linux-kernel - Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`

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Message-ID: <ZWms2SJ5uzYzw48p@Boquns-Mac-mini.home>
Date:   Fri, 1 Dec 2023 01:52:25 -0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`

On Fri, Dec 01, 2023 at 10:00:39AM +0100, Peter Zijlstra wrote:
> On Thu, Nov 30, 2023 at 07:25:01AM -0800, Boqun Feng wrote:
> 
> > seems to me, the plan for this is something like below:
> > 
> > 	asm!(
> > 		"cmp {}, 42",
> > 		"jeq {}",
> > 		in(reg) val,
> > 		label { println!("a"); },
> > 		fallthrough { println!("b"); }
> >     	);
> 
> Because rust has horrible syntax I can't parse, I can't tell if this is
> useful or not :/ Can this be used to implement arch_static_branch*() ?

I should think so:

	asm!("jmp {l_yes}", // jump to l_yes
	     "..."          // directives are supported
	     l_yes { return true; } // label "l_yes"
	     fallthrough { return false; } // otherwise return false
	)

Rust uses LLVM backend, so the inline asm should have the same ability
of clang.

But as I said, AFAIK jumping to label hasn't been implemented yet.

Regards,
Boqun