Add a gdb script to show backtrace with Mach-O symbols.

.gdbinit

@@ -0,0 +1,11 @@
+python sys.path.insert(0, '.')
+python import gdb_maloader
+
+define mreload
+  python reload(gdb_maloader)
+end
+
+define mbt
+  mreload
+  python gdb_maloader.bt()
+end

gdb_maloader.py

@@ -0,0 +1,29 @@
+import gdb
+import os
+import re
+import sys
+
+def bt():
+    # Find the newest frame.
+    frame = gdb.selected_frame()
+    while True:
+        next = frame.newer()
+        if not next:
+            break
+        frame = next
+
+    pipe = os.popen('c++filt', 'w')
+
+    i = 0
+    while frame:
+        s = gdb.execute('p dumpExportedSymbol((void*)0x%x)' % frame.pc(),
+                        to_string=True)
+        m = re.match(r'.*"(.*)"$', s)
+        if m:
+            pipe.write("%s\n" % m.group(1))
+        else:
+            pipe.write("0x%x\n" % frame.pc())
+        frame = frame.older()
+        i += 1
+
+    pipe.close()