Course: Android Internals Lecture 5: Dalvik VM

1. Android internals
Egor Elizarov
SPbSU 2012

2. Legal info
 Android internals by Egor Elizarov is licensed under a
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 Corrections, suggestions, contributions and translations are welcome!
2 Egor Elizarov SPbSU 2012

3. Lecture 5
Dalvik VM
yegor.yelizarov(at)gmail.com
Rev: 1.1
Last update: 05/30/2012 http://vk.com/android_internals
3 Egor Elizarov SPbSU 2012

4. Previous time

Vanilla

Kernel types

Android/Kernel interaction

“Androdized” kernel features

Bionic

Log system
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5. 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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6. Virtualization approaches

Paravirtualization

Full virtualization

HW assisted virtualization
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7. Process VM types
Register VM Stack VM

Limited number of
registers with addresses

Stack

State register

Reverse Polish notation

List of instructions

Load/Store
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8. Dalvik VM

Register based

Designed for low memory requirements

Relying on OS
– Memory management
– Thread support
– Process isolation
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9. 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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10. 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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11. Dalvik bytecode example
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12. ARM ASM example
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13. Interpreter core

Portable (C)

Fast (C + ASM)

JIT (C + ASM + JIT)

Debug (C + ASM + profiling & single stepping)
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14. Just-In-Time
Source: http://dl.google.com/googleio/2010/android-jit-compiler-androids-dalvik-vm.pdf
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15. Android application

No single entry point

Activities, Services, Broadcast Receivers,
Content Providers

Intents

New VM instance (Copy on write)
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16. Dalvik EXecutable
Source: http://stid.googlecode.com/files/2008-05-29-Presentation-Of-Dalvik-VM-Internals.pdf
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17. Zygote

Nascent VM process

Starts at boot time

Preloads and preinitializes classes

fork()s on command
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18. Java application caching
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19. Java application launching
Source: http://coltf.blogspot.com/p/android-os-processes-and-zygote.html
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20. 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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21. Next Time

Android IPC

Typical Android
subsystem
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22. 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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23. 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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24. 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)
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