You could potentially build on stable Rust by emitting the breakpoint instructions yourself, at least on popular platforms. For instance, `core::arch::asm!("int3")` on x86, or `core::arch::asm!("brk #1")` on ARM.
Also, this is providing motivation to want to stabilize a breakpoint mechanism, perhaps `core::arch::breakpoint()`. I'm going to propose an API Change Proposal (ACP) to the libs-api team to see if we can provide that in stable Rust.
estebank 2 hours ago [-]
Having a feature like this will significantly increase the demand of better incremental compilation, potentially with the need for patching specific items on existing binaries for speed. At that point you could get very close to an IDE debugging experience/speed with only rustc, a text editor and a debugger. (Inserting a bunch of NOPs on every function and supporting patching of JMPs in their place would likely go a long way for this.)
amluto 4 hours ago [-]
Plain int3 is a footgun: the CPU does not keep track of the address of the int3 (at least not until FRED), and it reports the address after int3. It’s impossible to reliably undo that in software, and most debuggers don’t even try, and the result is a failure to identify the location of the breakpoint. It’s problematic if the int3 is the last instruction in a basic block, and even worse if the optimizer thinks that whatever is after the int3 is unreachable.
If Rust’s standard library does this, please consider using int3;nop instead.
JoshTriplett 4 hours ago [-]
Good to know! I've seen the pattern of "int3; nop" before, but I've never seen the explanation for why. I'd always assumed it involved the desire to be able to live-patch a different instruction over it.
In Rust, we're using the `llvm.debugtrap` intrinsic. Does that DTRT?
rep_lodsb 2 hours ago [-]
The "canonical" INT 3 is a single byte opcode (CCh), so the debugger can just subtract 1 from the address pushed on the stack to get the breakpoint location.
There is another encoding (CD 03), but no assembler should emit it. It used to be possible for adversarial code to confuse debug interrupt handlers with this, but this should be fixed now.
BrainBacon 6 hours ago [-]
Thanks, yeah I considered using the instructions directly, but I was hoping for a more cross-platform option. For my purposes, developing in the Bevy engine, nightly isn't a huge blocker. Yeah, it would be really great to just have breakpoint support in stable Rust, thanks for doing the proposal! I'll consider stable support in the meantime.
amluto 4 hours ago [-]
Hah, the README says:
> Additonally, debugging may not land on the macro statements themselves.
See my comment above, and give int3;nop a try.
BrainBacon 3 hours ago [-]
Interesting. Unfortunately, I'm not well versed in assembly, is there a similar trick or requirement in arm and would that include Apple silicon, or is this something specific to `int3` on x86? That may explain why it was inconsistent during my development process, I didn't think to check if the inconsistency was platform dependent.
merksoftworks 3 hours ago [-]
Rusts current pretty printers in lldb and gdb are just not good enough for a fluid step debugging experience. I've had luck with intellij IDE's but it's very sad that the best we can do in a language with such good devex tooling is print debugging.
Theoretically you could generate debug scripts with a macro and embed them with
I find myself using debug_here (https://github.com/ethanpailes/debug-here) which does similar things but for desktop-class debugging. It hasn't been updated in a while, but it still works for me on Windows at least.
ewuhic 26 minutes ago [-]
Is there a good newby tutorial on how to use debugger with Rust (and debugger in general?) No videos please.
thramp 6 hours ago [-]
Oh, that’s super clever integration with tracing. Feel free to send us a PR; we’ll link to this as a related project in the docs!
We used to divide by zero but then someone decided that was ok.
revskill 7 hours ago [-]
What does nightly mean ? I hate that you could not know a specific version of a nightly.
landr0id 16 minutes ago [-]
It's a bit unfortunate wording but it basically requires any nightly toolchain version. It uses `std::intrinsics::breakpoint()` which is a compiler intrinstic. This has been available for a long time, but afaik will never be exposed on a stable toolchain.
>This feature is internal to the Rust compiler and is not intended for general use.
nindalf 7 hours ago [-]
The master branch of the Rust repo is built every night and distributed. That's a nightly build. Most people are on the stable release, which is updated every six weeks.
A minority use the nightly build for various reasons: a feature that hasn't reached stable yet, or because they want to help test the nightly releases and prevent bugs from reaching stable.
jtrueb 7 hours ago [-]
Is it a minority? Are there stats posted for this?
Only recently have I had some projects switching to stable after their required features stabilized.
89.4% of users surveyed use stable. 31.1% use nightly, but there's overlap there (e.g. I use nightly to try out new things but don't build things that depend on nightly). Only 11.5% of people say they use a crate that requires it.
littlestymaar 2 hours ago [-]
> Only recently have I had some projects switching to stable after their required features stabilized.
While this used to be very common back then (in 2016-18 many things where progressively stabilized and you had cornerstone libraries switching to stable at almost every release) it hasn't been so for the past 5 years.
Rust gets way less “exciting” new features nowadays, as the language has settled a lot (there are still moving parts, but they are the minority not the norm).
dvtkrlbs 7 hours ago [-]
You can pin versions with the rust-toolchain.toml file you need to be using Rustup afaik. Nightly is just the daily builds.
kookamamie 54 minutes ago [-]
I thought nightly is for nightly builds. I'll get my coat.
johnisgood 7 hours ago [-]
I assume any "nightly" version would work in this context, meaning it would not refer to a version from a year ago, as it would have already been made stable by that point, right?
traxys 7 hours ago [-]
"nightly" versions also allow to use unstable features, and unstable features may remain so for a very long time (potentially forever) without breaking, so an old nightly could maybe work
johnisgood 6 hours ago [-]
Right, not everything gets merged to stable. In that case: letting us know the specifics beyond "nightly" is advisable, IMO.
do_not_redeem 6 hours ago [-]
The readme does mention the specifics, immediately after mentioning nightly.
> BREAKPOINTS REQUIRE ENABLING THE EXPERIMENTAL core_intrinsics FEATURE
johnisgood 5 hours ago [-]
How do I know which versions of nightly support that feature, and that specific version of the feature though?
I like your username.
GolDDranks 4 hours ago [-]
Just use a recent nightly and you should be fine. Rust project doesn't offically provide support even for old stable versions, so "using nightly" with no specifics generally means using any nightly build, around or newer than, the current stable release.
monocasa 6 hours ago [-]
A lot of people pin a specific nightly since the feature they're depending on could change (or ostensibly it would be in stable), so they can keep working without continuously having to track nightly changes or deal with it breaking on a different system with a different nightly version.
That obviously only works for non-library uses of nightly.
Rendered at 20:47:47 GMT+0000 (Coordinated Universal Time) with Vercel.
Also, this is providing motivation to want to stabilize a breakpoint mechanism, perhaps `core::arch::breakpoint()`. I'm going to propose an API Change Proposal (ACP) to the libs-api team to see if we can provide that in stable Rust.
If Rust’s standard library does this, please consider using int3;nop instead.
In Rust, we're using the `llvm.debugtrap` intrinsic. Does that DTRT?
There is another encoding (CD 03), but no assembler should emit it. It used to be possible for adversarial code to confuse debug interrupt handlers with this, but this should be fixed now.
> Additonally, debugging may not land on the macro statements themselves.
See my comment above, and give int3;nop a try.
Theoretically you could generate debug scripts with a macro and embed them with
but I haven't seen anyone go through the trouble.Per https://dev-doc.rust-lang.org/nightly/unstable-book/library-...
>This feature is internal to the Rust compiler and is not intended for general use.
A minority use the nightly build for various reasons: a feature that hasn't reached stable yet, or because they want to help test the nightly releases and prevent bugs from reaching stable.
Only recently have I had some projects switching to stable after their required features stabilized.
89.4% of users surveyed use stable. 31.1% use nightly, but there's overlap there (e.g. I use nightly to try out new things but don't build things that depend on nightly). Only 11.5% of people say they use a crate that requires it.
While this used to be very common back then (in 2016-18 many things where progressively stabilized and you had cornerstone libraries switching to stable at almost every release) it hasn't been so for the past 5 years.
Rust gets way less “exciting” new features nowadays, as the language has settled a lot (there are still moving parts, but they are the minority not the norm).
> BREAKPOINTS REQUIRE ENABLING THE EXPERIMENTAL core_intrinsics FEATURE
I like your username.
That obviously only works for non-library uses of nightly.