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

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Message-ID: <e4a8e9c5-8c74-4fa3-87de-db25356e450b@ryhl.io>
Date: Tue, 8 Oct 2024 20:59:31 +0200
From: Alice Ryhl <alice@...l.io>
To: Alice Ryhl <aliceryhl@...gle.com>, Masahiro Yamada
 <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>
Cc: 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 10/8/24 4:24 PM, Alice Ryhl wrote:
> On Tue, Oct 8, 2024 at 3:49 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
>>
>> When using unstable features with the Rust compiler, you must either use
>> a nightly compiler release or set the RUSTC_BOOTSTRAP environment
>> variable. Otherwise, the compiler will emit a compiler error. This
>> environment variable is missing when rustc-option is executed, so add
>> the environment variable.
>>
>> This change is necessary to avoid two kinds of problems:
>>
>> 1. When using rustc-option to test whether a -Z flag is available, the
>>     check will always fail, even if the flag is available.
>> 2. If KBUILD_RUSTFLAGS happens to contain any -Z flags from the
>>     environment, even if unrelated to the flag being tested, then all
>>     invocations of rustc-option everywhere will fail.
>>
>> I was not actually able to trigger the second kind of problem with the
>> makefiles that exist today, but it seems like it could easily start
>> being a problem due to complicated interactions between changes. It is
>> better to fix this now so it doesn't surprise us later.
>>
>> I added the flag under try-run as this seemed like the easiest way to
>> make sure that the fix applies to all variations of rustc-option,
>> including new ones added in the future.
>>
>> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> 
> It should be "export". Also, this doesn't seem to be sufficient at
> all. Now I'm running into this error:
> 
> make[1]: Entering directory '/home/aliceryhl/lout'
> warning: ignoring --out-dir flag due to -o flag
> 
> 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`
> 
> error: aborting due to 1 previous error; 1 warning emitted
> 
> For more information about this error, try `rustc --explain E0463`.
> 
> I think this patch is going to need more work. Sorry for sending it prematurely.
v2 is here:
https://lore.kernel.org/all/20241008-rustc-option-bootstrap-v2-1-e6e155b8f9f3@google.com/