rust: upgrade to Rust 1.76.0rust-6.9

This is the next upgrade to the Rust toolchain, from 1.75.0 to 1.76.0
(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

No unstable features that we use were stabilized in Rust 1.76.0.

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 [3] for details.

# Required changes

`rustc` (and others) now warns when it cannot connect to the Make
jobserver, thus mark those invocations as recursive as needed. Please
see the previous commit for details.

# Other changes

Rust 1.76.0 does not emit the `.debug_pub{names,types}` sections anymore
for DWARFv4 [4][5]. For instance, in the uncompressed debug info case,
this debug information took:

    samples/rust/rust_minimal.o   ~64 KiB (~18% of total object size)
    rust/kernel.o                 ~92 KiB (~15%)
    rust/core.o                  ~114 KiB ( ~5%)

In the compressed debug info (zlib) case:

    samples/rust/rust_minimal.o   ~11 KiB (~6%)
    rust/kernel.o                 ~17 KiB (~5%)
    rust/core.o                   ~21 KiB (~1.5%)

In addition, the `rustc_codegen_gcc` backend now does not emit the
`.eh_frame` section when compiling under `-Cpanic=abort` [6], thus
removing the need for the patch in the CI to compile the kernel [7].
Moreover, it also now emits the `.comment` section too [6].

# `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-1760-2024-02-08 [1]
Link: https://rust-for-linux.com/rust-version-policy [2]
Link: https://github.com/Rust-for-Linux/linux/issues/2 [3]
Link: https://github.com/rust-lang/compiler-team/issues/688 [4]
Link: https://github.com/rust-lang/rust/pull/117962 [5]
Link: https://github.com/rust-lang/rust/pull/118068 [6]
Link: https://github.com/Rust-for-Linux/ci-rustc_codegen_gcc [7]
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240217002638.57373-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

2 files changed, 62 insertions, 19 deletions

diff --git a/rust/alloc/vec/into_iter.rs b/rust/alloc/vec/into_iter.rs
index aac0ec16aef1..136bfe94af6c 100644
--- a/rust/alloc/vec/into_iter.rs
+++ b/rust/alloc/vec/into_iter.rs
@@ -9,7 +9,8 @@ use crate::raw_vec::RawVec;
 use core::array;
 use core::fmt;
 use core::iter::{
-    FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
+    FusedIterator, InPlaceIterable, SourceIter, TrustedFused, TrustedLen,
+    TrustedRandomAccessNoCoerce,
 };
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
@@ -287,9 +288,7 @@ 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 { ptr::read(self.ptr.add(i)) } }
     }
 }
 
@@ -341,6 +340,10 @@ impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
 #[stable(feature = "fused", since = "1.26.0")]
 impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}
 
+#[doc(hidden)]
+#[unstable(issue = "none", feature = "trusted_fused")]
+unsafe impl<T, A: Allocator> TrustedFused for IntoIter<T, A> {}
+
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}
 
@@ -425,7 +428,10 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for IntoIter<T, A> {
 // also refer to the vec::in_place_collect module documentation to get an overview
 #[unstable(issue = "none", feature = "inplace_iteration")]
 #[doc(hidden)]
-unsafe impl<T, A: Allocator> InPlaceIterable for IntoIter<T, A> {}
+unsafe impl<T, A: Allocator> InPlaceIterable for IntoIter<T, A> {
+    const EXPAND_BY: Option<NonZeroUsize> = NonZeroUsize::new(1);
+    const MERGE_BY: Option<NonZeroUsize> = NonZeroUsize::new(1);
+}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
 #[doc(hidden)]
diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index 0d95fd7ef337..220fb9d6f45b 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -105,6 +105,7 @@ mod into_iter;
 #[cfg(not(no_global_oom_handling))]
 use self::is_zero::IsZero;
 
+#[cfg(not(no_global_oom_handling))]
 mod is_zero;
 
 #[cfg(not(no_global_oom_handling))]
@@ -123,7 +124,7 @@ use self::set_len_on_drop::SetLenOnDrop;
 mod set_len_on_drop;
 
 #[cfg(not(no_global_oom_handling))]
-use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop};
+use self::in_place_drop::{InPlaceDrop, InPlaceDstDataSrcBufDrop};
 
 #[cfg(not(no_global_oom_handling))]
 mod in_place_drop;
@@ -1893,7 +1894,32 @@ impl<T, A: Allocator> Vec<T, A> {
             return;
         }
 
-        /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
+        // Check if we ever want to remove anything.
+        // This allows to use copy_non_overlapping in next cycle.
+        // And avoids any memory writes if we don't need to remove anything.
+        let mut first_duplicate_idx: usize = 1;
+        let start = self.as_mut_ptr();
+        while first_duplicate_idx != len {
+            let found_duplicate = unsafe {
+                // SAFETY: first_duplicate always in range [1..len)
+                // Note that we start iteration from 1 so we never overflow.
+                let prev = start.add(first_duplicate_idx.wrapping_sub(1));
+                let current = start.add(first_duplicate_idx);
+                // We explicitly say in docs that references are reversed.
+                same_bucket(&mut *current, &mut *prev)
+            };
+            if found_duplicate {
+                break;
+            }
+            first_duplicate_idx += 1;
+        }
+        // Don't need to remove anything.
+        // We cannot get bigger than len.
+        if first_duplicate_idx == len {
+            return;
+        }
+
+        /* INVARIANT: vec.len() > read > write > write-1 >= 0 */
         struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
             /* Offset of the element we want to check if it is duplicate */
             read: usize,
@@ -1939,31 +1965,39 @@ impl<T, A: Allocator> Vec<T, A> {
             }
         }
 
-        let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
-        let ptr = gap.vec.as_mut_ptr();
-
         /* Drop items while going through Vec, it should be more efficient than
          * doing slice partition_dedup + truncate */
 
+        // Construct gap first and then drop item to avoid memory corruption if `T::drop` panics.
+        let mut gap =
+            FillGapOnDrop { read: first_duplicate_idx + 1, write: first_duplicate_idx, vec: self };
+        unsafe {
+            // SAFETY: we checked that first_duplicate_idx in bounds before.
+            // If drop panics, `gap` would remove this item without drop.
+            ptr::drop_in_place(start.add(first_duplicate_idx));
+        }
+
         /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
          * are always in-bounds and read_ptr never aliases prev_ptr */
         unsafe {
             while gap.read < len {
-                let read_ptr = ptr.add(gap.read);
-                let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
+                let read_ptr = start.add(gap.read);
+                let prev_ptr = start.add(gap.write.wrapping_sub(1));
 
-                if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
+                // We explicitly say in docs that references are reversed.
+                let found_duplicate = same_bucket(&mut *read_ptr, &mut *prev_ptr);
+                if found_duplicate {
                     // Increase `gap.read` now since the drop may panic.
                     gap.read += 1;
                     /* We have found duplicate, drop it in-place */
                     ptr::drop_in_place(read_ptr);
                 } else {
-                    let write_ptr = ptr.add(gap.write);
+                    let write_ptr = start.add(gap.write);
 
-                    /* Because `read_ptr` can be equal to `write_ptr`, we either
-                     * have to use `copy` or conditional `copy_nonoverlapping`.
-                     * Looks like the first option is faster. */
-                    ptr::copy(read_ptr, write_ptr, 1);
+                    /* read_ptr cannot be equal to write_ptr because at this point
+                     * we guaranteed to skip at least one element (before loop starts).
+                     */
+                    ptr::copy_nonoverlapping(read_ptr, write_ptr, 1);
 
                     /* We have filled that place, so go further */
                     gap.write += 1;
@@ -2844,6 +2878,7 @@ pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<
     <T as SpecFromElem>::from_elem(elem, n, alloc)
 }
 
+#[cfg(not(no_global_oom_handling))]
 trait ExtendFromWithinSpec {
     /// # Safety
     ///
@@ -2852,6 +2887,7 @@ trait ExtendFromWithinSpec {
     unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
 }
 
+#[cfg(not(no_global_oom_handling))]
 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
     default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
         // SAFETY:
@@ -2871,6 +2907,7 @@ impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
     unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
         let count = src.len();
@@ -2951,7 +2988,7 @@ impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
 /// ```
 /// use std::hash::BuildHasher;
 ///
-/// let b = std::collections::hash_map::RandomState::new();
+/// let b = std::hash::RandomState::new();
 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
 /// assert_eq!(b.hash_one(v), b.hash_one(s));