debugger-hs

A Haskell library for creating/metaprogramming GDB scripts.

Why?

GDB has Python integration, and while it is powerful, it has some problems:

Python code can end up interleaved in the GDB code, making it complicated really quickly.
Accessing variables between GDB and Python can get complicated too.

Besides that, also some things in GDB don't work as expected, such as commands that behave differently inside a user-defined command ("define"), which can lead to unexpected and buggy results.

If we use Haskell however, we get the following nice things:

A typesystem,
Can use full Haskell ecosystem for metaprogramming,
The generated output will be 100% GDB script only:
- easier to use afterwards,
- inspectable,
- no need for this package once the script has been generated.

How?

Partial evaluation/staged programming. You write a Haskell file that makes use of the DSL this package provides, and render it to a script that can be passed in to GDB like you would normally.

Here's an example of how you can use this library to generate a GDB script:

#!/usr/bin/env cabal
{- cabal:
build-depends: base, debugger-hs
-}

{-# LANGUAGE OverloadedStrings #-}
module Main where

import qualified Debugger.Builder as D
import qualified Debugger.Render as D
import qualified Debugger.Statement as D

-- First we build up a Haskell value that represents our GDB scripts.
script :: D.Builder ()
script = do
  bp <- D.break (D.Function "main")
  D.command bp $ do
    D.print "42"
    D.continue

-- And then we can render the GDB script to stdout:
main :: IO ()
main = do
  let gdbScript = D.runBuilder script
  D.renderIO gdbScript "./script.gdb"

If you save this file as "GDB.hs" and run it using cabal run GDB.hs, this will render the following GDB script and write it to "./script.gdb":

break main
set $var0 = $bpnum
command $var0
  print "42"
  continue
end

Now you can use the generated script with GDB as follows:

# Replace $PROGRAM with the program you want to debug.
$ gdb $PROGRAM -ex "source ./script.gdb"

TODO

Create core AST datatype
Create builder monad for easily constructing GDB scripts using Haskell do-syntax.
Write function for compiling AST -> GDB script
Add helper functions for easily adding breakpoints (using tools like grep)
Extend core AST datatype to support more functionality
Add LLDB support also?
DSL (to support GDB and LLDB at same time)?

mariszo/debugger-hs

debugger-hs

Why?

How?

TODO