1. 根目录:
2. tools
3. lib
4. bpf
5. Makefile

# Most of this file is copied from tools/lib/traceevent/Makefile

BPF_VERSION = 0
BPF_PATCHLEVEL = 0
BPF_EXTRAVERSION = 1

MAKEFLAGS += --no-print-directory


# Makefiles suck: This macro sets a default value of $(2) for the
# variable named by $(1), unless the variable has been set by
# environment or command line. This is necessary for CC and AR
# because make sets default values, so the simpler ?= approach
# won't work as expected.
define allow-override
  $(if $(or $(findstring environment,$(origin $(1))),\
            $(findstring command line,$(origin $(1)))),,\
    $(eval $(1) = $(2)))
endef

# Allow setting CC and AR, or setting CROSS_COMPILE as a prefix.
$(call allow-override,CC,$(CROSS_COMPILE)gcc)
$(call allow-override,AR,$(CROSS_COMPILE)ar)

INSTALL = install

# Use DESTDIR for installing into a different root directory.
# This is useful for building a package. The program will be
# installed in this directory as if it was the root directory.
# Then the build tool can move it later.
DESTDIR ?=
DESTDIR_SQ = '$(subst ','\'',$(DESTDIR))'

LP64 := $(shell echo __LP64__ | ${CC} ${CFLAGS} -E -x c - | tail -n 1)
ifeq ($(LP64), 1)
  libdir_relative = lib64
else
  libdir_relative = lib
endif

prefix ?= /usr/local
libdir = $(prefix)/$(libdir_relative)
man_dir = $(prefix)/share/man
man_dir_SQ = '$(subst ','\'',$(man_dir))'

export man_dir man_dir_SQ INSTALL
export DESTDIR DESTDIR_SQ

include ../../scripts/Makefile.include

# copy a bit from Linux kbuild

ifeq ("$(origin V)", "command line")
  VERBOSE = $(V)
endif
ifndef VERBOSE
  VERBOSE = 0
endif

ifeq ($(srctree),)
srctree := $(patsubst %/,%,$(dir $(shell pwd)))
srctree := $(patsubst %/,%,$(dir $(srctree)))
srctree := $(patsubst %/,%,$(dir $(srctree)))
#$(info Determined 'srctree' to be $(srctree))
endif

FEATURE_USER = .libbpf
FEATURE_TESTS = libelf libelf-getphdrnum libelf-mmap bpf
FEATURE_DISPLAY = libelf bpf

INCLUDES = -I. -I$(srctree)/tools/include -I$(srctree)/arch/$(ARCH)/include/uapi -I$(srctree)/include/uapi
FEATURE_CHECK_CFLAGS-bpf = $(INCLUDES)

include $(srctree)/tools/build/Makefile.feature

export prefix libdir src obj

# Shell quotes
libdir_SQ = $(subst ','\'',$(libdir))
libdir_relative_SQ = $(subst ','\'',$(libdir_relative))
plugin_dir_SQ = $(subst ','\'',$(plugin_dir))

LIB_FILE = libbpf.a libbpf.so

VERSION		= $(BPF_VERSION)
PATCHLEVEL	= $(BPF_PATCHLEVEL)
EXTRAVERSION	= $(BPF_EXTRAVERSION)

OBJ		= $@
N		=

LIBBPF_VERSION = $(BPF_VERSION).$(BPF_PATCHLEVEL).$(BPF_EXTRAVERSION)

# Set compile option CFLAGS
ifdef EXTRA_CFLAGS
  CFLAGS := $(EXTRA_CFLAGS)
else
  CFLAGS := -g -Wall
endif

ifeq ($(feature-libelf-mmap), 1)
  override CFLAGS += -DHAVE_LIBELF_MMAP_SUPPORT
endif

ifeq ($(feature-libelf-getphdrnum), 1)
  override CFLAGS += -DHAVE_ELF_GETPHDRNUM_SUPPORT
endif

# Append required CFLAGS
override CFLAGS += $(EXTRA_WARNINGS)
override CFLAGS += -Werror -Wall
override CFLAGS += -fPIC
override CFLAGS += $(INCLUDES)

ifeq ($(VERBOSE),1)
  Q =
else
  Q = @
endif

# Disable command line variables (CFLAGS) overide from top
# level Makefile (perf), otherwise build Makefile will get
# the same command line setup.
MAKEOVERRIDES=

all:

export srctree OUTPUT CC LD CFLAGS V
include $(srctree)/tools/build/Makefile.include

BPF_IN    := $(OUTPUT)libbpf-in.o
LIB_FILE := $(addprefix $(OUTPUT),$(LIB_FILE))

CMD_TARGETS = $(LIB_FILE)

TARGETS = $(CMD_TARGETS)

all: fixdep $(VERSION_FILES) all_cmd

all_cmd: $(CMD_TARGETS)

$(BPF_IN): force elfdep bpfdep
	$(Q)$(MAKE) $(build)=libbpf

$(OUTPUT)libbpf.so: $(BPF_IN)
	$(QUIET_LINK)$(CC) --shared $^ -o $@

$(OUTPUT)libbpf.a: $(BPF_IN)
	$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^

define update_dir
  (echo $1 > $@.tmp;				\
   if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
     rm -f $@.tmp;				\
   else						\
     echo '  UPDATE                 $@';	\
     mv -f $@.tmp $@;				\
   fi);
endef

define do_install
	if [ ! -d '$(DESTDIR_SQ)$2' ]; then		\
		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$2';	\
	fi;						\
	$(INSTALL) $1 '$(DESTDIR_SQ)$2'
endef

install_lib: all_cmd
	$(call QUIET_INSTALL, $(LIB_FILE)) \
		$(call do_install,$(LIB_FILE),$(libdir_SQ))

install: install_lib

### Cleaning rules

config-clean:
	$(call QUIET_CLEAN, config)
	$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null

clean:
	$(call QUIET_CLEAN, libbpf) $(RM) *.o *~ $(TARGETS) *.a *.so $(VERSION_FILES) .*.d \
		$(RM) LIBBPF-CFLAGS
	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf



PHONY += force elfdep bpfdep
force:

elfdep:
	@if [ "$(feature-libelf)" != "1" ]; then echo "No libelf found"; exit -1 ; fi

bpfdep:
	@if [ "$(feature-bpf)" != "1" ]; then echo "BPF API too old"; exit -1 ; fi

# Declare the contents of the .PHONY variable as phony.  We keep that
# information in a variable so we can use it in if_changed and friends.
.PHONY: $(PHONY)