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Date:   Fri, 1 Dec 2023 01:52:25 -0800
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Alice Ryhl <aliceryhl@google.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Carlos Llamas <cmllamas@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org,
        rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>
Subject: Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`
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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