u-boot Makefile分析 -- （1）
[Author: Bo Shen <[email protected]>]
[u-boot: 2014.01-rc1, e03c76c30342797a25ef9350e51c8daa0b56f1df]
下面进行u-boot Makefile分析
1. u-boot的固定版本信息，与编译时生成的时间与动态版本信息。
1 # 2 # (C) Copyright 2000-2013 3 # Wolfgang Denk, DENX Software Engineering, [email protected]. 4 # 5 # SPDX-License-Identifier: GPL-2.0+ 6 # 7 8 VERSION = 2014 9 PATCHLEVEL = 01 10 SUBLEVEL = 11 EXTRAVERSION = -rc1 12 ifneq "$(SUBLEVEL)" "" 13 U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION) 14 else 15 U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL)$(EXTRAVERSION) 16 endif 17 TIMESTAMP_FILE = $(obj)include/generated/timestamp_autogenerated.h 18 VERSION_FILE = $(obj)include/generated/version_autogenerated.h 191~6: Header (license information)
8~11: u-boot版本的基本信息
12~6: 判断SUBLEVEL是否为空来决定U_BOOT_VERSION
17~ 8: 编译时生成的时间信息，版本信息，后续详解。
2. 编译u-boot的主机信息
20 HOSTARCH := $(shell uname -m | \ 21 sed -e s/i.86/x86/ \ 22 -e s/sun4u/sparc64/ \ 23 -e s/arm.*/arm/ \ 24 -e s/sa110/arm/ \ 25 -e s/ppc64/powerpc/ \ 26 -e s/ppc/powerpc/ \ 27 -e s/macppc/powerpc/\ 28 -e s/sh.*/sh/) 29 30 HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \ 31 sed -e 's/\(cygwin\).*/cygwin/') 32 33 export HOSTARCH HOSTOS20~28: 通过执行一个shell命令去获取主机的架构，然后做一些替换动作（如：将sa110换成arm）。具体关于uname的命令，请自行查阅。
30~31: 通过执行一个shell命令去获取主机操作系统，然后将大写字转换成小写字母。
33: export主机的架构与操作系统。
3. 将VENDOR赋空值
35 # Deal with colliding definitions from tcsh etc. 36 VENDOR= 37
4. 判断是否需要安静的编译。
38 ######################################################################### 39 # Allow for silent builds 40 ifeq (,$(findstring s,$(MAKEFLAGS))) 41 XECHO = echo 42 else 43 XECHO = : 44 endif判断make的flag是否带有s, 如果有，则是静态编译。如执行make -s, 你将不会看到作何编译信息输出。
5. 判断是否编译生成的object文件放到单独的文件夹中。具体看注释就明白了。
46 #########################################################################
47 #
48 # U-boot build supports generating object files in a separate external
49 # directory. Two use cases are supported:
50 #
51 # 1) Add O= to the make command line
52 # 'make O=/tmp/build all'
53 #
54 # 2) Set environment variable BUILD_DIR to point to the desired location
55 # 'export BUILD_DIR=/tmp/build'
56 # 'make'
57 #
58 # The second approach can also be used with a MAKEALL script
59 # 'export BUILD_DIR=/tmp/build'
60 # './MAKEALL'
61 #
62 # Command line 'O=' setting overrides BUILD_DIR environment variable.
63 #
64 # When none of the above methods is used the local build is performed and
65 # the object files are placed in the source directory.
66 #
67
68 ifeq ("$(origin O)", "command line")
69 BUILD_DIR := $(O)
70 endif
6. 检查是否需要进行源代码检查，具体看注释也就明白了。如果需要检查源代码，需要sparse命令的支持。
72 # Call a source code checker (by default, "sparse") as part of the
73 # C compilation.
74 #
75 # Use 'make C=1' to enable checking of re-compiled files.
76 #
77 # See the linux kernel file "Documentation/sparse.txt" for more details,
78 # including where to get the "sparse" utility.
79
80 ifdef C
81 ifeq ("$(origin C)", "command line")
82 CHECKSRC := $(C)
83 endif
84 endif
85 ifndef CHECKSRC
86 CHECKSRC = 0
87 endif
88 export CHECKSRC
7. 判断第五步中的BUILD_DIR是否为空，如不为空
90 ifneq ($(BUILD_DIR),)
91 saved-output := $(BUILD_DIR)
92
93 # Attempt to create a output directory.
94 $(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})
95
96 # Verify if it was successful.
97 BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
98 $(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
99 endif # ifneq ($(BUILD_DIR),)
90: 如BUILD_DIR不为空，则进行后续动作。
93~94: 则判断BUILD_DIR是否存在，如不存在，创建这个文件夹，
97~99: 检查文件夹是否创建成功。不成功，输出错误信息。