config.mk主要功能是配置单板信息和编译环境，将会被u-boot的makefile所调用，本文仍然侧重于句法分析。
#########################################################################
# 脚本所在的目录通常在U-boot源码顶层目录下，所以CURDIR = SRCTREE，所以dir = 空
ifeq ($(CURDIR),$(SRCTREE))
dir :=
else
dir := $(subst $(SRCTREE)/,,$(CURDIR))
endif
# 不相等的情况下才会建立相应的目录，这里不会被执行
ifneq ($(OBJTREE),$(SRCTREE))
# Create object files for SPL in a separate directory
ifeq ($(CONFIG_SPL_BUILD),y)
obj := $(if $(dir),$(SPLTREE)/$(dir)/,$(SPLTREE)/)
else
obj := $(if $(dir),$(OBJTREE)/$(dir)/,$(OBJTREE)/)
endif
src := $(if $(dir),$(SRCTREE)/$(dir)/,$(SRCTREE)/)
$(shell mkdir -p $(obj))
else
# Create object files for SPL in a separate directory
# CONFIG_SPL_BUILD = y的时候才会建立执行的存放编译文件的目录，这里也不执行
ifeq ($(CONFIG_SPL_BUILD),y)
obj := $(if $(dir),$(SPLTREE)/$(dir)/,$(SPLTREE)/)
$(shell mkdir -p $(obj))
else
# 所以最后的结果是obj为空，src也为空
obj :=
endif
src :=
endif
# clean the slate ...
# 清除标志
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =
#########################################################################
# HOSTCPPFLAGS的值为空，HOSTCFLAGS = -Wall -Wstrict-prototypes -O2
# -fomit-frame-pointer
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer \
$(HOSTCPPFLAGS)
HOSTSTRIP = strip
# Mac OS X / Darwin's C preprocessor is Apple specific. It
# generates numerous errors and warnings. We want to bypass it
# and use GNU C's cpp. To do this we pass the -traditional-cpp
# option to the compiler. Note that the -traditional-cpp flag
# DOES NOT have the same semantics as GNU C's flag, all it does
# is invoke the GNU preprocessor in stock ANSI/ISO C fashion.
#
# Apple's linker is similar, thanks to the new 2 stage linking
# multiple symbol definitions are treated as errors, hence the
# -multiply_defined suppress option to turn off this error.
#
# 如果HOSTOS是darwin体系，则做专门处理
ifeq ($(HOSTOS),darwin)
# get major and minor product version (e.g. '10' and '6' for Snow Leopard)
DARWIN_MAJOR_VERSION = $(shell sw_vers -productVersion | cut -f 1 -d '.')
DARWIN_MINOR_VERSION = $(shell sw_vers -productVersion | cut -f 2 -d '.')
os_x_before = $(shell if [ $(DARWIN_MAJOR_VERSION) -le $(1) -a \
$(DARWIN_MINOR_VERSION) -le $(2) ] ; then echo "$(3)"; else echo "$(4)"; fi ;)
# Snow Leopards build environment has no longer restrictions as described above
HOSTCC = $(call os_x_before, 10, 5, "cc", "gcc")
HOSTCFLAGS += $(call os_x_before, 10, 4, "-traditional-cpp")
HOSTLDFLAGS += $(call os_x_before, 10, 5, "-multiply_defined suppress")
else
# 除了darwin外其他都采用gcc
HOSTCC = gcc
endif
ifeq ($(HOSTOS),cygwin)
HOSTCFLAGS += -ansi
endif
# We build some files with extra pedantic flags to try to minimize things
# that won't build on some weird host compiler -- though there are lots of
# exceptions for files that aren't complaint.
# filter-out为反过滤函数，HOSTCFLAGS中的"-pedantic"全部删掉
# HOSTCFLAGS_NOPED = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
# HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
# -pedantic
HOSTCFLAGS_NOPED = $(filter-out -pedantic,$(HOSTCFLAGS))
HOSTCFLAGS += -pedantic
#########################################################################
#
# Option checker, gcc version (courtesy linux kernel) to ensure
# only supported compiler options are used
#
# 选项检查器，确保支持编译选项的唯一可用的gcc版本
# cc-option-sys=空 cc-option=空
# strip函数的作用是去掉字符串的空格，call函数作用是把它后面的参数一次赋值给$(1),$(2),...
# findstring函数是从字符串中超找指定内容，$(findstring $1,$(CC_OPTIONS))
# 就是从CC_OPTIONS从查找$(1)的内容，找到则返回$(1)，找不到则返回空
CC_OPTIONS_CACHE_FILE := $(OBJTREE)/include/generated/cc_options.mk
CC_TEST_OFILE := $(OBJTREE)/include/generated/cc_test_file.o
-include $(CC_OPTIONS_CACHE_FILE)
#########################################################################
# cc-option用于检查编译器CC是否支持某选项。将2个选项作为参数传递给cc-option函数，该函数# 调用CC编译器检查参数1是否支持，若支持则函数返回参数1，否则返回参数2 （因此CC编译器必须支# 持参数1或参数2，若两个都不支持则会编译出错）。可以像下面这样调用cc-option函数，并将支持# 的选项添加到FLAGS中: FLAGS +=$(call cc-option,option1,option2)
cc-option-sys = $(shell mkdir -p $(dir $(CC_TEST_OFILE)); \
if $(CC) $(CFLAGS) $(1) -S -xc /dev/null -o $(CC_TEST_OFILE) \
> /dev/null 2>&1; then \
echo 'CC_OPTIONS += $(strip $1)' >> $(CC_OPTIONS_CACHE_FILE); \
echo "$(1)"; fi)
ifeq ($(CONFIG_CC_OPT_CACHE_DISABLE),y)
cc-option = $(strip $(if $(call cc-option-sys,$1),$1,$2))
else
cc-option = $(strip $(if $(findstring $1,$(CC_OPTIONS)),$1,\
$(if $(call cc-option-sys,$1),$1,$2)))
endif
#########################################################################
# cc-version = 0404
# binutils-version = 0221
cc-version = $(shell $(SHELL) $(SRCTREE)/tools/gcc-version.sh $(CC))
binutils-version = $(shell $(SHELL) $(SRCTREE)/tools/binutils-version.sh $(AS))
#########################################################################
# Include the make variables (CC, etc...)
# AS = as
AS = $(CROSS_COMPILE)as
#########################################################################
# 链接器固定使用GNU ld
# LD = ld
LD = $(shell if $(CROSS_COMPILE)ld.bfd -v > /dev/null 2>&1; \
then echo "$(CROSS_COMPILE)ld.bfd"; else echo "$(CROSS_COMPILE)ld"; fi;)
#########################################################################
# 定义交叉工具链集
# CC = gcc
# CPP = gcc -E
# AR = ar
# NM = nm
# LDR = ldr
# STRIP = strip
# OBJCOPY = objcopy
# OBJDUMP = objdump
# RANLIB = RANLIB
# DTC = dtc
CC = $(CROSS_COMPILE)gcc
CPP = $(CC) -E
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
LDR = $(CROSS_COMPILE)ldr
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
RANLIB = $(CROSS_COMPILE)RANLIB
DTC = dtc
#########################################################################
# 加载产生的单板配置文件autoconf.mk和config.mk，均在include目录下
# config.mk中内容是ARCH CPU BOARD VENDOR SOC5个变量信息
# autoconf.mk为单板配置宏的集合,打开/关闭 用 y/n表示
sinclude $(OBJTREE)/include/autoconf.mk
sinclude $(OBJTREE)/include/config.mk
#########################################################################
# Some architecture config.mk files need to know what CPUDIR is set to,
# so calculate CPUDIR before including ARCH/SOC/CPU config.mk files.
# Check if arch/$ARCH/cpu/$CPU exists, otherwise assume arch/$ARCH/cpu contains
# CPU-specific code.
# 翻译上面这段英文:
# 需要知道CPUDIR的设置来查找一些架构的config.mk文件，所以在加载ARCH/SOC/config.mk和
# ARCH/CPU/config.mk之前要设置好CPUDIR路径。检查目录arch/$ARCH/cpu/$CPU是否存在，
# 否则认为arch/$ARCH/cpu目录下包含有CPU相关的代码。翻译完毕!
# 看看ifneq的执行:
# 首先这里CPUDIR = arch/$(ARCH)/cpu/$(CPU) = arch/arm/cpu/armv7
# wildcard函数用来匹配 arch/arm/cpu/armv7这一目录，意思就是如果不存在这个目录
# 则CPUDIR=arch/$(ARCH)/cpu=arch/arm/cpu，否则就保持采用
# CPUDIR=arch/arm/cpu/armv7
CPUDIR=arch/$(ARCH)/cpu/$(CPU)
ifneq ($(SRCTREE)/$(CPUDIR),$(wildcard $(SRCTREE)/$(CPUDIR)))
CPUDIR=arch/$(ARCH)/cpu
endif
#########################################################################
# 加载 $(TOPDIR)/arch/arm/config.mk
# 加载 $(TOPDIR)/arch/arm/config.mk
sinclude $(TOPDIR)/arch/$(ARCH)/config.mk # 加载架构编译选项文件
sinclude $(TOPDIR)/arch/arm/cpu/armv7/config.mk # 加载CPU相关编译选项文件
#########################################################################
# 定义有SOC = s5pc1xx，所以加载$(TOPDIR)/arch/arm/cpu/armv7/s5pc1xx/config.mk
ifdef SOC
sinclude $(TOPDIR)/$(CPUDIR)/$(SOC)/config.mk # include SoC specific rules
endif
#########################################################################
# 定义有VENDOR = samsung，所以BOARDDIR = samsung/smdkc100
ifdef VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
#########################################################################
# 定义有BOARD = smdkc100,所以加载$(TOPDIR)/board/samsung/smdkc100/config.mk
ifdef BOARD
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk # 加载单板编译选项文件
endif
#########################################################################
# 我们不会在任何地方使用ARFLAGS了，所以有人不更新$(AR)就试图处理旧代码的时候就会报错
# ARFLAGS = $(error update your Makefile to use cmd_link_o_target and not AR)
# RELFLAGS=$(PLATFORM_RELFLAGS)=-fno-common -ffixed-r8 -msoft-float
# DBGFLAGS = -g
# OPTFLAGS = -Os
# OBJCFLAGS = --gap-fill=0xff
# gccincdir = $(shell $(CC) -print-file-name=include)=交叉工具链include目录在宿# 主机中的位置CPPFLAGS = -g -Os -fno-common -ffixed-r8 -msoft-float -D__KERNEL__
ARFLAGS = $(error update your Makefile to use cmd_link_o_target and not AR)
RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG
OPTFLAGS= -Os # -fomit-frame-pointer
OBJCFLAGS += --gap-fill=0xff
gccincdir := $(shell $(CC) -print-file-name=include)
CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS) \
-D__KERNEL__
# Enable garbage collection of un-used sections for SPL
ifeq ($(CONFIG_SPL_BUILD),y)
CPPFLAGS += -ffunction-sections -fdata-sections
LDFLAGS_FINAL += --gc-sections
endif
##########################################################
# U-Boot编译时将使用TEXT_BASE作为代码段连接的起始地址
# CONFIG_SYS_TEXT_BASE不为空，所以CPPFLAGS会多出一项:
# -DCONFIG_SYS_TEXT_BASE=0x34800000
ifneq ($(CONFIG_SYS_TEXT_BASE),)
CPPFLAGS += -DCONFIG_SYS_TEXT_BASE=$(CONFIG_SYS_TEXT_BASE)
endif
ifneq ($(CONFIG_SPL_TEXT_BASE),)
CPPFLAGS += -DCONFIG_SPL_TEXT_BASE=$(CONFIG_SPL_TEXT_BASE)
endif
ifneq ($(CONFIG_SPL_PAD_TO),)
CPPFLAGS += -DCONFIG_SPL_PAD_TO=$(CONFIG_SPL_PAD_TO)
endif
ifeq ($(CONFIG_SPL_BUILD),y)
CPPFLAGS += -DCONFIG_SPL_BUILD
endif
ifneq ($(RESET_VECTOR_ADDRESS),)
CPPFLAGS += -DRESET_VECTOR_ADDRESS=$(RESET_VECTOR_ADDRESS)
endif
ifneq ($(OBJTREE),$(SRCTREE))
CPPFLAGS += -I$(OBJTREE)/include2 -I$(OBJTREE)/include
endif
##########################################################
# 添加-I$(TOPDIR)/include路径到CPPFLAGS中，还有
# -fno-builtin -ffreestanding -nostdinc -isystem $(gccincdir)
# -pipe $(PLATFORM_CPPFLAGS)也添加进CPPFLAGS中
CPPFLAGS += -I$(TOPDIR)/include
CPPFLAGS += -fno-builtin -ffreestanding -nostdinc \
-isystem $(gccincdir) -pipe $(PLATFORM_CPPFLAGS)
##########################################################
# 没有定义BUILD_TAG，执行else分支,赋值CFLAGS
ifdef BUILD_TAG
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes \
-DBUILD_TAG='"$(BUILD_TAG)"'
else
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
endif
##########################################################
# 利用call函数，使得$1=cc-option ,$2=-fno-stack-protector
# CFLAGS_SSP= $1$2 = -fno-stack-protector,然后把CFLAGS_SSP
# 追加给CFLAGS
CFLAGS_SSP := $(call cc-option,-fno-stack-protector)
CFLAGS += $(CFLAGS_SSP)
# Some toolchains enable security related warning flags by default,
# but they don't make much sense in the u-boot world, so disable them.
# 上面英文意思是一些工具链默认使用了一些安全警告选项，但是在U-boot的世界中我们不必要在意
# 太多这些警告，所以禁用它们。
# CFLAGS_WARN = -Wno-format-nonliteral -Wno-format-security，然后追加
# 到编译选项变量CFLAGS中
CFLAGS_WARN := $(call cc-option,-Wno-format-nonliteral) \
$(call cc-option,-Wno-format-security)
CFLAGS += $(CFLAGS_WARN)
# Report stack usage if supported
# 如果支持的话开启报告堆栈使用状态，通过参数-fstack-usage开启，追加到CFLAGS中
CFLAGS_STACK := $(call cc-option,-fstack-usage)
CFLAGS += $(CFLAGS_STACK)
# $(CPPFLAGS) sets -g, which causes gcc to pass a suitable -g<format>
# option to the assembler.
# CPPFLAGS设置了-g参数，
AFLAGS_DEBUG :=
# turn jbsr into jsr for m68k
ifeq ($(ARCH),m68k)
ifeq ($(findstring 3.4,$(shell $(CC) --version)),3.4)
AFLAGS_DEBUG := -Wa,-gstabs,-S
endif
endif
AFLAGS := $(AFLAGS_DEBUG) -D__ASSEMBLY__ $(CPPFLAGS)
LDFLAGS += $(PLATFORM_LDFLAGS)
LDFLAGS_FINAL += -Bstatic
# 设置U-boot的链接选项
LDFLAGS_u-boot += -T $(obj)u-boot.lds $(LDFLAGS_FINAL)
ifneq ($(CONFIG_SYS_TEXT_BASE),)
LDFLAGS_u-boot += -Ttext $(CONFIG_SYS_TEXT_BASE)
endif
# 设置U-boot的链接选项，当uboot是采用spl时的情况
LDFLAGS_u-boot-spl += -T $(obj)u-boot-spl.lds $(LDFLAGS_FINAL)
ifneq ($(CONFIG_SPL_TEXT_BASE),)
LDFLAGS_u-boot-spl += -Ttext $(CONFIG_SPL_TEXT_BASE)
endif
# Location of a usable BFD library, where we define "usable" as
# "built for ${HOST}, supports ${TARGET}". Sensible values are
# - When cross-compiling: the root of the cross-environment
# - Linux/ppc (native): /usr
# - NetBSD/ppc (native): you lose ... (must extract these from the
# binutils build directory, plus the native and U-Boot include
# files don't like each other)
#
# So far, this is used only by tools/gdb/Makefile.
# 非arm架构设置，不执行
ifeq ($(HOSTOS),darwin)
BFD_ROOT_DIR = /usr/local/tools
else
ifeq ($(HOSTARCH),$(ARCH))
# native
BFD_ROOT_DIR = /usr
else
#BFD_ROOT_DIR = /LinuxPPC/CDK # Linux/i386
#BFD_ROOT_DIR = /usr/pkg/cross # NetBSD/i386
BFD_ROOT_DIR = /opt/powerpc
endif
endif
#########################################################################
# 设置各种编译选项的环境变量供Makefile使用
export HOSTCC HOSTCFLAGS HOSTLDFLAGS PEDCFLAGS HOSTSTRIP CROSS_COMPILE \
AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP MAKE
export CONFIG_SYS_TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS
#########################################################################
# Allow boards to use custom optimize flags on a per dir/file basis
# BCURDIR = U-boot源码顶层目录，其他的太长了就不打出来了
BCURDIR = $(subst $(SRCTREE)/,,$(CURDIR:$(obj)%=%))
ALL_AFLAGS = $(AFLAGS) $(AFLAGS_$(BCURDIR)/$(@F)) $(AFLAGS_$(BCURDIR))
ALL_CFLAGS = $(CFLAGS) $(CFLAGS_$(BCURDIR)/$(@F)) $(CFLAGS_$(BCURDIR))
EXTRA_CPPFLAGS = $(CPPFLAGS_$(BCURDIR)/$(@F)) $(CPPFLAGS_$(BCURDIR))
ALL_CFLAGS += $(EXTRA_CPPFLAGS)
###########################################################################
# The _DEP version uses the $< file target (for dependency generation)
# See rules.mk
# 指定隐含的编译规则，例如：根据以上的定义，以“.s”结尾的目标文件将根据第一条规则由同名但后
# 缀为“.S”的源文件来生成，若不存在“.S”结尾的同名文件则根据最后一条规则由同名的“.c”文件生
# 成。
EXTRA_CPPFLAGS_DEP = $(CPPFLAGS_$(BCURDIR)/$(addsuffix .o,$(basename $<))) \
$(CPPFLAGS_$(BCURDIR))
$(obj)%.s: %.S
$(CPP) $(ALL_AFLAGS) -o $@ $<
$(obj)%.o: %.S
$(CC) $(ALL_AFLAGS) -o $@ $< -c
$(obj)%.o: %.c
$(CC) $(ALL_CFLAGS) -o $@ $< -c
$(obj)%.i: %.c
$(CPP) $(ALL_CFLAGS) -o $@ $< -c
$(obj)%.s: %.c
$(CC) $(ALL_CFLAGS) -o $@ $< -c -S
#########################################################################
# If the list of objects to link is empty, just create an empty built-in.o
# $1为空，if返回空，cmd_link_o_target = rm -f; arm-linux-ar rcs
cmd_link_o_target = $(if $(strip $1),\
$(LD) $(LDFLAGS) -r -o $@ $1,\
rm -f $@; $(AR) rcs $@ )
#########################################################################
