luc-tielen / debugger-hs

Write your GDB scripts in Haskell!

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)?