[PATCH v4 16/20] Kbuild: add Rust support

[Miguel Ojeda]

Hi John Paul,

On Sat, Feb 12, 2022 at 7:27 PM John Paul Adrian Glaubitz
<glaubitz at physik.fu-berlin.de> wrote:
>
> Is there any particular reason why this list excludes MIPS*, i386, big-endian
> PowerPC and SPARC targets which are already supported by the Rust programming
> language?

The variations we have so far were intended to showcase the Rust
support in several major architectures, rather than cover everything.
But as long as LLVM (& the kernel, i.e. ClangBuiltLinux) supports the
target (and as long there are no compiler/toolchain issues), you
should be able to try it.

> Are the arch/$ARCH/rust/target.json files everything that's needed for supporting
> the other targets?

Mostly -- there is also `rust/kernel/c_types.rs` and you may need to
tweak `rust/compiler_builtins.rs`, but not much more.

Note that for the target spec files, the short-term plan is to
generate dynamically the target spec file according to what the
architecture requests, instead of using these static files. Longer
term, we need a Rust-stable way to setup custom targets from upstream
`rustc` (though it is not clear yet how it will look, e.g. it could be
via command-line flags).

Cheers,
Miguel