Reborn Runtime

This is a simple program allowing ARM32 code to easily call "native" code.

By running an ARM32 program inside this runtime, it gains the ability to call raw_trampoline. This function copies its arguments and passes them to the trampoline function inside libmedia-layer-trampoline.so.

The runtime also automatically uses QEMU on x86_64 systems.

Terminology

• "Guest" code is the main ARM32 program.
• "Host" code is the native code located in libmedia-layer-trampoline.so.

Example

There is a simple C example here. It sends a given string to the host, which returns the string's length multiplied by two.

Early Returning

raw_trampoline supports returning before the host code has finished executing. This can be enabled by passing true to allow_early_return. However, this is only supported in certain circumstances, can cause race-conditions, and prevents the guest code from receiving the host's return value.

Syscall Versus Pipe Trampolines

The runtime supports two methods of passing data between the guest and host.

• System Call
  • Data is passed through a custom system-call added to QEMU.
  • Only supported on x86_64.
• Pipes
  • Data is passed through standard UNIX pipes.
  • Supports early-returning.
  • Can be forced using an environmental variable.

Licensing

The runtime itself is licensed with GPLv2 to comply with QEMU's license. However, the raw_trampoline function and associated headers are licensed with the Unlicense as they do not directly link to the runtime.