src/third_party/pyelftools/elftools/construct/debug.py

   1 """
   2 Debugging utilities for constructs
   3 """
   4 from __future__ import print_function
   5 import sys
   6 import traceback
   7 import pdb
   8 import inspect
   9 from .core import Construct, Subconstruct
  10 from .lib import HexString, Container, ListContainer
  11
  12
  13 class Probe(Construct):
  14     """
  15     A probe: dumps the context, stack frames, and stream content to the screen
  16     to aid the debugging process.
  17     See also Debugger.
  18
  19     Parameters:
  20     * name - the display name
  21     * show_stream - whether or not to show stream contents. default is True.
  22       the stream must be seekable.
  23     * show_context - whether or not to show the context. default is True.
  24     * show_stack - whether or not to show the upper stack frames. default
  25       is True.
  26     * stream_lookahead - the number of bytes to dump when show_stack is set.
  27       default is 100.
  28
  29     Example:
  30     Struct("foo",
  31         UBInt8("a"),
  32         Probe("between a and b"),
  33         UBInt8("b"),
  34     )
  35     """
  36     __slots__ = [
  37         "printname", "show_stream", "show_context", "show_stack",
  38         "stream_lookahead"
  39     ]
  40     counter = 0
  41
  42     def __init__(self, name = None, show_stream = True,
  43                  show_context = True, show_stack = True,
  44                  stream_lookahead = 100):
  45         Construct.__init__(self, None)
  46         if name is None:
  47             Probe.counter += 1
  48             name = "<unnamed %d>" % (Probe.counter,)
  49         self.printname = name
  50         self.show_stream = show_stream
  51         self.show_context = show_context
  52         self.show_stack = show_stack
  53         self.stream_lookahead = stream_lookahead
  54     def __repr__(self):
  55         return "%s(%r)" % (self.__class__.__name__, self.printname)
  56     def _parse(self, stream, context):
  57         self.printout(stream, context)
  58     def _build(self, obj, stream, context):
  59         self.printout(stream, context)
  60     def _sizeof(self, context):
  61         return 0
  62
  63     def printout(self, stream, context):
  64         obj = Container()
  65         if self.show_stream:
  66             obj.stream_position = stream.tell()
  67             follows = stream.read(self.stream_lookahead)
  68             if not follows:
  69                 obj.following_stream_data = "EOF reached"
  70             else:
  71                 stream.seek(-len(follows), 1)
  72                 obj.following_stream_data = HexString(follows)
  73             print
  74
  75         if self.show_context:
  76             obj.context = context
  77
  78         if self.show_stack:
  79             obj.stack = ListContainer()
  80             frames = [s[0] for s in inspect.stack()][1:-1]
  81             frames.reverse()
  82             for f in frames:
  83                 a = Container()
  84                 a.__update__(f.f_locals)
  85                 obj.stack.append(a)
  86
  87         print("=" * 80)
  88         print("Probe", self.printname)
  89         print(obj)
  90         print("=" * 80)
  91
  92 class Debugger(Subconstruct):
  93     """
  94     A pdb-based debugger. When an exception occurs in the subcon, a debugger
  95     will appear and allow you to debug the error (and even fix on-the-fly).
  96
  97     Parameters:
  98     * subcon - the subcon to debug
  99
 100     Example:
 101     Debugger(
 102         Enum(UBInt8("foo"),
 103             a = 1,
 104             b = 2,
 105             c = 3
 106         )
 107     )
 108     """
 109     __slots__ = ["retval"]
 110     def _parse(self, stream, context):
 111         try:
 112             return self.subcon._parse(stream, context)
 113         except Exception:
 114             self.retval = NotImplemented
 115             self.handle_exc("(you can set the value of 'self.retval', "
 116                 "which will be returned)")
 117             if self.retval is NotImplemented:
 118                 raise
 119             else:
 120                 return self.retval
 121     def _build(self, obj, stream, context):
 122         try:
 123             self.subcon._build(obj, stream, context)
 124         except Exception:
 125             self.handle_exc()
 126     def handle_exc(self, msg = None):
 127         print("=" * 80)
 128         print("Debugging exception of %s:" % (self.subcon,))
 129         print("".join(traceback.format_exception(*sys.exc_info())[1:]))
 130         if msg:
 131             print(msg)
 132         pdb.post_mortem(sys.exc_info()[2])
 133         print("=" * 80)
 134