Merge from rustc

35 files changed, 324 insertions, 361 deletions

diff --git a/library/std/Cargo.toml b/library/std/Cargo.toml
index 63c65b8ef39..358bd25ff1b 100644
--- a/library/std/Cargo.toml
+++ b/library/std/Cargo.toml
@@ -17,7 +17,7 @@ cfg-if = { version = "1.0", features = ['rustc-dep-of-std'] }
 panic_unwind = { path = "../panic_unwind", optional = true }
 panic_abort = { path = "../panic_abort" }
 core = { path = "../core", public = true }
-compiler_builtins = { version = "0.1.130" }
+compiler_builtins = { version = "0.1.133" }
 profiler_builtins = { path = "../profiler_builtins", optional = true }
 unwind = { path = "../unwind" }
 hashbrown = { version = "0.15", default-features = false, features = [
@@ -39,7 +39,7 @@ miniz_oxide = { version = "0.7.0", optional = true, default-features = false }
 addr2line = { version = "0.22.0", optional = true, default-features = false }
 
 [target.'cfg(not(all(windows, target_env = "msvc")))'.dependencies]
-libc = { version = "0.2.156", default-features = false, features = [
+libc = { version = "0.2.159", default-features = false, features = [
     'rustc-dep-of-std',
 ], public = true }
 
diff --git a/library/std/build.rs b/library/std/build.rs
index 7d37d4e9d7d..032326556bd 100644
--- a/library/std/build.rs
+++ b/library/std/build.rs
@@ -7,6 +7,7 @@ fn main() {
     let target_vendor =
         env::var("CARGO_CFG_TARGET_VENDOR").expect("CARGO_CFG_TARGET_VENDOR was not set");
     let target_env = env::var("CARGO_CFG_TARGET_ENV").expect("CARGO_CFG_TARGET_ENV was not set");
+    let target_abi = env::var("CARGO_CFG_TARGET_ABI").expect("CARGO_CFG_TARGET_ABI was not set");
     let target_pointer_width: u32 = env::var("CARGO_CFG_TARGET_POINTER_WIDTH")
         .expect("CARGO_CFG_TARGET_POINTER_WIDTH was not set")
         .parse()
@@ -101,7 +102,7 @@ fn main() {
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
-        ("x86_64", "windows") if target_env == "gnu" => false,
+        ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
         // Infinite recursion <https://github.com/llvm/llvm-project/issues/97981>
         ("csky", _) => false,
         ("hexagon", _) => false,
@@ -129,7 +130,7 @@ fn main() {
         // ABI unsupported  <https://github.com/llvm/llvm-project/issues/41838>
         ("sparc", _) => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
-        ("x86_64", "windows") if target_env == "gnu" => false,
+        ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
         // 64-bit Linux is about the only platform to have f128 symbols by default
         (_, "linux") if target_pointer_width == 64 => true,
         // Almost all OSs are missing symbol. compiler-builtins will have to add them.
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 124ef121b18..675140ff18f 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -394,7 +394,8 @@ impl File {
     ///
     /// # Errors
     ///
-    /// This function will return an error if `path` does not already exist.
+    /// This function will return an error if `path` does not already exist,
+    /// or if memory allocation fails for the new buffer.
     /// Other errors may also be returned according to [`OpenOptions::open`].
     ///
     /// # Examples
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index dd6458c38c6..8fedcb241d0 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2382,8 +2382,6 @@ pub trait BufRead: Read {
     /// about Ferris from a binary string, skipping the fun fact:
     ///
     /// ```
-    /// #![feature(bufread_skip_until)]
-    ///
     /// use std::io::{self, BufRead};
     ///
     /// let mut cursor = io::Cursor::new(b"Ferris\0Likes long walks on the beach\0Crustacean\0");
@@ -2407,7 +2405,7 @@ pub trait BufRead: Read {
     /// assert_eq!(num_bytes, 11);
     /// assert_eq!(animal, b"Crustacean\0");
     /// ```
-    #[unstable(feature = "bufread_skip_until", issue = "111735")]
+    #[stable(feature = "bufread_skip_until", since = "CURRENT_RUSTC_VERSION")]
     fn skip_until(&mut self, byte: u8) -> Result<usize> {
         skip_until(self, byte)
     }
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index bf242e715bd..35b38ed783f 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -370,7 +370,12 @@ impl Stdin {
     /// Locks this handle and reads a line of input, appending it to the specified buffer.
     ///
     /// For detailed semantics of this method, see the documentation on
-    /// [`BufRead::read_line`].
+    /// [`BufRead::read_line`]. In particular:
+    /// * Previous content of the buffer will be preserved. To avoid appending
+    ///   to the buffer, you need to [`clear`] it first.
+    /// * The trailing newline character, if any, is included in the buffer.
+    ///
+    /// [`clear`]: String::clear
     ///
     /// # Examples
     ///
diff --git a/library/std/src/keyword_docs.rs b/library/std/src/keyword_docs.rs
index 9f4d244b547..453b2708daa 100644
--- a/library/std/src/keyword_docs.rs
+++ b/library/std/src/keyword_docs.rs
@@ -2349,12 +2349,13 @@ mod async_keyword {}
 /// [`async`]: ../std/keyword.async.html
 mod await_keyword {}
 
+// FIXME(dyn_compat_renaming): Update URL and link text.
 #[doc(keyword = "dyn")]
 //
 /// `dyn` is a prefix of a [trait object]'s type.
 ///
 /// The `dyn` keyword is used to highlight that calls to methods on the associated `Trait`
-/// are [dynamically dispatched]. To use the trait this way, it must be 'object safe'.
+/// are [dynamically dispatched]. To use the trait this way, it must be 'dyn-compatible'[^1].
 ///
 /// Unlike generic parameters or `impl Trait`, the compiler does not know the concrete type that
 /// is being passed. That is, the type has been [erased].
@@ -2382,6 +2383,7 @@ mod await_keyword {}
 /// [ref-trait-obj]: ../reference/types/trait-object.html
 /// [ref-obj-safety]: ../reference/items/traits.html#object-safety
 /// [erased]: https://en.wikipedia.org/wiki/Type_erasure
+/// [^1]: Formerly known as 'object safe'.
 mod dyn_keyword {}
 
 #[doc(keyword = "union")]
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 65a9aa66c7c..057a57f7997 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -414,9 +414,6 @@
 // tidy-alphabetical-start
 #![feature(const_collections_with_hasher)]
 #![feature(const_hash)]
-#![feature(const_ip)]
-#![feature(const_ipv4)]
-#![feature(const_ipv6)]
 #![feature(thread_local_internals)]
 // tidy-alphabetical-end
 //
diff --git a/library/std/src/os/wasi/mod.rs b/library/std/src/os/wasi/mod.rs
index 33b50c9e53b..2ee6aa46600 100644
--- a/library/std/src/os/wasi/mod.rs
+++ b/library/std/src/os/wasi/mod.rs
@@ -36,6 +36,8 @@
 pub mod ffi;
 pub mod fs;
 pub mod io;
+
+#[cfg(all(target_os = "wasi", target_env = "p1"))]
 pub mod net;
 
 /// A prelude for conveniently writing platform-specific code.
diff --git a/library/std/src/rt.rs b/library/std/src/rt.rs
index 0a841f07e3b..80e7c3c026b 100644
--- a/library/std/src/rt.rs
+++ b/library/std/src/rt.rs
@@ -102,9 +102,24 @@ unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
         sys::init(argc, argv, sigpipe)
     };
 
-    // Set up the current thread to give it the right name.
-    let thread = Thread::new_main();
-    thread::set_current(thread);
+    // Set up the current thread handle to give it the right name.
+    //
+    // When code running before main uses `ReentrantLock` (for example by
+    // using `println!`), the thread ID can become initialized before we
+    // create this handle. Since `set_current` fails when the ID of the
+    // handle does not match the current ID, we should attempt to use the
+    // current thread ID here instead of unconditionally creating a new
+    // one. Also see #130210.
+    let thread = Thread::new_main(thread::current_id());
+    if let Err(_thread) = thread::set_current(thread) {
+        // `thread::current` will create a new handle if none has been set yet.
+        // Thus, if someone uses it before main, this call will fail. That's a
+        // bad idea though, as we then cannot set the main thread name here.
+        //
+        // FIXME: detect the main thread in `thread::current` and use the
+        //        correct name there.
+        rtabort!("code running before main must not use thread::current");
+    }
 }
 
 /// Clean up the thread-local runtime state. This *should* be run after all other
diff --git a/library/std/src/sys/pal/sgx/net.rs b/library/std/src/sys/pal/sgx/net.rs
index 44913ffe3a9..c966886d163 100644
--- a/library/std/src/sys/pal/sgx/net.rs
+++ b/library/std/src/sys/pal/sgx/net.rs
@@ -78,9 +78,8 @@ fn io_err_to_addr(result: io::Result<&SocketAddr>) -> io::Result<String> {
     }
 }
 
-fn addr_to_sockaddr(addr: &Option<String>) -> io::Result<SocketAddr> {
-    addr.as_ref()
-        .ok_or(io::ErrorKind::AddrNotAvailable)?
+fn addr_to_sockaddr(addr: Option<&str>) -> io::Result<SocketAddr> {
+    addr.ok_or(io::ErrorKind::AddrNotAvailable)?
         .to_socket_addrs()
         // unwrap OK: if an iterator is returned, we're guaranteed to get exactly one entry
         .map(|mut it| it.next().unwrap())
@@ -161,11 +160,11 @@ impl TcpStream {
     }
 
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-        addr_to_sockaddr(&self.peer_addr)
+        addr_to_sockaddr(self.peer_addr.as_deref())
     }
 
     pub fn socket_addr(&self) -> io::Result<SocketAddr> {
-        addr_to_sockaddr(&self.inner.local_addr)
+        addr_to_sockaddr(self.inner.local_addr.as_deref())
     }
 
     pub fn shutdown(&self, _: Shutdown) -> io::Result<()> {
@@ -255,13 +254,14 @@ impl TcpListener {
     }
 
     pub fn socket_addr(&self) -> io::Result<SocketAddr> {
-        addr_to_sockaddr(&self.inner.local_addr)
+        addr_to_sockaddr(self.inner.local_addr.as_deref())
     }
 
     pub fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
         let (fd, local_addr, peer_addr) = usercalls::accept_stream(self.inner.inner.raw())?;
         let peer_addr = Some(peer_addr);
-        let ret_peer = addr_to_sockaddr(&peer_addr).unwrap_or_else(|_| ([0; 4], 0).into());
+        let ret_peer =
+            addr_to_sockaddr(peer_addr.as_deref()).unwrap_or_else(|_| ([0; 4], 0).into());
         Ok((TcpStream { inner: Socket::new(fd, local_addr), peer_addr }, ret_peer))
     }
 
diff --git a/library/std/src/sys/pal/unix/fs.rs b/library/std/src/sys/pal/unix/fs.rs
index 39aabf0b2d6..567577b2b4d 100644
--- a/library/std/src/sys/pal/unix/fs.rs
+++ b/library/std/src/sys/pal/unix/fs.rs
@@ -899,7 +899,7 @@ impl DirEntry {
             target_os = "android",
             target_os = "hurd"
         ),
-        not(miri)
+        not(miri) // no dirfd on Miri
     ))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
         let fd = cvt(unsafe { dirfd(self.dir.dirp.0) })?;
@@ -1538,7 +1538,7 @@ impl fmt::Debug for File {
             Some(PathBuf::from(OsString::from_vec(buf)))
         }
 
-        #[cfg(all(target_os = "freebsd", target_arch = "x86_64"))]
+        #[cfg(target_os = "freebsd")]
         fn get_path(fd: c_int) -> Option<PathBuf> {
             let info = Box::<libc::kinfo_file>::new_zeroed();
             let mut info = unsafe { info.assume_init() };
@@ -1566,7 +1566,7 @@ impl fmt::Debug for File {
         #[cfg(not(any(
             target_os = "linux",
             target_os = "vxworks",
-            all(target_os = "freebsd", target_arch = "x86_64"),
+            target_os = "freebsd",
             target_os = "netbsd",
             target_os = "illumos",
             target_os = "solaris",
diff --git a/library/std/src/sys/pal/unix/process/process_common.rs b/library/std/src/sys/pal/unix/process/process_common.rs
index d9c41d43487..13290fed762 100644
--- a/library/std/src/sys/pal/unix/process/process_common.rs
+++ b/library/std/src/sys/pal/unix/process/process_common.rs
@@ -312,8 +312,8 @@ impl Command {
     }
 
     #[allow(dead_code)]
-    pub fn get_cwd(&self) -> &Option<CString> {
-        &self.cwd
+    pub fn get_cwd(&self) -> Option<&CStr> {
+        self.cwd.as_deref()
     }
     #[allow(dead_code)]
     pub fn get_uid(&self) -> Option<uid_t> {
diff --git a/library/std/src/sys/pal/unix/process/process_unix.rs b/library/std/src/sys/pal/unix/process/process_unix.rs
index 5d30f388da1..4551d49e841 100644
--- a/library/std/src/sys/pal/unix/process/process_unix.rs
+++ b/library/std/src/sys/pal/unix/process/process_unix.rs
@@ -335,7 +335,7 @@ impl Command {
                 cvt(libc::setuid(u as uid_t))?;
             }
         }
-        if let Some(ref cwd) = *self.get_cwd() {
+        if let Some(cwd) = self.get_cwd() {
             cvt(libc::chdir(cwd.as_ptr()))?;
         }
 
diff --git a/library/std/src/sys/pal/unix/process/process_vxworks.rs b/library/std/src/sys/pal/unix/process/process_vxworks.rs
index 2d9a304c495..38daf6af918 100644
--- a/library/std/src/sys/pal/unix/process/process_vxworks.rs
+++ b/library/std/src/sys/pal/unix/process/process_vxworks.rs
@@ -57,7 +57,7 @@ impl Command {
                 t!(cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO)));
             }
 
-            if let Some(ref cwd) = *self.get_cwd() {
+            if let Some(cwd) = self.get_cwd() {
                 t!(cvt(libc::chdir(cwd.as_ptr())));
             }
 
diff --git a/library/std/src/sys/pal/unix/thread.rs b/library/std/src/sys/pal/unix/thread.rs
index 2f2d6e6add3..04024661836 100644
--- a/library/std/src/sys/pal/unix/thread.rs
+++ b/library/std/src/sys/pal/unix/thread.rs
@@ -117,13 +117,15 @@ impl Thread {
     pub fn set_name(name: &CStr) {
         const PR_SET_NAME: libc::c_int = 15;
         unsafe {
-            libc::prctl(
+            let res = libc::prctl(
                 PR_SET_NAME,
                 name.as_ptr(),
                 0 as libc::c_ulong,
                 0 as libc::c_ulong,
                 0 as libc::c_ulong,
             );
+            // We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
+            debug_assert_eq!(res, 0);
         }
     }
 
diff --git a/library/std/src/sys/pal/wasip2/net.rs b/library/std/src/sys/pal/wasip2/net.rs
index c40eb229ba9..06e623df843 100644
--- a/library/std/src/sys/pal/wasip2/net.rs
+++ b/library/std/src/sys/pal/wasip2/net.rs
@@ -2,13 +2,12 @@
 
 use libc::{c_int, c_void, size_t};
 
-use super::fd::WasiFd;
 use crate::ffi::CStr;
 use crate::io::{self, BorrowedBuf, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::net::{Shutdown, SocketAddr};
-use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
+use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use crate::sys::unsupported;
-use crate::sys_common::net::{TcpListener, getsockopt, setsockopt, sockaddr_to_addr};
+use crate::sys_common::net::{getsockopt, setsockopt, sockaddr_to_addr};
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 use crate::time::{Duration, Instant};
 use crate::{cmp, mem, str};
@@ -71,7 +70,9 @@ pub fn cvt_gai(err: c_int) -> io::Result<()> {
 
 pub fn init() {}
 
-pub struct Socket(WasiFd);
+pub struct WasiSocket(OwnedFd);
+
+pub struct Socket(WasiSocket);
 
 impl Socket {
     pub fn new(addr: &SocketAddr, ty: c_int) -> io::Result<Socket> {
@@ -327,53 +328,90 @@ impl Socket {
     }
 }
 
-impl AsInner<WasiFd> for Socket {
+impl AsInner<OwnedFd> for WasiSocket {
     #[inline]
-    fn as_inner(&self) -> &WasiFd {
+    fn as_inner(&self) -> &OwnedFd {
         &self.0
     }
 }
 
-impl IntoInner<WasiFd> for Socket {
-    fn into_inner(self) -> WasiFd {
+impl IntoInner<OwnedFd> for WasiSocket {
+    fn into_inner(self) -> OwnedFd {
         self.0
     }
 }
 
-impl FromInner<WasiFd> for Socket {
-    fn from_inner(inner: WasiFd) -> Socket {
-        Socket(inner)
+impl FromInner<OwnedFd> for WasiSocket {
+    fn from_inner(owned_fd: OwnedFd) -> Self {
+        Self(owned_fd)
     }
 }
 
-impl AsFd for Socket {
+impl AsFd for WasiSocket {
     fn as_fd(&self) -> BorrowedFd<'_> {
         self.0.as_fd()
     }
 }
 
-impl AsRawFd for Socket {
+impl AsRawFd for WasiSocket {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
         self.0.as_raw_fd()
     }
 }
 
-impl IntoRawFd for Socket {
+impl IntoRawFd for WasiSocket {
     fn into_raw_fd(self) -> RawFd {
         self.0.into_raw_fd()
     }
 }
 
-impl FromRawFd for Socket {
+impl FromRawFd for WasiSocket {
     unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
         unsafe { Self(FromRawFd::from_raw_fd(raw_fd)) }
     }
 }
 
-impl AsInner<Socket> for TcpListener {
+impl AsInner<WasiSocket> for Socket {
+    #[inline]
+    fn as_inner(&self) -> &WasiSocket {
+        &self.0
+    }
+}
+
+impl IntoInner<WasiSocket> for Socket {
+    fn into_inner(self) -> WasiSocket {
+        self.0
+    }
+}
+
+impl FromInner<WasiSocket> for Socket {
+    fn from_inner(sock: WasiSocket) -> Socket {
+        Socket(sock)
+    }
+}
+
+impl AsFd for Socket {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        self.0.as_fd()
+    }
+}
+
+impl AsRawFd for Socket {
     #[inline]
-    fn as_inner(&self) -> &Socket {
-        &self.socket()
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl IntoRawFd for Socket {
+    fn into_raw_fd(self) -> RawFd {
+        self.0.into_raw_fd()
+    }
+}
+
+impl FromRawFd for Socket {
+    unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
+        unsafe { Self(FromRawFd::from_raw_fd(raw_fd)) }
     }
 }
diff --git a/library/std/src/sys/pal/windows/c.rs b/library/std/src/sys/pal/windows/c.rs
index b65ad7dbe8c..9ce3e912caf 100644
--- a/library/std/src/sys/pal/windows/c.rs
+++ b/library/std/src/sys/pal/windows/c.rs
@@ -175,9 +175,9 @@ extern "system" {
     pub fn WakeByAddressAll(address: *const c_void);
 }
 
+// These are loaded by `load_synch_functions`.
 #[cfg(target_vendor = "win7")]
 compat_fn_optional! {
-    crate::sys::compat::load_synch_functions();
     pub fn WaitOnAddress(
         address: *const c_void,
         compareaddress: *const c_void,
diff --git a/library/std/src/sys/pal/windows/compat.rs b/library/std/src/sys/pal/windows/compat.rs
index c8e25dd0c94..42999da1664 100644
--- a/library/std/src/sys/pal/windows/compat.rs
+++ b/library/std/src/sys/pal/windows/compat.rs
@@ -198,11 +198,10 @@ macro_rules! compat_fn_with_fallback {
 
 /// Optionally loaded functions.
 ///
-/// Actual loading of the function defers to $load_functions.
+/// Relies on the functions being pre-loaded elsewhere.
 #[cfg(target_vendor = "win7")]
 macro_rules! compat_fn_optional {
-    ($load_functions:expr;
-    $(
+    ($(
         $(#[$meta:meta])*
         $vis:vis fn $symbol:ident($($argname:ident: $argtype:ty),*) $(-> $rettype:ty)?;
     )+) => (
@@ -221,9 +220,6 @@ macro_rules! compat_fn_optional {
 
                 #[inline(always)]
                 pub fn option() -> Option<F> {
-                    // Miri does not understand the way we do preloading
-                    // therefore load the function here instead.
-                    #[cfg(miri)] $load_functions;
                     NonNull::new(PTR.load(Ordering::Relaxed)).map(|f| unsafe { mem::transmute(f) })
                 }
             }
diff --git a/library/std/src/sys/pal/windows/mod.rs b/library/std/src/sys/pal/windows/mod.rs
index 1ea253e5e52..a9886012e8e 100644
--- a/library/std/src/sys/pal/windows/mod.rs
+++ b/library/std/src/sys/pal/windows/mod.rs
@@ -346,7 +346,6 @@ pub fn abort_internal() -> ! {
     }
 }
 
-// miri is sensitive to changes here so check that miri is happy if touching this
 #[cfg(miri)]
 pub fn abort_internal() -> ! {
     crate::intrinsics::abort();
diff --git a/library/std/src/sys/sync/condvar/mod.rs b/library/std/src/sys/sync/condvar/mod.rs
index 6849cacf88e..d0c998a5597 100644
--- a/library/std/src/sys/sync/condvar/mod.rs
+++ b/library/std/src/sys/sync/condvar/mod.rs
@@ -12,7 +12,10 @@ cfg_if::cfg_if! {
     ))] {
         mod futex;
         pub use futex::Condvar;
-    } else if #[cfg(target_family = "unix")] {
+    } else if #[cfg(any(
+        target_family = "unix",
+        target_os = "teeos",
+    ))] {
         mod pthread;
         pub use pthread::Condvar;
     } else if #[cfg(all(target_os = "windows", target_vendor = "win7"))] {
@@ -24,9 +27,6 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "solid_asp3")] {
         mod itron;
         pub use itron::Condvar;
-    } else if #[cfg(target_os = "teeos")] {
-        mod teeos;
-        pub use teeos::Condvar;
     } else if #[cfg(target_os = "xous")] {
         mod xous;
         pub use xous::Condvar;
diff --git a/library/std/src/sys/sync/condvar/pthread.rs b/library/std/src/sys/sync/condvar/pthread.rs
index 5b5e7770b06..986cd0cb7d1 100644
--- a/library/std/src/sys/sync/condvar/pthread.rs
+++ b/library/std/src/sys/sync/condvar/pthread.rs
@@ -2,31 +2,25 @@ use crate::cell::UnsafeCell;
 use crate::ptr;
 use crate::sync::atomic::AtomicPtr;
 use crate::sync::atomic::Ordering::Relaxed;
-use crate::sys::sync::{Mutex, mutex};
+use crate::sys::sync::{Mutex, OnceBox};
 #[cfg(not(target_os = "nto"))]
 use crate::sys::time::TIMESPEC_MAX;
 #[cfg(target_os = "nto")]
 use crate::sys::time::TIMESPEC_MAX_CAPPED;
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
 use crate::time::Duration;
 
 struct AllocatedCondvar(UnsafeCell<libc::pthread_cond_t>);
 
 pub struct Condvar {
-    inner: LazyBox<AllocatedCondvar>,
+    inner: OnceBox<AllocatedCondvar>,
     mutex: AtomicPtr<libc::pthread_mutex_t>,
 }
 
-#[inline]
-fn raw(c: &Condvar) -> *mut libc::pthread_cond_t {
-    c.inner.0.get()
-}
-
 unsafe impl Send for AllocatedCondvar {}
 unsafe impl Sync for AllocatedCondvar {}
 
-impl LazyInit for AllocatedCondvar {
-    fn init() -> Box<Self> {
+impl AllocatedCondvar {
+    fn new() -> Box<Self> {
         let condvar = Box::new(AllocatedCondvar(UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER)));
 
         cfg_if::cfg_if! {
@@ -37,7 +31,7 @@ impl LazyInit for AllocatedCondvar {
                 target_vendor = "apple",
             ))] {
                 // `pthread_condattr_setclock` is unfortunately not supported on these platforms.
-            } else if #[cfg(any(target_os = "espidf", target_os = "horizon"))] {
+            } else if #[cfg(any(target_os = "espidf", target_os = "horizon", target_os = "teeos"))] {
                 // NOTE: ESP-IDF's PTHREAD_COND_INITIALIZER support is not released yet
                 // So on that platform, init() should always be called
                 // Moreover, that platform does not have pthread_condattr_setclock support,
@@ -82,7 +76,11 @@ impl Drop for AllocatedCondvar {
 
 impl Condvar {
     pub const fn new() -> Condvar {
-        Condvar { inner: LazyBox::new(), mutex: AtomicPtr::new(ptr::null_mut()) }
+        Condvar { inner: OnceBox::new(), mutex: AtomicPtr::new(ptr::null_mut()) }
+    }
+
+    fn get(&self) -> *mut libc::pthread_cond_t {
+        self.inner.get_or_init(AllocatedCondvar::new).0.get()
     }
 
     #[inline]
@@ -98,21 +96,21 @@ impl Condvar {
 
     #[inline]
     pub fn notify_one(&self) {
-        let r = unsafe { libc::pthread_cond_signal(raw(self)) };
+        let r = unsafe { libc::pthread_cond_signal(self.get()) };
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
     pub fn notify_all(&self) {
-        let r = unsafe { libc::pthread_cond_broadcast(raw(self)) };
+        let r = unsafe { libc::pthread_cond_broadcast(self.get()) };
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
     pub unsafe fn wait(&self, mutex: &Mutex) {
-        let mutex = mutex::raw(mutex);
+        let mutex = mutex.get_assert_locked();
         self.verify(mutex);
-        let r = libc::pthread_cond_wait(raw(self), mutex);
+        let r = libc::pthread_cond_wait(self.get(), mutex);
         debug_assert_eq!(r, 0);
     }
 
@@ -129,7 +127,7 @@ impl Condvar {
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
         use crate::sys::time::Timespec;
 
-        let mutex = mutex::raw(mutex);
+        let mutex = mutex.get_assert_locked();
         self.verify(mutex);
 
         #[cfg(not(target_os = "nto"))]
@@ -144,7 +142,7 @@ impl Condvar {
             .and_then(|t| t.to_timespec_capped())
             .unwrap_or(TIMESPEC_MAX_CAPPED);
 
-        let r = libc::pthread_cond_timedwait(raw(self), mutex, &timeout);
+        let r = libc::pthread_cond_timedwait(self.get(), mutex, &timeout);
         assert!(r == libc::ETIMEDOUT || r == 0);
         r == 0
     }
@@ -162,7 +160,7 @@ impl Condvar {
         use crate::sys::time::SystemTime;
         use crate::time::Instant;
 
-        let mutex = mutex::raw(mutex);
+        let mutex = mutex.get_assert_locked();
         self.verify(mutex);
 
         // OSX implementation of `pthread_cond_timedwait` is buggy
@@ -188,7 +186,7 @@ impl Condvar {
             .and_then(|t| t.to_timespec())
             .unwrap_or(TIMESPEC_MAX);
 
-        let r = libc::pthread_cond_timedwait(raw(self), mutex, &timeout);
+        let r = libc::pthread_cond_timedwait(self.get(), mutex, &timeout);
         debug_assert!(r == libc::ETIMEDOUT || r == 0);
 
         // ETIMEDOUT is not a totally reliable method of determining timeout due
diff --git a/library/std/src/sys/sync/condvar/sgx.rs b/library/std/src/sys/sync/condvar/sgx.rs
index ecb5872f60d..e60715e4b59 100644
--- a/library/std/src/sys/sync/condvar/sgx.rs
+++ b/library/std/src/sys/sync/condvar/sgx.rs
@@ -1,44 +1,39 @@
 use crate::sys::pal::waitqueue::{SpinMutex, WaitQueue, WaitVariable};
-use crate::sys::sync::Mutex;
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
+use crate::sys::sync::{Mutex, OnceBox};
 use crate::time::Duration;
 
-/// FIXME: `UnsafeList` is not movable.
-struct AllocatedCondvar(SpinMutex<WaitVariable<()>>);
-
 pub struct Condvar {
-    inner: LazyBox<AllocatedCondvar>,
-}
-
-impl LazyInit for AllocatedCondvar {
-    fn init() -> Box<Self> {
-        Box::new(AllocatedCondvar(SpinMutex::new(WaitVariable::new(()))))
-    }
+    // FIXME: `UnsafeList` is not movable.
+    inner: OnceBox<SpinMutex<WaitVariable<()>>>,
 }
 
 impl Condvar {
     pub const fn new() -> Condvar {
-        Condvar { inner: LazyBox::new() }
+        Condvar { inner: OnceBox::new() }
+    }
+
+    fn get(&self) -> &SpinMutex<WaitVariable<()>> {
+        self.inner.get_or_init(|| Box::new(SpinMutex::new(WaitVariable::new(()))))
     }
 
     #[inline]
     pub fn notify_one(&self) {
-        let _ = WaitQueue::notify_one(self.inner.0.lock());
+        let _ = WaitQueue::notify_one(self.get().lock());
     }
 
     #[inline]
     pub fn notify_all(&self) {
-        let _ = WaitQueue::notify_all(self.inner.0.lock());
+        let _ = WaitQueue::notify_all(self.get().lock());
     }
 
     pub unsafe fn wait(&self, mutex: &Mutex) {
-        let guard = self.inner.0.lock();
+        let guard = self.get().lock();
         WaitQueue::wait(guard, || unsafe { mutex.unlock() });
         mutex.lock()
     }
 
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
-        let success = WaitQueue::wait_timeout(&self.inner.0, dur, || unsafe { mutex.unlock() });
+        let success = WaitQueue::wait_timeout(self.get(), dur, || unsafe { mutex.unlock() });
         mutex.lock();
         success
     }
diff --git a/library/std/src/sys/sync/condvar/teeos.rs b/library/std/src/sys/sync/condvar/teeos.rs
deleted file mode 100644
index 943867cd761..00000000000
--- a/library/std/src/sys/sync/condvar/teeos.rs
+++ /dev/null
@@ -1,101 +0,0 @@
-use crate::cell::UnsafeCell;
-use crate::ptr;
-use crate::sync::atomic::AtomicPtr;
-use crate::sync::atomic::Ordering::Relaxed;
-use crate::sys::sync::mutex::{self, Mutex};
-use crate::sys::time::TIMESPEC_MAX;
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
-use crate::time::Duration;
-
-extern "C" {
-    pub fn pthread_cond_timedwait(
-        cond: *mut libc::pthread_cond_t,
-        lock: *mut libc::pthread_mutex_t,
-        adstime: *const libc::timespec,
-    ) -> libc::c_int;
-}
-
-struct AllocatedCondvar(UnsafeCell<libc::pthread_cond_t>);
-
-pub struct Condvar {
-    inner: LazyBox<AllocatedCondvar>,
-    mutex: AtomicPtr<libc::pthread_mutex_t>,
-}
-
-#[inline]
-fn raw(c: &Condvar) -> *mut libc::pthread_cond_t {
-    c.inner.0.get()
-}
-
-unsafe impl Send for AllocatedCondvar {}
-unsafe impl Sync for AllocatedCondvar {}
-
-impl LazyInit for AllocatedCondvar {
-    fn init() -> Box<Self> {
-        let condvar = Box::new(AllocatedCondvar(UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER)));
-
-        let r = unsafe { libc::pthread_cond_init(condvar.0.get(), crate::ptr::null()) };
-        assert_eq!(r, 0);
-
-        condvar
-    }
-}
-
-impl Drop for AllocatedCondvar {
-    #[inline]
-    fn drop(&mut self) {
-        let r = unsafe { libc::pthread_cond_destroy(self.0.get()) };
-        debug_assert_eq!(r, 0);
-    }
-}
-
-impl Condvar {
-    pub const fn new() -> Condvar {
-        Condvar { inner: LazyBox::new(), mutex: AtomicPtr::new(ptr::null_mut()) }
-    }
-
-    #[inline]
-    fn verify(&self, mutex: *mut libc::pthread_mutex_t) {
-        match self.mutex.compare_exchange(ptr::null_mut(), mutex, Relaxed, Relaxed) {
-            Ok(_) => {}                // Stored the address
-            Err(n) if n == mutex => {} // Lost a race to store the same address
-            _ => panic!("attempted to use a condition variable with two mutexes"),
-        }
-    }
-
-    #[inline]
-    pub fn notify_one(&self) {
-        let r = unsafe { libc::pthread_cond_signal(raw(self)) };
-        debug_assert_eq!(r, 0);
-    }
-
-    #[inline]
-    pub fn notify_all(&self) {
-        let r = unsafe { libc::pthread_cond_broadcast(raw(self)) };
-        debug_assert_eq!(r, 0);
-    }
-
-    #[inline]
-    pub unsafe fn wait(&self, mutex: &Mutex) {
-        let mutex = unsafe { mutex::raw(mutex) };
-        self.verify(mutex);
-        let r = unsafe { libc::pthread_cond_wait(raw(self), mutex) };
-        debug_assert_eq!(r, 0);
-    }
-
-    pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
-        use crate::sys::time::Timespec;
-
-        let mutex = unsafe { mutex::raw(mutex) };
-        self.verify(mutex);
-
-        let timeout = Timespec::now(libc::CLOCK_MONOTONIC)
-            .checked_add_duration(&dur)
-            .and_then(|t| t.to_timespec())
-            .unwrap_or(TIMESPEC_MAX);
-
-        let r = unsafe { pthread_cond_timedwait(raw(self), mutex, &timeout) };
-        assert!(r == libc::ETIMEDOUT || r == 0);
-        r == 0
-    }
-}
diff --git a/library/std/src/sys/sync/mod.rs b/library/std/src/sys/sync/mod.rs
index 52fac5902a2..0691e967851 100644
--- a/library/std/src/sys/sync/mod.rs
+++ b/library/std/src/sys/sync/mod.rs
@@ -1,11 +1,14 @@
 mod condvar;
 mod mutex;
 mod once;
+mod once_box;
 mod rwlock;
 mod thread_parking;
 
 pub use condvar::Condvar;
 pub use mutex::Mutex;
 pub use once::{Once, OnceState};
+#[allow(unused)] // Only used on some platforms.
+use once_box::OnceBox;
 pub use rwlock::RwLock;
 pub use thread_parking::Parker;
diff --git a/library/std/src/sys/sync/mutex/mod.rs b/library/std/src/sys/sync/mutex/mod.rs
index 73d9bd273de..360df3fc4b5 100644
--- a/library/std/src/sys/sync/mutex/mod.rs
+++ b/library/std/src/sys/sync/mutex/mod.rs
@@ -19,7 +19,7 @@ cfg_if::cfg_if! {
         target_os = "teeos",
     ))] {
         mod pthread;
-        pub use pthread::{Mutex, raw};
+        pub use pthread::Mutex;
     } else if #[cfg(all(target_os = "windows", target_vendor = "win7"))] {
         mod windows7;
         pub use windows7::{Mutex, raw};
diff --git a/library/std/src/sys/sync/mutex/pthread.rs b/library/std/src/sys/sync/mutex/pthread.rs
index 1c407bc2537..87c95f45f96 100644
--- a/library/std/src/sys/sync/mutex/pthread.rs
+++ b/library/std/src/sys/sync/mutex/pthread.rs
@@ -2,24 +2,19 @@ use crate::cell::UnsafeCell;
 use crate::io::Error;
 use crate::mem::{MaybeUninit, forget};
 use crate::sys::cvt_nz;
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
+use crate::sys::sync::OnceBox;
 
 struct AllocatedMutex(UnsafeCell<libc::pthread_mutex_t>);
 
 pub struct Mutex {
-    inner: LazyBox<AllocatedMutex>,
-}
-
-#[inline]
-pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
-    m.inner.0.get()
+    inner: OnceBox<AllocatedMutex>,
 }
 
 unsafe impl Send for AllocatedMutex {}
 unsafe impl Sync for AllocatedMutex {}
 
-impl LazyInit for AllocatedMutex {
-    fn init() -> Box<Self> {
+impl AllocatedMutex {
+    fn new() -> Box<Self> {
         let mutex = Box::new(AllocatedMutex(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER)));
 
         // Issue #33770
@@ -60,24 +55,6 @@ impl LazyInit for AllocatedMutex {
 
         mutex
     }
-
-    fn destroy(mutex: Box<Self>) {
-        // We're not allowed to pthread_mutex_destroy a locked mutex,
-        // so check first if it's unlocked.
-        if unsafe { libc::pthread_mutex_trylock(mutex.0.get()) == 0 } {
-            unsafe { libc::pthread_mutex_unlock(mutex.0.get()) };
-            drop(mutex);
-        } else {
-            // The mutex is locked. This happens if a MutexGuard is leaked.
-            // In this case, we just leak the Mutex too.
-            forget(mutex);
-        }
-    }
-
-    fn cancel_init(_: Box<Self>) {
-        // In this case, we can just drop it without any checks,
-        // since it cannot have been locked yet.
-    }
 }
 
 impl Drop for AllocatedMutex {
@@ -99,11 +76,33 @@ impl Drop for AllocatedMutex {
 impl Mutex {
     #[inline]
     pub const fn new() -> Mutex {
-        Mutex { inner: LazyBox::new() }
+        Mutex { inner: OnceBox::new() }
+    }
+
+    /// Gets access to the pthread mutex under the assumption that the mutex is
+    /// locked.
+    ///
+    /// This allows skipping the initialization check, as the mutex can only be
+    /// locked if it is already initialized, and allows relaxing the ordering
+    /// on the pointer load, since the allocation cannot have been modified
+    /// since the `lock` and the lock must have occurred on the current thread.
+    ///
+    /// # Safety
+    /// Causes undefined behaviour if the mutex is not locked.
+    #[inline]
+    pub(crate) unsafe fn get_assert_locked(&self) -> *mut libc::pthread_mutex_t {
+        unsafe { self.inner.get_unchecked().0.get() }
     }
 
     #[inline]
-    pub unsafe fn lock(&self) {
+    fn get(&self) -> *mut libc::pthread_mutex_t {
+        // If initialization fails, the mutex is destroyed. This is always sound,
+        // however, as the mutex cannot have been locked yet.
+        self.inner.get_or_init(AllocatedMutex::new).0.get()
+    }
+
+    #[inline]
+    pub fn lock(&self) {
         #[cold]
         #[inline(never)]
         fn fail(r: i32) -> ! {
@@ -111,7 +110,7 @@ impl Mutex {
             panic!("failed to lock mutex: {error}");
         }
 
-        let r = libc::pthread_mutex_lock(raw(self));
+        let r = unsafe { libc::pthread_mutex_lock(self.get()) };
         // As we set the mutex type to `PTHREAD_MUTEX_NORMAL` above, we expect
         // the lock call to never fail. Unfortunately however, some platforms
         // (Solaris) do not conform to the standard, and instead always provide
@@ -126,13 +125,29 @@ impl Mutex {
 
     #[inline]
     pub unsafe fn unlock(&self) {
-        let r = libc::pthread_mutex_unlock(raw(self));
+        let r = libc::pthread_mutex_unlock(self.get_assert_locked());
         debug_assert_eq!(r, 0);
     }
 
     #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        libc::pthread_mutex_trylock(raw(self)) == 0
+    pub fn try_lock(&self) -> bool {
+        unsafe { libc::pthread_mutex_trylock(self.get()) == 0 }
+    }
+}
+
+impl Drop for Mutex {
+    fn drop(&mut self) {
+        let Some(mutex) = self.inner.take() else { return };
+        // We're not allowed to pthread_mutex_destroy a locked mutex,
+        // so check first if it's unlocked.
+        if unsafe { libc::pthread_mutex_trylock(mutex.0.get()) == 0 } {
+            unsafe { libc::pthread_mutex_unlock(mutex.0.get()) };
+            drop(mutex);
+        } else {
+            // The mutex is locked. This happens if a MutexGuard is leaked.
+            // In this case, we just leak the Mutex too.
+            forget(mutex);
+        }
     }
 }
 
diff --git a/library/std/src/sys/sync/mutex/sgx.rs b/library/std/src/sys/sync/mutex/sgx.rs
index 65d1e880f7b..8529e857970 100644
--- a/library/std/src/sys/sync/mutex/sgx.rs
+++ b/library/std/src/sys/sync/mutex/sgx.rs
@@ -1,28 +1,24 @@
 use crate::sys::pal::waitqueue::{SpinMutex, WaitQueue, WaitVariable, try_lock_or_false};
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
-
-/// FIXME: `UnsafeList` is not movable.
-struct AllocatedMutex(SpinMutex<WaitVariable<bool>>);
+use crate::sys::sync::OnceBox;
 
 pub struct Mutex {
-    inner: LazyBox<AllocatedMutex>,
-}
-
-impl LazyInit for AllocatedMutex {
-    fn init() -> Box<Self> {
-        Box::new(AllocatedMutex(SpinMutex::new(WaitVariable::new(false))))
-    }
+    // FIXME: `UnsafeList` is not movable.
+    inner: OnceBox<SpinMutex<WaitVariable<bool>>>,
 }
 
 // Implementation according to “Operating Systems: Three Easy Pieces”, chapter 28
 impl Mutex {
     pub const fn new() -> Mutex {
-        Mutex { inner: LazyBox::new() }
+        Mutex { inner: OnceBox::new() }
+    }
+
+    fn get(&self) -> &SpinMutex<WaitVariable<bool>> {
+        self.inner.get_or_init(|| Box::new(SpinMutex::new(WaitVariable::new(false))))
     }
 
     #[inline]
     pub fn lock(&self) {
-        let mut guard = self.inner.0.lock();
+        let mut guard = self.get().lock();
         if *guard.lock_var() {
             // Another thread has the lock, wait
             WaitQueue::wait(guard, || {})
@@ -35,7 +31,9 @@ impl Mutex {
 
     #[inline]
     pub unsafe fn unlock(&self) {
-        let guard = self.inner.0.lock();
+        // SAFETY: the mutex was locked by the current thread, so it has been
+        // initialized already.
+        let guard = unsafe { self.inner.get_unchecked().lock() };
         if let Err(mut guard) = WaitQueue::notify_one(guard) {
             // No other waiters, unlock
             *guard.lock_var_mut() = false;
@@ -46,7 +44,7 @@ impl Mutex {
 
     #[inline]
     pub fn try_lock(&self) -> bool {
-        let mut guard = try_lock_or_false!(self.inner.0);
+        let mut guard = try_lock_or_false!(self.get());
         if *guard.lock_var() {
             // Another thread has the lock
             false
diff --git a/library/std/src/sys/sync/once_box.rs b/library/std/src/sys/sync/once_box.rs
new file mode 100644
index 00000000000..1422b5a1721
--- /dev/null
+++ b/library/std/src/sys/sync/once_box.rs
@@ -0,0 +1,82 @@
+//! A racily-initialized alternative to `OnceLock<Box<T>>`.
+//!
+//! This is used to implement synchronization primitives that need allocation,
+//! like the pthread versions.
+
+#![allow(dead_code)] // Only used on some platforms.
+
+use crate::mem::replace;
+use crate::ptr::null_mut;
+use crate::sync::atomic::AtomicPtr;
+use crate::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed};
+
+pub(crate) struct OnceBox<T> {
+    ptr: AtomicPtr<T>,
+}
+
+impl<T> OnceBox<T> {
+    #[inline]
+    pub const fn new() -> Self {
+        Self { ptr: AtomicPtr::new(null_mut()) }
+    }
+
+    /// Gets access to the value, assuming it is already initialized and this
+    /// initialization has been observed by the current thread.
+    ///
+    /// Since all modifications to the pointer have already been observed, the
+    /// pointer load in this function can be performed with relaxed ordering,
+    /// potentially allowing the optimizer to turn code like this:
+    /// ```rust, ignore
+    /// once_box.get_or_init(|| Box::new(42));
+    /// unsafe { once_box.get_unchecked() }
+    /// ```
+    /// into
+    /// ```rust, ignore
+    /// once_box.get_or_init(|| Box::new(42))
+    /// ```
+    ///
+    /// # Safety
+    /// This causes undefined behaviour if the assumption above is violated.
+    #[inline]
+    pub unsafe fn get_unchecked(&self) -> &T {
+        unsafe { &*self.ptr.load(Relaxed) }
+    }
+
+    #[inline]
+    pub fn get_or_init(&self, f: impl FnOnce() -> Box<T>) -> &T {
+        let ptr = self.ptr.load(Acquire);
+        match unsafe { ptr.as_ref() } {
+            Some(val) => val,
+            None => self.initialize(f),
+        }
+    }
+
+    #[inline]
+    pub fn take(&mut self) -> Option<Box<T>> {
+        let ptr = replace(self.ptr.get_mut(), null_mut());
+        if !ptr.is_null() { Some(unsafe { Box::from_raw(ptr) }) } else { None }
+    }
+
+    #[cold]
+    fn initialize(&self, f: impl FnOnce() -> Box<T>) -> &T {
+        let new_ptr = Box::into_raw(f());
+        match self.ptr.compare_exchange(null_mut(), new_ptr, AcqRel, Acquire) {
+            Ok(_) => unsafe { &*new_ptr },
+            Err(ptr) => {
+                // Lost the race to another thread.
+                // Drop the value we created, and use the one from the other thread instead.
+                drop(unsafe { Box::from_raw(new_ptr) });
+                unsafe { &*ptr }
+            }
+        }
+    }
+}
+
+unsafe impl<T: Send> Send for OnceBox<T> {}
+unsafe impl<T: Send + Sync> Sync for OnceBox<T> {}
+
+impl<T> Drop for OnceBox<T> {
+    fn drop(&mut self) {
+        self.take();
+    }
+}
diff --git a/library/std/src/sys/sync/rwlock/teeos.rs b/library/std/src/sys/sync/rwlock/teeos.rs
index ef9b1ab5154..76343022383 100644
--- a/library/std/src/sys/sync/rwlock/teeos.rs
+++ b/library/std/src/sys/sync/rwlock/teeos.rs
@@ -14,22 +14,22 @@ impl RwLock {
 
     #[inline]
     pub fn read(&self) {
-        unsafe { self.inner.lock() };
+        self.inner.lock()
     }
 
     #[inline]
     pub fn try_read(&self) -> bool {
-        unsafe { self.inner.try_lock() }
+        self.inner.try_lock()
     }
 
     #[inline]
     pub fn write(&self) {
-        unsafe { self.inner.lock() };
+        self.inner.lock()
     }
 
     #[inline]
     pub unsafe fn try_write(&self) -> bool {
-        unsafe { self.inner.try_lock() }
+        self.inner.try_lock()
     }
 
     #[inline]
diff --git a/library/std/src/sys/sync/thread_parking/mod.rs b/library/std/src/sys/sync/thread_parking/mod.rs
index 0ebc5e093ee..f4d8fa0a58c 100644
--- a/library/std/src/sys/sync/thread_parking/mod.rs
+++ b/library/std/src/sys/sync/thread_parking/mod.rs
@@ -23,6 +23,7 @@ cfg_if::cfg_if! {
         mod windows7;
         pub use windows7::Parker;
     } else if #[cfg(all(target_vendor = "apple", not(miri)))] {
+        // Doesn't work in Miri, see <https://github.com/rust-lang/miri/issues/2589>.
         mod darwin;
         pub use darwin::Parker;
     } else if #[cfg(target_os = "xous")] {
diff --git a/library/std/src/sys_common/lazy_box.rs b/library/std/src/sys_common/lazy_box.rs
deleted file mode 100644
index b45b05f63ba..00000000000
--- a/library/std/src/sys_common/lazy_box.rs
+++ /dev/null
@@ -1,88 +0,0 @@
-#![allow(dead_code)] // Only used on some platforms.
-
-// This is used to wrap pthread {Mutex, Condvar, RwLock} in.
-
-use crate::marker::PhantomData;
-use crate::ops::{Deref, DerefMut};
-use crate::ptr::null_mut;
-use crate::sync::atomic::AtomicPtr;
-use crate::sync::atomic::Ordering::{AcqRel, Acquire};
-
-pub(crate) struct LazyBox<T: LazyInit> {
-    ptr: AtomicPtr<T>,
-    _phantom: PhantomData<T>,
-}
-
-pub(crate) trait LazyInit {
-    /// This is called before the box is allocated, to provide the value to
-    /// move into the new box.
-    ///
-    /// It might be called more than once per LazyBox, as multiple threads
-    /// might race to initialize it concurrently, each constructing and initializing
-    /// their own box. All but one of them will be passed to `cancel_init` right after.
-    fn init() -> Box<Self>;
-
-    /// Any surplus boxes from `init()` that lost the initialization race
-    /// are passed to this function for disposal.
-    ///
-    /// The default implementation calls destroy().
-    fn cancel_init(x: Box<Self>) {
-        Self::destroy(x);
-    }
-
-    /// This is called to destroy a used box.
-    ///
-    /// The default implementation just drops it.
-    fn destroy(_: Box<Self>) {}
-}
-
-impl<T: LazyInit> LazyBox<T> {
-    #[inline]
-    pub const fn new() -> Self {
-        Self { ptr: AtomicPtr::new(null_mut()), _phantom: PhantomData }
-    }
-
-    #[inline]
-    fn get_pointer(&self) -> *mut T {
-        let ptr = self.ptr.load(Acquire);
-        if ptr.is_null() { self.initialize() } else { ptr }
-    }
-
-    #[cold]
-    fn initialize(&self) -> *mut T {
-        let new_ptr = Box::into_raw(T::init());
-        match self.ptr.compare_exchange(null_mut(), new_ptr, AcqRel, Acquire) {
-            Ok(_) => new_ptr,
-            Err(ptr) => {
-                // Lost the race to another thread.
-                // Drop the box we created, and use the one from the other thread instead.
-                T::cancel_init(unsafe { Box::from_raw(new_ptr) });
-                ptr
-            }
-        }
-    }
-}
-
-impl<T: LazyInit> Deref for LazyBox<T> {
-    type Target = T;
-    #[inline]
-    fn deref(&self) -> &T {
-        unsafe { &*self.get_pointer() }
-    }
-}
-
-impl<T: LazyInit> DerefMut for LazyBox<T> {
-    #[inline]
-    fn deref_mut(&mut self) -> &mut T {
-        unsafe { &mut *self.get_pointer() }
-    }
-}
-
-impl<T: LazyInit> Drop for LazyBox<T> {
-    fn drop(&mut self) {
-        let ptr = *self.ptr.get_mut();
-        if !ptr.is_null() {
-            T::destroy(unsafe { Box::from_raw(ptr) });
-        }
-    }
-}
diff --git a/library/std/src/sys_common/mod.rs b/library/std/src/sys_common/mod.rs
index aa27886ff6f..4f7a131f6bb 100644
--- a/library/std/src/sys_common/mod.rs
+++ b/library/std/src/sys_common/mod.rs
@@ -22,7 +22,6 @@ mod tests;
 
 pub mod fs;
 pub mod io;
-pub mod lazy_box;
 pub mod process;
 pub mod wstr;
 pub mod wtf8;
diff --git a/library/std/src/thread/current.rs b/library/std/src/thread/current.rs
index b38149a0da7..e6eb90c4c30 100644
--- a/library/std/src/thread/current.rs
+++ b/library/std/src/thread/current.rs
@@ -110,22 +110,24 @@ mod id {
     }
 }
 
-/// Sets the thread handle for the current thread.
-///
-/// Aborts if the handle or the ID has been set already.
-pub(crate) fn set_current(thread: Thread) {
-    if CURRENT.get() != NONE || id::get().is_some() {
-        // Using `panic` here can add ~3kB to the binary size. We have complete
-        // control over where this is called, so just abort if there is a bug.
-        rtabort!("thread::set_current should only be called once per thread");
+/// Tries to set the thread handle for the current thread. Fails if a handle was
+/// already set or if the thread ID of `thread` would change an already-set ID.
+pub(crate) fn set_current(thread: Thread) -> Result<(), Thread> {
+    if CURRENT.get() != NONE {
+        return Err(thread);
     }
 
-    id::set(thread.id());
+    match id::get() {
+        Some(id) if id == thread.id() => {}
+        None => id::set(thread.id()),
+        _ => return Err(thread),
+    }
 
     // Make sure that `crate::rt::thread_cleanup` will be run, which will
     // call `drop_current`.
     crate::sys::thread_local::guard::enable();
     CURRENT.set(thread.into_raw().cast_mut());
+    Ok(())
 }
 
 /// Gets the id of the thread that invokes it.
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index d1d4eabb9bd..39753888509 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -519,9 +519,14 @@ impl Builder {
 
         let f = MaybeDangling::new(f);
         let main = move || {
-            // Immediately store the thread handle to avoid setting it or its ID
-            // twice, which would cause an abort.
-            set_current(their_thread.clone());
+            if let Err(_thread) = set_current(their_thread.clone()) {
+                // Both the current thread handle and the ID should not be
+                // initialized yet. Since only the C runtime and some of our
+                // platform code run before this, this point shouldn't be
+                // reachable. Use an abort to save binary size (see #123356).
+                rtabort!("something here is badly broken!");
+            }
+
             if let Some(name) = their_thread.cname() {
                 imp::Thread::set_name(name);
             }
@@ -1159,9 +1164,6 @@ pub fn park_timeout(dur: Duration) {
 pub struct ThreadId(NonZero<u64>);
 
 impl ThreadId {
-    // DO NOT rely on this value.
-    const MAIN_THREAD: ThreadId = ThreadId(unsafe { NonZero::new_unchecked(1) });
-
     // Generate a new unique thread ID.
     pub(crate) fn new() -> ThreadId {
         #[cold]
@@ -1173,7 +1175,7 @@ impl ThreadId {
             if #[cfg(target_has_atomic = "64")] {
                 use crate::sync::atomic::AtomicU64;
 
-                static COUNTER: AtomicU64 = AtomicU64::new(1);
+                static COUNTER: AtomicU64 = AtomicU64::new(0);
 
                 let mut last = COUNTER.load(Ordering::Relaxed);
                 loop {
@@ -1189,7 +1191,7 @@ impl ThreadId {
             } else {
                 use crate::sync::{Mutex, PoisonError};
 
-                static COUNTER: Mutex<u64> = Mutex::new(1);
+                static COUNTER: Mutex<u64> = Mutex::new(0);
 
                 let mut counter = COUNTER.lock().unwrap_or_else(PoisonError::into_inner);
                 let Some(id) = counter.checked_add(1) else {
@@ -1326,9 +1328,9 @@ impl Thread {
         Self::new_inner(id, ThreadName::Unnamed)
     }
 
-    // Used in runtime to construct main thread
-    pub(crate) fn new_main() -> Thread {
-        Self::new_inner(ThreadId::MAIN_THREAD, ThreadName::Main)
+    /// Constructs the thread handle for the main thread.
+    pub(crate) fn new_main(id: ThreadId) -> Thread {
+        Self::new_inner(id, ThreadName::Main)
     }
 
     fn new_inner(id: ThreadId, name: ThreadName) -> Thread {
diff --git a/library/std/tests/run-time-detect.rs b/library/std/tests/run-time-detect.rs
index dcd5cd7f6b9..dd14c0266aa 100644
--- a/library/std/tests/run-time-detect.rs
+++ b/library/std/tests/run-time-detect.rs
@@ -82,6 +82,7 @@ fn aarch64_linux() {
     println!("sha2: {}", is_aarch64_feature_detected!("sha2"));
     println!("sha3: {}", is_aarch64_feature_detected!("sha3"));
     println!("sm4: {}", is_aarch64_feature_detected!("sm4"));
+    println!("sme-b16b16: {}", is_aarch64_feature_detected!("sme-b16b16"));
     println!("sme-f16f16: {}", is_aarch64_feature_detected!("sme-f16f16"));
     println!("sme-f64f64: {}", is_aarch64_feature_detected!("sme-f64f64"));
     println!("sme-f8f16: {}", is_aarch64_feature_detected!("sme-f8f16"));