Re: [PATCH v5 6/6] rust: use strict provenance APIs

[Tamir Duberstein]

On Mon, Mar 17, 2025 at 1:50 PM Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
>
> On Mon Mar 17, 2025 at 3:23 PM CET, Tamir Duberstein wrote:
> > Throughout the tree, use the strict provenance APIs stabilized in Rust
> > 1.84.0[1]. Retain backwards-compatibility by introducing forwarding
> > functions at the `kernel` crate root along with polyfills for rustc <
> > 1.84.0.
> >
> > Use `#[allow(clippy::incompatible_msrv)]` to avoid warnings on rustc <
> > 1.84.0 as our MSRV is 1.78.0.
> >
> > In the `kernel` crate, enable the strict provenance lints on rustc >=
> > 1.84.0; do this in `lib.rs` rather than `Makefile` to avoid introducing
> > compiler flags that are dependent on the rustc version in use.
> >
> > Link: https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html#strict-provenance-apis [1]
> > Suggested-by: Benno Lossin <benno.lossin@xxxxxxxxx>
> > Link: https://lore.kernel.org/all/D8EIXDMRXMJP.36TFCGWZBRS3Y@xxxxxxxxx/
> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
>
> One comment below, with that fixed:
>
> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
>
> > ---
> >  init/Kconfig           |   3 ++
> >  rust/kernel/alloc.rs   |   2 +-
> >  rust/kernel/devres.rs  |   4 +-
> >  rust/kernel/io.rs      |  14 +++----
> >  rust/kernel/lib.rs     | 108 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  rust/kernel/of.rs      |   2 +-
> >  rust/kernel/pci.rs     |   4 +-
> >  rust/kernel/str.rs     |  16 +++-----
> >  rust/kernel/uaccess.rs |  12 ++++--
> >  9 files changed, 138 insertions(+), 27 deletions(-)
>
>
> > +#[cfg(not(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE))]
> > +mod strict_provenance {
> > +    /// Gets the "address" portion of the pointer.
> > +    ///
> > +    /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.addr.
> > +    #[inline]
> > +    pub fn addr<T>(ptr: *const T) -> usize {
> > +        // This is core's implementation from
> > +        // https://github.com/rust-lang/rust/commit/4291332175d12e79e6061cdc3f5dccac2e28b969 through
> > +        // https://github.com/rust-lang/rust/blob/1.84.0/library/core/src/ptr/const_ptr.rs#L172
> > +        // which is the first version that satisfies `CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE`.
> > +        #[allow(clippy::undocumented_unsafe_blocks)]
> > +        unsafe {
> > +            #[allow(clippy::transmutes_expressible_as_ptr_casts)]
> > +            core::mem::transmute(ptr.cast::<()>())
> > +        }
>
> I think we should just use `ptr as usize` here instead. It's going away
> at some point and it will only affect optimizations (I don't even know
> if they exist at the moment) of old versions.

Why get cute? I'd rather defer to the standard library.