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@cyysu 2017-10-16T08:27:21.000000Z 字数 6705 阅读 1580

Makefile-项目篇(三)

  • 时间：2017年10月16日
  • 作者：Kali
  • 邮箱：cyysu.github.io@gmail.com
  • 版本：3.0
  • 描述：Makefile-项目三，Linux 4.4 Makefile讲解，同时还可以了解Linux的编译过程

Makefile系列教程

项目实战

  1. # 在本此项目中先给出前250行内容，我们慢慢分析这个顶层Makefile
  2. VERSION = 4
  3. PATCHLEVEL = 4
  4. SUBLEVEL = 92
  5. EXTRAVERSION =
  6. NAME = Blurry Fish Butt
  8. # *DOCUMENTATION*
  9. # To see a list of typical targets execute "make help"
  10. # More info can be located in ./README
  11. # Comments in this file are targeted only to the developer, do not
  12. # expect to learn how to build the kernel reading this file.
  14. # o Do not use make's built-in rules and variables
  15. #   (this increases performance and avoids hard-to-debug behaviour);
  16. # o Look for make include files relative to root of kernel src
  17. # 这里-r表示禁止使用隐含规则 -R禁止使用任何作用于变量上的隐含规则   
  18. MAKEFLAGS += -rR --include-dir=$(CURDIR)
  20. # Avoid funny character set dependencies
  21. # Makefile中的变量设置，如果不想传递变量到下一级的Makefile就可以采用unexport
  22. # 如果想传递所有的变量，直接写export
  23. # 但是Makefile中SHELL变量和MAKEFLAGS变量总是会传递到下一级Makefile
  24. unexport LC_ALL
  25. LC_COLLATE=C
  26. LC_NUMERIC=C
  27. export LC_COLLATE LC_NUMERIC
  29. # Avoid interference with shell env settings
  30. unexport GREP_OPTIONS
  32. # We are using a recursive build, so we need to do a little thinking
  33. # to get the ordering right.
  34. #
  35. # Most importantly: sub-Makefiles should only ever modify files in
  36. # their own directory. If in some directory we have a dependency on
  37. # a file in another dir (which doesn't happen often, but it's often
  38. # unavoidable when linking the built-in.o targets which finally
  39. # turn into vmlinux), we will call a sub make in that other dir, and
  40. # after that we are sure that everything which is in that other dir
  41. # is now up to date.
  42. #
  43. # The only cases where we need to modify files which have global
  44. # effects are thus separated out and done before the recursive
  45. # descending is started. They are now explicitly listed as the
  46. # prepare rule.
  48. # Beautify output
  49. # ---------------------------------------------------------------------------
  50. #
  51. # Normally, we echo the whole command before executing it. By making
  52. # that echo $($(quiet)$(cmd)), we now have the possibility to set
  53. # $(quiet) to choose other forms of output instead, e.g.
  54. #
  55. #         quiet_cmd_cc_o_c = Compiling $(RELDIR)/$@
  56. #         cmd_cc_o_c       = $(CC) $(c_flags) -c -o $@ $<
  57. #
  58. # If $(quiet) is empty, the whole command will be printed.
  59. # If it is set to "quiet_", only the short version will be printed.
  60. # If it is set to "silent_", nothing will be printed at all, since
  61. # the variable $(silent_cmd_cc_o_c) doesn't exist.
  62. #
  63. # A simple variant is to prefix commands with $(Q) - that's useful
  64. # for commands that shall be hidden in non-verbose mode.
  65. #
  66. #	$(Q)ln $@ :<
  67. #
  68. # If KBUILD_VERBOSE equals 0 then the above command will be hidden.
  69. # If KBUILD_VERBOSE equals 1 then the above command is displayed.
  70. #
  71. # To put more focus on warnings, be less verbose as default
  72. # Use 'make V=1' to see the full commands
  73. # 这里时为了控制是否打印信息，我们这个makefile 1000多行，如果那个过程出现了错误肯定需要调试的
  74. # origin函数表示判断这个变量的来源
  75. ifeq ("$(origin V)", "command line")
  76.   KBUILD_VERBOSE = $(V)
  77. endif
  78. ifndef KBUILD_VERBOSE
  79.   KBUILD_VERBOSE = 0
  80. endif
  82. # 这里的Q就表示不回显命令，只会显示结果
  83. ifeq ($(KBUILD_VERBOSE),1)
  84.   quiet =
  85.   Q =
  86. else
  87.   quiet=quiet_
  88.   Q = @
  89. endif
  91. # If the user is running make -s (silent mode), suppress echoing of
  92. # commands
  93. # 这个filter函数我们前面就知道了，
  94. ifneq ($(filter 4.%,$(MAKE_VERSION)),)   # make-4
  95. # firstword为取首单词函数
  96. ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
  97.   quiet=silent_
  98. endif
  99. else					# make-3.8x
  100. ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
  101.   quiet=silent_
  102. endif
  103. endif
  105. export quiet Q KBUILD_VERBOSE
  107. # kbuild supports saving output files in a separate directory.
  108. # To locate output files in a separate directory two syntaxes are supported.
  109. # In both cases the working directory must be the root of the kernel src.
  110. # 1) O=
  111. # Use "make O=dir/to/store/output/files/"
  112. #
  113. # 2) Set KBUILD_OUTPUT
  114. # Set the environment variable KBUILD_OUTPUT to point to the directory
  115. # where the output files shall be placed.
  116. # export KBUILD_OUTPUT=dir/to/store/output/files/
  117. # make
  118. #
  119. # The O= assignment takes precedence over the KBUILD_OUTPUT environment
  120. # variable.
  122. # KBUILD_SRC is set on invocation of make in OBJ directory
  123. # KBUILD_SRC is not intended to be used by the regular user (for now)
  124. ifeq ($(KBUILD_SRC),)
  126. # OK, Make called in directory where kernel src resides
  127. # Do we want to locate output files in a separate directory?
  128. # 这里的参数使用方法可以参考上面的注释信息
  129. ifeq ("$(origin O)", "command line")
  130.   KBUILD_OUTPUT := $(O)
  131. endif
  133. # That's our default target when none is given on the command line
  134. PHONY := _all
  135. _all:
  137. # Cancel implicit rules on top Makefile
  138. # 取消隐式推倒规则
  139. $(CURDIR)/Makefile Makefile: ;
  141. # 将$(CURDIR)中的：变成空格，然后查看里面的参数个数
  142. ifneq ($(words $(subst :, ,$(CURDIR))), 1)
  143.   $(error main directory cannot contain spaces nor colons)
  144. endif
  146. ifneq ($(KBUILD_OUTPUT),)
  147. # Invoke a second make in the output directory, passing relevant variables
  148. # check that the output directory actually exists
  149. saved-output := $(KBUILD_OUTPUT)
  150. KBUILD_OUTPUT := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) \
  151. 								&& /bin/pwd)
  152. $(if $(KBUILD_OUTPUT),, \
  153.      $(error failed to create output directory "$(saved-output)"))
  155. # make的环境变量叫MAKECMDGOALS，这个变量会存放你所指定的终极目标的列表。如果在命令行中没有指定目标，那么这个变量是空值
  156. PHONY += $(MAKECMDGOALS) sub-make
  158. # filter-out为Makefile反过滤函数
  159. $(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
  160.     @:
  162. # 这个就是进入子目录进行编译了   $(filter-out _all sub-make,$(MAKECMDGOALS) 这个就是向make传递的参数了
  163. sub-make: FORCE
  164.     $(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \
  165.     -f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))
  167. # Leave processing to above invocation of make
  168. skip-makefile := 1
  169. endif # ifneq ($(KBUILD_OUTPUT),)
  170. endif # ifeq ($(KBUILD_SRC),)
  172. # We process the rest of the Makefile if this is the final invocation of make
  173. ifeq ($(skip-makefile),)
  175. # Do not print "Entering directory ...",
  176. # but we want to display it when entering to the output directory
  177. # so that IDEs/editors are able to understand relative filenames.
  178. # 设置不打印进入目录和离开目录信息
  179. MAKEFLAGS += --no-print-directory
  181. # Call a source code checker (by default, "sparse") as part of the
  182. # C compilation.
  183. #
  184. # Use 'make C=1' to enable checking of only re-compiled files.
  185. # Use 'make C=2' to enable checking of *all* source files, regardless
  186. # of whether they are re-compiled or not.
  187. #
  188. # See the file "Documentation/sparse.txt" for more details, including
  189. # where to get the "sparse" utility.
  191. ifeq ("$(origin C)", "command line")
  192.   KBUILD_CHECKSRC = $(C)
  193. endif
  194. ifndef KBUILD_CHECKSRC
  195.   KBUILD_CHECKSRC = 0
  196. endif
  198. # Use make M=dir to specify directory of external module to build
  199. # Old syntax make ... SUBDIRS=$PWD is still supported
  200. # Setting the environment variable KBUILD_EXTMOD take precedence
  201. ifdef SUBDIRS
  202.   KBUILD_EXTMOD ?= $(SUBDIRS)
  203. endif
  205. ifeq ("$(origin M)", "command line")
  206.   KBUILD_EXTMOD := $(M)
  207. endif
  209. # If building an external module we do not care about the all: rule
  210. # but instead _all depend on modules
  211. PHONY += all
  212. ifeq ($(KBUILD_EXTMOD),)
  213. _all: all
  214. else
  215. _all: modules
  216. endif
  218. ifeq ($(KBUILD_SRC),)
  219.         # building in the source tree
  220.         srctree := .
  221. else
  222.         ifeq ($(KBUILD_SRC)/,$(dir $(CURDIR)))
  223.                 # building in a subdirectory of the source tree
  224.                 srctree := ..
  225.         else
  226.                 srctree := $(KBUILD_SRC)
  227.         endif
  228. endif
  229. objtree		:= .
  230. src		:= $(srctree)
  231. obj     := $(objtree)
  233. # 设置依赖查找路径
  234. VPATH       := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
  236. export srctree objtree VPATH
  238. # SUBARCH tells the usermode build what the underlying arch is.  That is set
  239. # first, and if a usermode build is happening, the "ARCH=um" on the command
  240. # line overrides the setting of ARCH below.  If a native build is happening,
  241. # then ARCH is assigned, getting whatever value it gets normally, and
  242. # SUBARCH is subsequently ignored.
  243. # uname -m 查看系统的架构，这个函数的作用时如果在编译Linux内核时不指定架构那么顶层Makefile就会自动获取
  244. SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
  245.                   -e s/sun4u/sparc64/ \
  246.                   -e s/arm.*/arm/ -e s/sa110/arm/ \
  247.                   -e s/s390x/s390/ -e s/parisc64/parisc/ \
  248.                   -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
  249.                   -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ )

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