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JITIN S HARMA
D E C O D I N G A N D R O I D
R U N T I M E
@js_2892
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What is Android
- Some Hardware
- Some Linux
- Some C++
- Some Java
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No content
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Boot-Up
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Boot-Up
Hardware Start-Up
02 Software Start-Up
ZYGOTE
03
01
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Boot-Up
init.rc
AndroidRuntime.cpp Zygote main()
Transition to
Java base execution
Linux Kernel Start
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Zygote
- Zygote Process acts a base process from which all processes are forked for subsequent
applications.
- This allows Android to run in a Multi-Process environment where all processes run independent of
each other.
- All resources preloaded by Zygote are accessed by subsequent applications through shared
memory.
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Zygote
System Server
Load core libraries
and resources
Starts Activity Manager
Notification Manager, Bluetooth Service,
Package Manager, Sensor Service…
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Zygote
System Server
Load core libraries
and resources
Starts Activity Manager
Notification Manager, Bluetooth Service,
Package Manager, Sensor Service…
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Zygote
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Phone is ON
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Building APK
java/kt files .class files .dex
javac
kotlinc
dx
APK
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Installing Application
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Manifest Parsing
- All data from AndroidManifest.xml is read and is written to data/system/packages.xml
- This file acts as a global source for all packages and is used by PackageManager API
- This happens only once either when device is booted or an application is being installed.
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Manifest Parsing
- Identifies various elements within your application
- At the same time manifest performs checks which can cause installation errors if elements are not
defined properly.
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Code Compilation and Other Stuff
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Code Compilation and Other Stuff
Dalvik ART
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dex and Dalvik Era
Android 1.0 - 4.4
(2008-2014)
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.dex
Dalvik VM
A register based VM optimised for
memory constrained device
.dex -> Dalvik Executable
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Stack Machines
value1
value2
value3
value4
value1 value2
operation
pop pop
value5
value3
value4
push
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Stack Machines Register Machines
value1
value2
value3
value4
value1 value2
operation
pop pop
value5
value3
value4
push
addr1 value1
operation
addr2 value2
addr3 value3
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Stack Machines Register Machines
value1
value2
value3
value4
value1 value2
operation
pop pop
value5
value3
value4
push
addr1 value1
operation
addr2 value2
addr3 value3
ARM Optimized
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dex
- Uses 16 bit instruction format.
- Bytecode tends to be larger due to register based architecture for storing addresses
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dex
- Uses 16 bit instruction format.
- Bytecode tends to be larger due to register based architecture for storing addresses
‣header
‣string_ids
‣type_ids
‣proto_ids
‣field_ids
‣method_ids
‣class_defs
‣call_site_ids
‣method_handles
‣data
‣link_data
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dex
- Uses 16 bit instruction format.
- Bytecode tends to be larger due to register based architecture for storing addresses
‣header
‣string_ids
‣type_ids
‣proto_ids
‣field_ids
‣method_ids
‣class_defs
‣call_site_ids
‣method_handles
‣data
‣link_data
Contains verification
signatures
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dex
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dex
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public class Data {
int id;
String name = "";
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
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public int getId() {
return id;
}
.METHOD getId : int
.MODIFIERS public
.REGISTERS 2
.CODE
iget v0, v1 field@8046
return v0
.METHOD setName : void
.PARAM java.lang.String
.MODIFIERS public
.REGISTERS 2
.CODE
iput-object v1, v0 field@8047
return-void
public void setName(String name) {
this.name = name;
}
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private fun forEachTest(): Int {
var sum = 0
(0..50).forEach {
sum += it
}
return sum
}
private fun forTest(): Int {
var sum = 0
for (i in 0 until 50) {
sum += i
}
return sum
}
VS
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private fun forTest(): Int {
var sum = 0
for (i in 0 until 50) {
sum += i
}
return sum
}
.METHOD forTest : int
.MODIFIERS private final
.REGISTERS 4
.CODE
const/4 v0, #0
const/4 v1, #0
const/16 v2, #50
if-ge v1, v2, 6
add-int/2addr v1, v0
add-int/lit8 v1, v1, #1
goto -7
return v0
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private fun forEachTest(): Int {
var sum = 0
(0..50).forEach {
sum += it
}
return sum
}
.METHOD forEachTest : int
.MODIFIERS private final
.REGISTERS 8
.CODE
const/4 v0, #0
new-instance v1, type@2439
const/4 v2, #0
const/16 v3, #50
invoke-direct {v1, v2, v3}, meth@20280
check-cast v1, type@1851
move v3, v2
invoke-interface {v1}, meth@15176
move-result-object v4
invoke-interface {v4}, meth@15640
move-result v5
if-eqz v5, 13
move-object v5, v4
check-cast v5, type@2142
invoke-virtual {v5}, meth@18564
move-result v5
move v6, v5
add-int/2addr v6, v0
goto -16
return v0
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A.class
B.class
Z.class
classes.dex
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A.class
B.class
Z.class
classes.dex
- Reduction in bytecode size during conversion.
- Duplicate constants from class files are converted to a single one.
- Each method needs have a reference which is limited by dex instruction format of 16 bits,
hence total method references which a single dex file can hold is 65,536 (2^16)
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dex++
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Multidexing
classes.dex
java/kt
classes2.dex classesN.dex
…
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Installation
data/dalvik-cache
data/data/com.example.myapplication
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dexopt
- Verification and Optimization of contents of .dex file
- Result differ from device to device.
- Starts a small version of VM to optimize dex files.
- Contents of system/framework/ can be used to optimize dex files outside Android OS.
- Code is optimized for runtime not memory.
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classes.dex
My Application
Zygote
Process
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Multidex.install(this)
classes.dex classes2.dex classes3.dex ….
System Application
classesN.dex
Inject values
into ClassLoader
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Multidex.install(this)
classes.dex classes2.dex classes3.dex ….
System Application
Must have Application class
classesN.dex
Inject values
into ClassLoader
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Multidex.install(this)
classes.dex classes2.dex classes3.dex ….
System Application
Must have Application class
Library dependencies
classesN.dex
Inject values
into ClassLoader
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Multidex.install(this)
classes.dex classes2.dex classes3.dex ….
System Application
Must have Application class
Library dependencies
(multiDexKeepFile)
classesN.dex
Inject values
into ClassLoader
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DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(dexFile.getAbsolutePath(),
getCodeCacheDir().getAbsolutePath(), null, context.getClassLoader());
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DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(dexFile.getAbsolutePath(),
getCodeCacheDir().getAbsolutePath(), null, context.getClassLoader());
Network
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DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(dexFile.getAbsolutePath(),
getCodeCacheDir().getAbsolutePath(), null, context.getClassLoader());
Class> dynamicClass = dexClassLoader.loadClass("com.example.myapplication.runtime");
Method dynamicMethod = dynamicClass.getDeclaredMethod("executeDataLoad", Integer.class, Integer.class);
Integer value = (Integer) dynamicMethod.invoke(dynamicClass.newInstance(), 1, 2);
Network
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DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(dexFile.getAbsolutePath(),
getCodeCacheDir().getAbsolutePath(), null, context.getClassLoader());
Class> dynamicClass = dexClassLoader.loadClass("com.example.myapplication.runtime");
Method dynamicMethod = dynamicClass.getDeclaredMethod("executeDataLoad", Integer.class, Integer.class);
Integer value = (Integer) dynamicMethod.invoke(dynamicClass.newInstance(), 1, 2);
Network
public Integer executeDataLoad(Integer value1, Integer value2) {
//
return result;
}
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DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(dexFile.getAbsolutePath(),
getCodeCacheDir().getAbsolutePath(), null, context.getClassLoader());
Class> dynamicClass = dexClassLoader.loadClass("com.example.myapplication.runtime");
Method dynamicMethod = dynamicClass.getDeclaredMethod("executeDataLoad", Integer.class, Integer.class);
Integer value = (Integer) dynamicMethod.invoke(dynamicClass.newInstance(), 1, 2);
Network
public Integer executeDataLoad(Integer value1, Integer value2) {
//
return result;
}
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JIT
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JIT
private void handleIntent() {
...
public RequestQueue getRequestQueue() {
if (requestQueue == null) {
requestQueue = Volley.newRequestQueue(this);
}
return requestQueue;
}
for (String s : networkRequestMap.keySet()) {
if (BuildConfig.DEBUG) {
//
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Tracing and Profiling
Low Memory
Optimized
(100K/200K)
Faster results
Google I/O 2010
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Shortcomings of Dalvik
Time
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ART (Android Runtime)
Android 5.0 - present
(2014-present)
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Embracing the GBs…
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Embracing the GBs…
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Revamped GC
- ART keeps track of application going in non-UI state.
- Seperate types of GC for low memory and non-low memory devices.
- GC pauses reduced from 2 to 1.
- Larger objects like bitmap have seperate heap for faster allocation.
- Young Objects are moved to stack for faster reclamation of memory.
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Dalvik
GC GC GC
1MB 3MB 5MB
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ART
GC GC GC
1MB 3MB 5MB
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ART
GC GC GC
1MB 3MB 5MB
9MB
Heap
Compaction
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AOT Compilation
classes.dex
classes2.dex
classesN.dex
.oat
dex2oat
- AOT works on principle of compile once and then run.
- Compilation takes significant time and memory since whole bytecode is converted to machine code
at installation.
- AOT compilers do not benefit from profile guided compilation which JIT compilers have instead use
a restrictive approach to do compilation.
Android
Runtime
VM
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.oat
header
instruction set
dex file count
dex2oat cmd line
code
data/app/
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DEX CODE:
0x0000: 5210 e10f | iget v0, v1, I com.example.myapplication.Data.id // field@4065
0x0002: 0f00 | return v0
public int getId() {
return id;
}
Java
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CODE:
(code_offset=0x00d6a3fc size_offset=0x00d6a3f8 size=68)...
0x00d6a3fc: 4885842400E0FFFF testq rax, [rsp + -8192]
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00d6a404: 4883EC18 subq rsp, 24
0x00d6a408: 48893C24 movq [rsp], rdi
0x00d6a40c: 89742428 mov [rsp + 40], esi
0x00d6a410: 6566833C250000000000 cmpw gs:[0], 0 ; state_and_flags
0x00d6a41a: 0F8516000000 jnz/ne +22 (0x00d6a436)
0x00d6a420: 8B442428 mov eax, [rsp + 40]
0x00d6a424: 8500 test eax, [rax]
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00d6a426: 8B480C mov ecx, [rax + 12]
suspend point dex PC: 0x0000
GC map objects: v1 ([sp + #40])
0x00d6a429: 894C2410 mov [rsp + 16], ecx
0x00d6a42d: 8B442410 mov eax, [rsp + 16]
0x00d6a431: 4883C418 addq rsp, 24
0x00d6a435: C3 ret
0x00d6a436: 65FF142538040000 call gs:[1080] ; pTestSuspend
……..
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Problems with AOT compilation
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JIT/AOT Hybrid
‣System boot after OS update will no longer optimise the app, a job solely performed by JIT.
‣dex2oat is still used for .oat creation but it uses profile data generated by JIT to do so.
‣Code may be executed by directed .dex interpretation or JIT cache or AOT compiled.
‣At any time JIT compiled data will be more efficient because of availability of better environment
data than AOT compiled code, and the same is preferred if both are present.
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DEX CODE:
0x0000: 5210 e10f | iget v0, v1, I com.example.myapplication.Data.id // field@4065
0x0002: 0f00 | return v0
public int getId() {
return id;
}
Java
CODE:
(code_offset=0x00000000 size_offset=0x00aea110 size=0)
NO CODE!
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Third party frameworks
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Future
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Future
A.I
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Thanks
@js_2892