u-boot-1.1.6顶层目录config.mk分析

#####################################
# 这个文件的主要任务就是：

1、定义交叉编译器

2、定义AR、调试、优化、预处理、C编译器、链接选项

3、指定编译规则
#####################################

ifneq ($(OBJTREE),$(SRCTREE)) #如果目标存放目录不等于源码目录（UBOOT顶层目录）
ifeq ($(CURDIR),$(SRCTREE))   #如果当前目录等于目标存放目录
dir :=   #让dir为空
else
dir := $(subst $(SRCTREE)/,,$(CURDIR)) #把$(CURDIR)中的$(SRCTREE)/替换称空，然后赋给dir
endif

obj := $(if $(dir),$(OBJTREE)/$(dir)/,$(OBJTREE)/) #如果dir不为空，则把$(OBJTREE)/$(dir)/赋给obj，否则把$(OBJTREE)/赋给obj
src := $(if $(dir),$(SRCTREE)/$(dir)/,$(SRCTREE)/) #如果src不为空，则把$(SRCTREE)/$(dir)/赋给src，否则把$(SRCTREE)/赋给src

$(shell mkdir -p $(obj)) #通过一个shell函数创建obj路径
else
obj :=
src :=
endif

# clean the slate ... 清除标记
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =

#
# When cross-compiling on NetBSD, we have to define __PPC__ or else we
# will pick up a va_list declaration that is incompatible with the
# actual argument lists emitted by the compiler.
#
# [Tested on NetBSD/i386 1.5 + cross-powerpc-netbsd-1.3]

ifeq ($(ARCH),ppc)
ifeq ($(CROSS_COMPILE),powerpc-netbsd-)
PLATFORM_CPPFLAGS+= -D__PPC__
endif
ifeq ($(CROSS_COMPILE),powerpc-openbsd-)
PLATFORM_CPPFLAGS+= -D__PPC__
endif
endif

ifeq ($(ARCH),arm)
ifeq ($(CROSS_COMPILE),powerpc-netbsd-)
PLATFORM_CPPFLAGS+= -D__ARM__
endif

 

ifeq ($(CROSS_COMPILE),powerpc-openbsd-)
PLATFORM_CPPFLAGS+= -D__ARM__
endif
endif

ifeq ($(ARCH),blackfin)
PLATFORM_CPPFLAGS+= -D__BLACKFIN__ -mno-underscore
endif

 

ifdef ARCH   #指定预编译体系结构选项
sinclude $(TOPDIR)/$(ARCH)_config.mk # include architecture dependend rules,$(TOPDIR)/$(ARCH)_config.mk 即/u-boot-1.1.6/arm_config.mk 
endif
#如果您希望对不存在且不能重新创建的makefile文件进行忽略，并且不产生错误信息，则使用-include指令代替include指令，格式如下：
#-include filenames...
#这种指令的作用就是对于任何不存在的makefile文件都不会产生错误（即使警告信息也不会产生）。如果希望保持和其它版本的make兼容，
#使用sinclude指令代替-include指令。

 

ifdef CPU    #定义编译时对齐，浮点等选项
sinclude $(TOPDIR)/cpu/$(CPU)/config.mk # include  CPU specific rules,即/u-boot-1.1.6/cpu/arm920t/config.mk
endif

 

ifdef SOC     #$(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk这个文件不存在
sinclude $(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk # include  SoC specific rules
endif

 

ifdef VENDOR 
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif

ifdef BOARD   #指定特定板子的镜像连接时的内存基地址，相当重要！
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk # include board specific rules，即/u-boot-1.1.6/board/smdk2410/config.mk
endif

#查看/u-boot-1.1.6/board/smdk2410/config.mk，里面只有一句话TEXT_BASE = 0x33F80000 ，即指定内存基地址

#########################################################################

CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
      else if [ -x /bin/bash ]; then echo /bin/bash; \
      else echo sh; fi ; fi)

ifeq ($(HOSTOS)-$(HOSTARCH),darwin-ppc)
HOSTCC  = cc
else
HOSTCC  = gcc
endif
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
HOSTSTRIP = strip

#########################################################################
#
# Option checker (courtesy linux kernel) to ensure
# only supported compiler options are used
# 检查一下选项，以确保我们只使用所支持的编译器
#
#这一句实际上使用了一个shell函数，本函数使用了if-then语句，检测条件分别为"-S, -o, -xc"，也用到了重定向，具体含义可以自己分析
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 ;)

#定义交叉编译链工具
# Include the make variables (CC, etc...)
# 这里$(CROSS_COMPILE)即你的交叉编译器安装目录
AS = $(CROSS_COMPILE)as
LD = $(CROSS_COMPILE)ld
CC = $(CROSS_COMPILE)gcc
CPP = $(CC) -E
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
RANLIB = $(CROSS_COMPILE)RANLIB

 

ifneq (,$(findstring s,$(MAKEFLAGS))) #如果函数$(findstring s,$(MAKEFLAGS))不为空，也就是说能从$(MAKEFLAGS)中找到字符s
ARFLAGS = cr           #定义AR选项
else
ARFLAGS = crv
endif
RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG   #定义调试选项
OPTFLAGS= -Os #-fomit-frame-pointer    #定义优化选项
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

#依赖目标$(LDSCRIPT),即/u-boot-1.1.6/board/smdk2410/u-boot.lds，这个文件定义了链接时，各个目标文件是如何组织的
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds

endif

endif
OBJCFLAGS += --gap-fill=0xff

gccincdir := $(shell $(CC) -print-file-name=include)

CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS)  \       #定义预处理选项
 -D__KERNEL__ -DTEXT_BASE=$(TEXT_BASE)  \

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 := $(CPPFLAGS) -Wall -Wstrict-prototypes \       #定义C编译器选项
 -DBUILD_TAG='"$(BUILD_TAG)"'
else
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
endif

# avoid trigraph warnings while parsing pci.h (produced by NIOS gcc-2.9)
# this option have to be placed behind -Wall -- that's why it is here
ifeq ($(ARCH),nios)
ifeq ($(findstring 2.9,$(shell $(CC) --version)),2.9)
CFLAGS := $(CPPFLAGS) -Wall -Wno-trigraphs
endif
endif

# $(CPPFLAGS) sets -g, which causes gcc to pass a suitable -g
# option to the assembler.
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 += -Bstatic -T $(LDSCRIPT) -Ttext $(TEXT_BASE) $(PLATFORM_LDFLAGS)    #定义链接选项

#指定了起始地址TEXT_BASE

 

# 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 ($(HOSTOS)-$(HOSTARCH),darwin-ppc)
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

ifeq ($(PCI_CLOCK),PCI_66M)
CFLAGS := $(CFLAGS) -DPCI_66M
endif

#########################################################################

export CONFIG_SHELL HPATH HOSTCC HOSTCFLAGS CROSS_COMPILE \
 AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP \
 MAKE
export TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS

 

 

#########################################################################
#指定编译规则

ifndef REMOTE_BUILD

%.s: %.S
 $(CPP) $(AFLAGS) -o $@ $<
%.o: %.S
 $(CC) $(AFLAGS) -c -o $@ $<
%.o: %.c
 $(CC) $(CFLAGS) -c -o $@ $<

else

$(obj)%.s: %.S
 $(CPP) $(AFLAGS) -o $@ $<
$(obj)%.o: %.S
 $(CC) $(AFLAGS) -c -o $@ $<
$(obj)%.o: %.c
 $(CC) $(CFLAGS) -c -o $@ $<
endif

#########################################################################