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System.loadLibrary(
“Unix, Native Code and
why bother”)
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Library
static
shared
static
dynamic
loading
(.o, .a, ...)
(.so, .dll, .dylib, ...)
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Program A Program B
static libs
(.a)
static libs
(.a)
static linking
compile-time
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Program A Program B
Program A Program B
static libs
(.a)
static libs
(.a)
shared libs
(.so)
static linking
dynamic linking
compile-time
run-time
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Library
static
shared
bookstore
library
Paul Richter
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source
code
compiler
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source
code
compiler
objects
(.o)
.o
.o
.o
.a
archive
.o
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source
code
compiler linker
objects
(.o)
.o
.o
.o
.a
archive
.o
executable
.so
.so
.so
.so
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source
code
compiler linker loader
objects
(.o)
.o
.o
.o
.a
archive
.o
executable
in-memory
image
.so
.so
.so
.so
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Building the objects
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lib1.c
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main.c
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Static Libraries
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Static Libraries
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Shared Libraries: Static Loading
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Shared Libraries: Static Loading
LD_LIBRARY_PATH
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Shared Libraries: Dynamic Loading
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main.c
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main.c
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Android
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Kernel
Display
driver
USB
driver
Camera
driver
WiFi
driver
Power
Mgmt.
Binder IPC
...
Application
Framework
Apps
Home Contacts Dialer Clock Your app
3rd party
app
...
Activity
Manager
Window
Manager
Package
Manager
Location
Manager
View
System
Content
Providers
...
Libraries Android Runtime
(Dalvik/ART) Core Libraries
Dalvik Virtual Machine (DVM)
Surface
Manager
OpenGL
Media
Framework
SQLite
WebKit
SSL
... Bionic
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Kernel
Display
driver
USB
driver
Camera
driver
WiFi
driver
Power
Mgmt.
Binder IPC
...
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Kernel
Display
driver
USB
driver
Camera
driver
WiFi
driver
Power
Mgmt.
Binder IPC
...
Libraries
Surface
Manager
OpenGL
Media
Framework
SQLite
WebKit
SSL
... Bionic
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Android
Bionic
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Bionic
libc libm libdl Linker libstdc++
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Bionic
libc libm libdl Linker libstdc++
License Size Speed
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Bionic
libc libm libdl Linker libstdc++
BSD +
Rewritten code +
Android specific services
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Bionic
libc libm libdl Linker libstdc++
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Bionic
libc libm libdl Linker libstdc++
Completely from scratch!
dlopen()
dlsym()
dlerror()
dlclose()
{
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Bionic
libc libm libdl Linker libstdc++
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Kernel
Display
driver
USB
driver
Camera
driver
WiFi
driver
Power
Mgmt.
Binder IPC
...
Libraries Android Runtime
(Dalvik/ART) Core Libraries
Dalvik Virtual Machine (DVM)
Surface
Manager
OpenGL
Media
Framework
SQLite
WebKit
SSL
... Bionic
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Kernel
Display
driver
USB
driver
Camera
driver
WiFi
driver
Power
Mgmt.
Binder IPC
...
Application
Framework
Apps
Home Contacts Dialer Clock Your app
3rd party
app
...
Activity
Manager
Window
Manager
Package
Manager
Location
Manager
View
System
Content
Providers
...
Libraries Android Runtime
(Dalvik/ART) Core Libraries
Dalvik Virtual Machine (DVM)
Surface
Manager
OpenGL
Media
Framework
SQLite
WebKit
SSL
... Bionic
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Kernel
Audio driver
Application
Framework
Apps
Your app
Media
Player
Libraries Android Runtime
(Dalvik/ART) Core Libraries
Dalvik Virtual Machine (DVM)
Media
Framework
Media
Player
Audio
Flinger
libaudio.so
JNI
dlopen()
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System.loadLibrary
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System.loadLibrary
Runtime.loadLibrary
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Runtime.java
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Runtime.java
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No content
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No content
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Win: main.dll
Linux: libmain.so
Mac: libmain.dylib
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No content
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LD_LIBRARY_PATH
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Runtime.java
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//TODO Runtime::doLoad
Runtime.java
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//TODO Runtime::doLoad
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//TODO Runtime::doLoad
LD_LIBRARY_PATH
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ClassLoader search
(for application libraries)
VM search
(for system libraries)
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Runtime.java
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Workaround for zygote’s LD_LIBRARY_PATH
Runtime.java
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Runtime.cpp
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Native.cpp
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Native.cpp
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Native.cpp
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Kernel
Application
Framework
Apps
Your app
Runtime.java
Libraries Android Runtime
Dalvik Virtual Machine (DVM)
Native.cpp Runtime.cpp
yourlib.so
JNI
dlopen()
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We learned...
● Static vs Shared Libraries
● Dynamic Loading
● Library paths (+ difference on android)
● Android’s internals
○ Bionic
○ Dynamic Loading with Dalvik
○ System.loadLibrary
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Thanks!
@juliozynger
soundcloud.com/jobs