Commit 1d2e9b67 authored by Nick Desaulniers's avatar Nick Desaulniers Committed by Russell King (Oracle)
Browse files

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

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: default avatarArd Biesheuvel <ardb@kernel.org>
Suggested-by: default avatarNathan Chancellor <nathan@kernel.org>
Reviewed-by: default avatarNathan Chancellor <nathan@kernel.org>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
parent 26b12e08

arch/arm/Makefile

+25 −11
Original line number Diff line number Diff line
@@ -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__