linux-kernel - [PATCH] MIPS: Support binutils configured with --enable-mips-fix-loongson3-llsc=yes

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Message-Id: <20210109193048.478339-1-aurelien@aurel32.net>
Date:   Sat,  9 Jan 2021 20:30:47 +0100
From:   Aurelien Jarno <aurelien@...el32.net>
To:     linux-kernel@...r.kernel.org
Cc:     Aurelien Jarno <aurelien@...el32.net>, stable@...r.kernel.org,
        YunQiang Su <syq@...ian.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-mips@...r.kernel.org (open list:MIPS)
Subject: [PATCH] MIPS: Support binutils configured with --enable-mips-fix-loongson3-llsc=yes

>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@...r.kernel.org # 5.1+
Cc: YunQiang Su <syq@...ian.org>
Signed-off-by: Aurelien Jarno <aurelien@...el32.net>
---
 arch/mips/Makefile            | 19 +++++++++++++++++++
 arch/mips/loongson64/Platform | 22 ----------------------
 2 files changed, 19 insertions(+), 22 deletions(-)

diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index cd4343edeb11..5ffdd67093bc 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -136,6 +136,25 @@ cflags-$(CONFIG_SB1XXX_CORELIS)	+= $(call cc-option,-mno-sched-prolog) \
 #
 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.
 #
diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
index ec42c5085905..e2354e128d9a 100644
--- a/arch/mips/loongson64/Platform
+++ b/arch/mips/loongson64/Platform
@@ -5,28 +5,6 @@
 
 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
 # as MIPS64 R2; older versions as just R1.  This leaves the possibility open
-- 
2.29.2