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Comment by jenadine | Hacker News Reader

And yet, the Linux kernel's Rust code uses unstable features only available on a nightly compiler.

Not optimal for ease of compilation and building old versions of the Kernel. (You need a specific version of the nightly compiler to build a specific version of the Kernel)

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Don't the C parts of Linux heavily depend on GCC extensions too? Seems depending on specific compiler features isn't really a blocker.

The difference probably is that GCC extensions have been stable for decades. Meanwhile Rust experimental features have breaking changes between versions. So a Rust version 6 months from now likely won't be able to compile the kernel we have today, but a GCC version in a decade will still work.

luckily downloading a specific nightly version is only a single rustup command

Besides supply chain attacks, what could go wrong ? /s

Kernel doesn't use Cargo.

rustup is also downloading binary toolchains

> Not optimal for ease of compilation and building old versions of the Kernel. (You need a specific version of the nightly compiler to build a specific version of the Kernel)

It's trivial to install a specific version of the toolchain though.

It really isn't if bootstrapping from source.

You don't generally need specific versions of GCC or Clang to build it I'm pretty sure.

> You don't generally need specific versions of GCC or Clang to build it I'm pretty sure.

You need a C11 compiler these days with loads of non-standard extensions. Note, for a very long time, one couldn't compile the Linux kernel with clang because it lacked this GCC specific behavior.

I'm not really sure you can turn around and say -- Oh, but now we feel differently about the C standard -- given how much is still non-standard. For instance, I don't believe Intel's C compiler will compile the kernel, etc.

What if I told you… there was a simple, constant environment variable you could set to make the stable compiler forget it isn’t a nightly?

the point is unstable features aren't guaranteed to not break after a compiler update. hence the specific version thing.

When it comes to nightly features use, it is good to note that a stable compiler, a nightly corresponding to the date beta for that stable was branched out and an arbitrary nightly are different. A branched-off nightly might have had beta back ports for fixing stable features that the nightly will not have, and a nightly feature that is subtly broken on stable but isn't used in std will not have received a backport. So using nightly feature on stable might mean every now and then skipping a stable version, and using a nightly compiler means having to do thorough testing after updating on arbitrary days. Any given nightly has high chances of being fine, but every update brings the possibility of bugs.

It's not ideal, but at least most of these are only used in the `kernel` crate, i.e. if there's a breaking change to these features it should be fixable without widespread changes.

Can you please share more details about this?

https://rust-for-linux.com/unstable-features#unstable-featur...

The Linux kernel has been using stable versions of Rust for some time now. You do not need nightly or beta Rust compilers to compile the kernel.

https://www.phoronix.com/news/Linux-Patches-Multiple-Rust-Ve...

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