linux-kernel - Re: [PATCH v2] rust: add global lock support

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Message-ID: <ZtXJGzse8CN30Cp3@Boquns-Mac-mini.local>
Date: Mon, 2 Sep 2024 07:18:03 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Benno Lossin <benno.lossin@...ton.me>, 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>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: add global lock support

On Mon, Sep 02, 2024 at 01:42:53PM +0200, Alice Ryhl wrote:
> On Mon, Sep 2, 2024 at 1:37 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > On Fri, Aug 30, 2024 at 3:22 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> > >
> > > On 30.08.24 07:34, Alice Ryhl wrote:
> > > > On Thu, Aug 29, 2024 at 8:17 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> > > >>
> > > >> On 27.08.24 10:41, Alice Ryhl wrote:
> > > >>> For architectures that don't use all-zeros for the unlocked case, we
> > > >>> will most likely have to hard-code the correct representation on the
> > > >>> Rust side.
> > > >>
> > > >> You mean in `unsafe_const_init`?
> > > >
> > > > No, I mean we would have `unsafe_const_new` directly set `state` to
> > > > the right value and let `unsafe_const_init` be a no-op.
> > >
> > > But how do you set the right value of a list_head? The value will be
> > > moved.
> >
> > Right ... we probably can't get around needing a macro. Can statics
> > even reference themselves?
> 
> Looks like they can:
> 
> use std::ptr::addr_of;
> 
> struct MyStruct {
>     ptr: *const MyStruct,
> }
> 
> static mut MY_STRUCT: MyStruct = MyStruct {
>     ptr: addr_of!(MY_STRUCT),

I'm guessing you're using nightly or new enough rustc, in the current
stable (1.80), this would complain using static mut without unsafe:

	https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=2954daab193caf14d1fb91492dcf325a

, which gets changed recently:

	https://github.com/rust-lang/rust/pull/125834

Regards,
Boqun

> };
> 
> Alice