loongson3_war in asm/sync.h for a
# description).
#
# We disable this in order to prevent the assembler meddling with the
# instruction that labels refer to, ie. if we label an ll instruction:
#
# 1: ll v0, 0(a0)
#
# ...then with the assembler fix applied the label may actually point at a sync
# instruction inserted by the assembler, and if we were using the label in an
# exception table the table would no longer contain the address of the ll
# instruction.
#
# Avoid this by explicitly disabling that assembler behaviour. If upstream
# binutils does not merge support for the flag then we can revisit & remove
# this later - for now it ensures vendor toolchains don't cause problems.
#
cflags-$(CONFIG_CPU_LOONGSON64) += $(call as-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
# #
# binutils from v2.25 on and gcc starting from v4.9.0 treat -march=loongson3a # binutils from v2.25 on and gcc starting from v4.9.0 treat -march=loongson3a
# as MIPS64 R2; older versions as just R1. This leaves the possibility open # as MIPS64 R2; older versions as just R1. This leaves the possibility open