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ARM: 9265/1: pass -march= only to compiler

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When both -march= and -Wa,-march= are specified for assembler or
assembler-with-cpp sources, GCC and Clang will prefer the -Wa,-march=
value but Clang will warn that -march= is unused.

warning: argument unused during compilation: '-march=armv6k'
[-Wunused-command-line-argument]

This is the top group of warnings we observe when using clang to
assemble the kernel via `ARCH=arm make LLVM=1`.

Split the arch-y make variable into two, so that -march= flags only get
passed to the compiler, not the assembler. -D flags are added to
KBUILD_CPPFLAGS which is used for both C and assembler-with-cpp sources.

Clang is trying to warn that it doesn't support different values for
-march= and -Wa,-march= (like GCC does, but the kernel doesn't need this)
though the value of the preprocessor define __thumb2__ is based on
-march=. Make sure to re-set __thumb2__ via -D flag for assembler
sources now that we're no longer passing -march= to the assembler. Set
it to a different value than the preprocessor would for -march= in case
-march= gets accidentally re-added to KBUILD_AFLAGS in the future.
Thanks to Ard and Nathan for this suggestion.

Link: https://github.com/ClangBuiltLinux/linux/issues/1315
Link: https://github.com/ClangBuiltLinux/linux/issues/1587
Link: https://github.com/llvm/llvm-project/issues/55656

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Nick Desaulniers 2022-10-24 20:46:05 +01:00 committed by Russell King (Oracle)
parent 26b12e084b
commit 1d2e9b67b0
1 changed files with 25 additions and 11 deletions
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36
arch/arm/Makefile
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@ -60,21 +60,34 @@ endif
KBUILD_CFLAGS += $(call cc-option,-fno-ipa-sra)
# This selects which instruction set is used.
arch-$(CONFIG_CPU_32v7M) :=-march=armv7-m
arch-$(CONFIG_CPU_32v7) :=-march=armv7-a
arch-$(CONFIG_CPU_32v6) :=-march=armv6
# Only override the compiler option if ARMv6. The ARMv6K extensions are
# always available in ARMv7
ifeq ($(CONFIG_CPU_32v6),y)
arch-$(CONFIG_CPU_32v6K) :=-march=armv6k
endif
arch-$(CONFIG_CPU_32v5) :=-march=armv5te
arch-$(CONFIG_CPU_32v4T) :=-march=armv4t
arch-$(CONFIG_CPU_32v4) :=-march=armv4
arch-$(CONFIG_CPU_32v3) :=-march=armv3m
# Note that GCC does not numerically define an architecture version
# macro, but instead defines a whole series of macros which makes
# testing for a specific architecture or later rather impossible.
arch-$(CONFIG_CPU_32v7M) :=-D__LINUX_ARM_ARCH__=7 -march=armv7-m
arch-$(CONFIG_CPU_32v7) :=-D__LINUX_ARM_ARCH__=7 -march=armv7-a
arch-$(CONFIG_CPU_32v6) :=-D__LINUX_ARM_ARCH__=6 -march=armv6
# Only override the compiler opt:ion if ARMv6. The ARMv6K extensions are
cpp-$(CONFIG_CPU_32v7M) :=-D__LINUX_ARM_ARCH__=7
cpp-$(CONFIG_CPU_32v7) :=-D__LINUX_ARM_ARCH__=7
cpp-$(CONFIG_CPU_32v6) :=-D__LINUX_ARM_ARCH__=6
# Only override the compiler option if ARMv6. The ARMv6K extensions are
# always available in ARMv7
ifeq ($(CONFIG_CPU_32v6),y)
arch-$(CONFIG_CPU_32v6K) :=-D__LINUX_ARM_ARCH__=6 -march=armv6k
cpp-$(CONFIG_CPU_32v6K) :=-D__LINUX_ARM_ARCH__=6
endif
arch-$(CONFIG_CPU_32v5) :=-D__LINUX_ARM_ARCH__=5 -march=armv5te
arch-$(CONFIG_CPU_32v4T) :=-D__LINUX_ARM_ARCH__=4 -march=armv4t
arch-$(CONFIG_CPU_32v4) :=-D__LINUX_ARM_ARCH__=4 -march=armv4
arch-$(CONFIG_CPU_32v3) :=-D__LINUX_ARM_ARCH__=3 -march=armv3m
cpp-$(CONFIG_CPU_32v5) :=-D__LINUX_ARM_ARCH__=5
cpp-$(CONFIG_CPU_32v4T) :=-D__LINUX_ARM_ARCH__=4
cpp-$(CONFIG_CPU_32v4) :=-D__LINUX_ARM_ARCH__=4
cpp-$(CONFIG_CPU_32v3) :=-D__LINUX_ARM_ARCH__=3
# This selects how we optimise for the processor.
tune-$(CONFIG_CPU_ARM7TDMI) :=-mtune=arm7tdmi
@ -119,15 +132,16 @@ 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 $(AFLAGS_NOWARN)
AFLAGS_ISA :=$(CFLAGS_ISA) -Wa$(comma)-mthumb
AFLAGS_ISA :=$(CFLAGS_ISA) -Wa$(comma)-mthumb -D__thumb2__=2
else
CFLAGS_ISA :=$(call cc-option,-marm,) $(AFLAGS_NOWARN)
AFLAGS_ISA :=$(CFLAGS_ISA)
endif
# Need -Uarm for gcc < 3.x
KBUILD_CPPFLAGS +=$(cpp-y)
KBUILD_CFLAGS +=$(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) $(tune-y) -include asm/unified.h -msoft-float
KBUILD_AFLAGS +=$(CFLAGS_ABI) $(AFLAGS_ISA) -Wa,$(arch-y) $(tune-y) -include asm/unified.h -msoft-float
CHECKFLAGS += -D__arm__