[lldb-dev] Debugging Python scripts (backtraces, variables) with LLDB

[Alexandru Croitor via lldb-dev]

Hello,

It's been a while since I asked this question on the mailing list ( 2~ years ago).

I am interested in what would be the current best way for implementing interleaved / mixed-mode Python backtraces when debugging the CPython interpreter.

So if I run lldb -- python /path/to/my/script, set a breakpoint somewhere in the C code, and then do "bt", I would see a list of both C stack frames and Python stack frames, and if I do "frame select x" for a python frame, I could inspect the Python locals for instance.

Last time I asked, Jim mentioned using a custom "thread provider". Would this still be the way to go?

I also saw mentions of Java / Go support in the VCS log, but the support was removed due to no maintainers, so I don't know if that would also be the best way of doing it for Python.

I would appreciate, if someone could point me to some relevant code that does something similar to what I'm asking, so I could use it as a base point for exploration.

Many thanks.

> On 8. Jul 2016, at 12:24, Alexandru Croitor <alexandru.croitor at qt.io> wrote:
> 
> Thanks for replying, it's good to know what the status is at least, as well as how it's done in GDB.
> 
>> On 06 Jul 2016, at 20:56, Jim Ingham <jingham at apple.com> wrote:
>> 
>> Nothing of this sort has been done to my knowledge, and I haven't heard of any plans to do so either.
>> 
>> It should certainly be possible, you just need to grub the C stack and recognize the pattern of a Python stack frame in it and where said frame stashes away the arguments & locals, and then re-present it as a Python frame.  The SB API's should make that fairly straight forward.
>> 
>> It looks like the Python work in gdb is based on a generic "frame filter" concept in the gdb Python API's.  That's something Greg and I talked about when working on gdb way back, and has been a future goal for lldb from the start, but it hasn't ever gotten beyond discussion to date.  We already have the notion of a "thread provider" which allows the Mach Kernel plugin to present its activations as threads in lldb.  You could do much the same thing in lldb, where a thread would have the native unwind based stack frame and then pluggable StackFrame provider that would show different representations of the stack.
>> 
>> If anybody is interested in taking on such a project, that would be very cool.
>> 
>> Jim
>> 
>>> On Jul 6, 2016, at 8:48 AM, Alexandru Croitor via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>>> 
>>> Hello,
>>> 
>>> I've searched for information wether it is possible to debug a python script using LLDB, and haven't found anything so far.
>>> 
>>> Specifically I'm interested in an LLDB counterpart to what GDB provides (the two main pages being https://wiki.python.org/moin/DebuggingWithGdb and http://fedoraproject.org/wiki/Features/EasierPythonDebugging ).
>>> 
>>> So python stack traces, python values, etc.
>>> 
>>> I assume this is not implemented, but are there any plans, or is it even feasible to implement?
>>> 
>>> Regards, Alex.
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>> 
>