break a c function in python, usage: source break.py, see: help pycbreak in gdb.

break.py

#! /usr/bin/env python 
try:
    import gdb 
except:
    print("gdb only")
    exit(0)

def version_error():
    print("python 2.7.3 only")
    exit(0)

import sys

for m, n in zip((2, 7, 3), sys.version_info):
    if m != n:
        version_error()

parse_and_eval = gdb.parse_and_eval

class CFunctionBreak(gdb.Breakpoint):
    def __init__(self, name): 
        super(CFunctionBreak, self).__init__( 
                spec = "PyCFunction_Call",
                type = gdb.WP_READ,
                wp_class = gdb.BP_READ_WATCHPOINT
                ) 
        self.functionname = name 
        self.flags = {
                0x0000: "METH_OLDARGS",
                0x0001: "METH_VARARGS",
                0x0002: "METH_KEYWORDS",
                0x0004: "METH_NOARGS",
                0x0008: "METH_O"
                }
        self.query = "((PyCFunctionObject *)func)->m_ml"


    def stop(self):
        function = parse_and_eval(self.query) 
        info = ("name: ", str(function['ml_name']),
                ", function: ", str(function['ml_meth']), 
                ", doc: ", str(function['ml_doc']),
                ", flags: ", self.translate_flags(int(function['ml_flags'])),
                "\n") 

        if self.functionname == str(function['ml_name']):
            print("".join(info)) 
        return False


    def translate_flags(self, functionflag):
        flaglist = []
        for flag in self.flags.keys():
            if functionflag & flag:
                flaglist.append(self.flags[flag]) 
        return "|".join(flaglist)   


class CFunctionCmd(gdb.Command):
    '''pycbreak {add, rm, enable, disable} function'''
    def __init__(self):
        super(CFunctionCmd, self).__init__(
                name="pycbreak",
                command_class = gdb.COMMAND_BREAKPOINTS,
                completer_class = gdb.COMPLETE_SYMBOL, 
                )
        self.breaklist = {}

    def invoke(self, argument, from_tty):
        args = gdb.string_to_argv(argument) 
        if len(args) < 2:
            raise gdb.GdbError("require more arguments, see: help pycbreak")
        if args[0] == 'add': 
            self.breaklist[args[1]] = CFunctionBreak(args[1])      
        elif args[0] == 'rm':
            try:
                self.breaklist[args[1]].delete() 
            except:    
                raise gdb.GdbError("There is no breakpoint: %s" % args[1]) 
        elif args[0] == "enable":
            try:
                self.breaklist[args[1]].enabled = True
            except: 
                raise gdb.GdbError("There is no breakpoint: %s" % args[1]) 
        elif args[0] == "disable":
            try:
                self.breaklist[args[1]].enabled = False
            except: 
                raise gdb.GdbError("There is no breakpoint: %s" % args[1]) 
        else:
            raise gdb.GdbError("unknown command %s" % args[0])

CFunctionCmd()