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

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Message-ID: <CAH5fLgiOe1ECCwE1cwczsT13iPyymdUTbV-9ZHeDrp_OGq5FgQ@mail.gmail.com>
Date: Thu, 1 Aug 2024 20:26:42 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Jason Baron <jbaron@...mai.com>, Ard Biesheuvel <ardb@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
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	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	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>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, "Peter Zijlstra (Intel)" <peterz@...radaed.org>, 
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	Conor Dooley <conor.dooley@...rochip.com>, Samuel Holland <samuel.holland@...ive.com>, 
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	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 Thu, Aug 1, 2024 at 12:28 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Jul 31, 2024 at 11:34:13PM +0200, Alice Ryhl wrote:
>
> > > Please work harder to not have to duplicate stuff like this.
> >
> > I really didn't want to duplicate it, but it's very hard to find a
> > performant alternative. Is there any way we could accept duplication
> > only in the cases where an 'i' parameter is used? I don't have the
> > choice of using a Rust helper for 'i' parameters.
> >
> > Perhaps one option could be to put the Rust code inside jump_label.h
> > and have the header file evaluate to either C or Rust depending on the
> > value of some #ifdefs?
> >
> > #ifndef RUST_ASM
> > /* existing C code goes here */
> > #endif
> > #ifdef RUST_ASM
> > // rust code goes here
> > #endif
> >
> > That way the duplication is all in a single file. It would also avoid
> > the need for duplicating the nop5 string, as the Rust case is still
> > going through the C preprocessor and can use the existing #define.
>
> I suppose that is slightly better, but ideally you generate the whole of
> the Rust thing from the C version. After all, Clang can already parse
> this.
>
> That said, with the below patch, I think you should be able to reuse the
> JUMP_TABLE_ENTRY macro like:
>
>         JUMP_TABLE_ENTRY({0}, {1}, {2} + {3})

Yeah, I think this can work. I will submit a follow-up patch that
removes the duplication soon.

Alice