Android internalsEgor ElizarovSPbSU 2012

Egor Elizarov SPbSU 20122

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Egor Elizarov SPbSU 20123

Lecture 5

Dalvik VM

yegor.yelizarov(at)gmail.com

http://vk.com/android_internalsRev: 1.1Last update: 05/30/2012

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Previous time

Vanilla

Kernel types

Android/Kernel interaction

“Androdized” kernel features

Bionic

Log system

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Virtual Machines

VM concept was introduced in 1960s in Cambridge

Defined by Popek & Goldberg in 1973 as "an efficient, isolated duplicate of a real machine"

System VM (Whole OS emulation)

Process VM (One program emulation)

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Virtualization approaches

Paravirtualization

Full virtualization

HW assisted virtualization

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Process VM types

Register VM

Limited number of registers with addresses

State register

List of instructions

Stack VM

Stack

Reverse Polish notation

Load/Store

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Dalvik VM

Register based

Designed for low memory requirements

Relying on OS– Memory management

– Thread support

– Process isolation

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Dalvik VM (2)

Allow multiple VM instances to run once

Supports Java Debug Wire Protocol

Based on Apache Harmony (Open Source Java)

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Dalvik bytecode

Quite similar to common real architectures

Fixed size frames with particular number of registers (one per method)

32-bit registers

Reach meta information for each method

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Dalvik bytecode example

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ARM ASM example

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Interpreter core

Portable (C)

Fast (C + ASM)

JIT (C + ASM + JIT)

Debug (C + ASM + profiling & single stepping)

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Just-In-Time

Source: http://dl.google.com/googleio/2010/android-jit-compiler-androids-dalvik-vm.pdf

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Android application

No single entry point

Activities, Services, Broadcast Receivers, Content Providers

Intents

New VM instance (Copy on write)

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Dalvik EXecutable

Source: http://stid.googlecode.com/files/2008-05-29-Presentation-Of-Dalvik-VM-Internals.pdf

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Zygote

Nascent VM process

Starts at boot time

Preloads and preinitializes classes

fork()s on command

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Java application caching

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Java application launching

Source: http://coltf.blogspot.com/p/android-os-processes-and-zygote.html

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Dalvik porting

Core libraries should work from scratch

Implement JNI call bridge

Use portable interpreter

Replace opcode stubs

Use debug execution mode for debugging

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Next Time

Android IPC

Typical Android subsystem

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Useful links

http://vk.com/android_internals

K.Sutner. Register Machines. Carnegie Mellon University. Fall 2011 URL: http://www.cs.cmu.edu/~cdm/pdf/RegisterMach-6up.pdf

M.Schoeberl. Design and implementation of an Effective Stack Machine. Viena, Austria. URL: http://ti.tuwien.ac.at/rts/people/schoeberl/publications/stack.pdf

Y. Shi, D. Gregg, A. Beatty, M. A. Ertl. Virtual Machine Showdown: Stack Versus Registers. Dublin, Viena. URL: http://static.usenix.org/events/vee05/full_papers/p153-yunhe.pdf

http://www.dalvikvm.com/

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Useful links (2)

http://pallergabor.uw.hu/common/understandingdalvikbytecode.pdf

$ANDROID_ROOT/dalvik/docs/

http://s.android.com/tech/dalvik/dalvik-bytecode.html

D. Bornstein. Dalvik VM Internals. 2008 URL: http://stid.googlecode.com/files/2008-05-29-Presentation-Of-Dalvik-VM-Internals.pdf

http://coltf.blogspot.com/p/android-os-processes-and-zygote.html

http://www.google.com/events/io/2010/sessions/jit-compiler-androids-dalvik-vm.html

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Thanks to

Sergey Matyukevich for review and advices (www.linkedin.com/pub/sergey-matyukevich/31/889/769)

Nikolay F. Fominykh for review and advices

Nikita Shulga for advices and notes (http://www.linkedin.com/pub/nikita-shulga/8/582/287)

Grigory Tolstolytkin for advices and notes (http://www.linkedin.com/pub/grigory-tolstolytkin/2a/b41/74)