[fluffything]

> But I’ve also come to the conclusion that Rust relies on libc way too much.

How did you come to this conclusion?

People using Rust rely on libc a lot.

For example, #![no_std] means "no standard-library", but it doesn't mean "no libc, no libunwind, etc.".

So a lot of people like to advertise their crates as "#![no_std]" compatible, because they compile with #![no_std], but then the first thing the crate does is linking against libc, against liballoc, against libm, .... or even the standard library itself...

So... if you are trying to build a binary that does not depend on libc or libstd, then there is no language feature to help you there.

#[no_std] binaries are not only unstable, but also probably not what you want, since that won't prevent you from linking any library that links libc, or the standard library, etc.

If you want to avoid libc, you have to enforce that, e.g., by checking in your build system that your binary doesn't contain any libc, libstd, etc. symbols (I just use nm for this). #![no_std] helps a bit here, but making sure you don't link any library that violates this is up to you.

[geofft]

To me, a #![no_std] library is useful for contexts where there isn't a platform libc (embedded systems, kernels, etc.) and you can't assume things like the existence of stdin or processes. On those systems, there may still be a dynamic allocator, because that's a super common feature in all but the most spartan environments. For those use cases, a #![no_std] library that links liballoc (and documents that it needs it) is totally okay, and often better than a more-limited library that only does static allocation - or conversely implementing all of libstd with runtime panics for most of it, just because your library needs to pass a Vec around. It's a balance.

The only case I think I've seen where a #![no_std] library ends up pulling in libc is if you haven't added a custom allocator and your platform's default allocator uses libc (and so you could switch to a libc-free allocator if you want). Are there other cases?

[codeflo]

There are lots of tiny practical annoyances you notice, starting with having to vet dependencies and transitive dependency upgrades extremely carefully. A major one is that dev-dependencies are very broken in a no_std environment. It’s obviously useful to have the std in your build.rs script, but unfortunately, Cargo merges dependencies and devDependencies in a way that’s simply incorrect.

The good news is that every problem I found had an actively discussed GitHub issue and the community is active, so there will be progress.

[geofft]

> unfortunately, Cargo merges dependencies and devDependencies in a way that’s simply incorrect.

Yeah, I've run into that, but IIRC this got solved super recently/is being solved. Probably https://github.com/rust-lang/cargo/pull/7820 ?

[fluffything]

> To me, a #![no_std] library is useful for contexts where there isn't a platform libc (embedded systems, kernels, etc.) and you can't assume things like the existence of stdin or processes.

"Could be useful for" (FTFY).

Unfortunately, for the reasons mentioned above, most #![no_std] libraries aren't useful for that, because they link libc and other libraries.

Most people don't do this intentionally. The compiler doesn't complain about:

    #![no_std]
    extern "C" { fn malloc(...) -> ...; }

so when somebody does it accidentally, everything works and they get no feedback.

When you then go and build a #![no_std] binary, and run it in a platform when libc is not available, only then you get an error. And at that point, good luck figuring out which of your 200 dependencies has the error.

In particular, if you are running `#[test]`s, doing that links standard, so if your program implicitly depends on libc somewhere, tests won't reveal that, because while testing, libc will be linked.

[geofft]

No, most #![no_std] libraries do not link libc in the way you describe (having a direct FFI dependency on malloc) - they link liballoc, which has a pluggable allocator interface. On some platforms and some configurations (including most normal userspace platforms), the default allocator used by liballoc uses malloc.

It's actually hard to go out of your way and call malloc directly, because FFI calls are unsafe. It's a lot easier to use Box/Vec/String/etc., all of which are defined in liballoc and use the pluggable allocator interface.

I know this because I've successfully used #![no_std] libraries in places where libc doesn't exist and no function named malloc exists, and they do work. If you're having a linker issue it's almost certainly because you haven't changed the default allocator - if you have an example of this I'd be happy to take a look at debugging it.

[fluffything]

> and they do work.

Maybe you are just using different no_std libraries that I am using, but pretty much all of the no_std libraries that I use have `libc` as a direct dependency.

Not only for malloc, many of them just needs to write something to stdout or a file, generate random numbers, ..., and that's hard to do without libc. Why they advertise themselves as no_std escapes my comprehension.

[geofft]

Huh, the libc crate itself claims #![no_std] support. I agree that's confusing and counterintuitive... I see what it means in terms of semantics but I don't understand why that's useful.

[fluffything]

The libc crate does correctly claim #![no_std] support, because #![no_std] means "Does not require the Rust standard library", and libc does not require it.

The two main issues I see with #![no_std] are:

* its a flag for "doesn't link the standard library" but the standard library is often too high-level for bare metal apps that want to be in precise control about everything that gets linked

* it isn't a contract of any kind, so you can't rely on it for anything. In fact, this code is correct and works as intended:

    #![no_std]
    extern crate std;

This is problematic, because many #![no_std] libraries end up linking libstd "by accident", even though that's probably not their intent.

So I agree with you that #![no_std] isn't a silver bullet. I think it is still useful in that it lets you avoid linking the standard library by default, which is necessary condition for embedded development. It is not a sufficient condition, in that in practice you actually want to forbid the standard library and other libraries from being linked, and not just "don't link them by default, but do so by accident".

[andoriyu]

`#![no_std]` really means that sysroot isn't available for your platform and you gotta roll your own.

Project I'm working on right now is `#[no_std]`, but my own sysroot covers 90% of real `std`. Which is why I even export it as `std`, so I can use pretty much all crates I would usually use. Because if your platform has an allocator, doesn't matter where it came from, then you can add `liballoc`. `libstd` = `libcore` + `liballoc` + locks + allocator + threads + a few other things that usually depend liballoc. Which means that you have nearly entire libstd available to you if your target platform has an allocator.

Most `#[no_std]` crates that depend on allocator clearly state that they depend on `liballoc` and that you gotta provide one. What I'm trying to say `#[no_std]` doesn't mean embed, it just means sysroot isnt' available for target.

[codeflo]

That’s true. But going the no_std route is very hard (the ecosystem isn’t big, and relying cargo and crates.io you’re almost guaranteed to link in the std or liballoc by accident at some point). Even when using the std intentionally, I really wouldn’t have expected that basic std functions like println require the libc.

[geofft]

I would not necessarily expect it but I appreciate it in a "systems" language where "systems" is defined as compatible with the existing traditional systems software on a machine. For example, it's nice if the stdbuf(1) command works on Rust binaries on glibc systems, and it's nice if a Rust binary calling a C library that writes with printf (or vice versa) don't maintain two separate output buffers.

To me, Go is the systems programming language for a world untethered by existing platform compatibility (and so, for instance, writing Go libraries to be called from C is awkward, calling C libraries from Go incurs overhead, Go has its own concurrency model, etc.) and Rust is the systems programming language for use cases where you'd otherwise want to use C (really "the platform's native systems language," but that's C on all the major platforms) but you want a better language. I appreciate that they both exist and target these different use cases.

[BuckRogers]

Is Go widely used compared to the others as a systems language at this point?

Over the years I’ve gathered that it’s more of a competitor for C# & Java rather than Rust & C(++).

[geofft]

Depends what you mean by "systems language" (many common definitions turn out to be equivalent to "drop-in replacement for the platform language," which makes the argument circular), but the choice of Go as an implementation language for Docker and Kubernetes puts it pretty firmly in the "systems language" space IMO. Container management requires more systems-level functionality than C# and Java are really geared towards (although you certainly could use them, perhaps with a tablespoon of FFI).

[andoriyu]

Uhm, docker is just a wrapper around linux's kernel features, plus image format. Image format being just bunch of tarballs that needs to be mounted by _something_ layer by layer.

You can write it any language that runs on OS with linux's kernel. There are similar things written and damn bash. Does that make bash a system language?

[apta]

The original version of Docker was written in Python, and the original version of Kubernetes was written in Java, so your argument doesn't hold.

[geofft]

Would this be the part of my argument that doesn't mention Python (which I personally consider a systems language) at all? Or the part of my argument where I say, "you certainly could use them"?

[GlitchMr]

Well, writing to standard output requires interacting with an operating system, so it's not surprising that it requires `std`. You cannot write to standard output without knowing what operating system you are compiling for.

Worth noting however that `writeln` only needs `core`, and as long you can provide an implementation of writing to standard output (pretty much create a struct and implement `core::fmt::Write` trait for it), creating `println` macro is trivial.

[steveklabnik]

An example of this: https://os.phil-opp.com/vga-text-mode/#a-println-macro