linux-kernel - Re: [PATCH v4 1/2] rust: add static_key

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Message-ID: <20240731170508.GJ33588@noisy.programming.kicks-ass.net>
Date: Wed, 31 Jul 2024 19:05:08 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
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	Alex Gaynor <alex.gaynor@...il.com>,
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	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	linux-trace-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
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	linux-riscv@...ts.infradead.org,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>, Bibo Mao <maobibo@...ngson.cn>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev
Subject: Re: [PATCH v4 1/2] rust: add static_key_false

On Fri, Jun 28, 2024 at 01:23:31PM +0000, Alice Ryhl wrote:

>  rust/kernel/arch/arm64/jump_label.rs     | 34 ++++++++++++++++++++++++++++
>  rust/kernel/arch/loongarch/jump_label.rs | 35 +++++++++++++++++++++++++++++
>  rust/kernel/arch/mod.rs                  | 24 ++++++++++++++++++++
>  rust/kernel/arch/riscv/jump_label.rs     | 38 ++++++++++++++++++++++++++++++++
>  rust/kernel/arch/x86/jump_label.rs       | 35 +++++++++++++++++++++++++++++
>  rust/kernel/lib.rs                       |  2 ++
>  rust/kernel/static_key.rs                | 32 +++++++++++++++++++++++++++
>  scripts/Makefile.build                   |  2 +-
>  8 files changed, 201 insertions(+), 1 deletion(-)

So I really find the amount of duplicated asm offensive. Is is far too
easy for any of this to get out of sync.

> diff --git a/rust/kernel/arch/x86/jump_label.rs b/rust/kernel/arch/x86/jump_label.rs
> new file mode 100644
> index 000000000000..383bed273c50
> --- /dev/null
> +++ b/rust/kernel/arch/x86/jump_label.rs
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! X86 Rust implementation of jump_label.h
> +
> +/// x86 implementation of arch_static_branch
> +#[macro_export]
> +#[cfg(target_arch = "x86_64")]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        core::arch::asm!(
> +            r#"
> +            1: .byte 0x0f,0x1f,0x44,0x00,0x00
> +
> +            .pushsection __jump_table,  "aw"
> +            .balign 8
> +            .long 1b - .
> +            .long {0} - .
> +            .quad {1} + {2} + {3} - .
> +            .popsection
> +            "#,
> +            label {
> +                break 'my_label true;
> +            },
> +            sym $key,
> +            const ::core::mem::offset_of!($keytyp, $field),
> +            const $crate::arch::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}

Note that this uses the forced 5 byte version, and not the dynamic sized
one. On top of that it hard-codes the nop5 string :/

Please work harder to not have to duplicate stuff like this.

NAK.