linux-kernel - Re: [PATCH v3] kbuild: rust: add PROCMACROLDFLAGS

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Message-ID: <CAH5fLghFZTG2X_mYE2yGJwPM31NrJdkA-cpZTCYsdghR8YdY8Q@mail.gmail.com>
Date: Wed, 13 Nov 2024 14:34:03 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, HONG Yifan <elsk@...gle.com>, 
	Alex Gaynor <alex.gaynor@...il.com>, Jonathan Corbet <corbet@....net>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, linux-kbuild@...r.kernel.org, 
	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>, rust-for-linux@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	patches@...ts.linux.dev
Subject: Re: [PATCH v3] kbuild: rust: add PROCMACROLDFLAGS

On Tue, Nov 12, 2024 at 7:45 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> From: HONG Yifan <elsk@...gle.com>
>
> These are flags to be passed when linking proc macros for the Rust
> toolchain. If unset, it defaults to $(KBUILD_HOSTLDFLAGS).
>
> This is needed because the list of flags to link hostprogs is not
> necessarily the same as the list of flags used to link libmacros.so.
> When we build proc macros, we need the latter, not the former (e.g. when
> using a Rust compiler binary linked to a different C library than host
> programs).
>
> To distinguish between the two, introduce this new variable to stand
> out from KBUILD_HOSTLDFLAGS used to link other host progs.
>
> Signed-off-by: HONG Yifan <elsk@...gle.com>
> Link: https://lore.kernel.org/r/20241017210430.2401398-2-elsk@google.com
> [ v3:
>
>   - `export`ed the variable. Otherwise it would not be visible in
>     `rust/Makefile`.

Despite the missing export, the previous version worked for us too.
I'm not sure why that is.

>   - Removed "additional" from the documentation and commit message,
>     since this actually replaces the other flags, unlike other cases.
>
>   - Added example of use case to documentation and commit message.
>     Thanks Alice for the details on what Google needs!
>
>   - Instead of `HOSTLDFLAGS`, used `KBUILD_HOSTLDFLAGS` as the fallback
>     to preserve the previous behavior as much as possible, as discussed
>     with Alice/Yifan. Thus moved the variable down too (currently we
>     do not modify `KBUILD_HOSTLDFLAGS` elsewhere) and avoided
>     mentioning `HOSTLDFLAGS` directly in the documentation.
>
>   - Fixed documentation header formatting.
>
>   - Reworded slightly.
>
>          - Miguel ]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

Tested-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>