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 "host" code.

The runtime also automatically uses QEMU on non-ARM systems.

Terminology

"Guest" code is the main ARM32 program. It is running inside the runtime.
"Host" code is the native code located in libtrampoline.so. It is running "alongside" the runtime.

Example

There is a simple C example here.

Syscall Vs. 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.
- 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.