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

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Message-ID: <CAGSQo02oVWxazut2nyh-9K9gK+937zKCfYMBkT4EQE2CddvZtg@mail.gmail.com>
Date: Tue, 8 Oct 2024 10:43:29 -0700
From: Matthew Maurer <mmaurer@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	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 v2] Kbuild: fix issues with rustc-option

Thanks for catching this - I had a specialized toolchain enabled which
didn't exercise the `RUSTC_BOOTSTRAP` issue, and without an unexpected
failure, didn't see the `--out-dir` flag conflict after I got the
request to add it.

Reviewed-By: Matthew Maurer <mmaurer@...gle.com>


On Tue, Oct 8, 2024 at 10:32 AM 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
>
> 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@...gle.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
> ---
>  rust/probe.rs             | 7 +++++++
>  scripts/Makefile.compiler | 5 +++--
>  2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/rust/probe.rs b/rust/probe.rs
> new file mode 100644
> index 000000000000..bf024e394408
> --- /dev/null
> +++ b/rust/probe.rs
> @@ -0,0 +1,7 @@
> +//! Nearly empty file passed to rustc-option by Make.
> +//!
> +//! The no_core attribute is needed because rustc-option otherwise fails due to
> +//! not being able to find the core part of the standard library.
> +
> +#![feature(no_core)]
> +#![no_core]
> diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> index 057305eae85c..08d5b7177ea8 100644
> --- a/scripts/Makefile.compiler
> +++ b/scripts/Makefile.compiler
> @@ -21,6 +21,7 @@ TMPOUT = $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_$$$$
>  # automatically cleaned up.
>  try-run = $(shell set -e;              \
>         TMP=$(TMPOUT)/tmp;              \
> +       export RUSTC_BOOTSTRAP=1;       \
>         trap "rm -rf $(TMPOUT)" EXIT;   \
>         mkdir -p $(TMPOUT);             \
>         if ($(1)) >/dev/null 2>&1;      \
> @@ -76,7 +77,7 @@ ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))
>  # __rustc-option
>  # Usage: MY_RUSTFLAGS += $(call __rustc-option,$(RUSTC),$(MY_RUSTFLAGS),-Cinstrument-coverage,-Zinstrument-coverage)
>  __rustc-option = $(call try-run,\
> -       $(1) $(2) $(3) --crate-type=rlib /dev/null --out-dir=$$TMPOUT -o "$$TMP",$(3),$(4))
> +       $(1) $(2) $(3) --crate-type=rlib $(srctree)/rust/probe.rs --out-dir=$$TMP,$(3),$(4))
>
>  # rustc-option
>  # Usage: rustflags-y += $(call rustc-option,-Cinstrument-coverage,-Zinstrument-coverage)
> @@ -86,4 +87,4 @@ rustc-option = $(call __rustc-option, $(RUSTC),\
>  # rustc-option-yn
>  # Usage: flag := $(call rustc-option-yn,-Cinstrument-coverage)
>  rustc-option-yn = $(call try-run,\
> -       $(RUSTC) $(KBUILD_RUSTFLAGS) $(1) --crate-type=rlib /dev/null --out-dir=$$TMPOUT -o "$$TMP",y,n)
> +       $(RUSTC) $(KBUILD_RUSTFLAGS) $(1) --crate-type=rlib $(srctree)/rust/probe.rs --out-dir=$$TMP,y,n)
>
> ---
> base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
> change-id: 20241008-rustc-option-bootstrap-607e5bf3114c
>
> Best regards,
> --
> Alice Ryhl <aliceryhl@...gle.com>
>