I am using pykd to debug an application which loads a dll only when some condition is met. How do I set a breakpoint in the dll which has not loaded yet in pykd such that my handler gets the callback? Currently my code looks something like this

class ExceptionHandler(pykd.eventHandler):
    def __init__(self):

    def onException(self, exceptionInfo):
        return pykd.eventResult.NoChange

    def onBreakpoint(self, id):
        return pykd.eventResult.NoChange

    def onThreadStart(self):
        return pykd.eventResult.NoChange

    def onThreadStop(self):
        return pykd.eventResult.NoChange

    def onLoadModule(self, base, name):
        print "onLoadModule " + name
        # sys.stdout.flush()
        # if name == "test_module":
        #     # test_module = pykd.module("test_module")
        #     # test_module.reload()
        #     # pykd.setBp(test_module.offset('test_function'), breakCount)
        #     # print pykd.dbgCommand("bl")
        #     print pykd.dbgCommand('bp test_module!test_function "r;gc"')
        #     # print pykd.dbgCommand("bl")
        #     # print "Breakpoint Set %x" % (test_module.offset('test_function'))
        #     print "Breakpoint Set"
        return pykd.eventResult.NoChange

    def onUnloadModule(self, base, name):
        return pykd.eventResult.NoChange

pykd.handler = ExceptionHandler()
pykd.startProcess("testmydelayedload.exe %s\\%s" % (os.getcwd(), sys.argv[1].strip()))
alloc_module = pykd.module("ntdll")
b0 = pykd.setBp(alloc_module.offset('RtlAllocateHeap')+0xe6, breakCount)
b1 = pykd.setBp(alloc_module.offset('RtlFreeHeap'), breakCount)
pykd.loadExt("C:\\Program Files\\Windows Kits\\10\\Debuggers\\x86\\winext\\ext.dll")

I have tried to manually set the breakpoint using pykd.dbgCommand but the callback is not triggered in that case. I tried to change the return value of onLoadModule to other than pykd.eventResult.NoChange while setting a bp. What am I missing?

  • Change bp to bu Dec 28 '17 at 8:43
  • @LievenKeersmaekers setting a bp with pykd.dbgCommand won't trigger the callback as I said. I want something which uses the pykd's api.
    – sudhackar
    Dec 28 '17 at 9:38
  • 1
    I just figured it out, the variable storing the bp should be global otherwise it won't work.
    – sudhackar
    Dec 28 '17 at 9:55

I just figured it out, the variable storing the bp should be global otherwise it won't work. It should be alive out of the class's context.

def onLoadModule(self, base, name):
        global test_function, test_module
        print "onLoadModule " + name
        if name == "jscript":
            test_module = pykd.module("jscript")
            test_function = pykd.setBp(test_module.offset('test_function'), breakCount)
            print "Breakpoint Set %x" % (test_module.offset('test_function'))
        return pykd.eventResult.NoChange

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