[Zion] Add a way to unwind the stack and recover from user-space faults.

zion/common/stack_unwind.cpp

@@ -0,0 +1,20 @@
+#include "common/stack_unwind.h"
+
+#include "debug/debug.h"
+
+namespace {
+
+bool IsValid(uint64_t* rbp) { return rbp && *rbp != kStackBaseSentinel; }
+
+}  // namespace
+
+void StackUnwind(uint64_t rbp) {
+  dbgln("-- Begin Stack --");
+  uint64_t* rbp_ptr = reinterpret_cast<uint64_t*>(rbp);
+  while (IsValid(rbp_ptr)) {
+    uint64_t rip = *(rbp_ptr + 1);
+    dbgln("RIP: {x}", rip);
+    rbp_ptr = reinterpret_cast<uint64_t*>(*rbp_ptr);
+  }
+  dbgln("-- End Stack --");
+}

zion/common/stack_unwind.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdint.h>
+
+const uint64_t kStackBaseSentinel = 0xABBACDCD'12345678;
+
+void StackUnwind(uint64_t rbp);