Makefile 语法分析.docx

Makefile 语法分析第一部分VERSION = 2# 给变量VERSION赋值PATCHLEVEL = 6# 给变量PATCHLEVEL赋值SUBLEVEL = 22# 给变量SUBLEVEL赋值EXTRAVERSION = .6# 给变量EXTRAVERSION赋值NAME = Holy Dancing Manatees, Batman!# 给变量NAME赋值# *DOCUMENTATION*# To see a list of typical targets execute make help# More info can be located in ./README# Comments in this file are targeted only to the developer, do not# expect to learn how to build the kernel reading this file.# Do not:# o use makes built-in rules and variables#??? (this increases performance and avoid hard-to-debug behavour);# o print Entering directory ...;MAKEFLAGS += -rR --no-print-directory# 操作符“+=”的作用是给变量（“+=”前面的MAKEFLAGS）追加值。# 如果变量（“+=”前面的MAKEFLAGS）之前没有定义过，那么，“+=”会自动变成“=”；# 如果前面有变量（“+=”前面的MAKEFLAGS）定义，那么“+=”会继承于前次操作的赋值符；# 如果前一次的是“:=”，那么“+=”会以“:=”作为其赋值符# 在执行make时的命令行选项参数被通过变量 “MAKEFLAGS”传递给子目录下的make程序。# 对于这个变量除非使用指示符“unexport”对它们进行声明，它们在整个make的执行过程中始终被自动的传递给所有的子make。# 还有个特殊变量SHELL与MAKEFLAGS一样，默认情况（没有用“unexport”声明）下在整个make的执行过程中被自动的传递给所有的子make。## -rR --no-print-directory# -r disable the built-in impilict rules. # -R disable the built-in variable setttings. # --no-print-directory。# We are using a recursive build, so we need to do a little thinking# to get the ordering right.## Most importantly: sub-Makefiles should only ever modify files in# their own directory. If in some directory we have a dependency on# a file in another dir (which doesnt happen often, but its often# unavoidable when linking the built-in.o targets which finally# turn into vmlinux), we will call a sub make in that other dir, and# after that we are sure that everything which is in that other dir# is now up to date.## The only cases where we need to modify files which have global# effects are thus separated out and done before the recursive# descending is started. They are now explicitly listed as the# prepare rule.# To put more focus on warnings, be less verbose as default# Use make V=1 to see the full commandsifdef Vifeq ($(origin V), command line)KBUILD_VERBOSE = $(V)endifendififndef KBU