linux-kernel - Re: [PATCH v3] Kbuild: fix issues with rustc-option

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Message-ID: <CAK7LNATSA32f8U1GfiDMwe0CYktTSdecR12Z1YoMZUYJgQCUoA@mail.gmail.com>
Date: Wed, 9 Oct 2024 21:51:29 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3] Kbuild: fix issues with rustc-option

On Wed, Oct 9, 2024 at 8:42 PM Alice Ryhl <aliceryhl@...gle.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
>
> Note that RUSTC_BOOTSTRAP is also defined in the top-level Makefile, but
> its value is unfortunately *not* inherited from the environment. That
> said, this is changing as of commit 98da874c4303 ("[SV 10593] Export
> variables to $(shell ...) commands"), which is part of Make 4.4.
>
> The probe may also fail with the error message below. To fix it, the
> /dev/null argument is replaced with a file containing the crate
> attribute #![no_core]. The #![no_core] attribute ensures that rustc does
> not look for the standard library. It's not possible to instead supply a
> standard library to rustc, as we need `rustc-option` before the Rust
> standard library is compiled.
>
>         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
>
> The --sysroot flag is provided as we would otherwise require it to be
> present in KBUILD_RUSTFLAGS. The --emit=obj flag is used to write the
> resulting rlib to /dev/null instead of writing it to a file in
> $(TMPOUT).
>
> I verified that the Kconfig version of rustc-option doesn't have the
> same issues.
>
> Fixes: c42297438aee ("kbuild: rust: Define probing macros for rustc")
> Co-developed-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Based on top of:
> https://lore.kernel.org/r/20241009102821.2675718-1-masahiroy@kernel.org
> ---
> Changes in v3:
> - Use stdin instead of a rust/probe.rs file.
> - Fix --out-dir argument.
> - Move RUSTC_BOOTSTRAP to __rustc-option.
> - Add --sysroot and --emit=obj flags.
> - Rebase on top of [PATCH] kbuild: refactor cc-option-yn, cc-disable-warning, rust-option-yn macros
> - Link to v2: https://lore.kernel.org/r/20241008-rustc-option-bootstrap-v2-1-e6e155b8f9f3@google.com


V3 looks good to me.

Miguel,
Will you apply this together with my rustc-option-yn refactoring?


Acked-by: Masahiro Yamada <masahiroy@...nel.org>







--
Best Regards
Masahiro Yamada