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

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Message-ID: <CAH5fLgg9ntk4Zn-kBB-XLHaqHz4NXNhrS526HahBG9T2MhUx5Q@mail.gmail.com>
Date: Mon, 2 Sep 2024 16:19:25 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.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 2, 2024 at 4:18 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> 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

That's a trivial matter. Adding the unsafe block makes it work on stable.

Alice