Add Command.repeat property for repeated commands (#272)

* Add Command.repeat property for repeated commands

* Support repeated invocations of the "hexdump" command

The output now looks like:

    pwndbg> hexdump $rsp 0x20
    +0000 0x7fffffffdb38  30 18 60 f7  ff 7f 00 00  00 00 00 00  00 00 00 00  │0.`.│....│....│....│
    +0010 0x7fffffffdb48  18 dc ff ff  ff 7f 00 00  00 00 00 00  01 00 00 00  │....│....│....│....│
    +0020 0x7fffffffdb58
    pwndbg>
    +0000 0x7fffffffdb58  d0 ee 41 00  00 00 00 00  00 00 00 00  00 00 00 00  │..A.│....│....│....│
    +0010 0x7fffffffdb68  23 ff 3e ed  14 92 d9 c6  60 05 42 00  00 00 00 00  │#.>.│....│`.B.│....│
    +0020 0x7fffffffdb78
    pwndbg>
    +0000 0x7fffffffdb78  10 dc ff ff  ff 7f 00 00  00 00 00 00  00 00 00 00  │....│....│....│....│
    +0010 0x7fffffffdb88  00 00 00 00  00 00 00 00  23 ff de 19  7c 6d 26 39  │....│....│#...│|m&9│
    +0020 0x7fffffffdb98

pwndbg/commands/__init__.py

@@ -27,6 +27,7 @@ class _Command(gdb.Command):
     """Generic command wrapper"""
     count    = 0
     commands = []
+    history  = {}
 
     def __init__(self, function, inc=True, prefix=False):
         super(_Command, self).__init__(function.__name__, gdb.COMMAND_USER, gdb.COMPLETE_EXPRESSION, prefix=prefix)
@@ -44,11 +45,46 @@ class _Command(gdb.Command):
     def invoke(self, argument, from_tty):
         argv = self.split_args(argument)
         try:
+            self.repeat = self.check_repeated(argument, from_tty)
             return self(*argv)
         except TypeError:
             if debug:
                 print(traceback.format_exc())
             raise
+        finally:
+            self.repeat = False
+
+    def check_repeated(self, argument, from_tty):
+        """Keep a record of all commands which come from the TTY.
+
+        Returns:
+            True if this command was executed by the user just hitting "enter".
+        """
+        # Don't care unless it's interactive use
+        if not from_tty:
+            return False
+
+        lines = gdb.execute('show commands', from_tty=False, to_string=True)
+        lines = lines.splitlines()
+
+        # No history
+        if not lines:
+            return False
+
+        last_line = lines[-1]
+        number, command = last_line.split(None, 1)
+        number = int(number)
+
+        # A new command was entered by the user
+        if number not in _Command.history:
+            _Command.history[number] = command
+            return False
+
+        # Somehow the command is different than we got before?
+        if not command.endswith(argument):
+            return False
+
+        return True
 
     def __call__(self, *args, **kwargs):
         try:

pwndbg/commands/hexdump.py

@@ -23,14 +23,18 @@ pwndbg.config.Parameter('hexdump-bytes',
                          'number of bytes printed by hexdump command')
 
 parser = argparse.ArgumentParser(description='Hexdumps data at the specified address (or at $sp)')
-parser.add_argument('address', nargs='?', default='$sp', 
+parser.add_argument('address', nargs='?', default='$sp',
                     help='Address to dump')
-parser.add_argument('count', nargs='?', default=pwndbg.config.hexdump_bytes, 
+parser.add_argument('count', nargs='?', default=pwndbg.config.hexdump_bytes,
                     help='Number of bytes to dump')
 
 @pwndbg.commands.ArgparsedCommand(parser)
 @pwndbg.commands.OnlyWhenRunning
 def hexdump(address=None, count=pwndbg.config.hexdump_bytes):
+
+    if hexdump.repeat:
+        address = hexdump.last_address
+
     address = int(address)
     address &= pwndbg.arch.ptrmask
     count   = max(int(count), 0)
@@ -41,9 +45,12 @@ def hexdump(address=None, count=pwndbg.config.hexdump_bytes):
 
     try:
         data = pwndbg.memory.read(address, count, partial=True)
+        hexdump.last_address = (address + count)
     except gdb.error as e:
         print(e)
         return
 
     for line in pwndbg.hexdump.hexdump(data, address=address, width=width):
         print(line)
+
+hexdump.last_address = 0