rr VS CodeLLDB

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.

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

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.

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... )

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...

https://github.com/rr-debugger/rr?tab=readme-ov-file#system-...

Ok, so apparently here they are called 'data formatters' instead of pretty printers or debug helpers... https://github.com/vadimcn/codelldb/wiki/Custom-Data-Formatters

For debugging lldb supports python scripts: https://github.com/vadimcn/codelldb/wiki/Data-visualization

I use VS Code on Linux to debug Zig. Haven't tried the others you mentioned, but it just emits standard DWARF symbols, so I'm guessing if you can debug C/C++ you could probably also do Zig with minimal changes? I just use the lldb VS code plugin[0], which works out of the box for me with no issues.

https://github.com/vadimcn/codelldb

It's pretty bad, unfortunately. As you discovered, using the gnu toolchain works better with code-lldb (see more info here), but it still isn't great. CLion is a little better, but costs money and lacks support in other ways compared to VSCode.

- I tried to install codelldb: https://github.com/vadimcn/vscode-lldb without success.

Are you on Windows or Linux? On Windows I've had nothing but trouble getting code-lldb to display debug info for any sort of nontrivial data structure due to this issue, which means I need to switch to x86_64-pc-windows-gnu, but then that breaks other upstream crates that use cc to compile C++ code.

I've been using vscode-lldb with VS Code on macos, and I've been very happy with the experience so far.

Check this: https://github.com/vadimcn/vscode-lldb/wiki/Breakpoints-are-not-getting-hit

yeah since they updated the rust compiler for windows to use a different style of debugger symbols and since they changed that in CodeLLDB the variables output have not been the same. Though i believe the owner has been trying to fix it. But any issues you do have report them on the codeLLDB git https://github.com/vadimcn/vscode-lldb