diff -r 000000000000 -r 6474c204b198 js/src/gdb/mozilla/JSString.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/gdb/mozilla/JSString.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,55 @@
+# Pretty-printers for SpiderMonkey strings.
+
+import gdb
+import mozilla.prettyprinters
+from mozilla.prettyprinters import pretty_printer, ptr_pretty_printer
+
+# Forget any printers from previous loads of this module.
+mozilla.prettyprinters.clear_module_printers(__name__)
+
+# Cache information about the JSString type for this objfile.
+class JSStringTypeCache(object):
+    def __init__(self, cache):
+        dummy = gdb.Value(0).cast(cache.JSString_ptr_t)
+        self.LENGTH_SHIFT = dummy['LENGTH_SHIFT']
+        self.FLAGS_MASK   = dummy['FLAGS_MASK']
+        self.ROPE_FLAGS   = dummy['ROPE_FLAGS']
+        self.ATOM_BIT     = dummy['ATOM_BIT']
+
+class Common(mozilla.prettyprinters.Pointer):
+    def __init__(self, value, cache):
+        super(Common, self).__init__(value, cache)
+        if not cache.mod_JSString:
+            cache.mod_JSString = JSStringTypeCache(cache)
+        self.stc = cache.mod_JSString
+
+@ptr_pretty_printer("JSString")
+class JSStringPtr(Common):
+    def display_hint(self):
+        return "string"
+
+    def jschars(self):
+        d = self.value['d']
+        lengthAndFlags = d['lengthAndFlags']
+        length = lengthAndFlags >> self.stc.LENGTH_SHIFT
+        is_rope = (lengthAndFlags & self.stc.FLAGS_MASK) == self.stc.ROPE_FLAGS
+        if is_rope:
+            for c in JSStringPtr(d['u1']['left'], self.cache).jschars():
+                yield c
+            for c in JSStringPtr(d['s']['u2']['right'], self.cache).jschars():
+                yield c
+        else:
+            chars = d['u1']['chars']
+            for i in xrange(length):
+                yield chars[i]
+
+    def to_string(self):
+        s = u''
+        for c in self.jschars():
+            s += unichr(c)
+        return s
+
+@ptr_pretty_printer("JSAtom")
+class JSAtomPtr(Common):
+    def to_string(self):
+        return self.value.cast(self.cache.JSString_ptr_t)