嵌入式开发(S5PV210)——u-boot的顶层config.mk分析

1、config.mk的作用

config.mk的作用是配置uboot编译的，比如配置交叉编译工具链，链接地址，编译选项，指定头文件路径等，但是config.mk的配置是建立在顶层mkconfig、主Makefile等配置之上的。

2、config.mk的调用

# load other configuration
include $(TOPDIR)/config.mk

config.mk是被主Makefile调用.

3、congfig.mk的分析：

3.1、autoconf.mk文件

#在 主Makefile 中生成
$(obj)include/autoconf.mk: $(obj)include/config.h
	@$(XECHO) Generating $@ ; \
	set -e ; \
	: Extract the config macros ; \
	$(CPP) $(CFLAGS) -DDO_DEPS_ONLY -dM include/common.h | \
		sed -n -f tools/scripts/define2mk.sed > $@

#在顶层mkconfig中生成 $(obj)include/config.h文件
#
# Create board specific header file
#
if [ "$APPEND" = "yes" ]	# Append to existing config file
then
	echo >> config.h
else
	> config.h		# Create new config file
fi
echo "/* Automatically generated - do not edit */" >>config.h
echo "#include <configs/$1.h>" >>config.h

#在config.mk文件中引用autoconf.mk
# Load generated board configuration
sinclude $(OBJTREE)/include/autoconf.mk

作用就是用来指导整个uboot的编译过程。这个文件的内容其实就是很多CONFIG_开头的宏（可以理解为变量），这些宏/变量会影响我们uboot编译过程的走向（原理就是条件编译）。在uboot代码中有很多地方使用条件编译进行编写，这个条件编译是用来实现可移植性的。
autoconfig.mk文件不是源码提供的，是配置过程中在主Makefile中生成的,依赖 $(obj)include/config.h，而 $(obj)include/config.h也不是源码提供的，是在顶层mkconfig中生成的，原材料在源码目录的inlcude/configs/xxx.h头文件。（X210开发板中为include/configs/x210_sd.h）。这个头文件里面全都是宏定义，这些宏定义就是我们对当前开发板的移植。每一个开发板的移植都对应这个目录下的一个头文件，这个头文件里每一个宏定义都很重要，这些配置的宏定义就是我们移植uboot的关键所在。

3.2、链接地址：TEXT_BASE

#主Makefile中
x210_sd_config :	unconfig
	@$(MKCONFIG) $(@:_config=) arm s5pc11x x210 samsung s5pc110
	@echo "TEXT_BASE = 0xc3e00000" > $(obj)board/samsung/x210/config.mk

#在config.mk中,包含board/samsung/x210/config.mk
ifdef	VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
ifdef	BOARD
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk	# include board specific rules
endif

ifneq ($(TEXT_BASE),)
CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE)
endif

LDFLAGS += -Bstatic -T $(LDSCRIPT) $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
LDFLAGS += -Ttext $(TEXT_BASE)
endif

#导出到环境变量
export	TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS

TEXT_BASE变量保存的是链接地址，在主Makefile中配置的时候写到$(obj)board/samsung/x210/config.mk文件里，在config.mk中包含board/samsung/x210/config.mk，引入TEXT_BASE变量。LDFLAGS += -Ttext $(TEXT_BASE)就是在链接的时候指定链接地址。

3.3、链接脚本

ifeq ($(CONFIG_NAND_U_BOOT),y)
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot-nand.lds
else
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds
endif

通过宏定义来决定此次编译选择哪一份链接脚本，上面就是通过条件编译来选择要使用的编译脚本。

4、config.mk的内容

#
# (C) Copyright 2000-2006
# Wolfgang Denk, DENX Software Engineering, [e-mail].
#
# See file CREDITS for list of people who contributed to this
# project.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of
# the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA 02111-1307 USA
#

#########################################################################
#这部分是不同的编译方式：原地编译和指定目录编译
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

# clean the slate ...
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

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

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
#
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...) 交叉编译工具链
#
AS	= $(CROSS_COMPILE)as
LD	= $(CROSS_COMPILE)ld
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

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

# Load generated board configuration
sinclude $(OBJTREE)/include/autoconf.mk

ifdef	ARCH
sinclude $(TOPDIR)/$(ARCH)_config.mk	# include architecture dependend rules
endif
ifdef	CPU
sinclude $(TOPDIR)/cpu/$(CPU)/config.mk	# include  CPU	specific rules
endif
ifdef	SOC
sinclude $(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk	# include  SoC	specific rules
endif
ifdef	VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
ifdef	BOARD
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk	# include board specific rules
endif

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

ifneq (,$(findstring s,$(MAKEFLAGS)))
ARFLAGS = cr
else
ARFLAGS = crv
endif
RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG
OPTFLAGS= -Os #-fomit-frame-pointer
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
OBJCFLAGS += --gap-fill=0xff

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

CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS)		\
	-D__KERNEL__
ifneq ($(TEXT_BASE),)
CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE)
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)

# 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<format>
# 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) $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
LDFLAGS += -Ttext $(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.

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

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

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

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