Android build system note

Keywords:Android, build system

Very useful record. Thank you!
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1. Android Compilation System Analysis
Compile scripts and System Variables
Build/envsetup. Sh script analysis
Before compiling the source code, you usually need to execute ../build/envsetup. Sh in the top-level directory of the android source code to use
The script envsetup. Sh defines some functions:
Function help ()
Function get_abs_build_var ()
Function get_build_var ()
Function check_product ()
Function check_variant ()
Function setpaths ()
Function printconfig ()
Function set_stuff_for_environment ()
Function set_sequence_number ()
Function settitle ()
Function choosetype ()
Function chooseproduct ()
Function choosevariant ()
Function tapas ()
Function choosecombo ()
Function print_lunch_menu ()
Function lunch ()
Function gettop
Function M ()
Function findmakefile ()
Function mm ()
Function Mmm ()
Function Croot ()
Function PID ()
Function gdbclient ()
Function jgrep ()
Function cgrep ()
Function resgrep ()
Function getprebuilt
Function tracedmdump ()
Function runhat ()
Function getbugreports ()
Function startviewserver ()
Function stopviewserver ()
Function isviewserverstarted ()
Function smoketest ()
Function runtest ()
Function runtest_py ()
Function godir ()

Choosecombo command analysis:
Function choosecombo ()
{
Choosesim $1
Echo
Echo
Choosetype $2

Echo
Echo
Chooseproduct $3

Echo
Echo
Choosevariant $4

Echo
Set_stuff_for_environment
Printconfig
}
The following options are selected in sequence:
Build for the simulator or the device?
1. Device
2. Simulator
Which wocould you like? [1]

Build Type choices are:
1. Release
2. Debug
Which wocould you like? [1]

Product choices are:
1. emulator
2. Generic
3. Sim
4. Littleton
You can also type the name of a product if you know it.
Which wocould you like? [Littleton]

Variant choices are:
1. User
2. userdebug
3. Eng
Which wocould you like? [ENG] user
After the default option is selected, the following will appear:
Target_product = Littleton
Target_build_variant = user
Target_simulator = false
Target_build_type = release
Target_arch = arm
Host_arch = x86
Host_ OS = Linux
Host_build_type = release
Build_id =
============
Function chooseproduct () function analysis:
Choices = ('/bin/ls build/target/board/*/boardconfig. mk vendor/*/boardconfig. mk 2>/dev/null ')
Read the board configuration file boardconfig. mk In the build/target/board/* directory.
Read the board configuration file boardconfig. mk in the directory of Vendor /*/.
Choices value:
Build/target/board/emulator/boardconfig. mk
Build/target/board/generic/boardconfig. mk
Build/target/board/SIM/boardconfig. mk
Vendor/Marvell/Littleton/boardconfig. mk
After:
For choice in $ {choices [@]}
Do
# The product name is the name of the directory containing
# The makefile we found, above.
Prodlist = ($ {prodlist [@]} 'dirname $ {choice} | xargs basename ')
Done
The prodlist value is:
Emulator generic SIM Littleton
Select the following menu:
Product choices are:
1. emulator
2. Generic
3. Sim
4. Littleton
If you select 4, The target_product value is Littleton.

Board_config_mk: =/
$ (Strip $ (wildcard/
$ (Src_target_dir)/board/$ (target_device)/boardconfig. mk/
Vendor/*/$ (target_device)/boardconfig. mk/
))

How to add a module
Local_path: = $ (call my-DIR)
# Compile a static library
Include $ (clear_vars)
Local_module = libhellos
Local_cflags = $ (l_cflags)
Local_src_files = hellos. c
Local_c_includes = $ (includes)
Local_shared_libraries: = libcutils
Local_copy_headers_to: = libhellos
Local_copy_headers: = hellos. h
Include $ (build_static_library)

# Compile a dynamic library
Include $ (clear_vars)
Local_module = libhellevels
Local_cflags = $ (l_cflags)
Local_src_files = hellevels. c
Local_c_includes = $ (includes)
Local_shared_libraries: = libcutils
Local_copy_headers_to: = libhellevels
Local_copy_headers: = hellevels. h
Include $ (build_shared_library)

Build_test = true
Ifeq ($ (build_test), true)
# Using static libraries
Include $ (clear_vars)
Local_module: = hellos
Local_static_libraries: = libhellos
Local_shared_libraries: =
Local_ldlibs + =-LDL
Local_cflags: = $ (l_cflags)
Local_src_files: = mains. c
Local_c_includes: = $ (includes)
Include $ (build_executable)

# Use a dynamic library
Include $ (clear_vars)
Local_module: = hellevels
Local_module_tags: = debug
Local_shared_libraries: = libc libcutils libhelfine
Local_ldlibs + =-LDL
Local_cflags: = $ (l_cflags)
Local_src_files: = maind. c
Local_c_includes: = $ (includes)
Include $ (build_executable)
Endif # ifeq ($ (wpa_build_supplicant), true)

########################
# Local_target_dir: = $ (target_out)/etc/WiFi
# Include $ (clear_vars)
# Local_module: = wpa_supplicant.conf
# Local_module_tags: = user
# Local_module_class: = etc
# Local_module_path: = $ (local_target_dir)
# Local_src_files: = $ (local_module)
# Include $ (build_prebuilt)
########################
System variable Parsing
Local_module-compiled target object
Local_src_files-compiled source file
Local_c_includes-directory of the header files to be included
Local_shared_libraries-External library required for Link
Local_prelink_module-whether prelink processing is required
Build_shared_library-specifies the library to be compiled into a dynamic library

Local_path-directory during compilation
$ (Call directory, directory ....) Directory import operator
If the directory has a folder named SRC, you can write $ (call SRC) in this way, then the complete path of the src directory will be obtained.

Include $ (clear_vars)-clear previous system variables
Clear_vars: = $ (build_system)/clear_vars.mk
Define clear_vars :=$ (build_system)/clear_vars.mk in build/CORE/config. mk
Include custom. mk files (that is, custom compilation rules) or reference other. mk files (system-defined compilation rules) in the system ).

Local_src_files-compiled source file
It can be in. C,. cpp,. Java,. S (Assembly file),. aidl, and other formats.
Different files are separated by spaces. If you compile a directory subdirectory, use a relative path, such as subdirectory/file name. You can also use $ (call Directory) to specify a directory to compile.
All. c/. CPP/. Java/. S/. aidl files. append files local_src_files + = files

Local_c_includes-directory of the header files to be included
It can be a system-defined path or a relative path. For example, the compilation directory contains an include directory, which is written as include/*. h.

Local_shared_libraries-External shared library required for Link
Local_static_libra Ries-External external static required for Link
Add local_java_libraries to the jar package

Local_module-compiled target object
Module refers to the native code of the system, usually for C, C ++ code
./System/CORE/SH/Android. mk: 32: local_module: = sh
./System/CORE/libcutils/Android. mk: 71: local_module: = libcutils
./System/CORE/cpio/Android. mk: 9: local_module: = mkbootfs
./System/CORE/mkbootimg/Android. mk: 8: local_module: = mkbootimg
./System/CORE/toolbox/Android. mk: 61: local_module: = toolbox
./System/CORE/logcat/Android. mk: 10: local_module: = logcat
./System/CORE/ADB/Android. mk: 65: local_module: = aDb
./System/CORE/ADB/Android. mk: 125: local_module: = adbd
./System/CORE/init/Android. mk: 20: local_module: = init
./System/CORE/vold/Android. mk: 24: local_module: = vold
./System/CORE/mountd/Android. mk: 13: local_module: = mountd

Local_package_name
The Java application name is defined using this variable.
./Packages/apps/music/Android. mk: 9: local_package_name: = Music
./Packages/apps/Browser/Android. mk: 14: local_package_name: = Browser
./Packages/apps/settings/Android. mk: 8: local_package_name: = settings
./Packages/apps/STK/Android. mk: 10: local_package_name: = STK
./Packages/apps/contacts/Android. mk: 10: local_package_name: = contacts
./Packages/apps/MMS/Android. mk: 8: local_package_name: = MMS
./Packages/apps/camera/Android. mk: 8: local_package_name: = camera
./Packages/apps/phone/Android. mk: 11: local_package_name: = phone
./Packages/apps/voicedialer/Android. mk: 8: local_package_name: = voicedialer

Build_shared_library-specifies the library to be compiled into a dynamic library.
The purpose of compilation. Use the include operator.
Uild_static_library to specify the static library to be compiled.
If it is a Java file, the system's compiling script host_java_library.mk will be used to specify it with build_package. Three compilations
-------------------
Include $ (build_static_library)
Build_static_library: = $ (build_system)/static_library.mk
-------------------
Include $ (build_shared_library)
./Build/CORE/config. mk: 50: build_shared_library :=$ (build_system)/shared_library.mk
-------------------
Include $ (build_host_shared_library)
Build_host_shared_library: = $ (build_system)/host_shared_library.mk
-------------------
Include $ (build_executable)
Build/CORE/config. mk: 51: build_executable: = $ (build_system)/executable. mk
-------------------
Include $ (build_host_executable)
./Build/CORE/config. mk: 53: build_host_executable: = $ (build_system)/host_executable.mk
-------------------
Build_host_java_library: = $ (build_system)/host_java_library.mk
-------------------
Build_java_library
./Build/CORE/config. mk: 58: build_java_library :=$ (build_system)/java_library.mk
------------------
Build_static_java_library
./Build/CORE/config. mk: 59: build_static_java_library :=$ (build_system)/static_java_library.mk
------------------
Build_host_java_library
./Build/CORE/config. mk: 60: build_host_java_library :=$ (build_system)/host_java_library.mk
------------------

Build_host_static_library: = $ (build_system)/host_static_library.mk
Build_host_shared_library: = $ (build_system)/host_shared_library.mk
Build_static_library: = $ (build_system)/static_library.mk
Build_raw_static_library: = $ (build_system)/raw_static_library.mk
Build_shared_library: = $ (build_system)/shared_library.mk
Build_executable: = $ (build_system)/executable. mk
Build_raw_executable: = $ (build_system)/raw_executable.mk
Build_host_executable: = $ (build_system)/host_executable.mk
Build_package: = $ (build_system)/package. mk
Build_host_prebuilt: = $ (build_system)/host_prebuilt.mk
Build_prebuilt: = $ (build_system)/prebuilt. mk
Build_multi_prebuilt: = $ (build_system)/multi_prebuilt.mk
Build_java_library: = $ (build_system)/java_library.mk
Build_static_java_library: = $ (build_system)/static_java_library.mk
Build_host_java_library: = $ (build_system)/host_java_library.mk
Build_droiddoc: = $ (build_system)/droiddoc. mk
Build_copy_headers: = $ (build_system)/copy_headers.mk
Build_key_char_map: = $ (build_system)/key_char_map.mk

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Local_prelink_module
Prelink uses the advance link instead of the runtime link to accelerate the loading of shared libraries. It not only speeds up startup, but also reduces some memory overhead,
It is a popular tool in various Linux architectures for reducing program loading time, shortening system startup time, and accelerating application startup. When the program is running
The overhead of dynamic links, especially relocation, is huge for large systems.
The process of dynamic linking and loading is costly. In most systems, function libraries are not often changed.
Actions are identical, especially for embedded systems. Therefore, this process can be pre-processed before it is run, that is, it takes some time
The prelink tool is used to process dynamic shared libraries and executable files, modify these binary files, and add the corresponding relocation information, saving
It is time-consuming to query the function address at startup, which can reduce the startup time of the program and reduce the memory consumption.
This kind of prelink method also has a price: each time a dynamic shared library is updated, the relevant executable files must be re-executed once to ensure
The token is valid because the symbol information and address in the new Shared library may be different from the original one. This is why the android framework code is changed,
At this time, related applications will be re-compiled.
This price may bring a little complexity to developers of embedded systems, but it is almost negligible for users.
--------------------
If the variable is set to false, the prelink operation is not performed.
Local_prelink_module: = false
Prlink is required by default and must be added to build/CORE/prelink-linux-arm.map
Libhellevels. So 0x96000000
This map file seems to be used to specify the address of the dynamic library. Some address range information is shown in the preceding comment. Pay attention to the number of intervals between the library and the library,
If this parameter is not specified, an address space conflict is prompted during compilation. In addition, pay attention to sorting. here we need to put the big data in front,
Sort by size in descending order.
Resolve the local_prelink_module variable
Build/CORE/dynamic_binary.mk: 94: ifeq ($ (local_prelink_module), true)
Ifeq ($ (local_prelink_module), true)
$ (Prelink_output): $ (prelink_input) $ (target_prelinker_map) $ (Apriori)
$ (Transform-to-prelinked)
Transform-to-prelinked definition:
./Build/CORE/definitions. mk: 1002: Define transform-to-prelinked
Define transform-to-prelinked
@ Mkdir-p $ (DIR $ @)
@ Echo "target prelink: $ (private_module) ($ @)"
$ (Hide) $ (Apriori )/
-- Prelinkmap $ (target_prelinker_map )/
-- Locals-only/
-- Quiet/
$ </
-- Output $ @
Endef
./Build/CORE/config. mk: 183: Apriori: = $ (host_out_executables)/Apriori $ (host_executable_suffix)
Prelink is not a commonly used prelink, but a prelink. Its source code is located in "<your_android>/build/tools/Apriori"
Reference:
Dynamic library Optimization-prelink Technology
Http://www.eefocus.com/article/09-04/71629s.html

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Local_arm_mode: = arm
Currently, most Android devices are based on ARM processors. Arm commands use two modes: thumb (two bytes per command) and arm command (four bytes per command)

Local_cflags + =-O3-fstrict-aliasing-fprefetch-loop-Arrays
By setting the compiler operation, the optimization level.-O0 indicates no optimization,-O1 indicates the default value, and-O3 indicates the highest optimization level.
Local_cflags + =-w-wall
Local_cflags + =-FPIC-dpic
Local_cflags + =-O2-g-dadb_host = 1-wall-wno-unused-Parameter
Local_cflags + =-d_xopen_source-d_gnu_source-dsh_history
Local_cflags + =-duseoverlay2
Select the appropriate compilation parameters according to the conditions.
Ifeq ($ (target_arch), arm)
Local_cflags + =-dandroid_gadget = 1
Local_cflags: = $ (pv_cflags)
Endif
Ifeq ($ (target_build_type), release)
Local_cflags + =-O2
Endif

Local_ldlibs: =-lpthread
Local_ldlibs + =-LDL

Ifdef use_marvell_mved
Local_whole_static_libraries + = lib_il_mpeg4aspdecmved_wmmx2lnx lib_il_h1_decmved_wmmx2lnx
Local_shared_libraries + = libmrvlmved
Else
Local_whole_static_libraries + = lib_il_h1_dec_wmmx2lnx lib_il_mpeg4aspdec_wmmx2lnx
Endif
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