ChatDBG 0.0.12

ChatDBG.

ChatDBG

by Emery Berger

ChatDBG is an experimental debugger for Python and native C/C++ code that integrates large language models into a standard debugger (pdb, lldb, and gdb) to help debug your code. With ChatDBG, you can ask your debugger "why" your program failed, and it will provide a suggested fix.

As far as we are aware, ChatDBG is the first debugger to automatically perform root cause analysis and to provide suggested fixes. This is an alpha release; we greatly welcome feedback and suggestions!

Installation

Install ChatDBG using pip (you need to do this whether you are debugging Python, C, or C++ code):

python3 -m pip install chatdbg

If you are using ChatDBG to debug Python programs, you are done. If you want to use ChatDBG to debug native code with gdb or lldb, follow the installation instructions below.

Installing as an lldb extension

lldb installation instructions

Install ChatDBG into the lldb debugger by running the following command:

Linux

python3 -m pip install ChatDBG
python3 -c 'import chatdbg; print(f"command script import {chatdbg.__path__[0]}/chatdbg_lldb.py")' >> ~/.lldbinit

Mac

xcrun python3 -m pip install ChatDBG
xcrun python3 -c 'import chatdbg; print(f"command script import {chatdbg.__path__[0]}/chatdbg_lldb.py")' >> ~/.lldbinit

This will install ChatDBG as an LLVM extension.

Installing as a gdb extension

gdb installation instructions

Install ChatDBG into the gdb debugger by running the following command:

python3 -m pip install ChatDBG
python3 -c 'import chatdbg; print(f"source {chatdbg.__path__[0]}/chatdbg_gdb.py")' >> ~/.gdbinit

This will install ChatDBG as a GDB extension.

Usage

Debugging Python

To use ChatDBG to debug Python programs, simply run your Python script with the -m flag:

python3 -m chatdbg -c continue yourscript.py

or just

chatdbg -c continue yourscript.py

ChatDBG is an extension of the standard Python debugger pdb. Like pdb, when your script encounters an uncaught exception, ChatDBG will enter post mortem debugging mode.

Unlike other debuggers, you can then use the why command to ask ChatDBG why your program failed and get a suggested fix.

ChatDBG example with Python

Traceback (most recent call last):
  File "yourscript.py", line 9, in <module>
    print(tryme(100))
  File "yourscript.py", line 4, in tryme
    if x / i > 2:
ZeroDivisionError: division by zero
Uncaught exception. Entering post mortem debugging
Running 'cont' or 'step' will restart the program
> yourscript.py(4)tryme()
-> if x / i > 2:
(ChatDBG Pdb) why

ChatDBG will then provide a helpful explanation of why your program failed and a suggested fix:

The root cause of the error is that the code is attempting to
divide by zero in the line "if x / i > 2". As i ranges from 0 to 99,
it will eventually reach the value of 0, causing a ZeroDivisionError.

A possible fix for this would be to add a check for i being equal to
zero before performing the division. This could be done by adding an
additional conditional statement, such as "if i == 0: continue", to
skip over the iteration when i is zero. The updated code would look
like this:

def tryme(x):
    count = 0
    for i in range(100):
        if i == 0:
            continue
        if x / i > 2:
            count += 1
    return count

if __name__ == '__main__':
    print(tryme(100))

Debugging native code (lldb / gdb)

To use ChatDBG with lldb or gdb, just run native code (compiled with -g for debugging symbols) with your choice of debugger; when it crashes, ask why. This also works for post mortem debugging (when you load a core with the -c option).

Example of using why in lldb

(ChatDBG lldb) run
Process 85494 launched: '/Users/emery/git/ChatDBG/test/a.out' (arm64)
TEST 1
TEST -422761288
TEST 0
TEST 0
TEST 0
TEST 0
TEST 0
TEST 0
Process 85494 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x100056200)
    frame #0: 0x0000000100002f64 a.out`foo(n=8, b=1) at test.cpp:7:22
   4     int x[] = { 1, 2, 3, 4, 5 };
   5     
   6     void foo(int n, float b) {
-> 7       cout << "TEST " << x[n * 10000] << endl;
   8     }
   9     
   10    int main()
Target 0: (a.out) stopped.

Now you can ask why:

(ChatDBG lldb) why
The root cause of this error is accessing an index of the array `x`
that is out of bounds. In `foo()`, the index is calculated as `n *
10000`, which can be much larger than the size of the array `x` (which
is only 5 elements). In the given trace, the program is trying to
access the memory address `0x100056200`, which is outside of the range
of allocated memory for the array `x`.

To fix this error, we need to ensure that the index is within the
bounds of the array. One way to do this is to check the value of `n`
before calculating the index, and ensure that it is less than the size
of the array divided by the size of the element. For example, we can
modify `foo()` as follows:

    ```
    void foo(int n, float b) {
      if (n < 0 || n >= sizeof(x)/sizeof(x[0])) {
        cout << "ERROR: Invalid index" << endl;
        return;
      }
      cout << "TEST " << x[n] << endl;
    }
    ```

This code checks if `n` is within the valid range, and prints an error
message if it is not. If `n` is within the range, the function prints
the value of the element at index `n` of `x`. With this modification,
the program will avoid accessing memory outside the bounds of the
array, and will print the expected output for valid indices.