TQ210——S5PV210 uboot顶层config.mk分析

#
# (C) Copyright 2000-2006
# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
#
# 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
#
#########################################################################
# $@  表示目标文件
# $^  表示所有的依赖文件
# $<  表示第一个依赖文件
# $?  表示比目标还要新的依赖文件列表
#########################################################################
# config.mk功能是配置单板信息和编译环境，被Makefile调用

#########################################################################
# 此脚本在uboot顶层目录。如果目标存放目录不等于源码目录（这里不会执行）
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))
# 所以上面的几行都不会执行，会执行下面这个，obj和src为空
else
obj :=
src :=
endif

# clean the slate ...
# 清楚标志
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]
# ARCH=arm，这段不会执行
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)
# 除了darwin-pcc外其他都采用gcc编译器
ifeq ($(HOSTOS)-$(HOSTARCH),darwin-ppc)
HOSTCC = cc
else
HOSTCC = gcc
endif
#########################################################################
# HOSTCPPFLAGS的值为空，HOSTCFLAGS = -Wall -Wstrict-prototypes -O2
# -fomit-frame-pointer
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用于检查编译器CC是否支持某选项。将2个选项作为参数传递给cc-option函数，
# 该函数调用CC编译器检查参数1是否支持，若支持则函数返回参数1，
# 否则返回参数2 （因此CC编译器必须支# 持参数1或参数2，若两个都不支持则会编译出错）
# 可以像下面这样调用cc-option函数，并将支持的选项添加到FLAGS中:
# FLAGS +=$(call cc-option,option1,option2)
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...)
# 下面一些是定义交叉工具链的集合
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

#########################################################################
# 加载产生的单板配置文件autoconf.mk和config.mk，均在include目录下
# config.mk中内容是ARCH CPU BOARD VENDOR SOC5个变量信息
# autoconf.mk为单板配置宏的集合,打开/关闭 用 y/n表示
# 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  CPUspecific 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)

# 没有定义BUILD_TAG，执行else分支,赋值CFLAGS
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
# 不执行
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.
# CPPFLAGS设置了-g参数
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)

# 设置uboot的链接选项
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 ${TARGET}".  Sensible values are
# - When cross-compiling: the root of the cross-environment
# - Linux/ppc (native): /usr
# - NetBSD/ppc (native): you lose ... (must extract these from the
#   binutils build directory, plus the native and U-Boot include
#   files don't like each other)
#
# So far, this is used only by tools/gdb/Makefile.
# 不是arm架构，不执行
ifeq ($(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

#########################################################################
# 输出这些信息为环境变量
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

#########################################################################
# 指定隐含的编译规则，例如：根据以上的定义，以“.s”结尾的目标文件将根据第一条规则由同名但后
# 缀为“.S”的源文件来生成，若不存在“.S”结尾的同名文件则根据最后一条规则由同名的“.c”文件生
# 成。
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

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