Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Juerg Haefliger <juerg.haefliger@canonical.com>
To:     linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk
Cc:     linux-kernel@vger.kernel.org,
        Juerg Haefliger <juergh@canonical.com>
Subject: [PATCH] ARM: Fix instruction set selection for GCC 11
Date:   Tue, 10 Aug 2021 08:13:50 +0200
Message-Id: <20210810061350.754134-1-juergh@canonical.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

GCC 11 on ARM now complains like the following when trying to determine if
an arch is supported. Presumably because it enforces the default option
'--with-float=hard' which GCC 10 didn't do?

  $ arm-linux-gnueabihf-gcc-11 -march=armv7-a -c -x c /dev/null
  cc1: error: ‘-mfloat-abi=hard’: selected architecture lacks an FPU

Due to that, the kernel build system selects the wrong compiler options
which throws errros like this during the build:

  /tmp/ccrHfZPj.s: Assembler messages:
  /tmp/ccrHfZPj.s:116: Error: selected processor does not support `dmb ish' in ARM mode
  /tmp/ccrHfZPj.s:150: Error: selected processor does not support `isb ' in ARM mode
  /tmp/ccrHfZPj.s:160: Error: selected processor does not support `mrrc p15,1,r4,r5,c14' in ARM mode
  /tmp/ccrHfZPj.s:245: Error: selected processor does not support `dmb ish' in ARM mode
  /tmp/ccrHfZPj.s:503: Error: selected processor does not support `dmb ish' in ARM mode
  /tmp/ccrHfZPj.s:527: Error: selected processor does not support `dmb ish' in ARM mode
  /tmp/ccrHfZPj.s:698: Error: selected processor does not support `dmb ish' in ARM mode
  /tmp/ccrHfZPj.s:731: Error: selected processor does not support `isb ' in ARM mode

Fix that by adding '-msoft-float' to KBUILD_CFLAGS before the definition of
the 'arch-$(CONFIG_CPU_<foo>)' instruction selection macros.

Signed-off-by: Juerg Haefliger <juergh@canonical.com>
---
 arch/arm/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 173da685a52e..d21198833997 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -56,6 +56,9 @@ endif
 #
 KBUILD_CFLAGS	+= $(call cc-option,-fno-ipa-sra)
 
+# Need -msoft-float for gcc 11 for the below instruction set selection
+KBUILD_CFLAGS	+= -msoft-float
+
 # This selects which instruction set is used.
 # Note that GCC does not numerically define an architecture version
 # macro, but instead defines a whole series of macros which makes
@@ -125,7 +128,7 @@ AFLAGS_ISA	:=$(CFLAGS_ISA)
 endif
 
 # Need -Uarm for gcc < 3.x
-KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
+KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -Uarm
 KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float
 
 CHECKFLAGS	+= -D__arm__
-- 
2.30.2