kernel: use MachineRegister for register contents

These data types in Tock have no semantic meaning other than they are
exactly the size of a register. To express that in code we use the
MachineRegister type.

kernel/src/grant.rs

@@ -139,6 +139,7 @@ use crate::processbuffer::{ReadOnlyProcessBuffer, ReadWriteProcessBuffer};
 use crate::processbuffer::{ReadOnlyProcessBufferRef, ReadWriteProcessBufferRef};
 use crate::upcall::{Upcall, UpcallError, UpcallId};
 use crate::utilities::capability_ptr::CapabilityPtr;
+use crate::utilities::machine_register::MachineRegister;
 use crate::ErrorCode;
 
 /// Tracks how many upcalls a grant instance supports automatically.
@@ -708,7 +709,7 @@ impl<'a> GrantKernelData<'a> {
 #[repr(C)]
 #[derive(Default)]
 struct SavedUpcall {
-    appdata: CapabilityPtr,
+    appdata: MachineRegister,
     fn_ptr: CapabilityPtr,
 }
 

kernel/src/process.rs

@@ -20,6 +20,7 @@ use crate::storage_permissions;
 use crate::syscall::{self, Syscall, SyscallReturn};
 use crate::upcall::UpcallId;
 use crate::utilities::capability_ptr::CapabilityPtr;
+use crate::utilities::machine_register::MachineRegister;
 use tock_tbf::types::CommandPermissions;
 
 // Export all process related types via `kernel::process::`.
@@ -1084,7 +1085,7 @@ pub struct FunctionCall {
     /// The third argument to the function.
     pub argument2: usize,
     /// The userdata provided by the process via `subscribe`
-    pub argument3: CapabilityPtr,
+    pub argument3: MachineRegister,
     /// The PC of the function to execute.
     pub pc: CapabilityPtr,
 }

kernel/src/syscall.rs

@@ -71,6 +71,7 @@ use core::fmt::Write;
 use crate::errorcode::ErrorCode;
 use crate::process;
 use crate::utilities::capability_ptr::CapabilityPtr;
+use crate::utilities::machine_register::MachineRegister;
 
 pub use crate::syscall_driver::{CommandReturn, SyscallDriver};
 
@@ -158,7 +159,7 @@ pub enum Syscall {
         /// Upcall pointer to the upcall function.
         upcall_ptr: CapabilityPtr,
         /// Userspace application data.
-        appdata: CapabilityPtr,
+        appdata: MachineRegister,
     },
 
     /// Structure representing an invocation of the Command system call class.
@@ -241,9 +242,9 @@ impl Syscall {
     pub fn from_register_arguments(
         syscall_number: u8,
         r0: usize,
-        r1: CapabilityPtr,
-        r2: CapabilityPtr,
-        r3: CapabilityPtr,
+        r1: MachineRegister,
+        r2: MachineRegister,
+        r3: MachineRegister,
     ) -> Option<Syscall> {
         match SyscallClass::try_from(syscall_number) {
             Ok(SyscallClass::Yield) => Some(Syscall::Yield {

kernel/src/upcall.rs

@@ -10,6 +10,7 @@ use crate::process;
 use crate::process::ProcessId;
 use crate::syscall::SyscallReturn;
 use crate::utilities::capability_ptr::CapabilityPtr;
+use crate::utilities::machine_register::MachineRegister;
 use crate::ErrorCode;
 
 /// Type to uniquely identify an upcall subscription across all drivers.
@@ -82,7 +83,7 @@ pub(crate) struct Upcall {
     pub(crate) upcall_id: UpcallId,
 
     /// The application data passed by the app when `subscribe()` was called.
-    pub(crate) appdata: CapabilityPtr,
+    pub(crate) appdata: MachineRegister,
 
     /// A pointer to the first instruction of the function in the app that
     /// corresponds to this upcall.
@@ -97,7 +98,7 @@ impl Upcall {
     pub(crate) fn new(
         process_id: ProcessId,
         upcall_id: UpcallId,
-        appdata: CapabilityPtr,
+        appdata: MachineRegister,
         fn_ptr: CapabilityPtr,
     ) -> Upcall {
         Upcall {