linux-kernel - [PATCH v2] ARM: warn if pre-UAL assembler syntax is used

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Message-Id: <a651d5eaf312c771c9d2e0160ddd905550bbd4e3.1585507235.git.stefan@agner.ch>
Date:   Sun, 29 Mar 2020 20:43:04 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     linux@...linux.org.uk
Cc:     arnd@...db.de, ard.biesheuvel@...aro.org, robin.murphy@....com,
        yamada.masahiro@...ionext.com, ndesaulniers@...gle.com,
        manojgupta@...gle.com, jiancai@...gle.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, Stefan Agner <stefan@...er.ch>
Subject: [PATCH v2] ARM: warn if pre-UAL assembler syntax is used

Remove the -mno-warn-deprecated assembler flag to make sure the GNU
assembler warns in case non-unified syntax is used.

This also prevents a warning when building with Clang and enabling its
integrated assembler:
clang-10: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'

GCC before 5.1 emits pre-UAL assembler. This can lead to warnings if
inline assembler explicitly switches to unified syntax by using the
".syntax unified" directive (e.g. arch/arm/include/asm/unified.h).
Hence keep the flag for GCC versions before 5.1.

This is a second attempt of commit e8c24bbda7d5 ("ARM: 8846/1: warn if
divided syntax assembler is used") which has subsequently been reverted
with commit b752bb405a13 ("Revert "ARM: 8846/1: warn if divided syntax
assembler is used"").

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
Changes in v2:
- Reference revert commit b752bb405a13 ("Revert "ARM: 8846/1: warn if
  divided syntax assembler is used"")
- Reword commit message

 arch/arm/Makefile | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 1fc32b611f8a..b37bb985a3c2 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -119,21 +119,25 @@ ifeq ($(CONFIG_CC_IS_CLANG),y)
 CFLAGS_ABI	+= -meabi gnu
 endif
 
-# Accept old syntax despite ".syntax unified"
-AFLAGS_NOWARN	:=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
-
 ifeq ($(CONFIG_THUMB2_KERNEL),y)
-CFLAGS_ISA	:=-mthumb -Wa,-mimplicit-it=always $(AFLAGS_NOWARN)
+CFLAGS_ISA	:=-mthumb -Wa,-mimplicit-it=always
 AFLAGS_ISA	:=$(CFLAGS_ISA) -Wa$(comma)-mthumb
 # Work around buggy relocation from gas if requested:
 ifeq ($(CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11),y)
 KBUILD_CFLAGS_MODULE	+=-fno-optimize-sibling-calls
 endif
 else
-CFLAGS_ISA	:=$(call cc-option,-marm,) $(AFLAGS_NOWARN)
+CFLAGS_ISA	:=$(call cc-option,-marm,)
 AFLAGS_ISA	:=$(CFLAGS_ISA)
 endif
 
+ifeq ($(CONFIG_CC_IS_GCC),y)
+ifeq ($(call cc-ifversion, -lt, 0501, y), y)
+# GCC <5.1 emits pre-UAL code and causes assembler warnings, suppress them
+CFLAGS_ISA	+=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
+endif
+endif
+
 # Need -Uarm for gcc < 3.x
 KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
 KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float
-- 
2.25.1