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DEVELOPING.md

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Random developer notes

Feel free to update the list below!

  • If you want to play with pwndbg functions under GDB, you can always use GDB's pi which launches python interpreter or just py <some python line>.

  • If there is possibility, don't use gdb.execute as this requires us to parse the string and so on; there are some cases in which there is no other choice. Most of the time we try to wrap GDB's API to our own/easier API.

  • We have our own pwndbg.config.Parameter (which extends gdb.Parameter) - all of our parameters can be seen using config or theme commands. If we want to do something when user changes config/theme - we can do it defining a function and decorating it with pwndbg.config.Trigger.

  • The dashboard/display/context we are displaying is done by pwndbg/commands/context.py which is invoked through GDB's prompt hook (which we defined in pwndbg/prompt.py as prompt_hook_on_stop).

  • All commands should be defined in pwndbg/commands - most of them lie in seperate files but some files contains many of them (e.g. commands corresponding to windbg debugger - in windbg.py or some misc commands in misc.py). We would also want to make all of them to use ArgparsedCommand (instead of Command or ParsedCommand decorators).

  • We change a bit GDB settings - this can be seen in pwndbg/__init__.py - there are also imports for all pwndbg submodules

  • We have a wrapper for GDB's events in pwndbg/events.py - thx to that we can e.g. invoke something based upon some event

  • We have a caching mechanism ("memoization") which we use through Python's decorators - those are defined in pwndbg/memoize.py - just check its usages

  • To block a function before the first prompt was displayed use the pwndbg.decorators.only_after_first_prompt decorator.

  • Memory accesses should be done through pwndbg/memory.py functions

  • Process properties can be retrieved thx to pwndbg/proc.py - e.g. using pwndbg.proc.pid will give us current process pid

  • We have an inthook to make it easier to work with Python 2 and gdb.Value objects - see the docstring in pwndbg/inthook.py . Specifically, it makes it so that you can call int() on a gdb.Value instance and get what you want.

  • We have a wrapper for handling exceptions that are thrown by commands - defined in pwndbg/exception.py - current approach seems to work fine - by using set exception-verbose on - we get a stacktrace. If we want to debug stuff we can always do set exception-debugger on.

  • Some of pwndbg's functionality - e.g. memory fetching - require us to have an instance of proper gdb.Type - the problem with that is that there is no way to define our own types - we have to ask gdb if it detected particular type in this particular binary (that sucks). We do it in pwndbg/typeinfo.py and it works most of the time. The known bug with that is that it might not work properly for Golang binaries compiled with debugging symbols.

  • We would like to add proper tests for pwndbg - see tests framework PR if you want to help on that.

Testing

Our tests are written using pytest. It uses some magic so that Python's assert can be used for asserting things in tests and it injects dependencies which are called fixtures, into test functions.

The fixtures should be defined in tests/conftest.py. If you need help with writing tests, feel free to reach out on gitub issues/pr or on our irc channel on freenode.