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Android编译中m、mm、mmm 详解

沈博延
2023-12-01

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

$@ 返回调用这个脚本时传入的参数
比如我们执行 m showcommands -d
经过 function m 的翻译后就执行
make -C /home/yajun/Android/an403 showcommands -d
当然如果 当前的目录不在源码树里面,gettop 就返回空,这样 m 的结果就时
~$ 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 }

从它的注释可以看出,当你在某个目录下执行 mm 的时候,
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
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

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_modulesONE_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 includeexternal/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


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