watchpoints
rr
watchpoints | rr | |
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7 | 102 | |
462 | 8,665 | |
- | 1.1% | |
1.5 | 9.6 | |
about 1 year ago | 3 days ago | |
Python | C++ | |
Apache License 2.0 | GNU General Public License v3.0 or later |
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watchpoints
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What a good debugger can do
It's sad that Python does not really support some of these debugging methods.
E.g. you cannot really watch variable changes. There are some workarounds, like writing a custom __setattr__ or __setattribute__ in case of an object, or checking all STORE_* operations. https://youtrack.jetbrains.com/issue/PY-30387 https://github.com/gaogaotiantian/watchpoints
Reverse debugging is also sth I would like to have, and there are a few projects to support this, but it's not really well supported in standard CPython. https://foss.heptapod.net/pypy/revdb https://pytrace.com/
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Is there a tool to run code and AFTER that look at execution step by step.
There is also the watchpoints module to track changes to variables, but I don't think you can use the two of them together since they both use the same underlying callback in Python.
- Watchpoints - an easy-to-use, intuitive variable/object monitor tool for Python that behaves similar to watchpoints in gdb.
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Show HN: Watchpoints, an easy to use watchpoints equivalent library for Python
It uses Python's built-in inspect module to get the caller frame. https://github.com/gaogaotiantian/watchpoints/blob/68bc13716...
It then uses sys.settrace (which is intended as an interface for debuggers) to step through the code and check whether the variable has been changed. Documentation on sys.settrace: https://docs.python.org/3/library/sys.html#sys.settrace
Python exposes most of its guts as part of the standard library, making clever hacks like this possible.
rr
- rr: Lightweight Recording and Deterministic Debugging
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Hermit is a hermetic and reproducible sandbox for running programs
I think this tool must share a lot techniques and use cases with rr. I wonder how it compares in various aspects.
https://rr-project.org/
rr "sells" as a "reversible debugger", but it obviously needs the determinism for its record and replay to work, and AFAIK it employs similar techniques regarding system call interception and serializing on a single CPU. The reversible debugger aspect is built on periodic snapshotting on top of it and replaying from those snapshots, AFAIK. They package it in a gdb compatible interface.
Hermit also lists record/replay as a motivation, although it doesn't list reversible debugging in general.
- Rr: Lightweight Recording and Deterministic Debugging
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Deep Bug
Interesting. Perhaps you can inspect the disassembly of the function in question when using Graal and HotSpot. It is likely related to that.
Another debugging technique we use for heisenbugs is to see if `rr` [1] can reproduce it. If it can then that's great as it allows you to go back in time to debug what may have caused the bug. But `rr` is often not great for concurrency bugs since it emulates a single-core machine. Though debugging a VM is generally a nightmare. What we desperately need is a debugger that can debug both the VM and the language running on top of it. Usually it's one or the other.
> In general I’d argue you haven’t fixed a bug unless you understand why it happened and why your fix worked, which makes this frustrating, since every indication is that the bug exists within proprietary code that is out of my reach.
Were you using Oracle GraalVM? GraalVM community edition is open source, so maybe it's worth checking if it is reproducible in that.
[1]: https://github.com/rr-debugger/rr
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So you think you want to write a deterministic hypervisor?
https://rr-project.org/ had the same problem. They use the retired conditional branch counter instead of instruction counter, and then instruction steeping until at the correct address.
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Is Something Bugging You?
That'll work great for your Distributed QSort Incorporated startup, where the only product is a sorting algorithm.
Formal software verification is very useful. But what can be usefully formalized is rather limited, and what can be formalized correctly in practice is even more limited. That means you need to restrict your scope to something sane and useful. As a result, in the real world running thousands of tests is practically useful. (Well, it depends on what those tests are; it's easy to write 1000s of tests that either test the same thing, or only test the things that will pass and not the things that would fail.) They are especially useful if running in a mode where the unexpected happens often, as it sounds like this system can do. (It's reminiscent of rr's chaos mode -- https://rr-project.org/ linking to https://robert.ocallahan.org/2016/02/introducing-rr-chaos-mo... )
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When "letting it crash" is not enough
The approach of check-pointing computation such that it is resumable and restartable sounds similar to a time-traveling debugger, like rr or WinDbg:
https://rr-project.org/
https://learn.microsoft.com/windows-hardware/drivers/debugge...
- When I got started I debugged using printf() today I debug with print()
- Rr: Record and Replay Debugger – Reverse Debugger
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OpenBSD KDE Plasma Desktop
https://github.com/rr-debugger/rr?tab=readme-ov-file#system-...