Merging upstream version 1.70.0+dfsg1.

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

41 files changed, 1164 insertions, 183 deletions

diff --git a/library/std/src/sys/common/alloc.rs b/library/std/src/sys/common/alloc.rs
index 403a5e627..a5fcbdf39 100644
--- a/library/std/src/sys/common/alloc.rs
+++ b/library/std/src/sys/common/alloc.rs
@@ -22,6 +22,7 @@ pub const MIN_ALIGN: usize = 8;
 #[cfg(any(
     target_arch = "x86_64",
     target_arch = "aarch64",
+    target_arch = "loongarch64",
     target_arch = "mips64",
     target_arch = "s390x",
     target_arch = "sparc64",
diff --git a/library/std/src/sys/common/mod.rs b/library/std/src/sys/common/mod.rs
index 29fc0835d..2b8782ddf 100644
--- a/library/std/src/sys/common/mod.rs
+++ b/library/std/src/sys/common/mod.rs
@@ -12,6 +12,7 @@
 
 pub mod alloc;
 pub mod small_c_string;
+pub mod thread_local;
 
 #[cfg(test)]
 mod tests;
diff --git a/library/std/src/sys/common/thread_local/fast_local.rs b/library/std/src/sys/common/thread_local/fast_local.rs
new file mode 100644
index 000000000..e229eb16a
--- /dev/null
+++ b/library/std/src/sys/common/thread_local/fast_local.rs
@@ -0,0 +1,254 @@
+#[doc(hidden)]
+#[macro_export]
+#[allow_internal_unstable(
+    thread_local_internals,
+    cfg_target_thread_local,
+    thread_local,
+    libstd_thread_internals
+)]
+#[allow_internal_unsafe]
+macro_rules! __thread_local_inner {
+    // used to generate the `LocalKey` value for const-initialized thread locals
+    (@key $t:ty, const $init:expr) => {{
+        #[cfg_attr(not(bootstrap), inline)]
+        #[deny(unsafe_op_in_unsafe_fn)]
+        unsafe fn __getit(
+            _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+        ) -> $crate::option::Option<&'static $t> {
+            const INIT_EXPR: $t = $init;
+            // If the platform has support for `#[thread_local]`, use it.
+            #[thread_local]
+            static mut VAL: $t = INIT_EXPR;
+
+            // If a dtor isn't needed we can do something "very raw" and
+            // just get going.
+            if !$crate::mem::needs_drop::<$t>() {
+                unsafe {
+                    return $crate::option::Option::Some(&VAL)
+                }
+            }
+
+            // 0 == dtor not registered
+            // 1 == dtor registered, dtor not run
+            // 2 == dtor registered and is running or has run
+            #[thread_local]
+            static mut STATE: $crate::primitive::u8 = 0;
+
+            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);
+                }
+            }
+
+            unsafe {
+                match STATE {
+                    // 0 == we haven't registered a destructor, so do
+                    //   so now.
+                    0 => {
+                        $crate::thread::__LocalKeyInner::<$t>::register_dtor(
+                            $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8,
+                            destroy,
+                        );
+                        STATE = 1;
+                        $crate::option::Option::Some(&VAL)
+                    }
+                    // 1 == the destructor is registered and the value
+                    //   is valid, so return the pointer.
+                    1 => $crate::option::Option::Some(&VAL),
+                    // otherwise the destructor has already run, so we
+                    // can't give access.
+                    _ => $crate::option::Option::None,
+                }
+            }
+        }
+
+        unsafe {
+            $crate::thread::LocalKey::new(__getit)
+        }
+    }};
+
+    // used to generate the `LocalKey` value for `thread_local!`
+    (@key $t:ty, $init:expr) => {
+        {
+            #[inline]
+            fn __init() -> $t { $init }
+
+            #[cfg_attr(not(bootstrap), inline)]
+            unsafe fn __getit(
+                init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+            ) -> $crate::option::Option<&'static $t> {
+                #[thread_local]
+                static __KEY: $crate::thread::__LocalKeyInner<$t> =
+                    $crate::thread::__LocalKeyInner::<$t>::new();
+
+                // FIXME: remove the #[allow(...)] marker when macros don't
+                // raise warning for missing/extraneous unsafe blocks anymore.
+                // See https://github.com/rust-lang/rust/issues/74838.
+                #[allow(unused_unsafe)]
+                unsafe {
+                    __KEY.get(move || {
+                        if let $crate::option::Option::Some(init) = init {
+                            if let $crate::option::Option::Some(value) = init.take() {
+                                return value;
+                            } else if $crate::cfg!(debug_assertions) {
+                                $crate::unreachable!("missing default value");
+                            }
+                        }
+                        __init()
+                    })
+                }
+            }
+
+            unsafe {
+                $crate::thread::LocalKey::new(__getit)
+            }
+        }
+    };
+    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
+        $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
+            $crate::__thread_local_inner!(@key $t, $($init)*);
+    }
+}
+
+#[doc(hidden)]
+pub mod fast {
+    use super::super::lazy::LazyKeyInner;
+    use crate::cell::Cell;
+    use crate::sys::thread_local_dtor::register_dtor;
+    use crate::{fmt, mem, panic};
+
+    #[derive(Copy, Clone)]
+    enum DtorState {
+        Unregistered,
+        Registered,
+        RunningOrHasRun,
+    }
+
+    // This data structure has been carefully constructed so that the fast path
+    // only contains one branch on x86. That optimization is necessary to avoid
+    // duplicated tls lookups on OSX.
+    //
+    // LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
+    pub struct Key<T> {
+        // If `LazyKeyInner::get` returns `None`, that indicates either:
+        //   * The value has never been initialized
+        //   * The value is being recursively initialized
+        //   * The value has already been destroyed or is being destroyed
+        // To determine which kind of `None`, check `dtor_state`.
+        //
+        // This is very optimizer friendly for the fast path - initialized but
+        // not yet dropped.
+        inner: LazyKeyInner<T>,
+
+        // Metadata to keep track of the state of the destructor. Remember that
+        // this variable is thread-local, not global.
+        dtor_state: Cell<DtorState>,
+    }
+
+    impl<T> fmt::Debug for Key<T> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            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) }
+        }
+
+        // note that this is just a publicly-callable function only for the
+        // const-initialized form of thread locals, basically a way to call the
+        // free `register_dtor` function defined elsewhere in std.
+        pub unsafe fn register_dtor(a: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
+            unsafe {
+                register_dtor(a, dtor);
+            }
+        }
+
+        pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
+            // SAFETY: See the definitions of `LazyKeyInner::get` and
+            // `try_initialize` for more information.
+            //
+            // The caller must ensure no mutable references are ever active to
+            // the inner cell or the inner T when this is called.
+            // The `try_initialize` is dependant on the passed `init` function
+            // for this.
+            unsafe {
+                match self.inner.get() {
+                    Some(val) => Some(val),
+                    None => self.try_initialize(init),
+                }
+            }
+        }
+
+        // `try_initialize` is only called once per fast thread local variable,
+        // except in corner cases where thread_local dtors reference other
+        // thread_local's, or it is being recursively initialized.
+        //
+        // Macos: Inlining this function can cause two `tlv_get_addr` calls to
+        // be performed for every call to `Key::get`.
+        // LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
+        #[inline(never)]
+        unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
+            // SAFETY: See comment above (this function doc).
+            if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } {
+                // SAFETY: See comment above (this function doc).
+                Some(unsafe { self.inner.initialize(init) })
+            } else {
+                None
+            }
+        }
+
+        // `try_register_dtor` is only called once per fast thread local
+        // variable, except in corner cases where thread_local dtors reference
+        // other thread_local's, or it is being recursively initialized.
+        unsafe fn try_register_dtor(&self) -> bool {
+            match self.dtor_state.get() {
+                DtorState::Unregistered => {
+                    // SAFETY: dtor registration happens before initialization.
+                    // Passing `self` as a pointer while using `destroy_value<T>`
+                    // is safe because the function will build a pointer to a
+                    // Key<T>, which is the type of self and so find the correct
+                    // size.
+                    unsafe { register_dtor(self as *const _ as *mut u8, destroy_value::<T>) };
+                    self.dtor_state.set(DtorState::Registered);
+                    true
+                }
+                DtorState::Registered => {
+                    // recursively initialized
+                    true
+                }
+                DtorState::RunningOrHasRun => false,
+            }
+        }
+    }
+
+    unsafe extern "C" fn destroy_value<T>(ptr: *mut u8) {
+        let ptr = ptr as *mut Key<T>;
+
+        // SAFETY:
+        //
+        // The pointer `ptr` has been built just above and comes from
+        // `try_register_dtor` where it is originally a Key<T> coming from `self`,
+        // making it non-NUL and of the correct type.
+        //
+        // Right before we run the user destructor be sure to set the
+        // `Option<T>` to `None`, and `dtor_state` to `RunningOrHasRun`. This
+        // causes future calls to `get` to run `try_initialize_drop` again,
+        // which will now fail, and return `None`.
+        //
+        // Wrap the call in a catch to ensure unwinding is caught in the event
+        // a panic takes place in a destructor.
+        if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe {
+            let value = (*ptr).inner.take();
+            (*ptr).dtor_state.set(DtorState::RunningOrHasRun);
+            drop(value);
+        })) {
+            rtabort!("thread local panicked on drop");
+        }
+    }
+}
diff --git a/library/std/src/sys/common/thread_local/mod.rs b/library/std/src/sys/common/thread_local/mod.rs
new file mode 100644
index 000000000..1fee84a04
--- /dev/null
+++ b/library/std/src/sys/common/thread_local/mod.rs
@@ -0,0 +1,109 @@
+//! The following module declarations are outside cfg_if because the internal
+//! `__thread_local_internal` macro does not seem to be exported properly when using cfg_if
+#![unstable(feature = "thread_local_internals", reason = "should not be necessary", issue = "none")]
+
+#[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics")))))]
+mod fast_local;
+#[cfg(all(
+    not(target_thread_local),
+    not(all(target_family = "wasm", not(target_feature = "atomics")))
+))]
+mod os_local;
+#[cfg(all(target_family = "wasm", not(target_feature = "atomics")))]
+mod static_local;
+
+#[cfg(not(test))]
+cfg_if::cfg_if! {
+    if #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] {
+        #[doc(hidden)]
+        pub use static_local::statik::Key;
+    } else if #[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics")))))] {
+        #[doc(hidden)]
+        pub use fast_local::fast::Key;
+    } else if #[cfg(all(not(target_thread_local), not(all(target_family = "wasm", not(target_feature = "atomics")))))] {
+        #[doc(hidden)]
+        pub use os_local::os::Key;
+    }
+}
+
+#[doc(hidden)]
+#[cfg(test)]
+pub use realstd::thread::__LocalKeyInner as Key;
+
+mod lazy {
+    use crate::cell::UnsafeCell;
+    use crate::hint;
+    use crate::mem;
+
+    pub struct LazyKeyInner<T> {
+        inner: UnsafeCell<Option<T>>,
+    }
+
+    impl<T> LazyKeyInner<T> {
+        pub const fn new() -> LazyKeyInner<T> {
+            LazyKeyInner { inner: UnsafeCell::new(None) }
+        }
+
+        pub unsafe fn get(&self) -> Option<&'static T> {
+            // SAFETY: The caller must ensure no reference is ever handed out to
+            // the inner cell nor mutable reference to the Option<T> inside said
+            // cell. This make it safe to hand a reference, though the lifetime
+            // of 'static is itself unsafe, making the get method unsafe.
+            unsafe { (*self.inner.get()).as_ref() }
+        }
+
+        /// The caller must ensure that no reference is active: this method
+        /// needs unique access.
+        pub unsafe fn initialize<F: FnOnce() -> T>(&self, init: F) -> &'static T {
+            // Execute the initialization up front, *then* move it into our slot,
+            // just in case initialization fails.
+            let value = init();
+            let ptr = self.inner.get();
+
+            // SAFETY:
+            //
+            // note that this can in theory just be `*ptr = Some(value)`, but due to
+            // the compiler will currently codegen that pattern with something like:
+            //
+            //      ptr::drop_in_place(ptr)
+            //      ptr::write(ptr, Some(value))
+            //
+            // Due to this pattern it's possible for the destructor of the value in
+            // `ptr` (e.g., if this is being recursively initialized) to re-access
+            // TLS, in which case there will be a `&` and `&mut` pointer to the same
+            // value (an aliasing violation). To avoid setting the "I'm running a
+            // destructor" flag we just use `mem::replace` which should sequence the
+            // operations a little differently and make this safe to call.
+            //
+            // The precondition also ensures that we are the only one accessing
+            // `self` at the moment so replacing is fine.
+            unsafe {
+                let _ = mem::replace(&mut *ptr, Some(value));
+            }
+
+            // SAFETY: With the call to `mem::replace` it is guaranteed there is
+            // a `Some` behind `ptr`, not a `None` so `unreachable_unchecked`
+            // will never be reached.
+            unsafe {
+                // After storing `Some` we want to get a reference to the contents of
+                // what we just stored. While we could use `unwrap` here and it should
+                // always work it empirically doesn't seem to always get optimized away,
+                // which means that using something like `try_with` can pull in
+                // panicking code and cause a large size bloat.
+                match *ptr {
+                    Some(ref x) => x,
+                    None => hint::unreachable_unchecked(),
+                }
+            }
+        }
+
+        /// The other methods hand out references while taking &self.
+        /// As such, callers of this method must ensure no `&` and `&mut` are
+        /// available and used at the same time.
+        #[allow(unused)]
+        pub unsafe fn take(&mut self) -> Option<T> {
+            // SAFETY: See doc comment for this method.
+            unsafe { (*self.inner.get()).take() }
+        }
+    }
+}
diff --git a/library/std/src/sys/common/thread_local/os_local.rs b/library/std/src/sys/common/thread_local/os_local.rs
new file mode 100644
index 000000000..1442a397e
--- /dev/null
+++ b/library/std/src/sys/common/thread_local/os_local.rs
@@ -0,0 +1,197 @@
+#[doc(hidden)]
+#[macro_export]
+#[allow_internal_unstable(
+    thread_local_internals,
+    cfg_target_thread_local,
+    thread_local,
+    libstd_thread_internals
+)]
+#[allow_internal_unsafe]
+macro_rules! __thread_local_inner {
+    // used to generate the `LocalKey` value for const-initialized thread locals
+    (@key $t:ty, const $init:expr) => {{
+        #[cfg_attr(not(bootstrap), inline)]
+        #[deny(unsafe_op_in_unsafe_fn)]
+        unsafe fn __getit(
+            _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+        ) -> $crate::option::Option<&'static $t> {
+            const INIT_EXPR: $t = $init;
+
+                        // On platforms without `#[thread_local]` we fall back to the
+            // same implementation as below for os thread locals.
+            #[inline]
+            const fn __init() -> $t { INIT_EXPR }
+            static __KEY: $crate::thread::__LocalKeyInner<$t> =
+                $crate::thread::__LocalKeyInner::new();
+            #[allow(unused_unsafe)]
+            unsafe {
+                __KEY.get(move || {
+                    if let $crate::option::Option::Some(init) = _init {
+                        if let $crate::option::Option::Some(value) = init.take() {
+                            return value;
+                        } else if $crate::cfg!(debug_assertions) {
+                            $crate::unreachable!("missing initial value");
+                        }
+                    }
+                    __init()
+                })
+            }
+        }
+
+        unsafe {
+            $crate::thread::LocalKey::new(__getit)
+        }
+    }};
+
+    // used to generate the `LocalKey` value for `thread_local!`
+    (@key $t:ty, $init:expr) => {
+        {
+            #[inline]
+            fn __init() -> $t { $init }
+
+            // `#[inline] does not work on windows-gnu due to linking errors around dllimports.
+            // See https://github.com/rust-lang/rust/issues/109797.
+            #[cfg_attr(not(windows), inline)]
+            unsafe fn __getit(
+                init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+            ) -> $crate::option::Option<&'static $t> {
+                static __KEY: $crate::thread::__LocalKeyInner<$t> =
+                    $crate::thread::__LocalKeyInner::new();
+
+                // FIXME: remove the #[allow(...)] marker when macros don't
+                // raise warning for missing/extraneous unsafe blocks anymore.
+                // See https://github.com/rust-lang/rust/issues/74838.
+                #[allow(unused_unsafe)]
+                unsafe {
+                    __KEY.get(move || {
+                        if let $crate::option::Option::Some(init) = init {
+                            if let $crate::option::Option::Some(value) = init.take() {
+                                return value;
+                            } else if $crate::cfg!(debug_assertions) {
+                                $crate::unreachable!("missing default value");
+                            }
+                        }
+                        __init()
+                    })
+                }
+            }
+
+            unsafe {
+                $crate::thread::LocalKey::new(__getit)
+            }
+        }
+    };
+    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
+        $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
+            $crate::__thread_local_inner!(@key $t, $($init)*);
+    }
+}
+
+#[doc(hidden)]
+pub mod os {
+    use super::super::lazy::LazyKeyInner;
+    use crate::cell::Cell;
+    use crate::sys_common::thread_local_key::StaticKey as OsStaticKey;
+    use crate::{fmt, marker, panic, ptr};
+
+    /// Use a regular global static to store this key; the state provided will then be
+    /// thread-local.
+    pub struct Key<T> {
+        // OS-TLS key that we'll use to key off.
+        os: OsStaticKey,
+        marker: marker::PhantomData<Cell<T>>,
+    }
+
+    impl<T> fmt::Debug for Key<T> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.debug_struct("Key").finish_non_exhaustive()
+        }
+    }
+
+    unsafe impl<T> Sync for Key<T> {}
+
+    struct Value<T: 'static> {
+        inner: LazyKeyInner<T>,
+        key: &'static Key<T>,
+    }
+
+    impl<T: 'static> Key<T> {
+        #[rustc_const_unstable(feature = "thread_local_internals", issue = "none")]
+        pub const fn new() -> Key<T> {
+            Key { os: OsStaticKey::new(Some(destroy_value::<T>)), marker: marker::PhantomData }
+        }
+
+        /// It is a requirement for the caller to ensure that no mutable
+        /// reference is active when this method is called.
+        pub unsafe fn get(&'static self, init: impl FnOnce() -> T) -> Option<&'static T> {
+            // SAFETY: See the documentation for this method.
+            let ptr = unsafe { self.os.get() as *mut Value<T> };
+            if ptr.addr() > 1 {
+                // SAFETY: the check ensured the pointer is safe (its destructor
+                // is not running) + it is coming from a trusted source (self).
+                if let Some(ref value) = unsafe { (*ptr).inner.get() } {
+                    return Some(value);
+                }
+            }
+            // SAFETY: At this point we are sure we have no value and so
+            // initializing (or trying to) is safe.
+            unsafe { self.try_initialize(init) }
+        }
+
+        // `try_initialize` is only called once per os thread local variable,
+        // except in corner cases where thread_local dtors reference other
+        // thread_local's, or it is being recursively initialized.
+        unsafe fn try_initialize(&'static self, init: impl FnOnce() -> T) -> Option<&'static T> {
+            // SAFETY: No mutable references are ever handed out meaning getting
+            // the value is ok.
+            let ptr = unsafe { self.os.get() as *mut Value<T> };
+            if ptr.addr() == 1 {
+                // destructor is running
+                return None;
+            }
+
+            let ptr = if ptr.is_null() {
+                // If the lookup returned null, we haven't initialized our own
+                // local copy, so do that now.
+                let ptr = Box::into_raw(Box::new(Value { inner: LazyKeyInner::new(), key: self }));
+                // SAFETY: At this point we are sure there is no value inside
+                // ptr so setting it will not affect anyone else.
+                unsafe {
+                    self.os.set(ptr as *mut u8);
+                }
+                ptr
+            } else {
+                // recursive initialization
+                ptr
+            };
+
+            // SAFETY: ptr has been ensured as non-NUL just above an so can be
+            // dereferenced safely.
+            unsafe { Some((*ptr).inner.initialize(init)) }
+        }
+    }
+
+    unsafe extern "C" fn destroy_value<T: 'static>(ptr: *mut u8) {
+        // SAFETY:
+        //
+        // The OS TLS ensures that this key contains a null value when this
+        // destructor starts to run. We set it back to a sentinel value of 1 to
+        // ensure that any future calls to `get` for this thread will return
+        // `None`.
+        //
+        // Note that to prevent an infinite loop we reset it back to null right
+        // before we return from the destructor ourselves.
+        //
+        // Wrap the call in a catch to ensure unwinding is caught in the event
+        // a panic takes place in a destructor.
+        if let Err(_) = panic::catch_unwind(|| unsafe {
+            let ptr = Box::from_raw(ptr as *mut Value<T>);
+            let key = ptr.key;
+            key.os.set(ptr::invalid_mut(1));
+            drop(ptr);
+            key.os.set(ptr::null_mut());
+        }) {
+            rtabort!("thread local panicked on drop");
+        }
+    }
+}
diff --git a/library/std/src/sys/common/thread_local/static_local.rs b/library/std/src/sys/common/thread_local/static_local.rs
new file mode 100644
index 000000000..ec4f2a12b
--- /dev/null
+++ b/library/std/src/sys/common/thread_local/static_local.rs
@@ -0,0 +1,115 @@
+#[doc(hidden)]
+#[macro_export]
+#[allow_internal_unstable(
+    thread_local_internals,
+    cfg_target_thread_local,
+    thread_local,
+    libstd_thread_internals
+)]
+#[allow_internal_unsafe]
+macro_rules! __thread_local_inner {
+    // used to generate the `LocalKey` value for const-initialized thread locals
+    (@key $t:ty, const $init:expr) => {{
+        #[inline] // see comments below
+        #[deny(unsafe_op_in_unsafe_fn)]
+        unsafe fn __getit(
+            _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+        ) -> $crate::option::Option<&'static $t> {
+            const INIT_EXPR: $t = $init;
+
+            // wasm without atomics maps directly to `static mut`, and dtors
+            // aren't implemented because thread dtors aren't really a thing
+            // on wasm right now
+            //
+            // FIXME(#84224) this should come after the `target_thread_local`
+            // block.
+            static mut VAL: $t = INIT_EXPR;
+            unsafe { $crate::option::Option::Some(&VAL) }
+        }
+
+        unsafe {
+            $crate::thread::LocalKey::new(__getit)
+        }
+    }};
+
+    // used to generate the `LocalKey` value for `thread_local!`
+    (@key $t:ty, $init:expr) => {
+        {
+            #[inline]
+            fn __init() -> $t { $init }
+            #[inline]
+            unsafe fn __getit(
+                init: $crate::option::Option<&mut $crate::option::Option<$t>>,
+            ) -> $crate::option::Option<&'static $t> {
+                static __KEY: $crate::thread::__LocalKeyInner<$t> =
+                    $crate::thread::__LocalKeyInner::new();
+
+                // FIXME: remove the #[allow(...)] marker when macros don't
+                // raise warning for missing/extraneous unsafe blocks anymore.
+                // See https://github.com/rust-lang/rust/issues/74838.
+                #[allow(unused_unsafe)]
+                unsafe {
+                    __KEY.get(move || {
+                        if let $crate::option::Option::Some(init) = init {
+                            if let $crate::option::Option::Some(value) = init.take() {
+                                return value;
+                            } else if $crate::cfg!(debug_assertions) {
+                                $crate::unreachable!("missing default value");
+                            }
+                        }
+                        __init()
+                    })
+                }
+            }
+
+            unsafe {
+                $crate::thread::LocalKey::new(__getit)
+            }
+        }
+    };
+    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
+        $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
+            $crate::__thread_local_inner!(@key $t, $($init)*);
+    }
+}
+
+/// On some targets like wasm there's no threads, so no need to generate
+/// thread locals and we can instead just use plain statics!
+#[doc(hidden)]
+pub mod statik {
+    use super::super::lazy::LazyKeyInner;
+    use crate::fmt;
+
+    pub struct Key<T> {
+        inner: LazyKeyInner<T>,
+    }
+
+    unsafe impl<T> Sync for Key<T> {}
+
+    impl<T> fmt::Debug for Key<T> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.debug_struct("Key").finish_non_exhaustive()
+        }
+    }
+
+    impl<T> Key<T> {
+        pub const fn new() -> Key<T> {
+            Key { inner: LazyKeyInner::new() }
+        }
+
+        pub unsafe fn get(&self, init: impl FnOnce() -> T) -> Option<&'static T> {
+            // SAFETY: The caller must ensure no reference is ever handed out to
+            // the inner cell nor mutable reference to the Option<T> inside said
+            // cell. This make it safe to hand a reference, though the lifetime
+            // of 'static is itself unsafe, making the get method unsafe.
+            let value = unsafe {
+                match self.inner.get() {
+                    Some(ref value) => value,
+                    None => self.inner.initialize(init),
+                }
+            };
+
+            Some(value)
+        }
+    }
+}
diff --git a/library/std/src/sys/hermit/fs.rs b/library/std/src/sys/hermit/fs.rs
index c966f2177..cf0b27176 100644
--- a/library/std/src/sys/hermit/fs.rs
+++ b/library/std/src/sys/hermit/fs.rs
@@ -202,7 +202,7 @@ impl OpenOptions {
             create: false,
             create_new: false,
             // system-specific
-            mode: 0x777,
+            mode: 0o777,
         }
     }
 
diff --git a/library/std/src/sys/hermit/futex.rs b/library/std/src/sys/hermit/futex.rs
index b64c174b0..427d8ff6f 100644
--- a/library/std/src/sys/hermit/futex.rs
+++ b/library/std/src/sys/hermit/futex.rs
@@ -16,7 +16,7 @@ pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -
 
     let r = unsafe {
         abi::futex_wait(
-            futex.as_mut_ptr(),
+            futex.as_ptr(),
             expected,
             timespec.as_ref().map_or(null(), |t| t as *const abi::timespec),
             abi::FUTEX_RELATIVE_TIMEOUT,
@@ -28,12 +28,12 @@ pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -
 
 #[inline]
 pub fn futex_wake(futex: &AtomicU32) -> bool {
-    unsafe { abi::futex_wake(futex.as_mut_ptr(), 1) > 0 }
+    unsafe { abi::futex_wake(futex.as_ptr(), 1) > 0 }
 }
 
 #[inline]
 pub fn futex_wake_all(futex: &AtomicU32) {
     unsafe {
-        abi::futex_wake(futex.as_mut_ptr(), i32::MAX);
+        abi::futex_wake(futex.as_ptr(), i32::MAX);
     }
 }
diff --git a/library/std/src/sys/hermit/mod.rs b/library/std/src/sys/hermit/mod.rs
index d34a4cfed..c7cb84667 100644
--- a/library/std/src/sys/hermit/mod.rs
+++ b/library/std/src/sys/hermit/mod.rs
@@ -15,7 +15,6 @@
 
 #![allow(missing_docs, nonstandard_style, unsafe_op_in_unsafe_fn)]
 
-use crate::intrinsics;
 use crate::os::raw::c_char;
 
 pub mod alloc;
@@ -76,9 +75,18 @@ pub fn abort_internal() -> ! {
     }
 }
 
-// FIXME: just a workaround to test the system
 pub fn hashmap_random_keys() -> (u64, u64) {
-    (1, 2)
+    let mut buf = [0; 16];
+    let mut slice = &mut buf[..];
+    while !slice.is_empty() {
+        let res = cvt(unsafe { abi::read_entropy(slice.as_mut_ptr(), slice.len(), 0) })
+            .expect("failed to generate random hashmap keys");
+        slice = &mut slice[res as usize..];
+    }
+
+    let key1 = buf[..8].try_into().unwrap();
+    let key2 = buf[8..].try_into().unwrap();
+    (u64::from_ne_bytes(key1), u64::from_ne_bytes(key2))
 }
 
 // This function is needed by the panic runtime. The symbol is named in
diff --git a/library/std/src/sys/hermit/net.rs b/library/std/src/sys/hermit/net.rs
index 5fb6281aa..d6f64a297 100644
--- a/library/std/src/sys/hermit/net.rs
+++ b/library/std/src/sys/hermit/net.rs
@@ -1,7 +1,7 @@
 #![allow(dead_code)]
 
 use crate::cmp;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedBuf, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::net::{Shutdown, SocketAddr};
 use crate::os::hermit::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, RawFd};
@@ -146,18 +146,35 @@ impl Socket {
         Ok(Socket(unsafe { FileDesc::from_raw_fd(fd) }))
     }
 
-    fn recv_with_flags(&self, buf: &mut [u8], flags: i32) -> io::Result<usize> {
-        let ret =
-            cvt(unsafe { netc::recv(self.0.as_raw_fd(), buf.as_mut_ptr(), buf.len(), flags) })?;
-        Ok(ret as usize)
+    fn recv_with_flags(&self, mut buf: BorrowedCursor<'_>, flags: i32) -> io::Result<()> {
+        let ret = cvt(unsafe {
+            netc::recv(
+                self.0.as_raw_fd(),
+                buf.as_mut().as_mut_ptr() as *mut u8,
+                buf.capacity(),
+                flags,
+            )
+        })?;
+        unsafe {
+            buf.advance(ret as usize);
+        }
+        Ok(())
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, 0)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), 0)?;
+        Ok(buf.len())
     }
 
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, netc::MSG_PEEK)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), netc::MSG_PEEK)?;
+        Ok(buf.len())
+    }
+
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.recv_with_flags(buf, 0)
     }
 
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
diff --git a/library/std/src/sys/mod.rs b/library/std/src/sys/mod.rs
index c080c176a..e767b2866 100644
--- a/library/std/src/sys/mod.rs
+++ b/library/std/src/sys/mod.rs
@@ -76,3 +76,12 @@ cfg_if::cfg_if! {
         pub mod c;
     }
 }
+
+cfg_if::cfg_if! {
+    // Fuchsia components default to full backtrace.
+    if #[cfg(target_os = "fuchsia")] {
+        pub const FULL_BACKTRACE_DEFAULT: bool = true;
+    } else {
+        pub const FULL_BACKTRACE_DEFAULT: bool = false;
+    }
+}
diff --git a/library/std/src/sys/sgx/abi/usercalls/alloc.rs b/library/std/src/sys/sgx/abi/usercalls/alloc.rs
index 0d934318c..01505e944 100644
--- a/library/std/src/sys/sgx/abi/usercalls/alloc.rs
+++ b/library/std/src/sys/sgx/abi/usercalls/alloc.rs
@@ -3,7 +3,6 @@
 use crate::arch::asm;
 use crate::cell::UnsafeCell;
 use crate::cmp;
-use crate::convert::TryInto;
 use crate::mem;
 use crate::ops::{CoerceUnsized, Deref, DerefMut, Index, IndexMut};
 use crate::ptr::{self, NonNull};
diff --git a/library/std/src/sys/sgx/fd.rs b/library/std/src/sys/sgx/fd.rs
index e5dc5b5ad..0c02a1076 100644
--- a/library/std/src/sys/sgx/fd.rs
+++ b/library/std/src/sys/sgx/fd.rs
@@ -1,7 +1,7 @@
 use fortanix_sgx_abi::Fd;
 
 use super::abi::usercalls;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::sys::{AsInner, FromInner, IntoInner};
 
@@ -30,6 +30,10 @@ impl FileDesc {
         usercalls::read(self.fd, &mut [IoSliceMut::new(buf)])
     }
 
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        crate::io::default_read_buf(|b| self.read(b), buf)
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         usercalls::read(self.fd, bufs)
     }
diff --git a/library/std/src/sys/sgx/net.rs b/library/std/src/sys/sgx/net.rs
index 4c4cd7d1d..923be5eb9 100644
--- a/library/std/src/sys/sgx/net.rs
+++ b/library/std/src/sys/sgx/net.rs
@@ -1,6 +1,6 @@
 use crate::error;
 use crate::fmt;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr, ToSocketAddrs};
 use crate::sync::Arc;
 use crate::sys::fd::FileDesc;
@@ -144,6 +144,10 @@ impl TcpStream {
         self.inner.inner.read(buf)
     }
 
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.inner.inner.read_buf(buf)
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.inner.inner.read_vectored(bufs)
     }
diff --git a/library/std/src/sys/solid/net.rs b/library/std/src/sys/solid/net.rs
index 1b98ef993..7d7bfae14 100644
--- a/library/std/src/sys/solid/net.rs
+++ b/library/std/src/sys/solid/net.rs
@@ -2,7 +2,7 @@ use super::abi;
 use crate::{
     cmp,
     ffi::CStr,
-    io::{self, ErrorKind, IoSlice, IoSliceMut},
+    io::{self, BorrowedBuf, BorrowedCursor, ErrorKind, IoSlice, IoSliceMut},
     mem,
     net::{Shutdown, SocketAddr},
     ptr, str,
@@ -294,19 +294,30 @@ impl Socket {
         self.0.duplicate().map(Socket)
     }
 
-    fn recv_with_flags(&self, buf: &mut [u8], flags: c_int) -> io::Result<usize> {
+    fn recv_with_flags(&self, mut buf: BorrowedCursor<'_>, flags: c_int) -> io::Result<()> {
         let ret = cvt(unsafe {
-            netc::recv(self.0.raw(), buf.as_mut_ptr() as *mut c_void, buf.len(), flags)
+            netc::recv(self.0.raw(), buf.as_mut().as_mut_ptr().cast(), buf.capacity(), flags)
         })?;
-        Ok(ret as usize)
+        unsafe {
+            buf.advance(ret as usize);
+        }
+        Ok(())
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, 0)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), 0)?;
+        Ok(buf.len())
     }
 
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, MSG_PEEK)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), MSG_PEEK)?;
+        Ok(buf.len())
+    }
+
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.recv_with_flags(buf, 0)
     }
 
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
diff --git a/library/std/src/sys/unix/fd.rs b/library/std/src/sys/unix/fd.rs
index 9874af4d3..ce5c048f2 100644
--- a/library/std/src/sys/unix/fd.rs
+++ b/library/std/src/sys/unix/fd.rs
@@ -469,6 +469,15 @@ impl<'a> Read for &'a FileDesc {
     fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf(cursor)
     }
+
+    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
+        (**self).read_vectored(bufs)
+    }
+
+    #[inline]
+    fn is_read_vectored(&self) -> bool {
+        (**self).is_read_vectored()
+    }
 }
 
 impl AsInner<OwnedFd> for FileDesc {
diff --git a/library/std/src/sys/unix/fs.rs b/library/std/src/sys/unix/fs.rs
index 7566fafda..abef170dd 100644
--- a/library/std/src/sys/unix/fs.rs
+++ b/library/std/src/sys/unix/fs.rs
@@ -34,7 +34,7 @@ use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
     target_os = "watchos",
 ))]
 use crate::sys::weak::syscall;
-#[cfg(any(target_os = "android", target_os = "macos"))]
+#[cfg(any(target_os = "android", target_os = "macos", target_os = "solaris"))]
 use crate::sys::weak::weak;
 
 use libc::{c_int, mode_t};
@@ -43,6 +43,7 @@ use libc::{c_int, mode_t};
     target_os = "macos",
     target_os = "ios",
     target_os = "watchos",
+    target_os = "solaris",
     all(target_os = "linux", target_env = "gnu")
 ))]
 use libc::c_char;
@@ -1497,8 +1498,8 @@ pub fn link(original: &Path, link: &Path) -> io::Result<()> {
                     // Android has `linkat` on newer versions, but we happen to know `link`
                     // always has the correct behavior, so it's here as well.
                     cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
-                } else if #[cfg(target_os = "macos")] {
-                    // On MacOS, older versions (<=10.9) lack support for linkat while newer
+                } else if #[cfg(any(target_os = "macos", target_os = "solaris"))] {
+                    // MacOS (<=10.9) and Solaris 10 lack support for linkat while newer
                     // versions have it. We want to use linkat if it is available, so we use weak!
                     // to check. `linkat` is preferable to `link` because it gives us a flag to
                     // specify how symlinks should be handled. We pass 0 as the flags argument,
@@ -1892,7 +1893,7 @@ mod remove_dir_impl {
         // file descriptor is automatically closed by libc::closedir() now, so give up ownership
         let new_parent_fd = dir_fd.into_raw_fd();
         // a valid root is not needed because we do not call any functions involving the full path
-        // of the DirEntrys.
+        // of the `DirEntry`s.
         let dummy_root = PathBuf::new();
         let inner = InnerReadDir { dirp, root: dummy_root };
         Ok((ReadDir::new(inner), new_parent_fd))
diff --git a/library/std/src/sys/unix/futex.rs b/library/std/src/sys/unix/futex.rs
index 8d5b54021..d310be6c7 100644
--- a/library/std/src/sys/unix/futex.rs
+++ b/library/std/src/sys/unix/futex.rs
@@ -273,8 +273,6 @@ pub mod zircon {
 
 #[cfg(target_os = "fuchsia")]
 pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
-    use crate::convert::TryFrom;
-
     // Sleep forever if the timeout is longer than fits in a i64.
     let deadline = timeout
         .and_then(|d| {
diff --git a/library/std/src/sys/unix/kernel_copy.rs b/library/std/src/sys/unix/kernel_copy.rs
index 73b9bef7e..16c8e0c0e 100644
--- a/library/std/src/sys/unix/kernel_copy.rs
+++ b/library/std/src/sys/unix/kernel_copy.rs
@@ -17,11 +17,9 @@
 //! Once it has obtained all necessary pieces and brought any wrapper types into a state where they
 //! can be safely bypassed it will attempt to use the `copy_file_range(2)`,
 //! `sendfile(2)` or `splice(2)` syscalls to move data directly between file descriptors.
-//! Since those syscalls have requirements that cannot be fully checked in advance and
-//! gathering additional information about file descriptors would require additional syscalls
-//! anyway it simply attempts to use them one after another (guided by inaccurate hints) to
-//! figure out which one works and falls back to the generic read-write copy loop if none of them
-//! does.
+//! Since those syscalls have requirements that cannot be fully checked in advance it attempts
+//! to use them one after another (guided by hints) to figure out which one works and
+//! falls back to the generic read-write copy loop if none of them does.
 //! Once a working syscall is found for a pair of file descriptors it will be called in a loop
 //! until the copy operation is completed.
 //!
@@ -84,14 +82,10 @@ pub(crate) fn copy_spec<R: Read + ?Sized, W: Write + ?Sized>(
 /// The methods on this type only provide hints, due to `AsRawFd` and `FromRawFd` the inferred
 /// type may be wrong.
 enum FdMeta {
-    /// We obtained the FD from a type that can contain any type of `FileType` and queried the metadata
-    /// because it is cheaper than probing all possible syscalls (reader side)
     Metadata(Metadata),
     Socket,
     Pipe,
-    /// We don't have any metadata, e.g. because the original type was `File` which can represent
-    /// any `FileType` and we did not query the metadata either since it did not seem beneficial
-    /// (writer side)
+    /// We don't have any metadata because the stat syscall failed
     NoneObtained,
 }
 
@@ -131,6 +125,39 @@ impl FdMeta {
     }
 }
 
+/// Returns true either if changes made to the source after a sendfile/splice call won't become
+/// visible in the sink or the source has explicitly opted into such behavior (e.g. by splicing
+/// a file into a pipe, the pipe being the source in this case).
+///
+/// This will prevent File -> Pipe and File -> Socket splicing/sendfile optimizations to uphold
+/// the Read/Write API semantics of io::copy.
+///
+/// Note: This is not 100% airtight, the caller can use the RawFd conversion methods to turn a
+/// regular file into a TcpSocket which will be treated as a socket here without checking.
+fn safe_kernel_copy(source: &FdMeta, sink: &FdMeta) -> bool {
+    match (source, sink) {
+        // Data arriving from a socket is safe because the sender can't modify the socket buffer.
+        // Data arriving from a pipe is safe(-ish) because either the sender *copied*
+        // the bytes into the pipe OR explicitly performed an operation that enables zero-copy,
+        // thus promising not to modify the data later.
+        (FdMeta::Socket, _) => true,
+        (FdMeta::Pipe, _) => true,
+        (FdMeta::Metadata(meta), _)
+            if meta.file_type().is_fifo() || meta.file_type().is_socket() =>
+        {
+            true
+        }
+        // Data going into non-pipes/non-sockets is safe because the "later changes may become visible" issue
+        // only happens for pages sitting in send buffers or pipes.
+        (_, FdMeta::Metadata(meta))
+            if !meta.file_type().is_fifo() && !meta.file_type().is_socket() =>
+        {
+            true
+        }
+        _ => false,
+    }
+}
+
 struct CopyParams(FdMeta, Option<RawFd>);
 
 struct Copier<'a, 'b, R: Read + ?Sized, W: Write + ?Sized> {
@@ -186,7 +213,8 @@ impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> {
             // So we just try and fallback if needed.
             // If current file offsets + write sizes overflow it may also fail, we do not try to fix that and instead
             // fall back to the generic copy loop.
-            if input_meta.potential_sendfile_source() {
+            if input_meta.potential_sendfile_source() && safe_kernel_copy(&input_meta, &output_meta)
+            {
                 let result = sendfile_splice(SpliceMode::Sendfile, readfd, writefd, max_write);
                 result.update_take(reader);
 
@@ -197,7 +225,9 @@ impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> {
                 }
             }
 
-            if input_meta.maybe_fifo() || output_meta.maybe_fifo() {
+            if (input_meta.maybe_fifo() || output_meta.maybe_fifo())
+                && safe_kernel_copy(&input_meta, &output_meta)
+            {
                 let result = sendfile_splice(SpliceMode::Splice, readfd, writefd, max_write);
                 result.update_take(reader);
 
@@ -298,13 +328,13 @@ impl CopyRead for &File {
 
 impl CopyWrite for File {
     fn properties(&self) -> CopyParams {
-        CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
+        CopyParams(fd_to_meta(self), Some(self.as_raw_fd()))
     }
 }
 
 impl CopyWrite for &File {
     fn properties(&self) -> CopyParams {
-        CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
+        CopyParams(fd_to_meta(*self), Some(self.as_raw_fd()))
     }
 }
 
@@ -401,13 +431,13 @@ impl CopyRead for StdinLock<'_> {
 
 impl CopyWrite for StdoutLock<'_> {
     fn properties(&self) -> CopyParams {
-        CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
+        CopyParams(fd_to_meta(self), Some(self.as_raw_fd()))
     }
 }
 
 impl CopyWrite for StderrLock<'_> {
     fn properties(&self) -> CopyParams {
-        CopyParams(FdMeta::NoneObtained, Some(self.as_raw_fd()))
+        CopyParams(fd_to_meta(self), Some(self.as_raw_fd()))
     }
 }
 
diff --git a/library/std/src/sys/unix/kernel_copy/tests.rs b/library/std/src/sys/unix/kernel_copy/tests.rs
index 3fe849e23..a524270e3 100644
--- a/library/std/src/sys/unix/kernel_copy/tests.rs
+++ b/library/std/src/sys/unix/kernel_copy/tests.rs
@@ -83,6 +83,48 @@ fn copies_append_mode_sink() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn dont_splice_pipes_from_files() -> Result<()> {
+    // splicing to a pipe and then modifying the source could lead to changes
+    // becoming visible in an unexpected order.
+
+    use crate::io::SeekFrom;
+    use crate::os::unix::fs::FileExt;
+    use crate::process::{ChildStdin, ChildStdout};
+    use crate::sys_common::FromInner;
+
+    let (read_end, write_end) = crate::sys::pipe::anon_pipe()?;
+
+    let mut read_end = ChildStdout::from_inner(read_end);
+    let mut write_end = ChildStdin::from_inner(write_end);
+
+    let tmp_path = tmpdir();
+    let file = tmp_path.join("to_be_modified");
+    let mut file =
+        crate::fs::OpenOptions::new().create_new(true).read(true).write(true).open(file)?;
+
+    const SZ: usize = libc::PIPE_BUF as usize;
+
+    // put data in page cache
+    let mut buf: [u8; SZ] = [0x01; SZ];
+    file.write_all(&buf).unwrap();
+
+    // copy page into pipe
+    file.seek(SeekFrom::Start(0)).unwrap();
+    assert!(io::copy(&mut file, &mut write_end).unwrap() == SZ as u64);
+
+    // modify file
+    buf[0] = 0x02;
+    file.write_at(&buf, 0).unwrap();
+
+    // read from pipe
+    read_end.read_exact(buf.as_mut_slice()).unwrap();
+
+    assert_eq!(buf[0], 0x01, "data in pipe should reflect the original, not later modifications");
+
+    Ok(())
+}
+
 #[bench]
 fn bench_file_to_file_copy(b: &mut test::Bencher) {
     const BYTES: usize = 128 * 1024;
diff --git a/library/std/src/sys/unix/net.rs b/library/std/src/sys/unix/net.rs
index 8e05b618d..573bfa658 100644
--- a/library/std/src/sys/unix/net.rs
+++ b/library/std/src/sys/unix/net.rs
@@ -1,6 +1,6 @@
 use crate::cmp;
 use crate::ffi::CStr;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedBuf, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::net::{Shutdown, SocketAddr};
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
@@ -242,19 +242,35 @@ impl Socket {
         self.0.duplicate().map(Socket)
     }
 
-    fn recv_with_flags(&self, buf: &mut [u8], flags: c_int) -> io::Result<usize> {
+    fn recv_with_flags(&self, mut buf: BorrowedCursor<'_>, flags: c_int) -> io::Result<()> {
         let ret = cvt(unsafe {
-            libc::recv(self.as_raw_fd(), buf.as_mut_ptr() as *mut c_void, buf.len(), flags)
+            libc::recv(
+                self.as_raw_fd(),
+                buf.as_mut().as_mut_ptr() as *mut c_void,
+                buf.capacity(),
+                flags,
+            )
         })?;
-        Ok(ret as usize)
+        unsafe {
+            buf.advance(ret as usize);
+        }
+        Ok(())
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, 0)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), 0)?;
+        Ok(buf.len())
     }
 
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, MSG_PEEK)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), MSG_PEEK)?;
+        Ok(buf.len())
+    }
+
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.recv_with_flags(buf, 0)
     }
 
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
@@ -427,6 +443,17 @@ impl Socket {
         Ok(passcred != 0)
     }
 
+    #[cfg(target_os = "freebsd")]
+    pub fn set_passcred(&self, passcred: bool) -> io::Result<()> {
+        setsockopt(self, libc::AF_LOCAL, libc::LOCAL_CREDS_PERSISTENT, passcred as libc::c_int)
+    }
+
+    #[cfg(target_os = "freebsd")]
+    pub fn passcred(&self) -> io::Result<bool> {
+        let passcred: libc::c_int = getsockopt(self, libc::AF_LOCAL, libc::LOCAL_CREDS_PERSISTENT)?;
+        Ok(passcred != 0)
+    }
+
     #[cfg(not(any(target_os = "solaris", target_os = "illumos")))]
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index 21b035fb3..a345af76f 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -7,7 +7,6 @@ mod tests;
 
 use crate::os::unix::prelude::*;
 
-use crate::convert::TryFrom;
 use crate::error::Error as StdError;
 use crate::ffi::{CStr, CString, OsStr, OsString};
 use crate::fmt;
@@ -115,7 +114,10 @@ pub fn set_errno(e: i32) {
 /// Gets a detailed string description for the given error number.
 pub fn error_string(errno: i32) -> String {
     extern "C" {
-        #[cfg_attr(any(target_os = "linux", target_env = "newlib"), link_name = "__xpg_strerror_r")]
+        #[cfg_attr(
+            all(any(target_os = "linux", target_env = "newlib"), not(target_env = "ohos")),
+            link_name = "__xpg_strerror_r"
+        )]
         fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: libc::size_t) -> c_int;
     }
 
diff --git a/library/std/src/sys/unix/pipe.rs b/library/std/src/sys/unix/pipe.rs
index a744d0ab6..dc17c9fac 100644
--- a/library/std/src/sys/unix/pipe.rs
+++ b/library/std/src/sys/unix/pipe.rs
@@ -1,4 +1,4 @@
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
 use crate::sys::fd::FileDesc;
@@ -49,6 +49,10 @@ impl AnonPipe {
         self.0.read(buf)
     }
 
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.0.read_buf(buf)
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.0.read_vectored(bufs)
     }
diff --git a/library/std/src/sys/unix/process/process_fuchsia.rs b/library/std/src/sys/unix/process/process_fuchsia.rs
index d4c7e58b3..e45c380a0 100644
--- a/library/std/src/sys/unix/process/process_fuchsia.rs
+++ b/library/std/src/sys/unix/process/process_fuchsia.rs
@@ -166,7 +166,6 @@ impl Process {
     }
 
     pub fn wait(&mut self) -> io::Result<ExitStatus> {
-        use crate::default::Default;
         use crate::sys::process::zircon::*;
 
         let mut proc_info: zx_info_process_t = Default::default();
@@ -199,7 +198,6 @@ impl Process {
     }
 
     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
-        use crate::default::Default;
         use crate::sys::process::zircon::*;
 
         let mut proc_info: zx_info_process_t = Default::default();
diff --git a/library/std/src/sys/unix/rand.rs b/library/std/src/sys/unix/rand.rs
index a6fe07873..0f347ffab 100644
--- a/library/std/src/sys/unix/rand.rs
+++ b/library/std/src/sys/unix/rand.rs
@@ -20,7 +20,8 @@ pub fn hashmap_random_keys() -> (u64, u64) {
     not(target_os = "netbsd"),
     not(target_os = "fuchsia"),
     not(target_os = "redox"),
-    not(target_os = "vxworks")
+    not(target_os = "vxworks"),
+    not(target_os = "emscripten")
 ))]
 mod imp {
     use crate::fs::File;
@@ -174,7 +175,7 @@ mod imp {
     }
 }
 
-#[cfg(target_os = "openbsd")]
+#[cfg(any(target_os = "openbsd", target_os = "emscripten"))]
 mod imp {
     use crate::sys::os::errno;
 
diff --git a/library/std/src/sys/unix/stdio.rs b/library/std/src/sys/unix/stdio.rs
index b3626c564..a26f20795 100644
--- a/library/std/src/sys/unix/stdio.rs
+++ b/library/std/src/sys/unix/stdio.rs
@@ -1,4 +1,4 @@
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
 use crate::os::unix::io::FromRawFd;
 use crate::sys::fd::FileDesc;
@@ -18,6 +18,10 @@ impl io::Read for Stdin {
         unsafe { ManuallyDrop::new(FileDesc::from_raw_fd(libc::STDIN_FILENO)).read(buf) }
     }
 
+    fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        unsafe { ManuallyDrop::new(FileDesc::from_raw_fd(libc::STDIN_FILENO)).read_buf(buf) }
+    }
+
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         unsafe { ManuallyDrop::new(FileDesc::from_raw_fd(libc::STDIN_FILENO)).read_vectored(bufs) }
     }
diff --git a/library/std/src/sys/unix/time.rs b/library/std/src/sys/unix/time.rs
index 0f11de8f5..6f5358340 100644
--- a/library/std/src/sys/unix/time.rs
+++ b/library/std/src/sys/unix/time.rs
@@ -174,6 +174,34 @@ impl From<libc::timespec> for Timespec {
     }
 }
 
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    target_pointer_width = "32",
+    not(target_arch = "riscv32")
+))]
+#[repr(C)]
+pub(in crate::sys::unix) struct __timespec64 {
+    pub(in crate::sys::unix) tv_sec: i64,
+    #[cfg(target_endian = "big")]
+    _padding: i32,
+    pub(in crate::sys::unix) tv_nsec: i32,
+    #[cfg(target_endian = "little")]
+    _padding: i32,
+}
+
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    target_pointer_width = "32",
+    not(target_arch = "riscv32")
+))]
+impl From<__timespec64> for Timespec {
+    fn from(t: __timespec64) -> Timespec {
+        Timespec::new(t.tv_sec, t.tv_nsec.into())
+    }
+}
+
 #[cfg(any(
     all(target_os = "macos", any(not(target_arch = "aarch64"))),
     target_os = "ios",
@@ -352,29 +380,23 @@ mod inner {
     impl Timespec {
         pub fn now(clock: libc::clockid_t) -> Timespec {
             // Try to use 64-bit time in preparation for Y2038.
-            #[cfg(all(target_os = "linux", target_env = "gnu", target_pointer_width = "32"))]
+            #[cfg(all(
+                target_os = "linux",
+                target_env = "gnu",
+                target_pointer_width = "32",
+                not(target_arch = "riscv32")
+            ))]
             {
                 use crate::sys::weak::weak;
 
                 // __clock_gettime64 was added to 32-bit arches in glibc 2.34,
                 // and it handles both vDSO calls and ENOSYS fallbacks itself.
-                weak!(fn __clock_gettime64(libc::clockid_t, *mut __timespec64) -> libc::c_int);
-
-                #[repr(C)]
-                struct __timespec64 {
-                    tv_sec: i64,
-                    #[cfg(target_endian = "big")]
-                    _padding: i32,
-                    tv_nsec: i32,
-                    #[cfg(target_endian = "little")]
-                    _padding: i32,
-                }
+                weak!(fn __clock_gettime64(libc::clockid_t, *mut super::__timespec64) -> libc::c_int);
 
                 if let Some(clock_gettime64) = __clock_gettime64.get() {
                     let mut t = MaybeUninit::uninit();
                     cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
-                    let t = unsafe { t.assume_init() };
-                    return Timespec::new(t.tv_sec, t.tv_nsec as i64);
+                    return Timespec::from(unsafe { t.assume_init() });
                 }
             }
 
diff --git a/library/std/src/sys/unsupported/net.rs b/library/std/src/sys/unsupported/net.rs
index a5204a084..bbc52703f 100644
--- a/library/std/src/sys/unsupported/net.rs
+++ b/library/std/src/sys/unsupported/net.rs
@@ -1,5 +1,5 @@
 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::sys::unsupported;
 use crate::time::Duration;
@@ -39,6 +39,10 @@ impl TcpStream {
         self.0
     }
 
+    pub fn read_buf(&self, _buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.0
+    }
+
     pub fn read_vectored(&self, _: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.0
     }
diff --git a/library/std/src/sys/unsupported/pipe.rs b/library/std/src/sys/unsupported/pipe.rs
index 0bba673b4..d7d8f297a 100644
--- a/library/std/src/sys/unsupported/pipe.rs
+++ b/library/std/src/sys/unsupported/pipe.rs
@@ -1,4 +1,4 @@
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 
 pub struct AnonPipe(!);
 
@@ -7,6 +7,10 @@ impl AnonPipe {
         self.0
     }
 
+    pub fn read_buf(&self, _buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.0
+    }
+
     pub fn read_vectored(&self, _bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.0
     }
diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index 0b9c8e61d..191db4b60 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -2,7 +2,7 @@
 #![allow(dead_code)]
 
 use super::err2io;
-use crate::io::{self, IoSlice, IoSliceMut, SeekFrom};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
 use crate::net::Shutdown;
 use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
@@ -46,6 +46,22 @@ impl WasiFd {
         unsafe { wasi::fd_read(self.as_raw_fd() as wasi::Fd, iovec(bufs)).map_err(err2io) }
     }
 
+    pub fn read_buf(&self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
+        unsafe {
+            let bufs = [wasi::Iovec {
+                buf: buf.as_mut().as_mut_ptr() as *mut u8,
+                buf_len: buf.capacity(),
+            }];
+            match wasi::fd_read(self.as_raw_fd() as wasi::Fd, &bufs) {
+                Ok(n) => {
+                    buf.advance(n);
+                    Ok(())
+                }
+                Err(e) => Err(err2io(e)),
+            }
+        }
+    }
+
     pub fn write(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
         unsafe { wasi::fd_write(self.as_raw_fd() as wasi::Fd, ciovec(bufs)).map_err(err2io) }
     }
diff --git a/library/std/src/sys/wasi/fs.rs b/library/std/src/sys/wasi/fs.rs
index d4866bbc3..3a205267e 100644
--- a/library/std/src/sys/wasi/fs.rs
+++ b/library/std/src/sys/wasi/fs.rs
@@ -441,7 +441,7 @@ impl File {
     }
 
     pub fn read_buf(&self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
-        crate::io::default_read_buf(|buf| self.read(buf), cursor)
+        self.fd.read_buf(cursor)
     }
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
diff --git a/library/std/src/sys/wasi/net.rs b/library/std/src/sys/wasi/net.rs
index cf4ebba1a..59d94a368 100644
--- a/library/std/src/sys/wasi/net.rs
+++ b/library/std/src/sys/wasi/net.rs
@@ -3,7 +3,7 @@
 use super::err2io;
 use super::fd::WasiFd;
 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::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
 use crate::sys::unsupported;
@@ -91,6 +91,10 @@ impl TcpStream {
         self.read_vectored(&mut [IoSliceMut::new(buf)])
     }
 
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.socket().as_inner().read_buf(buf)
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.socket().as_inner().read(bufs)
     }
diff --git a/library/std/src/sys/windows/args.rs b/library/std/src/sys/windows/args.rs
index 30356fa85..43c0cdb65 100644
--- a/library/std/src/sys/windows/args.rs
+++ b/library/std/src/sys/windows/args.rs
@@ -11,10 +11,11 @@ use crate::fmt;
 use crate::io;
 use crate::num::NonZeroU16;
 use crate::os::windows::prelude::*;
-use crate::path::PathBuf;
-use crate::sys::c;
+use crate::path::{Path, PathBuf};
+use crate::sys::path::get_long_path;
 use crate::sys::process::ensure_no_nuls;
 use crate::sys::windows::os::current_exe;
+use crate::sys::{c, to_u16s};
 use crate::sys_common::wstr::WStrUnits;
 use crate::vec;
 
@@ -311,7 +312,7 @@ pub(crate) fn make_bat_command_line(
 /// Takes a path and tries to return a non-verbatim path.
 ///
 /// This is necessary because cmd.exe does not support verbatim paths.
-pub(crate) fn to_user_path(mut path: Vec<u16>) -> io::Result<Vec<u16>> {
+pub(crate) fn to_user_path(path: &Path) -> io::Result<Vec<u16>> {
     use crate::ptr;
     use crate::sys::windows::fill_utf16_buf;
 
@@ -324,6 +325,8 @@ pub(crate) fn to_user_path(mut path: Vec<u16>) -> io::Result<Vec<u16>> {
     const N: u16 = b'N' as _;
     const C: u16 = b'C' as _;
 
+    let mut path = to_u16s(path)?;
+
     // Early return if the path is too long to remove the verbatim prefix.
     const LEGACY_MAX_PATH: usize = 260;
     if path.len() > LEGACY_MAX_PATH {
@@ -337,7 +340,13 @@ pub(crate) fn to_user_path(mut path: Vec<u16>) -> io::Result<Vec<u16>> {
             fill_utf16_buf(
                 |buffer, size| c::GetFullPathNameW(lpfilename, size, buffer, ptr::null_mut()),
                 |full_path: &[u16]| {
-                    if full_path == &path[4..path.len() - 1] { full_path.into() } else { path }
+                    if full_path == &path[4..path.len() - 1] {
+                        let mut path: Vec<u16> = full_path.into();
+                        path.push(0);
+                        path
+                    } else {
+                        path
+                    }
                 },
             )
         },
@@ -350,7 +359,9 @@ pub(crate) fn to_user_path(mut path: Vec<u16>) -> io::Result<Vec<u16>> {
                 |buffer, size| c::GetFullPathNameW(lpfilename, size, buffer, ptr::null_mut()),
                 |full_path: &[u16]| {
                     if full_path == &path[6..path.len() - 1] {
-                        full_path.into()
+                        let mut path: Vec<u16> = full_path.into();
+                        path.push(0);
+                        path
                     } else {
                         // Restore the 'C' in "UNC".
                         path[6] = b'C' as u16;
@@ -360,6 +371,6 @@ pub(crate) fn to_user_path(mut path: Vec<u16>) -> io::Result<Vec<u16>> {
             )
         },
         // For everything else, leave the path unchanged.
-        _ => Ok(path),
+        _ => get_long_path(path, false),
     }
 }
diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 5d150eca0..1f4092ad7 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -296,7 +296,6 @@ pub const STATUS_INVALID_PARAMETER: NTSTATUS = 0xc000000d_u32 as _;
 
 pub const STATUS_PENDING: NTSTATUS = 0x103 as _;
 pub const STATUS_END_OF_FILE: NTSTATUS = 0xC0000011_u32 as _;
-pub const STATUS_NOT_IMPLEMENTED: NTSTATUS = 0xC0000002_u32 as _;
 
 // Equivalent to the `NT_SUCCESS` C preprocessor macro.
 // See: https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/using-ntstatus-values
@@ -1282,6 +1281,46 @@ extern "system" {
     ) -> NTSTATUS;
 }
 
+#[link(name = "ntdll")]
+extern "system" {
+    pub fn NtCreateFile(
+        FileHandle: *mut HANDLE,
+        DesiredAccess: ACCESS_MASK,
+        ObjectAttributes: *const OBJECT_ATTRIBUTES,
+        IoStatusBlock: *mut IO_STATUS_BLOCK,
+        AllocationSize: *mut i64,
+        FileAttributes: ULONG,
+        ShareAccess: ULONG,
+        CreateDisposition: ULONG,
+        CreateOptions: ULONG,
+        EaBuffer: *mut c_void,
+        EaLength: ULONG,
+    ) -> NTSTATUS;
+    pub fn NtReadFile(
+        FileHandle: BorrowedHandle<'_>,
+        Event: HANDLE,
+        ApcRoutine: Option<IO_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;
+    pub fn NtWriteFile(
+        FileHandle: BorrowedHandle<'_>,
+        Event: HANDLE,
+        ApcRoutine: Option<IO_APC_ROUTINE>,
+        ApcContext: *mut c_void,
+        IoStatusBlock: &mut IO_STATUS_BLOCK,
+        Buffer: *const u8,
+        Length: ULONG,
+        ByteOffset: Option<&LARGE_INTEGER>,
+        Key: Option<&ULONG>,
+    ) -> NTSTATUS;
+    pub fn RtlNtStatusToDosError(Status: NTSTATUS) -> ULONG;
+}
+
 // 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.
 compat_fn_with_fallback! {
@@ -1322,52 +1361,6 @@ compat_fn_optional! {
 compat_fn_with_fallback! {
     pub static NTDLL: &CStr = ansi_str!("ntdll");
 
-    pub fn NtCreateFile(
-        FileHandle: *mut HANDLE,
-        DesiredAccess: ACCESS_MASK,
-        ObjectAttributes: *const OBJECT_ATTRIBUTES,
-        IoStatusBlock: *mut IO_STATUS_BLOCK,
-        AllocationSize: *mut i64,
-        FileAttributes: ULONG,
-        ShareAccess: ULONG,
-        CreateDisposition: ULONG,
-        CreateOptions: ULONG,
-        EaBuffer: *mut c_void,
-        EaLength: ULONG
-    ) -> NTSTATUS {
-        STATUS_NOT_IMPLEMENTED
-    }
-    pub fn NtReadFile(
-        FileHandle: BorrowedHandle<'_>,
-        Event: HANDLE,
-        ApcRoutine: Option<IO_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
-    }
-    pub fn NtWriteFile(
-        FileHandle: BorrowedHandle<'_>,
-        Event: HANDLE,
-        ApcRoutine: Option<IO_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
-    }
-    pub fn RtlNtStatusToDosError(
-        Status: NTSTATUS
-    ) -> ULONG {
-        Status as ULONG
-    }
     pub fn NtCreateKeyedEvent(
         KeyedEventHandle: LPHANDLE,
         DesiredAccess: ACCESS_MASK,
diff --git a/library/std/src/sys/windows/c/errors.rs b/library/std/src/sys/windows/c/errors.rs
index 23dcc119d..ad8da19b6 100644
--- a/library/std/src/sys/windows/c/errors.rs
+++ b/library/std/src/sys/windows/c/errors.rs
@@ -12,7 +12,7 @@ pub const ERROR_RESOURCE_CALL_TIMED_OUT: DWORD = 5910;
 pub const FRS_ERR_SYSVOL_POPULATE_TIMEOUT: DWORD = 8014;
 pub const DNS_ERROR_RECORD_TIMED_OUT: DWORD = 9705;
 
-// The followiung list was obtained from
+// The following list was obtained from
 //   `/usr/x86_64-w64-mingw32/include/winerror.h`
 // in the Debian package
 //   mingw-w64_6.0.0-3_all.deb
diff --git a/library/std/src/sys/windows/fs.rs b/library/std/src/sys/windows/fs.rs
index d2c597664..956db577d 100644
--- a/library/std/src/sys/windows/fs.rs
+++ b/library/std/src/sys/windows/fs.rs
@@ -1236,7 +1236,17 @@ pub fn link(_original: &Path, _link: &Path) -> io::Result<()> {
 }
 
 pub fn stat(path: &Path) -> io::Result<FileAttr> {
-    metadata(path, ReparsePoint::Follow)
+    match metadata(path, ReparsePoint::Follow) {
+        Err(err) if err.raw_os_error() == Some(c::ERROR_CANT_ACCESS_FILE as i32) => {
+            if let Ok(attrs) = lstat(path) {
+                if !attrs.file_type().is_symlink() {
+                    return Ok(attrs);
+                }
+            }
+            Err(err)
+        }
+        result => result,
+    }
 }
 
 pub fn lstat(path: &Path) -> io::Result<FileAttr> {
@@ -1393,24 +1403,40 @@ fn symlink_junction_inner(original: &Path, junction: &Path) -> io::Result<()> {
     opts.custom_flags(c::FILE_FLAG_OPEN_REPARSE_POINT | c::FILE_FLAG_BACKUP_SEMANTICS);
     let f = File::open(junction, &opts)?;
     let h = f.as_inner().as_raw_handle();
-
     unsafe {
         let mut data = Align8([MaybeUninit::<u8>::uninit(); c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE]);
         let data_ptr = data.0.as_mut_ptr();
+        let data_end = data_ptr.add(c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE);
         let db = data_ptr.cast::<c::REPARSE_MOUNTPOINT_DATA_BUFFER>();
         // Zero the header to ensure it's fully initialized, including reserved parameters.
         *db = mem::zeroed();
-        let buf = ptr::addr_of_mut!((*db).ReparseTarget).cast::<c::WCHAR>();
-        let mut i = 0;
+        let reparse_target_slice = {
+            let buf_start = ptr::addr_of_mut!((*db).ReparseTarget).cast::<c::WCHAR>();
+            // Compute offset in bytes and then divide so that we round down
+            // rather than hit any UB (admittedly this arithmetic should work
+            // out so that this isn't necessary)
+            let buf_len_bytes = usize::try_from(data_end.byte_offset_from(buf_start)).unwrap();
+            let buf_len_wchars = buf_len_bytes / core::mem::size_of::<c::WCHAR>();
+            core::slice::from_raw_parts_mut(buf_start, buf_len_wchars)
+        };
+
         // FIXME: this conversion is very hacky
-        let v = br"\??\";
-        let v = v.iter().map(|x| *x as u16);
-        for c in v.chain(original.as_os_str().encode_wide()) {
-            *buf.add(i) = c;
+        let iter = br"\??\"
+            .iter()
+            .map(|x| *x as u16)
+            .chain(original.as_os_str().encode_wide())
+            .chain(core::iter::once(0));
+        let mut i = 0;
+        for c in iter {
+            if i >= reparse_target_slice.len() {
+                return Err(crate::io::const_io_error!(
+                    crate::io::ErrorKind::InvalidFilename,
+                    "Input filename is too long"
+                ));
+            }
+            reparse_target_slice[i] = c;
             i += 1;
         }
-        *buf.add(i) = 0;
-        i += 1;
         (*db).ReparseTag = c::IO_REPARSE_TAG_MOUNT_POINT;
         (*db).ReparseTargetMaximumLength = (i * 2) as c::WORD;
         (*db).ReparseTargetLength = ((i - 1) * 2) as c::WORD;
diff --git a/library/std/src/sys/windows/handle.rs b/library/std/src/sys/windows/handle.rs
index ae33d48c6..b290f4070 100644
--- a/library/std/src/sys/windows/handle.rs
+++ b/library/std/src/sys/windows/handle.rs
@@ -327,7 +327,16 @@ impl<'a> Read for &'a Handle {
         (**self).read(buf)
     }
 
+    fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        (**self).read_buf(buf)
+    }
+
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         (**self).read_vectored(bufs)
     }
+
+    #[inline]
+    fn is_read_vectored(&self) -> bool {
+        (**self).is_read_vectored()
+    }
 }
diff --git a/library/std/src/sys/windows/net.rs b/library/std/src/sys/windows/net.rs
index e0701a498..ee1f5482b 100644
--- a/library/std/src/sys/windows/net.rs
+++ b/library/std/src/sys/windows/net.rs
@@ -1,7 +1,7 @@
 #![unstable(issue = "none", feature = "windows_net")]
 
 use crate::cmp;
-use crate::io::{self, IoSlice, IoSliceMut, Read};
+use crate::io::{self, BorrowedBuf, BorrowedCursor, IoSlice, IoSliceMut, Read};
 use crate::mem;
 use crate::net::{Shutdown, SocketAddr};
 use crate::os::windows::io::{
@@ -214,28 +214,38 @@ impl Socket {
         Ok(Self(self.0.try_clone()?))
     }
 
-    fn recv_with_flags(&self, buf: &mut [u8], flags: c_int) -> io::Result<usize> {
+    fn recv_with_flags(&self, mut buf: BorrowedCursor<'_>, flags: c_int) -> io::Result<()> {
         // On unix when a socket is shut down all further reads return 0, so we
         // do the same on windows to map a shut down socket to returning EOF.
-        let length = cmp::min(buf.len(), i32::MAX as usize) as i32;
-        let result =
-            unsafe { c::recv(self.as_raw_socket(), buf.as_mut_ptr() as *mut _, length, flags) };
+        let length = cmp::min(buf.capacity(), i32::MAX as usize) as i32;
+        let result = unsafe {
+            c::recv(self.as_raw_socket(), buf.as_mut().as_mut_ptr() as *mut _, length, flags)
+        };
 
         match result {
             c::SOCKET_ERROR => {
                 let error = unsafe { c::WSAGetLastError() };
 
                 if error == c::WSAESHUTDOWN {
-                    Ok(0)
+                    Ok(())
                 } else {
                     Err(io::Error::from_raw_os_error(error))
                 }
             }
-            _ => Ok(result as usize),
+            _ => {
+                unsafe { buf.advance(result as usize) };
+                Ok(())
+            }
         }
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), 0)?;
+        Ok(buf.len())
+    }
+
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
         self.recv_with_flags(buf, 0)
     }
 
@@ -277,7 +287,9 @@ impl Socket {
     }
 
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.recv_with_flags(buf, c::MSG_PEEK)
+        let mut buf = BorrowedBuf::from(buf);
+        self.recv_with_flags(buf.unfilled(), c::MSG_PEEK)?;
+        Ok(buf.len())
     }
 
     fn recv_from_with_flags(
diff --git a/library/std/src/sys/windows/path.rs b/library/std/src/sys/windows/path.rs
index beeca1917..c3573d14c 100644
--- a/library/std/src/sys/windows/path.rs
+++ b/library/std/src/sys/windows/path.rs
@@ -220,6 +220,19 @@ fn parse_next_component(path: &OsStr, verbatim: bool) -> (&OsStr, &OsStr) {
 ///
 /// This path may or may not have a verbatim prefix.
 pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
+    let path = to_u16s(path)?;
+    get_long_path(path, true)
+}
+
+/// Get a normalized absolute path that can bypass path length limits.
+///
+/// Setting prefer_verbatim to true suggests a stronger preference for verbatim
+/// paths even when not strictly necessary. This allows the Windows API to avoid
+/// repeating our work. However, if the path may be given back to users or
+/// passed to other application then it's preferable to use non-verbatim paths
+/// when possible. Non-verbatim paths are better understood by users and handled
+/// by more software.
+pub(crate) fn get_long_path(mut path: Vec<u16>, prefer_verbatim: bool) -> io::Result<Vec<u16>> {
     // Normally the MAX_PATH is 260 UTF-16 code units (including the NULL).
     // However, for APIs such as CreateDirectory[1], the limit is 248.
     //
@@ -243,7 +256,6 @@ pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
     // \\?\UNC\
     const UNC_PREFIX: &[u16] = &[SEP, SEP, QUERY, SEP, U, N, C, SEP];
 
-    let mut path = to_u16s(path)?;
     if path.starts_with(VERBATIM_PREFIX) || path.starts_with(NT_PREFIX) || path == &[0] {
         // Early return for paths that are already verbatim or empty.
         return Ok(path);
@@ -275,29 +287,34 @@ pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
         |mut absolute| {
             path.clear();
 
-            // Secondly, add the verbatim prefix. This is easier here because we know the
-            // path is now absolute and fully normalized (e.g. `/` has been changed to `\`).
-            let prefix = match absolute {
-                // C:\ => \\?\C:\
-                [_, COLON, SEP, ..] => VERBATIM_PREFIX,
-                // \\.\ => \\?\
-                [SEP, SEP, DOT, SEP, ..] => {
-                    absolute = &absolute[4..];
-                    VERBATIM_PREFIX
-                }
-                // Leave \\?\ and \??\ as-is.
-                [SEP, SEP, QUERY, SEP, ..] | [SEP, QUERY, QUERY, SEP, ..] => &[],
-                // \\ => \\?\UNC\
-                [SEP, SEP, ..] => {
-                    absolute = &absolute[2..];
-                    UNC_PREFIX
-                }
-                // Anything else we leave alone.
-                _ => &[],
-            };
-
-            path.reserve_exact(prefix.len() + absolute.len() + 1);
-            path.extend_from_slice(prefix);
+            // Only prepend the prefix if needed.
+            if prefer_verbatim || absolute.len() + 1 >= LEGACY_MAX_PATH {
+                // Secondly, add the verbatim prefix. This is easier here because we know the
+                // path is now absolute and fully normalized (e.g. `/` has been changed to `\`).
+                let prefix = match absolute {
+                    // C:\ => \\?\C:\
+                    [_, COLON, SEP, ..] => VERBATIM_PREFIX,
+                    // \\.\ => \\?\
+                    [SEP, SEP, DOT, SEP, ..] => {
+                        absolute = &absolute[4..];
+                        VERBATIM_PREFIX
+                    }
+                    // Leave \\?\ and \??\ as-is.
+                    [SEP, SEP, QUERY, SEP, ..] | [SEP, QUERY, QUERY, SEP, ..] => &[],
+                    // \\ => \\?\UNC\
+                    [SEP, SEP, ..] => {
+                        absolute = &absolute[2..];
+                        UNC_PREFIX
+                    }
+                    // Anything else we leave alone.
+                    _ => &[],
+                };
+
+                path.reserve_exact(prefix.len() + absolute.len() + 1);
+                path.extend_from_slice(prefix);
+            } else {
+                path.reserve_exact(absolute.len() + 1);
+            }
             path.extend_from_slice(absolute);
             path.push(0);
         },
diff --git a/library/std/src/sys/windows/pipe.rs b/library/std/src/sys/windows/pipe.rs
index 7b25edaa5..0780b2958 100644
--- a/library/std/src/sys/windows/pipe.rs
+++ b/library/std/src/sys/windows/pipe.rs
@@ -1,7 +1,7 @@
 use crate::os::windows::prelude::*;
 
 use crate::ffi::OsStr;
-use crate::io::{self, IoSlice, IoSliceMut, Read};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read};
 use crate::mem;
 use crate::path::Path;
 use crate::ptr;
@@ -252,6 +252,28 @@ impl AnonPipe {
         }
     }
 
+    pub fn read_buf(&self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
+        let result = unsafe {
+            let len = crate::cmp::min(buf.capacity(), c::DWORD::MAX as usize) as c::DWORD;
+            self.alertable_io_internal(c::ReadFileEx, buf.as_mut().as_mut_ptr() as _, len)
+        };
+
+        match result {
+            // The special treatment of BrokenPipe is to deal with Windows
+            // pipe semantics, which yields this error when *reading* from
+            // a pipe after the other end has closed; we interpret that as
+            // EOF on the pipe.
+            Err(ref e) if e.kind() == io::ErrorKind::BrokenPipe => Ok(()),
+            Err(e) => Err(e),
+            Ok(n) => {
+                unsafe {
+                    buf.advance(n);
+                }
+                Ok(())
+            }
+        }
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         self.inner.read_vectored(bufs)
     }
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index 10bc949e1..1c73b64e2 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -266,11 +266,7 @@ impl Command {
         let (program, mut cmd_str) = if is_batch_file {
             (
                 command_prompt()?,
-                args::make_bat_command_line(
-                    &args::to_user_path(program)?,
-                    &self.args,
-                    self.force_quotes_enabled,
-                )?,
+                args::make_bat_command_line(&program, &self.args, self.force_quotes_enabled)?,
             )
         } else {
             let cmd_str = make_command_line(&self.program, &self.args, self.force_quotes_enabled)?;
@@ -410,7 +406,7 @@ fn resolve_exe<'a>(
         if has_exe_suffix {
             // The application name is a path to a `.exe` file.
             // Let `CreateProcessW` figure out if it exists or not.
-            return path::maybe_verbatim(Path::new(exe_path));
+            return args::to_user_path(Path::new(exe_path));
         }
         let mut path = PathBuf::from(exe_path);
 
@@ -422,7 +418,7 @@ fn resolve_exe<'a>(
             // It's ok to use `set_extension` here because the intent is to
             // remove the extension that was just added.
             path.set_extension("");
-            return path::maybe_verbatim(&path);
+            return args::to_user_path(&path);
         }
     } else {
         ensure_no_nuls(exe_path)?;
@@ -510,7 +506,7 @@ where
 /// Check if a file exists without following symlinks.
 fn program_exists(path: &Path) -> Option<Vec<u16>> {
     unsafe {
-        let path = path::maybe_verbatim(path).ok()?;
+        let path = args::to_user_path(path).ok()?;
         // Getting attributes using `GetFileAttributesW` does not follow symlinks
         // and it will almost always be successful if the link exists.
         // There are some exceptions for special system files (e.g. the pagefile)