Difference between revisions of "Android Notes"
m (Android on OMAP might have some infos, too) |
m (Copy edited (e.g. ref. <https://en.wikipedia.org/wiki/Out_of_memory#Out_of_memory_management> and <https://en.wikipedia.org/wiki/BusyBox>).) |
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+ | [[Category: Android]] | ||
+ | |||
Here are some miscellaneous notes on Android. See [[Android_on_OMAP|Android on OMAP]], too. | Here are some miscellaneous notes on Android. See [[Android_on_OMAP|Android on OMAP]], too. | ||
− | |||
− | Google (Android) developer Arve Hjonevag added a lowmemorykiller feature to the staging area of the | + | |
− | Linux kernel in January of 2009. | + | == Technical information about system components == |
− | runs out (acting as a kind of cache manager, according to Arve). | + | === OOM Killer information === |
− | appears in | + | |
+ | Google (Android) developer Arve Hjonevag added a lowmemorykiller feature to the staging area of the Linux kernel in January of 2009. This feature tries to reclaim memory before the system runs out (acting as a kind of cache manager, according to Arve). In Linus' 2.6.28-rc tree this appears in | ||
Application lifecycle (and activity states) can be found here: | Application lifecycle (and activity states) can be found here: | ||
http://code.google.com/android/intro/lifecycle.html | http://code.google.com/android/intro/lifecycle.html | ||
− | Applications in different stages of their lifecycle receive a different oom_adj value, which affects | + | Applications in different stages of their lifecycle receive a different oom_adj value, which affects the probability of their being reaped. |
− | the probability of their being reaped. | ||
Initial lowmemorykiller thresholds are set by /etc/init.rc (with the following lines): | Initial lowmemorykiller thresholds are set by /etc/init.rc (with the following lines): | ||
− | # Define the oom_adj values for the classes of processes that can be | + | # Define the oom_adj values for the classes of processes that can be killed by the kernel. These are used in ActivityManagerService. |
− | |||
setprop ro.FOREGROUND_APP_ADJ 0 | setprop ro.FOREGROUND_APP_ADJ 0 | ||
setprop ro.VISIBLE_APP_ADJ 1 | setprop ro.VISIBLE_APP_ADJ 1 | ||
Line 25: | Line 25: | ||
setprop ro.EMPTY_APP_ADJ 15 | setprop ro.EMPTY_APP_ADJ 15 | ||
− | # Define the memory thresholds at which the above process classes will | + | # Define the memory thresholds at which the above process classes will be killed. These numbers are in pages (4k). |
− | |||
setprop ro.FOREGROUND_APP_MEM 1536 | setprop ro.FOREGROUND_APP_MEM 1536 | ||
setprop ro.VISIBLE_APP_MEM 2048 | setprop ro.VISIBLE_APP_MEM 2048 | ||
Line 46: | Line 45: | ||
Routines to actually calculate the oom_adj value, based on application state | Routines to actually calculate the oom_adj value, based on application state | ||
− | are in the ActivityManager. | + | are in the ActivityManager. See frameworks/base/services/java/com/android/server/am/ActivityManagerService.java:UpdateOomAdjLocked(...) and frameworks/base/core/java/android/os/Process.java:setOomAdj() => frameworks/base/core/jni/android_util_Process.cpp:android_os_Process_setOomAdj() |
+ | |||
+ | === Init sequence === | ||
+ | See this blog entry for an overview of the sequence of operations performed by the 'init' program: http://blog.csdn.net/loughsky/archive/2008/11/13/3293922.aspx | ||
+ | |||
+ | === Kernel power management === | ||
+ | See http://mjg59.livejournal.com/100221.html for a discussion of kernel modifications to support power management. | ||
+ | |||
+ | (Also, the comments are interesting, in that they delve into (and speculate about) the possible history of certain components of the Android system.) | ||
+ | |||
+ | === C Library (bionic) information === | ||
+ | See the excellent article: http://codingrelic.geekhold.com/2008/11/six-million-dollar-libc.html for an overview of bionic. | ||
+ | |||
+ | From: http://discuz-android.blogspot.com/2008/10/google-android-native-libc-bionic.html | ||
+ | |||
+ | Google developed a custom library for the C compiler (libc) called Bionic. This was necessary for three main reasons: | ||
+ | * License: they wanted to keep GPL out of user-space. Bionic code uses the BSD license. | ||
+ | * Size: the library has to be loaded in each process, so it needs to be small. Bionic is about 200K, or half the size of glibc (the GNU version of libc). | ||
+ | * Speed: limited CPU power means it needs to be fast. Bionic has a small size and fast code paths, including a very fast and small custom pthread implementation. | ||
− | and | + | Bionic has built-in support for important Android-specific services such as system properties and logging. It doesn’t support certain POSIX features, like C++ exceptions and wide chars, which were not needed on Android. Thus it’s not quite compatible with the GNU libc. All native code must be compiled against bionic, not glibc. |
− | |||
− | |||
− | == | + | ==== Threads ==== |
− | + | The bionic C library has its own thread API, not the same as either original LinuxThreads or | |
+ | NPTL. | ||
− | == | + | From: http://www.mail-archive.com/uclibc@uclibc.org/msg02787.html |
− | + | ||
+ | Android thread library (from bionic libc) is minimalist: | ||
+ | - Uses most of the Linux kernel thread features (futex, CLONE_THREAD) | ||
+ | unlike old linuxpthread. | ||
+ | - It doesn't support thread cancellation (see CAVEATS file) | ||
+ | - It misses some pthread functions: for example, no barrier, missing | ||
+ | *timedwait variant, etc. | ||
+ | - Very basic GDB support that only works through gdbserver | ||
+ | - Some theoretic race | ||
+ | |||
+ | == Development Tools == | ||
+ | === BusyBox === | ||
+ | Android ships with a utility suite (called 'toolbox') that is not BusyBox. | ||
+ | |||
+ | You can get a binary BusyBox for Android [http://benno.id.au/blog/2007/11/14/android-busybox here]. The site includes instructions for easy installation on your device. | ||
− | === | + | === Bootchart === |
The 'init' program in Android has built-in capability to gather the data needed to produce a | The 'init' program in Android has built-in capability to gather the data needed to produce a | ||
− | bootchart image. | + | bootchart image. See README.BOOTCHART in the directory system/core/init directory of the Android source repository for details. |
− | source repository for details. | + | |
+ | See [[Using Bootchart on Android]] | ||
+ | |||
+ | === Benchmarks === | ||
+ | Apparently, [http://code.google.com/p/droidbench/ droidbench] is an integrated benchmark program for Android. | ||
+ | |||
+ | == Development Tips == | ||
+ | === Debugging tips === | ||
+ | Quick stack dump - "kill -3 <pid>" will put a stack trace in the log file. (Use logcat to view.) | ||
+ | |||
+ | === Using 'fastboot' === | ||
+ | * [http://android-dls.com/wiki/index.php?title=Fastboot Fastboot quick overview] | ||
+ | * [http://www.gotontheinter.net/content/fastboot-cheat-sheet Fastboot cheat sheet] | ||
+ | |||
+ | === Re-flashing a device === | ||
+ | See [http://lwn.net/Articles/318712/ How (not) to brick the Android Developer Phone], Feb. 2009, LWN.net | ||
+ | |||
+ | [http://haykuro.theiphoneproject.org/?page_id=35 Android 101] by Haykuro - describes basic re-flashing of | ||
+ | a G1 (so has some non-ADP1 information). | ||
+ | |||
+ | ==== Tutorial on Android flash partitions ==== | ||
+ | [http://forum.xda-developers.com/showthread.php?t=443994 HOWTO: Unpack, Edit, and Repack Boot Images] is a good tutorial on Android Flash partitions. | ||
+ | |||
+ | ==== Nandroid (NAND flash backup tool) ==== | ||
+ | [http://www.gotontheinter.net/content/nandroid-v20-full-nand-backup-and-restore-tool Nandroid] is a tool for backing up your flash partitions. It is highly recommended if you plan to experiment with customizations of your system software. It requires BusyBox (not in regular Android images). | ||
+ | |||
+ | === Compiling native applications === | ||
+ | Because Android uses its own C library (not glibc), it is tricky to compile native applications for. | ||
+ | |||
+ | Here are some instructions for compiling "hello world" on the android phone: | ||
+ | http://android-tricks.blogspot.com/2009/02/hello-world-c-program-on-using-android.html | ||
== Building == | == Building == | ||
+ | See [http://lwn.net/Articles/331908/ Updating and rebuilding Android] LWN.net, May 2009 | ||
+ | |||
=== Building the kernel from scratch === | === Building the kernel from scratch === | ||
See http://honeypod.blogspot.com/2007/12/compile-android-kernel-from-source.html | See http://honeypod.blogspot.com/2007/12/compile-android-kernel-from-source.html | ||
− | |||
== Organizations == | == Organizations == | ||
* http://www.rethink-wireless.com/?article_id=1264 - Japan Consortium with 25 members - Open Embedded Software Foundation (OESF)- started in March to promote non-phone Android devices in Japan. | * http://www.rethink-wireless.com/?article_id=1264 - Japan Consortium with 25 members - Open Embedded Software Foundation (OESF)- started in March to promote non-phone Android devices in Japan. | ||
+ | |||
+ | == Android taxonomy == | ||
+ | The information in this wiki needs to be better organized. So I'm creating a taxonomy of topics for Android system developers. ''NOTE: This section of the page is a work-in-progress.'' | ||
+ | |||
+ | Categories of information: | ||
+ | * Kernel | ||
+ | ** Where to obtain | ||
+ | ** How to install on phone, on emulator | ||
+ | ** What version to use | ||
+ | ** Kernel features unique to android (wakelocks, binder) | ||
+ | ** Code names for boards/hardware | ||
+ | ** msm bsp highlights | ||
+ | * libc (bionic) | ||
+ | ** Where to obtain | ||
+ | ** License | ||
+ | ** How to install on phone, on emulator | ||
+ | ** Comparison with glibc, uclibc | ||
+ | * Development tools | ||
+ | ** Eclipse (I still can't use it) | ||
+ | ** traceview | ||
+ | ** Logs | ||
+ | ** Toolchains | ||
+ | ** Repository | ||
+ | ** ADB, Android, emulator | ||
+ | * Booting | ||
+ | ** Boot sequences (firmware, partitions, images) | ||
+ | ** Bootchart | ||
+ | ** Init | ||
+ | * Power management | ||
+ | ** Wakelocks | ||
+ | ** Application life-cycle | ||
+ | * Memory usage | ||
+ | ** OOM Killer, app life-cycle | ||
+ | ** Smem reports | ||
+ | ** Dalvik memory usage | ||
+ | * Security | ||
+ | * Programs (outside scope of this wiki - many other resources available) | ||
+ | ** API | ||
+ | ** Toolchains | ||
+ | ** Dalvik | ||
+ | ** DEX | ||
+ | ** JNI | ||
+ | * Scripts | ||
+ | ** ASE | ||
+ | * Hardware | ||
+ | * Distributions |
Latest revision as of 14:25, 21 January 2017
Here are some miscellaneous notes on Android. See Android on OMAP, too.
Contents
Technical information about system components
OOM Killer information
Google (Android) developer Arve Hjonevag added a lowmemorykiller feature to the staging area of the Linux kernel in January of 2009. This feature tries to reclaim memory before the system runs out (acting as a kind of cache manager, according to Arve). In Linus' 2.6.28-rc tree this appears in
Application lifecycle (and activity states) can be found here: http://code.google.com/android/intro/lifecycle.html
Applications in different stages of their lifecycle receive a different oom_adj value, which affects the probability of their being reaped.
Initial lowmemorykiller thresholds are set by /etc/init.rc (with the following lines):
# Define the oom_adj values for the classes of processes that can be killed by the kernel. These are used in ActivityManagerService. setprop ro.FOREGROUND_APP_ADJ 0 setprop ro.VISIBLE_APP_ADJ 1 setprop ro.SECONDARY_SERVER_ADJ 2 setprop ro.HIDDEN_APP_MIN_ADJ 7 setprop ro.CONTENT_PROVIDER_ADJ 14 setprop ro.EMPTY_APP_ADJ 15 # Define the memory thresholds at which the above process classes will be killed. These numbers are in pages (4k). setprop ro.FOREGROUND_APP_MEM 1536 setprop ro.VISIBLE_APP_MEM 2048 setprop ro.SECONDARY_SERVER_MEM 4096 setprop ro.HIDDEN_APP_MEM 5120 setprop ro.CONTENT_PROVIDER_MEM 5632 setprop ro.EMPTY_APP_MEM 6144 # Write value must be consistent with the above properties. write /sys/module/lowmemorykiller/parameters/adj 0,1,2,7,14,15 write /proc/sys/vm/overcommit_memory 1 write /sys/module/lowmemorykiller/parameters/minfree 1536,2048,4096,5120,5632,6144 class_start default # Set init its forked children's oom_adj. write /proc/1/oom_adj -16
Routines to actually calculate the oom_adj value, based on application state are in the ActivityManager. See frameworks/base/services/java/com/android/server/am/ActivityManagerService.java:UpdateOomAdjLocked(...) and frameworks/base/core/java/android/os/Process.java:setOomAdj() => frameworks/base/core/jni/android_util_Process.cpp:android_os_Process_setOomAdj()
Init sequence
See this blog entry for an overview of the sequence of operations performed by the 'init' program: http://blog.csdn.net/loughsky/archive/2008/11/13/3293922.aspx
Kernel power management
See http://mjg59.livejournal.com/100221.html for a discussion of kernel modifications to support power management.
(Also, the comments are interesting, in that they delve into (and speculate about) the possible history of certain components of the Android system.)
C Library (bionic) information
See the excellent article: http://codingrelic.geekhold.com/2008/11/six-million-dollar-libc.html for an overview of bionic.
From: http://discuz-android.blogspot.com/2008/10/google-android-native-libc-bionic.html
Google developed a custom library for the C compiler (libc) called Bionic. This was necessary for three main reasons:
- License: they wanted to keep GPL out of user-space. Bionic code uses the BSD license.
- Size: the library has to be loaded in each process, so it needs to be small. Bionic is about 200K, or half the size of glibc (the GNU version of libc).
- Speed: limited CPU power means it needs to be fast. Bionic has a small size and fast code paths, including a very fast and small custom pthread implementation.
Bionic has built-in support for important Android-specific services such as system properties and logging. It doesn’t support certain POSIX features, like C++ exceptions and wide chars, which were not needed on Android. Thus it’s not quite compatible with the GNU libc. All native code must be compiled against bionic, not glibc.
Threads
The bionic C library has its own thread API, not the same as either original LinuxThreads or NPTL.
From: http://www.mail-archive.com/uclibc@uclibc.org/msg02787.html
Android thread library (from bionic libc) is minimalist: - Uses most of the Linux kernel thread features (futex, CLONE_THREAD) unlike old linuxpthread. - It doesn't support thread cancellation (see CAVEATS file) - It misses some pthread functions: for example, no barrier, missing *timedwait variant, etc. - Very basic GDB support that only works through gdbserver - Some theoretic race
Development Tools
BusyBox
Android ships with a utility suite (called 'toolbox') that is not BusyBox.
You can get a binary BusyBox for Android here. The site includes instructions for easy installation on your device.
Bootchart
The 'init' program in Android has built-in capability to gather the data needed to produce a bootchart image. See README.BOOTCHART in the directory system/core/init directory of the Android source repository for details.
See Using Bootchart on Android
Benchmarks
Apparently, droidbench is an integrated benchmark program for Android.
Development Tips
Debugging tips
Quick stack dump - "kill -3 <pid>" will put a stack trace in the log file. (Use logcat to view.)
Using 'fastboot'
Re-flashing a device
See How (not) to brick the Android Developer Phone, Feb. 2009, LWN.net
Android 101 by Haykuro - describes basic re-flashing of a G1 (so has some non-ADP1 information).
Tutorial on Android flash partitions
HOWTO: Unpack, Edit, and Repack Boot Images is a good tutorial on Android Flash partitions.
Nandroid (NAND flash backup tool)
Nandroid is a tool for backing up your flash partitions. It is highly recommended if you plan to experiment with customizations of your system software. It requires BusyBox (not in regular Android images).
Compiling native applications
Because Android uses its own C library (not glibc), it is tricky to compile native applications for.
Here are some instructions for compiling "hello world" on the android phone: http://android-tricks.blogspot.com/2009/02/hello-world-c-program-on-using-android.html
Building
See Updating and rebuilding Android LWN.net, May 2009
Building the kernel from scratch
See http://honeypod.blogspot.com/2007/12/compile-android-kernel-from-source.html
Organizations
- http://www.rethink-wireless.com/?article_id=1264 - Japan Consortium with 25 members - Open Embedded Software Foundation (OESF)- started in March to promote non-phone Android devices in Japan.
Android taxonomy
The information in this wiki needs to be better organized. So I'm creating a taxonomy of topics for Android system developers. NOTE: This section of the page is a work-in-progress.
Categories of information:
- Kernel
- Where to obtain
- How to install on phone, on emulator
- What version to use
- Kernel features unique to android (wakelocks, binder)
- Code names for boards/hardware
- msm bsp highlights
- libc (bionic)
- Where to obtain
- License
- How to install on phone, on emulator
- Comparison with glibc, uclibc
- Development tools
- Eclipse (I still can't use it)
- traceview
- Logs
- Toolchains
- Repository
- ADB, Android, emulator
- Booting
- Boot sequences (firmware, partitions, images)
- Bootchart
- Init
- Power management
- Wakelocks
- Application life-cycle
- Memory usage
- OOM Killer, app life-cycle
- Smem reports
- Dalvik memory usage
- Security
- Programs (outside scope of this wiki - many other resources available)
- API
- Toolchains
- Dalvik
- DEX
- JNI
- Scripts
- ASE
- Hardware
- Distributions