Quick notes

Posted Mar 28, 2025 12:24 UTC (Fri) by jgg (subscriber, #55211)
In reply to: Quick notes by ojeda
Parent article: A process for handling Rust code in the core kernel

> I just tried Ubuntu 24.04 LTS in a fresh VM, and I could build v6.14 without issue with the versioned packages mentioned in the instructions.

You can build it, but not following the instructions in Documentation/rust/quick-start.rst:

$ sudo apt install rustc-1.80 rust-1.80-src bindgen-0.65 rustfmt-1.80 rust-1.80-clippy
$ export RUST_LIB_SRC=/usr/src/rustc-$(rustc-1.80 --version | cut -d' ' -f2)/library
$ make LLVM=1 rustavailable
***
*** Rust bindings generator 'bindgen' could not be found.
***
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***
make[1]: *** [/tmp/x/Makefile:1798: rustavailable] Error 1
make: *** [Makefile:251: __sub-make] Error 2

So what is the make command?

$ make LLVM=1 BINDGEN=bindgen-0.65 rustavailable
***
*** Rust compiler 'rustc' is too old.
*** Your version: 1.75.0
*** Minimum version: 1.78.0

Ugh.

$ make LLVM=1 BINDGEN=bindgen-0.65 RUSTC=rustc-1.80 rustavailable
Failed to run rustfmt: No such file or directory (os error 2) (non-fatal, continuing)
***
*** Rust bindings generator 'bindgen-0.65' < 0.69.5 together with libclang >= 19.1
*** may not work due to a bug (https://github.com/rust-lang/rust-bindgen/pull/2824),
*** unless patched (like Debian's).
*** Your bindgen version: 0.65.1
*** Your libclang version: 19.1.7
***
clang: unknown C compiler

Uh.. OK..

$ make LLVM=1 LLVM_SUFFIX=-17 BINDGEN=bindgen-0.65 RUSTC=rustc-1.80 rustavailable
Failed to run rustfmt: No such file or directory (os error 2) (non-fatal, continuing)
***
*** Rust bindings generator 'bindgen-0.65' < 0.69.5 together with libclang >= 19.1
*** may not work due to a bug (https://github.com/rust-lang/rust-bindgen/pull/2824),
*** unless patched (like Debian's).
*** Your bindgen version: 0.65.1
*** Your libclang version: 19.1.7
***
***
*** libclang (used by the Rust bindings generator 'bindgen-0.65')
*** version does not match Clang's. This may be a problem.
*** libclang version: 19.1.7
*** Clang version: 17.0.6
***
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***
Rust is available!

Progress?

I have lots of libclang's:

$ ls /lib/x86_64-linux-gnu/libclang*
/lib/x86_64-linux-gnu/libclang-17.so.1@ /lib/x86_64-linux-gnu/libclang-19.so.19
/lib/x86_64-linux-gnu/libclang-17.so.17 /lib/x86_64-linux-gnu/libclang-cpp.so.17@
/lib/x86_64-linux-gnu/libclang-18.so.1@ /lib/x86_64-linux-gnu/libclang-cpp.so.18@
/lib/x86_64-linux-gnu/libclang-18.so.18 /lib/x86_64-linux-gnu/libclang-cpp.so.18.1@
/lib/x86_64-linux-gnu/libclang-19.so.1@ /lib/x86_64-linux-gnu/libclang-cpp.so.19.1

Maybe don't automatically pick the wrong one :\

$ make LLVM=1 LLVM_SUFFIX=-17 BINDGEN=bindgen-0.65 RUSTC=rustc-1.80 LIBCLANG_PATH=/lib/x86_64-linux-gnu/libclang-17.so.1 rustavailable
Rust is available!

Yay, finally..

The instructions in quick-start really should say the special make command required as well.

Quick notes

Posted Mar 28, 2025 15:13 UTC (Fri) by ojeda (subscriber, #143370) [Link] (1 responses)

> You can build it, but not following the instructions

You can definitely argue the instructions could be more detailed, but the existing instructions are currently meant as examples on installing the toolchain, not as a full guide on building the kernel for each particular distribution/LTS/set of packages/setup.

> Maybe don't automatically pick the wrong one :\

Hmm... I don't think we should automatically override whatever the user's tool (or its distribution) does.

> The instructions in quick-start really should say the special make command required as well.

I wouldn't say it is really special. In a fresh 24.04 LTS, using the install command provided, this works:

make LLVM=1 RUSTC=rustc-1.80 BINDGEN=bindgen-0.65 rustavailable

`LLVM=1` is common and `RUSTC`/`BINDGEN` are needed just like in the C side when using different binaries.

The biggest pitfalls are the `RUST_LIB_SRC` one and the `bindgen` bugs -- they are mentioned and they were reported to upstream Ubuntu.

Now, yes, an example `make` for cases that we know that work could help, or perhaps a list of related variables, but we cannot try to cover every setup either, so it is a balance.

Over time, this will get easier, e.g. Ubuntu 25.04 will be better -- no versioned packages needed.

And others like Fedora just work already.

Quick notes

Posted Mar 28, 2025 18:25 UTC (Fri) by jgg (subscriber, #55211) [Link]

It is not every setup, it is Ubuntu 24.04 LTS which is listed in its own section in the documentation with its own steps. Put the command that is required to make it work reliably so people can make it work. It is not easy to find all these weird make variables that are needed.