rust: upgrade to Rust 1.75.0

This is the next upgrade to the Rust toolchain, from 1.74.1 to 1.75.0
(i.e. the latest) [1].

See the upgrade policy [2] and the comments on the first upgrade in
commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2").

# Unstable features

The `const_maybe_uninit_zeroed` unstable feature [3] was stabilized in
Rust 1.75.0, which we were using in the PHYLIB abstractions.

The only unstable features allowed to be used outside the `kernel` crate
are still `new_uninit,offset_of`, though other code to be upstreamed
may increase the list.

Please see [4] for details.

# Other improvements

Rust 1.75.0 stabilized `pointer_byte_offsets` [5] which we could
potentially use as an alternative for `ptr_metadata` in the future.

# Required changes

For this upgrade, no changes were required (i.e. on our side).

# `alloc` upgrade and reviewing

The vast majority of changes are due to our `alloc` fork being upgraded
at once.

There are two kinds of changes to be aware of: the ones coming from
upstream, which we should follow as closely as possible, and the updates
needed in our added fallible APIs to keep them matching the newer
infallible APIs coming from upstream.

Instead of taking a look at the diff of this patch, an alternative
approach is reviewing a diff of the changes between upstream `alloc` and
the kernel's. This allows to easily inspect the kernel additions only,
especially to check if the fallible methods we already have still match
the infallible ones in the new version coming from upstream.

Another approach is reviewing the changes introduced in the additions in
the kernel fork between the two versions. This is useful to spot
potentially unintended changes to our additions.

To apply these approaches, one may follow steps similar to the following
to generate a pair of patches that show the differences between upstream
Rust and the kernel (for the subset of `alloc` we use) before and after
applying this patch:

    # Get the difference with respect to the old version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > old.patch
    git -C linux restore rust/alloc

    # Apply this patch.
    git -C linux am rust-upgrade.patch

    # Get the difference with respect to the new version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > new.patch
    git -C linux restore rust/alloc

Now one may check the `new.patch` to take a look at the additions (first
approach) or at the difference between those two patches (second
approach). For the latter, a side-by-side tool is recommended.

Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1750-2023-12-28 [1]
Link: https://rust-for-linux.com/rust-version-policy [2]
Link: rust-lang/rust#91850 [3]
Link: Rust-for-Linux/linux#2 [4]
Link: rust-lang/rust#96283 [5]
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20231224172128.271447-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/process/changes.rst

@@ -31,7 +31,7 @@ you probably needn't concern yourself with pcmciautils.
 ====================== ===============  ========================================
 GNU C                  5.1              gcc --version
 Clang/LLVM (optional)  11.0.0           clang --version
-Rust (optional)        1.74.1           rustc --version
+Rust (optional)        1.75.0           rustc --version
 bindgen (optional)     0.65.1           bindgen --version
 GNU make               3.82             make --version
 bash                   4.2              bash --version

rust/alloc/alloc.rs

@@ -379,13 +379,20 @@ pub const fn handle_alloc_error(layout: Layout) -> ! {
         panic!("allocation failed");
     }
 
+    #[inline]
     fn rt_error(layout: Layout) -> ! {
         unsafe {
             __rust_alloc_error_handler(layout.size(), layout.align());
         }
     }
 
-    unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
+    #[cfg(not(feature = "panic_immediate_abort"))]
+    unsafe {
+        core::intrinsics::const_eval_select((layout,), ct_error, rt_error)
+    }
+
+    #[cfg(feature = "panic_immediate_abort")]
+    ct_error(layout)
 }
 
 // For alloc test `std::alloc::handle_alloc_error` can be used directly.

rust/alloc/boxed.rs

@@ -161,7 +161,7 @@ use core::marker::Tuple;
 use core::marker::Unsize;
 use core::mem::{self, SizedTypeProperties};
 use core::ops::{
-    CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Generator, GeneratorState, Receiver,
+    CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut, DispatchFromDyn, Receiver,
 };
 use core::pin::Pin;
 use core::ptr::{self, NonNull, Unique};
@@ -211,7 +211,7 @@ impl<T> Box<T> {
     /// ```
     /// let five = Box::new(5);
     /// ```
-    #[cfg(all(not(no_global_oom_handling)))]
+    #[cfg(not(no_global_oom_handling))]
     #[inline(always)]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
@@ -2110,28 +2110,28 @@ impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> {
 #[stable(feature = "pin", since = "1.33.0")]
 impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {}
 
-#[unstable(feature = "generator_trait", issue = "43122")]
-impl<G: ?Sized + Generator<R> + Unpin, R, A: Allocator> Generator<R> for Box<G, A>
+#[unstable(feature = "coroutine_trait", issue = "43122")]
+impl<G: ?Sized + Coroutine<R> + Unpin, R, A: Allocator> Coroutine<R> for Box<G, A>
 where
     A: 'static,
 {
     type Yield = G::Yield;
     type Return = G::Return;
 
-    fn resume(mut self: Pin<&mut Self>, arg: R) -> GeneratorState<Self::Yield, Self::Return> {
+    fn resume(mut self: Pin<&mut Self>, arg: R) -> CoroutineState<Self::Yield, Self::Return> {
         G::resume(Pin::new(&mut *self), arg)
     }
 }
 
-#[unstable(feature = "generator_trait", issue = "43122")]
-impl<G: ?Sized + Generator<R>, R, A: Allocator> Generator<R> for Pin<Box<G, A>>
+#[unstable(feature = "coroutine_trait", issue = "43122")]
+impl<G: ?Sized + Coroutine<R>, R, A: Allocator> Coroutine<R> for Pin<Box<G, A>>
 where
     A: 'static,
 {
     type Yield = G::Yield;
     type Return = G::Return;
 
-    fn resume(mut self: Pin<&mut Self>, arg: R) -> GeneratorState<Self::Yield, Self::Return> {
+    fn resume(mut self: Pin<&mut Self>, arg: R) -> CoroutineState<Self::Yield, Self::Return> {
         G::resume((*self).as_mut(), arg)
     }
 }
@@ -2448,4 +2448,8 @@ impl<T: core::error::Error> core::error::Error for Box<T> {
     fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
         core::error::Error::source(&**self)
     }
+
+    fn provide<'b>(&'b self, request: &mut core::error::Request<'b>) {
+        core::error::Error::provide(&**self, request);
+    }
 }

rust/alloc/lib.rs

@@ -80,6 +80,8 @@
     not(no_sync),
     target_has_atomic = "ptr"
 ))]
+#![cfg_attr(not(bootstrap), doc(rust_logo))]
+#![cfg_attr(not(bootstrap), feature(rustdoc_internals))]
 #![no_std]
 #![needs_allocator]
 // Lints:
@@ -115,7 +117,6 @@
 #![feature(const_eval_select)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_write)]
-#![feature(const_maybe_uninit_zeroed)]
 #![feature(const_pin)]
 #![feature(const_refs_to_cell)]
 #![feature(const_size_of_val)]
@@ -141,7 +142,7 @@
 #![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_uninit_array_transpose)]
 #![feature(pattern)]
-#![feature(pointer_byte_offsets)]
+#![feature(ptr_addr_eq)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
@@ -168,7 +169,7 @@
 //
 // Language features:
 // tidy-alphabetical-start
-#![cfg_attr(not(test), feature(generator_trait))]
+#![cfg_attr(not(test), feature(coroutine_trait))]
 #![cfg_attr(test, feature(panic_update_hook))]
 #![cfg_attr(test, feature(test))]
 #![feature(allocator_internals)]

rust/alloc/raw_vec.rs

@@ -338,10 +338,13 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// The same as `reserve`, but returns on errors instead of panicking or aborting.
     pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         if self.needs_to_grow(len, additional) {
-            self.grow_amortized(len, additional)
-        } else {
-            Ok(())
+            self.grow_amortized(len, additional)?;
+        }
+        unsafe {
+            // Inform the optimizer that the reservation has succeeded or wasn't needed
+            core::intrinsics::assume(!self.needs_to_grow(len, additional));
         }
+        Ok(())
     }
 
     /// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting.
@@ -378,7 +381,14 @@ impl<T, A: Allocator> RawVec<T, A> {
         len: usize,
         additional: usize,
     ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
+        if self.needs_to_grow(len, additional) {
+            self.grow_exact(len, additional)?;
+        }
+        unsafe {
+            // Inform the optimizer that the reservation has succeeded or wasn't needed
+            core::intrinsics::assume(!self.needs_to_grow(len, additional));
+        }
+        Ok(())
     }
 
     /// Shrinks the buffer down to the specified capacity. If the given amount
@@ -569,6 +579,7 @@ fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
 // ensure that the code generation related to these panics is minimal as there's
 // only one location which panics rather than a bunch throughout the module.
 #[cfg(not(no_global_oom_handling))]
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 fn capacity_overflow() -> ! {
     panic!("capacity overflow");
 }

rust/alloc/vec/mod.rs

@@ -1376,7 +1376,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
     /// [`as_ptr`]: Vec::as_ptr
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
-    #[cfg_attr(not(bootstrap), rustc_never_returns_null_ptr)]
+    #[rustc_never_returns_null_ptr]
     #[inline]
     pub fn as_ptr(&self) -> *const T {
         // We shadow the slice method of the same name to avoid going through
@@ -1436,7 +1436,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
     /// [`as_ptr`]: Vec::as_ptr
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
-    #[cfg_attr(not(bootstrap), rustc_never_returns_null_ptr)]
+    #[rustc_never_returns_null_ptr]
     #[inline]
     pub fn as_mut_ptr(&mut self) -> *mut T {
         // We shadow the slice method of the same name to avoid going through
@@ -1565,7 +1565,8 @@ impl<T, A: Allocator> Vec<T, A> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn swap_remove(&mut self, index: usize) -> T {
         #[cold]
-        #[inline(never)]
+        #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+        #[track_caller]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("swap_remove index (is {index}) should be < len (is {len})");
         }
@@ -1606,7 +1607,8 @@ impl<T, A: Allocator> Vec<T, A> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn insert(&mut self, index: usize, element: T) {
         #[cold]
-        #[inline(never)]
+        #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+        #[track_caller]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("insertion index (is {index}) should be <= len (is {len})");
         }
@@ -1667,7 +1669,7 @@ impl<T, A: Allocator> Vec<T, A> {
     #[track_caller]
     pub fn remove(&mut self, index: usize) -> T {
         #[cold]
-        #[inline(never)]
+        #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
         #[track_caller]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("removal index (is {index}) should be < len (is {len})");
@@ -2097,6 +2099,7 @@ impl<T, A: Allocator> Vec<T, A> {
         } else {
             unsafe {
                 self.len -= 1;
+                core::intrinsics::assume(self.len < self.capacity());
                 Some(ptr::read(self.as_ptr().add(self.len())))
             }
         }
@@ -2299,7 +2302,8 @@ impl<T, A: Allocator> Vec<T, A> {
         A: Clone,
     {
         #[cold]
-        #[inline(never)]
+        #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+        #[track_caller]
         fn assert_failed(at: usize, len: usize) -> ! {
             panic!("`at` split index (is {at}) should be <= len (is {len})");
         }

rust/kernel/lib.rs

@@ -14,7 +14,6 @@
 #![no_std]
 #![feature(allocator_api)]
 #![feature(coerce_unsized)]
-#![feature(const_maybe_uninit_zeroed)]
 #![feature(dispatch_from_dyn)]
 #![feature(new_uninit)]
 #![feature(offset_of)]

scripts/min-tool-version.sh

@@ -33,7 +33,7 @@ llvm)
 	fi
 	;;
 rustc)
-	echo 1.74.1
+	echo 1.75.0
 	;;
 bindgen)
 	echo 0.65.1