tree dbd5d29d2bfa2df2b69e6aeb6cfa956ae60dd7e8
parent 72a967363995cd0e805edfb35876aad9063a6d36
author Johnathan Van Why <jrvanwhy@google.com> 1607057289 -0800
committer Johnathan Van Why <jrvanwhy@google.com> 1607057482 -0800

Rework the use of `usize` versus `u32` in RawSyscalls.

I previously used `usize` for every value, because `usize` is register-sized on all platforms. However, I no longer think that is the correct thing to do. Having the values be register-sized only matters for `libtock_runtime::TockSyscalls`; it does not matter for `libtock_unittest::FakeSyscalls`. For the fake system calls, it is better to pass u32 where possible to minimize the number of invalid value representable in the API.

This rework follows a simple rule: values that can potentially contain pointers have type `usize`; all other register values have type `u32`. This extends to the function signature of `subscribe` callbacks: unsafe extern fn(u32, u32, u32, usize).