Dalvik

• Dalvik Virtual Machine
  • Android init 启动过程分析
  • Android的优化
  • Improving Android Boot Time
    • Trying to Improve Android Boot Time With Readahead
  • Android- reduce boot time
  • 提高android启动速度研究

FFI(Foreign Function Interface)

• Foreign function interface
  • Ada language bindings
  • C++ has a trivial FFI with C
  • JNI
  • CNI
  • The FFIs of Common Lisp and Haskell
  • The major dynamic languages, such as Python, Perl, Tcl, and Ruby, all provide easy access to native code written in C/C++

JNI Call Bridge

• dalvik/vm/arch/*
  • dalvik/vm/arch/generic
    • the FFI-based version of JNI call bridge
    • The open-source FFI library (Foreign Function Interface) is used when a custom bridge is unavailable.

• 上課講義摘錄之23：JNI與Android VM之關係
• Android JNI实例

dvmLoadNativeCode

• [path to mydroid]/dalvik/vm/Native.[c|h]
  • dvmLoadNativeCode() // Load native code from the specified absolute pathname.
    • dlopen()

dvmPlatformInvoke

void dvmPlatformInvoke(void* pEnv, ClassObject* clazz, int argInfo,  int argc, const u4* argv, const char* signature, void* func, JValue* pReturn) 
// This will invoke a C/C++ function declared
return_type func(JNIEnv* pEnv, Object* this [, args])
// For a "static" method
return_type func(JNIEnv* pEnv, ClassObject* clazz [, args])

dvmPlatformInvokeHints

u4 dvmPlatformInvokeHints(const DexProto* proto)

• jniArgInfo (32-bit int) layout
  • This function is a placeholder/template and should be duplicated in the appropriate arch/<target>/ directory for new target ports.
  • The hints field should be defined and constructed in conjunction with dvmPlatformInvoke.
  • If valid hints can't be constructed, this function should return a negative value.
  • In that case, the caller will set the S bit in the jniArgInfo word and convert the arguments the slow way.

SRRRHHHH HHHHHHHH HHHHHHHH HHHHHHHH

1. The high order 4 bits of this word are the same for all targets, while the lower 28 are used for hints to allow accelerated JNI bridge transfers.
2. S - if set, ignore the hints and do things the hard way (scan signature)
3. R - return-type enumeration
4. H - target-specific hints

• Dalvik VM
  • dalvik/dalvikvm
  • dalvik/vm/native

Porting

• Dalvik Porting Guide
• Porting Dalvik

• Google Developer Day 2008 China - Android: Dalvik VM by Dan Bornstein
• Dalvik 程式碼分析與示範 (一), (二), (三)
• Dalvik 記憶體管理

VMs

• register-based architecture
  • Java VMs are stack machines
  • Virtual Machine Showdown: Stack Versus Registers

• Dalvik VM Internals, Slideshow

• Google 2008 台北程式開發日‎ - Android: Dalvik VM Internals

• android-dalvik-vm-on-java

Dalvik EXcutable(.dex) Format

• dx is used to convert Java .class files into the .dex format
• Dex File Format

Bytecode

• Bytecode for the Dalvik VM
• Understanding the Dalvik bytecode with the Dedexer tool

Class with internal native functions

• [path to mydroid]/dalvik/vm/InternalNative.c
  • java_lang_Runtime[] // java/lang/Runtime class

• The way Dalvik VM native code uses Java objects Options
• android dalvik vm oo

gc

• android dalvik vm alloc

Interpreter

• The portable interpreter is largely contained within a single C function, and should compile on any system that supports gcc. (If you don't have gcc, you may need to disable the "threaded" execution model, which relies on gcc's "goto table" implementation; look for the THREADED_INTERP define.)
• The fast interpreter uses hand-coded assembly fragments. If none are available for the current architecture, the build system will create an interpreter out of C "stubs". The resulting "all stubs" interpreter is quite a bit slower than the portable interpreter, making "fast" something of a misnomer.

• dalvik.vm.execution-mode system property

adb shell "echo dalvik.vm.execution-mode = int:portable >> /data/local.prop"

• 解释器汇编代码运行原理

Mterp Interpreter Structure

• There may be significant performance advantages to rewriting the interpreter core in assembly language, using architecture-specific optimizations. In Dalvik this can be done one instruction at a time. The simplest way to implement an interpreter is to have a large "switch" statement. After each instruction is handled, the interpreter returns to the top of the loop, fetches the next instruction, and jumps to the appropriate label.
• An improvement on this is called "threaded" execution. The instruction fetch and dispatch are included at the end of every instruction handler. This makes the interpreter a little larger overall, but you get to avoid the (potentially expensive) branch back to the top of the switch statement.
• Dalvik mterp goes one step further, using a computed goto instead of a goto table. Instead of looking up the address in a table, which requires an extra memory fetch on every instruction, mterp multiplies the opcode number by a fixed value. By default, each handler is allowed 64 bytes of space. Not all handlers fit in 64 bytes. Those that don't can have subroutines or simply continue on to additional code outside the basic space. Some of this is handled automatically by Dalvik, but there's no portable way to detect overflow of a 64-byte handler until the VM starts executing. The choice of 64 bytes is somewhat arbitrary, but has worked out well for ARM and x86.
• In the course of development it's useful to have C and assembly implementations of each handler, and be able to flip back and forth between them when hunting problems down. In mterp this is relatively straightforward. You can always see the files being fed to the compiler and assembler for your platform by looking in the dalvik/vm/mterp/out directory.
• The interpreter sources live in dalvik/vm/mterp. If you haven't yet, you should read dalvik/vm/mterp/README.txt now.

• android dalvik vm opcodes

Zygote

• dalvik.system.Zygote
  • allows a VM instance to be partially initialized and then fork()'d from the partially initialized state
  • fork
    • Forks a new Zygote instance
  • forkAndSpecialize
    • Forks a new VM instance
  • forkSystemServer
    • start the system server process

• zygote服务启动
• Android系统进程Zygote启动过程的源代码分析

preloaded-classes list

framework/base/preloaded-classed

• Question about preload class.
  • preloaded-class的生成方法

1. Set LOG_CLASS_LOADING to 1 in dalvik/vm/oo/Class.c
2. Disable preloading in frameworks/base/core/java/com/android/internal/os/ZygoteInit.java by commenting out the call to preloadClasses()
3. Rebuild. If nothing else has changed, you can avoid rebuilding everything.
make -j8 dalvikvm framework snod
4. Push to device.
adb reboot bootloader && fastboot -w flashall

• Android Hacks: Scan Android classpath
• Android内核剖析
  • 9.3.3 加载preload-classes

preloaded resource

framework/base/core/res/res/values/arrays.xml

package scan

• android apk安装原理分析

• Core Libraries

Apache Harmony

• Apache Harmony - Open Source Java SE

• dalvik/libcore
  • Much of the code comes directly from the Apache Harmony project.
  • Dalvik does not align to Java SE nor Java ME Class Library profiles.
  • The core libraries pull in code from many other projects, including OpenSSL, zlib, and ICU.
  • The native code in the core libraries is written in C/C++ and is expected to work without modification in a Linux environment.

• A JIT Compiler for Android’s Dalvik VM