linux-kernel - [PATCH 4.9 85/92] MIPS: Disable Loongson MMI instructions for kernel build

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Message-Id: <20191016214847.735987212@linuxfoundation.org>
Date:   Wed, 16 Oct 2019 14:50:58 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Paul Burton <paul.burton@...s.com>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-mips@...r.kernel.org
Subject: [PATCH 4.9 85/92] MIPS: Disable Loongson MMI instructions for kernel build

From: Paul Burton <paul.burton@...s.com>

commit 2f2b4fd674cadd8c6b40eb629e140a14db4068fd upstream.

GCC 9.x automatically enables support for Loongson MMI instructions when
using some -march= flags, and then errors out when -msoft-float is
specified with:

  cc1: error: ‘-mloongson-mmi’ must be used with ‘-mhard-float’

The kernel shouldn't be using these MMI instructions anyway, just as it
doesn't use floating point instructions. Explicitly disable them in
order to fix the build with GCC 9.x.

Signed-off-by: Paul Burton <paul.burton@...s.com>
Fixes: 3702bba5eb4f ("MIPS: Loongson: Add GCC 4.4 support for Loongson2E")
Fixes: 6f7a251a259e ("MIPS: Loongson: Add basic Loongson 2F support")
Fixes: 5188129b8c9f ("MIPS: Loongson-3: Improve -march option and move it to Platform")
Cc: Huacai Chen <chenhc@...ote.com>
Cc: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: stable@...r.kernel.org # v2.6.32+
Cc: linux-mips@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/loongson64/Platform |    4 ++++
 arch/mips/vdso/Makefile       |    1 +
 2 files changed, 5 insertions(+)

--- a/arch/mips/loongson64/Platform
+++ b/arch/mips/loongson64/Platform
@@ -43,6 +43,10 @@ else
       $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
 endif
 
+# Some -march= flags enable MMI instructions, and GCC complains about that
+# support being enabled alongside -msoft-float. Thus explicitly disable MMI.
+cflags-y += $(call cc-option,-mno-loongson-mmi)
+
 #
 # Loongson Machines' Support
 #
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -8,6 +8,7 @@ ccflags-vdso := \
 	$(filter -mmicromips,$(KBUILD_CFLAGS)) \
 	$(filter -march=%,$(KBUILD_CFLAGS)) \
 	$(filter -m%-float,$(KBUILD_CFLAGS)) \
+	$(filter -mno-loongson-%,$(KBUILD_CFLAGS)) \
 	-D__VDSO__
 cflags-vdso := $(ccflags-vdso) \
 	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \