Analysis of the compiling process of u-boot

Keywords: shell Makefile Cygwin Linux

Article directory

U-boot Makefile national construction process

Host build environment configuration process

Define host system architecture
Define host operating system type
Define SHELL script interpreter
Set compile output directory
Configuration process related to target machine

mkconfig script

Pass to mkconfig script parameter
Check the validity of parameters
Create a link to a catalog board related catalog
Build 'include/config.mk' file
Build 'include/config.h' file

make command execution process
Top level directory 'config,mk' analysis

Contains configuration files related to the development board
`File u-boot.lds

U-boot Makefile national construction process

Host build environment configuration process

Define host system architecture

HOSTARCH := $(shell uname -m | \
		sed -e s/i.86/i386/ \
	    -e s/sun4u/sparc64/ \
	    -e s/arm.*/arm/ \
	    -e s/sa110/arm/ \
	    -e s/powerpc/ppc/ \
	    -e s/ppc64/ppc/ \
	    -e s/macppc/ppc/)

$(shell xxx) is the statement after the shell, which is executed according to the shell script.

sed -e s/in/out / is to replace the input in with out

Running example:

andrew@andrew-Thurley:~/work/test$ uname -m
x86_64
# . is a single character wildcard
andrew@andrew-Thurley:~/work/test$ uname -m |sed -e s/x86.64/x86/ 
x86

Define host operating system type

HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
	    sed -e 's/\(cygwin\).*/cygwin/')

TR '[: Upper:]' [: lower:] 'is used to convert all uppercase letters in standard input to lowercase letters

Execution example

andrew@andrew-Thurley:~/work/test$ uname -s | tr '[:upper:]' '[:lower:]' | sed -e 's/\(cygwin\).*/cygwin/'
linux

Define SHELL script interpreter

The Makefile at the top of uboot defines shell, the interpreter of shell script, through the following code. The function of "$BASH" is essentially to generate the string "BASH", which is essentially to generate the string "BASH". The function of the previous $is to show that the second $is a common character.

# Set shell to bash if possible, otherwise fall back to sh
SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
	else if [ -x /bin/bash ]; then echo /bin/bash; \
	else echo sh; fi; fi)

The function of the above script is that if $BASH environment variable is defined in the shell of the current Makefile, and the file $BASH is executable, the value of shell is "$BASH". If / bin/bash is executable, the value of shell is "/ bin/bash". If neither of the above is true, assign sh to the shell variable.

Set compile output directory

ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif

$(origin O) indicates the output of the (origin O) function. The output of $(origin variable) is a string, which is determined by the way variable is defined. If variable is a parameter of make, $(origin variable) outputs the common line string.
The effect of the above method is make O=/tmp/buildall, because O is the parameter of make, so $(origin variable) outputs common line, and BUILD_DIR is / tmp/buildall.

The next configuration is as follows:

ifneq ($(BUILD_DIR),) #If the directory exists, assign the directory to saved output
saved-output := $(BUILD_DIR)

# Attempt to create a output directory.
# Directory exists and then executes, directory does not exist create directory
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})

# Verify if it was successful.
# Make sure the directory exists
BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
# Check the catalog
$(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
endif # ifneq ($(BUILD_DIR),)

CURDIR represents the current directory
If OBJTREE does not define build dir, the output directory is CURDIR, that is, the place where make is executed. That is, when make is executed without a specified directory, the u-boot generated will be on the top directory.
$(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR)) if BUILD_DIR exists, BUILD_DIR will be used; if no share exists, CURDIR will be used.

OBJTREE		:= $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
SRCTREE		:= $(CURDIR)
TOPDIR		:= $(SRCTREE)
LNDIR		:= $(OBJTREE)
export	TOPDIR SRCTREE OBJTREE

MKCONFIG	:= $(SRCTREE)/mkconfig
export MKCONFIG

ifneq ($(OBJTREE),$(SRCTREE))
REMOTE_BUILD	:= 1
export REMOTE_BUILD
endif

Define obj and Src variables before including config.mk, and put them into the environment temporarily.
export obj src

# $(obj) and (src) are defined in config.mk but here in main Makefile
# we also need them before config.mk is included which is the case for
# some targets like unconfig, clean, clobber, distclean, etc.
ifneq ($(OBJTREE),$(SRCTREE))
obj := $(OBJTREE)/
src := $(SRCTREE)/
else
obj :=
src :=
endif
export obj src

Configuration process related to target machine

There are configurations related to the specific development board in the top-level Makefile. The @ function does not show that obj is the directory of the compiled output when executing the command. Therefore, the unconfig function is to know the configuration file generated by the last execution of the make * * config command.
$(@: _config =) replaces_config of all the parameters passed in with null, where @ refers to the target of the rule, using the syntax of @ (text:patternA=patternB), replacing all text ending in patternA with patternB, so the function of $(@: _config =) is to remove_config after smdk2410_config to get smdk2410

The final effect is equivalent to:
@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 samsung s3c24x0
==>
./mkconfig smdk2410 arm arm920t smdk2410 samsung s3c24x0

This method is given in mkconfig
# Parameters: Target Architecture CPU Board [VENDOR] [SOC]

unconfig:
	@rm -f $(obj)include/config.h $(obj)include/config.mk \
		$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp \
		$(obj)include/autoconf.mk $(obj)include/autoconf.mk.dep

smdk2410_config	:	unconfig
	@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 samsung s3c24x0

mkconfig script

Pass to mkconfig script parameter

The meaning passed to the mkconfig script is as follows:

Smdk2410, target (model of target board)
Arm, architecture (CPU architecture of target board)
ARM920T, CPU (specific CPU model used by CPU)
smdk2410, development board name
samsung,VENDOR manufacturer name
S3c24x0, SOC (system on chip)

Where the environment variable $ා represents the number of parameters passed to the script.
The function of shift is that the original parameter $1 will be lost, and the later parameter will be shifted forward.

APPEND=no	# Default: Create new config file
BOARD_NAME=""	# Name to print in make output
TARGETS=""

while [ $# -gt 0 ] ; do
	case "$1" in
	--) shift ; break ;;
	-a) shift ; APPEND=yes ;;
	-n) shift ; BOARD_NAME="${1%%_config}" ; shift ;;
	-t) shift ; TARGETS="`echo $1 | sed 's:_: :g'` ${TARGETS}" ; shift ;;
	*)  break ;;
	esac
done

[ "${BOARD_NAME}" ] || BOARD_NAME="$1"

After the execution of the above code, BOARD_NAME = smdk2410, because the mkconfig execution statement of the top-level Makefile construction is:. / mkconfig smdk2410 arm ARM920T smdk2410 sampling s3c24x0

Check the validity of parameters

The following code is used to check the validity of parameters. If the number of parameters is less than 4 or more than 6, it will be considered illegal.

[ $# -lt 4 ] && exit 1
[ $# -gt 6 ] && exit 1

if [ "${ARCH}" -a "${ARCH}" != "$2" ]; then
	echo "Failed: \$ARCH=${ARCH}, should be '$2' for ${BOARD_NAME}" 1>&2
	exit 1
fi

Create a link to a catalog board related catalog

If compile output to external directory, the following code game oh.
When the "$srctree"! = "$objtree" condition is set, the output external directory is defined.

#
# Create link to architecture specific headers
#
if [ "$SRCTREE" != "$OBJTREE" ] ; then
	mkdir -p ${OBJTREE}/include
	mkdir -p ${OBJTREE}/include2
	cd ${OBJTREE}/include2
	rm -f asm
	ln -s ${SRCTREE}/include/asm-$2 asm
	LNPREFIX="../../include2/asm/"
	cd ../include
	rm -rf asm-$2
	rm -f asm
	mkdir asm-$2
	ln -s asm-$2 asm

If the target file is set to output to the directory where the source file is located, a symbolic connection is established to the ASM arm directory under the include directory in the top directory. The code is as follows: ln -s asm-, asm, that is, LN - s ASM arm ASM

else
	cd ./include
	rm -f asm
	ln -s asm-$2 asm
fi

The script then establishes the symbolic link include / ASM arm / arch through the following code. If & 6 (SOC) is empty, it will link to the directory include / ASM arm / arch-arm920t. Otherwise, it will link to the directory include / ASM arm / arch-s3cx0. In fact, the directory include / ASM arm / arch-arm920t does not exist, so the sixth parameter must be filled in. Otherwise, the compilation will fail.

rm -f asm-$2/arch

if [ -z "$6" -o "$6" = "NULL" ] ; then
	ln -s ${LNPREFIX}arch-$3 asm-$2/arch
else
	ln -s ${LNPREFIX}arch-$6 asm-$2/arch
fi

The development board is an arm based proc linked to proc armv.

if [ "$2" = "arm" ] ; then
	rm -f asm-$2/proc
	ln -s ${LNPREFIX}proc-armv asm-$2/proc
fi

Build the include/config.mk file

#
# Create include file for Make
#
echo "ARCH   = $2" >  config.mk
echo "CPU    = $3" >> config.mk
echo "BOARD  = $4" >> config.mk

[ "$5" ] && [ "$5" != "NULL" ] && echo "VENDOR = $5" >> config.mk

[ "$6" ] && [ "$6" != "NULL" ] && echo "SOC    = $6" >> config.mk

What the above code implements

ARCH   = arm
CPU    = arm920t
BOARD  = smdk2410
VENDOR = samsung
SOC    = s3c24x0

Build the include/config.h file

#
# Create board specific header file
#
if [ "$APPEND" = "yes" ]	# Append to existing config file
then
	echo >> config.h  #Add a enter key
else
	> config.h		# Create new config file
fi
echo "/* Automatically generated - do not edit */" >>config.h

for i in ${TARGETS} ; do
	echo "#define CONFIG_MK_${i} 1" >>config.h ;
done

echo "#include <configs/$1.h>" >>config.h
echo "#include <asm/config.h>" >>config.h

exit 0

make command execution process

After making clear the construction environment of the host and the related configuration of the target machine, the following analyzes the process of executing the make command and finally generating the u-boot image.

Normal execution of make smdk2410 ﹐ config will enter the directory of ifeq.

If the environment of the host and the development board is the same, the host compiler is used, and the cross compilation tool definition is empty.

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

Next, it contains config.mk under the top-level directory.

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

# The "tools" are needed early, so put this first
# Don't include stuff already done in $(LIBS)
SUBDIRS	= tools \
	  examples/standalone \
	  examples/api

.PHONY : $(SUBDIRS)

ifeq ($(obj)include/config.mk,$(wildcard $(obj)include/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
include $(obj)include/config.mk
export	ARCH CPU BOARD VENDOR SOC

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

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

#########################################################################
# 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/net/sk98lin/libsk98lin.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
TAG_SUBDIRS += cpu/mpc8xxx
endif
ifeq ($(CPU),mpc86xx)
LIBS += cpu/mpc8xxx/ddr/libddr.a
LIBS += cpu/mpc8xxx/lib8xxx.a
TAG_SUBDIRS += cpu/mpc8xxx
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/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))

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

# Always append ALL so that arch config.mk's can add custom ones
ALL += $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND) $(U_BOOT_ONENAND)

all:		$(ALL)

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

$(obj)u-boot.srec:	$(obj)u-boot
		$(OBJCOPY) -O srec $< $@

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

$(obj)u-boot.ldr:	$(obj)u-boot
		$(obj)tools/envcrc --binary > $(obj)env-ldr.o
		$(LDR) -T $(CONFIG_BFIN_CPU) -c $@ $< $(LDR_FLAGS)

$(obj)u-boot.ldr.hex:	$(obj)u-boot.ldr
		$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@ -I binary

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

$(obj)u-boot.img:	$(obj)u-boot.bin
		./tools/mkimage -A $(ARCH) -T firmware -C none \
		-a $(TEXT_BASE) -e 0 \
		-n $(shell sed -n -e 's/.*U_BOOT_VERSION//p' $(VERSION_FILE) | \
			sed -e 's/"[	 ]*$$/ for $(BOARD) board"/') \
		-d $< $@

$(obj)u-boot.kwb:       $(obj)u-boot.bin
		$(obj)tools/mkimage -n $(KWD_CONFIG) -T kwbimage \
		-a $(TEXT_BASE) -e $(TEXT_BASE) -d $< $@

$(obj)u-boot.sha1:	$(obj)u-boot.bin
		$(obj)tools/ubsha1 $(obj)u-boot.bin

$(obj)u-boot.dis:	$(obj)u-boot
		$(OBJDUMP) -d $< > $@

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) $$UNDEF_SYM $(__OBJS) \
			--start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \
			-Map u-boot.map -o u-boot
$(obj)u-boot:	depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds
		$(GEN_UBOOT)
ifeq ($(CONFIG_KALLSYMS),y)
		smap=`$(call SYSTEM_MAP,u-boot) | \
			awk '$$2 ~ /[tTwW]/ {printf $$1 $$3 "\\\\000"}'` ; \
		$(CC) $(CFLAGS) -DSYSTEM_MAP="\"$${smap}\"" \
			-c common/system_map.c -o $(obj)common/system_map.o
		$(GEN_UBOOT) $(obj)common/system_map.o
endif

$(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 $(obj),,$@))

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

$(LDSCRIPT):	depend
		$(MAKE) -C $(dir $@) $(notdir $@)

$(obj)u-boot.lds: $(LDSCRIPT)
		$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -ansi -D__ASSEMBLY__ -P - <$^ >$@

$(NAND_SPL):	$(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
		$(MAKE) -C nand_spl/board/$(BOARDDIR) all

$(U_BOOT_NAND):	$(NAND_SPL) $(obj)u-boot.bin
		cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin

$(ONENAND_IPL):	$(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
		$(MAKE) -C onenand_ipl/board/$(BOARDDIR) all

$(U_BOOT_ONENAND):	$(ONENAND_IPL) $(obj)u-boot.bin
		cat $(ONENAND_BIN) $(obj)u-boot.bin > $(obj)u-boot-onenand.bin

$(VERSION_FILE):
		@( printf '#define U_BOOT_VERSION "U-Boot %s%s"\n' "$(U_BOOT_VERSION)" \
		 '$(shell $(TOPDIR)/tools/setlocalversion $(TOPDIR))' ) > $@.tmp
		@cmp -s $@ $@.tmp && rm -f $@.tmp || mv -f $@.tmp $@

$(TIMESTAMP_FILE):
		@date +'#define U_BOOT_DATE "%b %d %C%y"' > $@
		@date +'#define U_BOOT_TIME "%T"' >> $@

gdbtools:
		$(MAKE) -C tools/gdb all || exit 1

updater:
		$(MAKE) -C tools/updater all || exit 1

env:
		$(MAKE) -C tools/env all MTD_VERSION=${MTD_VERSION} || exit 1

depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
		for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; done

TAG_SUBDIRS += include
TAG_SUBDIRS += lib_generic board/$(BOARDDIR)
TAG_SUBDIRS += cpu/$(CPU)
TAG_SUBDIRS += lib_$(ARCH)
TAG_SUBDIRS += fs/cramfs
TAG_SUBDIRS += fs/fat
TAG_SUBDIRS += fs/fdos
TAG_SUBDIRS += fs/jffs2
TAG_SUBDIRS += fs/yaffs2
TAG_SUBDIRS += net
TAG_SUBDIRS += disk
TAG_SUBDIRS += common
TAG_SUBDIRS += drivers/bios_emulator
TAG_SUBDIRS += drivers/block
TAG_SUBDIRS += drivers/gpio
TAG_SUBDIRS += drivers/hwmon
TAG_SUBDIRS += drivers/i2c
TAG_SUBDIRS += drivers/input
TAG_SUBDIRS += drivers/misc
TAG_SUBDIRS += drivers/mmc
TAG_SUBDIRS += drivers/mtd
TAG_SUBDIRS += drivers/mtd/nand
TAG_SUBDIRS += drivers/mtd/onenand
TAG_SUBDIRS += drivers/mtd/spi
TAG_SUBDIRS += drivers/net
TAG_SUBDIRS += drivers/net/sk98lin
TAG_SUBDIRS += drivers/pci
TAG_SUBDIRS += drivers/pcmcia
TAG_SUBDIRS += drivers/qe
TAG_SUBDIRS += drivers/rtc
TAG_SUBDIRS += drivers/serial
TAG_SUBDIRS += drivers/spi
TAG_SUBDIRS += drivers/usb
TAG_SUBDIRS += drivers/video

tags ctags:
		ctags -w -o $(obj)ctags `find $(SUBDIRS) $(TAG_SUBDIRS) \
						-name '*.[ch]' -print`

etags:
		etags -a -o $(obj)etags `find $(SUBDIRS) $(TAG_SUBDIRS) \
						-name '*.[ch]' -print`
cscope:
		find $(SUBDIRS) $(TAG_SUBDIRS) -name '*.[ch]' -print \
						> cscope.files
		cscope -b -q -k

SYSTEM_MAP = \
		$(NM) $1 | \
		grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \
		LC_ALL=C sort
$(obj)System.map:	$(obj)u-boot
		@$(call SYSTEM_MAP,$<) > $(obj)System.map

#
# Auto-generate the autoconf.mk file (which is included by all makefiles)
#
# This target actually generates 2 files; autoconf.mk and autoconf.mk.dep.
# the dep file is only include in this top level makefile to determine when
# to regenerate the autoconf.mk file.
$(obj)include/autoconf.mk.dep: $(obj)include/config.h include/common.h
	@$(XECHO) Generating $@ ; \
	set -e ; \
	: Generate the dependancies ; \
	$(CC) -x c -DDO_DEPS_ONLY -M $(HOSTCFLAGS) $(CPPFLAGS) \
		-MQ $(obj)include/autoconf.mk include/common.h > $@

$(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 > $@.tmp && \
	mv $@.tmp $@

#########################################################################
else	# !config.mk
all $(obj)u-boot.hex $(obj)u-boot.srec $(obj)u-boot.bin \
$(obj)u-boot.img $(obj)u-boot.dis $(obj)u-boot \
$(SUBDIRS) $(TIMESTAMP_FILE) $(VERSION_FILE) gdbtools updater env depend \
dep tags ctags etags cscope $(obj)System.map:
	@echo "System not configured - see README" >&2
	@ exit 1
endif	# config.mk

Top level directory config,mk analysis

Set compilation options

# clean the slate ...
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =

Check if the compiler supports function definitions for certain options

#########################################################################
#
# 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 ;)

Function usage
You can call the CC option function to this
GFLAGS += $(call cc-option, option1, option2)

CFLAGS += $(call cc-option,-fno-stack-protector)

Perform cross compilation tool

#
# 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

For the arm development board, cross figure in the above code is defined in lib arm / config.mk
CROSS_COMPILE ?= arm-linux-

Contains configuration files related to the development board

In the following code, the value of $(ARCH) is "arm", so include lib_arm/config.mk

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

ifdef	ARCH
sinclude $(TOPDIR)/lib_$(ARCH)/config.mk	# include architecture dependend rules
endif

The function of dependency is to generate dependency. Executing this command will enter the subdirectory represented by $(subirs) once, and execute the make ﹐ dependent command to generate. Dependency files in each subdirectory, and list the dependency files of each target file in the. Dependent file.

$(obj)u-boot:	depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds
		$(GEN_UBOOT)

u-boot.lds file

# Specify that the output executable is 32-bit ARM instruction, ELF format of small end mode
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
# Specify the output executable platform as ARM
OUTPUT_ARCH(arm)

# Specify the entry of the program as "start"
ENTRY(_start)
SECTIONS
{
    # Specifies the starting address of the target code from 0x00, "." represents the current location
	. = 0x00000000;
    # Mark 4-byte alignment
	. = ALIGN(4);
	.text :
	{
        # Indicates that start.o is the first. o file in the code snippet
		cpu/arm920t/start.o	(.text)
        # The rest of the code snippet
		*(.text)
	}

	. = ALIGN(4);
	.rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }

	. = ALIGN(4);
    # Data segment
	.data : { *(.data) }

	. = ALIGN(4);
	.got : { *(.got) }

	. = .;
	__u_boot_cmd_start = .;
	.u_boot_cmd : { *(.u_boot_cmd) }
	__u_boot_cmd_end = .;

	. = ALIGN(4);
    # __The bss_start label points to the start of the BSS segment
	__bss_start = .;
    # Here is a piece of memory in the bss section to store the bit initialization variables in the program.
	.bss (NOLOAD) : { *(.bss) . = ALIGN(4); }
	_end = .;
}

Posted by taya on Sat, 26 Oct 2019 23:17:31 -0700

Programmer Group