Add from_raw and into_raw methods to RestoreState.

[reitermarkus]

I have a use case where I need to re-expose _critical_section_1_0_acquire/_critical_section_1_0_release to a shared library that is dynamically loaded.

Specifically, using the elf_loader crate, I need to do this:

unsafe fn _critical_section_1_0_acquire() -> RawRestoreState {
  unsafe { critical_section::acquire().into_raw() }
}

unsafe fn _critical_section_1_0_release(restore_state: RawRestoreState) {
  unsafe { critical_section::release(RestoreState::from_raw(restore_state)) };
}


 SyntheticModule::new(
  "__host",
  [
    SyntheticSymbol::function(
      "_critical_section_1_0_acquire",
      _critical_section_1_0_acquire as *const (),
    ),
    SyntheticSymbol::function(
      "_critical_section_1_0_release",
      _critical_section_1_0_release as *const (),
    ),
  ],
)

[jannic]

In your use case, doesn't this cause an infinite recursion?

unsafe fn _critical_section_1_0_acquire() -> RawRestoreState {
  unsafe { critical_section::acquire().into_raw() }
}

critical_section::acquire() is implemented as:

pub unsafe fn acquire() -> RestoreState {
    extern "Rust" {
        fn _critical_section_1_0_acquire() -> RawRestoreState;
    }

    #[allow(clippy::unit_arg)]
    RestoreState(_critical_section_1_0_acquire())
}

Ignoring that I don't understand your use case, the PR itself looks sound.

[reitermarkus]

In your use case, doesn't this cause an infinite recursion?

No, the unsafe fn _critical_section_1_0_acquire isn't marked no_mangle, and could actually have any name. Only the string given to SyntheticSymbol::function is used for the lookup table exposed to the shared library.