Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

83 files changed, 1251 insertions, 553 deletions

diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index c722bad2e..a083b6560 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/library/std/src/collections/hash/map.rs
@@ -623,28 +623,27 @@ impl<K, V, S> HashMap<K, V, S> {
     /// If the closure returns false, or panics, the element remains in the map and will not be
     /// yielded.
     ///
-    /// Note that `drain_filter` lets you mutate every value in the filter closure, regardless of
+    /// Note that `extract_if` lets you mutate every value in the filter closure, regardless of
     /// whether you choose to keep or remove it.
     ///
-    /// If the iterator is only partially consumed or not consumed at all, each of the remaining
-    /// elements will still be subjected to the closure and removed and dropped if it returns true.
+    /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
+    /// or the iteration short-circuits, then the remaining elements will be retained.
+    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
     ///
-    /// It is unspecified how many more elements will be subjected to the closure
-    /// if a panic occurs in the closure, or a panic occurs while dropping an element,
-    /// or if the `DrainFilter` value is leaked.
+    /// [`retain`]: HashMap::retain
     ///
     /// # Examples
     ///
     /// Splitting a map into even and odd keys, reusing the original map:
     ///
     /// ```
-    /// #![feature(hash_drain_filter)]
+    /// #![feature(hash_extract_if)]
     /// use std::collections::HashMap;
     ///
     /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
-    /// let drained: HashMap<i32, i32> = map.drain_filter(|k, _v| k % 2 == 0).collect();
+    /// let extracted: HashMap<i32, i32> = map.extract_if(|k, _v| k % 2 == 0).collect();
     ///
-    /// let mut evens = drained.keys().copied().collect::<Vec<_>>();
+    /// let mut evens = extracted.keys().copied().collect::<Vec<_>>();
     /// let mut odds = map.keys().copied().collect::<Vec<_>>();
     /// evens.sort();
     /// odds.sort();
@@ -654,12 +653,12 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[rustc_lint_query_instability]
-    #[unstable(feature = "hash_drain_filter", issue = "59618")]
-    pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, K, V, F>
+    #[unstable(feature = "hash_extract_if", issue = "59618")]
+    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, K, V, F>
     where
         F: FnMut(&K, &mut V) -> bool,
     {
-        DrainFilter { base: self.base.drain_filter(pred) }
+        ExtractIf { base: self.base.extract_if(pred) }
     }
 
     /// Retains only the elements specified by the predicate.
@@ -1578,28 +1577,29 @@ impl<'a, K, V> Drain<'a, K, V> {
 
 /// A draining, filtering iterator over the entries of a `HashMap`.
 ///
-/// This `struct` is created by the [`drain_filter`] method on [`HashMap`].
+/// This `struct` is created by the [`extract_if`] method on [`HashMap`].
 ///
-/// [`drain_filter`]: HashMap::drain_filter
+/// [`extract_if`]: HashMap::extract_if
 ///
 /// # Example
 ///
 /// ```
-/// #![feature(hash_drain_filter)]
+/// #![feature(hash_extract_if)]
 ///
 /// use std::collections::HashMap;
 ///
 /// let mut map = HashMap::from([
 ///     ("a", 1),
 /// ]);
-/// let iter = map.drain_filter(|_k, v| *v % 2 == 0);
+/// let iter = map.extract_if(|_k, v| *v % 2 == 0);
 /// ```
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-pub struct DrainFilter<'a, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ExtractIf<'a, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
-    base: base::DrainFilter<'a, K, V, F>,
+    base: base::ExtractIf<'a, K, V, F>,
 }
 
 /// A mutable iterator over the values of a `HashMap`.
@@ -2479,8 +2479,8 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, V, F> Iterator for DrainFilter<'_, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, V, F> Iterator for ExtractIf<'_, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
@@ -2496,16 +2496,16 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, V, F> FusedIterator for DrainFilter<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, V, F> FusedIterator for ExtractIf<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<'a, K, V, F> fmt::Debug for DrainFilter<'a, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<'a, K, V, F> fmt::Debug for ExtractIf<'a, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("DrainFilter").finish_non_exhaustive()
+        f.debug_struct("ExtractIf").finish_non_exhaustive()
     }
 }
 
@@ -2543,12 +2543,12 @@ impl<'a, K, V> Entry<'a, K, V> {
     /// ```
     /// use std::collections::HashMap;
     ///
-    /// let mut map: HashMap<&str, String> = HashMap::new();
-    /// let s = "hoho".to_string();
+    /// let mut map = HashMap::new();
+    /// let value = "hoho";
     ///
-    /// map.entry("poneyland").or_insert_with(|| s);
+    /// map.entry("poneyland").or_insert_with(|| value);
     ///
-    /// assert_eq!(map["poneyland"], "hoho".to_string());
+    /// assert_eq!(map["poneyland"], "hoho");
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/std/src/collections/hash/map/tests.rs b/library/std/src/collections/hash/map/tests.rs
index 6b89518e2..91a3776e7 100644
--- a/library/std/src/collections/hash/map/tests.rs
+++ b/library/std/src/collections/hash/map/tests.rs
@@ -944,7 +944,7 @@ fn test_raw_entry() {
     }
 }
 
-mod test_drain_filter {
+mod test_extract_if {
     use super::*;
 
     use crate::panic::{catch_unwind, AssertUnwindSafe};
@@ -968,7 +968,7 @@ mod test_drain_filter {
     #[test]
     fn empty() {
         let mut map: HashMap<i32, i32> = HashMap::new();
-        map.drain_filter(|_, _| unreachable!("there's nothing to decide on"));
+        map.extract_if(|_, _| unreachable!("there's nothing to decide on")).for_each(drop);
         assert!(map.is_empty());
     }
 
@@ -976,7 +976,7 @@ mod test_drain_filter {
     fn consuming_nothing() {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
-        assert!(map.drain_filter(|_, _| false).eq_sorted(crate::iter::empty()));
+        assert!(map.extract_if(|_, _| false).eq_sorted(crate::iter::empty()));
         assert_eq!(map.len(), 3);
     }
 
@@ -984,7 +984,7 @@ mod test_drain_filter {
     fn consuming_all() {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.clone().collect();
-        assert!(map.drain_filter(|_, _| true).eq_sorted(pairs));
+        assert!(map.extract_if(|_, _| true).eq_sorted(pairs));
         assert!(map.is_empty());
     }
 
@@ -993,7 +993,7 @@ mod test_drain_filter {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
         assert!(
-            map.drain_filter(|_, v| {
+            map.extract_if(|_, v| {
                 *v += 6;
                 false
             })
@@ -1008,7 +1008,7 @@ mod test_drain_filter {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
         assert!(
-            map.drain_filter(|_, v| {
+            map.extract_if(|_, v| {
                 *v += 6;
                 true
             })
@@ -1034,14 +1034,15 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         catch_unwind(move || {
-            drop(map.drain_filter(|_, _| {
+            map.extract_if(|_, _| {
                 PREDS.fetch_add(1, Ordering::SeqCst);
                 true
-            }))
+            })
+            .for_each(drop)
         })
         .unwrap_err();
 
-        assert_eq!(PREDS.load(Ordering::SeqCst), 3);
+        assert_eq!(PREDS.load(Ordering::SeqCst), 2);
         assert_eq!(DROPS.load(Ordering::SeqCst), 3);
     }
 
@@ -1060,10 +1061,11 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         catch_unwind(AssertUnwindSafe(|| {
-            drop(map.drain_filter(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
+            map.extract_if(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
                 0 => true,
                 _ => panic!(),
-            }))
+            })
+            .for_each(drop)
         }))
         .unwrap_err();
 
@@ -1088,7 +1090,7 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         {
-            let mut it = map.drain_filter(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
+            let mut it = map.extract_if(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
                 0 => true,
                 _ => panic!(),
             });
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index ac906e682..ec59634df 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/library/std/src/collections/hash/set.rs
@@ -262,25 +262,24 @@ impl<T, S> HashSet<T, S> {
     /// If the closure returns false, the value will remain in the list and will not be yielded
     /// by the iterator.
     ///
-    /// If the iterator is only partially consumed or not consumed at all, each of the remaining
-    /// values will still be subjected to the closure and removed and dropped if it returns true.
+    /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
+    /// or the iteration short-circuits, then the remaining elements will be retained.
+    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
     ///
-    /// It is unspecified how many more values will be subjected to the closure
-    /// if a panic occurs in the closure, or if a panic occurs while dropping a value, or if the
-    /// `DrainFilter` itself is leaked.
+    /// [`retain`]: HashSet::retain
     ///
     /// # Examples
     ///
     /// Splitting a set into even and odd values, reusing the original set:
     ///
     /// ```
-    /// #![feature(hash_drain_filter)]
+    /// #![feature(hash_extract_if)]
     /// use std::collections::HashSet;
     ///
     /// let mut set: HashSet<i32> = (0..8).collect();
-    /// let drained: HashSet<i32> = set.drain_filter(|v| v % 2 == 0).collect();
+    /// let extracted: HashSet<i32> = set.extract_if(|v| v % 2 == 0).collect();
     ///
-    /// let mut evens = drained.into_iter().collect::<Vec<_>>();
+    /// let mut evens = extracted.into_iter().collect::<Vec<_>>();
     /// let mut odds = set.into_iter().collect::<Vec<_>>();
     /// evens.sort();
     /// odds.sort();
@@ -290,12 +289,12 @@ impl<T, S> HashSet<T, S> {
     /// ```
     #[inline]
     #[rustc_lint_query_instability]
-    #[unstable(feature = "hash_drain_filter", issue = "59618")]
-    pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, T, F>
+    #[unstable(feature = "hash_extract_if", issue = "59618")]
+    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, T, F>
     where
         F: FnMut(&T) -> bool,
     {
-        DrainFilter { base: self.base.drain_filter(pred) }
+        ExtractIf { base: self.base.extract_if(pred) }
     }
 
     /// Retains only the elements specified by the predicate.
@@ -868,7 +867,9 @@ where
     /// Returns whether the value was newly inserted. That is:
     ///
     /// - If the set did not previously contain this value, `true` is returned.
-    /// - If the set already contained this value, `false` is returned.
+    /// - If the set already contained this value, `false` is returned,
+    ///   and the set is not modified: original value is not replaced,
+    ///   and the value passed as argument is dropped.
     ///
     /// # Examples
     ///
@@ -1310,27 +1311,27 @@ pub struct Drain<'a, K: 'a> {
 
 /// A draining, filtering iterator over the items of a `HashSet`.
 ///
-/// This `struct` is created by the [`drain_filter`] method on [`HashSet`].
+/// This `struct` is created by the [`extract_if`] method on [`HashSet`].
 ///
-/// [`drain_filter`]: HashSet::drain_filter
+/// [`extract_if`]: HashSet::extract_if
 ///
 /// # Examples
 ///
 /// ```
-/// #![feature(hash_drain_filter)]
+/// #![feature(hash_extract_if)]
 ///
 /// use std::collections::HashSet;
 ///
 /// let mut a = HashSet::from([1, 2, 3]);
 ///
-/// let mut drain_filtered = a.drain_filter(|v| v % 2 == 0);
+/// let mut extract_ifed = a.extract_if(|v| v % 2 == 0);
 /// ```
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-pub struct DrainFilter<'a, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+pub struct ExtractIf<'a, K, F>
 where
     F: FnMut(&K) -> bool,
 {
-    base: base::DrainFilter<'a, K, F>,
+    base: base::ExtractIf<'a, K, F>,
 }
 
 /// A lazy iterator producing elements in the intersection of `HashSet`s.
@@ -1576,8 +1577,8 @@ impl<K: fmt::Debug> fmt::Debug for Drain<'_, K> {
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, F> Iterator for DrainFilter<'_, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, F> Iterator for ExtractIf<'_, K, F>
 where
     F: FnMut(&K) -> bool,
 {
@@ -1593,16 +1594,16 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, F> FusedIterator for DrainFilter<'_, K, F> where F: FnMut(&K) -> bool {}
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, F> FusedIterator for ExtractIf<'_, K, F> where F: FnMut(&K) -> bool {}
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<'a, K, F> fmt::Debug for DrainFilter<'a, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<'a, K, F> fmt::Debug for ExtractIf<'a, K, F>
 where
     F: FnMut(&K) -> bool,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("DrainFilter").finish_non_exhaustive()
+        f.debug_struct("ExtractIf").finish_non_exhaustive()
     }
 }
 
diff --git a/library/std/src/collections/hash/set/tests.rs b/library/std/src/collections/hash/set/tests.rs
index 941a0450c..e0cd80b44 100644
--- a/library/std/src/collections/hash/set/tests.rs
+++ b/library/std/src/collections/hash/set/tests.rs
@@ -3,6 +3,7 @@ use super::HashSet;
 
 use crate::panic::{catch_unwind, AssertUnwindSafe};
 use crate::sync::atomic::{AtomicU32, Ordering};
+use crate::sync::Arc;
 
 #[test]
 fn test_zero_capacities() {
@@ -418,18 +419,18 @@ fn test_retain() {
 }
 
 #[test]
-fn test_drain_filter() {
+fn test_extract_if() {
     let mut x: HashSet<_> = [1].iter().copied().collect();
     let mut y: HashSet<_> = [1].iter().copied().collect();
 
-    x.drain_filter(|_| true);
-    y.drain_filter(|_| false);
+    x.extract_if(|_| true).for_each(drop);
+    y.extract_if(|_| false).for_each(drop);
     assert_eq!(x.len(), 0);
     assert_eq!(y.len(), 1);
 }
 
 #[test]
-fn test_drain_filter_drop_panic_leak() {
+fn test_extract_if_drop_panic_leak() {
     static PREDS: AtomicU32 = AtomicU32::new(0);
     static DROPS: AtomicU32 = AtomicU32::new(0);
 
@@ -446,19 +447,20 @@ fn test_drain_filter_drop_panic_leak() {
     let mut set = (0..3).map(|i| D(i)).collect::<HashSet<_>>();
 
     catch_unwind(move || {
-        drop(set.drain_filter(|_| {
+        set.extract_if(|_| {
             PREDS.fetch_add(1, Ordering::SeqCst);
             true
-        }))
+        })
+        .for_each(drop)
     })
     .ok();
 
-    assert_eq!(PREDS.load(Ordering::SeqCst), 3);
+    assert_eq!(PREDS.load(Ordering::SeqCst), 2);
     assert_eq!(DROPS.load(Ordering::SeqCst), 3);
 }
 
 #[test]
-fn test_drain_filter_pred_panic_leak() {
+fn test_extract_if_pred_panic_leak() {
     static PREDS: AtomicU32 = AtomicU32::new(0);
     static DROPS: AtomicU32 = AtomicU32::new(0);
 
@@ -473,10 +475,11 @@ fn test_drain_filter_pred_panic_leak() {
     let mut set: HashSet<_> = (0..3).map(|_| D).collect();
 
     catch_unwind(AssertUnwindSafe(|| {
-        drop(set.drain_filter(|_| match PREDS.fetch_add(1, Ordering::SeqCst) {
+        set.extract_if(|_| match PREDS.fetch_add(1, Ordering::SeqCst) {
             0 => true,
             _ => panic!(),
-        }))
+        })
+        .for_each(drop)
     }))
     .ok();
 
@@ -502,3 +505,22 @@ fn const_with_hasher() {
     const X: HashSet<(), ()> = HashSet::with_hasher(());
     assert_eq!(X.len(), 0);
 }
+
+#[test]
+fn test_insert_does_not_overwrite_the_value() {
+    let first_value = Arc::new(17);
+    let second_value = Arc::new(17);
+
+    let mut set = HashSet::new();
+    let inserted = set.insert(first_value.clone());
+    assert!(inserted);
+
+    let inserted = set.insert(second_value);
+    assert!(!inserted);
+
+    assert!(
+        Arc::ptr_eq(set.iter().next().unwrap(), &first_value),
+        "Insert must not overwrite the value, so the contained value pointer \
+            must be the same as first value pointer we inserted"
+    );
+}
diff --git a/library/std/src/f32.rs b/library/std/src/f32.rs
index 408244b2c..bed90418b 100644
--- a/library/std/src/f32.rs
+++ b/library/std/src/f32.rs
@@ -528,7 +528,7 @@ impl f32 {
 
     /// The positive difference of two numbers.
     ///
-    /// * If `self <= other`: `0:0`
+    /// * If `self <= other`: `0.0`
     /// * Else: `self - other`
     ///
     /// # Examples
diff --git a/library/std/src/f64.rs b/library/std/src/f64.rs
index 6782b861f..e72de05ca 100644
--- a/library/std/src/f64.rs
+++ b/library/std/src/f64.rs
@@ -530,7 +530,7 @@ impl f64 {
 
     /// The positive difference of two numbers.
     ///
-    /// * If `self <= other`: `0:0`
+    /// * If `self <= other`: `0.0`
     /// * Else: `self - other`
     ///
     /// # Examples
diff --git a/library/std/src/ffi/mod.rs b/library/std/src/ffi/mod.rs
index d987bf69b..3ddb87487 100644
--- a/library/std/src/ffi/mod.rs
+++ b/library/std/src/ffi/mod.rs
@@ -127,6 +127,14 @@
 //! trait, which provides a [`from_wide`] method to convert a native Windows
 //! string (without the terminating nul character) to an [`OsString`].
 //!
+//! ## On all platforms
+//!
+//! On all platforms, [`OsStr`] consists of a sequence of bytes that is encoded as a superset of
+//! UTF-8; see [`OsString`] for more details on its encoding on different platforms.
+//!
+//! For limited, inexpensive conversions from and to bytes, see [`OsStr::as_os_str_bytes`] and
+//! [`OsStr::from_os_str_bytes_unchecked`].
+//!
 //! [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
 //! [Unicode code point]: https://www.unicode.org/glossary/#code_point
 //! [`env::set_var()`]: crate::env::set_var "env::set_var"
diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index 5c0541d3c..e7bad9d54 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -667,6 +667,51 @@ impl OsStr {
         s.as_ref()
     }
 
+    /// Converts a slice of bytes to an OS string slice without checking that the string contains
+    /// valid `OsStr`-encoded data.
+    ///
+    /// The byte encoding is an unspecified, platform-specific, self-synchronizing superset of UTF-8.
+    /// By being a self-synchronizing superset of UTF-8, this encoding is also a superset of 7-bit
+    /// ASCII.
+    ///
+    /// See the [module's toplevel documentation about conversions][conversions] for safe,
+    /// cross-platform [conversions] from/to native representations.
+    ///
+    /// # Safety
+    ///
+    /// As the encoding is unspecified, callers must pass in bytes that originated as a mixture of
+    /// validated UTF-8 and bytes from [`OsStr::as_os_str_bytes`] from within the same rust version
+    /// built for the same target platform.  For example, reconstructing an `OsStr` from bytes sent
+    /// over the network or stored in a file will likely violate these safety rules.
+    ///
+    /// Due to the encoding being self-synchronizing, the bytes from [`OsStr::as_os_str_bytes`] can be
+    /// split either immediately before or immediately after any valid non-empty UTF-8 substring.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// #![feature(os_str_bytes)]
+    ///
+    /// use std::ffi::OsStr;
+    ///
+    /// let os_str = OsStr::new("Mary had a little lamb");
+    /// let bytes = os_str.as_os_str_bytes();
+    /// let words = bytes.split(|b| *b == b' ');
+    /// let words: Vec<&OsStr> = words.map(|word| {
+    ///     // SAFETY:
+    ///     // - Each `word` only contains content that originated from `OsStr::as_os_str_bytes`
+    ///     // - Only split with ASCII whitespace which is a non-empty UTF-8 substring
+    ///     unsafe { OsStr::from_os_str_bytes_unchecked(word) }
+    /// }).collect();
+    /// ```
+    ///
+    /// [conversions]: super#conversions
+    #[inline]
+    #[unstable(feature = "os_str_bytes", issue = "111544")]
+    pub unsafe fn from_os_str_bytes_unchecked(bytes: &[u8]) -> &Self {
+        Self::from_inner(Slice::from_os_str_bytes_unchecked(bytes))
+    }
+
     #[inline]
     fn from_inner(inner: &Slice) -> &OsStr {
         // SAFETY: OsStr is just a wrapper of Slice,
@@ -700,7 +745,7 @@ impl OsStr {
                   without modifying the original"]
     #[inline]
     pub fn to_str(&self) -> Option<&str> {
-        self.inner.to_str()
+        self.inner.to_str().ok()
     }
 
     /// Converts an `OsStr` to a <code>[Cow]<[str]></code>.
@@ -837,13 +882,24 @@ impl OsStr {
         OsString { inner: Buf::from_box(boxed) }
     }
 
-    /// Gets the underlying byte representation.
+    /// Converts an OS string slice to a byte slice.  To convert the byte slice back into an OS
+    /// string slice, use the [`OsStr::from_os_str_bytes_unchecked`] function.
+    ///
+    /// The byte encoding is an unspecified, platform-specific, self-synchronizing superset of UTF-8.
+    /// By being a self-synchronizing superset of UTF-8, this encoding is also a superset of 7-bit
+    /// ASCII.
+    ///
+    /// Note: As the encoding is unspecified, any sub-slice of bytes that is not valid UTF-8 should
+    /// be treated as opaque and only comparable within the same rust version built for the same
+    /// target platform.  For example, sending the slice over the network or storing it in a file
+    /// will likely result in incompatible byte slices.  See [`OsString`] for more encoding details
+    /// and [`std::ffi`] for platform-specific, specified conversions.
     ///
-    /// Note: it is *crucial* that this API is not externally public, to avoid
-    /// revealing the internal, platform-specific encodings.
+    /// [`std::ffi`]: crate::ffi
     #[inline]
-    pub(crate) fn bytes(&self) -> &[u8] {
-        unsafe { &*(&self.inner as *const _ as *const [u8]) }
+    #[unstable(feature = "os_str_bytes", issue = "111544")]
+    pub fn as_os_str_bytes(&self) -> &[u8] {
+        self.inner.as_os_str_bytes()
     }
 
     /// Converts this string to its ASCII lower case equivalent in-place.
@@ -1109,6 +1165,24 @@ impl<'a> From<Cow<'a, OsStr>> for OsString {
     }
 }
 
+#[stable(feature = "str_tryfrom_osstr_impl", since = "1.72.0")]
+impl<'a> TryFrom<&'a OsStr> for &'a str {
+    type Error = crate::str::Utf8Error;
+
+    /// Tries to convert an `&OsStr` to a `&str`.
+    ///
+    /// ```
+    /// use std::ffi::OsStr;
+    ///
+    /// let os_str = OsStr::new("foo");
+    /// let as_str = <&str>::try_from(os_str).unwrap();
+    /// assert_eq!(as_str, "foo");
+    /// ```
+    fn try_from(value: &'a OsStr) -> Result<Self, Self::Error> {
+        value.inner.to_str()
+    }
+}
+
 #[stable(feature = "box_default_extra", since = "1.17.0")]
 impl Default for Box<OsStr> {
     #[inline]
@@ -1131,7 +1205,7 @@ impl Default for &OsStr {
 impl PartialEq for OsStr {
     #[inline]
     fn eq(&self, other: &OsStr) -> bool {
-        self.bytes().eq(other.bytes())
+        self.as_os_str_bytes().eq(other.as_os_str_bytes())
     }
 }
 
@@ -1158,23 +1232,23 @@ impl Eq for OsStr {}
 impl PartialOrd for OsStr {
     #[inline]
     fn partial_cmp(&self, other: &OsStr) -> Option<cmp::Ordering> {
-        self.bytes().partial_cmp(other.bytes())
+        self.as_os_str_bytes().partial_cmp(other.as_os_str_bytes())
     }
     #[inline]
     fn lt(&self, other: &OsStr) -> bool {
-        self.bytes().lt(other.bytes())
+        self.as_os_str_bytes().lt(other.as_os_str_bytes())
     }
     #[inline]
     fn le(&self, other: &OsStr) -> bool {
-        self.bytes().le(other.bytes())
+        self.as_os_str_bytes().le(other.as_os_str_bytes())
     }
     #[inline]
     fn gt(&self, other: &OsStr) -> bool {
-        self.bytes().gt(other.bytes())
+        self.as_os_str_bytes().gt(other.as_os_str_bytes())
     }
     #[inline]
     fn ge(&self, other: &OsStr) -> bool {
-        self.bytes().ge(other.bytes())
+        self.as_os_str_bytes().ge(other.as_os_str_bytes())
     }
 }
 
@@ -1193,7 +1267,7 @@ impl PartialOrd<str> for OsStr {
 impl Ord for OsStr {
     #[inline]
     fn cmp(&self, other: &OsStr) -> cmp::Ordering {
-        self.bytes().cmp(other.bytes())
+        self.as_os_str_bytes().cmp(other.as_os_str_bytes())
     }
 }
 
@@ -1243,7 +1317,7 @@ impl_cmp!(Cow<'a, OsStr>, OsString);
 impl Hash for OsStr {
     #[inline]
     fn hash<H: Hasher>(&self, state: &mut H) {
-        self.bytes().hash(state)
+        self.as_os_str_bytes().hash(state)
     }
 }
 
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 89dfdfafd..c2d82169d 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -1755,8 +1755,14 @@ impl DirEntry {
         self.0.file_type().map(FileType)
     }
 
-    /// Returns the bare file name of this directory entry without any other
-    /// leading path component.
+    /// Returns the file name of this directory entry without any
+    /// leading path component(s).
+    ///
+    /// As an example,
+    /// the output of the function will result in "foo" for all the following paths:
+    /// - "./foo"
+    /// - "/the/foo"
+    /// - "../../foo"
     ///
     /// # Examples
     ///
diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index e2480bcbb..9ff01b9c3 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -1640,6 +1640,10 @@ fn test_file_times() {
     use crate::os::ios::fs::FileTimesExt;
     #[cfg(target_os = "macos")]
     use crate::os::macos::fs::FileTimesExt;
+    #[cfg(target_os = "tvos")]
+    use crate::os::tvos::fs::FileTimesExt;
+    #[cfg(target_os = "tvos")]
+    use crate::os::tvos::fs::FileTimesExt;
     #[cfg(target_os = "watchos")]
     use crate::os::watchos::fs::FileTimesExt;
     #[cfg(windows)]
@@ -1651,9 +1655,21 @@ fn test_file_times() {
     let accessed = SystemTime::UNIX_EPOCH + Duration::from_secs(12345);
     let modified = SystemTime::UNIX_EPOCH + Duration::from_secs(54321);
     times = times.set_accessed(accessed).set_modified(modified);
-    #[cfg(any(windows, target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(
+        windows,
+        target_os = "macos",
+        target_os = "ios",
+        target_os = "watchos",
+        target_os = "tvos",
+    ))]
     let created = SystemTime::UNIX_EPOCH + Duration::from_secs(32123);
-    #[cfg(any(windows, target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(
+        windows,
+        target_os = "macos",
+        target_os = "ios",
+        target_os = "watchos",
+        target_os = "tvos",
+    ))]
     {
         times = times.set_created(created);
     }
@@ -1678,7 +1694,13 @@ fn test_file_times() {
     let metadata = file.metadata().unwrap();
     assert_eq!(metadata.accessed().unwrap(), accessed);
     assert_eq!(metadata.modified().unwrap(), modified);
-    #[cfg(any(windows, target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(
+        windows,
+        target_os = "macos",
+        target_os = "ios",
+        target_os = "watchos",
+        target_os = "tvos",
+    ))]
     {
         assert_eq!(metadata.created().unwrap(), created);
     }
diff --git a/library/std/src/io/buffered/bufreader.rs b/library/std/src/io/buffered/bufreader.rs
index 4f339a18a..7097dfef8 100644
--- a/library/std/src/io/buffered/bufreader.rs
+++ b/library/std/src/io/buffered/bufreader.rs
@@ -47,13 +47,13 @@ use buffer::Buffer;
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct BufReader<R> {
-    inner: R,
+pub struct BufReader<R: ?Sized> {
     buf: Buffer,
+    inner: R,
 }
 
 impl<R: Read> BufReader<R> {
-    /// Creates a new `BufReader<R>` with a default buffer capacity. The default is currently 8 KB,
+    /// Creates a new `BufReader<R>` with a default buffer capacity. The default is currently 8 KiB,
     /// but may change in the future.
     ///
     /// # Examples
@@ -95,7 +95,7 @@ impl<R: Read> BufReader<R> {
     }
 }
 
-impl<R> BufReader<R> {
+impl<R: ?Sized> BufReader<R> {
     /// Gets a reference to the underlying reader.
     ///
     /// It is inadvisable to directly read from the underlying reader.
@@ -213,26 +213,29 @@ impl<R> BufReader<R> {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn into_inner(self) -> R {
+    pub fn into_inner(self) -> R
+    where
+        R: Sized,
+    {
         self.inner
     }
 
     /// Invalidates all data in the internal buffer.
     #[inline]
-    fn discard_buffer(&mut self) {
+    pub(in crate::io) fn discard_buffer(&mut self) {
         self.buf.discard_buffer()
     }
 }
 
 // This is only used by a test which asserts that the initialization-tracking is correct.
 #[cfg(test)]
-impl<R> BufReader<R> {
+impl<R: ?Sized> BufReader<R> {
     pub fn initialized(&self) -> usize {
         self.buf.initialized()
     }
 }
 
-impl<R: Seek> BufReader<R> {
+impl<R: ?Sized + Seek> BufReader<R> {
     /// Seeks relative to the current position. If the new position lies within the buffer,
     /// the buffer will not be flushed, allowing for more efficient seeks.
     /// This method does not return the location of the underlying reader, so the caller
@@ -257,7 +260,7 @@ impl<R: Seek> BufReader<R> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<R: Read> Read for BufReader<R> {
+impl<R: ?Sized + Read> Read for BufReader<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         // If we don't have any buffered data and we're doing a massive read
         // (larger than our internal buffer), bypass our internal buffer
@@ -371,7 +374,7 @@ impl<R: Read> Read for BufReader<R> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<R: Read> BufRead for BufReader<R> {
+impl<R: ?Sized + Read> BufRead for BufReader<R> {
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         self.buf.fill_buf(&mut self.inner)
     }
@@ -384,11 +387,11 @@ impl<R: Read> BufRead for BufReader<R> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<R> fmt::Debug for BufReader<R>
 where
-    R: fmt::Debug,
+    R: ?Sized + fmt::Debug,
 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("BufReader")
-            .field("reader", &self.inner)
+            .field("reader", &&self.inner)
             .field(
                 "buffer",
                 &format_args!("{}/{}", self.buf.filled() - self.buf.pos(), self.capacity()),
@@ -398,7 +401,7 @@ where
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<R: Seek> Seek for BufReader<R> {
+impl<R: ?Sized + Seek> Seek for BufReader<R> {
     /// Seek to an offset, in bytes, in the underlying reader.
     ///
     /// The position used for seeking with <code>[SeekFrom::Current]\(_)</code> is the
@@ -491,7 +494,7 @@ impl<R: Seek> Seek for BufReader<R> {
     }
 }
 
-impl<T> SizeHint for BufReader<T> {
+impl<T: ?Sized> SizeHint for BufReader<T> {
     #[inline]
     fn lower_bound(&self) -> usize {
         SizeHint::lower_bound(self.get_ref()) + self.buffer().len()
diff --git a/library/std/src/io/buffered/bufwriter.rs b/library/std/src/io/buffered/bufwriter.rs
index 14c455d4f..0f04f2911 100644
--- a/library/std/src/io/buffered/bufwriter.rs
+++ b/library/std/src/io/buffered/bufwriter.rs
@@ -67,8 +67,7 @@ use crate::ptr;
 /// [`TcpStream`]: crate::net::TcpStream
 /// [`flush`]: BufWriter::flush
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct BufWriter<W: Write> {
-    inner: W,
+pub struct BufWriter<W: ?Sized + Write> {
     // The buffer. Avoid using this like a normal `Vec` in common code paths.
     // That is, don't use `buf.push`, `buf.extend_from_slice`, or any other
     // methods that require bounds checking or the like. This makes an enormous
@@ -78,10 +77,11 @@ pub struct BufWriter<W: Write> {
     // write the buffered data a second time in BufWriter's destructor. This
     // flag tells the Drop impl if it should skip the flush.
     panicked: bool,
+    inner: W,
 }
 
 impl<W: Write> BufWriter<W> {
-    /// Creates a new `BufWriter<W>` with a default buffer capacity. The default is currently 8 KB,
+    /// Creates a new `BufWriter<W>` with a default buffer capacity. The default is currently 8 KiB,
     /// but may change in the future.
     ///
     /// # Examples
@@ -115,6 +115,69 @@ impl<W: Write> BufWriter<W> {
         BufWriter { inner, buf: Vec::with_capacity(capacity), panicked: false }
     }
 
+    /// Unwraps this `BufWriter<W>`, returning the underlying writer.
+    ///
+    /// The buffer is written out before returning the writer.
+    ///
+    /// # Errors
+    ///
+    /// An [`Err`] will be returned if an error occurs while flushing the buffer.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use std::io::BufWriter;
+    /// use std::net::TcpStream;
+    ///
+    /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
+    ///
+    /// // unwrap the TcpStream and flush the buffer
+    /// let stream = buffer.into_inner().unwrap();
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
+        match self.flush_buf() {
+            Err(e) => Err(IntoInnerError::new(self, e)),
+            Ok(()) => Ok(self.into_parts().0),
+        }
+    }
+
+    /// Disassembles this `BufWriter<W>`, returning the underlying writer, and any buffered but
+    /// unwritten data.
+    ///
+    /// If the underlying writer panicked, it is not known what portion of the data was written.
+    /// In this case, we return `WriterPanicked` for the buffered data (from which the buffer
+    /// contents can still be recovered).
+    ///
+    /// `into_parts` makes no attempt to flush data and cannot fail.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io::{BufWriter, Write};
+    ///
+    /// let mut buffer = [0u8; 10];
+    /// let mut stream = BufWriter::new(buffer.as_mut());
+    /// write!(stream, "too much data").unwrap();
+    /// stream.flush().expect_err("it doesn't fit");
+    /// let (recovered_writer, buffered_data) = stream.into_parts();
+    /// assert_eq!(recovered_writer.len(), 0);
+    /// assert_eq!(&buffered_data.unwrap(), b"ata");
+    /// ```
+    #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
+    pub fn into_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>) {
+        let buf = mem::take(&mut self.buf);
+        let buf = if !self.panicked { Ok(buf) } else { Err(WriterPanicked { buf }) };
+
+        // SAFETY: forget(self) prevents double dropping inner
+        let inner = unsafe { ptr::read(&self.inner) };
+        mem::forget(self);
+
+        (inner, buf)
+    }
+}
+
+impl<W: ?Sized + Write> BufWriter<W> {
     /// Send data in our local buffer into the inner writer, looping as
     /// necessary until either it's all been sent or an error occurs.
     ///
@@ -284,67 +347,6 @@ impl<W: Write> BufWriter<W> {
         self.buf.capacity()
     }
 
-    /// Unwraps this `BufWriter<W>`, returning the underlying writer.
-    ///
-    /// The buffer is written out before returning the writer.
-    ///
-    /// # Errors
-    ///
-    /// An [`Err`] will be returned if an error occurs while flushing the buffer.
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use std::io::BufWriter;
-    /// use std::net::TcpStream;
-    ///
-    /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
-    ///
-    /// // unwrap the TcpStream and flush the buffer
-    /// let stream = buffer.into_inner().unwrap();
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
-        match self.flush_buf() {
-            Err(e) => Err(IntoInnerError::new(self, e)),
-            Ok(()) => Ok(self.into_parts().0),
-        }
-    }
-
-    /// Disassembles this `BufWriter<W>`, returning the underlying writer, and any buffered but
-    /// unwritten data.
-    ///
-    /// If the underlying writer panicked, it is not known what portion of the data was written.
-    /// In this case, we return `WriterPanicked` for the buffered data (from which the buffer
-    /// contents can still be recovered).
-    ///
-    /// `into_parts` makes no attempt to flush data and cannot fail.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::io::{BufWriter, Write};
-    ///
-    /// let mut buffer = [0u8; 10];
-    /// let mut stream = BufWriter::new(buffer.as_mut());
-    /// write!(stream, "too much data").unwrap();
-    /// stream.flush().expect_err("it doesn't fit");
-    /// let (recovered_writer, buffered_data) = stream.into_parts();
-    /// assert_eq!(recovered_writer.len(), 0);
-    /// assert_eq!(&buffered_data.unwrap(), b"ata");
-    /// ```
-    #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
-    pub fn into_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>) {
-        let buf = mem::take(&mut self.buf);
-        let buf = if !self.panicked { Ok(buf) } else { Err(WriterPanicked { buf }) };
-
-        // SAFETY: forget(self) prevents double dropping inner
-        let inner = unsafe { ptr::read(&self.inner) };
-        mem::forget(self);
-
-        (inner, buf)
-    }
-
     // Ensure this function does not get inlined into `write`, so that it
     // remains inlineable and its common path remains as short as possible.
     // If this function ends up being called frequently relative to `write`,
@@ -511,7 +513,7 @@ impl fmt::Debug for WriterPanicked {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write> Write for BufWriter<W> {
+impl<W: ?Sized + Write> Write for BufWriter<W> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         // Use < instead of <= to avoid a needless trip through the buffer in some cases.
@@ -640,20 +642,20 @@ impl<W: Write> Write for BufWriter<W> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write> fmt::Debug for BufWriter<W>
+impl<W: ?Sized + Write> fmt::Debug for BufWriter<W>
 where
     W: fmt::Debug,
 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("BufWriter")
-            .field("writer", &self.inner)
+            .field("writer", &&self.inner)
             .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
             .finish()
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write + Seek> Seek for BufWriter<W> {
+impl<W: ?Sized + Write + Seek> Seek for BufWriter<W> {
     /// Seek to the offset, in bytes, in the underlying writer.
     ///
     /// Seeking always writes out the internal buffer before seeking.
@@ -664,7 +666,7 @@ impl<W: Write + Seek> Seek for BufWriter<W> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write> Drop for BufWriter<W> {
+impl<W: ?Sized + Write> Drop for BufWriter<W> {
     fn drop(&mut self) {
         if !self.panicked {
             // dtors should not panic, so we ignore a failed flush
diff --git a/library/std/src/io/buffered/linewriter.rs b/library/std/src/io/buffered/linewriter.rs
index a26a4ab33..3d4ae7041 100644
--- a/library/std/src/io/buffered/linewriter.rs
+++ b/library/std/src/io/buffered/linewriter.rs
@@ -64,7 +64,7 @@ use crate::io::{self, buffered::LineWriterShim, BufWriter, IntoInnerError, IoSli
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct LineWriter<W: Write> {
+pub struct LineWriter<W: ?Sized + Write> {
     inner: BufWriter<W>,
 }
 
@@ -109,27 +109,6 @@ impl<W: Write> LineWriter<W> {
         LineWriter { inner: BufWriter::with_capacity(capacity, inner) }
     }
 
-    /// Gets a reference to the underlying writer.
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use std::fs::File;
-    /// use std::io::LineWriter;
-    ///
-    /// fn main() -> std::io::Result<()> {
-    ///     let file = File::create("poem.txt")?;
-    ///     let file = LineWriter::new(file);
-    ///
-    ///     let reference = file.get_ref();
-    ///     Ok(())
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn get_ref(&self) -> &W {
-        self.inner.get_ref()
-    }
-
     /// Gets a mutable reference to the underlying writer.
     ///
     /// Caution must be taken when calling methods on the mutable reference
@@ -184,8 +163,31 @@ impl<W: Write> LineWriter<W> {
     }
 }
 
+impl<W: ?Sized + Write> LineWriter<W> {
+    /// Gets a reference to the underlying writer.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use std::fs::File;
+    /// use std::io::LineWriter;
+    ///
+    /// fn main() -> std::io::Result<()> {
+    ///     let file = File::create("poem.txt")?;
+    ///     let file = LineWriter::new(file);
+    ///
+    ///     let reference = file.get_ref();
+    ///     Ok(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get_ref(&self) -> &W {
+        self.inner.get_ref()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write> Write for LineWriter<W> {
+impl<W: ?Sized + Write> Write for LineWriter<W> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         LineWriterShim::new(&mut self.inner).write(buf)
     }
@@ -216,7 +218,7 @@ impl<W: Write> Write for LineWriter<W> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W: Write> fmt::Debug for LineWriter<W>
+impl<W: ?Sized + Write> fmt::Debug for LineWriter<W>
 where
     W: fmt::Debug,
 {
diff --git a/library/std/src/io/buffered/linewritershim.rs b/library/std/src/io/buffered/linewritershim.rs
index 0175d2693..f2a55da05 100644
--- a/library/std/src/io/buffered/linewritershim.rs
+++ b/library/std/src/io/buffered/linewritershim.rs
@@ -11,11 +11,11 @@ use crate::sys_common::memchr;
 /// `BufWriters` to be temporarily given line-buffering logic; this is what
 /// enables Stdout to be alternately in line-buffered or block-buffered mode.
 #[derive(Debug)]
-pub struct LineWriterShim<'a, W: Write> {
+pub struct LineWriterShim<'a, W: ?Sized + Write> {
     buffer: &'a mut BufWriter<W>,
 }
 
-impl<'a, W: Write> LineWriterShim<'a, W> {
+impl<'a, W: ?Sized + Write> LineWriterShim<'a, W> {
     pub fn new(buffer: &'a mut BufWriter<W>) -> Self {
         Self { buffer }
     }
@@ -49,7 +49,7 @@ impl<'a, W: Write> LineWriterShim<'a, W> {
     }
 }
 
-impl<'a, W: Write> Write for LineWriterShim<'a, W> {
+impl<'a, W: ?Sized + Write> Write for LineWriterShim<'a, W> {
     /// Write some data into this BufReader with line buffering. This means
     /// that, if any newlines are present in the data, the data up to the last
     /// newline is sent directly to the underlying writer, and data after it
diff --git a/library/std/src/io/copy.rs b/library/std/src/io/copy.rs
index 1d9d93f5b..ef1f4031e 100644
--- a/library/std/src/io/copy.rs
+++ b/library/std/src/io/copy.rs
@@ -1,6 +1,9 @@
-use super::{BorrowedBuf, BufWriter, ErrorKind, Read, Result, Write, DEFAULT_BUF_SIZE};
+use super::{BorrowedBuf, BufReader, BufWriter, ErrorKind, Read, Result, Write, DEFAULT_BUF_SIZE};
 use crate::mem::MaybeUninit;
 
+#[cfg(test)]
+mod tests;
+
 /// Copies the entire contents of a reader into a writer.
 ///
 /// This function will continuously read data from `reader` and then
@@ -71,32 +74,113 @@ where
     R: Read,
     W: Write,
 {
-    BufferedCopySpec::copy_to(reader, writer)
+    let read_buf = BufferedReaderSpec::buffer_size(reader);
+    let write_buf = BufferedWriterSpec::buffer_size(writer);
+
+    if read_buf >= DEFAULT_BUF_SIZE && read_buf >= write_buf {
+        return BufferedReaderSpec::copy_to(reader, writer);
+    }
+
+    BufferedWriterSpec::copy_from(writer, reader)
+}
+
+/// Specialization of the read-write loop that reuses the internal
+/// buffer of a BufReader. If there's no buffer then the writer side
+/// should be used intead.
+trait BufferedReaderSpec {
+    fn buffer_size(&self) -> usize;
+
+    fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64>;
+}
+
+impl<T> BufferedReaderSpec for T
+where
+    Self: Read,
+    T: ?Sized,
+{
+    #[inline]
+    default fn buffer_size(&self) -> usize {
+        0
+    }
+
+    default fn copy_to(&mut self, _to: &mut (impl Write + ?Sized)) -> Result<u64> {
+        unimplemented!("only called from specializations");
+    }
+}
+
+impl<I> BufferedReaderSpec for BufReader<I>
+where
+    Self: Read,
+    I: ?Sized,
+{
+    fn buffer_size(&self) -> usize {
+        self.capacity()
+    }
+
+    fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
+        let mut len = 0;
+
+        loop {
+            // Hack: this relies on `impl Read for BufReader` always calling fill_buf
+            // if the buffer is empty, even for empty slices.
+            // It can't be called directly here since specialization prevents us
+            // from adding I: Read
+            match self.read(&mut []) {
+                Ok(_) => {}
+                Err(e) if e.kind() == ErrorKind::Interrupted => continue,
+                Err(e) => return Err(e),
+            }
+            let buf = self.buffer();
+            if self.buffer().len() == 0 {
+                return Ok(len);
+            }
+
+            // In case the writer side is a BufWriter then its write_all
+            // implements an optimization that passes through large
+            // buffers to the underlying writer. That code path is #[cold]
+            // but we're still avoiding redundant memcopies when doing
+            // a copy between buffered inputs and outputs.
+            to.write_all(buf)?;
+            len += buf.len() as u64;
+            self.discard_buffer();
+        }
+    }
 }
 
 /// Specialization of the read-write loop that either uses a stack buffer
 /// or reuses the internal buffer of a BufWriter
-trait BufferedCopySpec: Write {
-    fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64>;
+trait BufferedWriterSpec: Write {
+    fn buffer_size(&self) -> usize;
+
+    fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64>;
 }
 
-impl<W: Write + ?Sized> BufferedCopySpec for W {
-    default fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
-        stack_buffer_copy(reader, writer)
+impl<W: Write + ?Sized> BufferedWriterSpec for W {
+    #[inline]
+    default fn buffer_size(&self) -> usize {
+        0
+    }
+
+    default fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
+        stack_buffer_copy(reader, self)
     }
 }
 
-impl<I: Write> BufferedCopySpec for BufWriter<I> {
-    fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
-        if writer.capacity() < DEFAULT_BUF_SIZE {
-            return stack_buffer_copy(reader, writer);
+impl<I: Write + ?Sized> BufferedWriterSpec for BufWriter<I> {
+    fn buffer_size(&self) -> usize {
+        self.capacity()
+    }
+
+    fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
+        if self.capacity() < DEFAULT_BUF_SIZE {
+            return stack_buffer_copy(reader, self);
         }
 
         let mut len = 0;
         let mut init = 0;
 
         loop {
-            let buf = writer.buffer_mut();
+            let buf = self.buffer_mut();
             let mut read_buf: BorrowedBuf<'_> = buf.spare_capacity_mut().into();
 
             unsafe {
@@ -127,7 +211,7 @@ impl<I: Write> BufferedCopySpec for BufWriter<I> {
                     Err(e) => return Err(e),
                 }
             } else {
-                writer.flush_buf()?;
+                self.flush_buf()?;
                 init = 0;
             }
         }
diff --git a/library/std/src/io/copy/tests.rs b/library/std/src/io/copy/tests.rs
new file mode 100644
index 000000000..8c816af15
--- /dev/null
+++ b/library/std/src/io/copy/tests.rs
@@ -0,0 +1,108 @@
+use crate::cmp::{max, min};
+use crate::io::*;
+
+#[test]
+fn copy_copies() {
+    let mut r = repeat(0).take(4);
+    let mut w = sink();
+    assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
+
+    let mut r = repeat(0).take(1 << 17);
+    assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
+}
+
+struct ShortReader {
+    cap: usize,
+    read_size: usize,
+    observed_buffer: usize,
+}
+
+impl Read for ShortReader {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
+        let bytes = min(self.cap, self.read_size);
+        self.cap -= bytes;
+        self.observed_buffer = max(self.observed_buffer, buf.len());
+        Ok(bytes)
+    }
+}
+
+struct WriteObserver {
+    observed_buffer: usize,
+}
+
+impl Write for WriteObserver {
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        self.observed_buffer = max(self.observed_buffer, buf.len());
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> Result<()> {
+        Ok(())
+    }
+}
+
+#[test]
+fn copy_specializes_bufwriter() {
+    let cap = 117 * 1024;
+    let buf_sz = 16 * 1024;
+    let mut r = ShortReader { cap, observed_buffer: 0, read_size: 1337 };
+    let mut w = BufWriter::with_capacity(buf_sz, WriteObserver { observed_buffer: 0 });
+    assert_eq!(
+        copy(&mut r, &mut w).unwrap(),
+        cap as u64,
+        "expected the whole capacity to be copied"
+    );
+    assert_eq!(r.observed_buffer, buf_sz, "expected a large buffer to be provided to the reader");
+    assert!(w.get_mut().observed_buffer > DEFAULT_BUF_SIZE, "expected coalesced writes");
+}
+
+#[test]
+fn copy_specializes_bufreader() {
+    let mut source = vec![0; 768 * 1024];
+    source[1] = 42;
+    let mut buffered = BufReader::with_capacity(256 * 1024, Cursor::new(&mut source));
+
+    let mut sink = Vec::new();
+    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
+    assert_eq!(source.as_slice(), sink.as_slice());
+
+    let buf_sz = 71 * 1024;
+    assert!(buf_sz > DEFAULT_BUF_SIZE, "test precondition");
+
+    let mut buffered = BufReader::with_capacity(buf_sz, Cursor::new(&mut source));
+    let mut sink = WriteObserver { observed_buffer: 0 };
+    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
+    assert_eq!(
+        sink.observed_buffer, buf_sz,
+        "expected a large buffer to be provided to the writer"
+    );
+}
+
+#[cfg(unix)]
+mod io_benches {
+    use crate::fs::File;
+    use crate::fs::OpenOptions;
+    use crate::io::prelude::*;
+    use crate::io::BufReader;
+
+    use test::Bencher;
+
+    #[bench]
+    fn bench_copy_buf_reader(b: &mut Bencher) {
+        let mut file_in = File::open("/dev/zero").expect("opening /dev/zero failed");
+        // use dyn to avoid specializations unrelated to readbuf
+        let dyn_in = &mut file_in as &mut dyn Read;
+        let mut reader = BufReader::with_capacity(256 * 1024, dyn_in.take(0));
+        let mut writer =
+            OpenOptions::new().write(true).open("/dev/null").expect("opening /dev/null failed");
+
+        const BYTES: u64 = 1024 * 1024;
+
+        b.bytes = BYTES;
+
+        b.iter(|| {
+            reader.get_mut().set_limit(BYTES);
+            crate::io::copy(&mut reader, &mut writer).unwrap()
+        });
+    }
+}
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 8a007d095..71d91f213 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -1416,17 +1416,18 @@ pub trait Write {
     ///
     /// This function will attempt to write the entire contents of `buf`, but
     /// the entire write might not succeed, or the write may also generate an
-    /// error. A call to `write` represents *at most one* attempt to write to
+    /// error. Typically, a call to `write` represents one attempt to write to
     /// any wrapped object.
     ///
     /// Calls to `write` are not guaranteed to block waiting for data to be
     /// written, and a write which would otherwise block can be indicated through
     /// an [`Err`] variant.
     ///
-    /// If the return value is [`Ok(n)`] then it must be guaranteed that
-    /// `n <= buf.len()`. A return value of `0` typically means that the
-    /// underlying object is no longer able to accept bytes and will likely not
-    /// be able to in the future as well, or that the buffer provided is empty.
+    /// If this method consumed `n > 0` bytes of `buf` it must return [`Ok(n)`].
+    /// If the return value is `Ok(n)` then `n` must satisfy `n <= buf.len()`.
+    /// A return value of `Ok(0)` typically means that the underlying object is
+    /// no longer able to accept bytes and will likely not be able to in the
+    /// future as well, or that the buffer provided is empty.
     ///
     /// # Errors
     ///
@@ -2754,7 +2755,7 @@ trait SizeHint {
     }
 }
 
-impl<T> SizeHint for T {
+impl<T: ?Sized> SizeHint for T {
     #[inline]
     default fn lower_bound(&self) -> usize {
         0
diff --git a/library/std/src/io/util/tests.rs b/library/std/src/io/util/tests.rs
index ce5e2c9da..1baa94e64 100644
--- a/library/std/src/io/util/tests.rs
+++ b/library/std/src/io/util/tests.rs
@@ -1,68 +1,9 @@
-use crate::cmp::{max, min};
 use crate::io::prelude::*;
-use crate::io::{
-    copy, empty, repeat, sink, BorrowedBuf, BufWriter, Empty, Repeat, Result, SeekFrom, Sink,
-    DEFAULT_BUF_SIZE,
-};
+use crate::io::{empty, repeat, sink, BorrowedBuf, Empty, Repeat, SeekFrom, Sink};
 
 use crate::mem::MaybeUninit;
 
 #[test]
-fn copy_copies() {
-    let mut r = repeat(0).take(4);
-    let mut w = sink();
-    assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
-
-    let mut r = repeat(0).take(1 << 17);
-    assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
-}
-
-struct ShortReader {
-    cap: usize,
-    read_size: usize,
-    observed_buffer: usize,
-}
-
-impl Read for ShortReader {
-    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
-        let bytes = min(self.cap, self.read_size);
-        self.cap -= bytes;
-        self.observed_buffer = max(self.observed_buffer, buf.len());
-        Ok(bytes)
-    }
-}
-
-struct WriteObserver {
-    observed_buffer: usize,
-}
-
-impl Write for WriteObserver {
-    fn write(&mut self, buf: &[u8]) -> Result<usize> {
-        self.observed_buffer = max(self.observed_buffer, buf.len());
-        Ok(buf.len())
-    }
-
-    fn flush(&mut self) -> Result<()> {
-        Ok(())
-    }
-}
-
-#[test]
-fn copy_specializes_bufwriter() {
-    let cap = 117 * 1024;
-    let buf_sz = 16 * 1024;
-    let mut r = ShortReader { cap, observed_buffer: 0, read_size: 1337 };
-    let mut w = BufWriter::with_capacity(buf_sz, WriteObserver { observed_buffer: 0 });
-    assert_eq!(
-        copy(&mut r, &mut w).unwrap(),
-        cap as u64,
-        "expected the whole capacity to be copied"
-    );
-    assert_eq!(r.observed_buffer, buf_sz, "expected a large buffer to be provided to the reader");
-    assert!(w.get_mut().observed_buffer > DEFAULT_BUF_SIZE, "expected coalesced writes");
-}
-
-#[test]
 fn sink_sinks() {
     let mut s = sink();
     assert_eq!(s.write(&[]).unwrap(), 0);
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 318a46d1b..72b9ad348 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -188,6 +188,13 @@
 //! [array]: prim@array
 //! [slice]: prim@slice
 
+// To run std tests without x.py without ending up with two copies of std, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no affect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
+// miri-test-libstd also prefers to make std use the sysroot versions of the dependencies.
+#![cfg_attr(feature = "miri-test-libstd", feature(rustc_private))]
+//
 #![cfg_attr(not(feature = "restricted-std"), stable(feature = "rust1", since = "1.0.0"))]
 #![cfg_attr(feature = "restricted-std", unstable(feature = "restricted_std", issue = "none"))]
 #![doc(
@@ -202,12 +209,6 @@
     no_global_oom_handling,
     not(no_global_oom_handling)
 ))]
-// To run std tests without x.py without ending up with two copies of std, Miri needs to be
-// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
-// rustc itself never sets the feature, so this line has no affect there.
-#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
-// miri-test-libstd also prefers to make std use the sysroot versions of the dependencies.
-#![cfg_attr(feature = "miri-test-libstd", feature(rustc_private))]
 // Don't link to std. We are std.
 #![no_std]
 // Tell the compiler to link to either panic_abort or panic_unwind
diff --git a/library/std/src/macros.rs b/library/std/src/macros.rs
index fcc5cfafd..ba1b8cbfa 100644
--- a/library/std/src/macros.rs
+++ b/library/std/src/macros.rs
@@ -154,7 +154,7 @@ macro_rules! println {
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
-/// Writing to non-blocking stdout can cause an error, which will lead
+/// Writing to non-blocking stderr can cause an error, which will lead
 /// this macro to panic.
 ///
 /// # Examples
@@ -189,7 +189,7 @@ macro_rules! eprint {
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
-/// Writing to non-blocking stdout can cause an error, which will lead
+/// Writing to non-blocking stderr can cause an error, which will lead
 /// this macro to panic.
 ///
 /// # Examples
diff --git a/library/std/src/net/socket_addr/tests.rs b/library/std/src/net/socket_addr/tests.rs
index dfc6dabbe..6a065cfba 100644
--- a/library/std/src/net/socket_addr/tests.rs
+++ b/library/std/src/net/socket_addr/tests.rs
@@ -85,7 +85,7 @@ fn ipv6_socket_addr_to_string() {
     // IPv4-compatible address.
     assert_eq!(
         SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc000, 0x280), 8080, 0, 0).to_string(),
-        "[::192.0.2.128]:8080"
+        "[::c000:280]:8080"
     );
 
     // IPv6 address with no zero segments.
diff --git a/library/std/src/net/tcp/tests.rs b/library/std/src/net/tcp/tests.rs
index 7a3c66e45..db367cfa0 100644
--- a/library/std/src/net/tcp/tests.rs
+++ b/library/std/src/net/tcp/tests.rs
@@ -47,6 +47,17 @@ fn connect_error() {
 }
 
 #[test]
+#[cfg_attr(target_env = "sgx", ignore)] // FIXME: https://github.com/fortanix/rust-sgx/issues/31
+fn connect_timeout_error() {
+    let socket_addr = next_test_ip4();
+    let result = TcpStream::connect_timeout(&socket_addr, Duration::MAX);
+    assert!(!matches!(result, Err(e) if e.kind() == ErrorKind::TimedOut));
+
+    let _listener = TcpListener::bind(&socket_addr).unwrap();
+    assert!(TcpStream::connect_timeout(&socket_addr, Duration::MAX).is_ok());
+}
+
+#[test]
 fn listen_localhost() {
     let socket_addr = next_test_ip4();
     let listener = t!(TcpListener::bind(&socket_addr));
diff --git a/library/std/src/os/ios/fs.rs b/library/std/src/os/ios/fs.rs
index 6d4d54b7c..b319527a5 100644
--- a/library/std/src/os/ios/fs.rs
+++ b/library/std/src/os/ios/fs.rs
@@ -6,7 +6,7 @@ use crate::sys_common::{AsInner, AsInnerMut, IntoInner};
 use crate::time::SystemTime;
 
 #[allow(deprecated)]
-use crate::os::ios::raw;
+use super::raw;
 
 /// OS-specific extensions to [`fs::Metadata`].
 ///
diff --git a/library/std/src/os/mod.rs b/library/std/src/os/mod.rs
index 5b54cc5f2..634c3cc4a 100644
--- a/library/std/src/os/mod.rs
+++ b/library/std/src/os/mod.rs
@@ -137,6 +137,9 @@ pub mod redox;
 pub mod solaris;
 #[cfg(target_os = "solid_asp3")]
 pub mod solid;
+#[cfg(target_os = "tvos")]
+#[path = "ios/mod.rs"]
+pub(crate) mod tvos;
 #[cfg(target_os = "vita")]
 pub mod vita;
 #[cfg(target_os = "vxworks")]
diff --git a/library/std/src/os/unix/mod.rs b/library/std/src/os/unix/mod.rs
index 6fe111118..401ec1e7a 100644
--- a/library/std/src/os/unix/mod.rs
+++ b/library/std/src/os/unix/mod.rs
@@ -73,6 +73,8 @@ mod platform {
     pub use crate::os::redox::*;
     #[cfg(target_os = "solaris")]
     pub use crate::os::solaris::*;
+    #[cfg(target_os = "tvos")]
+    pub use crate::os::tvos::*;
     #[cfg(target_os = "vita")]
     pub use crate::os::vita::*;
     #[cfg(target_os = "vxworks")]
@@ -96,6 +98,7 @@ pub mod thread;
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "watchos",
     target_os = "macos",
     target_os = "netbsd",
diff --git a/library/std/src/os/unix/net/ancillary.rs b/library/std/src/os/unix/net/ancillary.rs
index 7565fbc0d..218536689 100644
--- a/library/std/src/os/unix/net/ancillary.rs
+++ b/library/std/src/os/unix/net/ancillary.rs
@@ -11,12 +11,19 @@ use crate::slice::from_raw_parts;
 use crate::sys::net::Socket;
 
 // FIXME(#43348): Make libc adapt #[doc(cfg(...))] so we don't need these fake definitions here?
-#[cfg(all(doc, not(target_os = "linux"), not(target_os = "android"), not(target_os = "netbsd")))]
+#[cfg(all(
+    doc,
+    not(target_os = "linux"),
+    not(target_os = "android"),
+    not(target_os = "netbsd"),
+    not(target_os = "freebsd")
+))]
 #[allow(non_camel_case_types)]
 mod libc {
     pub use libc::c_int;
     pub struct ucred;
     pub struct cmsghdr;
+    pub struct sockcred2;
     pub type pid_t = i32;
     pub type gid_t = u32;
     pub type uid_t = u32;
diff --git a/library/std/src/os/unix/net/stream.rs b/library/std/src/os/unix/net/stream.rs
index bf2a51b5e..e20170873 100644
--- a/library/std/src/os/unix/net/stream.rs
+++ b/library/std/src/os/unix/net/stream.rs
@@ -11,6 +11,7 @@ use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, Owned
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "macos",
     target_os = "watchos",
     target_os = "netbsd",
@@ -30,6 +31,7 @@ use crate::time::Duration;
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "macos",
     target_os = "watchos",
     target_os = "netbsd",
@@ -238,6 +240,7 @@ impl UnixStream {
         target_os = "dragonfly",
         target_os = "freebsd",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "macos",
         target_os = "watchos",
         target_os = "netbsd",
diff --git a/library/std/src/os/unix/process.rs b/library/std/src/os/unix/process.rs
index 729c63d18..2b40b672d 100644
--- a/library/std/src/os/unix/process.rs
+++ b/library/std/src/os/unix/process.rs
@@ -15,7 +15,7 @@ use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 use cfg_if::cfg_if;
 
 cfg_if! {
-    if #[cfg(any(target_os = "vxworks", target_os = "espidf", target_os = "horizon"))] {
+    if #[cfg(any(target_os = "vxworks", target_os = "espidf", target_os = "horizon", target_os = "vita"))] {
         type UserId = u16;
         type GroupId = u16;
     } else if #[cfg(target_os = "nto")] {
diff --git a/library/std/src/os/unix/ucred.rs b/library/std/src/os/unix/ucred.rs
index 95967eac2..6a0cc2d2c 100644
--- a/library/std/src/os/unix/ucred.rs
+++ b/library/std/src/os/unix/ucred.rs
@@ -36,7 +36,7 @@ pub use self::impl_linux::peer_cred;
 ))]
 pub use self::impl_bsd::peer_cred;
 
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 pub use self::impl_mac::peer_cred;
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
@@ -98,7 +98,7 @@ pub mod impl_bsd {
     }
 }
 
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 pub mod impl_mac {
     use super::UCred;
     use crate::os::unix::io::AsRawFd;
diff --git a/library/std/src/os/unix/ucred/tests.rs b/library/std/src/os/unix/ucred/tests.rs
index e63a2fc24..dd99ecdd8 100644
--- a/library/std/src/os/unix/ucred/tests.rs
+++ b/library/std/src/os/unix/ucred/tests.rs
@@ -8,6 +8,7 @@ use libc::{getegid, geteuid, getpid};
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "macos",
     target_os = "watchos",
     target_os = "openbsd"
@@ -26,7 +27,13 @@ fn test_socket_pair() {
 }
 
 #[test]
-#[cfg(any(target_os = "linux", target_os = "ios", target_os = "macos", target_os = "watchos"))]
+#[cfg(any(
+    target_os = "linux",
+    target_os = "ios",
+    target_os = "macos",
+    target_os = "watchos",
+    target_os = "tvos",
+))]
 fn test_socket_pair_pids(arg: Type) -> RetType {
     // Create two connected sockets and get their peer credentials.
     let (sock_a, sock_b) = UnixStream::pair().unwrap();
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index febdeb514..28cd3c4e4 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -193,7 +193,7 @@ impl<'a> Prefix<'a> {
     fn len(&self) -> usize {
         use self::Prefix::*;
         fn os_str_len(s: &OsStr) -> usize {
-            s.bytes().len()
+            s.as_os_str_bytes().len()
         }
         match *self {
             Verbatim(x) => 4 + os_str_len(x),
@@ -299,20 +299,6 @@ where
     }
 }
 
-unsafe fn u8_slice_as_os_str(s: &[u8]) -> &OsStr {
-    // SAFETY: See note at the top of this module to understand why this and
-    // `OsStr::bytes` are used:
-    //
-    // This casts are safe as OsStr is internally a wrapper around [u8] on all
-    // platforms.
-    //
-    // Note that currently this relies on the special knowledge that std has;
-    // these types are single-element structs but are not marked
-    // repr(transparent) or repr(C) which would make these casts not allowable
-    // outside std.
-    unsafe { &*(s as *const [u8] as *const OsStr) }
-}
-
 // Detect scheme on Redox
 fn has_redox_scheme(s: &[u8]) -> bool {
     cfg!(target_os = "redox") && s.contains(&b':')
@@ -330,7 +316,7 @@ fn has_physical_root(s: &[u8], prefix: Option<Prefix<'_>>) -> bool {
 
 // basic workhorse for splitting stem and extension
 fn rsplit_file_at_dot(file: &OsStr) -> (Option<&OsStr>, Option<&OsStr>) {
-    if file.bytes() == b".." {
+    if file.as_os_str_bytes() == b".." {
         return (Some(file), None);
     }
 
@@ -338,18 +324,23 @@ fn rsplit_file_at_dot(file: &OsStr) -> (Option<&OsStr>, Option<&OsStr>) {
     // and back. This is safe to do because (1) we only look at ASCII
     // contents of the encoding and (2) new &OsStr values are produced
     // only from ASCII-bounded slices of existing &OsStr values.
-    let mut iter = file.bytes().rsplitn(2, |b| *b == b'.');
+    let mut iter = file.as_os_str_bytes().rsplitn(2, |b| *b == b'.');
     let after = iter.next();
     let before = iter.next();
     if before == Some(b"") {
         (Some(file), None)
     } else {
-        unsafe { (before.map(|s| u8_slice_as_os_str(s)), after.map(|s| u8_slice_as_os_str(s))) }
+        unsafe {
+            (
+                before.map(|s| OsStr::from_os_str_bytes_unchecked(s)),
+                after.map(|s| OsStr::from_os_str_bytes_unchecked(s)),
+            )
+        }
     }
 }
 
 fn split_file_at_dot(file: &OsStr) -> (&OsStr, Option<&OsStr>) {
-    let slice = file.bytes();
+    let slice = file.as_os_str_bytes();
     if slice == b".." {
         return (file, None);
     }
@@ -364,7 +355,12 @@ fn split_file_at_dot(file: &OsStr) -> (&OsStr, Option<&OsStr>) {
     };
     let before = &slice[..i];
     let after = &slice[i + 1..];
-    unsafe { (u8_slice_as_os_str(before), Some(u8_slice_as_os_str(after))) }
+    unsafe {
+        (
+            OsStr::from_os_str_bytes_unchecked(before),
+            Some(OsStr::from_os_str_bytes_unchecked(after)),
+        )
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -743,7 +739,7 @@ impl<'a> Components<'a> {
             // separately via `include_cur_dir`
             b".." => Some(Component::ParentDir),
             b"" => None,
-            _ => Some(Component::Normal(unsafe { u8_slice_as_os_str(comp) })),
+            _ => Some(Component::Normal(unsafe { OsStr::from_os_str_bytes_unchecked(comp) })),
         }
     }
 
@@ -900,7 +896,7 @@ impl<'a> Iterator for Components<'a> {
                     let raw = &self.path[..self.prefix_len()];
                     self.path = &self.path[self.prefix_len()..];
                     return Some(Component::Prefix(PrefixComponent {
-                        raw: unsafe { u8_slice_as_os_str(raw) },
+                        raw: unsafe { OsStr::from_os_str_bytes_unchecked(raw) },
                         parsed: self.prefix.unwrap(),
                     }));
                 }
@@ -972,7 +968,7 @@ impl<'a> DoubleEndedIterator for Components<'a> {
                 State::Prefix if self.prefix_len() > 0 => {
                     self.back = State::Done;
                     return Some(Component::Prefix(PrefixComponent {
-                        raw: unsafe { u8_slice_as_os_str(self.path) },
+                        raw: unsafe { OsStr::from_os_str_bytes_unchecked(self.path) },
                         parsed: self.prefix.unwrap(),
                     }));
                 }
@@ -1481,17 +1477,17 @@ impl PathBuf {
     fn _set_extension(&mut self, extension: &OsStr) -> bool {
         let file_stem = match self.file_stem() {
             None => return false,
-            Some(f) => f.bytes(),
+            Some(f) => f.as_os_str_bytes(),
         };
 
         // truncate until right after the file stem
         let end_file_stem = file_stem[file_stem.len()..].as_ptr().addr();
-        let start = self.inner.bytes().as_ptr().addr();
+        let start = self.inner.as_os_str_bytes().as_ptr().addr();
         let v = self.as_mut_vec();
         v.truncate(end_file_stem.wrapping_sub(start));
 
         // add the new extension, if any
-        let new = extension.bytes();
+        let new = extension.as_os_str_bytes();
         if !new.is_empty() {
             v.reserve_exact(new.len() + 1);
             v.push(b'.');
@@ -2011,11 +2007,11 @@ impl Path {
     // The following (private!) function allows construction of a path from a u8
     // slice, which is only safe when it is known to follow the OsStr encoding.
     unsafe fn from_u8_slice(s: &[u8]) -> &Path {
-        unsafe { Path::new(u8_slice_as_os_str(s)) }
+        unsafe { Path::new(OsStr::from_os_str_bytes_unchecked(s)) }
     }
     // The following (private!) function reveals the byte encoding used for OsStr.
     fn as_u8_slice(&self) -> &[u8] {
-        self.inner.bytes()
+        self.inner.as_os_str_bytes()
     }
 
     /// Directly wraps a string slice as a `Path` slice.
diff --git a/library/std/src/personality.rs b/library/std/src/personality.rs
index 63f0ad4f1..386a399f5 100644
--- a/library/std/src/personality.rs
+++ b/library/std/src/personality.rs
@@ -29,7 +29,7 @@ cfg_if::cfg_if! {
         all(target_family = "windows", target_env = "gnu"),
         target_os = "psp",
         target_os = "solid_asp3",
-        all(target_family = "unix", not(target_os = "espidf")),
+        all(target_family = "unix", not(target_os = "espidf"), not(target_os = "l4re")),
         all(target_vendor = "fortanix", target_env = "sgx"),
     ))] {
         mod gcc;
diff --git a/library/std/src/personality/gcc.rs b/library/std/src/personality/gcc.rs
index 82edb11cb..6552d96ca 100644
--- a/library/std/src/personality/gcc.rs
+++ b/library/std/src/personality/gcc.rs
@@ -85,7 +85,7 @@ const UNWIND_DATA_REG: (i32, i32) = (4, 5); // a0, a1
 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
 
 cfg_if::cfg_if! {
-    if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "watchos"), not(target_os = "netbsd")))] {
+    if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "tvos"), not(target_os = "watchos"), not(target_os = "netbsd")))] {
         // ARM EHABI personality routine.
         // https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
         //
diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs
index 8266e8990..80289ca08 100644
--- a/library/std/src/primitive_docs.rs
+++ b/library/std/src/primitive_docs.rs
@@ -308,7 +308,7 @@ mod prim_never {}
 ///
 /// ```no_run
 /// // Undefined behaviour
-/// unsafe { char::from_u32_unchecked(0x110000) };
+/// let _ = unsafe { char::from_u32_unchecked(0x110000) };
 /// ```
 ///
 /// USVs are also the exact set of values that may be encoded in UTF-8. Because
diff --git a/library/std/src/process.rs b/library/std/src/process.rs
index 9da74a5dd..8f3201b00 100644
--- a/library/std/src/process.rs
+++ b/library/std/src/process.rs
@@ -1904,8 +1904,8 @@ impl FromInner<imp::ExitCode> for ExitCode {
 }
 
 impl Child {
-    /// Forces the child process to exit. If the child has already exited, an [`InvalidInput`]
-    /// error is returned.
+    /// Forces the child process to exit. If the child has already exited, `Ok(())`
+    /// is returned.
     ///
     /// The mapping to [`ErrorKind`]s is not part of the compatibility contract of the function.
     ///
@@ -1920,7 +1920,7 @@ impl Child {
     ///
     /// let mut command = Command::new("yes");
     /// if let Ok(mut child) = command.spawn() {
-    ///     child.kill().expect("command wasn't running");
+    ///     child.kill().expect("command couldn't be killed");
     /// } else {
     ///     println!("yes command didn't start");
     /// }
diff --git a/library/std/src/process/tests.rs b/library/std/src/process/tests.rs
index d7f4d335d..366b59146 100644
--- a/library/std/src/process/tests.rs
+++ b/library/std/src/process/tests.rs
@@ -582,3 +582,18 @@ fn run_canonical_bat_script() {
     assert!(output.status.success());
     assert_eq!(String::from_utf8_lossy(&output.stdout).trim(), "Hello, fellow Rustaceans!");
 }
+
+#[test]
+fn terminate_exited_process() {
+    let mut cmd = if cfg!(target_os = "android") {
+        let mut p = shell_cmd();
+        p.args(&["-c", "true"]);
+        p
+    } else {
+        known_command()
+    };
+    let mut p = cmd.stdout(Stdio::null()).spawn().unwrap();
+    p.wait().unwrap();
+    assert!(p.kill().is_ok());
+    assert!(p.kill().is_ok());
+}
diff --git a/library/std/src/sync/barrier.rs b/library/std/src/sync/barrier.rs
index 11836b7b6..e39254aa4 100644
--- a/library/std/src/sync/barrier.rs
+++ b/library/std/src/sync/barrier.rs
@@ -13,9 +13,10 @@ use crate::sync::{Condvar, Mutex};
 /// use std::sync::{Arc, Barrier};
 /// use std::thread;
 ///
-/// let mut handles = Vec::with_capacity(10);
-/// let barrier = Arc::new(Barrier::new(10));
-/// for _ in 0..10 {
+/// let n = 10;
+/// let mut handles = Vec::with_capacity(n);
+/// let barrier = Arc::new(Barrier::new(n));
+/// for _ in 0..n {
 ///     let c = Arc::clone(&barrier);
 ///     // The same messages will be printed together.
 ///     // You will NOT see any interleaving.
@@ -105,9 +106,10 @@ impl Barrier {
     /// use std::sync::{Arc, Barrier};
     /// use std::thread;
     ///
-    /// let mut handles = Vec::with_capacity(10);
-    /// let barrier = Arc::new(Barrier::new(10));
-    /// for _ in 0..10 {
+    /// let n = 10;
+    /// let mut handles = Vec::with_capacity(n);
+    /// let barrier = Arc::new(Barrier::new(n));
+    /// for _ in 0..n {
     ///     let c = Arc::clone(&barrier);
     ///     // The same messages will be printed together.
     ///     // You will NOT see any interleaving.
diff --git a/library/std/src/sync/mpmc/waker.rs b/library/std/src/sync/mpmc/waker.rs
index 4912ca4f8..9aab1b941 100644
--- a/library/std/src/sync/mpmc/waker.rs
+++ b/library/std/src/sync/mpmc/waker.rs
@@ -66,26 +66,32 @@ impl Waker {
     /// Attempts to find another thread's entry, select the operation, and wake it up.
     #[inline]
     pub(crate) fn try_select(&mut self) -> Option<Entry> {
-        self.selectors
-            .iter()
-            .position(|selector| {
-                // Does the entry belong to a different thread?
-                selector.cx.thread_id() != current_thread_id()
-                    && selector // Try selecting this operation.
-                        .cx
-                        .try_select(Selected::Operation(selector.oper))
-                        .is_ok()
-                    && {
-                        // Provide the packet.
-                        selector.cx.store_packet(selector.packet);
-                        // Wake the thread up.
-                        selector.cx.unpark();
-                        true
-                    }
-            })
-            // Remove the entry from the queue to keep it clean and improve
-            // performance.
-            .map(|pos| self.selectors.remove(pos))
+        if self.selectors.is_empty() {
+            None
+        } else {
+            let thread_id = current_thread_id();
+
+            self.selectors
+                .iter()
+                .position(|selector| {
+                    // Does the entry belong to a different thread?
+                    selector.cx.thread_id() != thread_id
+                        && selector // Try selecting this operation.
+                            .cx
+                            .try_select(Selected::Operation(selector.oper))
+                            .is_ok()
+                        && {
+                            // Provide the packet.
+                            selector.cx.store_packet(selector.packet);
+                            // Wake the thread up.
+                            selector.cx.unpark();
+                            true
+                        }
+                })
+                // Remove the entry from the queue to keep it clean and improve
+                // performance.
+                .map(|pos| self.selectors.remove(pos))
+        }
     }
 
     /// Notifies all operations waiting to be ready.
diff --git a/library/std/src/sync/mpsc/mod.rs b/library/std/src/sync/mpsc/mod.rs
index 0e0c87d1c..c00134c8b 100644
--- a/library/std/src/sync/mpsc/mod.rs
+++ b/library/std/src/sync/mpsc/mod.rs
@@ -347,8 +347,8 @@ pub struct Sender<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: Send> Send for Sender<T> {}
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> !Sync for Sender<T> {}
+#[stable(feature = "mpsc_sender_sync", since = "1.72.0")]
+unsafe impl<T: Send> Sync for Sender<T> {}
 
 /// The sending-half of Rust's synchronous [`sync_channel`] type.
 ///
diff --git a/library/std/src/sync/once.rs b/library/std/src/sync/once.rs
index 1b17c3108..8c46080e4 100644
--- a/library/std/src/sync/once.rs
+++ b/library/std/src/sync/once.rs
@@ -91,7 +91,7 @@ impl Once {
     /// return).
     ///
     /// If the given closure recursively invokes `call_once` on the same [`Once`]
-    /// instance the exact behavior is not specified, allowed outcomes are
+    /// instance, the exact behavior is not specified: allowed outcomes are
     /// a panic or a deadlock.
     ///
     /// # Examples
diff --git a/library/std/src/sys/common/small_c_string.rs b/library/std/src/sys/common/small_c_string.rs
index 01acd5191..963d17a47 100644
--- a/library/std/src/sys/common/small_c_string.rs
+++ b/library/std/src/sys/common/small_c_string.rs
@@ -19,7 +19,7 @@ pub fn run_path_with_cstr<T, F>(path: &Path, f: F) -> io::Result<T>
 where
     F: FnOnce(&CStr) -> io::Result<T>,
 {
-    run_with_cstr(path.as_os_str().bytes(), f)
+    run_with_cstr(path.as_os_str().as_os_str_bytes(), f)
 }
 
 #[inline]
diff --git a/library/std/src/sys/common/tests.rs b/library/std/src/sys/common/tests.rs
index fb6f5d6af..0a1cbcbe8 100644
--- a/library/std/src/sys/common/tests.rs
+++ b/library/std/src/sys/common/tests.rs
@@ -8,7 +8,7 @@ use core::iter::repeat;
 fn stack_allocation_works() {
     let path = Path::new("abc");
     let result = run_path_with_cstr(path, |p| {
-        assert_eq!(p, &*CString::new(path.as_os_str().bytes()).unwrap());
+        assert_eq!(p, &*CString::new(path.as_os_str().as_os_str_bytes()).unwrap());
         Ok(42)
     });
     assert_eq!(result.unwrap(), 42);
@@ -25,7 +25,7 @@ fn heap_allocation_works() {
     let path = repeat("a").take(384).collect::<String>();
     let path = Path::new(&path);
     let result = run_path_with_cstr(path, |p| {
-        assert_eq!(p, &*CString::new(path.as_os_str().bytes()).unwrap());
+        assert_eq!(p, &*CString::new(path.as_os_str().as_os_str_bytes()).unwrap());
         Ok(42)
     });
     assert_eq!(result.unwrap(), 42);
diff --git a/library/std/src/sys/common/thread_local/fast_local.rs b/library/std/src/sys/common/thread_local/fast_local.rs
index 447044a79..bc5da1a18 100644
--- a/library/std/src/sys/common/thread_local/fast_local.rs
+++ b/library/std/src/sys/common/thread_local/fast_local.rs
@@ -33,20 +33,21 @@ pub macro thread_local_inner {
             // 1 == dtor registered, dtor not run
             // 2 == dtor registered and is running or has run
             #[thread_local]
-            static mut STATE: $crate::primitive::u8 = 0;
+            static STATE: $crate::cell::Cell<$crate::primitive::u8> = $crate::cell::Cell::new(0);
 
+            // Safety: Performs `drop_in_place(ptr as *mut $t)`, and requires
+            // all that comes with it.
             unsafe extern "C" fn destroy(ptr: *mut $crate::primitive::u8) {
-                let ptr = ptr as *mut $t;
-
-                unsafe {
-                    $crate::debug_assert_eq!(STATE, 1);
-                    STATE = 2;
-                    $crate::ptr::drop_in_place(ptr);
-                }
+                $crate::thread::local_impl::abort_on_dtor_unwind(|| {
+                    let old_state = STATE.replace(2);
+                    $crate::debug_assert_eq!(old_state, 1);
+                    // Safety: safety requirement is passed on to caller.
+                    unsafe { $crate::ptr::drop_in_place(ptr.cast::<$t>()); }
+                });
             }
 
             unsafe {
-                match STATE {
+                match STATE.get() {
                     // 0 == we haven't registered a destructor, so do
                     //   so now.
                     0 => {
@@ -54,7 +55,7 @@ pub macro thread_local_inner {
                             $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8,
                             destroy,
                         );
-                        STATE = 1;
+                        STATE.set(1);
                         $crate::option::Option::Some(&VAL)
                     }
                     // 1 == the destructor is registered and the value
@@ -148,7 +149,6 @@ impl<T> fmt::Debug for Key<T> {
         f.debug_struct("Key").finish_non_exhaustive()
     }
 }
-
 impl<T> Key<T> {
     pub const fn new() -> Key<T> {
         Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) }
diff --git a/library/std/src/sys/common/thread_local/mod.rs b/library/std/src/sys/common/thread_local/mod.rs
index 77f645883..975509bd4 100644
--- a/library/std/src/sys/common/thread_local/mod.rs
+++ b/library/std/src/sys/common/thread_local/mod.rs
@@ -101,3 +101,24 @@ mod lazy {
         }
     }
 }
+
+/// Run a callback in a scenario which must not unwind (such as a `extern "C"
+/// fn` declared in a user crate). If the callback unwinds anyway, then
+/// `rtabort` with a message about thread local panicking on drop.
+#[inline]
+pub fn abort_on_dtor_unwind(f: impl FnOnce()) {
+    // Using a guard like this is lower cost.
+    let guard = DtorUnwindGuard;
+    f();
+    core::mem::forget(guard);
+
+    struct DtorUnwindGuard;
+    impl Drop for DtorUnwindGuard {
+        #[inline]
+        fn drop(&mut self) {
+            // This is not terribly descriptive, but it doesn't need to be as we'll
+            // already have printed a panic message at this point.
+            rtabort!("thread local panicked on drop");
+        }
+    }
+}
diff --git a/library/std/src/sys/unix/args.rs b/library/std/src/sys/unix/args.rs
index 9ed4d9c1e..eafd6821f 100644
--- a/library/std/src/sys/unix/args.rs
+++ b/library/std/src/sys/unix/args.rs
@@ -168,7 +168,7 @@ mod imp {
     }
 }
 
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 mod imp {
     use super::Args;
     use crate::ffi::CStr;
@@ -209,7 +209,7 @@ mod imp {
     // for i in (0..[args count])
     //      res.push([args objectAtIndex:i])
     // res
-    #[cfg(any(target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(target_os = "ios", target_os = "tvos", target_os = "watchos"))]
     pub fn args() -> Args {
         use crate::ffi::OsString;
         use crate::mem;
diff --git a/library/std/src/sys/unix/env.rs b/library/std/src/sys/unix/env.rs
index 8c3ef88d8..929e9dae7 100644
--- a/library/std/src/sys/unix/env.rs
+++ b/library/std/src/sys/unix/env.rs
@@ -31,6 +31,17 @@ pub mod os {
     pub const EXE_EXTENSION: &str = "";
 }
 
+#[cfg(target_os = "tvos")]
+pub mod os {
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "tvos";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".dylib";
+    pub const DLL_EXTENSION: &str = "dylib";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
+}
+
 #[cfg(target_os = "watchos")]
 pub mod os {
     pub const FAMILY: &str = "unix";
diff --git a/library/std/src/sys/unix/fd.rs b/library/std/src/sys/unix/fd.rs
index cb630eede..85e020ae4 100644
--- a/library/std/src/sys/unix/fd.rs
+++ b/library/std/src/sys/unix/fd.rs
@@ -44,6 +44,7 @@ const READ_LIMIT: usize = libc::ssize_t::MAX as usize;
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "macos",
     target_os = "netbsd",
     target_os = "openbsd",
@@ -69,6 +70,7 @@ const fn max_iov() -> usize {
     target_os = "emscripten",
     target_os = "freebsd",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "linux",
     target_os = "macos",
     target_os = "netbsd",
@@ -181,6 +183,7 @@ impl FileDesc {
         target_os = "fuchsia",
         target_os = "illumos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "linux",
         target_os = "macos",
         target_os = "netbsd",
@@ -222,6 +225,7 @@ impl FileDesc {
     #[cfg(any(
         all(target_os = "android", target_pointer_width = "32"),
         target_os = "ios",
+        target_os = "tvos",
         target_os = "macos",
     ))]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
@@ -320,6 +324,7 @@ impl FileDesc {
         target_os = "fuchsia",
         target_os = "illumos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "linux",
         target_os = "macos",
         target_os = "netbsd",
@@ -361,6 +366,7 @@ impl FileDesc {
     #[cfg(any(
         all(target_os = "android", target_pointer_width = "32"),
         target_os = "ios",
+        target_os = "tvos",
         target_os = "macos",
     ))]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
@@ -402,7 +408,10 @@ impl FileDesc {
         }
     }
     #[cfg(any(
-        all(target_env = "newlib", not(any(target_os = "espidf", target_os = "horizon"))),
+        all(
+            target_env = "newlib",
+            not(any(target_os = "espidf", target_os = "horizon", target_os = "vita"))
+        ),
         target_os = "solaris",
         target_os = "illumos",
         target_os = "emscripten",
@@ -424,10 +433,10 @@ impl FileDesc {
             Ok(())
         }
     }
-    #[cfg(any(target_os = "espidf", target_os = "horizon"))]
+    #[cfg(any(target_os = "espidf", target_os = "horizon", target_os = "vita"))]
     pub fn set_cloexec(&self) -> io::Result<()> {
-        // FD_CLOEXEC is not supported in ESP-IDF and Horizon OS but there's no need to,
-        // because neither supports spawning processes.
+        // FD_CLOEXEC is not supported in ESP-IDF, Horizon OS and Vita but there's no need to,
+        // because none of them supports spawning processes.
         Ok(())
     }
 
diff --git a/library/std/src/sys/unix/fs.rs b/library/std/src/sys/unix/fs.rs
index 09e9ae272..fbc7f04ce 100644
--- a/library/std/src/sys/unix/fs.rs
+++ b/library/std/src/sys/unix/fs.rs
@@ -15,6 +15,7 @@ use crate::mem;
     target_os = "redox",
     target_os = "illumos",
     target_os = "nto",
+    target_os = "vita",
 ))]
 use crate::mem::MaybeUninit;
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd};
@@ -31,6 +32,7 @@ use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
     all(target_os = "linux", target_env = "gnu"),
     target_os = "macos",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "watchos",
 ))]
 use crate::sys::weak::syscall;
@@ -42,6 +44,7 @@ use libc::{c_int, mode_t};
 #[cfg(any(
     target_os = "macos",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "watchos",
     target_os = "solaris",
     all(target_os = "linux", target_env = "gnu")
@@ -58,6 +61,7 @@ use libc::fstatat64;
     target_os = "redox",
     target_os = "illumos",
     target_os = "nto",
+    target_os = "vita",
 ))]
 use libc::readdir as readdir64;
 #[cfg(target_os = "linux")]
@@ -74,6 +78,7 @@ use libc::readdir64_r;
     target_os = "fuchsia",
     target_os = "redox",
     target_os = "nto",
+    target_os = "vita",
 )))]
 use libc::readdir_r as readdir64_r;
 #[cfg(target_os = "android")]
@@ -283,6 +288,7 @@ unsafe impl Sync for Dir {}
     target_os = "fuchsia",
     target_os = "redox",
     target_os = "nto",
+    target_os = "vita"
 ))]
 pub struct DirEntry {
     dir: Arc<InnerReadDir>,
@@ -304,10 +310,16 @@ pub struct DirEntry {
     target_os = "fuchsia",
     target_os = "redox",
     target_os = "nto",
+    target_os = "vita",
 ))]
 struct dirent64_min {
     d_ino: u64,
-    #[cfg(not(any(target_os = "solaris", target_os = "illumos", target_os = "nto")))]
+    #[cfg(not(any(
+        target_os = "solaris",
+        target_os = "illumos",
+        target_os = "nto",
+        target_os = "vita"
+    )))]
     d_type: u8,
 }
 
@@ -319,6 +331,7 @@ struct dirent64_min {
     target_os = "fuchsia",
     target_os = "redox",
     target_os = "nto",
+    target_os = "vita",
 )))]
 pub struct DirEntry {
     dir: Arc<InnerReadDir>,
@@ -349,7 +362,7 @@ pub struct FilePermissions {
 pub struct FileTimes {
     accessed: Option<SystemTime>,
     modified: Option<SystemTime>,
-    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos", target_os = "tvos"))]
     created: Option<SystemTime>,
 }
 
@@ -508,6 +521,7 @@ impl FileAttr {
         target_os = "openbsd",
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
     ))]
     pub fn created(&self) -> io::Result<SystemTime> {
@@ -519,7 +533,9 @@ impl FileAttr {
         target_os = "openbsd",
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
+        target_os = "vita",
     )))]
     pub fn created(&self) -> io::Result<SystemTime> {
         cfg_has_statx! {
@@ -541,6 +557,11 @@ impl FileAttr {
                             currently",
         ))
     }
+
+    #[cfg(target_os = "vita")]
+    pub fn created(&self) -> io::Result<SystemTime> {
+        Ok(SystemTime::new(self.stat.st_ctime as i64, 0))
+    }
 }
 
 #[cfg(target_os = "nto")]
@@ -594,7 +615,7 @@ impl FileTimes {
         self.modified = Some(t);
     }
 
-    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos", target_os = "tvos"))]
     pub fn set_created(&mut self, t: SystemTime) {
         self.created = Some(t);
     }
@@ -645,6 +666,7 @@ impl Iterator for ReadDir {
         target_os = "redox",
         target_os = "illumos",
         target_os = "nto",
+        target_os = "vita",
     ))]
     fn next(&mut self) -> Option<io::Result<DirEntry>> {
         if self.end_of_stream {
@@ -725,6 +747,7 @@ impl Iterator for ReadDir {
                     continue;
                 }
 
+                #[cfg(not(target_os = "vita"))]
                 let entry = dirent64_min {
                     d_ino: *offset_ptr!(entry_ptr, d_ino) as u64,
                     #[cfg(not(any(
@@ -735,6 +758,9 @@ impl Iterator for ReadDir {
                     d_type: *offset_ptr!(entry_ptr, d_type) as u8,
                 };
 
+                #[cfg(target_os = "vita")]
+                let entry = dirent64_min { d_ino: 0u64 };
+
                 return Some(Ok(DirEntry {
                     entry,
                     name: name.to_owned(),
@@ -752,6 +778,7 @@ impl Iterator for ReadDir {
         target_os = "redox",
         target_os = "illumos",
         target_os = "nto",
+        target_os = "vita",
     )))]
     fn next(&mut self) -> Option<io::Result<DirEntry>> {
         if self.end_of_stream {
@@ -842,6 +869,7 @@ impl DirEntry {
         target_os = "haiku",
         target_os = "vxworks",
         target_os = "nto",
+        target_os = "vita",
     ))]
     pub fn file_type(&self) -> io::Result<FileType> {
         self.metadata().map(|m| m.file_type())
@@ -853,6 +881,7 @@ impl DirEntry {
         target_os = "haiku",
         target_os = "vxworks",
         target_os = "nto",
+        target_os = "vita",
     )))]
     pub fn file_type(&self) -> io::Result<FileType> {
         match self.entry.d_type {
@@ -870,6 +899,7 @@ impl DirEntry {
     #[cfg(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "linux",
         target_os = "emscripten",
@@ -903,6 +933,7 @@ impl DirEntry {
     #[cfg(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "netbsd",
         target_os = "openbsd",
@@ -921,6 +952,7 @@ impl DirEntry {
     #[cfg(not(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "netbsd",
         target_os = "openbsd",
@@ -939,6 +971,7 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox",
         target_os = "nto",
+        target_os = "vita",
     )))]
     fn name_cstr(&self) -> &CStr {
         unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()) }
@@ -951,6 +984,7 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox",
         target_os = "nto",
+        target_os = "vita",
     ))]
     fn name_cstr(&self) -> &CStr {
         &self.name
@@ -1080,11 +1114,21 @@ impl File {
         cvt_r(|| unsafe { os_fsync(self.as_raw_fd()) })?;
         return Ok(());
 
-        #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+        #[cfg(any(
+            target_os = "macos",
+            target_os = "ios",
+            target_os = "tvos",
+            target_os = "watchos",
+        ))]
         unsafe fn os_fsync(fd: c_int) -> c_int {
             libc::fcntl(fd, libc::F_FULLFSYNC)
         }
-        #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "watchos")))]
+        #[cfg(not(any(
+            target_os = "macos",
+            target_os = "ios",
+            target_os = "tvos",
+            target_os = "watchos",
+        )))]
         unsafe fn os_fsync(fd: c_int) -> c_int {
             libc::fsync(fd)
         }
@@ -1094,7 +1138,12 @@ impl File {
         cvt_r(|| unsafe { os_datasync(self.as_raw_fd()) })?;
         return Ok(());
 
-        #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+        #[cfg(any(
+            target_os = "macos",
+            target_os = "ios",
+            target_os = "tvos",
+            target_os = "watchos",
+        ))]
         unsafe fn os_datasync(fd: c_int) -> c_int {
             libc::fcntl(fd, libc::F_FULLFSYNC)
         }
@@ -1113,6 +1162,7 @@ impl File {
             target_os = "android",
             target_os = "freebsd",
             target_os = "ios",
+            target_os = "tvos",
             target_os = "linux",
             target_os = "macos",
             target_os = "netbsd",
@@ -1222,7 +1272,7 @@ impl File {
                     io::ErrorKind::Unsupported,
                     "setting file times not supported",
                 ))
-            } else if #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))] {
+            } else if #[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))] {
                 let mut buf = [mem::MaybeUninit::<libc::timespec>::uninit(); 3];
                 let mut num_times = 0;
                 let mut attrlist: libc::attrlist = unsafe { mem::zeroed() };
@@ -1543,7 +1593,7 @@ pub fn link(original: &Path, link: &Path) -> io::Result<()> {
     run_path_with_cstr(original, |original| {
         run_path_with_cstr(link, |link| {
             cfg_if::cfg_if! {
-                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon"))] {
+                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon", target_os = "vita"))] {
                     // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
                     // it implementation-defined whether `link` follows symlinks, so rely on the
                     // `symlink_hard_link` test in library/std/src/fs/tests.rs to check the behavior.
@@ -1666,6 +1716,8 @@ fn open_to_and_set_permissions(
         .truncate(true)
         .open(to)?;
     let writer_metadata = writer.metadata()?;
+    // fchmod is broken on vita
+    #[cfg(not(target_os = "vita"))]
     if writer_metadata.is_file() {
         // Set the correct file permissions, in case the file already existed.
         // Don't set the permissions on already existing non-files like
@@ -1680,6 +1732,7 @@ fn open_to_and_set_permissions(
     target_os = "android",
     target_os = "macos",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "watchos",
 )))]
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
@@ -1707,7 +1760,7 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     }
 }
 
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     use crate::sync::atomic::{AtomicBool, Ordering};
 
@@ -1844,11 +1897,12 @@ pub fn chroot(dir: &Path) -> io::Result<()> {
 
 pub use remove_dir_impl::remove_dir_all;
 
-// Fallback for REDOX, ESP-ID, Horizon, and Miri
+// Fallback for REDOX, ESP-ID, Horizon, Vita and Miri
 #[cfg(any(
     target_os = "redox",
     target_os = "espidf",
     target_os = "horizon",
+    target_os = "vita",
     target_os = "nto",
     miri
 ))]
@@ -1861,6 +1915,7 @@ mod remove_dir_impl {
     target_os = "redox",
     target_os = "espidf",
     target_os = "horizon",
+    target_os = "vita",
     target_os = "nto",
     miri
 )))]
diff --git a/library/std/src/sys/unix/kernel_copy.rs b/library/std/src/sys/unix/kernel_copy.rs
index 16c8e0c0e..7d49bbdcb 100644
--- a/library/std/src/sys/unix/kernel_copy.rs
+++ b/library/std/src/sys/unix/kernel_copy.rs
@@ -466,7 +466,7 @@ impl<T: CopyRead> CopyRead for Take<T> {
     }
 }
 
-impl<T: CopyRead> CopyRead for BufReader<T> {
+impl<T: ?Sized + CopyRead> CopyRead for BufReader<T> {
     fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> {
         let buf = self.buffer();
         let buf = &buf[0..min(buf.len(), outer_limit.try_into().unwrap_or(usize::MAX))];
@@ -495,7 +495,7 @@ impl<T: CopyRead> CopyRead for BufReader<T> {
     }
 }
 
-impl<T: CopyWrite> CopyWrite for BufWriter<T> {
+impl<T: ?Sized + CopyWrite> CopyWrite for BufWriter<T> {
     fn properties(&self) -> CopyParams {
         self.get_ref().properties()
     }
diff --git a/library/std/src/sys/unix/l4re.rs b/library/std/src/sys/unix/l4re.rs
index ee016887e..fe9559f2a 100644
--- a/library/std/src/sys/unix/l4re.rs
+++ b/library/std/src/sys/unix/l4re.rs
@@ -10,7 +10,7 @@ macro_rules! unimpl {
 pub mod net {
     #![allow(warnings)]
     use crate::fmt;
-    use crate::io::{self, IoSlice, IoSliceMut};
+    use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
     use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr};
     use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
     use crate::sys::fd::FileDesc;
@@ -218,6 +218,10 @@ pub mod net {
             unimpl!();
         }
 
+        pub fn read_buf(&self, _: BorrowedCursor<'_>) -> io::Result<()> {
+            unimpl!();
+        }
+
         pub fn read_vectored(&self, _: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
             unimpl!();
         }
diff --git a/library/std/src/sys/unix/locks/pthread_condvar.rs b/library/std/src/sys/unix/locks/pthread_condvar.rs
index 192fa216d..2dc1b0c60 100644
--- a/library/std/src/sys/unix/locks/pthread_condvar.rs
+++ b/library/std/src/sys/unix/locks/pthread_condvar.rs
@@ -32,6 +32,7 @@ impl LazyInit for AllocatedCondvar {
             if #[cfg(any(
                 target_os = "macos",
                 target_os = "ios",
+                target_os = "tvos",
                 target_os = "watchos",
                 target_os = "l4re",
                 target_os = "android",
@@ -124,6 +125,7 @@ impl Condvar {
     #[cfg(not(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "android",
         target_os = "espidf",
@@ -158,6 +160,7 @@ impl Condvar {
     #[cfg(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "android",
         target_os = "espidf",
diff --git a/library/std/src/sys/unix/mod.rs b/library/std/src/sys/unix/mod.rs
index bb9e65e68..326f1481e 100644
--- a/library/std/src/sys/unix/mod.rs
+++ b/library/std/src/sys/unix/mod.rs
@@ -88,6 +88,7 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
             // The poll on Darwin doesn't set POLLNVAL for closed fds.
             target_os = "macos",
             target_os = "ios",
+            target_os = "tvos",
             target_os = "watchos",
             target_os = "redox",
             target_os = "l4re",
@@ -164,12 +165,7 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     }
 
     unsafe fn reset_sigpipe(#[allow(unused_variables)] sigpipe: u8) {
-        #[cfg(not(any(
-            target_os = "emscripten",
-            target_os = "fuchsia",
-            target_os = "horizon",
-            target_os = "vita"
-        )))]
+        #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia", target_os = "horizon")))]
         {
             // We don't want to add this as a public type to std, nor do we
             // want to `include!` a file from the compiler (which would break
@@ -207,7 +203,6 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     target_os = "emscripten",
     target_os = "fuchsia",
     target_os = "horizon",
-    target_os = "vita"
 )))]
 static UNIX_SIGPIPE_ATTR_SPECIFIED: crate::sync::atomic::AtomicBool =
     crate::sync::atomic::AtomicBool::new(false);
@@ -217,7 +212,6 @@ static UNIX_SIGPIPE_ATTR_SPECIFIED: crate::sync::atomic::AtomicBool =
     target_os = "emscripten",
     target_os = "fuchsia",
     target_os = "horizon",
-    target_os = "vita",
 )))]
 pub(crate) fn unix_sigpipe_attr_specified() -> bool {
     UNIX_SIGPIPE_ATTR_SPECIFIED.load(crate::sync::atomic::Ordering::Relaxed)
@@ -395,7 +389,7 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "macos")] {
         #[link(name = "System")]
         extern "C" {}
-    } else if #[cfg(any(target_os = "ios", target_os = "watchos"))] {
+    } else if #[cfg(any(target_os = "ios", target_os = "tvos", target_os = "watchos"))] {
         #[link(name = "System")]
         #[link(name = "objc")]
         #[link(name = "Security", kind = "framework")]
@@ -408,6 +402,9 @@ cfg_if::cfg_if! {
     } else if #[cfg(all(target_os = "linux", target_env = "uclibc"))] {
         #[link(name = "dl")]
         extern "C" {}
+    } else if #[cfg(target_os = "vita")] {
+        #[link(name = "pthread", kind = "static", modifiers = "-bundle")]
+        extern "C" {}
     }
 }
 
diff --git a/library/std/src/sys/unix/net.rs b/library/std/src/sys/unix/net.rs
index 39edb136c..7258c222a 100644
--- a/library/std/src/sys/unix/net.rs
+++ b/library/std/src/sys/unix/net.rs
@@ -454,12 +454,18 @@ impl Socket {
         Ok(passcred != 0)
     }
 
-    #[cfg(not(any(target_os = "solaris", target_os = "illumos")))]
+    #[cfg(not(any(target_os = "solaris", target_os = "illumos", target_os = "vita")))]
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
         cvt(unsafe { libc::ioctl(self.as_raw_fd(), libc::FIONBIO, &mut nonblocking) }).map(drop)
     }
 
+    #[cfg(target_os = "vita")]
+    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
+        let option = nonblocking as libc::c_int;
+        setsockopt(self, libc::SOL_SOCKET, libc::SO_NONBLOCK, option)
+    }
+
     #[cfg(any(target_os = "solaris", target_os = "illumos"))]
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         // FIONBIO is inadequate for sockets on illumos/Solaris, so use the
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index 8edfd3313..a68c14758 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -63,7 +63,13 @@ extern "C" {
     #[cfg_attr(any(target_os = "solaris", target_os = "illumos"), link_name = "___errno")]
     #[cfg_attr(target_os = "nto", link_name = "__get_errno_ptr")]
     #[cfg_attr(
-        any(target_os = "macos", target_os = "ios", target_os = "freebsd", target_os = "watchos"),
+        any(
+            target_os = "macos",
+            target_os = "ios",
+            target_os = "tvos",
+            target_os = "freebsd",
+            target_os = "watchos"
+        ),
         link_name = "__error"
     )]
     #[cfg_attr(target_os = "haiku", link_name = "_errnop")]
@@ -375,7 +381,7 @@ pub fn current_exe() -> io::Result<PathBuf> {
     Ok(PathBuf::from(OsString::from_vec(e)))
 }
 
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 pub fn current_exe() -> io::Result<PathBuf> {
     unsafe {
         let mut sz: u32 = 0;
@@ -609,6 +615,7 @@ pub fn home_dir() -> Option<PathBuf> {
     #[cfg(any(
         target_os = "android",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "emscripten",
         target_os = "redox",
@@ -623,6 +630,7 @@ pub fn home_dir() -> Option<PathBuf> {
     #[cfg(not(any(
         target_os = "android",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "emscripten",
         target_os = "redox",
diff --git a/library/std/src/sys/unix/os_str.rs b/library/std/src/sys/unix/os_str.rs
index 488217f39..f7333fd5a 100644
--- a/library/std/src/sys/unix/os_str.rs
+++ b/library/std/src/sys/unix/os_str.rs
@@ -193,17 +193,22 @@ impl Buf {
 
 impl Slice {
     #[inline]
-    fn from_u8_slice(s: &[u8]) -> &Slice {
+    pub fn as_os_str_bytes(&self) -> &[u8] {
+        &self.inner
+    }
+
+    #[inline]
+    pub unsafe fn from_os_str_bytes_unchecked(s: &[u8]) -> &Slice {
         unsafe { mem::transmute(s) }
     }
 
     #[inline]
     pub fn from_str(s: &str) -> &Slice {
-        Slice::from_u8_slice(s.as_bytes())
+        unsafe { Slice::from_os_str_bytes_unchecked(s.as_bytes()) }
     }
 
-    pub fn to_str(&self) -> Option<&str> {
-        str::from_utf8(&self.inner).ok()
+    pub fn to_str(&self) -> Result<&str, crate::str::Utf8Error> {
+        str::from_utf8(&self.inner)
     }
 
     pub fn to_string_lossy(&self) -> Cow<'_, str> {
diff --git a/library/std/src/sys/unix/os_str/tests.rs b/library/std/src/sys/unix/os_str/tests.rs
index 22ba0c923..91bc0e61a 100644
--- a/library/std/src/sys/unix/os_str/tests.rs
+++ b/library/std/src/sys/unix/os_str/tests.rs
@@ -2,7 +2,7 @@ use super::*;
 
 #[test]
 fn slice_debug_output() {
-    let input = Slice::from_u8_slice(b"\xF0hello,\tworld");
+    let input = unsafe { Slice::from_os_str_bytes_unchecked(b"\xF0hello,\tworld") };
     let expected = r#""\xF0hello,\tworld""#;
     let output = format!("{input:?}");
 
@@ -11,8 +11,7 @@ fn slice_debug_output() {
 
 #[test]
 fn display() {
-    assert_eq!(
-        "Hello\u{FFFD}\u{FFFD} There\u{FFFD} Goodbye",
-        Slice::from_u8_slice(b"Hello\xC0\x80 There\xE6\x83 Goodbye").to_string(),
-    );
+    assert_eq!("Hello\u{FFFD}\u{FFFD} There\u{FFFD} Goodbye", unsafe {
+        Slice::from_os_str_bytes_unchecked(b"Hello\xC0\x80 There\xE6\x83 Goodbye").to_string()
+    },);
 }
diff --git a/library/std/src/sys/unix/path.rs b/library/std/src/sys/unix/path.rs
index a98a69e2d..935245f63 100644
--- a/library/std/src/sys/unix/path.rs
+++ b/library/std/src/sys/unix/path.rs
@@ -30,7 +30,7 @@ pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
 
     // Get the components, skipping the redundant leading "." component if it exists.
     let mut components = path.strip_prefix(".").unwrap_or(path).components();
-    let path_os = path.as_os_str().bytes();
+    let path_os = path.as_os_str().as_os_str_bytes();
 
     let mut normalized = if path.is_absolute() {
         // "If a pathname begins with two successive <slash> characters, the
diff --git a/library/std/src/sys/unix/process/process_common.rs b/library/std/src/sys/unix/process/process_common.rs
index afd03d79c..640648e87 100644
--- a/library/std/src/sys/unix/process/process_common.rs
+++ b/library/std/src/sys/unix/process/process_common.rs
@@ -164,9 +164,9 @@ pub enum ProgramKind {
 
 impl ProgramKind {
     fn new(program: &OsStr) -> Self {
-        if program.bytes().starts_with(b"/") {
+        if program.as_os_str_bytes().starts_with(b"/") {
             Self::Absolute
-        } else if program.bytes().contains(&b'/') {
+        } else if program.as_os_str_bytes().contains(&b'/') {
             // If the program has more than one component in it, it is a relative path.
             Self::Relative
         } else {
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index 612d43fe2..0ce93af66 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -15,6 +15,8 @@ use crate::sys::weak::raw_syscall;
 
 #[cfg(any(
     target_os = "macos",
+    target_os = "watchos",
+    target_os = "tvos",
     target_os = "freebsd",
     all(target_os = "linux", target_env = "gnu"),
     all(target_os = "linux", target_env = "musl"),
@@ -28,15 +30,38 @@ use libc::RTP_ID as pid_t;
 #[cfg(not(target_os = "vxworks"))]
 use libc::{c_int, pid_t};
 
-#[cfg(not(any(target_os = "vxworks", target_os = "l4re")))]
+#[cfg(not(any(
+    target_os = "vxworks",
+    target_os = "l4re",
+    target_os = "tvos",
+    target_os = "watchos",
+)))]
 use libc::{gid_t, uid_t};
 
 cfg_if::cfg_if! {
     if #[cfg(all(target_os = "nto", target_env = "nto71"))] {
         use crate::thread;
         use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
-        // arbitrary number of tries:
-        const MAX_FORKSPAWN_TRIES: u32 = 4;
+        use crate::time::Duration;
+        use crate::sync::LazyLock;
+        // Get smallest amount of time we can sleep.
+        // Return a common value if it cannot be determined.
+        fn get_clock_resolution() -> Duration {
+            static MIN_DELAY: LazyLock<Duration, fn() -> Duration> = LazyLock::new(|| {
+                let mut mindelay = libc::timespec { tv_sec: 0, tv_nsec: 0 };
+                if unsafe { libc::clock_getres(libc::CLOCK_MONOTONIC, &mut mindelay) } == 0
+                {
+                    Duration::from_nanos(mindelay.tv_nsec as u64)
+                } else {
+                    Duration::from_millis(1)
+                }
+            });
+            *MIN_DELAY
+        }
+        // Arbitrary minimum sleep duration for retrying fork/spawn
+        const MIN_FORKSPAWN_SLEEP: Duration = Duration::from_nanos(1);
+        // Maximum duration of sleeping before giving up and returning an error
+        const MAX_FORKSPAWN_SLEEP: Duration = Duration::from_millis(1000);
     }
 }
 
@@ -66,7 +91,6 @@ impl Command {
         if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
             return Ok((ret, ours));
         }
-
         let (input, output) = sys::pipe::anon_pipe()?;
 
         // Whatever happens after the fork is almost for sure going to touch or
@@ -148,9 +172,31 @@ impl Command {
         crate::sys_common::process::wait_with_output(proc, pipes)
     }
 
+    // WatchOS and TVOS headers mark the `fork`/`exec*` functions with
+    // `__WATCHOS_PROHIBITED __TVOS_PROHIBITED`, and indicate that the
+    // `posix_spawn*` functions should be used instead. It isn't entirely clear
+    // what `PROHIBITED` means here (e.g. if calls to these functions are
+    // allowed to exist in dead code), but it sounds bad, so we go out of our
+    // way to avoid that all-together.
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    const ERR_APPLE_TV_WATCH_NO_FORK_EXEC: Error = io::const_io_error!(
+        ErrorKind::Unsupported,
+        "`fork`+`exec`-based process spawning is not supported on this target",
+    );
+
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
+        return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
+    }
+
     // Attempts to fork the process. If successful, returns Ok((0, -1))
     // in the child, and Ok((child_pid, -1)) in the parent.
-    #[cfg(not(any(target_os = "linux", all(target_os = "nto", target_env = "nto71"))))]
+    #[cfg(not(any(
+        target_os = "linux",
+        target_os = "watchos",
+        target_os = "tvos",
+        all(target_os = "nto", target_env = "nto71"),
+    )))]
     unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
         cvt(libc::fork()).map(|res| (res, -1))
     }
@@ -163,12 +209,25 @@ impl Command {
     unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
         use crate::sys::os::errno;
 
-        let mut tries_left = MAX_FORKSPAWN_TRIES;
+        let mut delay = MIN_FORKSPAWN_SLEEP;
+
         loop {
             let r = libc::fork();
-            if r == -1 as libc::pid_t && tries_left > 0 && errno() as libc::c_int == libc::EBADF {
-                thread::yield_now();
-                tries_left -= 1;
+            if r == -1 as libc::pid_t && errno() as libc::c_int == libc::EBADF {
+                if delay < get_clock_resolution() {
+                    // We cannot sleep this short (it would be longer).
+                    // Yield instead.
+                    thread::yield_now();
+                } else if delay < MAX_FORKSPAWN_SLEEP {
+                    thread::sleep(delay);
+                } else {
+                    return Err(io::const_io_error!(
+                        ErrorKind::WouldBlock,
+                        "forking returned EBADF too often",
+                    ));
+                }
+                delay *= 2;
+                continue;
             } else {
                 return cvt(r).map(|res| (res, -1));
             }
@@ -308,6 +367,7 @@ impl Command {
     // allocation). Instead we just close it manually. This will never
     // have the drop glue anyway because this code never returns (the
     // child will either exec() or invoke libc::exit)
+    #[cfg(not(any(target_os = "tvos", target_os = "watchos")))]
     unsafe fn do_exec(
         &mut self,
         stdio: ChildPipes,
@@ -414,8 +474,19 @@ impl Command {
         Err(io::Error::last_os_error())
     }
 
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    unsafe fn do_exec(
+        &mut self,
+        _stdio: ChildPipes,
+        _maybe_envp: Option<&CStringArray>,
+    ) -> Result<!, io::Error> {
+        return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
+    }
+
     #[cfg(not(any(
         target_os = "macos",
+        target_os = "tvos",
+        target_os = "watchos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
@@ -433,6 +504,9 @@ impl Command {
     // directly.
     #[cfg(any(
         target_os = "macos",
+        // FIXME: `target_os = "ios"`?
+        target_os = "tvos",
+        target_os = "watchos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
@@ -480,17 +554,28 @@ impl Command {
             attrp: *const posix_spawnattr_t,
             argv: *const *mut c_char,
             envp: *const *mut c_char,
-        ) -> i32 {
-            let mut tries_left = MAX_FORKSPAWN_TRIES;
+        ) -> io::Result<i32> {
+            let mut delay = MIN_FORKSPAWN_SLEEP;
             loop {
                 match libc::posix_spawnp(pid, file, file_actions, attrp, argv, envp) {
-                    libc::EBADF if tries_left > 0 => {
-                        thread::yield_now();
-                        tries_left -= 1;
+                    libc::EBADF => {
+                        if delay < get_clock_resolution() {
+                            // We cannot sleep this short (it would be longer).
+                            // Yield instead.
+                            thread::yield_now();
+                        } else if delay < MAX_FORKSPAWN_SLEEP {
+                            thread::sleep(delay);
+                        } else {
+                            return Err(io::const_io_error!(
+                                ErrorKind::WouldBlock,
+                                "posix_spawnp returned EBADF too often",
+                            ));
+                        }
+                        delay *= 2;
                         continue;
                     }
                     r => {
-                        return r;
+                        return Ok(r);
                     }
                 }
             }
@@ -508,7 +593,7 @@ impl Command {
         }
         let addchdir = match self.get_cwd() {
             Some(cwd) => {
-                if cfg!(target_os = "macos") {
+                if cfg!(any(target_os = "macos", target_os = "tvos", target_os = "watchos")) {
                     // There is a bug in macOS where a relative executable
                     // path like "../myprogram" will cause `posix_spawn` to
                     // successfully launch the program, but erroneously return
@@ -620,14 +705,20 @@ impl Command {
             let spawn_fn = libc::posix_spawnp;
             #[cfg(target_os = "nto")]
             let spawn_fn = retrying_libc_posix_spawnp;
-            cvt_nz(spawn_fn(
+
+            let spawn_res = spawn_fn(
                 &mut p.pid,
                 self.get_program_cstr().as_ptr(),
                 file_actions.0.as_ptr(),
                 attrs.0.as_ptr(),
                 self.get_argv().as_ptr() as *const _,
                 envp as *const _,
-            ))?;
+            );
+
+            #[cfg(target_os = "nto")]
+            let spawn_res = spawn_res?;
+
+            cvt_nz(spawn_res)?;
             Ok(Some(p))
         }
     }
@@ -671,12 +762,9 @@ impl Process {
     pub fn kill(&mut self) -> io::Result<()> {
         // If we've already waited on this process then the pid can be recycled
         // and used for another process, and we probably shouldn't be killing
-        // random processes, so just return an error.
+        // random processes, so return Ok because the process has exited already.
         if self.status.is_some() {
-            Err(io::const_io_error!(
-                ErrorKind::InvalidInput,
-                "invalid argument: can't kill an exited process",
-            ))
+            Ok(())
         } else {
             cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
@@ -788,31 +876,47 @@ fn signal_string(signal: i32) -> &'static str {
         libc::SIGILL => " (SIGILL)",
         libc::SIGTRAP => " (SIGTRAP)",
         libc::SIGABRT => " (SIGABRT)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGBUS => " (SIGBUS)",
         libc::SIGFPE => " (SIGFPE)",
         libc::SIGKILL => " (SIGKILL)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGUSR1 => " (SIGUSR1)",
         libc::SIGSEGV => " (SIGSEGV)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGUSR2 => " (SIGUSR2)",
         libc::SIGPIPE => " (SIGPIPE)",
         libc::SIGALRM => " (SIGALRM)",
         libc::SIGTERM => " (SIGTERM)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGCHLD => " (SIGCHLD)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGCONT => " (SIGCONT)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGSTOP => " (SIGSTOP)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGTSTP => " (SIGTSTP)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGTTIN => " (SIGTTIN)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGTTOU => " (SIGTTOU)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGURG => " (SIGURG)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGXCPU => " (SIGXCPU)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGXFSZ => " (SIGXFSZ)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGVTALRM => " (SIGVTALRM)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGPROF => " (SIGPROF)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGWINCH => " (SIGWINCH)",
-        #[cfg(not(target_os = "haiku"))]
+        #[cfg(not(any(target_os = "haiku", target_os = "l4re")))]
         libc::SIGIO => " (SIGIO)",
         #[cfg(target_os = "haiku")]
         libc::SIGPOLL => " (SIGPOLL)",
+        #[cfg(not(target_os = "l4re"))]
         libc::SIGSYS => " (SIGSYS)",
         // For information on Linux signals, run `man 7 signal`
         #[cfg(all(
diff --git a/library/std/src/sys/unix/process/process_vxworks.rs b/library/std/src/sys/unix/process/process_vxworks.rs
index c40e7ada0..f70d3cb39 100644
--- a/library/std/src/sys/unix/process/process_vxworks.rs
+++ b/library/std/src/sys/unix/process/process_vxworks.rs
@@ -144,12 +144,9 @@ impl Process {
     pub fn kill(&mut self) -> io::Result<()> {
         // If we've already waited on this process then the pid can be recycled
         // and used for another process, and we probably shouldn't be killing
-        // random processes, so just return an error.
+        // random processes, so return Ok because the process has exited already.
         if self.status.is_some() {
-            Err(io::const_io_error!(
-                ErrorKind::InvalidInput,
-                "invalid argument: can't kill an exited process",
-            ))
+            Ok(())
         } else {
             cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
diff --git a/library/std/src/sys/unix/rand.rs b/library/std/src/sys/unix/rand.rs
index d8b63546b..d471be33e 100644
--- a/library/std/src/sys/unix/rand.rs
+++ b/library/std/src/sys/unix/rand.rs
@@ -14,6 +14,7 @@ pub fn hashmap_random_keys() -> (u64, u64) {
     unix,
     not(target_os = "macos"),
     not(target_os = "ios"),
+    not(target_os = "tvos"),
     not(target_os = "watchos"),
     not(target_os = "openbsd"),
     not(target_os = "freebsd"),
@@ -198,7 +199,7 @@ mod imp {
 // once per thread in `hashmap_random_keys`. Therefore `SecRandomCopyBytes` is
 // only used on iOS where direct access to `/dev/urandom` is blocked by the
 // sandbox.
-#[cfg(any(target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "ios", target_os = "tvos", target_os = "watchos"))]
 mod imp {
     use crate::io;
     use crate::ptr;
diff --git a/library/std/src/sys/unix/thread.rs b/library/std/src/sys/unix/thread.rs
index 7307d9b2c..4f2d9cf36 100644
--- a/library/std/src/sys/unix/thread.rs
+++ b/library/std/src/sys/unix/thread.rs
@@ -150,7 +150,7 @@ impl Thread {
         }
     }
 
-    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
     pub fn set_name(name: &CStr) {
         unsafe {
             let name = truncate_cstr::<{ libc::MAXTHREADNAMESIZE }>(name);
@@ -284,7 +284,13 @@ impl Drop for Thread {
     }
 }
 
-#[cfg(any(target_os = "linux", target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(
+    target_os = "linux",
+    target_os = "macos",
+    target_os = "ios",
+    target_os = "tvos",
+    target_os = "watchos",
+))]
 fn truncate_cstr<const MAX_WITH_NUL: usize>(cstr: &CStr) -> [libc::c_char; MAX_WITH_NUL] {
     let mut result = [0; MAX_WITH_NUL];
     for (src, dst) in cstr.to_bytes().iter().zip(&mut result[..MAX_WITH_NUL - 1]) {
@@ -300,6 +306,7 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
             target_os = "emscripten",
             target_os = "fuchsia",
             target_os = "ios",
+            target_os = "tvos",
             target_os = "linux",
             target_os = "macos",
             target_os = "solaris",
@@ -345,6 +352,29 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
                 }
             }
 
+            #[cfg(target_os = "netbsd")]
+            {
+                unsafe {
+                    let set = libc::_cpuset_create();
+                    if !set.is_null() {
+                        let mut count: usize = 0;
+                        if libc::pthread_getaffinity_np(libc::pthread_self(), libc::_cpuset_size(set), set) == 0 {
+                            for i in 0..u64::MAX {
+                                match libc::_cpuset_isset(i, set) {
+                                    -1 => break,
+                                    0 => continue,
+                                    _ => count = count + 1,
+                                }
+                            }
+                        }
+                        libc::_cpuset_destroy(set);
+                        if let Some(count) = NonZeroUsize::new(count) {
+                            return Ok(count);
+                        }
+                    }
+                }
+            }
+
             let mut cpus: libc::c_uint = 0;
             let mut cpus_size = crate::mem::size_of_val(&cpus);
 
diff --git a/library/std/src/sys/unix/thread_parking/pthread.rs b/library/std/src/sys/unix/thread_parking/pthread.rs
index 43046ed07..ae805d843 100644
--- a/library/std/src/sys/unix/thread_parking/pthread.rs
+++ b/library/std/src/sys/unix/thread_parking/pthread.rs
@@ -46,6 +46,7 @@ unsafe fn wait_timeout(
     #[cfg(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "espidf",
         target_os = "horizon",
@@ -73,6 +74,7 @@ unsafe fn wait_timeout(
     #[cfg(not(any(
         target_os = "macos",
         target_os = "ios",
+        target_os = "tvos",
         target_os = "watchos",
         target_os = "espidf",
         target_os = "horizon",
@@ -120,10 +122,12 @@ impl Parker {
             if #[cfg(any(
                 target_os = "macos",
                 target_os = "ios",
+                target_os = "tvos",
                 target_os = "watchos",
                 target_os = "l4re",
                 target_os = "android",
-                target_os = "redox"
+                target_os = "redox",
+                target_os = "vita",
             ))] {
                 addr_of_mut!((*parker).cvar).write(UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER));
             } else if #[cfg(any(target_os = "espidf", target_os = "horizon"))] {
diff --git a/library/std/src/sys/unix/time.rs b/library/std/src/sys/unix/time.rs
index a9fbc7ab1..17b4130c2 100644
--- a/library/std/src/sys/unix/time.rs
+++ b/library/std/src/sys/unix/time.rs
@@ -219,7 +219,8 @@ impl From<__timespec64> for Timespec {
 #[cfg(any(
     all(target_os = "macos", any(not(target_arch = "aarch64"))),
     target_os = "ios",
-    target_os = "watchos"
+    target_os = "watchos",
+    target_os = "tvos"
 ))]
 mod inner {
     use crate::sync::atomic::{AtomicU64, Ordering};
@@ -339,7 +340,8 @@ mod inner {
 #[cfg(not(any(
     all(target_os = "macos", any(not(target_arch = "aarch64"))),
     target_os = "ios",
-    target_os = "watchos"
+    target_os = "watchos",
+    target_os = "tvos"
 )))]
 mod inner {
     use crate::fmt;
diff --git a/library/std/src/sys/unix/weak.rs b/library/std/src/sys/unix/weak.rs
index 62ffee70b..61088ff16 100644
--- a/library/std/src/sys/unix/weak.rs
+++ b/library/std/src/sys/unix/weak.rs
@@ -28,7 +28,7 @@ use crate::ptr;
 use crate::sync::atomic::{self, AtomicPtr, Ordering};
 
 // We can use true weak linkage on ELF targets.
-#[cfg(not(any(target_os = "macos", target_os = "ios")))]
+#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "tvos")))]
 pub(crate) macro weak {
     (fn $name:ident($($t:ty),*) -> $ret:ty) => (
         let ref $name: ExternWeak<unsafe extern "C" fn($($t),*) -> $ret> = {
@@ -43,7 +43,7 @@ pub(crate) macro weak {
 }
 
 // On non-ELF targets, use the dlsym approximation of weak linkage.
-#[cfg(any(target_os = "macos", target_os = "ios"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos"))]
 pub(crate) use self::dlsym as weak;
 
 pub(crate) struct ExternWeak<F: Copy> {
diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index 9a8b2a0be..1b50c2ea6 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -96,7 +96,7 @@ impl WasiFd {
         unsafe { wasi::fd_sync(self.as_raw_fd() as wasi::Fd).map_err(err2io) }
     }
 
-    pub fn advise(&self, offset: u64, len: u64, advice: wasi::Advice) -> io::Result<()> {
+    pub(crate) fn advise(&self, offset: u64, len: u64, advice: wasi::Advice) -> io::Result<()> {
         unsafe {
             wasi::fd_advise(self.as_raw_fd() as wasi::Fd, offset, len, advice).map_err(err2io)
         }
@@ -179,7 +179,7 @@ impl WasiFd {
         }
     }
 
-    pub fn filestat_get(&self) -> io::Result<wasi::Filestat> {
+    pub(crate) fn filestat_get(&self) -> io::Result<wasi::Filestat> {
         unsafe { wasi::fd_filestat_get(self.as_raw_fd() as wasi::Fd).map_err(err2io) }
     }
 
@@ -199,7 +199,7 @@ impl WasiFd {
         unsafe { wasi::fd_filestat_set_size(self.as_raw_fd() as wasi::Fd, size).map_err(err2io) }
     }
 
-    pub fn path_filestat_get(
+    pub(crate) fn path_filestat_get(
         &self,
         flags: wasi::Lookupflags,
         path: &str,
diff --git a/library/std/src/sys/wasi/fs.rs b/library/std/src/sys/wasi/fs.rs
index 8d1dbf591..437aae3ae 100644
--- a/library/std/src/sys/wasi/fs.rs
+++ b/library/std/src/sys/wasi/fs.rs
@@ -104,7 +104,7 @@ impl FileAttr {
         Ok(SystemTime::from_wasi_timestamp(self.meta.ctim))
     }
 
-    pub fn as_wasi(&self) -> &wasi::Filestat {
+    pub(crate) fn as_wasi(&self) -> &wasi::Filestat {
         &self.meta
     }
 }
@@ -142,7 +142,7 @@ impl FileType {
         self.bits == wasi::FILETYPE_SYMBOLIC_LINK
     }
 
-    pub fn bits(&self) -> wasi::Filetype {
+    pub(crate) fn bits(&self) -> wasi::Filetype {
         self.bits
     }
 }
diff --git a/library/std/src/sys/windows/args.rs b/library/std/src/sys/windows/args.rs
index 5bfd8b52e..6b597f499 100644
--- a/library/std/src/sys/windows/args.rs
+++ b/library/std/src/sys/windows/args.rs
@@ -226,7 +226,7 @@ pub(crate) fn append_arg(cmd: &mut Vec<u16>, arg: &Arg, force_quotes: bool) -> i
     // that it actually gets passed through on the command line or otherwise
     // it will be dropped entirely when parsed on the other end.
     ensure_no_nuls(arg)?;
-    let arg_bytes = arg.bytes();
+    let arg_bytes = arg.as_os_str_bytes();
     let (quote, escape) = match quote {
         Quote::Always => (true, true),
         Quote::Auto => {
@@ -297,7 +297,9 @@ pub(crate) fn make_bat_command_line(
         // * `|<>` pipe/redirect characters.
         const SPECIAL: &[u8] = b"\t &()[]{}^=;!'+,`~%|<>";
         let force_quotes = match arg {
-            Arg::Regular(arg) if !force_quotes => arg.bytes().iter().any(|c| SPECIAL.contains(c)),
+            Arg::Regular(arg) if !force_quotes => {
+                arg.as_os_str_bytes().iter().any(|c| SPECIAL.contains(c))
+            }
             _ => force_quotes,
         };
         append_arg(&mut cmd, arg, force_quotes)?;
diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 2bc40c474..d9ccba0e9 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -12,13 +12,13 @@ use crate::os::windows::io::{AsRawHandle, BorrowedHandle};
 use crate::ptr;
 use core::ffi::NonZero_c_ulong;
 
-#[path = "c/windows_sys.rs"] // c.rs is included from two places so we need to specify this
 mod windows_sys;
 pub use windows_sys::*;
 
 pub type DWORD = c_ulong;
 pub type NonZeroDWORD = NonZero_c_ulong;
 pub type LARGE_INTEGER = c_longlong;
+#[cfg_attr(target_vendor = "uwp", allow(unused))]
 pub type LONG = c_long;
 pub type UINT = c_uint;
 pub type WCHAR = u16;
@@ -267,6 +267,8 @@ pub unsafe fn getaddrinfo(
     windows_sys::getaddrinfo(node.cast::<u8>(), service.cast::<u8>(), hints, res)
 }
 
+cfg_if::cfg_if! {
+if #[cfg(not(target_vendor = "uwp"))] {
 pub unsafe fn NtReadFile(
     filehandle: BorrowedHandle<'_>,
     event: HANDLE,
@@ -313,6 +315,8 @@ pub unsafe fn NtWriteFile(
         key.map(|k| k as *const u32).unwrap_or(ptr::null()),
     )
 }
+}
+}
 
 // Functions that aren't available on every version of Windows that we support,
 // but we still use them and just provide some form of a fallback implementation.
@@ -376,4 +380,98 @@ compat_fn_with_fallback! {
     ) -> NTSTATUS {
         panic!("keyed events not available")
     }
+
+    // These functions are available on UWP when lazily loaded. They will fail WACK if loaded statically.
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtCreateFile(
+        filehandle: *mut HANDLE,
+        desiredaccess: FILE_ACCESS_RIGHTS,
+        objectattributes: *const OBJECT_ATTRIBUTES,
+        iostatusblock: *mut IO_STATUS_BLOCK,
+        allocationsize: *const i64,
+        fileattributes: FILE_FLAGS_AND_ATTRIBUTES,
+        shareaccess: FILE_SHARE_MODE,
+        createdisposition: NTCREATEFILE_CREATE_DISPOSITION,
+        createoptions: NTCREATEFILE_CREATE_OPTIONS,
+        eabuffer: *const ::core::ffi::c_void,
+        ealength: u32
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtReadFile(
+        filehandle: BorrowedHandle<'_>,
+        event: HANDLE,
+        apcroutine: PIO_APC_ROUTINE,
+        apccontext: *mut c_void,
+        iostatusblock: &mut IO_STATUS_BLOCK,
+        buffer: *mut crate::mem::MaybeUninit<u8>,
+        length: ULONG,
+        byteoffset: Option<&LARGE_INTEGER>,
+        key: Option<&ULONG>
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtWriteFile(
+        filehandle: BorrowedHandle<'_>,
+        event: HANDLE,
+        apcroutine: PIO_APC_ROUTINE,
+        apccontext: *mut c_void,
+        iostatusblock: &mut IO_STATUS_BLOCK,
+        buffer: *const u8,
+        length: ULONG,
+        byteoffset: Option<&LARGE_INTEGER>,
+        key: Option<&ULONG>
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn RtlNtStatusToDosError(Status: NTSTATUS) -> u32 {
+        Status as u32
+    }
+}
+
+// # Arm32 shim
+//
+// AddVectoredExceptionHandler and WSAStartup use platform-specific types.
+// However, Microsoft no longer supports thumbv7a so definitions for those targets
+// are not included in the win32 metadata. We work around that by defining them here.
+//
+// Where possible, these definitions should be kept in sync with https://docs.rs/windows-sys
+cfg_if::cfg_if! {
+if #[cfg(not(target_vendor = "uwp"))] {
+    #[link(name = "kernel32")]
+    extern "system" {
+        pub fn AddVectoredExceptionHandler(
+            first: u32,
+            handler: PVECTORED_EXCEPTION_HANDLER,
+        ) -> *mut c_void;
+    }
+    pub type PVECTORED_EXCEPTION_HANDLER = Option<
+        unsafe extern "system" fn(exceptioninfo: *mut EXCEPTION_POINTERS) -> i32,
+    >;
+    #[repr(C)]
+    pub struct EXCEPTION_POINTERS {
+        pub ExceptionRecord: *mut EXCEPTION_RECORD,
+        pub ContextRecord: *mut CONTEXT,
+    }
+    #[cfg(target_arch = "arm")]
+    pub enum CONTEXT {}
+}}
+
+#[link(name = "ws2_32")]
+extern "system" {
+    pub fn WSAStartup(wversionrequested: u16, lpwsadata: *mut WSADATA) -> i32;
+}
+#[cfg(target_arch = "arm")]
+#[repr(C)]
+pub struct WSADATA {
+    pub wVersion: u16,
+    pub wHighVersion: u16,
+    pub szDescription: [u8; 257],
+    pub szSystemStatus: [u8; 129],
+    pub iMaxSockets: u16,
+    pub iMaxUdpDg: u16,
+    pub lpVendorInfo: PSTR,
 }
diff --git a/library/std/src/sys/windows/c/windows_sys.lst b/library/std/src/sys/windows/c/windows_sys.lst
index 3e454199f..631aedd26 100644
--- a/library/std/src/sys/windows/c/windows_sys.lst
+++ b/library/std/src/sys/windows/c/windows_sys.lst
@@ -1930,6 +1930,7 @@ Windows.Win32.Foundation.SetLastError
 Windows.Win32.Foundation.STATUS_DELETE_PENDING
 Windows.Win32.Foundation.STATUS_END_OF_FILE
 Windows.Win32.Foundation.STATUS_INVALID_PARAMETER
+Windows.Win32.Foundation.STATUS_NOT_IMPLEMENTED
 Windows.Win32.Foundation.STATUS_PENDING
 Windows.Win32.Foundation.STATUS_SUCCESS
 Windows.Win32.Foundation.TRUE
@@ -2170,7 +2171,6 @@ Windows.Win32.Networking.WinSock.WSARecv
 Windows.Win32.Networking.WinSock.WSASend
 Windows.Win32.Networking.WinSock.WSASERVICE_NOT_FOUND
 Windows.Win32.Networking.WinSock.WSASocketW
-Windows.Win32.Networking.WinSock.WSAStartup
 Windows.Win32.Networking.WinSock.WSASYSCALLFAILURE
 Windows.Win32.Networking.WinSock.WSASYSNOTREADY
 Windows.Win32.Networking.WinSock.WSATRY_AGAIN
@@ -2418,12 +2418,10 @@ Windows.Win32.System.Console.STD_HANDLE
 Windows.Win32.System.Console.STD_INPUT_HANDLE
 Windows.Win32.System.Console.STD_OUTPUT_HANDLE
 Windows.Win32.System.Console.WriteConsoleW
-Windows.Win32.System.Diagnostics.Debug.AddVectoredExceptionHandler
 Windows.Win32.System.Diagnostics.Debug.ARM64_NT_NEON128
 Windows.Win32.System.Diagnostics.Debug.CONTEXT
 Windows.Win32.System.Diagnostics.Debug.CONTEXT
 Windows.Win32.System.Diagnostics.Debug.CONTEXT
-Windows.Win32.System.Diagnostics.Debug.EXCEPTION_POINTERS
 Windows.Win32.System.Diagnostics.Debug.EXCEPTION_RECORD
 Windows.Win32.System.Diagnostics.Debug.FACILITY_CODE
 Windows.Win32.System.Diagnostics.Debug.FACILITY_NT_BIT
@@ -2436,7 +2434,6 @@ Windows.Win32.System.Diagnostics.Debug.FORMAT_MESSAGE_IGNORE_INSERTS
 Windows.Win32.System.Diagnostics.Debug.FORMAT_MESSAGE_OPTIONS
 Windows.Win32.System.Diagnostics.Debug.FormatMessageW
 Windows.Win32.System.Diagnostics.Debug.M128A
-Windows.Win32.System.Diagnostics.Debug.PVECTORED_EXCEPTION_HANDLER
 Windows.Win32.System.Diagnostics.Debug.XSAVE_FORMAT
 Windows.Win32.System.Diagnostics.Debug.XSAVE_FORMAT
 Windows.Win32.System.Environment.FreeEnvironmentStringsW
diff --git a/library/std/src/sys/windows/c/windows_sys.rs b/library/std/src/sys/windows/c/windows_sys.rs
index 36a30f6ba..023770871 100644
--- a/library/std/src/sys/windows/c/windows_sys.rs
+++ b/library/std/src/sys/windows/c/windows_sys.rs
@@ -40,13 +40,6 @@ extern "system" {
 }
 #[link(name = "kernel32")]
 extern "system" {
-    pub fn AddVectoredExceptionHandler(
-        first: u32,
-        handler: PVECTORED_EXCEPTION_HANDLER,
-    ) -> *mut ::core::ffi::c_void;
-}
-#[link(name = "kernel32")]
-extern "system" {
     pub fn CancelIo(hfile: HANDLE) -> BOOL;
 }
 #[link(name = "kernel32")]
@@ -712,10 +705,6 @@ extern "system" {
 }
 #[link(name = "ws2_32")]
 extern "system" {
-    pub fn WSAStartup(wversionrequested: u16, lpwsadata: *mut WSADATA) -> i32;
-}
-#[link(name = "ws2_32")]
-extern "system" {
     pub fn accept(s: SOCKET, addr: *mut SOCKADDR, addrlen: *mut i32) -> SOCKET;
 }
 #[link(name = "ws2_32")]
@@ -3029,17 +3018,6 @@ pub const ERROR_XML_PARSE_ERROR: WIN32_ERROR = 1465u32;
 pub type EXCEPTION_DISPOSITION = i32;
 pub const EXCEPTION_MAXIMUM_PARAMETERS: u32 = 15u32;
 #[repr(C)]
-pub struct EXCEPTION_POINTERS {
-    pub ExceptionRecord: *mut EXCEPTION_RECORD,
-    pub ContextRecord: *mut CONTEXT,
-}
-impl ::core::marker::Copy for EXCEPTION_POINTERS {}
-impl ::core::clone::Clone for EXCEPTION_POINTERS {
-    fn clone(&self) -> Self {
-        *self
-    }
-}
-#[repr(C)]
 pub struct EXCEPTION_RECORD {
     pub ExceptionCode: NTSTATUS,
     pub ExceptionFlags: u32,
@@ -3748,9 +3726,6 @@ pub const PROFILE_SERVER: PROCESS_CREATION_FLAGS = 1073741824u32;
 pub const PROFILE_USER: PROCESS_CREATION_FLAGS = 268435456u32;
 pub const PROGRESS_CONTINUE: u32 = 0u32;
 pub type PSTR = *mut u8;
-pub type PVECTORED_EXCEPTION_HANDLER = ::core::option::Option<
-    unsafe extern "system" fn(exceptioninfo: *mut EXCEPTION_POINTERS) -> i32,
->;
 pub type PWSTR = *mut u16;
 pub const READ_CONTROL: FILE_ACCESS_RIGHTS = 131072u32;
 pub const REALTIME_PRIORITY_CLASS: PROCESS_CREATION_FLAGS = 256u32;
@@ -3888,6 +3863,7 @@ pub type STARTUPINFOW_FLAGS = u32;
 pub const STATUS_DELETE_PENDING: NTSTATUS = -1073741738i32;
 pub const STATUS_END_OF_FILE: NTSTATUS = -1073741807i32;
 pub const STATUS_INVALID_PARAMETER: NTSTATUS = -1073741811i32;
+pub const STATUS_NOT_IMPLEMENTED: NTSTATUS = -1073741822i32;
 pub const STATUS_PENDING: NTSTATUS = 259i32;
 pub const STATUS_SUCCESS: NTSTATUS = 0i32;
 pub const STD_ERROR_HANDLE: STD_HANDLE = 4294967284u32;
diff --git a/library/std/src/sys/windows/net.rs b/library/std/src/sys/windows/net.rs
index 2404bbe2b..1ae42cb7e 100644
--- a/library/std/src/sys/windows/net.rs
+++ b/library/std/src/sys/windows/net.rs
@@ -159,7 +159,7 @@ impl Socket {
                 }
 
                 let mut timeout = c::timeval {
-                    tv_sec: timeout.as_secs() as c_long,
+                    tv_sec: cmp::min(timeout.as_secs(), c_long::MAX as u64) as c_long,
                     tv_usec: (timeout.subsec_nanos() / 1000) as c_long,
                 };
 
diff --git a/library/std/src/sys/windows/os_str.rs b/library/std/src/sys/windows/os_str.rs
index 2f2b0e56e..16c4f55c6 100644
--- a/library/std/src/sys/windows/os_str.rs
+++ b/library/std/src/sys/windows/os_str.rs
@@ -152,11 +152,21 @@ impl Buf {
 
 impl Slice {
     #[inline]
+    pub fn as_os_str_bytes(&self) -> &[u8] {
+        self.inner.as_bytes()
+    }
+
+    #[inline]
+    pub unsafe fn from_os_str_bytes_unchecked(s: &[u8]) -> &Slice {
+        mem::transmute(Wtf8::from_bytes_unchecked(s))
+    }
+
+    #[inline]
     pub fn from_str(s: &str) -> &Slice {
         unsafe { mem::transmute(Wtf8::from_str(s)) }
     }
 
-    pub fn to_str(&self) -> Option<&str> {
+    pub fn to_str(&self) -> Result<&str, crate::str::Utf8Error> {
         self.inner.as_str()
     }
 
diff --git a/library/std/src/sys/windows/path.rs b/library/std/src/sys/windows/path.rs
index c3573d14c..c9c2d10e6 100644
--- a/library/std/src/sys/windows/path.rs
+++ b/library/std/src/sys/windows/path.rs
@@ -1,7 +1,6 @@
 use super::{c, fill_utf16_buf, to_u16s};
 use crate::ffi::{OsStr, OsString};
 use crate::io;
-use crate::mem;
 use crate::path::{Path, PathBuf, Prefix};
 use crate::ptr;
 
@@ -11,16 +10,6 @@ mod tests;
 pub const MAIN_SEP_STR: &str = "\\";
 pub const MAIN_SEP: char = '\\';
 
-/// # Safety
-///
-/// `bytes` must be a valid wtf8 encoded slice
-#[inline]
-unsafe fn bytes_as_os_str(bytes: &[u8]) -> &OsStr {
-    // &OsStr is layout compatible with &Slice, which is compatible with &Wtf8,
-    // which is compatible with &[u8].
-    mem::transmute(bytes)
-}
-
 #[inline]
 pub fn is_sep_byte(b: u8) -> bool {
     b == b'/' || b == b'\\'
@@ -33,12 +22,12 @@ pub fn is_verbatim_sep(b: u8) -> bool {
 
 /// Returns true if `path` looks like a lone filename.
 pub(crate) fn is_file_name(path: &OsStr) -> bool {
-    !path.bytes().iter().copied().any(is_sep_byte)
+    !path.as_os_str_bytes().iter().copied().any(is_sep_byte)
 }
 pub(crate) fn has_trailing_slash(path: &OsStr) -> bool {
-    let is_verbatim = path.bytes().starts_with(br"\\?\");
+    let is_verbatim = path.as_os_str_bytes().starts_with(br"\\?\");
     let is_separator = if is_verbatim { is_verbatim_sep } else { is_sep_byte };
-    if let Some(&c) = path.bytes().last() { is_separator(c) } else { false }
+    if let Some(&c) = path.as_os_str_bytes().last() { is_separator(c) } else { false }
 }
 
 /// Appends a suffix to a path.
@@ -60,7 +49,7 @@ impl<'a, const LEN: usize> PrefixParser<'a, LEN> {
     fn get_prefix(path: &OsStr) -> [u8; LEN] {
         let mut prefix = [0; LEN];
         // SAFETY: Only ASCII characters are modified.
-        for (i, &ch) in path.bytes().iter().take(LEN).enumerate() {
+        for (i, &ch) in path.as_os_str_bytes().iter().take(LEN).enumerate() {
             prefix[i] = if ch == b'/' { b'\\' } else { ch };
         }
         prefix
@@ -93,7 +82,7 @@ impl<'a> PrefixParserSlice<'a, '_> {
     }
 
     fn prefix_bytes(&self) -> &'a [u8] {
-        &self.path.bytes()[..self.index]
+        &self.path.as_os_str_bytes()[..self.index]
     }
 
     fn finish(self) -> &'a OsStr {
@@ -101,7 +90,7 @@ impl<'a> PrefixParserSlice<'a, '_> {
         // &[u8] and back. This is safe to do because (1) we only look at ASCII
         // contents of the encoding and (2) new &OsStr values are produced only
         // from ASCII-bounded slices of existing &OsStr values.
-        unsafe { bytes_as_os_str(&self.path.bytes()[self.index..]) }
+        unsafe { OsStr::from_os_str_bytes_unchecked(&self.path.as_os_str_bytes()[self.index..]) }
     }
 }
 
@@ -173,7 +162,7 @@ fn parse_drive(path: &OsStr) -> Option<u8> {
         drive.is_ascii_alphabetic()
     }
 
-    match path.bytes() {
+    match path.as_os_str_bytes() {
         [drive, b':', ..] if is_valid_drive_letter(drive) => Some(drive.to_ascii_uppercase()),
         _ => None,
     }
@@ -182,7 +171,7 @@ fn parse_drive(path: &OsStr) -> Option<u8> {
 // Parses a drive prefix exactly, e.g. "C:"
 fn parse_drive_exact(path: &OsStr) -> Option<u8> {
     // only parse two bytes: the drive letter and the drive separator
-    if path.bytes().get(2).map(|&x| is_sep_byte(x)).unwrap_or(true) {
+    if path.as_os_str_bytes().get(2).map(|&x| is_sep_byte(x)).unwrap_or(true) {
         parse_drive(path)
     } else {
         None
@@ -196,21 +185,26 @@ fn parse_drive_exact(path: &OsStr) -> Option<u8> {
 fn parse_next_component(path: &OsStr, verbatim: bool) -> (&OsStr, &OsStr) {
     let separator = if verbatim { is_verbatim_sep } else { is_sep_byte };
 
-    match path.bytes().iter().position(|&x| separator(x)) {
+    match path.as_os_str_bytes().iter().position(|&x| separator(x)) {
         Some(separator_start) => {
             let separator_end = separator_start + 1;
 
-            let component = &path.bytes()[..separator_start];
+            let component = &path.as_os_str_bytes()[..separator_start];
 
             // Panic safe
             // The max `separator_end` is `bytes.len()` and `bytes[bytes.len()..]` is a valid index.
-            let path = &path.bytes()[separator_end..];
+            let path = &path.as_os_str_bytes()[separator_end..];
 
             // SAFETY: `path` is a valid wtf8 encoded slice and each of the separators ('/', '\')
             // is encoded in a single byte, therefore `bytes[separator_start]` and
             // `bytes[separator_end]` must be code point boundaries and thus
             // `bytes[..separator_start]` and `bytes[separator_end..]` are valid wtf8 slices.
-            unsafe { (bytes_as_os_str(component), bytes_as_os_str(path)) }
+            unsafe {
+                (
+                    OsStr::from_os_str_bytes_unchecked(component),
+                    OsStr::from_os_str_bytes_unchecked(path),
+                )
+            }
         }
         None => (path, OsStr::new("")),
     }
@@ -329,7 +323,7 @@ pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
     // Verbatim paths should not be modified.
     if prefix.map(|x| x.is_verbatim()).unwrap_or(false) {
         // NULs in verbatim paths are rejected for consistency.
-        if path.bytes().contains(&0) {
+        if path.as_os_str_bytes().contains(&0) {
             return Err(io::const_io_error!(
                 io::ErrorKind::InvalidInput,
                 "strings passed to WinAPI cannot contain NULs",
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index df3667c0f..e3493cbb8 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -395,7 +395,7 @@ fn resolve_exe<'a>(
     // Test if the file name has the `exe` extension.
     // This does a case-insensitive `ends_with`.
     let has_exe_suffix = if exe_path.len() >= EXE_SUFFIX.len() {
-        exe_path.bytes()[exe_path.len() - EXE_SUFFIX.len()..]
+        exe_path.as_os_str_bytes()[exe_path.len() - EXE_SUFFIX.len()..]
             .eq_ignore_ascii_case(EXE_SUFFIX.as_bytes())
     } else {
         false
@@ -425,7 +425,7 @@ fn resolve_exe<'a>(
         // From the `CreateProcessW` docs:
         // > If the file name does not contain an extension, .exe is appended.
         // Note that this rule only applies when searching paths.
-        let has_extension = exe_path.bytes().contains(&b'.');
+        let has_extension = exe_path.as_os_str_bytes().contains(&b'.');
 
         // Search the directories given by `search_paths`.
         let result = search_paths(parent_paths, child_paths, |mut path| {
@@ -595,7 +595,16 @@ pub struct Process {
 
 impl Process {
     pub fn kill(&mut self) -> io::Result<()> {
-        cvt(unsafe { c::TerminateProcess(self.handle.as_raw_handle(), 1) })?;
+        let result = unsafe { c::TerminateProcess(self.handle.as_raw_handle(), 1) };
+        if result == c::FALSE {
+            let error = unsafe { c::GetLastError() };
+            // TerminateProcess returns ERROR_ACCESS_DENIED if the process has already been
+            // terminated (by us, or for any other reason). So check if the process was actually
+            // terminated, and if so, do not return an error.
+            if error != c::ERROR_ACCESS_DENIED || self.try_wait().is_err() {
+                return Err(crate::io::Error::from_raw_os_error(error as i32));
+            }
+        }
         Ok(())
     }
 
diff --git a/library/std/src/sys/windows/rand.rs b/library/std/src/sys/windows/rand.rs
index bca4e38d9..5d8fd1378 100644
--- a/library/std/src/sys/windows/rand.rs
+++ b/library/std/src/sys/windows/rand.rs
@@ -1,5 +1,3 @@
-use crate::ffi::c_void;
-use crate::io;
 use crate::mem;
 use crate::ptr;
 use crate::sys::c;
@@ -25,6 +23,9 @@ pub fn hashmap_random_keys() -> (u64, u64) {
 #[cfg(not(target_vendor = "uwp"))]
 #[inline(never)]
 fn fallback_rng() -> (u64, u64) {
+    use crate::ffi::c_void;
+    use crate::io;
+
     let mut v = (0, 0);
     let ret = unsafe {
         c::RtlGenRandom(&mut v as *mut _ as *mut c_void, mem::size_of_val(&v) as c::ULONG)
diff --git a/library/std/src/sys/windows/stdio.rs b/library/std/src/sys/windows/stdio.rs
index 2e3e0859d..3fcaaa508 100644
--- a/library/std/src/sys/windows/stdio.rs
+++ b/library/std/src/sys/windows/stdio.rs
@@ -11,6 +11,9 @@ use crate::sys::cvt;
 use crate::sys::handle::Handle;
 use core::str::utf8_char_width;
 
+#[cfg(test)]
+mod tests;
+
 // Don't cache handles but get them fresh for every read/write. This allows us to track changes to
 // the value over time (such as if a process calls `SetStdHandle` while it's running). See #40490.
 pub struct Stdin {
@@ -383,6 +386,10 @@ fn utf16_to_utf8(utf16: &[u16], utf8: &mut [u8]) -> io::Result<usize> {
     debug_assert!(utf16.len() <= c::c_int::MAX as usize);
     debug_assert!(utf8.len() <= c::c_int::MAX as usize);
 
+    if utf16.is_empty() {
+        return Ok(0);
+    }
+
     let result = unsafe {
         c::WideCharToMultiByte(
             c::CP_UTF8,              // CodePage
diff --git a/library/std/src/sys/windows/stdio/tests.rs b/library/std/src/sys/windows/stdio/tests.rs
new file mode 100644
index 000000000..1e53e0bee
--- /dev/null
+++ b/library/std/src/sys/windows/stdio/tests.rs
@@ -0,0 +1,6 @@
+use super::utf16_to_utf8;
+
+#[test]
+fn zero_size_read() {
+    assert_eq!(utf16_to_utf8(&[], &mut []).unwrap(), 0);
+}
diff --git a/library/std/src/sys_common/net.rs b/library/std/src/sys_common/net.rs
index 652c695fc..2976a9f57 100644
--- a/library/std/src/sys_common/net.rs
+++ b/library/std/src/sys_common/net.rs
@@ -18,7 +18,7 @@ use crate::ffi::{c_int, c_void};
 cfg_if::cfg_if! {
     if #[cfg(any(
         target_os = "dragonfly", target_os = "freebsd",
-        target_os = "ios", target_os = "macos", target_os = "watchos",
+        target_os = "ios", target_os = "tvos", target_os = "macos", target_os = "watchos",
         target_os = "openbsd", target_os = "netbsd", target_os = "illumos",
         target_os = "solaris", target_os = "haiku", target_os = "l4re", target_os = "nto"))] {
         use crate::sys::net::netc::IPV6_JOIN_GROUP as IPV6_ADD_MEMBERSHIP;
diff --git a/library/std/src/sys_common/wtf8.rs b/library/std/src/sys_common/wtf8.rs
index ff96c35fb..c9d3e13cf 100644
--- a/library/std/src/sys_common/wtf8.rs
+++ b/library/std/src/sys_common/wtf8.rs
@@ -570,7 +570,7 @@ impl Wtf8 {
     /// Since the byte slice is not checked for valid WTF-8, this functions is
     /// marked unsafe.
     #[inline]
-    unsafe fn from_bytes_unchecked(value: &[u8]) -> &Wtf8 {
+    pub unsafe fn from_bytes_unchecked(value: &[u8]) -> &Wtf8 {
         mem::transmute(value)
     }
 
@@ -614,19 +614,20 @@ impl Wtf8 {
         Wtf8CodePoints { bytes: self.bytes.iter() }
     }
 
+    /// Access raw bytes of WTF-8 data
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.bytes
+    }
+
     /// Tries to convert the string to UTF-8 and return a `&str` slice.
     ///
     /// Returns `None` if the string contains surrogates.
     ///
     /// This does not copy the data.
     #[inline]
-    pub fn as_str(&self) -> Option<&str> {
-        // Well-formed WTF-8 is also well-formed UTF-8
-        // if and only if it contains no surrogate.
-        match self.next_surrogate(0) {
-            None => Some(unsafe { str::from_utf8_unchecked(&self.bytes) }),
-            Some(_) => None,
-        }
+    pub fn as_str(&self) -> Result<&str, str::Utf8Error> {
+        str::from_utf8(&self.bytes)
     }
 
     /// Creates an owned `Wtf8Buf` from a borrowed `Wtf8`.
diff --git a/library/std/src/sys_common/wtf8/tests.rs b/library/std/src/sys_common/wtf8/tests.rs
index 1a302d646..a07bbe6d7 100644
--- a/library/std/src/sys_common/wtf8/tests.rs
+++ b/library/std/src/sys_common/wtf8/tests.rs
@@ -521,11 +521,11 @@ fn wtf8_code_points() {
 
 #[test]
 fn wtf8_as_str() {
-    assert_eq!(Wtf8::from_str("").as_str(), Some(""));
-    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Some("aé 💩"));
+    assert_eq!(Wtf8::from_str("").as_str(), Ok(""));
+    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Ok("aé 💩"));
     let mut string = Wtf8Buf::new();
     string.push(CodePoint::from_u32(0xD800).unwrap());
-    assert_eq!(string.as_str(), None);
+    assert!(string.as_str().is_err());
 }
 
 #[test]
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index f712c8727..e4581c2de 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -195,7 +195,7 @@ mod local;
 
 cfg_if::cfg_if! {
     if #[cfg(test)] {
-        // Avoid duplicating the global state assoicated with thread-locals between this crate and
+        // Avoid duplicating the global state associated with thread-locals between this crate and
         // realstd. Miri relies on this.
         pub use realstd::thread::{local_impl, AccessError, LocalKey};
     } else {
@@ -206,7 +206,7 @@ cfg_if::cfg_if! {
         #[doc(hidden)]
         #[unstable(feature = "thread_local_internals", issue = "none")]
         pub mod local_impl {
-            pub use crate::sys::common::thread_local::{thread_local_inner, Key};
+            pub use crate::sys::common::thread_local::{thread_local_inner, Key, abort_on_dtor_unwind};
         }
     }
 }
@@ -889,7 +889,7 @@ impl Drop for PanicGuard {
 /// it is guaranteed that this function will not panic (it may abort the
 /// process if the implementation encounters some rare errors).
 ///
-/// # park and unpark
+/// # `park` and `unpark`
 ///
 /// Every thread is equipped with some basic low-level blocking support, via the
 /// [`thread::park`][`park`] function and [`thread::Thread::unpark`][`unpark`]
@@ -910,14 +910,6 @@ impl Drop for PanicGuard {
 ///   if it wasn't already. Because the token is initially absent, [`unpark`]
 ///   followed by [`park`] will result in the second call returning immediately.
 ///
-/// In other words, each [`Thread`] acts a bit like a spinlock that can be
-/// locked and unlocked using `park` and `unpark`.
-///
-/// Notice that being unblocked does not imply any synchronization with someone
-/// that unparked this thread, it could also be spurious.
-/// For example, it would be a valid, but inefficient, implementation to make both [`park`] and
-/// [`unpark`] return immediately without doing anything.
-///
 /// The API is typically used by acquiring a handle to the current thread,
 /// placing that handle in a shared data structure so that other threads can
 /// find it, and then `park`ing in a loop. When some desired condition is met, another
@@ -931,6 +923,23 @@ impl Drop for PanicGuard {
 ///
 /// * It can be implemented very efficiently on many platforms.
 ///
+/// # Memory Ordering
+///
+/// Calls to `park` _synchronize-with_ calls to `unpark`, meaning that memory
+/// operations performed before a call to `unpark` are made visible to the thread that
+/// consumes the token and returns from `park`. Note that all `park` and `unpark`
+/// operations for a given thread form a total order and `park` synchronizes-with
+/// _all_ prior `unpark` operations.
+///
+/// In atomic ordering terms, `unpark` performs a `Release` operation and `park`
+/// performs the corresponding `Acquire` operation. Calls to `unpark` for the same
+/// thread form a [release sequence].
+///
+/// Note that being unblocked does not imply a call was made to `unpark`, because
+/// wakeups can also be spurious. For example, a valid, but inefficient,
+/// implementation could have `park` and `unpark` return immediately without doing anything,
+/// making *all* wakeups spurious.
+///
 /// # Examples
 ///
 /// ```
@@ -944,7 +953,7 @@ impl Drop for PanicGuard {
 /// let parked_thread = thread::spawn(move || {
 ///     // We want to wait until the flag is set. We *could* just spin, but using
 ///     // park/unpark is more efficient.
-///     while !flag2.load(Ordering::Acquire) {
+///     while !flag2.load(Ordering::Relaxed) {
 ///         println!("Parking thread");
 ///         thread::park();
 ///         // We *could* get here spuriously, i.e., way before the 10ms below are over!
@@ -961,7 +970,7 @@ impl Drop for PanicGuard {
 /// // There is no race condition here, if `unpark`
 /// // happens first, `park` will return immediately.
 /// // Hence there is no risk of a deadlock.
-/// flag.store(true, Ordering::Release);
+/// flag.store(true, Ordering::Relaxed);
 /// println!("Unpark the thread");
 /// parked_thread.thread().unpark();
 ///
@@ -970,6 +979,7 @@ impl Drop for PanicGuard {
 ///
 /// [`unpark`]: Thread::unpark
 /// [`thread::park_timeout`]: park_timeout
+/// [release sequence]: https://en.cppreference.com/w/cpp/atomic/memory_order#Release_sequence
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn park() {
     let guard = PanicGuard;
diff --git a/library/std/src/thread/tests.rs b/library/std/src/thread/tests.rs
index b65e2572c..5d6b9e94e 100644
--- a/library/std/src/thread/tests.rs
+++ b/library/std/src/thread/tests.rs
@@ -42,6 +42,7 @@ fn test_named_thread() {
     all(target_os = "linux", target_env = "gnu"),
     target_os = "macos",
     target_os = "ios",
+    target_os = "tvos",
     target_os = "watchos"
 ))]
 #[test]