LCU14 100-dalvik is dead long live dalvik

Dalvik is Dead, Long Live Dalvik!
LCU14-September 2014
Stuart Monteith
Systems & Software

Outline
▪What is Dalvik™?
▪Porting Dalvik onto AArch64
▪ART
▪Working on AOSP1
▪Q&A
2
1 - Android™ Open Source Project

Android™ & Dalvik™
4
Applications
Application Framework
Libraries
Kernel
Android™ Runtime
Core Libraries
Dalvik VM
Bionic
SSL
…

What is Dalvik™?
▪ Dalvik is a virtual machine
▪ A managed runtime
▪ Interpreter
▪ Executes Java™ class files translated into
Dalvik “dex” bytecode
▪ Exception handling
▪ Object oriented
▪ References rather than pointers
▪ Garbage collection
▪ Concurrency
▪ Platform independence
5
Native
Code
Interpreter
Heap
OS
Bytecode

Compiling for Dalvik
*.java
javac
*.class
Development Installation
/data/dalvik-cache/
*.dex *.apk *.odex
6
dx
dexopt

Devices
7
Phone `08 Phone `14 Tablet `10 Tablet `14
Relative to Phone in 2008
30
22.5
15
7.5
0
CPU RAM Pixels

Dalvik Evolution
▪ Just-In-Time (JIT) Compiler - Android™ 2.2 “Froyo”, May 2010
▪ Concurrent Garbage collection - Android 2.3 “Gingerbread”, December 2010
▪ SMP1 support - Android 3.0 “Honeycomb”, February 2011
8
1 - Symmetric MultiProcessing

Tracing JIT
▪ Just-In-Time Compiler
▪ Compiles code at runtime
▪ Only code that is executed is compiled
▪ Only “Hot code” is compiled
▪ Interpreter executes bytecode instruction by instruction
▪ Profiles code
▪ Sends linear sequences of code to JIT
▪ Native code branched to from interpreter
▪ However…
▪ Code produced is not ideal
▪ Still, 5x faster than interpreter alone
9

Traces
10
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0004: move-wide v2, v0!
0005: if-ge v6, v13, 001d // +0018!
0007: mul-double v4, v2, v2!
000b: sub-double/2addr v4, v7!
000c: add-double/2addr v4, v9!
000d: const-wide/high16 v7, #long 4611686018427387904 // #4000!
000f: mul-double/2addr v2, v7!
0010: mul-double/2addr v0, v2!
0011: add-double/2addr v0, v11!
0017: const-wide/high16 v7, #long 4616189618054758400 // #4010!
0019: cmpl-double v2, v2, v7!
001b: if-lez v2, 0026 // +000b!
001d: sget v0, LMandle;.threshold:I // field@0001!
001f: int-to-double v0, v0!
0020: int-to-double v2, v13!
0021: div-double/2addr v0, v2!
0024: double-to-int v0, v0!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025

Traces
11
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025
0000: const-wide/16 v0, 0
0002: const/4 v2, #int 0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d

Traces
12
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025
: : : : : :!
0017: const-wide/high16 v7, #long!
001b: if-lez v2, 0026 // +000b!

Traces
0026: add-int/lit8 v2,
v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025!
0005: if-ge v6, v13, 001d
13
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025

Traces
14
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025
07:!
T0!
1b:

Traces
15
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025
07:!
T0!
1b:
26:!
T1!
05:
1d:
1d:

Traces
16
0000: const-wide/16 v0, #int 0 // #0!
0002: const/4 v2, #int 0 // #0!
0003: move v6, v2!
0005: if-ge v6, v13, 001d // +0018!
001b: if-lez v2, 0026 // +000b!
0025: return v0!
0026: add-int/lit8 v2, v6, #int 1 // #01!
0028: move v6, v2!
002a: goto 0005 // -0025
07:!
T0!
1b:
26:!
T1!
05:
1d:!
T2!
25:
00:!
T3!
05:

Garbage Collection
17
Thread!
Stack
A
B
C
D
E
F

Garbage Collection (Mark)
18
Thread!
Stack
A
B
C
D
E
F

Garbage Collection (Sweep)
19
Thread!
Stack
A
B
C
D
E
F
X
X

Porting Dalvik™ onto AArch64
20

ARM’s AArch64 Porting effort
▪ Model, kernel, bionic and shell below
▪ LCU14-411 From zero to booting Nano-Android
▪ Not just a recompile!
▪ Dalvik™ VM implementation
▪ Portable C interpreter, garbage collection, class loading, JNI
▪ Compressed references
▪ Java™ core libraries - platform/libcore:
▪ java.* classes
▪ int always 32-bit, long always 64-bit
▪ Java: int pointer; ➤ long pointer;!
▪ C: jint pointer; ➤ jlong pointer;!
▪ pointer = (jlong)(void*) nativeStructure;!
▪ Build system
21

ARM’s AArch64 Porting effort (2)
▪ Then:
▪ AArch64 assembler interpreter
▪ Slightly before with VIXL
▪ VIXL - library for simulating, assembling and disassembling ARMv8 A64
instructions.
▪ Just-In-Time compiler
▪ The rest of the Android™libraries
▪ End result - Android with only 64-bit binaries
▪ Initially 64-bit Dalvik™ running on host in November 2012
▪ On ARM’s ARMv8 models on command line in February 2013
▪ Then AOSP on models from July 2013
22

Dalvik is Dead, Long Live ART!
▪ After porting AOSP to AArch64 - ART came along in October 2013
▪ Not all was lost:
▪ Able to boot AOSP from July 2013 (4.2/4.3) through to 4.4 on Dalvik™ for
AArch64
▪ Demonstrated AOSP on Juno 2014
23

ART
▪ Introduced October 2013 as experimental runtime in Android™ 4.4 “KitKat”
▪ First release in Android “L”
▪ Less lag, more performance
▪ Productised through 2014
▪ ART also introduces 64-bit support into Android
▪ ARM contributed compiler backend components from Dalvik for AArch64
▪ + JNI compiler, glue, fixes, performance features/tweaks
25

Unchanged
▪ Dalvik™ Virtual Machine
▪ Java™ applications as before
▪ Garbage collection, class loading, object references, all as before
▪ It is not translating programs into C/C++
▪ Native code works as before (Java Native Interface - JNI)
▪ Eclipse + ADT or Android Studio, NDK are essentially unchanged
▪ Targeting the same platform - Android
▪ Debugging
▪ dalvikvm!
▪ Zygote
▪ app_process - Android’s command for starting VMs.
26

Changed
▪ Garbage collection + allocation
▪ Parallel, less pauses
▪ C++ Interpreter
▪ Ahead-of-time compilation (AOT)
▪ Support for 64-bit execution
▪ Diagnostics
▪ Stricter JNI
▪ Stricter bytecode verification
27

Initialization
▪ No JITing during startup
▪ Compilation time spent at installation
▪ boot.art:
▪ Part of the heap stored on flash
▪ Built as part of firmware image
▪ Pre-initialized VM heap
▪ ~12 MB on AOSP
▪ Zygote as before
▪ Initialize
▪ Wait for binder request to fork new apps
28

Threads
▪ Stacks now unified - each thread has one stack each
▪ Original Dalvik™ implementation had separately allocated VM stack
▪ ART has VM, interpreted, compiler and JNI frames all on same stack
▪ Stack characteristics may be different
▪ Stack overflow + null pointer exceptions detected through fault handlers
▪ Trap and handle
▪ Thread local allocation
▪ Threads can allocate objects without getting global heap lock
29

Garbage Collection
▪ More pluggable
▪ Provisions in runtime for different GC schemes
▪ Parallel & Concurrent
▪ More threads doing the work
▪ Background collection
▪ More throughput, less responsive
▪ Mark & Sweep, semi-space, large objects, variations
30

64-bit Support
▪ Two Zygotes, one 32-bit , one 64-bit
▪ 64-bit is the default
▪ Files duplicated on flash - 32/64-bit.
▪ Compressed references
▪ 32-bit object references
▪ Mapped within bottom 4 GB of memory
▪ Heap size: 256 MB
▪ Hard-float ABI
▪ Parameters passed in floating-point registers
▪ JNI 64-bit libraries
▪ Apps with 32-bit JNI run by 32-bit Zygote
31
Zygote32 Zygote64
fork()
32 bit App 64 bit App
32-bit App 64-bit App

Compiling for ART
*.java
javac
*.class
Development Installation
/data/dalvik-cache/arm!
*.dex *.apk *.odex
32
dx
dex2oat
or!
/data/dalvik-cache/arm64

Compilation
▪ Compiler driver
▪ Portable compiler
▪ Sea of nodes IR
▪ Quick compiler
▪ Optimising compiler
▪ More platform independent code
▪ ARM, MIPS & x86 with 64-bit variants
▪ Performed at install time
▪ Compiler compiles with multiple threads in parallel
▪ Good code quality without onerous compile time
33

Working on AOSP
▪ Google working in the open with ART in AOSP
▪ ARM, MIPS, Intel & ARM partners contribute
▪ 64-bit porting work has been a proving ground for this approach
▪ Ideas are nice, but code is better
▪ Understand who is doing what
▪ Check, post to the Google groups (see android-platform, etc.)
▪ Important to test on more than just ARM platforms - check MIPS & x86
▪ Frequently unstable: reversions, build system restructuring
▪ Android is big, and components have interdependencies
35

Working on AOSP
▪ AOSP’s gerrit has useful features
▪ Use it to track new changes in projects through email
▪ Volume can be high - can filter on git fields
▪ esp. if you are working on a particular feature
▪ Keep a working branch - pull it forward as quickly as possible though
▪ Use and add to the unit tests
▪ art # mma test-art
36

Thank You
The trademarks featured in this presentation are registered and/or unregistered trademarks of ARM Limited (or its
subsidiaries) in the EU and/or elsewhere. All rights reserved. Any other marks featured may be trademarks of their
respective owners
37

Sessions
▪ Today:
▪ LCU14-104: Everything’s Done! Android™ for 64-bit ARMv8, What’s next?
◦ Next in this room
▪ LCU14-108: Panel: Faster, Better and more Open AOSP Support
◦ 12:10, this room
▪ Wednesday:
▪ LCU14-309: Introducing Android NDK for 64bit ARMv8 SOCs
◦ 12:10 Grand Peninsula A
▪ Thursday:
▪ LCU14-411: From zero to booting Nano-Android with 64bit support
◦ 12:10 Grand Peninsula C
▪ Friday
▪ LCU14-502: Android User-Space Tests: Multimedia codec tests, Status and Open Discussions
◦ 09:15 Grand Peninsula B
38

References
▪ Introducing ART: https://source.android.com/devices/tech/dalvik/art.html
▪ ART compatibility: https://developer.android.com/guide/practices/verifying-apps-art.html
▪ Google I/O 2014, The ART Runtime: https://www.youtube.com/watch?v=EBlTzQsUoOw
▪ VIXL: https://github.com/armvixl/vixl
▪ ARM Juno: http://www.arm.com/products/tools/development-boards/versatile-express/
juno-arm-development-platform.php
▪ AOSP Gerrit: https://android-review.googlesource.com/
▪ Linaro's Android team: https://wiki.linaro.org/Platform/Android
▪ Bug Reports: https://source.android.com/source/report-bugs.html
▪ ARM Connected Community: http://community.arm.com/groups/android-community
▪ ARMv8 Reference Manual: http://infocenter.arm.com/help/index.jsp?topic=/
com.arm.doc.ddi0487a.c/index.html
39

Notices
!
▪ The Android™ robot is reproduced or modified from work created and shared by Google and
used according to terms described in the Creative Commons 3.0 Attribution License.
40

Multi-lib: A 64bit 'primary' boot
42
6 CONFIDENTIAL

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