rust: upgrade to Rust 1.77.0

This is the next upgrade to the Rust toolchain, from 1.76.0 to 1.77.0
(i.e. the latest) [1].

See the upgrade policy [2] and the comments on the first upgrade in
commit 3ed03f4 ("rust: upgrade to Rust 1.68.2").

# Unstable features

The `offset_of` feature (single-field `offset_of!`) that we were using
got stabilized in Rust 1.77.0 [3].

Therefore, now the only unstable features allowed to be used outside the
`kernel` crate is `new_uninit`, though other code to be upstreamed may
increase the list.

Please see [4] for details.

# Required changes

Rust 1.77.0 merged the `unused_tuple_struct_fields` lint into `dead_code`,
thus upgrading it from `allow` to `warn` [5]. In turn, this makes `rustc`
complain about the `ThisModule`'s pointer field being never read. Thus
locally `allow` it for the moment, since we will have users later on
(e.g. Binder needs a `as_ptr` method [6]).

# Other changes

Rust 1.77.0 introduces the `--check-cfg` feature [7], for which there
is a Call for Testing going on [8]. We were requested to test it and
we found it useful [9] -- we will likely enable it in the future.

# `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-1770-2024-03-21 [1]
Link: https://rust-for-linux.com/rust-version-policy [2]
Link: rust-lang/rust#118799 [3]
Link: #2 [4]
Link: rust-lang/rust#118297 [5]
Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-2-08ba9197f637@google.com/#Z31rust:kernel:lib.rs [6]
Link: https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html [7]
Link: rust-lang/rfcs#3013 (comment) [8]
Link: rust-lang/rust#82450 (comment) [9]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20240217002717.57507-1-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)        1.76.0           rustc --version
+Rust (optional)        1.77.0           rustc --version
 bindgen (optional)     0.65.1           bindgen --version
 GNU make               3.82             make --version
 bash                   4.2              bash --version

rust/alloc/alloc.rs

@@ -5,7 +5,7 @@
 #![stable(feature = "alloc_module", since = "1.28.0")]
 
 #[cfg(not(test))]
-use core::intrinsics;
+use core::hint;
 
 #[cfg(not(test))]
 use core::ptr::{self, NonNull};
@@ -210,7 +210,7 @@ impl Global {
                 let new_size = new_layout.size();
 
                 // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
-                intrinsics::assume(new_size >= old_layout.size());
+                hint::assert_unchecked(new_size >= old_layout.size());
 
                 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
                 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
@@ -301,7 +301,7 @@ unsafe impl Allocator for Global {
             // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
             new_size if old_layout.align() == new_layout.align() => unsafe {
                 // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
-                intrinsics::assume(new_size <= old_layout.size());
+                hint::assert_unchecked(new_size <= old_layout.size());
 
                 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
                 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;

rust/alloc/boxed.rs

@@ -26,6 +26,7 @@
 //! Creating a recursive data structure:
 //!
 //! ```
+//! ##[allow(dead_code)]
 //! #[derive(Debug)]
 //! enum List<T> {
 //!     Cons(T, Box<List<T>>),
@@ -194,8 +195,7 @@ mod thin;
 #[fundamental]
 #[stable(feature = "rust1", since = "1.0.0")]
 // The declaration of the `Box` struct must be kept in sync with the
-// `alloc::alloc::box_free` function or ICEs will happen. See the comment
-// on `box_free` for more details.
+// compiler or ICEs will happen.
 pub struct Box<
     T: ?Sized,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,

rust/alloc/lib.rs

@@ -105,7 +105,6 @@
 #![feature(allocator_api)]
 #![feature(array_chunks)]
 #![feature(array_into_iter_constructors)]
-#![feature(array_methods)]
 #![feature(array_windows)]
 #![feature(ascii_char)]
 #![feature(assert_matches)]
@@ -122,7 +121,6 @@
 #![feature(const_size_of_val)]
 #![feature(const_waker)]
 #![feature(core_intrinsics)]
-#![feature(core_panic)]
 #![feature(deprecated_suggestion)]
 #![feature(dispatch_from_dyn)]
 #![feature(error_generic_member_access)]
@@ -132,6 +130,7 @@
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(hasher_prefixfree_extras)]
+#![feature(hint_assert_unchecked)]
 #![feature(inline_const)]
 #![feature(inplace_iteration)]
 #![feature(iter_advance_by)]
@@ -141,6 +140,8 @@
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_uninit_array_transpose)]
+#![feature(non_null_convenience)]
+#![feature(panic_internals)]
 #![feature(pattern)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
@@ -149,7 +150,6 @@
 #![feature(set_ptr_value)]
 #![feature(sized_type_properties)]
 #![feature(slice_from_ptr_range)]
-#![feature(slice_group_by)]
 #![feature(slice_ptr_get)]
 #![feature(slice_ptr_len)]
 #![feature(slice_range)]
@@ -182,6 +182,7 @@
 #![feature(const_ptr_write)]
 #![feature(const_trait_impl)]
 #![feature(const_try)]
+#![feature(decl_macro)]
 #![feature(dropck_eyepatch)]
 #![feature(exclusive_range_pattern)]
 #![feature(fundamental)]

rust/alloc/raw_vec.rs

@@ -4,7 +4,7 @@
 
 use core::alloc::LayoutError;
 use core::cmp;
-use core::intrinsics;
+use core::hint;
 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ptr::{self, NonNull, Unique};
 use core::slice;
@@ -317,7 +317,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// # Panics
     ///
-    /// Panics if the new capacity exceeds `isize::MAX` bytes.
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
     ///
     /// # Aborts
     ///
@@ -358,7 +358,7 @@ impl<T, A: Allocator> RawVec<T, A> {
         }
         unsafe {
             // Inform the optimizer that the reservation has succeeded or wasn't needed
-            core::intrinsics::assume(!self.needs_to_grow(len, additional));
+            hint::assert_unchecked(!self.needs_to_grow(len, additional));
         }
         Ok(())
     }
@@ -381,7 +381,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// # Panics
     ///
-    /// Panics if the new capacity exceeds `isize::MAX` bytes.
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
     ///
     /// # Aborts
     ///
@@ -402,7 +402,7 @@ impl<T, A: Allocator> RawVec<T, A> {
         }
         unsafe {
             // Inform the optimizer that the reservation has succeeded or wasn't needed
-            core::intrinsics::assume(!self.needs_to_grow(len, additional));
+            hint::assert_unchecked(!self.needs_to_grow(len, additional));
         }
         Ok(())
     }
@@ -553,7 +553,7 @@ where
         debug_assert_eq!(old_layout.align(), new_layout.align());
         unsafe {
             // The allocator checks for alignment equality
-            intrinsics::assume(old_layout.align() == new_layout.align());
+            hint::assert_unchecked(old_layout.align() == new_layout.align());
             alloc.grow(ptr, old_layout, new_layout)
         }
     } else {
@@ -591,7 +591,6 @@ fn handle_reserve(result: Result<(), TryReserveError>) {
 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
 // an extra guard for this in case we're running on a platform which can use
 // all 4GB in user-space, e.g., PAE or x32.
-
 #[inline]
 fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
     if usize::BITS < 64 && alloc_size > isize::MAX as usize {

rust/alloc/slice.rs

@@ -53,14 +53,14 @@ pub use core::slice::{from_mut, from_ref};
 pub use core::slice::{from_mut_ptr_range, from_ptr_range};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{from_raw_parts, from_raw_parts_mut};
+#[stable(feature = "slice_group_by", since = "1.77.0")]
+pub use core::slice::{ChunkBy, ChunkByMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{Chunks, Windows};
 #[stable(feature = "chunks_exact", since = "1.31.0")]
 pub use core::slice::{ChunksExact, ChunksExactMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{ChunksMut, Split, SplitMut};
-#[unstable(feature = "slice_group_by", issue = "80552")]
-pub use core::slice::{GroupBy, GroupByMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{Iter, IterMut};
 #[stable(feature = "rchunks", since = "1.31.0")]

rust/alloc/vec/into_iter.rs

@@ -20,6 +20,17 @@ use core::ops::Deref;
 use core::ptr::{self, NonNull};
 use core::slice::{self};
 
+macro non_null {
+    (mut $place:expr, $t:ident) => {{
+        #![allow(unused_unsafe)] // we're sometimes used within an unsafe block
+        unsafe { &mut *(ptr::addr_of_mut!($place) as *mut NonNull<$t>) }
+    }},
+    ($place:expr, $t:ident) => {{
+        #![allow(unused_unsafe)] // we're sometimes used within an unsafe block
+        unsafe { *(ptr::addr_of!($place) as *const NonNull<$t>) }
+    }},
+}
+
 /// An iterator that moves out of a vector.
 ///
 /// This `struct` is created by the `into_iter` method on [`Vec`](super::Vec)
@@ -43,10 +54,12 @@ pub struct IntoIter<
     // the drop impl reconstructs a RawVec from buf, cap and alloc
     // to avoid dropping the allocator twice we need to wrap it into ManuallyDrop
     pub(super) alloc: ManuallyDrop<A>,
-    pub(super) ptr: *const T,
-    pub(super) end: *const T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that
-                              // ptr == end is a quick test for the Iterator being empty, that works
-                              // for both ZST and non-ZST.
+    pub(super) ptr: NonNull<T>,
+    /// If T is a ZST, this is actually ptr+len. This encoding is picked so that
+    /// ptr == end is a quick test for the Iterator being empty, that works
+    /// for both ZST and non-ZST.
+    /// For non-ZSTs the pointer is treated as `NonNull<T>`
+    pub(super) end: *const T,
 }
 
 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
@@ -70,7 +83,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
     /// ```
     #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
     pub fn as_slice(&self) -> &[T] {
-        unsafe { slice::from_raw_parts(self.ptr, self.len()) }
+        unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len()) }
     }
 
     /// Returns the remaining items of this iterator as a mutable slice.
@@ -99,7 +112,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
     }
 
     fn as_raw_mut_slice(&mut self) -> *mut [T] {
-        ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
+        ptr::slice_from_raw_parts_mut(self.ptr.as_ptr(), self.len())
     }
 
     /// Drops remaining elements and relinquishes the backing allocation.
@@ -126,7 +139,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
         // this creates less assembly
         self.cap = 0;
         self.buf = unsafe { NonNull::new_unchecked(RawVec::NEW.ptr()) };
-        self.ptr = self.buf.as_ptr();
+        self.ptr = self.buf;
         self.end = self.buf.as_ptr();
 
         // Dropping the remaining elements can panic, so this needs to be
@@ -138,9 +151,9 @@ impl<T, A: Allocator> IntoIter<T, A> {
 
     /// Forgets to Drop the remaining elements while still allowing the backing allocation to be freed.
     pub(crate) fn forget_remaining_elements(&mut self) {
-        // For th ZST case, it is crucial that we mutate `end` here, not `ptr`.
+        // For the ZST case, it is crucial that we mutate `end` here, not `ptr`.
         // `ptr` must stay aligned, while `end` may be unaligned.
-        self.end = self.ptr;
+        self.end = self.ptr.as_ptr();
     }
 
     #[cfg(not(no_global_oom_handling))]
@@ -162,7 +175,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
                 // say that they're all at the beginning of the "allocation".
                 0..this.len()
             } else {
-                this.ptr.sub_ptr(buf)..this.end.sub_ptr(buf)
+                this.ptr.sub_ptr(this.buf)..this.end.sub_ptr(buf)
             };
             let cap = this.cap;
             let alloc = ManuallyDrop::take(&mut this.alloc);
@@ -189,37 +202,43 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        if self.ptr == self.end {
-            None
-        } else if T::IS_ZST {
-            // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
-            // reducing the `end`.
-            self.end = self.end.wrapping_byte_sub(1);
-
-            // Make up a value of this ZST.
-            Some(unsafe { mem::zeroed() })
+        if T::IS_ZST {
+            if self.ptr.as_ptr() == self.end as *mut _ {
+                None
+            } else {
+                // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
+                // reducing the `end`.
+                self.end = self.end.wrapping_byte_sub(1);
+
+                // Make up a value of this ZST.
+                Some(unsafe { mem::zeroed() })
+            }
         } else {
-            let old = self.ptr;
-            self.ptr = unsafe { self.ptr.add(1) };
+            if self.ptr == non_null!(self.end, T) {
+                None
+            } else {
+                let old = self.ptr;
+                self.ptr = unsafe { old.add(1) };
 
-            Some(unsafe { ptr::read(old) })
+                Some(unsafe { ptr::read(old.as_ptr()) })
+            }
         }
     }
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         let exact = if T::IS_ZST {
-            self.end.addr().wrapping_sub(self.ptr.addr())
+            self.end.addr().wrapping_sub(self.ptr.as_ptr().addr())
         } else {
-            unsafe { self.end.sub_ptr(self.ptr) }
+            unsafe { non_null!(self.end, T).sub_ptr(self.ptr) }
         };
         (exact, Some(exact))
     }
 
     #[inline]
     fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
         let step_size = self.len().min(n);
-        let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
+        let to_drop = ptr::slice_from_raw_parts_mut(self.ptr.as_ptr(), step_size);
         if T::IS_ZST {
             // See `next` for why we sub `end` here.
             self.end = self.end.wrapping_byte_sub(step_size);
@@ -261,7 +280,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
             // Safety: `len` indicates that this many elements are available and we just checked that
             // it fits into the array.
             unsafe {
-                ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, len);
+                ptr::copy_nonoverlapping(self.ptr.as_ptr(), raw_ary.as_mut_ptr() as *mut T, len);
                 self.forget_remaining_elements();
                 return Err(array::IntoIter::new_unchecked(raw_ary, 0..len));
             }
@@ -270,7 +289,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // Safety: `len` is larger than the array size. Copy a fixed amount here to fully initialize
         // the array.
         return unsafe {
-            ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, N);
+            ptr::copy_nonoverlapping(self.ptr.as_ptr(), raw_ary.as_mut_ptr() as *mut T, N);
             self.ptr = self.ptr.add(N);
             Ok(raw_ary.transpose().assume_init())
         };
@@ -288,26 +307,33 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // Also note the implementation of `Self: TrustedRandomAccess` requires
         // that `T: Copy` so reading elements from the buffer doesn't invalidate
         // them for `Drop`.
-        unsafe { if T::IS_ZST { mem::zeroed() } else { ptr::read(self.ptr.add(i)) } }
+        unsafe { if T::IS_ZST { mem::zeroed() } else { self.ptr.add(i).read() } }
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     #[inline]
     fn next_back(&mut self) -> Option<T> {
-        if self.end == self.ptr {
-            None
-        } else if T::IS_ZST {
-            // See above for why 'ptr.offset' isn't used
-            self.end = self.end.wrapping_byte_sub(1);
-
-            // Make up a value of this ZST.
-            Some(unsafe { mem::zeroed() })
+        if T::IS_ZST {
+            if self.end as *mut _ == self.ptr.as_ptr() {
+                None
+            } else {
+                // See above for why 'ptr.offset' isn't used
+                self.end = self.end.wrapping_byte_sub(1);
+
+                // Make up a value of this ZST.
+                Some(unsafe { mem::zeroed() })
+            }
         } else {
-            self.end = unsafe { self.end.sub(1) };
+            if non_null!(self.end, T) == self.ptr {
+                None
+            } else {
+                let new_end = unsafe { non_null!(self.end, T).sub(1) };
+                *non_null!(mut self.end, T) = new_end;
 
-            Some(unsafe { ptr::read(self.end) })
+                Some(unsafe { ptr::read(new_end.as_ptr()) })
+            }
         }
     }
 
@@ -333,7 +359,11 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
     fn is_empty(&self) -> bool {
-        self.ptr == self.end
+        if T::IS_ZST {
+            self.ptr.as_ptr() == self.end as *mut _
+        } else {
+            self.ptr == non_null!(self.end, T)
+        }
     }
 }