arch/x86/Makefile - third_party/linux - Git at Google

 # SPDX-License-Identifier: GPL-2.0
 # Unified Makefile for i386 and x86_64

 # select defconfig based on actual architecture
 ifeq ($(ARCH),x86)
   ifeq ($(shell uname -m),x86_64)
         KBUILD_DEFCONFIG := x86_64_defconfig
   else
         KBUILD_DEFCONFIG := i386_defconfig
   endif
 else
         KBUILD_DEFCONFIG := $(ARCH)_defconfig
 endif

 # For gcc stack alignment is specified with -mpreferred-stack-boundary,
 # clang has the option -mstack-alignment for that purpose.
 ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
       cc_stack_align4 := -mpreferred-stack-boundary=2
       cc_stack_align8 := -mpreferred-stack-boundary=3
 else ifneq ($(call cc-option, -mstack-alignment=16),)
       cc_stack_align4 := -mstack-alignment=4
       cc_stack_align8 := -mstack-alignment=8
 endif

 # How to compile the 16-bit code.  Note we always compile for -march=i386;
 # that way we can complain to the user if the CPU is insufficient.
 #
 # The -m16 option is supported by GCC >= 4.9 and clang >= 3.5. For
 # older versions of GCC, include an *assembly* header to make sure that
 # gcc doesn't play any games behind our back.
 CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h
 M16_CFLAGS	 := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))

 REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
 		   -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)

 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
 REALMODE_CFLAGS += $(CLANG_FLAGS)
 export REALMODE_CFLAGS

 # BITS is used as extension for files which are available in a 32 bit
 # and a 64 bit version to simplify shared Makefiles.
 # e.g.: obj-y += foo_$(BITS).o
 export BITS

 ifdef CONFIG_X86_NEED_RELOCS
         LDFLAGS_vmlinux := --emit-relocs --discard-none
 endif

 #
 # Prevent GCC from generating any FP code by mistake.
 #
 # This must happen before we try the -mpreferred-stack-boundary, see:
 #
 #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
 #
 KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
 KBUILD_CFLAGS += $(call cc-option,-mno-avx,)

 # Intel CET isn't enabled in the kernel
 KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)

 ifeq ($(CONFIG_X86_32),y)
         BITS := 32
         UTS_MACHINE := i386
         CHECKFLAGS += -D__i386__

         biarch := $(call cc-option,-m32)
         KBUILD_AFLAGS += $(biarch)
         KBUILD_CFLAGS += $(biarch)

         KBUILD_CFLAGS += -msoft-float -mregparm=3 -freg-struct-return

         # Never want PIC in a 32-bit kernel, prevent breakage with GCC built
         # with nonstandard options
         KBUILD_CFLAGS += -fno-pic

         # Align the stack to the register width instead of using the default
         # alignment of 16 bytes. This reduces stack usage and the number of
         # alignment instructions.
         KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align4))

         # CPU-specific tuning. Anything which can be shared with UML should go here.
         include arch/x86/Makefile_32.cpu
         KBUILD_CFLAGS += $(cflags-y)

         # temporary until string.h is fixed
         KBUILD_CFLAGS += -ffreestanding
 else
         BITS := 64
         UTS_MACHINE := x86_64
         CHECKFLAGS += -D__x86_64__

         biarch := -m64
         KBUILD_AFLAGS += -m64
         KBUILD_CFLAGS += -m64

         # Align jump targets to 1 byte, not the default 16 bytes:
         KBUILD_CFLAGS += $(call cc-option,-falign-jumps=1)

         # Pack loops tightly as well:
         KBUILD_CFLAGS += $(call cc-option,-falign-loops=1)

         # Don't autogenerate traditional x87 instructions
         KBUILD_CFLAGS += $(call cc-option,-mno-80387)
         KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387)

         # By default gcc and clang use a stack alignment of 16 bytes for x86.
         # However the standard kernel entry on x86-64 leaves the stack on an
         # 8-byte boundary. If the compiler isn't informed about the actual
         # alignment it will generate extra alignment instructions for the
         # default alignment which keep the stack *mis*aligned.
         # Furthermore an alignment to the register width reduces stack usage
         # and the number of alignment instructions.
         KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align8))

 	# Use -mskip-rax-setup if supported.
 	KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)

         # FIXME - should be integrated in Makefile.cpu (Makefile_32.cpu)
         cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)
         cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)

         cflags-$(CONFIG_MCORE2) += \
                 $(call cc-option,-march=core2,$(call cc-option,-mtune=generic))
 	cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
 		$(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
         cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=generic)
         KBUILD_CFLAGS += $(cflags-y)

         KBUILD_CFLAGS += -mno-red-zone
         KBUILD_CFLAGS += -mcmodel=kernel

         # -funit-at-a-time shrinks the kernel .text considerably
         # unfortunately it makes reading oopses harder.
         KBUILD_CFLAGS += $(call cc-option,-funit-at-a-time)
 endif

 ifdef CONFIG_X86_X32
 	x32_ld_ok := $(call try-run,\
 			/bin/echo -e '1: .quad 1b' | \
 			$(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" - && \
 			$(OBJCOPY) -O elf32-x86-64 "$$TMP" "$$TMPO" && \
 			$(LD) -m elf32_x86_64 "$$TMPO" -o "$$TMP",y,n)
         ifeq ($(x32_ld_ok),y)
                 CONFIG_X86_X32_ABI := y
                 KBUILD_AFLAGS += -DCONFIG_X86_X32_ABI
                 KBUILD_CFLAGS += -DCONFIG_X86_X32_ABI
         else
                 $(warning CONFIG_X86_X32 enabled but no binutils support)
         endif
 endif
 export CONFIG_X86_X32_ABI

 #
 # If the function graph tracer is used with mcount instead of fentry,
 # '-maccumulate-outgoing-args' is needed to prevent a GCC bug
 # (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109)
 #
 ifdef CONFIG_FUNCTION_GRAPH_TRACER
   ifndef CONFIG_HAVE_FENTRY
 	ACCUMULATE_OUTGOING_ARGS := 1
   else
     ifeq ($(call cc-option-yn, -mfentry), n)
 	ACCUMULATE_OUTGOING_ARGS := 1

 	# GCC ignores '-maccumulate-outgoing-args' when used with '-Os'.
 	# If '-Os' is enabled, disable it and print a warning.
         ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
           undefine CONFIG_CC_OPTIMIZE_FOR_SIZE
           $(warning Disabling CONFIG_CC_OPTIMIZE_FOR_SIZE.  Your compiler does not have -mfentry so you cannot optimize for size with CONFIG_FUNCTION_GRAPH_TRACER.)
         endif

     endif
   endif
 endif

 ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
 	# This compiler flag is not supported by Clang:
 	KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
 endif

 # Stackpointer is addressed different for 32 bit and 64 bit x86
 sp-$(CONFIG_X86_32) := esp
 sp-$(CONFIG_X86_64) := rsp

 # do binutils support CFI?
 cfi := $(call as-instr,.cfi_startproc\n.cfi_rel_offset $(sp-y)$(comma)0\n.cfi_endproc,-DCONFIG_AS_CFI=1)
 # is .cfi_signal_frame supported too?
 cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)
 cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)

 # does binutils support specific instructions?
 asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
 asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
 asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)
 avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
 avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
 avx512_instr :=$(call as-instr,vpmovm2b %k1$(comma)%zmm5,-DCONFIG_AS_AVX512=1)
 sha1_ni_instr :=$(call as-instr,sha1msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA1_NI=1)
 sha256_ni_instr :=$(call as-instr,sha256msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA256_NI=1)

 KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr)
 KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr)

 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)

 #
 # The 64-bit kernel must be aligned to 2MB.  Pass -z max-page-size=0x200000 to
 # the linker to force 2MB page size regardless of the default page size used
 # by the linker.
 #
 ifdef CONFIG_X86_64
 KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
 endif

 # Speed up the build
 KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
 KBUILD_CFLAGS += -fno-asynchronous-unwind-tables

 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
   KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
   # Additionally, avoid generating expensive indirect jumps which
   # are subject to retpolines for small number of switch cases.
   # clang turns off jump table generation by default when under
   # retpoline builds, however, gcc does not for x86. This has
   # only been fixed starting from gcc stable version 8.4.0 and
   # onwards, but not for older ones. See gcc bug #86952.
   ifndef CONFIG_CC_IS_CLANG
     KBUILD_CFLAGS += $(call cc-option,-fno-jump-tables)
   endif
 endif

 archscripts: scripts_basic
 	$(Q)$(MAKE) $(build)=arch/x86/tools relocs

 ###
 # Syscall table generation

 archheaders:
 	$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all

 ###
 # Kernel objects

 head-y := arch/x86/kernel/head_$(BITS).o
 head-y += arch/x86/kernel/head$(BITS).o
 head-y += arch/x86/kernel/ebda.o
 head-y += arch/x86/kernel/platform-quirks.o

 libs-y  += arch/x86/lib/

 # See arch/x86/Kbuild for content of core part of the kernel
 core-y += arch/x86/

 # drivers-y are linked after core-y
 drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
 drivers-$(CONFIG_PCI)            += arch/x86/pci/

 # must be linked after kernel/
 drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/

 # suspend and hibernation support
 drivers-$(CONFIG_PM) += arch/x86/power/

 drivers-$(CONFIG_FB) += arch/x86/video/

 ####
 # boot loader support. Several targets are kept for legacy purposes

 boot := arch/x86/boot

 BOOT_TARGETS = bzlilo bzdisk fdimage fdimage144 fdimage288 isoimage

 PHONY += bzImage $(BOOT_TARGETS)

 # Default kernel to build
 all: bzImage

 # KBUILD_IMAGE specify target image being built
 KBUILD_IMAGE := $(boot)/bzImage

 bzImage: vmlinux
 ifeq ($(CONFIG_X86_DECODER_SELFTEST),y)
 	$(Q)$(MAKE) $(build)=arch/x86/tools posttest
 endif
 	$(Q)$(MAKE) $(build)=$(boot) $(KBUILD_IMAGE)
 	$(Q)mkdir -p $(objtree)/arch/$(UTS_MACHINE)/boot
 	$(Q)ln -fsn ../../x86/boot/bzImage $(objtree)/arch/$(UTS_MACHINE)/boot/$@

 $(BOOT_TARGETS): vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $@

 PHONY += install
 install:
 	$(Q)$(MAKE) $(build)=$(boot) $@

 PHONY += vdso_install
 vdso_install:
 	$(Q)$(MAKE) $(build)=arch/x86/entry/vdso $@

 archprepare: checkbin
 checkbin:
 ifndef CONFIG_CC_HAS_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 endif
 ifdef CONFIG_RETPOLINE
 ifeq ($(RETPOLINE_CFLAGS),)
 	@echo "You are building kernel with non-retpoline compiler." >&2
 	@echo "Please update your compiler." >&2
 	@false
 endif
 endif

 archclean:
 	$(Q)rm -rf $(objtree)/arch/i386
 	$(Q)rm -rf $(objtree)/arch/x86_64
 	$(Q)$(MAKE) $(clean)=$(boot)
 	$(Q)$(MAKE) $(clean)=arch/x86/tools

 define archhelp
   echo  '* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)'
   echo  '  install      - Install kernel using'
   echo  '                  (your) ~/bin/$(INSTALLKERNEL) or'
   echo  '                  (distribution) /sbin/$(INSTALLKERNEL) or'
   echo  '                  install to $$(INSTALL_PATH) and run lilo'
   echo  '  fdimage      - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)'
   echo  '  fdimage144   - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)'
   echo  '  fdimage288   - Create 2.8MB boot floppy image (arch/x86/boot/fdimage)'
   echo  '  isoimage     - Create a boot CD-ROM image (arch/x86/boot/image.iso)'
   echo  '                  bzdisk/fdimage*/isoimage also accept:'
   echo  '                  FDARGS="..."  arguments for the booted kernel'
   echo  '                  FDINITRD=file initrd for the booted kernel'
 endef
	# SPDX-License-Identifier: GPL-2.0
	# Unified Makefile for i386 and x86_64

	# select defconfig based on actual architecture
	ifeq ($(ARCH),x86)
	ifeq ($(shell uname -m),x86_64)
	KBUILD_DEFCONFIG := x86_64_defconfig
	else
	KBUILD_DEFCONFIG := i386_defconfig
	endif
	else
	KBUILD_DEFCONFIG := $(ARCH)_defconfig
	endif

	# For gcc stack alignment is specified with -mpreferred-stack-boundary,
	# clang has the option -mstack-alignment for that purpose.
	ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
	cc_stack_align4 := -mpreferred-stack-boundary=2
	cc_stack_align8 := -mpreferred-stack-boundary=3
	else ifneq ($(call cc-option, -mstack-alignment=16),)
	cc_stack_align4 := -mstack-alignment=4
	cc_stack_align8 := -mstack-alignment=8
	endif

	# How to compile the 16-bit code. Note we always compile for -march=i386;
	# that way we can complain to the user if the CPU is insufficient.
	#
	# The -m16 option is supported by GCC >= 4.9 and clang >= 3.5. For
	# older versions of GCC, include an assembly header to make sure that
	# gcc doesn't play any games behind our back.
	CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h
	M16_CFLAGS := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))

	REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
	-Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
	-fno-strict-aliasing -fomit-frame-pointer -fno-pic \
	-mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)

	REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
	REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
	REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
	REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
	REALMODE_CFLAGS += $(CLANG_FLAGS)
	export REALMODE_CFLAGS

	# BITS is used as extension for files which are available in a 32 bit
	# and a 64 bit version to simplify shared Makefiles.
	# e.g.: obj-y += foo_$(BITS).o
	export BITS

	ifdef CONFIG_X86_NEED_RELOCS
	LDFLAGS_vmlinux := --emit-relocs --discard-none
	endif

	#
	# Prevent GCC from generating any FP code by mistake.
	#
	# This must happen before we try the -mpreferred-stack-boundary, see:
	#
	# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
	#
	KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
	KBUILD_CFLAGS += $(call cc-option,-mno-avx,)

	# Intel CET isn't enabled in the kernel
	KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)

	ifeq ($(CONFIG_X86_32),y)
	BITS := 32
	UTS_MACHINE := i386
	CHECKFLAGS += -D__i386__

	biarch := $(call cc-option,-m32)
	KBUILD_AFLAGS += $(biarch)
	KBUILD_CFLAGS += $(biarch)

	KBUILD_CFLAGS += -msoft-float -mregparm=3 -freg-struct-return

	# Never want PIC in a 32-bit kernel, prevent breakage with GCC built
	# with nonstandard options
	KBUILD_CFLAGS += -fno-pic

	# Align the stack to the register width instead of using the default
	# alignment of 16 bytes. This reduces stack usage and the number of
	# alignment instructions.
	KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align4))

	# CPU-specific tuning. Anything which can be shared with UML should go here.
	include arch/x86/Makefile_32.cpu
	KBUILD_CFLAGS += $(cflags-y)

	# temporary until string.h is fixed
	KBUILD_CFLAGS += -ffreestanding
	else
	BITS := 64
	UTS_MACHINE := x86_64
	CHECKFLAGS += -D__x86_64__

	biarch := -m64
	KBUILD_AFLAGS += -m64
	KBUILD_CFLAGS += -m64

	# Align jump targets to 1 byte, not the default 16 bytes:
	KBUILD_CFLAGS += $(call cc-option,-falign-jumps=1)

	# Pack loops tightly as well:
	KBUILD_CFLAGS += $(call cc-option,-falign-loops=1)

	# Don't autogenerate traditional x87 instructions
	KBUILD_CFLAGS += $(call cc-option,-mno-80387)
	KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387)

	# By default gcc and clang use a stack alignment of 16 bytes for x86.
	# However the standard kernel entry on x86-64 leaves the stack on an
	# 8-byte boundary. If the compiler isn't informed about the actual
	# alignment it will generate extra alignment instructions for the
	# default alignment which keep the stack misaligned.
	# Furthermore an alignment to the register width reduces stack usage
	# and the number of alignment instructions.
	KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align8))

	# Use -mskip-rax-setup if supported.
	KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)

	# FIXME - should be integrated in Makefile.cpu (Makefile_32.cpu)
	cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)
	cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)

	cflags-$(CONFIG_MCORE2) += \
	$(call cc-option,-march=core2,$(call cc-option,-mtune=generic))
	cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
	$(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
	cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=generic)
	KBUILD_CFLAGS += $(cflags-y)

	KBUILD_CFLAGS += -mno-red-zone
	KBUILD_CFLAGS += -mcmodel=kernel

	# -funit-at-a-time shrinks the kernel .text considerably
	# unfortunately it makes reading oopses harder.
	KBUILD_CFLAGS += $(call cc-option,-funit-at-a-time)
	endif

	ifdef CONFIG_X86_X32
	x32_ld_ok := $(call try-run,\
	/bin/echo -e '1: .quad 1b' \| \
	$(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" - && \
	$(OBJCOPY) -O elf32-x86-64 "$$TMP" "$$TMPO" && \
	$(LD) -m elf32_x86_64 "$$TMPO" -o "$$TMP",y,n)
	ifeq ($(x32_ld_ok),y)
	CONFIG_X86_X32_ABI := y
	KBUILD_AFLAGS += -DCONFIG_X86_X32_ABI
	KBUILD_CFLAGS += -DCONFIG_X86_X32_ABI
	else
	$(warning CONFIG_X86_X32 enabled but no binutils support)
	endif
	endif
	export CONFIG_X86_X32_ABI

	#
	# If the function graph tracer is used with mcount instead of fentry,
	# '-maccumulate-outgoing-args' is needed to prevent a GCC bug
	# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109)
	#
	ifdef CONFIG_FUNCTION_GRAPH_TRACER
	ifndef CONFIG_HAVE_FENTRY
	ACCUMULATE_OUTGOING_ARGS := 1
	else
	ifeq ($(call cc-option-yn, -mfentry), n)
	ACCUMULATE_OUTGOING_ARGS := 1

	# GCC ignores '-maccumulate-outgoing-args' when used with '-Os'.
	# If '-Os' is enabled, disable it and print a warning.
	ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
	undefine CONFIG_CC_OPTIMIZE_FOR_SIZE
	$(warning Disabling CONFIG_CC_OPTIMIZE_FOR_SIZE. Your compiler does not have -mfentry so you cannot optimize for size with CONFIG_FUNCTION_GRAPH_TRACER.)
	endif

	endif
	endif
	endif

	ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
	# This compiler flag is not supported by Clang:
	KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
	endif

	# Stackpointer is addressed different for 32 bit and 64 bit x86
	sp-$(CONFIG_X86_32) := esp
	sp-$(CONFIG_X86_64) := rsp

	# do binutils support CFI?
	cfi := $(call as-instr,.cfi_startproc\n.cfi_rel_offset $(sp-y)$(comma)0\n.cfi_endproc,-DCONFIG_AS_CFI=1)
	# is .cfi_signal_frame supported too?
	cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)
	cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)

	# does binutils support specific instructions?
	asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
	asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
	asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)
	avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
	avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
	avx512_instr :=$(call as-instr,vpmovm2b %k1$(comma)%zmm5,-DCONFIG_AS_AVX512=1)
	sha1_ni_instr :=$(call as-instr,sha1msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA1_NI=1)
	sha256_ni_instr :=$(call as-instr,sha256msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA256_NI=1)

	KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr)
	KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr)

	KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)

	#
	# The 64-bit kernel must be aligned to 2MB. Pass -z max-page-size=0x200000 to
	# the linker to force 2MB page size regardless of the default page size used
	# by the linker.
	#
	ifdef CONFIG_X86_64
	KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
	endif

	# Speed up the build
	KBUILD_CFLAGS += -pipe
	# Workaround for a gcc prelease that unfortunately was shipped in a suse release
	KBUILD_CFLAGS += -Wno-sign-compare
	#
	KBUILD_CFLAGS += -fno-asynchronous-unwind-tables

	# Avoid indirect branches in kernel to deal with Spectre
	ifdef CONFIG_RETPOLINE
	KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
	# Additionally, avoid generating expensive indirect jumps which
	# are subject to retpolines for small number of switch cases.
	# clang turns off jump table generation by default when under
	# retpoline builds, however, gcc does not for x86. This has
	# only been fixed starting from gcc stable version 8.4.0 and
	# onwards, but not for older ones. See gcc bug #86952.
	ifndef CONFIG_CC_IS_CLANG
	KBUILD_CFLAGS += $(call cc-option,-fno-jump-tables)
	endif
	endif

	archscripts: scripts_basic
	$(Q)$(MAKE) $(build)=arch/x86/tools relocs

	###
	# Syscall table generation

	archheaders:
	$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all

	###
	# Kernel objects

	head-y := arch/x86/kernel/head_$(BITS).o
	head-y += arch/x86/kernel/head$(BITS).o
	head-y += arch/x86/kernel/ebda.o
	head-y += arch/x86/kernel/platform-quirks.o

	libs-y += arch/x86/lib/

	# See arch/x86/Kbuild for content of core part of the kernel
	core-y += arch/x86/

	# drivers-y are linked after core-y
	drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
	drivers-$(CONFIG_PCI) += arch/x86/pci/

	# must be linked after kernel/
	drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/

	# suspend and hibernation support
	drivers-$(CONFIG_PM) += arch/x86/power/

	drivers-$(CONFIG_FB) += arch/x86/video/

	####
	# boot loader support. Several targets are kept for legacy purposes

	boot := arch/x86/boot

	BOOT_TARGETS = bzlilo bzdisk fdimage fdimage144 fdimage288 isoimage

	PHONY += bzImage $(BOOT_TARGETS)

	# Default kernel to build
	all: bzImage

	# KBUILD_IMAGE specify target image being built
	KBUILD_IMAGE := $(boot)/bzImage

	bzImage: vmlinux
	ifeq ($(CONFIG_X86_DECODER_SELFTEST),y)
	$(Q)$(MAKE) $(build)=arch/x86/tools posttest
	endif
	$(Q)$(MAKE) $(build)=$(boot) $(KBUILD_IMAGE)
	$(Q)mkdir -p $(objtree)/arch/$(UTS_MACHINE)/boot
	$(Q)ln -fsn ../../x86/boot/bzImage $(objtree)/arch/$(UTS_MACHINE)/boot/$@

	$(BOOT_TARGETS): vmlinux
	$(Q)$(MAKE) $(build)=$(boot) $@

	PHONY += install
	install:
	$(Q)$(MAKE) $(build)=$(boot) $@

	PHONY += vdso_install
	vdso_install:
	$(Q)$(MAKE) $(build)=arch/x86/entry/vdso $@

	archprepare: checkbin
	checkbin:
	ifndef CONFIG_CC_HAS_ASM_GOTO
	@echo Compiler lacks asm-goto support.
	@exit 1
	endif
	ifdef CONFIG_RETPOLINE
	ifeq ($(RETPOLINE_CFLAGS),)
	@echo "You are building kernel with non-retpoline compiler." >&2
	@echo "Please update your compiler." >&2
	@false
	endif
	endif

	archclean:
	$(Q)rm -rf $(objtree)/arch/i386
	$(Q)rm -rf $(objtree)/arch/x86_64
	$(Q)$(MAKE) $(clean)=$(boot)
	$(Q)$(MAKE) $(clean)=arch/x86/tools

	define archhelp
	echo '* bzImage - Compressed kernel image (arch/x86/boot/bzImage)'
	echo ' install - Install kernel using'
	echo ' (your) ~/bin/$(INSTALLKERNEL) or'
	echo ' (distribution) /sbin/$(INSTALLKERNEL) or'
	echo ' install to $$(INSTALL_PATH) and run lilo'
	echo ' fdimage - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)'
	echo ' fdimage144 - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)'
	echo ' fdimage288 - Create 2.8MB boot floppy image (arch/x86/boot/fdimage)'
	echo ' isoimage - Create a boot CD-ROM image (arch/x86/boot/image.iso)'
	echo ' bzdisk/fdimage*/isoimage also accept:'
	echo ' FDARGS="..." arguments for the booted kernel'
	echo ' FDINITRD=file initrd for the booted kernel'
	endef