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

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Message-ID: <CAK7LNATxzHKNm+z9_BkJZf0=tA_iSQWowB6j3ef6GVP8M+mvyQ@mail.gmail.com>
Date: Wed, 9 Oct 2024 19:43:58 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Matthew Maurer <mmaurer@...gle.com>, 
	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

On Wed, Oct 9, 2024 at 7:01 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Wed, Oct 9, 2024 at 11:23 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > Miguel, can you link this issue? I don't think I saw it.
>
> https://github.com/Rust-for-Linux/linux/pull/1087#issuecomment-2218445303
>
> (It was in the Lore message I linked yesterday, sorry, I should have
> been more explicit)
>
> > Masahiro, are you able to clarify how to pass TMPOUT to rustc?
> >
> > __rustc-option = $(call try-run2,\
> >        $(1) $(2) $(3) --crate-type=rlib $(srctree)/rust/probe.rs
> > --out-dir=$(TMPOUT),$(3),$(4))
> >
> > Should I use $(TMPOUT) or $$TMPOUT for this case? Right now, only TMP
> > is defined inside try-run. I am assuming that there is a reason for
> > having TMP be defined in try-run, rather than just using $(TMP)
> > everywhere. Does the same reason apply to TMPOUT? Should I add a
> > TMPOUT=$(TMPOUT) inside try-run?
>
> `TMPOUT` is defined already in that `Makefile`, thus you can directly
> expand it. However, `TMP` is defined inside the `shell` function, and
> thus `$$TMP` is used so that that script (inside the `shell`) expands
> it instead.
>
> This is why Masahiro was saying that the `TMPOUT=$(TMPOUT)` was
> unnecessary, i.e. it would work, but we can just expand it directly.
>
> Something like this, combining everything [1] seems to work for me.
>
> i.e. passing the file inline, `RUSTC_BOOTSTRAP=1`, avoiding an output
> file, keeping `--out-dir` for intermediates files. I added using a
> null sysroot too (and skipping if already given, since that is an
> error).
>
> I will test it a bit more with KASAN etc.
>
> Cheers,
> Miguel
>
> [1]
>
> diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> index 057305eae85c..3ce6a808764a 100644
> --- a/scripts/Makefile.compiler
> +++ b/scripts/Makefile.compiler
> @@ -76,7 +76,9 @@ 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))
> +       echo '//!\n#![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)
>


Could you please add a comment line to remember the future clean-up?

e.g.

# TODO: remove RUSTC_BOOTSTRAP=1 when we raise the minimum GNU Make
version to 4.4



I also like the commit description to record that
RUSTC_BOOTSTRAP=1 is needed for GNU Make prier to commit 98da874c4303
("[SV 10593] Export variables to $(shell ...) commands"), i.e.,
GNU Make 4.3 or older.




--
Best Regards
Masahiro Yamada