Add support in dbg.debug_obj for printing the obj body.

src/lib/dbg.rs

@@ -9,7 +9,7 @@ native "rust" mod rustrt {
   fn debug_opaque[T](&T x);
   fn debug_box[T](@T x);
   fn debug_tag[T](&T x);
-  fn debug_obj[T](&T x, uint nmethods);
+  fn debug_obj[T](&T x, uint nmethods, uint nbytes);
   fn debug_fn[T](&T x);
 }
 
@@ -33,8 +33,17 @@ fn debug_tag[T](&T x) {
   rustrt.debug_tag[T](x);
 }
 
-fn debug_obj[T](&T x, uint nmethods) {
+/**
-  rustrt.debug_obj[T](x, nmethods);
+ * `nmethods` is the number of methods we expect the object to have.  The
+ * runtime will print this many words of the obj vtbl).
+ *
+ * `nbytes` is the number of bytes of body data we expect the object to have.
+ * The runtime will print this many bytes of the obj body.  You probably want
+ * this to at least be 4u, since an implicit captured tydesc pointer sits in
+ * the front of any obj's data tuple.x
+ */
+fn debug_obj[T](&T x, uint nmethods, uint nbytes) {
+  rustrt.debug_obj[T](x, nmethods, nbytes);
 }
 
 fn debug_fn[T](&T x) {

src/rt/rust_builtin.cpp

@@ -308,7 +308,8 @@ struct rust_obj {
 };
 
 extern "C" CDECL void
-debug_obj(rust_task *task, type_desc *t, rust_obj *obj, size_t nmethods)
+debug_obj(rust_task *task, type_desc *t, rust_obj *obj,
+          size_t nmethods, size_t nbytes)
 {
     task->log(rust_log::STDLIB,
               "debug_obj with %" PRIdPTR " methods", nmethods);
@@ -318,6 +319,11 @@ debug_obj(rust_task *task, type_desc *t, rust_obj *obj, size_t nmethods)
 
     for (uintptr_t *p = obj->vtbl; p < obj->vtbl + nmethods; ++p)
         task->log(rust_log::STDLIB, "  vtbl word: 0x%" PRIxPTR, *p);
+
+    for (uintptr_t i = 0; i < nbytes; ++i)
+        task->log(rust_log::STDLIB,
+                  "  body byte %" PRIdPTR ": 0x%" PRIxPTR,
+                  i, obj->body->data[i]);
 }
 
 struct rust_fn {