diff --git a/js/public/OldDebugAPI.h b/js/public/OldDebugAPI.h
index 9b604f71078b..9e67bb466ca8 100644
--- a/js/public/OldDebugAPI.h
+++ b/js/public/OldDebugAPI.h
@@ -37,6 +37,69 @@ JS_GetScriptFilename(JSScript *script);
 
 namespace JS {
 
+class FrameDescription
+{
+  public:
+    explicit FrameDescription(const js::FrameIter& iter);
+    FrameDescription(const FrameDescription &rhs);
+    ~FrameDescription();
+
+    unsigned lineno() {
+        if (!linenoComputed_) {
+            lineno_ = JS_PCToLineNumber(nullptr, script_, pc_);
+            linenoComputed_ = true;
+        }
+        return lineno_;
+    }
+
+    const char *filename() const {
+        return filename_;
+    }
+
+    JSFlatString *funDisplayName() const {
+        return funDisplayName_ ? JS_ASSERT_STRING_IS_FLAT(funDisplayName_) : nullptr;
+    }
+
+    // Both these locations should be traced during GC but otherwise not used;
+    // they are implementation details.
+    Heap<JSScript*> &markedLocation1() {
+        return script_;
+    }
+    Heap<JSString*> &markedLocation2() {
+        return funDisplayName_;
+    }
+
+  private:
+    void operator=(const FrameDescription &) MOZ_DELETE;
+
+    // These fields are always initialized:
+    Heap<JSString*> funDisplayName_;
+    const char *filename_;
+
+    // One of script_ xor scriptSource_ is non-null.
+    Heap<JSScript*> script_;
+    js::ScriptSource *scriptSource_;
+
+    // For script_-having frames, lineno_ is lazily computed as an optimization.
+    bool linenoComputed_;
+    unsigned lineno_;
+
+    // pc_ is non-null iff script_ is non-null. If !pc_, linenoComputed_ = true.
+    jsbytecode *pc_;
+};
+
+struct StackDescription
+{
+    unsigned nframes;
+    FrameDescription *frames;
+};
+
+extern JS_PUBLIC_API(StackDescription *)
+DescribeStack(JSContext *cx, unsigned maxFrames);
+
+extern JS_PUBLIC_API(void)
+FreeStackDescription(JSContext *cx, StackDescription *desc);
+
 extern JS_PUBLIC_API(char *)
 FormatStackDump(JSContext *cx, char *buf, bool showArgs, bool showLocals, bool showThisProps);
 
diff --git a/js/src/vm/OldDebugAPI.cpp b/js/src/vm/OldDebugAPI.cpp
index 234f4a6a0de4..260b1bb77335 100644
--- a/js/src/vm/OldDebugAPI.cpp
+++ b/js/src/vm/OldDebugAPI.cpp
@@ -895,6 +895,85 @@ js_CallContextDebugHandler(JSContext *cx)
     }
 }
 
+/*
+ * A contructor that crates a FrameDescription from a ScriptFrameIter, to avoid
+ * constructing a FrameDescription on the stack just to append it to a vector.
+ * FrameDescription contains Heap<T> fields that should not live on the stack.
+ */
+JS::FrameDescription::FrameDescription(const FrameIter& iter)
+  : scriptSource_(nullptr),
+    linenoComputed_(false),
+    pc_(nullptr)
+{
+    if (iter.isNonEvalFunctionFrame())
+        funDisplayName_ = iter.functionDisplayAtom();
+
+    if (iter.hasScript()) {
+        script_ = iter.script();
+        pc_ = iter.pc();
+        filename_ = script_->filename();
+    } else {
+        scriptSource_ = iter.scriptSource();
+        scriptSource_->incref();
+        filename_ = scriptSource_->filename();
+        lineno_ = iter.computeLine();
+        linenoComputed_ = true;
+    }
+}
+
+JS::FrameDescription::FrameDescription(const FrameDescription &rhs)
+  : funDisplayName_(rhs.funDisplayName_),
+    filename_(rhs.filename_),
+    script_(rhs.script_),
+    scriptSource_(rhs.scriptSource_),
+    linenoComputed_(rhs.linenoComputed_),
+    lineno_(rhs.lineno_),
+    pc_(rhs.pc_)
+{
+    if (scriptSource_)
+        scriptSource_->incref();
+}
+
+
+JS::FrameDescription::~FrameDescription()
+{
+    if (scriptSource_)
+        scriptSource_->decref();
+}
+
+JS_PUBLIC_API(JS::StackDescription *)
+JS::DescribeStack(JSContext *cx, unsigned maxFrames)
+{
+    Vector<FrameDescription> frames(cx);
+
+    NonBuiltinFrameIter i(cx, FrameIter::ALL_CONTEXTS,
+                          FrameIter::GO_THROUGH_SAVED,
+                          cx->compartment()->principals);
+    for ( ; !i.done(); ++i) {
+        if (!frames.append(i))
+            return nullptr;
+        if (frames.length() == maxFrames)
+            break;
+    }
+
+    JS::StackDescription *desc = js_new<JS::StackDescription>();
+    if (!desc)
+        return nullptr;
+
+    desc->nframes = frames.length();
+    desc->frames = frames.extractRawBuffer();
+    return desc;
+}
+
+JS_PUBLIC_API(void)
+JS::FreeStackDescription(JSContext *cx, JS::StackDescription *desc)
+{
+    for (size_t i = 0; i < desc->nframes; ++i)
+        desc->frames[i].~FrameDescription();
+    js_free(desc->frames);
+    js_delete(desc);
+}
+
 namespace {
 
 class AutoPropertyDescArray