Makefile.build

1 make -f scripts/Makefile.buildobj=scripts/basic

gcc -Wp,-MD,scripts/basic/.fixdep.d-Wall -Wmissing-prototypes -Wstrict-prototypes -O2-fomit-frame-pointer -o scripts/basic/fixdepscripts/basic/fixdep.c

gcc -Wp,-MD,scripts/basic/.docproc.d-Wall -Wmissing-prototypes -Wstrict-prototypes -O2-fomit-frame-pointer -o scripts/basic/docprocscripts/basic/docproc.c

rm -f .tmp_quiet_recordmcount

2 在makefile.build中

__build: $(if$(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \

$(if $(KBUILD_MODULES),$(obj-m)$(modorder-target)) \

$(subdir-ym) $(always)

@:

在scripts/basic/Makefile中定义

hostprogs-y := fixdep docproc

always := $(hostprogs-y)

而生成fixdepdocproc的规则在Makefile.host中定义。

3 分析Makefile.host

此文件中定义了一些规则在hostsystem上生成二进制文件，在内核编译过程中会用到这些二进制文件，如文件的预处理。

hostprogs-y=fixdep docproc

__hostprogs := $(sort $(hostprogs-y)$(hostprogs-m))

host-cmulti := $(foreachm,$(__hostprogs),$(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))

若$($(m)-cxxobjs)为非空则返回空，若为空则返回$(if$($(m)-objs),$(m))，$($(m)-objs)为空返回空，因此host-cmulti为空的。

$($(m)-objs)，并没有定义fixdep－objs或hostprogs-objs因此为空。

Targets什么用？？？？

接下来它会执行这条规则：

quiet_cmd_host-csingle = HOSTCC $@

cmd_host-csingle = $(HOSTCC)$(hostc_flags) -o $@ $< \

$(HOST_LOADLIBES)$(HOSTLOADLIBES_$(@F))

$(host-csingle): $(obj)/%: $(src)/%.cFORCE

$(call if_changed_dep,host-csingle)

其规则是在cmd_host-csingle中定义的，在调用的if_changed_dep函数中最终是调用了cmd_host-csingle生成目标文件fixdep和docproc

if_changed_dep在scripts/Kbuild.include中

# Execute the command and alsopostprocess generated .d dependencies file.

if_changed_dep = $(if $(strip$(any-prereq) $(arg-check) ), \

@set -e; \

$(echo-cmd) $(cmd_$(1)); \

scripts/basic/fixdep $(depfile) $@'$(make-cmd)' > $(dot-target).tmp;\

rm -f $(depfile); \

mv -f $(dot-target).tmp$(dot-target).cmd)

# if_changed - execute command ifany prerequisite is newer than

# target, or commandline has changed

# if_changed_dep - as if_changed, butuses fixdep to reveal dependencies

# including usedconfig symbols

# if_changed_rule - as if_changed butexecute rule instead

fixdep docproc 二者分别什么作用？？？