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

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

[Alice Ryhl]

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@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.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

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
---
 scripts/Makefile.compiler | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
index 73d611d383b2..e0842496d26e 100644
--- a/scripts/Makefile.compiler
+++ b/scripts/Makefile.compiler
@@ -73,8 +73,11 @@ 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)
+# TODO: remove RUSTC_BOOTSTRAP=1 when we raise the minimum GNU Make version to 4.4
 __rustc-option = $(call try-run,\
-	$(1) $(2) $(3) --crate-type=rlib /dev/null --out-dir=$$TMPOUT -o "$$TMP",$(3),$(4))
+	echo '#![allow(missing_docs)]#![feature(no_core)]#![no_core]' | RUSTC_BOOTSTRAP=1\
+	$(1) --sysroot=/dev/null $(filter-out --sysroot=/dev/null,$(2)) $(3)\
+	--crate-type=rlib --out-dir=$(TMPOUT) --emit=obj=- - >/dev/null,$(3),$(4))
 
 # rustc-option
 # Usage: rustflags-y += $(call rustc-option,-Cinstrument-coverage,-Zinstrument-coverage)

---
base-commit: 1ba227507e8459788bf0e192700347c941e3e218
change-id: 20241008-rustc-option-bootstrap-607e5bf3114c

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>

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

[Masahiro Yamada]

On Wed, Oct 9, 2024 at 8:42 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
>
> 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@kernel.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@google.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@kernel.org>







--
Best Regards
Masahiro Yamada

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

[Miguel Ojeda]

On Wed, Oct 9, 2024 at 1:42 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> Note that RUSTC_BOOTSTRAP is also defined in the top-level Makefile, but
> its value is unfortunately *not* inherited from the environment. That

I would perhaps say ", but Make-exported variables are not inherited"
or similar to be a bit more precise (because the external environment,
as in the `make` environment, is exported unlike those variables).

> 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.

The error message mentions `std`, so to clarify I would perhaps add
".... standard library (i.e. `core`)" or similar, i.e. one could think
`no_std` is enough otherwise (which would be better if we could, since
it is stable unlike `no_core`, but we don't want it here either).

> 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).

"the resulting object file" (i.e. the rlib is not written even if we
wrote to a file).

> I verified that the Kconfig version of rustc-option doesn't have the
> same issues.

Thanks for checking this. We may want to make it closer to what we do
her, but that can be done later.

Cheers,
Miguel

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

[Miguel Ojeda]

On Wed, Oct 9, 2024 at 2:52 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> V3 looks good to me.
>
> Miguel,
> Will you apply this together with my rustc-option-yn refactoring?
>
> Acked-by: Masahiro Yamada <masahiroy@kernel.org>

Sure -- thanks!

Cheers,
Miguel

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

[Alice Ryhl]

On Wed, Oct 9, 2024 at 2:53 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Wed, Oct 9, 2024 at 1:42 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > Note that RUSTC_BOOTSTRAP is also defined in the top-level Makefile, but
> > its value is unfortunately *not* inherited from the environment. That
>
> I would perhaps say ", but Make-exported variables are not inherited"
> or similar to be a bit more precise (because the external environment,
> as in the `make` environment, is exported unlike those variables).
>
> > 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.
>
> The error message mentions `std`, so to clarify I would perhaps add
> ".... standard library (i.e. `core`)" or similar, i.e. one could think
> `no_std` is enough otherwise (which would be better if we could, since
> it is stable unlike `no_core`, but we don't want it here either).
>
> > 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).
>
> "the resulting object file" (i.e. the rlib is not written even if we
> wrote to a file).
>
> > I verified that the Kconfig version of rustc-option doesn't have the
> > same issues.
>
> Thanks for checking this. We may want to make it closer to what we do
> her, but that can be done later.
>
> Cheers,
> Miguel

That all sounds good to me. Feel free to make the suggested rewordings
when you apply this. Otherwise I can send a v4 if you prefer.

Alice

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

[Miguel Ojeda]

On Wed, Oct 9, 2024 at 2:58 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> That all sounds good to me. Feel free to make the suggested rewordings
> when you apply this. Otherwise I can send a v4 if you prefer.

No worries (but thanks!).

Cheers,
Miguel

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

[Miguel Ojeda]

On Wed, Oct 9, 2024 at 1:42 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
>
> 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@kernel.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Applied to `rust-fixes` -- thanks everyone!

    [ Reworded as discussed in the list. - Miguel ]

Cheers,
Miguel