linux-kernel - Re: [PATCH v5 13/26] rust: alloc: implement kernel `Vec` type

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAH5fLgjDMuiR07jc=aa-3radEOgU8iMn-u+XttepuWr9r_doYQ@mail.gmail.com>
Date: Thu, 15 Aug 2024 09:30:36 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...sung.com, akpm@...ux-foundation.org, 
	daniel.almeida@...labora.com, faith.ekstrand@...labora.com, 
	boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com, 
	zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com, 
	ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 13/26] rust: alloc: implement kernel `Vec` type

On Thu, Aug 15, 2024 at 12:46 AM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On Wed, Aug 14, 2024 at 10:42:28AM +0200, Alice Ryhl wrote:
> > > +#[macro_export]
> > > +macro_rules! kvec {
> > > +    () => (
> > > +        {
> > > +            $crate::alloc::KVec::new()
> > > +        }
> > > +    );
> > > +    ($elem:expr; $n:expr) => (
> > > +        {
> > > +            $crate::alloc::KVec::from_elem($elem, $n, GFP_KERNEL)
> > > +        }
> > > +    );
> > > +    ($($x:expr),+ $(,)?) => (
> > > +        {
> > > +            match $crate::alloc::KBox::new([$($x),+], GFP_KERNEL) {
> > > +                Ok(b) => Ok($crate::alloc::KBox::into_vec(b)),
> > > +                Err(e) => Err(e),
> >
> > Hmm. This currently generates code that:
> >
> > 1. Creates the array.
> > 2. Allocates the memory.
> > 3. Moves the array into the box.
> >
> > Whereas the stdlib macro swaps step 1 and 2.
>
> Isn't stdlib [1] doing the same thing I do?
>
> [1] https://doc.rust-lang.org/1.80.1/src/alloc/macros.rs.html#49

Stdlib is using something called #[rustc_box] which has the effect I described.

> > You can do the same by utilizing new_uninit. A sketch:
> >
> > match KBox::<[_; _]>::new_uninit(GFP_KERNEL) {
>
> How do we get the size here? `#![feature(generic_arg_infer)]` seems to be
> unstable.

It probably works if you don't specify the type at all:
`KBox::new_uninit`. But you should double check.

> >     Ok(b) => Ok(KVec::from(KBox::write(b, [$($x),+]))),
> >     Err(e) => Err(e),
> > }