Introduction

Users view

Android users cannot access the rich multimedia content available in Apple iTunes.

iOS users cannot easily access Flash-based Web content.

Developers view

Have to develop apps for multiple platforms.

Companies view

Hard to promote new platforms because of lack huge app base of existing platforms.

Virtual Machine

Virtual machines (VMs) are useful to run apps intended for one platform on a different platform.

Problems:

Mobile devices are more resource constrained.

Mobile devices are tightly integrated with standardised interfaces such as GPU. 

Cider

An OS compatibility architecture that can simultaneously run apps written and compiled for different mobile ecosystems.

Implement a prototype to run iOS apps on Android.

Concepts

• domestic binary: developed for a given device's OS
• foreign apps: apps for other platforms
• persona: an execution mode assigned to each thread

Overview of Android and iOS

Android & iOS architecture

Android

• Linux kernel
• Apps compiled to Dalvik bytecode, runs in a seperate Dalvik VM instance

iOS

• XNU kernel, a hybrid combination of BSD and Mach
• Apps compiled to native binaries in an extended Mach-O format

Architecture

System Integration

• Emulate the FS
• User-level services: launchd, configd, notifyd
• A proxy service: CiderPress

Difference

• different binary format
• different syscall interfaces
• extensive use of OS services not available on Linux, such as Mach IPC

Techniques

• Kernel ABI
• Duct Tape
• Diplomatic Functions

Kernel ABI

• build a Mach-O binary loader
• a translation layer for async signal delivery

Duct Tape

• Reimplement is time-consuming and error-prone, different kernels have completely different APIs and data structures
• Duct Tape: a compile-time code adaptation layer that supports cross-kernel compilation
• Translate foreign kernel API such as synchronization, memory allocation, process control and list management.

Duct Tape (cont.)

• Three zones: domestic, foreign, duct tape
• Use duct tape to build three subsystems:
  • pthread
  • Mach IPC
  • Apple's I/O kit

Diplomatic Functions

• ioctl passes driver-specific request code and a pointer to memory
• behaviour is driver-specific
• cannot simply implement kernel-level support for foreign, closed libraries which directly manipulate hardware through proprietary interfaces

Diplomatic Functions (cont.)

1. save arguments on stack
2. set_persona syscall invoked from foreign thread
3. restore arguments from stack
4. run the domestic function
5. save return value on stack
6. set_persona syscall to change to foreign persona
7. continue to run foreign code

iOS subsystems on Android

Devices

• cross-compile Apple I/O Kit framework
• expose device to I/O kit using a small hook in the Linux device_add function

Input

• Get input from CiderPress and send the Mach IPC to the foreign thread

Graphics

• Replace Graphics call into Native OpenGL call

Evaluation

Setup

• Nexus 7
  • 1.3 GHz quad-core NVIDIA Tegra 3 CPU, 1GB RAM, 7" 1280x800
• iPad mini
  • 1 GHz dual-core A5 CPU, 512MB RAM, 7.9" 1024x768
• lmbench
• PassMark

Get iOS Apps

• Only accessible on App Store
• re-package to .ipa file to install on Android

Micro Benchmark

• CPU operations
• signal handling
• process creation
• IO

lower is better

Application Benchmark

higher is better