Index: object.c
===================================================================
--- object.c	(revision 63540)
+++ object.c	(working copy)
@@ -895,7 +895,24 @@
     return obj;
 }
 
+/*
+ *  call-seq:
+ *    obj.show_stack -> obj
+ *
+ *  Outputs the current stack to stderr (similar to when there's an internal error).
+ *
+ *  This method is only expected to work on C Ruby.
+ */
 
+void rb_vmdebug_stack_show_raw_current(void); /* sloppy, should move to header file */
+static VALUE
+rb_obj_show_stack(VALUE obj)
+{
+    rb_vmdebug_stack_show_raw_current();
+    return obj;
+}
+
+
 /*
  * Document-method: inherited
  *
@@ -4098,6 +4115,7 @@
     rb_define_method(rb_mKernel, "kind_of?", rb_obj_is_kind_of, 1);
     rb_define_method(rb_mKernel, "is_a?", rb_obj_is_kind_of, 1);
     rb_define_method(rb_mKernel, "tap", rb_obj_tap, 0);
+    rb_define_method(rb_mKernel, "show_stack", rb_obj_show_stack, 0);
 
     rb_define_global_function("sprintf", rb_f_sprintf, -1); /* in sprintf.c */
     rb_define_global_function("format", rb_f_sprintf, -1);  /* in sprintf.c */
Index: vm.c
===================================================================
--- vm.c	(revision 63540)
+++ vm.c	(working copy)
@@ -453,6 +453,23 @@
     return hash;
 }
 
+/*
+ *  call-seq:
+ *    RubyVM.show_stack -> nil
+ *
+ *  Outputs the current stack to stderr (similar to when there's an internal error).
+ *
+ *  This method is only expected to work on C Ruby.
+ */
+
+void rb_vmdebug_stack_show_raw_current(void); /* sloppy, should move to header file */
+static VALUE
+vm_show_stack(int argc, VALUE *argv, VALUE self)
+{
+    rb_vmdebug_stack_show_raw_current();
+    return Qnil;
+}
+
 /* control stack frame */
 
 static void
@@ -2840,6 +2857,8 @@
     rb_undef_alloc_func(rb_cRubyVM);
     rb_undef_method(CLASS_OF(rb_cRubyVM), "new");
     rb_define_singleton_method(rb_cRubyVM, "stat", vm_stat, -1);
+    
+    rb_define_singleton_method(rb_cRubyVM, "show_stack", vm_show_stack, 0);
 
     /* FrozenCore (hidden) */
     fcore = rb_class_new(rb_cBasicObject);
Index: vm_dump.c
===================================================================
--- vm_dump.c	(revision 63540)
+++ vm_dump.c	(working copy)
@@ -137,6 +137,74 @@
     fprintf(stderr, "\n");
 }
 
+// new function, to show stack during execution
+// modified from rb_vmdebug_stack_dump_raw
+void rb_vmdebug_stack_show_raw_current(void)
+{
+    const rb_execution_context_t *ec = GET_EC();
+    const rb_control_frame_t *cfp = (rb_control_frame_t*) (ec->vm_stack + ec->vm_stack_size) - 1;
+    const rb_control_frame_t *cfp_end = ec->cfp;
+    VALUE *sp = cfp_end->sp, *ep;
+    VALUE *p, *st, *t;
+
+
+    fprintf(stderr, "-- Control Frames "
+	    "-----------------------------------------------\n");
+    while (cfp > cfp_end) {   // skip show_stack method itself
+	control_frame_dump(ec, cfp);
+	cfp--;
+    }
+    fprintf(stderr, "\n");
+
+    fprintf(stderr, "-- Internal Stack ------------\n");
+    for (p = sp-4, st = ec->vm_stack, cfp = cfp_end+1; p-3 >= ec->vm_stack; p--) {
+        ep = (VALUE *)cfp->ep;
+	fprintf(stderr, "%04ld (%p): %016"PRIxVALUE, (long)(p - st), p, *p);
+
+	t = (VALUE *)*p;
+	if (ec->vm_stack <= t && t < sp) {
+	    fprintf(stderr, " (= %ld)", (long)((VALUE *)t - ec->vm_stack));
+	}
+        else if (p == ep) {
+            fprintf(stderr, " (flags) <- Environment Pointer");
+            fprintf(stderr, " (%ld)", ((rb_control_frame_t *)(ec->vm_stack + ec->vm_stack_size) - cfp));
+        }
+        else if (p == ep-1) {
+            fprintf(stderr, " (specval)");
+        }
+        else if (p == ep-2) {
+            fprintf(stderr, " (me_cref)");
+            cfp++;
+        }
+        else {
+            VALUE klass = rb_obj_class(*p);
+            VALUE val = rb_mod_name(klass);
+            if (!NIL_P(val)) {
+                fprintf(stderr, " %s", RSTRING_PTR(val));
+                if (FIXNUM_P(*p))
+                    fprintf(stderr, ":    %d", FIX2INT(*p));
+                else if (RB_TYPE_P(*p, T_FLOAT))
+	            fprintf(stderr, ":      %g", RFLOAT_VALUE(*p));
+                else if (klass == rb_cFalseClass)
+                    fprintf(stderr, ": false");
+                else if (klass == rb_cTrueClass)
+                    fprintf(stderr, ":  true");
+                else if (klass == rb_cNilClass)
+                    fprintf(stderr, ":   nil");
+                else if (klass == rb_cSymbol)
+                    fprintf(stderr, ":     :%s", RSTRING_PTR(rb_sym_to_s(*p)));
+                else if (klass == rb_cString && RSTRING_LEN(*p)<= 20)
+                    fprintf(stderr, ":     '%s'", RSTRING_PTR(*p));
+            }
+        }
+        if (p == (VALUE *)cfp->sp)
+            fprintf(stderr, " <- Stack Pointer (%ld)", ((rb_control_frame_t *)(ec->vm_stack + ec->vm_stack_size) - cfp));
+
+	fprintf(stderr, "\n");
+    }
+    fprintf(stderr, "\n");
+}
+
 void
 rb_vmdebug_stack_dump_raw(const rb_execution_context_t *ec, const rb_control_frame_t *cfp)
 {