1. 根目录:
2. arch
3. x86
4. entry
5. vdso
6. Makefile

#
# Building vDSO images for x86.
#

KBUILD_CFLAGS += $(DISABLE_LTO)
KASAN_SANITIZE := n

VDSO64-$(CONFIG_X86_64)		:= y
VDSOX32-$(CONFIG_X86_X32_ABI)	:= y
VDSO32-$(CONFIG_X86_32)		:= y
VDSO32-$(CONFIG_IA32_EMULATION)	:= y

# files to link into the vdso
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o

# files to link into kernel
obj-y				+= vma.o

# vDSO images to build
vdso_img-$(VDSO64-y)		+= 64
vdso_img-$(VDSOX32-y)		+= x32
vdso_img-$(VDSO32-y)		+= 32

obj-$(VDSO32-y)			+= vdso32-setup.o

vobjs := $(foreach F,$(vobjs-y),$(obj)/$F)

$(obj)/vdso.o: $(obj)/vdso.so

targets += vdso.lds $(vobjs-y)

# Build the vDSO image C files and link them in.
vdso_img_objs := $(vdso_img-y:%=vdso-image-%.o)
vdso_img_cfiles := $(vdso_img-y:%=vdso-image-%.c)
vdso_img_sodbg := $(vdso_img-y:%=vdso%.so.dbg)
obj-y += $(vdso_img_objs)
targets += $(vdso_img_cfiles)
targets += $(vdso_img_sodbg)
.SECONDARY: $(vdso_img-y:%=$(obj)/vdso-image-%.c) \
	$(vdso_img-y:%=$(obj)/vdso%.so)

export CPPFLAGS_vdso.lds += -P -C

VDSO_LDFLAGS_vdso.lds = -m64 -Wl,-soname=linux-vdso.so.1 \
			-Wl,--no-undefined \
			-Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096 \
			$(DISABLE_LTO)

$(obj)/vdso64.so.dbg: $(src)/vdso.lds $(vobjs) FORCE
	$(call if_changed,vdso)

HOST_EXTRACFLAGS += -I$(srctree)/tools/include -I$(srctree)/include/uapi -I$(srctree)/arch/x86/include/uapi
hostprogs-y			+= vdso2c

quiet_cmd_vdso2c = VDSO2C  $@
define cmd_vdso2c
	$(obj)/vdso2c $< $(<:%.dbg=%) $@
endef

$(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
	$(call if_changed,vdso2c)

#
# Don't omit frame pointers for ease of userspace debugging, but do
# optimize sibling calls.
#
CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
       -fno-omit-frame-pointer -foptimize-sibling-calls \
       -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO

$(vobjs): KBUILD_CFLAGS += $(CFL)

#
# vDSO code runs in userspace and -pg doesn't help with profiling anyway.
#
CFLAGS_REMOVE_vdso-note.o = -pg
CFLAGS_REMOVE_vclock_gettime.o = -pg
CFLAGS_REMOVE_vgetcpu.o = -pg
CFLAGS_REMOVE_vvar.o = -pg

#
# X32 processes use x32 vDSO to access 64bit kernel data.
#
# Build x32 vDSO image:
# 1. Compile x32 vDSO as 64bit.
# 2. Convert object files to x32.
# 3. Build x32 VDSO image with x32 objects, which contains 64bit codes
# so that it can reach 64bit address space with 64bit pointers.
#

CPPFLAGS_vdsox32.lds = $(CPPFLAGS_vdso.lds)
VDSO_LDFLAGS_vdsox32.lds = -Wl,-m,elf32_x86_64 \
			   -Wl,-soname=linux-vdso.so.1 \
			   -Wl,-z,max-page-size=4096 \
			   -Wl,-z,common-page-size=4096

# 64-bit objects to re-brand as x32
vobjs64-for-x32 := $(filter-out $(vobjs-nox32),$(vobjs-y))

# x32-rebranded versions
vobjx32s-y := $(vobjs64-for-x32:.o=-x32.o)

# same thing, but in the output directory
vobjx32s := $(foreach F,$(vobjx32s-y),$(obj)/$F)

# Convert 64bit object file to x32 for x32 vDSO.
quiet_cmd_x32 = X32     $@
      cmd_x32 = $(OBJCOPY) -O elf32-x86-64 $< $@

$(obj)/%-x32.o: $(obj)/%.o FORCE
	$(call if_changed,x32)

targets += vdsox32.lds $(vobjx32s-y)

$(obj)/%.so: OBJCOPYFLAGS := -S
$(obj)/%.so: $(obj)/%.so.dbg
	$(call if_changed,objcopy)

$(obj)/vdsox32.so.dbg: $(src)/vdsox32.lds $(vobjx32s) FORCE
	$(call if_changed,vdso)

CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
VDSO_LDFLAGS_vdso32.lds = -m32 -Wl,-m,elf_i386 -Wl,-soname=linux-gate.so.1

# This makes sure the $(obj) subdirectory exists even though vdso32/
# is not a kbuild sub-make subdirectory.
override obj-dirs = $(dir $(obj)) $(obj)/vdso32/

targets += vdso32/vdso32.lds
targets += vdso32/note.o vdso32/vclock_gettime.o vdso32/system_call.o
targets += vdso32/vclock_gettime.o

KBUILD_AFLAGS_32 := $(filter-out -m64,$(KBUILD_AFLAGS)) -DBUILD_VDSO
$(obj)/vdso32.so.dbg: KBUILD_AFLAGS = $(KBUILD_AFLAGS_32)
$(obj)/vdso32.so.dbg: asflags-$(CONFIG_X86_64) += -m32

KBUILD_CFLAGS_32 := $(filter-out -m64,$(KBUILD_CFLAGS))
KBUILD_CFLAGS_32 := $(filter-out -mcmodel=kernel,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
$(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)

$(obj)/vdso32.so.dbg: FORCE \
		      $(obj)/vdso32/vdso32.lds \
		      $(obj)/vdso32/vclock_gettime.o \
		      $(obj)/vdso32/note.o \
		      $(obj)/vdso32/system_call.o
	$(call if_changed,vdso)

#
# The DSO images are built using a special linker script.
#
quiet_cmd_vdso = VDSO    $@
      cmd_vdso = $(CC) -nostdlib -o $@ \
		       $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
		       -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \
		 sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'

VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-style=both) \
	$(call cc-ldoption, -Wl$(comma)--build-id) -Wl,-Bsymbolic $(LTO_CFLAGS)
GCOV_PROFILE := n

#
# Install the unstripped copies of vdso*.so.  If our toolchain supports
# build-id, install .build-id links as well.
#
quiet_cmd_vdso_install = INSTALL $(@:install_%=%)
define cmd_vdso_install
	cp $< "$(MODLIB)/vdso/$(@:install_%=%)"; \
	if readelf -n $< |grep -q 'Build ID'; then \
	  buildid=`readelf -n $< |grep 'Build ID' |sed -e 's/^.*Build ID: \(.*\)$$/\1/'`; \
	  first=`echo $$buildid | cut -b-2`; \
	  last=`echo $$buildid | cut -b3-`; \
	  mkdir -p "$(MODLIB)/vdso/.build-id/$$first"; \
	  ln -sf "../../$(@:install_%=%)" "$(MODLIB)/vdso/.build-id/$$first/$$last.debug"; \
	fi
endef

vdso_img_insttargets := $(vdso_img_sodbg:%.dbg=install_%)

$(MODLIB)/vdso: FORCE
	@mkdir -p $(MODLIB)/vdso

$(vdso_img_insttargets): install_%: $(obj)/%.dbg $(MODLIB)/vdso FORCE
	$(call cmd,vdso_install)

PHONY += vdso_install $(vdso_img_insttargets)
vdso_install: $(vdso_img_insttargets) FORCE

clean-files := vdso32.so vdso32.so.dbg vdso64* vdso-image-*.c vdsox32.so*