linux-kernel - Re: [PATCH] LoongArch: rust: Use rustc option -Zdirect-access-external-data

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Message-ID: <CANiq72m35W=8V77Rcu7MKw29EXEFq102tOL_Myyx1UvMuJYUBA@mail.gmail.com>
Date: Mon, 8 Jul 2024 19:52:44 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: WANG Rui <wangrui@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, 
	Xi Ruoyao <xry111@...111.site>, Xuefeng Li <lixuefeng@...ngson.cn>, loongarch@...ts.linux.dev, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: rust: Use rustc option -Zdirect-access-external-data

On Wed, Jul 3, 2024 at 1:24 PM WANG Rui <wangrui@...ngson.cn> wrote:
>
> -Zdirect-access-external-data is a new Rust compiler option added
> in Rust 1.78, which we use to optimize the access of external data
> in the Linux kernel's Rust code. This patch modifies the Rust code
> in vmlinux to directly access externa data, using PC-REL instead of
> GOT. However, Rust code whithin modules is constrained by the PC-REL
> addressing range and is explicitly set to use an indirect method.
>
> Signed-off-by: WANG Rui <wangrui@...ngson.cn>

I have created a tracking issue for this in
https://github.com/rust-lang/rust/issues/127488 since there was only
the MCP, I hope that helps.

I also added it to our #2 list of unstable features -- please feel
free to ping me in the future if you add others that you will need in
the kernel, I am happy to add the entry even before you send the patch
to the kernel in order to track things (in fact, even if it is not
implemented we can still track it in the other lists).

Acked-by: Miguel Ojeda <ojeda@...nel.org>

Cheers,
Miguel