uboot2010.03 Makefile分析 .

转载自：http://blog.csdn.net/yyttiao/article/details/7899530

 

对于Makefile 由于源码特别长，所以，我在这里就一边摘录一边分析

# Include autoconf.mk before config.mk so that the config options are available
# to all top level build files. We need the dummy all: target to prevent the
# dependency target in autoconf.mk.dep from being the default.
all:
sinclude $(obj)include/autoconf.mk.dep
sinclude $(obj)include/autoconf.mk

# load ARCH, BOARD, and CPU configuration
# 该文件为配置时生成的
include $(obj)include/config.mk
export  ARCH CPU BOARD VENDOR SOC

# set default to nothing for native builds
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?= arm-linux-
endif

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

# Include autoconf.mk before config.mk so that the config options are available
# to all top level build files. We need the dummy all: target to prevent the
# dependency target in autoconf.mk.dep from being the default.
all:
sinclude $(obj)include/autoconf.mk.dep
sinclude $(obj)include/autoconf.mk

# load ARCH, BOARD, and CPU configuration
# 该文件为配置时生成的
include $(obj)include/config.mk
export	ARCH CPU BOARD VENDOR SOC

# set default to nothing for native builds
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?= arm-linux-
endif

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

这段代码中，上面的解释已经很到位了.我这里就不多说了，直接看一个相对比较重要的文件include $(TOPDIR)/config.mk
不知道怎么分析好.就挑几个重点讲下.
1:编译器的变量声明
2:连接脚本
3:连接选项

1:编译器的变量声明

#
# Include the make variables (CC, etc...)
#
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

#
# Include the make variables (CC, etc...)
#
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

这里就知道为什么交叉编译器只需要指定前缀的原因了。

2:连接脚本

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

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

LDSCRIPT会根据是否启用nand_boot的选项,来选择连接脚本,连接脚本可以指定代码生成的先后位置,比如把nand相关的函数指定到最前面.
uboot就是通过该连接脚本来使start.S这段代码放到整个程序的最前面,这样才能保证arm能正常启动

3:连接选项

LDFLAGS += -Bstatic -T $(obj)u-boot.lds $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
    LDFLAGS += -Ttext $(TEXT_BASE)
endif

LDFLAGS += -Bstatic -T $(obj)u-boot.lds $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
    LDFLAGS += -Ttext $(TEXT_BASE)
endif

LDFLAGS指明在连接的时候，指定连接地址,还有连接脚本的参数之类的.
剩下的就自己分析吧....

再回到Makefile,指定要编译的对象了

#########################################################################
# U-Boot objects....order is important (i.e. start must be first)

OBJS = cpu/$(CPU)/start.o
ifeq ($(CPU),i386)
    OBJS += cpu/$(CPU)/start16.o
    OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),ppc4xx)
    OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc85xx)
    OBJS += cpu/$(CPU)/resetvec.o
endif

OBJS := $(addprefix $(obj),$(OBJS))

LIBS = lib_generic/libgeneric.a
LIBS += lib_generic/lzma/liblzma.a
LIBS += lib_generic/lzo/liblzo.a
LIBS += $(shell if [ -f board/$(VENDOR)/common/Makefile ]; then echo \
"board/$(VENDOR)/common/lib$(VENDOR).a"; fi)
LIBS += cpu/$(CPU)/lib$(CPU).a
ifdef SOC
    LIBS += cpu/$(CPU)/$(SOC)/lib$(SOC).a
endif
ifeq ($(CPU),ixp)
    LIBS += cpu/ixp/npe/libnpe.a
endif
LIBS += lib_$(ARCH)/lib$(ARCH).a
LIBS += fs/cramfs/libcramfs.a fs/fat/libfat.a fs/fdos/libfdos.a fs/jffs2/libjffs2.a \
fs/reiserfs/libreiserfs.a fs/ext2/libext2fs.a fs/yaffs2/libyaffs2.a \
fs/ubifs/libubifs.a
LIBS += net/libnet.a
LIBS += disk/libdisk.a
LIBS += drivers/bios_emulator/libatibiosemu.a
LIBS += drivers/block/libblock.a
LIBS += drivers/dma/libdma.a
LIBS += drivers/fpga/libfpga.a
LIBS += drivers/gpio/libgpio.a
LIBS += drivers/hwmon/libhwmon.a
LIBS += drivers/i2c/libi2c.a
LIBS += drivers/input/libinput.a
LIBS += drivers/misc/libmisc.a
LIBS += drivers/mmc/libmmc.a
LIBS += drivers/mtd/libmtd.a
LIBS += drivers/mtd/nand/libnand.a
LIBS += drivers/mtd/onenand/libonenand.a
LIBS += drivers/mtd/ubi/libubi.a
LIBS += drivers/mtd/spi/libspi_flash.a
LIBS += drivers/net/libnet.a
LIBS += drivers/net/phy/libphy.a
LIBS += drivers/pci/libpci.a
LIBS += drivers/pcmcia/libpcmcia.a
LIBS += drivers/power/libpower.a
LIBS += drivers/spi/libspi.a
ifeq ($(CPU),mpc83xx)
    LIBS += drivers/qe/qe.a
endif
ifeq ($(CPU),mpc85xx)
    LIBS += drivers/qe/qe.a
    LIBS += cpu/mpc8xxx/ddr/libddr.a
    LIBS += cpu/mpc8xxx/lib8xxx.a
endif
ifeq ($(CPU),mpc86xx)
    LIBS += cpu/mpc8xxx/ddr/libddr.a
    LIBS += cpu/mpc8xxx/lib8xxx.a
endif
LIBS += drivers/rtc/librtc.a
LIBS += drivers/serial/libserial.a
LIBS += drivers/twserial/libtws.a
LIBS += drivers/usb/gadget/libusb_gadget.a
LIBS += drivers/usb/host/libusb_host.a
LIBS += drivers/usb/musb/libusb_musb.a
LIBS += drivers/usb/phy/libusb_phy.a
LIBS += drivers/video/libvideo.a
LIBS += drivers/watchdog/libwatchdog.a
LIBS += common/libcommon.a
LIBS += libfdt/libfdt.a
LIBS += api/libapi.a
LIBS += post/libpost.a

LIBS := $(addprefix $(obj),$(LIBS))
.PHONY : $(LIBS) $(TIMESTAMP_FILE) $(VERSION_FILE)

LIBBOARD = board/$(BOARDDIR)/lib$(BOARD).a
LIBBOARD := $(addprefix $(obj),$(LIBBOARD))

# Add GCC lib
ifdef USE_PRIVATE_LIBGCC
ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
    PLATFORM_LIBGCC = -L $(OBJTREE)/lib_$(ARCH) -lgcc
else
    PLATFORM_LIBGCC = -L $(USE_PRIVATE_LIBGCC) -lgcc
endif
else
    PLATFORM_LIBGCC = -L $(shell dirname `$(CC) $(CFLAGS) -print-libgcc-file-name`) -lgcc
endif
PLATFORM_LIBS += $(PLATFORM_LIBGCC)
export PLATFORM_LIBS

# Special flags for CPP when processing the linker script.
# Pass the version down so we can handle backwards compatibility
# on the fly.
LDPPFLAGS += \
-include $(TOPDIR)/include/u-boot/u-boot.lds.h \
$(shell $(LD) --version | \
sed -ne 's/GNU ld version \([0-9][0-9]*\)\.\([0-9][0-9]*\).*/-DLD_MAJOR=\1 -DLD_MINOR=\2/p')

ifeq ($(CONFIG_NAND_U_BOOT),y)
    NAND_SPL = nand_spl
    U_BOOT_NAND = $(obj)u-boot-nand.bin
endif

ifeq ($(CONFIG_ONENAND_U_BOOT),y)
    ONENAND_IPL = onenand_ipl
    U_BOOT_ONENAND = $(obj)u-boot-onenand.bin
    ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
endif

__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS)) $(subst $(obj),,$(LIBBOARD))

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

#########################################################################
# U-Boot objects....order is important (i.e. start must be first)

OBJS = cpu/$(CPU)/start.o
ifeq ($(CPU),i386)
    OBJS += cpu/$(CPU)/start16.o
    OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),ppc4xx)
    OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc85xx)
    OBJS += cpu/$(CPU)/resetvec.o
endif

OBJS := $(addprefix $(obj),$(OBJS))

LIBS = lib_generic/libgeneric.a
LIBS += lib_generic/lzma/liblzma.a
LIBS += lib_generic/lzo/liblzo.a
LIBS += $(shell if [ -f board/$(VENDOR)/common/Makefile ]; then echo \
"board/$(VENDOR)/common/lib$(VENDOR).a"; fi)
LIBS += cpu/$(CPU)/lib$(CPU).a
ifdef SOC
    LIBS += cpu/$(CPU)/$(SOC)/lib$(SOC).a
endif
ifeq ($(CPU),ixp)
    LIBS += cpu/ixp/npe/libnpe.a
endif
LIBS += lib_$(ARCH)/lib$(ARCH).a
LIBS += fs/cramfs/libcramfs.a fs/fat/libfat.a fs/fdos/libfdos.a fs/jffs2/libjffs2.a \
fs/reiserfs/libreiserfs.a fs/ext2/libext2fs.a fs/yaffs2/libyaffs2.a \
fs/ubifs/libubifs.a
LIBS += net/libnet.a
LIBS += disk/libdisk.a
LIBS += drivers/bios_emulator/libatibiosemu.a
LIBS += drivers/block/libblock.a
LIBS += drivers/dma/libdma.a
LIBS += drivers/fpga/libfpga.a
LIBS += drivers/gpio/libgpio.a
LIBS += drivers/hwmon/libhwmon.a
LIBS += drivers/i2c/libi2c.a
LIBS += drivers/input/libinput.a
LIBS += drivers/misc/libmisc.a
LIBS += drivers/mmc/libmmc.a
LIBS += drivers/mtd/libmtd.a
LIBS += drivers/mtd/nand/libnand.a
LIBS += drivers/mtd/onenand/libonenand.a
LIBS += drivers/mtd/ubi/libubi.a
LIBS += drivers/mtd/spi/libspi_flash.a
LIBS += drivers/net/libnet.a
LIBS += drivers/net/phy/libphy.a
LIBS += drivers/pci/libpci.a
LIBS += drivers/pcmcia/libpcmcia.a
LIBS += drivers/power/libpower.a
LIBS += drivers/spi/libspi.a
ifeq ($(CPU),mpc83xx)
    LIBS += drivers/qe/qe.a
endif
ifeq ($(CPU),mpc85xx)
    LIBS += drivers/qe/qe.a
    LIBS += cpu/mpc8xxx/ddr/libddr.a
    LIBS += cpu/mpc8xxx/lib8xxx.a
endif
ifeq ($(CPU),mpc86xx)
    LIBS += cpu/mpc8xxx/ddr/libddr.a
    LIBS += cpu/mpc8xxx/lib8xxx.a
endif
LIBS += drivers/rtc/librtc.a
LIBS += drivers/serial/libserial.a
LIBS += drivers/twserial/libtws.a
LIBS += drivers/usb/gadget/libusb_gadget.a
LIBS += drivers/usb/host/libusb_host.a
LIBS += drivers/usb/musb/libusb_musb.a
LIBS += drivers/usb/phy/libusb_phy.a
LIBS += drivers/video/libvideo.a
LIBS += drivers/watchdog/libwatchdog.a
LIBS += common/libcommon.a
LIBS += libfdt/libfdt.a
LIBS += api/libapi.a
LIBS += post/libpost.a

LIBS := $(addprefix $(obj),$(LIBS))
.PHONY : $(LIBS) $(TIMESTAMP_FILE) $(VERSION_FILE)

LIBBOARD = board/$(BOARDDIR)/lib$(BOARD).a
LIBBOARD := $(addprefix $(obj),$(LIBBOARD))

# Add GCC lib
ifdef USE_PRIVATE_LIBGCC
ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
    PLATFORM_LIBGCC = -L $(OBJTREE)/lib_$(ARCH) -lgcc
else
    PLATFORM_LIBGCC = -L $(USE_PRIVATE_LIBGCC) -lgcc
endif
else
    PLATFORM_LIBGCC = -L $(shell dirname `$(CC) $(CFLAGS) -print-libgcc-file-name`) -lgcc
endif
PLATFORM_LIBS += $(PLATFORM_LIBGCC)
export PLATFORM_LIBS

# Special flags for CPP when processing the linker script.
# Pass the version down so we can handle backwards compatibility
# on the fly.
LDPPFLAGS += \
-include $(TOPDIR)/include/u-boot/u-boot.lds.h \
$(shell $(LD) --version | \
sed -ne 's/GNU ld version \([0-9][0-9]*\)\.\([0-9][0-9]*\).*/-DLD_MAJOR=\1 -DLD_MINOR=\2/p')

ifeq ($(CONFIG_NAND_U_BOOT),y)
    NAND_SPL = nand_spl
    U_BOOT_NAND = $(obj)u-boot-nand.bin
endif

ifeq ($(CONFIG_ONENAND_U_BOOT),y)
    ONENAND_IPL = onenand_ipl
    U_BOOT_ONENAND = $(obj)u-boot-onenand.bin
    ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
endif

__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS)) $(subst $(obj),,$(LIBBOARD))

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

由上面的可以看出
OBJS 对应的是 .o文件
LIBS对应的是 .a文件
LIBBOARD 对应的是目录
等等.主要看下这3个是怎么被处理的

$(OBJS):    depend
    $(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))

$(LIBS):    depend $(SUBDIRS)
    $(MAKE) -C $(dir $(subst $(obj),,$@))

$(LIBBOARD):    depend $(LIBS)
    $(MAKE) -C $(dir $(subst $(obj),,$@))

$(OBJS):	depend
    $(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))

$(LIBS):	depend $(SUBDIRS)
    $(MAKE) -C $(dir $(subst $(obj),,$@))

$(LIBBOARD):	depend $(LIBS)
    $(MAKE) -C $(dir $(subst $(obj),,$@))

由这里可以看出，会逐个的make出来

最后就是连接的过程了.连接会调用

GEN_UBOOT = \
    UNDEF_SYM=`$(OBJDUMP) -x $(LIBBOARD) $(LIBS) | \
    sed -n -e 's/.*\($(SYM_PREFIX)__u_boot_cmd_.*\)/-u\1/p'|sort|uniq`;\
    cd $(LNDIR) && $(LD) $(LDFLAGS) $$UNDEF_SYM $(__OBJS) \
    --start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \
    -Map u-boot.map -o u-boot
$(obj)u-boot:   depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds

GEN_UBOOT = \
    UNDEF_SYM=`$(OBJDUMP) -x $(LIBBOARD) $(LIBS) | \
    sed -n -e 's/.*\($(SYM_PREFIX)__u_boot_cmd_.*\)/-u\1/p'|sort|uniq`;\
    cd $(LNDIR) && $(LD) $(LDFLAGS) $$UNDEF_SYM $(__OBJS) \
    --start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \
    -Map u-boot.map -o u-boot
$(obj)u-boot:	depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds

最终会连接成功.后面只要通过

$(obj)u-boot.bin:   $(obj)u-boot
$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@

$(obj)u-boot.bin:	$(obj)u-boot
$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@

将二进制内容拷贝出来，那么uboot.bin就生成了

来看一下连接脚本吧

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
    . = 0x00000000;
    . = ALIGN(4);
    .text :
    {
        cpu/arm1176/start.o (.text)
        cpu/arm1176/s3c64xx/cpu_init.o (.text)
       *(.text)
    }
    . = ALIGN(4);
    .rodata :
    {
        *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*)))
    }
    . = ALIGN(4);
    .data : {
        *(.data)
    }
    . = ALIGN(4);
    .got :
    {
        *(.got)
    }
    __u_boot_cmd_start = .;
    .u_boot_cmd :
    {
        *(.u_boot_cmd)
    }
    __u_boot_cmd_end = .;
    . = ALIGN(4);
    .mmudata :
    {
        *(.mmudata)
    }
    . = ALIGN(4);
    __bss_start = .;
    .bss :
    {
        *(.bss) . = ALIGN(4);
    }
    _end = .;
}

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
    . = 0x00000000;
    . = ALIGN(4);
    .text :
    {
        cpu/arm1176/start.o (.text)
        cpu/arm1176/s3c64xx/cpu_init.o (.text)
       *(.text)
    }
    . = ALIGN(4);
    .rodata : 
    { 
        *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) 
    }
    . = ALIGN(4);
    .data : {
        *(.data) 
    }
    . = ALIGN(4);
    .got : 
    {
        *(.got) 
    }
    __u_boot_cmd_start = .;
    .u_boot_cmd : 
    { 
        *(.u_boot_cmd) 
    }
    __u_boot_cmd_end = .;
    . = ALIGN(4);
    .mmudata : 
    { 
        *(.mmudata) 
    }
    . = ALIGN(4);
    __bss_start = .;
    .bss : 
    { 
        *(.bss) . = ALIGN(4); 
    }
    _end = .;
}

从这个链接脚本可以看出，uboot将整个程序进行了如下的布置
.text :
.rodata :
.data :
.got :
.u_boot_cmd :
.mmudata :
.bss :
代码段被首先链接，在代码段内第一个就是start.s 因为这就是uboot启动的第一条代码的地方，看一下map文件
Memory Configuration

Name                  Origin                        Length                Attributes
*default*             0x00000000             0xffffffff

Linker script and memory map

0x00000000  . = 0x0
0x00000000 . = ALIGN (0x4)

.text                 0x57e00000                  0x27b8c
cpu/arm1176/start.o(.text)
.text                 0x57e00000                  0x440              cpu/arm1176/start.o
                        0x57e00040                                           _end_vect
                        0x57e0004c                                           _bss_start
                        0x57e00050                                          _bss_end
                        0x57e00048                                          _armboot_start
                        0x57e00114                                          copy_from_nand
                        0x57e00000                                          _start

从map文件中，可以看到0x57e00000=_start 被放到了一条的位置（0x57e00000就是链接脚本指定的连接地址）
接着打开cpu/arm1176/start.S

.globl _start
_start: b   reset
#ifndef CONFIG_NAND_SPL
ldr pc, _undefined_instruction
ldr pc, _software_interrupt
ldr pc, _prefetch_abort
ldr pc, _data_abort
ldr pc, _not_used
ldr pc, _irq
ldr pc, _fiq

.globl _start
_start: b	reset
#ifndef CONFIG_NAND_SPL
ldr	pc, _undefined_instruction
ldr	pc, _software_interrupt
ldr	pc, _prefetch_abort
ldr	pc, _data_abort
ldr	pc, _not_used
ldr	pc, _irq
ldr	pc, _fiq

第一条语句 b reset就被放到了_start的位置，这样uboot启动之后，就会开始执行这条语句，uboot的移植也会从这开始分析了

完。

Thanks a lot！