diff -r 000000000000 -r 6474c204b198 js/src/gdb/lib-for-tests/prolog.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/gdb/lib-for-tests/prolog.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,75 @@
+import gdb
+import os
+import re
+import sys
+import traceback
+
+# testlibdir is set on the GDB command line, via --eval-command python testlibdir=...
+sys.path[0:0] = [testlibdir]
+
+# Run the C++ fragment named |fragment|, stopping on entry to |function|
+# ('breakpoint', by default) and then select the calling frame.
+def run_fragment(fragment, function='breakpoint'):
+    # Arrange to stop at a reasonable place in the test program.
+    bp = gdb.Breakpoint(function);
+    try:
+        gdb.execute("run %s" % (fragment,))
+        # Check that we did indeed stop by hitting the breakpoint we set.
+        assert bp.hit_count == 1
+    finally:
+        bp.delete()
+    gdb.execute('frame 1')
+
+# Assert that |actual| is equal to |expected|; if not, complain in a helpful way.
+def assert_eq(actual, expected):
+    if actual != expected:
+        raise AssertionError, """Unexpected result:
+expected: %r
+actual:   %r""" % (expected, actual)
+
+# Assert that |value|'s pretty-printed form is |form|. If |value| is a
+# string, then evaluate it with gdb.parse_and_eval to produce a value.
+def assert_pretty(value, form):
+    if isinstance(value, str):
+        value = gdb.parse_and_eval(value)
+    assert_eq(str(value), form)
+
+# Check that the list of registered pretty-printers includes one named
+# |printer|, with a subprinter named |subprinter|.
+def assert_subprinter_registered(printer, subprinter):
+    # Match a line containing |printer| followed by a colon, and then a
+    # series of more-indented lines containing |subprinter|.
+
+    names = { 'printer': re.escape(printer), 'subprinter': re.escape(subprinter) }
+    pat = r'^( +)%(printer)s *\n(\1 +.*\n)*\1 +%(subprinter)s *\n' % names
+    output = gdb.execute('info pretty-printer', to_string=True)
+    if not re.search(pat, output, re.MULTILINE):
+        raise AssertionError, ("assert_subprinter_registered failed to find pretty-printer:\n"
+                               "  %s:%s\n"
+                               "'info pretty-printer' says:\n"
+                               "%s" % (printer, subprinter, output))
+
+# Request full stack traces for Python errors.
+gdb.execute('set python print-stack full')
+
+# Tell GDB not to ask the user about the things we tell it to do.
+gdb.execute('set confirm off', False)
+
+# Some print settings that make testing easier.
+gdb.execute('set print static-members off')
+gdb.execute('set print address off')
+gdb.execute('set print pretty off')
+gdb.execute('set width 0')
+
+try:
+    # testscript is set on the GDB command line, via:
+    # --eval-command python testscript=...
+    execfile(testscript)
+except AssertionError as err:
+    sys.stderr.write('\nAssertion traceback:\n')
+    (t, v, tb) = sys.exc_info()
+    traceback.print_tb(tb)
+    sys.stderr.write('\nTest assertion failed:\n')
+    sys.stderr.write(str(err))
+    sys.exit(1)
+