Android编译中m、mm、mmm 详解
Android 完成编译的时候先执行 source build/envsetup.sh。 在这个shell 脚本中定义了 help, croot, m, mm, mmm 等 function
之后在当前目录下执行help 可以发现它给出的信息和此前见过linux 下面help 的信息不一样了：
Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment: - croot: Changes directory to the top of the tree. - m: Makes from the top of the tree. - mm: Builds all of the modules in the current directory. - mmm: Builds all of the modules in the supplied directories. - cgrep: Greps on all local C/C++ files. - jgrep: Greps on all local Java files. - resgrep: Greps on all local res/*.xml files. - godir: Go to the directory containing a file.
关于source
source 命令会把对应脚本中的内容读取到当前的bash 解释器中，在当前的执行环境中执行；其中定义的 function 以及通过 export 声明的变量等在 source 执行结束之后依然存在于当前的bash 环境中。比如我们常用的 source .bashrc 或者 source .profile 等目的是为了引用刚刚改动过的环境变量。
m 的解释
m 的定义如下：
561 function m()
562 {
563 T=$(gettop)
564 if [ "$T" ]; then
565 make -C $T $@
566 else
567 echo "Couldn't locate the top of the tree. Try setting TOP."
568 fi
569 }
570 当你在任何一个目录下打 m 的时候， 它会执行上面的function.
gettop 返回源码的顶层目录，如果这个目录存在，比如在我的机器上是：
~/Android/an403/external/webkit/Source/WebKit/android/jni/test$ gettop /home/mypc/Android/an403
比如我们执行 m showcommands -d
经过 function m 的翻译后就执行
make -C /home/yajun/Android/an403 showcommands -d当然如果 当前的目录不在源码树里面，gettop 就返回空，这样 m 的结果就时
~$ m Couldn't locate the top of the tree. Try setting TOP.
下面主要讲解mm
mm 的定义如下，功能是 Builds all of the modules in the current directory.
591 function mm()
592 {
593 # If we're sitting in the root of the build tree, just do a
594 # normal make.
595 if [ -f build/core/envsetup.mk -a -f Makefile ]; then
596 make $@
597 else
598 # Find the closest Android.mk file.
599 T=$(gettop)
600 local M=$(findmakefile)
601 # Remove the path to top as the makefilepath needs to be relative
602 local M=`echo $M|sed 's:'$T'/::'`
603 if [ ! "$T" ]; then
604 echo "Couldn't locate the top of the tree. Try setting TOP."
605 elif [ ! "$M" ]; then
606 echo "Couldn't locate a makefile from the current directory."
607 else
608 ONE_SHOT_MAKEFILE=$M make -C $T all_modules $@
609 fi
610 fi
611 }
它首先现判断当前目录是不是 TOP 目录，如果是，就直接开始make 了～
如果不是，就调用findmakefile 寻找 Android.mk , 搜索的路径是 当前目录-> 父目录 -> 父目录 -> ... -> 到根目录
571 function findmakefile()
572 {
573 TOPFILE=build/core/envsetup.mk
574 # We redirect cd to /dev/null in case it's aliased to
575 # a command that prints something as a side-effect
576 # (like pushd)
577 local HERE=$PWD
578 T=
579 while [ \( ! \( -f $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
580 T=$PWD
581 if [ -f "$T/Android.mk" ]; then
582 echo $T/Android.mk
583 cd $HERE > /dev/null
584 return
585 fi
586 cd .. > /dev/null
587 done
588 cd $HERE > /dev/null
589 }
文章写到一半 CSDN 挂了。。。
当在某个目录下找到Android.mk后，就把它echo 出来。然后 cd $HERE 返回调用 findmakefile 的目录。
以我在 /home/yajun/Android/an403/external/webkit/Source/WebKit/android/benchmark/ 下执行 mm 为例
以我在 /home/yajun/Android/an403/external/webkit/Source/WebKit/android/benchmark/ 下执行 mm 为例
findmakefile 的返回结果是 /home/yajun/Android/an403/external/webkit/Source/WebKit/android/benchmark/Android.mk
而 gettop 的返回结果是 /home/yajun/Android/an403
所以执行local M=`echo $M|sed 's:'$T'/::'` 之后， M =external/webkit/Source/WebKit/android/benchmark/Android.mk
ONE_SHOT_MAKEFILE=$M make -C $T all_modules $@ 展开后就是
ONE_SHOT_MAKEFILE=external/webkit/Source/WebKit/android/benchmark/Android.mk make -C /home/yajun/Android/an403 all_modules
ONE_SHOT_MAKEFILE=external/webkit/Source/WebKit/android/benchmark/Android.mk make -C /home/yajun/Android/an403 all_modules
到后面怎么make 的？（）
上面的执行就可以看作是：
make -C /home/yajun/Android/an403 all_modules ONE_SHOT_MAKEFILE=external/webkit/Source/WebKit/android/benchmark/Android.mk
接下来的执行会进入到 build/core/main.mk 中，在这里会 include external/webkit/Source/WebKit/android/benchmark/Android.mk
439 ifneq ($(ONE_SHOT_MAKEFILE),) 440 # We've probably been invoked by the "mm" shell function 441 # with a subdirectory's makefile. 442 include $(ONE_SHOT_MAKEFILE) 443 # Change CUSTOM_MODULES to include only modules that were 444 # defined by this makefile; this will install all of those 445 # modules as a side-effect. Do this after including ONE_SHOT_MAKEFILE 446 # so that the modules will be installed in the same place they 447 # would have been with a normal make. 448 CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS))) 449 FULL_BUILD := 450 # Stub out the notice targets, which probably aren't defined 451 # when using ONE_SHOT_MAKEFILE. 452 NOTICE-HOST-%: ; 453 NOTICE-TARGET-%: ; 454 455 else # ONE_SHOT_MAKEFILE把其中的变量读取进来：
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES := \
main.cpp
# Pull the webkit definitions from the base webkit makefile.
LOCAL_SHARED_LIBRARIES := libwebcore $(WEBKIT_SHARED_LIBRARIES)
LOCAL_LDLIBS := $(WEBKIT_LDLIBS)
LOCAL_MODULE := webcore_test
LOCAL_MODULE_TAGS := optional
include $(BUILD_EXECUTABLE)
这一段开始的地方会 include $(CLEAR_VARS), 我们可用在下面的地方找到
build/core/config.mk:54:CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk
它所做的事情是Clear out values of all variables used by rule templates.
LOCAL_MODULE:= LOCAL_MODULE_PATH:= LOCAL_MODULE_STEM:= LOCAL_DONT_CHECK_MODULE:= LOCAL_CHECKED_MODULE:= LOCAL_BUILT_MODULE:= 。。。 。。。在最后一句会 include $(BUILD_EXECUTABLE) 它的定义在：build/core/config.mk:60:BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk
ifeq ($(strip $(LOCAL_MODULE_CLASS)),)
LOCAL_MODULE_CLASS := EXECUTABLES
endif
ifeq ($(strip $(LOCAL_MODULE_SUFFIX)),)
LOCAL_MODULE_SUFFIX := $(TARGET_EXECUTABLE_SUFFIX)
endif
include $(BUILD_SYSTEM)/dynamic_binary.mk
ifeq ($(LOCAL_FORCE_STATIC_EXECUTABLE),true)
$(linked_module): $(TARGET_CRTBEGIN_STATIC_O) $(all_objects) $(all_libraries) $(TARGET_CRTEND_O)
$(transform-o-to-static-executable)
else
$(linked_module): $(TARGET_CRTBEGIN_DYNAMIC_O) $(all_objects) $(all_libraries) $(TARGET_CRTEND_O)
$(transform-o-to-executable)
endif
到这里相信写过 Makefile 的朋友顿时觉得熟悉了吧，只是这里的 target, dependencies, executable commands 都被变量代替了：
$(linked_module): $(TARGET_CRTBEGIN_DYNAMIC_O) $(all_objects) $(all_libraries) $(TARGET_CRTEND_O)
$(transform-o-to-executable)
如果想进一步了解这里做了什么事情，我们需要知道上面的变量都是什么值，最方便的做法是把他们打印出来。
include $(BUILD_SYSTEM)/dynamic_binary.mk $(warning "-------------------------------------------") $(warning "linked_modle=$(linked_module)") $(warning "TARGET_CRTBEGIN_DYNAMIC_O=$(TARGET_CRTBEGIN_DYNAMIC_O)") $(warning "all_objects=$(all_objects)") $(warning "all_libraries=$(all_libraries)") $(warning "TARGET_CRTEND_O=$(TARGET_CRTEND_O)") $(warning "transform-o-to-executable=$(transform-o-to-executable)") $(warning "--------------------------------------------") ifeq ($(LOCAL_FORCE_STATIC_EXECUTABLE),true)
可以然后就可以看出来这里做要 build 出来的是什么东西啦：
build/core/executable.mk:16: "-------------------------------------------" build/core/executable.mk:17: "linked_modle=out/target/product/generic/obj/EXECUTABLES/webcore_test_intermediates/LINKED/webcore_test" build/core/executable.mk:18: "TARGET_CRTBEGIN_DYNAMIC_O=out/target/product/generic/obj/lib/crtbegin_dynamic.o" build/core/executable.mk:19: "all_objects= out/target/product/generic/obj/EXECUTABLES/webcore_test_intermediates/main.o " build/core/executable.mk:20: "all_libraries=out/target/product/generic/obj/lib/libwebcore.so out/target/product/generic/obj/lib/libc.so out/target/product/generic/obj/lib/libstdc++.so out/target/product/generic/obj/lib/libm.so " build/core/executable.mk:21: "TARGET_CRTEND_O=out/target/product/generic/obj/lib/crtend_android.o" build/core/executable.mk:22: "transform-o-to-executable=@mkdir -p @echo "target Executable: ()" -nostdlib -Bdynamic -Wl,-T,build/core/armelf.x -Wl,-dynamic-linker,/system/bin/linker -Wl,--gc-sections -Wl,-z,nocopyreloc -o -Lout/target/product/generic/obj/lib -Wl,-rpath-link=out/target/product/generic/obj/lib out/target/product/generic/obj/lib/crtbegin_dynamic.o -Wl,-z,noexecstack -Wl,--icf=safe -Wl,--fix-cortex-a8 prebuilt/linux-x86/toolchain/arm-linux-androideabi-4.4.x/bin/../lib/gcc/arm-linux-androideabi/4.4.3/armv7-a/libgcc.a out/target/product/generic/obj/lib/crtend_android.o" build/core/executable.mk:23: "--------------------------------------------"
我们现看一下上面第八行的 dynamic_binary.mk 做了什么事情：
include $(BUILD_SYSTEM)/dynamic_binary.mk