ChatDBG 0.0.5

ChatDBG.

ChatDBG

by Emery Berger

ChatDBG is an experimental debugger (for Python and (new) native code) that integrates large language models 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:

python3 -m pip install chatdbg

Usage (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.

For example:

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:
(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))

Usage (lldb)

(Currently only tested on Mac.)

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

xcrun python3 -m pip install ChatDBG

Now run

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.

You can now run native code (compiled with -g for debugging symbols) with lldb; when it crashes, ask why.

(lldb) run
Process 91113 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 91113 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x100056200)
    frame #0: 0x0000000100002f68 a.out`foo(n=8) at test.cpp:7:22
   4     int x[] = { 1, 2, 3, 4, 5 };
   5     
   6     void foo(int n) {
-> 7       cout << "TEST " << x[n * 10000] << endl;
   8     }
   9     
   10    int main()
Target 0: (a.out) stopped.

Now you can ask why:

(lldb) why
The root cause of this error is an out-of-bounds memory access. The
program is trying to access an element of the `x` array that is beyond
its allocated size. Specifically, when `n` is large enough (greater
than or equal to 1), the expression `n * 10000` causes the program to
access memory beyond the end of the `x` array.

To fix this error, we can check that the index is within bounds before
accessing the array. One way to do this is to compare `n * 10000` with
the size of the array before accessing the element:

    ```
    void foo(int n) {
      if (n * 10000 < sizeof(x)/sizeof(int)) {
        cout << "TEST " << x[n * 10000] << endl;
      } else {
        cout << "ERROR: index out of bounds" << endl;
      }
    }
    ```

This code first computes `sizeof(x)/sizeof(int)`, which gives the
number of elements in the `x` array. It then checks whether `n *
10000` is less than this size before accessing the `x` array. If `n *
10000` is greater than or equal to the size of the array, it prints an
error message instead of accessing the `x` array.