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Show HN: Uscope, a new Linux debugger written from scratch

262 points| jcalabro | 1 year ago |github.com

Hi! I've been building a debugger on my nights and weekends because it's fun, and I personally need a better debugger for my work. GDB and LLDB pain me greatly; we can and will do better!

As explained in the README, it's still very early-days and it's not ready for use yet, but check back often because it's improving all the time!

Check out https://calabro.io/uscope for a more detailed explanation.

Thanks for taking a look!

132 comments

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feelamee|1 year ago

> The available Linux debuggers are gdb and lldb. They both suck. They crash all the time, don't understand the data types I care about, and they don't make the data I need available at my fingertips as quickly as possible.

quote from https://calabro.io/uscope

Of course gdb, lldb have their problems (e.g. smashing tui with app output, what can be easily fixed, or very very very very long tab-tab completion, and crashing of course), but I dont know anything better. I am forced to use visual studio at work and its debugger really sucks - it can't even compare strings in conditional breakpoint, it cant even skip all std::function / std::bind garbage to let me step in callback, it can't watch evaluated expressions. Probably it can evaluate exprs (immediate window?), but there are very little guides about this.

So, gdb is winner for me now. rr (record-repeat)[0] also looks very nice, but it require hardware support(((

[0] https://rr-project.org/

AlotOfReading|1 year ago

If you're willing to deal with enterprise pricing, Undo [0] implements something reasonably comparable to rr without the hardware timer requirements.

[0] https://undo.io/

alcover|1 year ago

  > gdb(..) smashing tui with app output
this got me losing my mind. How/why propose this tempting TUI mode when the result looks like a broken arcade game ??

How do you people comfortably debug C in Linux ? I know VSCode looks nice but by principle I can't accept to use such a beast to basically edit code..

khuey|1 year ago

rr should work on any remotely modern Intel system, and generally on AMD's Zen CPUs too. Unless you're in a virtualized environment (some of which are supported) or a more esoteric architecture rr probably works on your silicon.

imron|1 year ago

Which visual studio are you using?

It’s been a number of years since I’ve used it but Visual Studio PRO could do all these things - at least as long as I was using it (since visual c++ 5).

VS Code on the other hand is no where near as featured or powerful.

caspper69|1 year ago

Man, if you read my comments lately you would think I'm a Microsoft fanboy, sheesh.

But honestly, in all my years, Visual Studio has been (by far) the best non-commercial (or should I say built-in?) debugger that I've used, and that includes gdb.

I am not a huge c++ on Windows guy though, so YMMV.

Here are a few guides that you may find helpful (and I am also going to include the beginner one, but please do not take that as an indictment of your skill level, I am including only for completeness).

These are all for VS2022:

C++ Debugging Tutorial: https://learn.microsoft.com/en-us/visualstudio/debugger/gett...

C++ Breakpoint Debugging: https://learn.microsoft.com/en-us/visualstudio/debugger/usin...

Breakpoint/Watch Expressions (pay attention to the debugger intrinsics): https://learn.microsoft.com/en-us/visualstudio/debugger/expr...

High Level Debugger Tour: https://learn.microsoft.com/en-us/visualstudio/debugger/debu...

VS2022 Debugging TOC: https://learn.microsoft.com/en-us/visualstudio/debugger/?vie...

My apologies if you've already found these references and they don't do you any good, but your issues just don't sound like the types of issues I've ever experienced with the debugger, and sometimes MS' documentation is just disorganized and incomplete.

n4r9|1 year ago

Out of interest what are your main use cases for needing conditional breakpoints?

godelski|1 year ago

  > Build as a library so other people can build other interesting things as well
I LOVE this!

I firmly believe so much tech has gone to shit because things are no longer hackable. We say "move fast and break things" but we try so hard to prevent that that when we do break things we just create bigger messes and debt, so no one cleans it up. It seems slower to write hackable code but that's in the moment. In the long run it is much faster. Not to mention you get added benefits of others being able to contribute more easily with a lower likelihood of actually breaking shit.

Analemma_|1 year ago

Is gdb another thing like gcc where the un-hackability and un-extendability was a deliberate choice by rms to ensure nobody would ever build proprietary toolchains on top of it?

IAmLiterallyAB|1 year ago

Yay this is awesome! GDB is a buggy (https://sourceware.org/bugzilla/show_bug.cgi?id=18772 https://sourceware.org/bugzilla/show_bug.cgi?id=9425) mess and rough code quality, I've wanted a do something like this for a while.

To be 100% clear, it's not using gdb/gdbserver under the hood right?

The bugs I linked above are over a decade old, and I have to patch them every time I compile GDB server. Ultimately (IIRC) GDB needs to rework how it handles signals (to their credit, ptrace is a horribly stupid API, especially before PTRACE_SEIZE, so I don't blame them for having issues)

mort96|1 year ago

Interesting, LLDB also has a serious bug related to ^c! In LLDB, if you run 'lldb -o run /path/to/executable', it won't pause on SIGINT. As a result, you can't have an ergonomic setup where you have e.g a make target to run your software under LLDB, you always need to manually type 'run' for ^c to work.

jcranmer|1 year ago

This is definitely an ambitious project, and I worry that you are biting off more than you can chew in doing so. (I've attempted my fair share of debugger projects in the past).

At a low level, one of the main problems is that Linux's kernel interfaces for debugging are just absolute trash. (I see you have multithreaded support mentioned as a future task item, and that's one of the areas where you discover just how bad it really is). And of course ptrace composes somewhat poorly with, well, anything else, so if you want to use perf_event or eBPF to help drive the low-level stuff, well, combining everything into a single event loop is just painful. (Oh, and the documentation for all of this stuff sucks.)

At the medium level, everything is hampered by the number of secret handshakes that go on between the compiler, the linker, the runtime loader, the debugger. And the chronic issue that, in the debugger, you have to be prepared for the possibility that everything is just catastrophically wrong: your stack might be garbage (or downright nonexistent), the thread-local storage register might be a garbage value, variables may have values that don't make sense. After all, you're resorting to a debugger when things don't work, and part of the reason why it might not be working is because you've accidentally corrupted everything.

And at the high level, there's the UI which, as someone who doesn't work on UI, I find terrifying in its own right.

Trying to solve not one of these issues, but all of them, at once, in a new project is ambitious. I'd personally prefer a lot more a project that only tried to tackle one slice of the stack, not all of it.

HexDecOctBin|1 year ago

Yup, Linux is nowhere the Unix successor we deserved. I have started multiple systems projects in Linux and gave always given up due to how shoddy the foundations are. It seems like the kernel just copies whatever cool feature they find in Solaris, BSD, Plan 9 or even NT without paying any attention to their composability, while the user space people are just a clique trying to force their way on everyone (why is the loader part of libc again?).

titzer|1 year ago

Nice project!

One killer feature would be the ability to connect to the debugger via a socket and control it. Gdb has this interface and for some use cases it's great.

As one of those long-tail "native" languages, Virgil might benefit from this. So far, I've had a student build a DWARF backend, and the experience from that is that DWARF is way too complicated and consequently implementations are broken and crappy in many ways. I think DWARF draws the wrong dividing line here. Control of the machine and customizing the source-level support to the language is probably better.

mindcrime|1 year ago

Speaking as a Java guy, remote debugging is SO useful (at times anyway). Thankfully the JVM has built in support for a remote debugging protocol[1] and there are good debuggers that can connect to a running Java system (if it was started with the correct command line flags) and do symbolic debugging over the network.

There can be certain situations where the network latency can make things difficult, but generally speaking I find it an incredibly useful facility to have.

[1]: https://docs.oracle.com/javase/8/docs/technotes/guides/jpda/...

peterfirefly|1 year ago

> the experience from that is that DWARF is way too complicated

The representation and the compression are far too intertwined :(

sroussey|1 year ago

Have it use the WebKit debugger protocol and we can use browser dev tools as the UI.

:p

meitham|1 year ago

Very happy to see the increasing momentum in the zig community

koek67|1 year ago

Nice work! I remember meeting you at Systems Distributed in NYC where you mentioned this project, so cool to see the progress. Well done!

zwieback|1 year ago

Everyone here seems to thing GDB is awful. It's been a while for me but I remember using front-ends like Eclipse's CDT or similar and didn't find that experience so bad. Do most people use GDB straight-up? I haven't done that in probably 15 years although it's nice to have a lightweight command line on small embedded systems.

jcelerier|1 year ago

> Everyone here seems to thing GDB is awful. It's been a while for me but I remember using front-ends like Eclipse's CDT or similar and didn't find that experience so bad. Do most people use GDB straight-up? I haven't done that in probably 15 years although it's nice to have a lightweight command line on small embedded systems.

the issue is not with gdb's UX - you can build as many cool UI / UX on top of it as you want. The problem is that gdb will sometimes take 5 minutes to start debugging (and that's without debuginfod), straight up crash, be unable to resolve obvious symbols etc. which are all back-end bugs. For me developing a medium-sized C++ app, it's really hell to use and usually printf debugging is MUCH faster in the sense that I have the time to find and fix my problem through an iterative recompile cycle sometimes before gdb has even finished parsing my binary

boricj|1 year ago

I do use GDB straight up for native programs and microcontrollers, mostly out of laziness. I haven't set up VS Code debugging at my current day job yet and it's been 6 months.

Out of the box GDB is kinda awful, especially for C++ codebases. I should probably look into scripting at some point, but meh. Even then, as far as I know I'm the best at using a debugger at work by a wide margin, but I attribute that more to my knowledge of low-level programming than my ability to use most of the basic GDB commands. Also, it tends to crash once a month or so.

If I needed to debug a userland program on a small Linux embedded system, I'd probably whip out gdbserver and attach gdb to the target remotely. I haven't done that in a while though.

jcelerier|1 year ago

example from today, timed with a stopwatch, on a 5950X 5GHz CPU: from the moment I click on "debug" in my IDE,

- lldb takes 40 seconds to reach "main"

- 2 minutes 36 total to reach the GUI and start being able to reproduce things

- gdb coredumps as soon as I want to put a breakpoint so it's unuseable

    $ lldb --version
    lldb version 19.1.7
    $ gdb  --version
    GNU gdb (GDB) 16.1

mort96|1 year ago

This is exciting! I use GDB and LLDB, but their TUIs/CLIs make certain things difficult (I feel like debugging seriously benefits from a proper GUI) and graphical front-ends I've tried are pretty janky. Looking forward to trying it out, but I'm excited to see something happening in this space.

mplemay|1 year ago

This opinion is not backed by facts, any insight about linux (or even the languages in question), or even related to this post. Nevertheless, I wonder if it was a good idea to allow rust contributions to the linux project. From all of the bits and pieces I read about zig (including this project), I feel like it would have been better aligned (than rust) to pick up where the mainly C codebase left off.

renox|1 year ago

Zig isn't 1.0 so..

whytevuhuni|1 year ago

Not really. Zig's answer to safety is mostly based on runtime panics, and the kernel really, really hates panics.

As such, the only thing left is better ergonomics, and that's not really worth the effort to switch.

Rust isn't being adopted because it's an easier language to code in, and in fact it's being adopted in spite of the fact that it's harder to code in. And that's because to some kernel devs, the promise of better security and fewer vulnerabilities is worth that much.

On the other hand, Zig is great for user-space applications. The stuff to replace GNU's coreutils with.

timeon|1 year ago

Yes it would be better C, but compared to Rust, is that enough?

gregthelaw|1 year ago

Congrats on this work -- writing a debugger from scratch is a big job. I have cloned the repo, will take a proper look this w/e.

quotemstr|1 year ago

It's not clear to me why we'd need a new debugger instead of GDB enhancements. GDB has an extensible, modern C++ codebase with literal decades of hard earned knowledge baked into it.

How are we better off rewriting it, especially if the rewrite isn't memory safe?

chc4|1 year ago

> GDB has an extensible, modern C++ codebase with literal decades of hard earned knowledge baked into it.

I literally laughed outloud at this. Have you ever actually opened a GDB source file? It is, as a whole, extremely poor quality code. Almost all of it is doing C string manipulation and raw pointer arithmetic; almost none of it uses C++ smart pointers, nevermind the rest of "modern C++"; the vast majority is completely uncommented, and "literal decades of hard earned knowledge" can be better translated as "literal decades of historical baggage, cruft, and hacks". I regularly cause GDB to segfault in normal, mundane operations.

godelski|1 year ago

  > It's not clear to me why we'd need a new debugger
People build things for fun. Stop asking "why" and ask "why not?"

No one can really predict what's needed and where we need to go, so let people just explore. Sometimes they won't find things, but sometimes they do. And if they don't, they still gain useful knowledge that pays dividends later on anyways.

It's Hacker News, let people hack.

ziddoap|1 year ago

Consider this part of the post:

>I've been building a debugger on my nights and weeks because it's fun

modeless|1 year ago

GDB is awful and a replacement is sorely needed. It's buggy and slow and feature poor and has a terrible UI and a terrible API which makes all the frontends terrible in turn. I haven't looked at its code but I'm betting it's terrible too.

bregma|1 year ago

Well, you can start by tearing down all the fences and firing that Chesterton guy's sorry ass. After all, even a 32-bit ARMv7 uses .eh_unwind sections to crawl the stack for a backtrace, right?

Then, you can focus on resolving edge cases that can cause papercuts. Make sure the solutions are at the expense of the happy path because that's all been solved long ago so there's no need to pay attention to it.

breatheoften|1 year ago

Super supportive as I really value debuggers as tools even tho they are horror shows to use!

> Similarly, the following features are non-goals of the project:

> Supporting non-native languages (i.e. Java, Python, etc.)

But I think that position is likely a mistake in terms of leaving killer features on the table and baking in architecture decisions that might continue to make these kinds of features impossible / very low-class experiences.

Properly integrating with the python interpreter to be able to debug python + c/cpp extensions running in the same process is a huge missing whole in the debugger market.

I don't know how other people do it but I 'solve' this problem by attaching either a python debugger or lldb to the python process -- meaning I can debug either python or the cpp but not both at the same time. The experience is very lacking. Even just seeing the python call-stack while paused at a cpp breakpoint would be huge.

mamcx|1 year ago

One thing that as far as I know no single debuggers has (except FoxPro from DOS) is the ability to show a large list of things, but well

In general, if something is large (text, arrays, etc) all bets are off.

Basically, something like this:

https://github.com/okbob/pspg

---

The second thing that is very hard with debuggers, is to tell them what to skip.

In the normal sense of 'I don't wanna debug Rust std' but also 'What the heck, why is stepping into #[Debug]???'

armitron|1 year ago

GDB (I don't use LLDB) is fully programmable and has multiple user interfaces (TUI, Emacs, DDD, graphical frontends and various .gdbinit configurations that emulate SoftICE L&F).

It's a power tool and takes some time and effort to learn and master. Superficially dismissing it / wasting your time with something that in all likelihood will end up going nowhere while lacking most features that make GDB great, does not a good recommendation make.

At least you'll probably learn a thing or two while you implement it, but I'd rather not waste my time using it.

drewg123|1 year ago

How entwined is it with Linux specific APIs? Eg, how hard would it be to port to FreeBSD?

ribs|1 year ago

TotalView (which I rep), Linaro DDT - thoughts? (Yes, they’re both proprietary)

cintellis|1 year ago

how much do those cost approx? for an individual hobbyist developer

bieganski|1 year ago

> The available Linux debuggers are gdb and lldb. They both suck. They crash all the time, don't understand the data types I care about, and they don't make the data I need available at my fingertips as quickly as possible.

Okay, so this is the author's answer to the most important question: "why?"

For me this is a serious issue, making strong statements without any single backing example. If you experience crashes, please report to the maintainers - i guarantee that you won't be ignored. You say that it's missing some data that you need? Fine, but be precise - what data?

Otherwise it sounds like a "yeah, let's make a project for fun and pretend that it's serious by finding sort-of-justification/use case" (i'm not telling that it is the case for you - i'm telling that it sounds like it, based on your own description).

Also, would you feel nice if i put in my project's README a note that the project of you, the one that you put your effort to, "sucks"?

dumah|1 year ago

There are almost 4000 open issues on gdb reported more than five years ago.

In this conversation are reports of an annoying bug that requires a user patch gdb and it's existed for almost twenty years.

It was years before anyone was even assigned because of a bug in their bug tracking system, and they haven't addressed any further comments over the decades.

omnicognate|1 year ago

I'd rather the time taken enumerating the deficiencies of existing debuggers be spent building something better instead. I doubt many people that have used gdb/lldb need convincing that that's possible. If it is needed, Microsoft's windbg (far from what's possible but light years ahead of gdb/lldb) is a proof by construction.

rickydroll|1 year ago

Make it debug systemd config problems and I'd be thrilled.

adolph|1 year ago

To clarify “from scratch” as in from basic materials and not “in scratch” as in the MIT graphical programming g system[0]. It appears to be written in Zig[1], which I find interesting for analysis.

0. https://scratch.mit.edu/

1. https://github.com/jcalabro/uscope

TZubiri|1 year ago

lol, I think no one expected a linux debugger to be written in the visual programming language for kids.

AdmiralAsshat|1 year ago

"written from scratch" is one of those phrases that seems to cause any submission to instantly hit HN frontpage, along with "for fun and profit", "considered harmful", and a couple others.