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

[Matthew Maurer]

Err, slight amendment - I think you want `-o $$TMP`, and not
`--out-dir $$TMPOUT`

You definitely don't want `--out-dir $$TMP`, but the other two
settings above would be defensible.


On Tue, Oct 8, 2024 at 10:43 AM Matthew Maurer <mmaurer@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
>
>
> On Tue, Oct 8, 2024 at 10:32 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx
> > ---
> >  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@xxxxxxxxxx>
> >