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![Prelink map build/core/prelink-linux-arm.map # 0xC0000000 - 0xFFFFFFFF Kernel # 0xB0100000 - 0xBFFFFFFF Thread 0 Stack # 0xB0000000 - 0xB00FFFFF Linker # 0xA0000000 - 0xBFFFFFFF Prelinked System Libraries # 0x90000000 - 0x9FFFFFFF Prelinked App Libraries # 0x80000000 - 0x8FFFFFFF Non-prelinked Libraries # 0x40000000 - 0x7FFFFFFF mmap'd stuff # 0x10000000 - 0x3FFFFFFF Thread Stacks # 0x00000000 - 0x0FFFFFFF .text / .data / heap # core system libraries libdl.so 0xAFF00000 # [<64K] libc.so 0xAFD00000 # [~2M] libstdc++.so 0xAFC00000 # [<64K] libm.so 0xAFB00000 # [~1M] liblog.so 0xAFA00000 # [<64K] libcutils.so 0xAF900000 # [~1M] libthread_db.so 0xAF800000 # [<64K] libz.so 0xAF700000 # [~1M] libevent.so 0xAF600000 # [???] libssl.so 0xAF400000 # [~2M] libcrypto.so 0xAF000000 # [~4M] libsysutils.so 0xAEF00000 # [~1M] ... 17](https://image.slidesharecdn.com/androidlinux20110522-110521212538-phpapp01/75/Android-is-NOT-just-Java-on-Linux-17-2048.jpg)
Uploaded byTetsuyuki Kobayashi
Android is NOT just 'Java on Linux'
The document discusses the architecture of the Android operating system, highlighting its differences from traditional Linux systems. It emphasizes that Android operates only with the Linux kernel and is designed specifically for Java applications, utilizing the Dalvik VM for execution. Additionally, it covers various components such as the boot sequence, Bionic libraries, and Android-specific kernel drivers like Binder and Wake Lock.
In this document
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The presentation introduces Android, emphasizing it is not merely 'Java on Linux'. It outlines that Android uses the Linux kernel but has a unique user environment.
Focuses on the architecture of Android including init, runtime, Zygote, Dalvik VM, and kernel drivers, setting the stage for deeper exploration.
Details the boot sequence in Android, focusing on the init process and its static linking compared to typical Linux systems.
Explains Bionic, Android's standard library system, and the role of prelinking for managing memory and optimizing the system.
Describes the Zygote process, its role in application startup, memory management, and how it efficiently loads classes.
Provides a detailed look at the Dalvik VM, its execution of dex code, and how to invoke it through different commands.
Discusses Android-specific kernel drivers including binder, ashmem, wake lock, alarms, and the logging system.
Wraps up how to access and build Android source, emphasizing the differences from standard Linux and the focus on Java.
Summarizes the distinct architecture of Android versus normal Linux, dedicated to Java applications and optimized for smaller systems.
Android is NOT just 'Java on Linux'
- 1. Android is NOT just 'Java on Linux' 2011.5.22 2011.10.26 updated Tetsuyuki Kobayashi 1
- 2. Let's talk aboutinside of Android. http://www.kmckk.co.jp/eng/kzma9/ 2 http://www.kmckk.co.jp/eng/jet_index.html
- 3. Who am I? 20+ years involved in embedded systems 10 years in real time OS, such as iTRON 10 years in embedded Java Virtual Machine Now GCC, Linux, QEMU, Android, … Blogs http://d.hatena.ne.jp/embedded/ (Personal) http://blog.kmckk.com/ (Corporate) http://kobablog.wordpress.com/(English) Twitter @tetsu_koba 3
- 4. Android is NOTjust 'Java on Linux' Android uses Linux kernel. Only kernel. User land is totally different from usual Linux system. Android applications are written in Java language. Class libraries are similar to Java SE but not equal. Dalvik VM eats only dex code need to translate from Java byte code in advance 4
- 5. Let's explore insideof Android Assuming you know Linux and Java very well :) 5
- 6. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 6
- 7. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 7
- 8.
- 9. Java is thefirst class citizen in Android Dalvik VM is the center of Android runtime. Almost all daemon services are written in Java. Application life cycle is described by Java API 9
- 10. Java is thefirst class citizen in Android NDK native library called from Java via JNI This is just a library. Application life cycle is the same as Java. Native activity Only C/C++ to make Apps. (just hidden JNI part into system.) not short-cut for C/C++ 10
- 11. Typical Directory Treeof Android ro: mounted as read only / /(root) (root) initrd (ro) rw: mounted as read and write yaffs2 (ro) /system /system bin etc lib /data yaffs2 (rw) /data usr /cache yaffs2 (rw) /cache /mnt/sdcard removable storage (rw) /mnt/sdcard cf. Usual Linux system assumes all file system are read/writable. 11
- 12. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 12
- 13. Boot sequence 13 quoted from http://hmtsay.blogspot.com/2010/10/android-startup.html
- 14. init located on /init need kernel boot parameter to add “init=/init” Static linked. cf. typical linux init is dynamic linked. Doesn't affect even dynamic link system collapsed. http://blog.kmckk.com/archives/3137191.html 14
- 15. Bionic The standard libraries libc, libm, pthread, dynamic linker linker has implicit crash dump function http://kobablog.wordpress.com/2011/05/12/debuggerd-of-android/ Came from *BSD, not glibc Currently, doesn't support C++ exception and RTTI. latest NDK supports these by static linking. 15
- 16. Prelinking Locate dynamic link libraries ahead of time. 'apriori' command. Different from 'prelink' command from Red Hat. Optimized for small embedded system Allocate fixed address to libraries . Assume 3GB memory space is large enough to put all libraries together. Assume not adding/removing libraries. 16
- 17. Prelink map build/core/prelink-linux-arm.map # 0xC0000000 - 0xFFFFFFFF Kernel # 0xB0100000 - 0xBFFFFFFF Thread 0 Stack # 0xB0000000 - 0xB00FFFFF Linker # 0xA0000000 - 0xBFFFFFFF Prelinked System Libraries # 0x90000000 - 0x9FFFFFFF Prelinked App Libraries # 0x80000000 - 0x8FFFFFFF Non-prelinked Libraries # 0x40000000 - 0x7FFFFFFF mmap'd stuff # 0x10000000 - 0x3FFFFFFF Thread Stacks # 0x00000000 - 0x0FFFFFFF .text / .data / heap # core system libraries libdl.so 0xAFF00000 # [<64K] libc.so 0xAFD00000 # [~2M] libstdc++.so 0xAFC00000 # [<64K] libm.so 0xAFB00000 # [~1M] liblog.so 0xAFA00000 # [<64K] libcutils.so 0xAF900000 # [~1M] libthread_db.so 0xAF800000 # [<64K] libz.so 0xAF700000 # [~1M] libevent.so 0xAF600000 # [???] libssl.so 0xAF400000 # [~2M] libcrypto.so 0xAF000000 # [~4M] libsysutils.so 0xAEF00000 # [~1M] ... 17
- 18.
- 19. Zygote fork Zygote process Child process classes classes classes classes classes classes dynamic link classes classes dynamic link Dalvik VM classes libraries Dalvik VM classes libraries classes classes classes classes dynamic link Dalvik VM classes libraries Physical memory space (Actually these are mapped by pages.) 19
- 20. Zygote Zygote process preloads typical (approx. 1800) classes and dynamic link libraries so that childlen start quickly. Copy-on-write Only when new process writes page, new page is allocated. All pages not be written are shared among all zygote children. Exec system call is not used in zygote. Exec wipes the page mapping table of the process. It means exec discards zygote cache. 20
- 21. UID, GID ofApplications UID(user id) and GID(group id) is used for managing multi-user in usual Linux system. Android use this mechanism to isolate applications. Each application has unique UID. Can not read/write other application's files. Zygote is running as UID=0 (root). After forking child process, its UID is changed by setuid system call. 21
- 22. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 22
- 23. Dalvik VM executes dex code, which is translated from Java byte code 16bit, register based cf. Java bytecode is 8bit, stack based has JIT from Android 2.2 (Froyo) http://blog.kmckk.com/archives/2691473.html has concurrent GC from Android 2.3 (Gingerbread) http://source.android.com/tech/dalvik/ 23
- 24. Java class libraries Different from Java ME, which is used in traditional Japanese phone. Similar to Java SE. But not equal. Different window/graphics. No AWT, No Swing. No RMI. Take care to use user defined class loader dynamic generated classes doesn't work because Dalvik VM doesn't eat Java class files but Dex files. 24
- 25. Caveats of NDKprogramming Dynamic libraries built by NDK are linked with application process. forked from Zygote but UID != 0 (root). consider about permissions. Don't use fork & exec system calls. Back ground process should be made as android .app.Service. Don't use GCC's TLS extension (__thread). Simple Android dynamic linker does not support it. java.lang.ThreadLocal is available in Java. 25
- 26. 3 commands toinvoke Dalvik VM /system/bin/app_process This is the 'Zygote' process. /system/bin/dalvikvm Similar to usual 'java' command. Try 'dalvikvm -h' to show command line help. /system/bin/dvz Send request to Zygote process. See my blog (Sorry in Japanese) http://blog.kmckk.com/archives/3551546.html 26
- 27. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 27
- 28. Linux kernel Many common Linux device drivers are available. Android specific kernel drivers binder ashmem wake lock logger … http://elinux.org/Android_Kernel_Features These source code is not yet merged to kernel main line repository. 28
- 29. Binder /dev/binder Base of Inter Process Method Invocation Not for general purpose. Tuned for specific transaction. Multi-thread aware Have internal data per thread (CF. Socket have internal data per fd.) Doesn't use ”write” and ”read” system calls. Write and read at once by ”ioctl”. http://blog.kmckk.com/archives/3676340.html 29
- 30. Ashmem Android / Anonymous SHared MEMory subsystem $(TOP)/system/core/cutils/ashmem.h int ashmem_create_region(const char *name, size_t size) → returns fd int ashmem_set_prot_region(int fd, int prot) int ashmem_pin_region(int fd, size_t offset, size_t len) int ashmem_unpin_region(int fd, size_t offset, size_t len) Kernel reclaims not ‘pin’ ed memory Similar to weak reference of Java. Useful to implement cache. android.os.MemoryFile from Java program 30
- 31. Wake lock Lock to prevent entering sleep mode. My memos http://blog.kmckk.com/archives/3298375.html http://blog.kmckk.com/archives/3304836.html eLinux wiki http://elinux.org/Android_Power_Management 31
- 32. Alarm kernel implementation to support Android's AlarmManager. Wake up even when it was in sleep mode. 32
- 33. Low memory killer At the shortage of memory, the kernel select a process seems low priority and kill it. (!!) It's OK. because specification in the Android application life cycle, application should be preserve its own status. http://blog.kmckk.com/archives/2795577.html 33
- 34. Logger Android has unique system-wide log system http://blog.kmckk.com/archives/2936958.html http://elinux.org/Android_Logging_System 34
- 35. Overview of AndroidLogging System Target Java program Java program System.out /System.err com.android.internal.os Native program android.util.Log com.android.internal.os Host Native program android.util.Log AndroidPrintStream AndroidPrintStream DDMS stdout logcat logcat stdout liblog /stderr liblog adbserver adbd adbd adbserver User Kernel adb logcat main 64KB radio logger logger 64KB /dev/log/main /dev/log/main /dev/log/radio event /dev/log/radio system /dev/log/event 256KB /dev/log/event /dev/log/system 64KB /dev/log/system 35
- 36. Today's topic Androidsystem architecture Init – runtime – Zygoto Dalvik VM Android specific kernel drivers How to build Android 36
- 37. How to buildAndroid All source code is available for download except Google specific services (Google map, Android market, … ) Easy to download source and build them See AOSP web site http://source.android.com/ Or, my blog http://blog.kmckk.com/archives/3722957.html 37
- 38. Conclusion Android system architecture is totally different from normal Linux systems. Android uses Linux kernel only, further more, adding android specific kernel drivers. Designed for Java applications. Tuned for small system. 38
- 39. Q&A Thank you forlistening! Any comments to blogs are welcome. 39