Add function pointer test

Author: maximecb

vm/src/vm.rs

@@ -1994,6 +1994,24 @@ mod tests
         eval_i64(" push FN; call_fp 0; ret; FN: push_i8 33; ret;", 33);
     }
 
+    #[test]
+    fn test_patch_fp()
+    {
+        // Patch a function's code address into the data segment at runtime,
+        // then load it back and call it via call_fp
+        eval_i64(
+            ".data; FPTR: .u64 0; .code; push FPTR; push FN; store_u64; push FPTR; load_u64; call_fp 0; ret; FN: push_i8 33; ret;",
+            33
+        );
+
+        // Same, but the code address is assembled into the data segment
+        // statically using the .addr64 directive
+        eval_i64(
+            ".data; FPTR: .addr64 FN; .code; push FPTR; load_u64; call_fp 0; ret; FN: push_i8 33; ret;",
+            33
+        );
+    }
+
     #[test]
     fn test_syscalls()
     {