Fixed stack unwind bugs (works!)

kernel/src/std/unwind/unwinder.rs

@@ -27,7 +27,7 @@ pub struct Unwinder {
     unwind_ctx: UnwindContext<usize, StoreOnHeap>,
     /// The current values of ABI/architecture independent registers. There are
     /// used by DWARF.
-    regs: RegisterSet,
+    pub regs: RegisterSet,
     /// The current CFA address.
     cfa: u64,
     /// Is this the first iteration?
@@ -112,7 +112,10 @@ impl FallibleIterator for Unwinder {
         };
 
         // REVIEWME: Must be a nicer way of doing this.
-        let pc = pc - 1;
+        let Some(pc) = pc.checked_sub(1) else {
+            // REVIEWME: This should handle underflow now.
+            return Ok(None);
+        };
 
         self.regs.set_pc(pc);