版本信息： u-boot-2010-06顶层目录下的config.mk文件主要完成如下功能的配置：
1、确定生成可执行文件过程中需要的各种工具，如编译器(arm-linux-gcc)、连接器(arm-linux-ld)、反汇编器(arm-linux-objdump)等
2、确定CPU、板相关的配置文件，存在于各个目录下的config.mk
3、确定编译、链接、转换等过程的操作选项
4、根据步骤3确定的编译连接选项生成需要的文件
config.mk完整内容及必要注释如下
注：config.mk文件注释符改为/* 注释内容 */
ifneq ($(OBJTREE),$(SRCTREE))
ifeq ($(CURDIR),$(SRCTREE))
dir :=
else
dir := $(subst $(SRCTREE)/,,$(CURDIR))
endif
obj := $(if $(dir),$(OBJTREE)/$(dir)/,$(OBJTREE)/)
src := $(if $(dir),$(SRCTREE)/$(dir)/,$(SRCTREE)/)
$(shell mkdir -p $(obj))
else
obj :=
src :=
endif
/* obj = 空，src = 空
* dir = 空
*/
/* clean the slate ... */
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =
/* HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
* -Wall: 打印出编译时所有的错误或警告信息
* -Wstrict-prototypes: 编译时，若产生与数据类型不相符的问题，打印出提示或警告信息。当在不同体系结构间移植时，加上该选项可避免很多错误
* -O: 编译代码时的优化等级，共有五种：-O0、-O1、-O2、-O3和-Os
* -fomit-frame-pointer: 对于不需要帧指针的函数,不要在寄存器中保存帧指针
* 代码优化时打开-fomit-frame-pointer，函数调用时不保存frame指针，也就不能用backtrace()来查看函数栈调用
* backtrace()系列函数见[http://blog.csdn.net/u013686019/article/details/42128771](Linux中backtrace()系列函数的应用实例)
*/
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer \
$(HOSTCPPFLAGS)
/* HOSTSTRIP = strip
* strip能清除执行文件中不必要的标示符及调试信息，可减小文件大小而不影响正常使用，、
* 与压缩不同的是，文件一旦strip后就不能恢复原样
* strip后的文件不包含调试信息
*/
HOSTSTRIP = strip
/*
* Mac OS X / Darwin's C preprocessor is Apple specific. It
* generates numerous errors and warnings. We want to bypass it
* and use GNU C's cpp. To do this we pass the -traditional-cpp
* option to the compiler. Note that the -traditional-cpp flag
* DOES NOT have the same semantics as GNU C's flag, all it does
* is invoke the GNU preprocessor in stock ANSI/ISO C fashion.
*
* Apple's linker is similar, thanks to the new 2 stage linking
* multiple symbol definitions are treated as errors, hence the
* -multiply_defined suppress option to turn off this error.
*/
ifeq ($(HOSTOS),darwin)
......
else
HOSTCC = gcc
endif
ifeq ($(HOSTOS),cygwin)
......
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.
*/
HOSTCFLAGS_NOPED = $(filter-out -pedantic,$(HOSTCFLAGS))
/* -pedantic: 当GCC在编译不符合ANSI/ISO C语言标准的源代码时，如果在编译指令中加上了-pedantic选项
* 那么源程序中使用了扩展语法的地方将产生相应的警告信息
*/
HOSTCFLAGS += -pedantic
#########################################################################
/* Option checker (courtesy linux kernel) to ensure
* only supported compiler options are used
* cc-option变量保存了一个测试编译选项的命令，其他地方会经常用call函数来调用它，测试编译选项
* if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1;then
echo "$(1)";
else
echo "$(2)";
fi;
* -S：编译后立即结束，不进行汇编等操作
* -o /dev/null : 生成文件到/dev/null，即不生成任何编译结果,要编译的文件也为空
* -xc: 指定按c语言编译
* 用此语句如：call cc-option,-a,-b 则如果支持-a选项则返回-a否则返回-b
*/
cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
/* Include the make variables (CC, etc...) */
AS = $(CROSS_COMPILE)as /* 汇编工具 */
LD = $(CROSS_COMPILE)ld /* 链接工具 */
CC = $(CROSS_COMPILE)gcc /* 编译工具 */
CPP = $(CC) -E /* 预处理 */
AR = $(CROSS_COMPILE)ar /* 归档工具 */
NM = $(CROSS_COMPILE)nm /* 列出object文件中的符号 */
LDR = $(CROSS_COMPILE)ldr
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy /* 转换可执行文件格式工具 */
OBJDUMP = $(CROSS_COMPILE)objdump /* 反汇编工具 */
RANLIB = $(CROSS_COMPILE)RANLIB /* 产生归档文件索引 */
#########################################################################
/* Load generated board configuration */
/* sinclude:
* 在Makefile中可使用"sinclude"代替"include"，用来忽略由于包含文件不存在或者无法创建时的错误
*/
sinclude $(OBJTREE)/include/autoconf.mk
/* Some architecture config.mk files need to know what CPUDIR is set to,
* so calculate CPUDIR before including ARCH/SOC/CPU config.mk files.
* Check if arch/$ARCH/cpu/$CPU exists, otherwise assume arch/$ARCH/cpu contains
* CPU-specific code.
*/
CPUDIR=arch/$(ARCH)/cpu/$(CPU)
ifneq ($(SRCTREE)/$(CPUDIR),$(wildcard $(SRCTREE)/$(CPUDIR)))
CPUDIR=arch/$(ARCH)/cpu
endif
/* CPUDIR=arch/arm/cpu/arm920t */
/* include architecture dependend rules: arch/arm/config.mk */
sinclude $(TOPDIR)/arch/$(ARCH)/config.mk
/* include CPU specific rules: arch/arm/cpu/arm920t/config.mk */
sinclude $(TOPDIR)/$(CPUDIR)/config.mk
ifdef SOC
/* include SoC specific rules: arch/arm/cpu/arm920t/s3c24x0/config.mk */
sinclude $(TOPDIR)/$(CPUDIR)/$(SOC)/config.mk
endif
ifdef VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
/* BOARDDIR = samsung/smdk2410 */
ifdef BOARD
/* include board specific rules: board/samsung/smdk2410/config.mk */
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk
endif
#########################################################################
ifneq (,$(findstring s,$(MAKEFLAGS)))
ARFLAGS = cr
else
ARFLAGS = crv
endif
RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG
OPTFLAGS= -Os #-fomit-frame-pointer
/* LDSCRIPT = arch/arm/cpu/arm920t/u-boot.lds，在在文件arch/arm/config.mk中赋值 */
ifndef LDSCRIPT
#LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds.debug
ifeq ($(CONFIG_NAND_U_BOOT),y)
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot-nand.lds
else
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds
endif
endif
/* 段之间的空隙用0xff填充 */
OBJCFLAGS += --gap-fill=0xff
gccincdir := $(shell $(CC) -print-file-name=include)
/* CPPFLAGS变量综合了DBGFLAGS，OPTFLAGS，RELFLAGS编译选项，并定义了__KERBEL__
* -D: 设置宏定义__KERNEL__
*/
CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS) \
-D__KERNEL__
ifneq ($(TEXT_BASE),)
CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE)
endif
ifneq ($(RESET_VECTOR_ADDRESS),)
CPPFLAGS += -DRESET_VECTOR_ADDRESS=$(RESET_VECTOR_ADDRESS)
endif
ifneq ($(OBJTREE),$(SRCTREE))
CPPFLAGS += -I$(OBJTREE)/include2 -I$(OBJTREE)/include
endif
CPPFLAGS += -I$(TOPDIR)/include
CPPFLAGS += -fno-builtin -ffreestanding -nostdinc \
-isystem $(gccincdir) -pipe $(PLATFORM_CPPFLAGS)
ifdef BUILD_TAG
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes \
-DBUILD_TAG='"$(BUILD_TAG)"'
else
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
endif
CFLAGS += $(call cc-option,-fno-stack-protector)
/* $(CPPFLAGS) sets -g, which causes gcc to pass a suitable -g<format> */
/* option to the assembler. */
AFLAGS_DEBUG :=
AFLAGS := $(AFLAGS_DEBUG) -D__ASSEMBLY__ $(CPPFLAGS)
LDFLAGS += -Bstatic -T $(obj)u-boot.lds $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
LDFLAGS += -Ttext $(TEXT_BASE)
endif
/* LDFLAGS = -Bstatic -T u-boot.lds -Ttext 0x33F80000 */
/* CFLAGS = -g -Os -fno-common -ffixed-r8 -msoft-float -D__KERNEL__ -DTEXT_BASE=0x33F80000 -I/u-boot-2010.06/include -fno-builtin -ffreestanding -nostdinc -isystem /usr/local/arm/4.2.2-eabi/usr/bin-ccache/../lib/gcc/arm-unknown-linux-gnueabi/4.2.2/include -pipe -DCONFIG_ARM -D__ARM__ -marm -mabi=aapcs-linux -mno-thumb-interwork -march=armv4 -Wall -Wstrict-prototypes -fno-stack-protector */
/* Location of a usable BFD library, where we define "usable" as
* "built for ${HOST}, supports ${TARGET}". Sensible values are
* - When cross-compiling: the root of the cross-environment
* - Linux/ppc (native): /usr
* - NetBSD/ppc (native): you lose ... (must extract these from the
* binutils build directory, plus the native and U-Boot include
* files don't like each other)
*
* So far, this is used only by tools/gdb/Makefile.
*/
ifeq ($(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
#########################################################################
export HOSTCC HOSTCFLAGS HOSTLDFLAGS PEDCFLAGS HOSTSTRIP CROSS_COMPILE \
AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP MAKE
export TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS
#########################################################################
/* 下面几行规定了各种文件的编译时用到的编译选项 */
/* Allow boards to use custom optimize flags on a per dir/file basis */
BCURDIR = $(subst $(SRCTREE)/,,$(CURDIR:$(obj)%=%))
/* BCURDIR = 顶层目录 */
$(obj)%.s: %.S
$(CPP) $(AFLAGS) $(AFLAGS_$(BCURDIR)/$(@F)) $(AFLAGS_$(BCURDIR)) \
-o $@ $<
$(obj)%.o: %.S
$(CC) $(AFLAGS) $(AFLAGS_$(BCURDIR)/$(@F)) $(AFLAGS_$(BCURDIR)) \
-o $@ $< -c
$(obj)%.o: %.c
$(CC) $(CFLAGS) $(CFLAGS_$(BCURDIR)/$(@F)) $(CFLAGS_$(BCURDIR)) \
-o $@ $< -c
$(obj)%.i: %.c
$(CPP) $(CFLAGS) $(CFLAGS_$(BCURDIR)/$(@F)) $(CFLAGS_$(BCURDIR)) \
-o $@ $< -c
$(obj)%.s: %.c
$(CC) $(CFLAGS) $(CFLAGS_$(BCURDIR)/$(@F)) $(CFLAGS_$(BCURDIR)) \
-o $@ $< -c -S