linux-kernel - Re: [PATCH] Kbuild: add RUSTC

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Message-ID: <CANiq72mCuqCE3fA2jgaaA4fyj1kNzYm61C2600vAf0CT5=JP0A@mail.gmail.com>
Date: Tue, 8 Oct 2024 22:05:46 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Alice Ryhl <aliceryhl@...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] Kbuild: add RUSTC_BOOTSTRAP to rustc-option

On Tue, Oct 8, 2024 at 8:45 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Really?
>
> $(shell ...) inherits env variables in my understanding.

I mean the Make-exported variables (not the external environment),
i.e. `RUSTC_BOOTSTRAP=1` that we export in the main `Makefile`. Those
are not exported into the `shell` function.

However, it turns out this changes in GNU Make 4.4 in commit
98da874c4303 ("[SV 10593] Export variables to $(shell ...) commands"):

    * WARNING: Backward-incompatibility!
      Previously makefile variables marked as export were not exported
to commands
      started by the $(shell ...) function.  Now, all exported variables are
      exported to $(shell ...).  If this leads to recursion during
expansion, then
      for backward-compatibility the value from the original
environment is used.
      To detect this change search for 'shell-export' in the .FEATURES variable.

And indeed:

    export A := .PHONY: a
    $(shell echo $$A)
    a: ; @echo exported

Gives:

    $ make-4.3
    make: 'a' is up to date.

    $ make-4.4.1
    exported

Cheers,
Miguel