rt: Account for the size of stack_canary in create_stack

Author: brson

src/rt/rust_stack.h

@@ -13,13 +13,19 @@ struct stk_seg {
     uint8_t data[];
 };
 
+// A value that goes at the end of the stack and must not be touched
+const uint8_t stack_canary[] = {0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD};
+
 void
 add_stack_canary(stk_seg *stk);
 
 template <class T>
 stk_seg *
 create_stack(T allocer, size_t sz) {
-  size_t total_sz = sizeof(stk_seg) + sz;
+  size_t total_sz = sizeof(stk_seg) + sz + sizeof(stack_canary);
   stk_seg *stk = (stk_seg *)allocer->malloc(total_sz, "stack");
   memset(stk, 0, sizeof(stk_seg));
   add_stack_canary(stk);