Re: [PATCH v2] Kbuild: fix issues with rustc-option

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Oct 8, 2024 at 7:32 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> Fix a few different compiler errors that cause rustc-option to give
> wrong results.
>
> If KBUILD_RUSTFLAGS or the flags being tested contain any -Z flags, then
> the error below is generated. The RUSTC_BOOTSTRAP environment variable
> is added to fix this error.
>
>         error: the option `Z` is only accepted on the nightly compiler
>         help: consider switching to a nightly toolchain: `rustup default nightly`
>         note: selecting a toolchain with `+toolchain` arguments require a rustup proxy;
>               see <https://rust-lang.github.io/rustup/concepts/index.html>
>         note: for more information about Rust's stability policy, see
>               <https://doc.rust-lang.org/book/appendix-07-nightly-rust.html#unstable-features>
>         error: 1 nightly option were parsed
>
> The probe may also fail incorrectly with the below error message. To fix
> it, the /dev/null argument is replaced with a new rust/probe.rs file
> that doesn't need even the core part of the standard library.
>
> error[E0463]: can't find crate for `std`
>   |
>   = note: the `aarch64-unknown-none` target may not be installed
>   = help: consider downloading the target with `rustup target add aarch64-unknown-none`
>   = help: consider building the standard library from source with `cargo build -Zbuild-std`
>
> The -o and --out-dir parameters are altered to fix this warning:
>
>         warning: ignoring --out-dir flag due to -o flag
>
> I verified that the Kconfig version of rustc-option doesn't have the
> same issues.
>
> Fixes: c42297438aee ("kbuild: rust: Define probing macros for rustc")
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Changes in v2:
> - Add `export` to RUSTC_BOOTSTRAP.
> - Fix error about core being missing.
> - Fix warning about -o flag.
> - Link to v1: https://lore.kernel.org/r/20241008-rustc-option-bootstrap-v1-1-9eb06261d4f7@google.com

v3 sent here:
https://lore.kernel.org/all/20241009-rustc-option-bootstrap-v3-1-5fa0d520efba@google.com/

Alice