Makefile模板分析

这是象棋小子根据u-boot的Makefile制作的简易Makefile模板，简单易用，本文通过分析该Makefile，帮助理解u-boot的Makefile。

首先看文件结构图：

.
├── apps
│   ├── main.c
│   └── Makefile
├── config.mk
├── Makefile
├── rules.mk
├── start_code
│   ├── Exception.c
│   ├── Exception.h
│   ├── LowLevelInit.S
│   ├── Makefile
│   ├── MMU.c
│   ├── MMU.h
│   ├── NAND.c
│   ├── NAND.h
│   ├── s3c2416.h
│   ├── s3c2416.lds
│   └── s3c2416.S
└── tree.txt

2 directories, 17 files

/目录下有config.mk Makefile rules.mk三个文件，

config.mk主要配置编译选项，该文件被所有Makefile所包含：

TEXT_BASE=0x30000000
export TEXT_BASE

CROSS_COMPILE = arm-linux-
export CROSS_COMPILE

DEBUG = n

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
export    AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP

LDSCRIPT = $(TOPDIR)/start_code/s3c2416.lds
LIBS     := -lc
LDFLAGS := -Bstatic -T $(LDSCRIPT) -Ttext $(TEXT_BASE) $(LIBS)

AFLAGS :=

ARFLAGS := cr

CFLAGS := -Wall -Wstrict-prototypes
CFLAGS += -I $(TOPDIR)/start_code -I $(TOPDIR)/apps
ifeq ($(DEBUG), y)
CFLAGS += -g
else
CFLAGS += -O2
endif

export LDFLAGS AFLAGS CFLAGS ARFLAGS

%.o: %.S
    @echo "assembling $<..."
    @$(CC) $(AFLAGS) -c -o $@ $<
%.o: %.s
    @echo "assembling $<..."
    @$(CC) $(AFLAGS) -c -o $@ $<
%.o: %.c
    @echo "compiling $<..."
    @$(CC) $(CFLAGS) -c -o $@ $<
%.o: %.C
    @echo "compiling $<..."
    @$(CC) $(CFLAGS) -c -o $@ $<

再来看顶层Makefile，顶层Makefile主要是定义编译目标，包括需要编译的目录:

#
# Copyright (C) Dinghong Huang([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
#

TOPDIR        := $(shell pwd)
export TOPDIR

SUBDIRS = $(TOPDIR)/start_code $(TOPDIR)/apps

include config.mk

FOLDERS    := $(notdir $(SUBDIRS))
LIBS    := $(addsuffix .a, $(addprefix /lib, $(FOLDERS)))
__LIBS    := $(join $(SUBDIRS), $(LIBS))

ALL = s3c2416.bin s3c2416.dis s3c2416.srec

.PHONY: all clean depend $(SUBDIRS)          /* 声明这些目标不需要判断依赖文件的时间戳，例如当执行make all时，每次都会执行all:下面的命令，而不用判断依赖文件是否被修改（但要求依赖文件必须存在） */

all: $(ALL)
s3c2416.hex: s3c2416.elf
    @echo "creating hex file $@ from $<..."
    @$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@

s3c2416.srec: s3c2416.elf
    @echo "creating srec file $@ from $<..."
    @$(OBJCOPY) ${OBJCFLAGS} -O srec $< $@

s3c2416.bin: s3c2416.elf
    @echo "creating bin file $@ from $<..."
    @$(OBJCOPY) ${OBJCFLAGS} -R .mmudata -S -O binary $< $@

s3c2416.dis: s3c2416.elf
    @echo "creating dis file $@ from $<..."
    @$(OBJDUMP) -d $< > $@

s3c2416.elf: depend $(SUBDIRS) $(LDSCRIPT)
    @echo "Linking..."
    @$(LD) $(LDFLAGS) --start-group $(__LIBS) --end-group -Map s3c2416.map -o s3c2416.elf

depend:
    @for dir in $(SUBDIRS); do $(MAKE) --no-print-directory -C $$dir _depend; done

$(SUBDIRS):
    @$(MAKE) -C $@ all

clean:
    rm -f s3c2416.elf s3c2416.map s3c2416.srec s3c2416.bin s3c2416.dis
    @for dir in $(SUBDIRS); do $(MAKE) -C $$dir clean; done

这里复习一下shell 中的$@等特殊变量，注意与Makefile的$@不一样
shell：
$# 是传给脚本的参数个数
$0 是脚本本身的名字
$1 是传递给该shell脚本的第一个参数
$2 是传递给该shell脚本的第二个参数
$@ 是传给脚本的所有参数的列表
$* 是以一个单字符串显示所有向脚本传递的参数，与位置变量不同，参数可超过9个
$$ 是脚本运行的当前进程ID号
$? 是显示最后命令的退出状态，0表示没有错误，其他表示有错误

Makefile：
$@ 代表目标
$^ 代表所有的依赖对象
$< 代表第一个依赖对象

相对而言，rule.mk就很简单了，只是用来将.c或.s文件替换为.o目标文件：

.PHONY: _depend
_depend: .depend
.depend: Makefile $(TOPDIR)/config.mk $(SRCS)
    @rm -f $@
    @for f in $(SRCS); do \
        g=`basename $$f | sed -e 's/\(.*\)\.\w/\1.o/'`; \
        $(CC) -M $(CFLAGS) -MQ $$g $$f >> $@ ; \
    done

app目录下的makefile：

include $(TOPDIR)/config.mk


OBJS    = main.o

SRCS    := $(OBJS:.o=.c)
CURDIR    := $(shell pwd)
FOLDER    := $(notdir $(CURDIR))
LIB    := lib$(FOLDER).a

.PHONY: all clean
all: .depend $(LIB)

$(LIB): $(OBJS)
    @$(AR) $(ARFLAGS) $@ $(OBJS)

clean:
    rm -f .depend *.o $(LIB)


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

# defines $(obj).depend target
include $(TOPDIR)/rules.mk

sinclude .depend

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

start_code目录下的Makefile：

include $(TOPDIR)/config.mk

SOBJS    := s3c2416.o LowLevelInit.o
COBJS    := MMU.o NAND.o Exception.o

SRCS    := $(SOBJS:.o=.S) $(COBJS:.o=.c)
OBJS    := $(SOBJS) $(COBJS)
CURDIR    := $(shell pwd)
FOLDER    := $(notdir $(CURDIR))
LIB    := lib$(FOLDER).a

.PHONY: all clean
all: .depend $(LIB)

$(LIB): $(OBJS)
    @$(AR) $(ARFLAGS) $@ $(OBJS)

clean:
    rm -f .depend *.o $(LIB)


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

# defines $(obj).depend target
include $(TOPDIR)/rules.mk

sinclude .depend

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

参考：
http://blog.csdn.net/huang20083200056/article/details/24305373