feat(kernel): console cap gates DebugPutchar, no uart fast path; spawn start arg in a0; delegate returns slot

crates/kernel/src/board.rs

@@ -20,6 +20,13 @@ pub struct BoardDevice {
     pub irq: Option<IrqId>,
 }
 
+/// Where `grant_boot_authority` put init's machine-wide capabilities.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct BootCaps {
+    pub system_control: CapSlot,
+    pub console: CapSlot,
+}
+
 /// Where `grant_boot_authority` put one device's capabilities in init.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct BoardCaps {
@@ -46,13 +53,14 @@ impl<P: Platform> Kernel<P> {
     }
 
     /// Gives `init` (with Delegate) caps to every device region and IRQ, then SystemControl.
-    /// Writes each device's slots into `placed` in order; returns the SystemControl slot.
+    /// Writes each device's slots into `placed` in order; returns the SystemControl
+    /// and Console slots.
     pub fn grant_boot_authority(
         &mut self,
         init: ProcessId,
         devices: &[BoardDevice],
         placed: &mut [Option<BoardCaps>],
-    ) -> Result<CapSlot, KernelError> {
+    ) -> Result<BootCaps, KernelError> {
         let delegate = PermissionSet::empty().with(Permission::Delegate);
         let control = delegate.with(Permission::Execute);
         let mmio = delegate.with(Permission::Read).with(Permission::Write);
@@ -70,7 +78,10 @@ impl<P: Platform> Kernel<P> {
                 *slot = Some(BoardCaps { region, irq });
             }
         }
-        self.grant_cap(init, Resource::SystemControl, control)
+        Ok(BootCaps {
+            system_control: self.grant_cap(init, Resource::SystemControl, control)?,
+            console: self.grant_cap(init, Resource::Console, delegate.with(Permission::Write))?,
+        })
     }
 
     /// The device region that starts at `base`.