# signal

This code allows `rt` to run on Linux and other POSIX systems for simulation
and testing. Asynchronous syscalls and ticks are implemented as signals.

Context switches happen in user space with a single thread, switching stacks
and saving and restoring the non-volatile state in assembly. The asynchronous
syscall handler relies on the signal handler entry and return to save and
restore volatile state. Synchronous syscalls are implemented as an assembly
function, and so saving and restoring volatile state is not needed, because the
caller expects it to be clobbered.

Currently `x86_64` and `aarch64` are supported. Linux and macOS are supported,
but other POSIX-like OSes might work.