Merging upstream version 1.73.0+dfsg1.

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

45 files changed, 1468 insertions, 252 deletions

diff --git a/library/std/src/sys/common/alloc.rs b/library/std/src/sys/common/alloc.rs
index a5fcbdf39..d58aa6c27 100644
--- a/library/std/src/sys/common/alloc.rs
+++ b/library/std/src/sys/common/alloc.rs
@@ -8,7 +8,9 @@ use crate::ptr;
     target_arch = "x86",
     target_arch = "arm",
     target_arch = "m68k",
+    target_arch = "csky",
     target_arch = "mips",
+    target_arch = "mips32r6",
     target_arch = "powerpc",
     target_arch = "powerpc64",
     target_arch = "sparc",
@@ -24,6 +26,7 @@ pub const MIN_ALIGN: usize = 8;
     target_arch = "aarch64",
     target_arch = "loongarch64",
     target_arch = "mips64",
+    target_arch = "mips64r6",
     target_arch = "s390x",
     target_arch = "sparc64",
     target_arch = "riscv64",
diff --git a/library/std/src/sys/common/thread_local/fast_local.rs b/library/std/src/sys/common/thread_local/fast_local.rs
index bc5da1a18..c0a9619bf 100644
--- a/library/std/src/sys/common/thread_local/fast_local.rs
+++ b/library/std/src/sys/common/thread_local/fast_local.rs
@@ -87,10 +87,6 @@ pub macro thread_local_inner {
                 static __KEY: $crate::thread::local_impl::Key<$t> =
                     $crate::thread::local_impl::Key::<$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 {
diff --git a/library/std/src/sys/common/thread_local/os_local.rs b/library/std/src/sys/common/thread_local/os_local.rs
index 5d48ce1e0..7cf291921 100644
--- a/library/std/src/sys/common/thread_local/os_local.rs
+++ b/library/std/src/sys/common/thread_local/os_local.rs
@@ -24,7 +24,6 @@ pub macro thread_local_inner {
             const fn __init() -> $t { INIT_EXPR }
             static __KEY: $crate::thread::local_impl::Key<$t> =
                 $crate::thread::local_impl::Key::new();
-            #[allow(unused_unsafe)]
             unsafe {
                 __KEY.get(move || {
                     if let $crate::option::Option::Some(init) = _init {
@@ -59,10 +58,6 @@ pub macro thread_local_inner {
                 static __KEY: $crate::thread::local_impl::Key<$t> =
                     $crate::thread::local_impl::Key::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 {
diff --git a/library/std/src/sys/common/thread_local/static_local.rs b/library/std/src/sys/common/thread_local/static_local.rs
index 80322a978..5cb6c541a 100644
--- a/library/std/src/sys/common/thread_local/static_local.rs
+++ b/library/std/src/sys/common/thread_local/static_local.rs
@@ -43,10 +43,6 @@ pub macro thread_local_inner {
                 static __KEY: $crate::thread::local_impl::Key<$t> =
                     $crate::thread::local_impl::Key::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 {
diff --git a/library/std/src/sys/hermit/fs.rs b/library/std/src/sys/hermit/fs.rs
index 4bb735668..6aa4ea7f5 100644
--- a/library/std/src/sys/hermit/fs.rs
+++ b/library/std/src/sys/hermit/fs.rs
@@ -335,6 +335,7 @@ impl File {
         false
     }
 
+    #[inline]
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }
diff --git a/library/std/src/sys/hermit/os.rs b/library/std/src/sys/hermit/os.rs
index e53dbae61..c79197a9a 100644
--- a/library/std/src/sys/hermit/os.rs
+++ b/library/std/src/sys/hermit/os.rs
@@ -112,6 +112,34 @@ pub struct Env {
     iter: vec::IntoIter<(OsString, OsString)>,
 }
 
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
 impl !Send for Env {}
 impl !Sync for Env {}
 
diff --git a/library/std/src/sys/hermit/thread.rs b/library/std/src/sys/hermit/thread.rs
index 2507f7069..332151e40 100644
--- a/library/std/src/sys/hermit/thread.rs
+++ b/library/std/src/sys/hermit/thread.rs
@@ -1,6 +1,5 @@
 #![allow(dead_code)]
 
-use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
@@ -99,7 +98,7 @@ impl Thread {
 }
 
 pub fn available_parallelism() -> io::Result<NonZeroUsize> {
-    unsupported()
+    unsafe { Ok(NonZeroUsize::new_unchecked(abi::get_processor_count())) }
 }
 
 pub mod guard {
diff --git a/library/std/src/sys/hermit/time.rs b/library/std/src/sys/hermit/time.rs
index 5440d85df..7d91460ab 100644
--- a/library/std/src/sys/hermit/time.rs
+++ b/library/std/src/sys/hermit/time.rs
@@ -40,7 +40,7 @@ impl Timespec {
     }
 
     fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
-        let mut secs = self.tv_sec.checked_add_unsigned(other.as_secs())?;
+        let mut secs = self.t.tv_sec.checked_add_unsigned(other.as_secs())?;
 
         // Nano calculations can't overflow because nanos are <1B which fit
         // in a u32.
@@ -53,7 +53,7 @@ impl Timespec {
     }
 
     fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
-        let mut secs = self.tv_sec.checked_sub_unsigned(other.as_secs())?;
+        let mut secs = self.t.tv_sec.checked_sub_unsigned(other.as_secs())?;
 
         // Similar to above, nanos can't overflow.
         let mut nsec = self.t.tv_nsec as i32 - other.subsec_nanos() as i32;
diff --git a/library/std/src/sys/mod.rs b/library/std/src/sys/mod.rs
index c72be1380..beea3f23c 100644
--- a/library/std/src/sys/mod.rs
+++ b/library/std/src/sys/mod.rs
@@ -23,6 +23,7 @@
 #![allow(missing_debug_implementations)]
 
 pub mod common;
+mod personality;
 
 cfg_if::cfg_if! {
     if #[cfg(unix)] {
@@ -60,3 +61,52 @@ cfg_if::cfg_if! {
         pub const FULL_BACKTRACE_DEFAULT: bool = false;
     }
 }
+
+#[cfg(not(test))]
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "android")] {
+        pub use self::android::log2f32;
+        pub use self::android::log2f64;
+    } else {
+        #[inline]
+        pub fn log2f32(n: f32) -> f32 {
+            unsafe { crate::intrinsics::log2f32(n) }
+        }
+
+        #[inline]
+        pub fn log2f64(n: f64) -> f64 {
+            unsafe { crate::intrinsics::log2f64(n) }
+        }
+    }
+}
+
+// Solaris/Illumos requires a wrapper around log, log2, and log10 functions
+// because of their non-standard behavior (e.g., log(-n) returns -Inf instead
+// of expected NaN).
+#[cfg(not(test))]
+#[cfg(any(target_os = "solaris", target_os = "illumos"))]
+#[inline]
+pub fn log_wrapper<F: Fn(f64) -> f64>(n: f64, log_fn: F) -> f64 {
+    if n.is_finite() {
+        if n > 0.0 {
+            log_fn(n)
+        } else if n == 0.0 {
+            f64::NEG_INFINITY // log(0) = -Inf
+        } else {
+            f64::NAN // log(-n) = NaN
+        }
+    } else if n.is_nan() {
+        n // log(NaN) = NaN
+    } else if n > 0.0 {
+        n // log(Inf) = Inf
+    } else {
+        f64::NAN // log(-Inf) = NaN
+    }
+}
+
+#[cfg(not(test))]
+#[cfg(not(any(target_os = "solaris", target_os = "illumos")))]
+#[inline]
+pub fn log_wrapper<F: Fn(f64) -> f64>(n: f64, log_fn: F) -> f64 {
+    log_fn(n)
+}
diff --git a/library/std/src/sys/personality/dwarf/eh.rs b/library/std/src/sys/personality/dwarf/eh.rs
new file mode 100644
index 000000000..79624703a
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/eh.rs
@@ -0,0 +1,208 @@
+//! Parsing of GCC-style Language-Specific Data Area (LSDA)
+//! For details see:
+//!  * <https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html>
+//!  * <https://itanium-cxx-abi.github.io/cxx-abi/exceptions.pdf>
+//!  * <https://www.airs.com/blog/archives/460>
+//!  * <https://www.airs.com/blog/archives/464>
+//!
+//! A reference implementation may be found in the GCC source tree
+//! (`<root>/libgcc/unwind-c.c` as of this writing).
+
+#![allow(non_upper_case_globals)]
+#![allow(unused)]
+
+use super::DwarfReader;
+use core::mem;
+use core::ptr;
+
+pub const DW_EH_PE_omit: u8 = 0xFF;
+pub const DW_EH_PE_absptr: u8 = 0x00;
+
+pub const DW_EH_PE_uleb128: u8 = 0x01;
+pub const DW_EH_PE_udata2: u8 = 0x02;
+pub const DW_EH_PE_udata4: u8 = 0x03;
+pub const DW_EH_PE_udata8: u8 = 0x04;
+pub const DW_EH_PE_sleb128: u8 = 0x09;
+pub const DW_EH_PE_sdata2: u8 = 0x0A;
+pub const DW_EH_PE_sdata4: u8 = 0x0B;
+pub const DW_EH_PE_sdata8: u8 = 0x0C;
+
+pub const DW_EH_PE_pcrel: u8 = 0x10;
+pub const DW_EH_PE_textrel: u8 = 0x20;
+pub const DW_EH_PE_datarel: u8 = 0x30;
+pub const DW_EH_PE_funcrel: u8 = 0x40;
+pub const DW_EH_PE_aligned: u8 = 0x50;
+
+pub const DW_EH_PE_indirect: u8 = 0x80;
+
+#[derive(Copy, Clone)]
+pub struct EHContext<'a> {
+    pub ip: usize,                             // Current instruction pointer
+    pub func_start: usize,                     // Address of the current function
+    pub get_text_start: &'a dyn Fn() -> usize, // Get address of the code section
+    pub get_data_start: &'a dyn Fn() -> usize, // Get address of the data section
+}
+
+pub enum EHAction {
+    None,
+    Cleanup(usize),
+    Catch(usize),
+    Filter(usize),
+    Terminate,
+}
+
+pub const USING_SJLJ_EXCEPTIONS: bool = cfg!(all(target_os = "ios", target_arch = "arm"));
+
+pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result<EHAction, ()> {
+    if lsda.is_null() {
+        return Ok(EHAction::None);
+    }
+
+    let func_start = context.func_start;
+    let mut reader = DwarfReader::new(lsda);
+
+    let start_encoding = reader.read::<u8>();
+    // base address for landing pad offsets
+    let lpad_base = if start_encoding != DW_EH_PE_omit {
+        read_encoded_pointer(&mut reader, context, start_encoding)?
+    } else {
+        func_start
+    };
+
+    let ttype_encoding = reader.read::<u8>();
+    if ttype_encoding != DW_EH_PE_omit {
+        // Rust doesn't analyze exception types, so we don't care about the type table
+        reader.read_uleb128();
+    }
+
+    let call_site_encoding = reader.read::<u8>();
+    let call_site_table_length = reader.read_uleb128();
+    let action_table = reader.ptr.add(call_site_table_length as usize);
+    let ip = context.ip;
+
+    if !USING_SJLJ_EXCEPTIONS {
+        while reader.ptr < action_table {
+            let cs_start = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
+            let cs_len = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
+            let cs_lpad = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
+            let cs_action_entry = reader.read_uleb128();
+            // Callsite table is sorted by cs_start, so if we've passed the ip, we
+            // may stop searching.
+            if ip < func_start + cs_start {
+                break;
+            }
+            if ip < func_start + cs_start + cs_len {
+                if cs_lpad == 0 {
+                    return Ok(EHAction::None);
+                } else {
+                    let lpad = lpad_base + cs_lpad;
+                    return Ok(interpret_cs_action(action_table as *mut u8, cs_action_entry, lpad));
+                }
+            }
+        }
+        // Ip is not present in the table. This indicates a nounwind call.
+        Ok(EHAction::Terminate)
+    } else {
+        // SjLj version:
+        // The "IP" is an index into the call-site table, with two exceptions:
+        // -1 means 'no-action', and 0 means 'terminate'.
+        match ip as isize {
+            -1 => return Ok(EHAction::None),
+            0 => return Ok(EHAction::Terminate),
+            _ => (),
+        }
+        let mut idx = ip;
+        loop {
+            let cs_lpad = reader.read_uleb128();
+            let cs_action_entry = reader.read_uleb128();
+            idx -= 1;
+            if idx == 0 {
+                // Can never have null landing pad for sjlj -- that would have
+                // been indicated by a -1 call site index.
+                let lpad = (cs_lpad + 1) as usize;
+                return Ok(interpret_cs_action(action_table as *mut u8, cs_action_entry, lpad));
+            }
+        }
+    }
+}
+
+unsafe fn interpret_cs_action(
+    action_table: *mut u8,
+    cs_action_entry: u64,
+    lpad: usize,
+) -> EHAction {
+    if cs_action_entry == 0 {
+        // If cs_action_entry is 0 then this is a cleanup (Drop::drop). We run these
+        // for both Rust panics and foreign exceptions.
+        EHAction::Cleanup(lpad)
+    } else {
+        // If lpad != 0 and cs_action_entry != 0, we have to check ttype_index.
+        // If ttype_index == 0 under the condition, we take cleanup action.
+        let action_record = (action_table as *mut u8).offset(cs_action_entry as isize - 1);
+        let mut action_reader = DwarfReader::new(action_record);
+        let ttype_index = action_reader.read_sleb128();
+        if ttype_index == 0 {
+            EHAction::Cleanup(lpad)
+        } else if ttype_index > 0 {
+            // Stop unwinding Rust panics at catch_unwind.
+            EHAction::Catch(lpad)
+        } else {
+            EHAction::Filter(lpad)
+        }
+    }
+}
+
+#[inline]
+fn round_up(unrounded: usize, align: usize) -> Result<usize, ()> {
+    if align.is_power_of_two() { Ok((unrounded + align - 1) & !(align - 1)) } else { Err(()) }
+}
+
+unsafe fn read_encoded_pointer(
+    reader: &mut DwarfReader,
+    context: &EHContext<'_>,
+    encoding: u8,
+) -> Result<usize, ()> {
+    if encoding == DW_EH_PE_omit {
+        return Err(());
+    }
+
+    // DW_EH_PE_aligned implies it's an absolute pointer value
+    if encoding == DW_EH_PE_aligned {
+        reader.ptr = reader.ptr.with_addr(round_up(reader.ptr.addr(), mem::size_of::<usize>())?);
+        return Ok(reader.read::<usize>());
+    }
+
+    let mut result = match encoding & 0x0F {
+        DW_EH_PE_absptr => reader.read::<usize>(),
+        DW_EH_PE_uleb128 => reader.read_uleb128() as usize,
+        DW_EH_PE_udata2 => reader.read::<u16>() as usize,
+        DW_EH_PE_udata4 => reader.read::<u32>() as usize,
+        DW_EH_PE_udata8 => reader.read::<u64>() as usize,
+        DW_EH_PE_sleb128 => reader.read_sleb128() as usize,
+        DW_EH_PE_sdata2 => reader.read::<i16>() as usize,
+        DW_EH_PE_sdata4 => reader.read::<i32>() as usize,
+        DW_EH_PE_sdata8 => reader.read::<i64>() as usize,
+        _ => return Err(()),
+    };
+
+    result += match encoding & 0x70 {
+        DW_EH_PE_absptr => 0,
+        // relative to address of the encoded value, despite the name
+        DW_EH_PE_pcrel => reader.ptr.expose_addr(),
+        DW_EH_PE_funcrel => {
+            if context.func_start == 0 {
+                return Err(());
+            }
+            context.func_start
+        }
+        DW_EH_PE_textrel => (*context.get_text_start)(),
+        DW_EH_PE_datarel => (*context.get_data_start)(),
+        _ => return Err(()),
+    };
+
+    if encoding & DW_EH_PE_indirect != 0 {
+        result = *ptr::from_exposed_addr::<usize>(result);
+    }
+
+    Ok(result)
+}
diff --git a/library/std/src/sys/personality/dwarf/mod.rs b/library/std/src/sys/personality/dwarf/mod.rs
new file mode 100644
index 000000000..652fbe95a
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/mod.rs
@@ -0,0 +1,73 @@
+//! Utilities for parsing DWARF-encoded data streams.
+//! See <http://www.dwarfstd.org>,
+//! DWARF-4 standard, Section 7 - "Data Representation"
+
+// This module is used only by x86_64-pc-windows-gnu for now, but we
+// are compiling it everywhere to avoid regressions.
+#![allow(unused)]
+
+#[cfg(test)]
+mod tests;
+
+pub mod eh;
+
+use core::mem;
+
+pub struct DwarfReader {
+    pub ptr: *const u8,
+}
+
+#[repr(C, packed)]
+struct Unaligned<T>(T);
+
+impl DwarfReader {
+    pub fn new(ptr: *const u8) -> DwarfReader {
+        DwarfReader { ptr }
+    }
+
+    // DWARF streams are packed, so e.g., a u32 would not necessarily be aligned
+    // on a 4-byte boundary. This may cause problems on platforms with strict
+    // alignment requirements. By wrapping data in a "packed" struct, we are
+    // telling the backend to generate "misalignment-safe" code.
+    pub unsafe fn read<T: Copy>(&mut self) -> T {
+        let Unaligned(result) = *(self.ptr as *const Unaligned<T>);
+        self.ptr = self.ptr.add(mem::size_of::<T>());
+        result
+    }
+
+    // ULEB128 and SLEB128 encodings are defined in Section 7.6 - "Variable
+    // Length Data".
+    pub unsafe fn read_uleb128(&mut self) -> u64 {
+        let mut shift: usize = 0;
+        let mut result: u64 = 0;
+        let mut byte: u8;
+        loop {
+            byte = self.read::<u8>();
+            result |= ((byte & 0x7F) as u64) << shift;
+            shift += 7;
+            if byte & 0x80 == 0 {
+                break;
+            }
+        }
+        result
+    }
+
+    pub unsafe fn read_sleb128(&mut self) -> i64 {
+        let mut shift: u32 = 0;
+        let mut result: u64 = 0;
+        let mut byte: u8;
+        loop {
+            byte = self.read::<u8>();
+            result |= ((byte & 0x7F) as u64) << shift;
+            shift += 7;
+            if byte & 0x80 == 0 {
+                break;
+            }
+        }
+        // sign-extend
+        if shift < u64::BITS && (byte & 0x40) != 0 {
+            result |= (!0 as u64) << shift;
+        }
+        result as i64
+    }
+}
diff --git a/library/std/src/sys/personality/dwarf/tests.rs b/library/std/src/sys/personality/dwarf/tests.rs
new file mode 100644
index 000000000..1644f3708
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/tests.rs
@@ -0,0 +1,19 @@
+use super::*;
+
+#[test]
+fn dwarf_reader() {
+    let encoded: &[u8] = &[1, 2, 3, 4, 5, 6, 7, 0xE5, 0x8E, 0x26, 0x9B, 0xF1, 0x59, 0xFF, 0xFF];
+
+    let mut reader = DwarfReader::new(encoded.as_ptr());
+
+    unsafe {
+        assert!(reader.read::<u8>() == u8::to_be(1u8));
+        assert!(reader.read::<u16>() == u16::to_be(0x0203));
+        assert!(reader.read::<u32>() == u32::to_be(0x04050607));
+
+        assert!(reader.read_uleb128() == 624485);
+        assert!(reader.read_sleb128() == -624485);
+
+        assert!(reader.read::<i8>() == i8::to_be(-1));
+    }
+}
diff --git a/library/std/src/sys/personality/emcc.rs b/library/std/src/sys/personality/emcc.rs
new file mode 100644
index 000000000..cb52ae89b
--- /dev/null
+++ b/library/std/src/sys/personality/emcc.rs
@@ -0,0 +1,20 @@
+//! On Emscripten Rust panics are wrapped in C++ exceptions, so we just forward
+//! to `__gxx_personality_v0` which is provided by Emscripten.
+
+use crate::ffi::c_int;
+use unwind as uw;
+
+// This is required by the compiler to exist (e.g., it's a lang item), but it's
+// never actually called by the compiler.  Emscripten EH doesn't use a
+// personality function at all, it instead uses __cxa_find_matching_catch.
+// Wasm error handling would use __gxx_personality_wasm0.
+#[lang = "eh_personality"]
+unsafe extern "C" fn rust_eh_personality(
+    _version: c_int,
+    _actions: uw::_Unwind_Action,
+    _exception_class: uw::_Unwind_Exception_Class,
+    _exception_object: *mut uw::_Unwind_Exception,
+    _context: *mut uw::_Unwind_Context,
+) -> uw::_Unwind_Reason_Code {
+    core::intrinsics::abort()
+}
diff --git a/library/std/src/sys/personality/gcc.rs b/library/std/src/sys/personality/gcc.rs
new file mode 100644
index 000000000..e477a0cd7
--- /dev/null
+++ b/library/std/src/sys/personality/gcc.rs
@@ -0,0 +1,294 @@
+//! Implementation of panics backed by libgcc/libunwind (in some form).
+//!
+//! For background on exception handling and stack unwinding please see
+//! "Exception Handling in LLVM" (llvm.org/docs/ExceptionHandling.html) and
+//! documents linked from it.
+//! These are also good reads:
+//!  * <https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html>
+//!  * <https://monoinfinito.wordpress.com/series/exception-handling-in-c/>
+//!  * <https://www.airs.com/blog/index.php?s=exception+frames>
+//!
+//! ## A brief summary
+//!
+//! Exception handling happens in two phases: a search phase and a cleanup
+//! phase.
+//!
+//! In both phases the unwinder walks stack frames from top to bottom using
+//! information from the stack frame unwind sections of the current process's
+//! modules ("module" here refers to an OS module, i.e., an executable or a
+//! dynamic library).
+//!
+//! For each stack frame, it invokes the associated "personality routine", whose
+//! address is also stored in the unwind info section.
+//!
+//! In the search phase, the job of a personality routine is to examine
+//! exception object being thrown, and to decide whether it should be caught at
+//! that stack frame. Once the handler frame has been identified, cleanup phase
+//! begins.
+//!
+//! In the cleanup phase, the unwinder invokes each personality routine again.
+//! This time it decides which (if any) cleanup code needs to be run for
+//! the current stack frame. If so, the control is transferred to a special
+//! branch in the function body, the "landing pad", which invokes destructors,
+//! frees memory, etc. At the end of the landing pad, control is transferred
+//! back to the unwinder and unwinding resumes.
+//!
+//! Once stack has been unwound down to the handler frame level, unwinding stops
+//! and the last personality routine transfers control to the catch block.
+
+use super::dwarf::eh::{self, EHAction, EHContext};
+use crate::ffi::c_int;
+use libc::uintptr_t;
+use unwind as uw;
+
+// Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
+// and TargetLowering::getExceptionSelectorRegister() for each architecture,
+// then mapped to DWARF register numbers via register definition tables
+// (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
+// See also https://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
+
+#[cfg(target_arch = "x86")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
+
+#[cfg(target_arch = "x86_64")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
+
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
+
+#[cfg(target_arch = "m68k")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // D0, D1
+
+#[cfg(any(
+    target_arch = "mips",
+    target_arch = "mips32r6",
+    target_arch = "mips64",
+    target_arch = "mips64r6"
+))]
+const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
+
+#[cfg(target_arch = "csky")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
+
+#[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
+const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
+
+#[cfg(target_arch = "s390x")]
+const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
+
+#[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
+const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
+
+#[cfg(target_arch = "hexagon")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
+
+#[cfg(any(target_arch = "riscv64", target_arch = "riscv32"))]
+const UNWIND_DATA_REG: (i32, i32) = (10, 11); // x10, x11
+
+#[cfg(target_arch = "loongarch64")]
+const UNWIND_DATA_REG: (i32, i32) = (4, 5); // a0, a1
+
+// The following code is based on GCC's C and C++ personality routines.  For reference, see:
+// https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
+// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
+
+cfg_if::cfg_if! {
+    if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "tvos"), not(target_os = "watchos"), not(target_os = "netbsd")))] {
+        // ARM EHABI personality routine.
+        // https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
+        //
+        // iOS uses the default routine instead since it uses SjLj unwinding.
+        #[lang = "eh_personality"]
+        unsafe extern "C" fn rust_eh_personality(
+            state: uw::_Unwind_State,
+            exception_object: *mut uw::_Unwind_Exception,
+            context: *mut uw::_Unwind_Context,
+        ) -> uw::_Unwind_Reason_Code {
+            let state = state as c_int;
+            let action = state & uw::_US_ACTION_MASK as c_int;
+            let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
+                // Backtraces on ARM will call the personality routine with
+                // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
+                // we want to continue unwinding the stack, otherwise all our backtraces
+                // would end at __rust_try
+                if state & uw::_US_FORCE_UNWIND as c_int != 0 {
+                    return continue_unwind(exception_object, context);
+                }
+                true
+            } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
+                false
+            } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
+                return continue_unwind(exception_object, context);
+            } else {
+                return uw::_URC_FAILURE;
+            };
+
+            // The DWARF unwinder assumes that _Unwind_Context holds things like the function
+            // and LSDA pointers, however ARM EHABI places them into the exception object.
+            // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
+            // take only the context pointer, GCC personality routines stash a pointer to
+            // exception_object in the context, using location reserved for ARM's
+            // "scratch register" (r12).
+            uw::_Unwind_SetGR(context, uw::UNWIND_POINTER_REG, exception_object as uw::_Unwind_Ptr);
+            // ...A more principled approach would be to provide the full definition of ARM's
+            // _Unwind_Context in our libunwind bindings and fetch the required data from there
+            // directly, bypassing DWARF compatibility functions.
+
+            let eh_action = match find_eh_action(context) {
+                Ok(action) => action,
+                Err(_) => return uw::_URC_FAILURE,
+            };
+            if search_phase {
+                match eh_action {
+                    EHAction::None | EHAction::Cleanup(_) => {
+                        return continue_unwind(exception_object, context);
+                    }
+                    EHAction::Catch(_) | EHAction::Filter(_) => {
+                        // EHABI requires the personality routine to update the
+                        // SP value in the barrier cache of the exception object.
+                        (*exception_object).private[5] =
+                            uw::_Unwind_GetGR(context, uw::UNWIND_SP_REG);
+                        return uw::_URC_HANDLER_FOUND;
+                    }
+                    EHAction::Terminate => return uw::_URC_FAILURE,
+                }
+            } else {
+                match eh_action {
+                    EHAction::None => return continue_unwind(exception_object, context),
+                    EHAction::Filter(_) if state & uw::_US_FORCE_UNWIND as c_int != 0 => return continue_unwind(exception_object, context),
+                    EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
+                        uw::_Unwind_SetGR(
+                            context,
+                            UNWIND_DATA_REG.0,
+                            exception_object as uintptr_t,
+                        );
+                        uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+                        uw::_Unwind_SetIP(context, lpad);
+                        return uw::_URC_INSTALL_CONTEXT;
+                    }
+                    EHAction::Terminate => return uw::_URC_FAILURE,
+                }
+            }
+
+            // On ARM EHABI the personality routine is responsible for actually
+            // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
+            unsafe fn continue_unwind(
+                exception_object: *mut uw::_Unwind_Exception,
+                context: *mut uw::_Unwind_Context,
+            ) -> uw::_Unwind_Reason_Code {
+                if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
+                    uw::_URC_CONTINUE_UNWIND
+                } else {
+                    uw::_URC_FAILURE
+                }
+            }
+            // defined in libgcc
+            extern "C" {
+                fn __gnu_unwind_frame(
+                    exception_object: *mut uw::_Unwind_Exception,
+                    context: *mut uw::_Unwind_Context,
+                ) -> uw::_Unwind_Reason_Code;
+            }
+        }
+    } else {
+        // Default personality routine, which is used directly on most targets
+        // and indirectly on Windows x86_64 via SEH.
+        unsafe extern "C" fn rust_eh_personality_impl(
+            version: c_int,
+            actions: uw::_Unwind_Action,
+            _exception_class: uw::_Unwind_Exception_Class,
+            exception_object: *mut uw::_Unwind_Exception,
+            context: *mut uw::_Unwind_Context,
+        ) -> uw::_Unwind_Reason_Code {
+            if version != 1 {
+                return uw::_URC_FATAL_PHASE1_ERROR;
+            }
+            let eh_action = match find_eh_action(context) {
+                Ok(action) => action,
+                Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
+            };
+            if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
+                match eh_action {
+                    EHAction::None | EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND,
+                    EHAction::Catch(_) | EHAction::Filter(_) => uw::_URC_HANDLER_FOUND,
+                    EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
+                }
+            } else {
+                match eh_action {
+                    EHAction::None => uw::_URC_CONTINUE_UNWIND,
+                    // Forced unwinding hits a terminate action.
+                    EHAction::Filter(_) if actions as i32 & uw::_UA_FORCE_UNWIND as i32 != 0 => uw::_URC_CONTINUE_UNWIND,
+                    EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
+                        uw::_Unwind_SetGR(
+                            context,
+                            UNWIND_DATA_REG.0,
+                            exception_object as uintptr_t,
+                        );
+                        uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+                        uw::_Unwind_SetIP(context, lpad);
+                        uw::_URC_INSTALL_CONTEXT
+                    }
+                    EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
+                }
+            }
+        }
+
+        cfg_if::cfg_if! {
+            if #[cfg(all(windows, any(target_arch = "aarch64", target_arch = "x86_64"), target_env = "gnu"))] {
+                // On x86_64 MinGW targets, the unwinding mechanism is SEH however the unwind
+                // handler data (aka LSDA) uses GCC-compatible encoding.
+                #[lang = "eh_personality"]
+                #[allow(nonstandard_style)]
+                unsafe extern "C" fn rust_eh_personality(
+                    exceptionRecord: *mut uw::EXCEPTION_RECORD,
+                    establisherFrame: uw::LPVOID,
+                    contextRecord: *mut uw::CONTEXT,
+                    dispatcherContext: *mut uw::DISPATCHER_CONTEXT,
+                ) -> uw::EXCEPTION_DISPOSITION {
+                    uw::_GCC_specific_handler(
+                        exceptionRecord,
+                        establisherFrame,
+                        contextRecord,
+                        dispatcherContext,
+                        rust_eh_personality_impl,
+                    )
+                }
+            } else {
+                // The personality routine for most of our targets.
+                #[lang = "eh_personality"]
+                unsafe extern "C" fn rust_eh_personality(
+                    version: c_int,
+                    actions: uw::_Unwind_Action,
+                    exception_class: uw::_Unwind_Exception_Class,
+                    exception_object: *mut uw::_Unwind_Exception,
+                    context: *mut uw::_Unwind_Context,
+                ) -> uw::_Unwind_Reason_Code {
+                    rust_eh_personality_impl(
+                        version,
+                        actions,
+                        exception_class,
+                        exception_object,
+                        context,
+                    )
+                }
+            }
+        }
+    }
+}
+
+unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction, ()> {
+    let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
+    let mut ip_before_instr: c_int = 0;
+    let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
+    let eh_context = EHContext {
+        // The return address points 1 byte past the call instruction,
+        // which could be in the next IP range in LSDA range table.
+        //
+        // `ip = -1` has special meaning, so use wrapping sub to allow for that
+        ip: if ip_before_instr != 0 { ip } else { ip.wrapping_sub(1) },
+        func_start: uw::_Unwind_GetRegionStart(context),
+        get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
+        get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
+    };
+    eh::find_eh_action(lsda, &eh_context)
+}
diff --git a/library/std/src/sys/personality/mod.rs b/library/std/src/sys/personality/mod.rs
new file mode 100644
index 000000000..386a399f5
--- /dev/null
+++ b/library/std/src/sys/personality/mod.rs
@@ -0,0 +1,46 @@
+//! This module contains the implementation of the `eh_personality` lang item.
+//!
+//! The actual implementation is heavily dependent on the target since Rust
+//! tries to use the native stack unwinding mechanism whenever possible.
+//!
+//! This personality function is still required with `-C panic=abort` because
+//! it is used to catch foreign exceptions from `extern "C-unwind"` and turn
+//! them into aborts.
+//!
+//! Additionally, ARM EHABI uses the personality function when generating
+//! backtraces.
+
+mod dwarf;
+
+#[cfg(not(test))]
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "emscripten")] {
+        mod emcc;
+    } else if #[cfg(target_env = "msvc")] {
+        // This is required by the compiler to exist (e.g., it's a lang item),
+        // but it's never actually called by the compiler because
+        // _CxxFrameHandler3 is the personality function that is always used.
+        // Hence this is just an aborting stub.
+        #[lang = "eh_personality"]
+        fn rust_eh_personality() {
+            core::intrinsics::abort()
+        }
+    } else if #[cfg(any(
+        all(target_family = "windows", target_env = "gnu"),
+        target_os = "psp",
+        target_os = "solid_asp3",
+        all(target_family = "unix", not(target_os = "espidf"), not(target_os = "l4re")),
+        all(target_vendor = "fortanix", target_env = "sgx"),
+    ))] {
+        mod gcc;
+    } else {
+        // Targets that don't support unwinding.
+        // - family=wasm
+        // - os=none ("bare metal" targets)
+        // - os=uefi
+        // - os=espidf
+        // - os=hermit
+        // - nvptx64-nvidia-cuda
+        // - arch=avr
+    }
+}
diff --git a/library/std/src/sys/sgx/os.rs b/library/std/src/sys/sgx/os.rs
index 5da0257f3..86f4c7d3d 100644
--- a/library/std/src/sys/sgx/os.rs
+++ b/library/std/src/sys/sgx/os.rs
@@ -96,14 +96,61 @@ fn create_env_store() -> &'static EnvStore {
     unsafe { &*(ENV.load(Ordering::Relaxed) as *const EnvStore) }
 }
 
-pub type Env = vec::IntoIter<(OsString, OsString)>;
+pub struct Env {
+    iter: vec::IntoIter<(OsString, OsString)>,
+}
+
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
+impl !Send for Env {}
+impl !Sync for Env {}
+
+impl Iterator for Env {
+    type Item = (OsString, OsString);
+    fn next(&mut self) -> Option<(OsString, OsString)> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
 
 pub fn env() -> Env {
     let clone_to_vec = |map: &HashMap<OsString, OsString>| -> Vec<_> {
         map.iter().map(|(k, v)| (k.clone(), v.clone())).collect()
     };
 
-    get_env_store().map(|env| clone_to_vec(&env.lock().unwrap())).unwrap_or_default().into_iter()
+    let iter = get_env_store()
+        .map(|env| clone_to_vec(&env.lock().unwrap()))
+        .unwrap_or_default()
+        .into_iter();
+    Env { iter }
 }
 
 pub fn getenv(k: &OsStr) -> Option<OsString> {
diff --git a/library/std/src/sys/sgx/thread.rs b/library/std/src/sys/sgx/thread.rs
index 1608b8cb6..7ac9d1d64 100644
--- a/library/std/src/sys/sgx/thread.rs
+++ b/library/std/src/sys/sgx/thread.rs
@@ -121,8 +121,16 @@ impl Thread {
         rtassert!(wait_error.kind() == io::ErrorKind::WouldBlock);
     }
 
+    /// SGX should protect in-enclave data from the outside (attacker),
+    /// so there should be no data leakage to the OS,
+    /// and therefore also no 1-1 mapping between SGX thread names and OS thread names.
+    ///
+    /// This is why the method is intentionally No-Op.
     pub fn set_name(_name: &CStr) {
-        // FIXME: could store this pointer in TLS somewhere
+        // Note that the internally visible SGX thread name is already provided
+        // by the platform-agnostic (target-agnostic) Rust thread code.
+        // This can be observed in the [`std::thread::tests::test_named_thread`] test,
+        // which succeeds as-is with the SGX target.
     }
 
     pub fn sleep(dur: Duration) {
diff --git a/library/std/src/sys/solid/os.rs b/library/std/src/sys/solid/os.rs
index 6135921f0..9f4e66d62 100644
--- a/library/std/src/sys/solid/os.rs
+++ b/library/std/src/sys/solid/os.rs
@@ -81,10 +81,42 @@ pub fn current_exe() -> io::Result<PathBuf> {
 
 static ENV_LOCK: RwLock<()> = RwLock::new(());
 
+pub fn env_read_lock() -> impl Drop {
+    ENV_LOCK.read().unwrap_or_else(PoisonError::into_inner)
+}
+
 pub struct Env {
     iter: vec::IntoIter<(OsString, OsString)>,
 }
 
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
 impl !Send for Env {}
 impl !Sync for Env {}
 
@@ -106,7 +138,7 @@ pub fn env() -> Env {
     }
 
     unsafe {
-        let _guard = ENV_LOCK.read();
+        let _guard = env_read_lock();
         let mut result = Vec::new();
         if !environ.is_null() {
             while !(*environ).is_null() {
@@ -140,17 +172,21 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    let s = run_with_cstr(k.as_bytes(), |k| {
-        let _guard = ENV_LOCK.read();
-        Ok(unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char)
-    })
-    .ok()?;
+    run_with_cstr(k.as_bytes(), |k| {
+        let _guard = env_read_lock();
+        let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
 
-    if s.is_null() {
-        None
-    } else {
-        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
-    }
+        if v.is_null() {
+            Ok(None)
+        } else {
+            // SAFETY: `v` cannot be mutated while executing this line since we've a read lock
+            let bytes = unsafe { CStr::from_ptr(v) }.to_bytes().to_vec();
+
+            Ok(Some(OsStringExt::from_vec(bytes)))
+        }
+    })
+    .ok()
+    .flatten()
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
diff --git a/library/std/src/sys/unix/cmath.rs b/library/std/src/sys/unix/cmath.rs
index 2bf80d7a4..5346d2291 100644
--- a/library/std/src/sys/unix/cmath.rs
+++ b/library/std/src/sys/unix/cmath.rs
@@ -30,4 +30,8 @@ extern "C" {
     pub fn tanf(n: f32) -> f32;
     pub fn tanh(n: f64) -> f64;
     pub fn tanhf(n: f32) -> f32;
+    pub fn tgamma(n: f64) -> f64;
+    pub fn tgammaf(n: f32) -> f32;
+    pub fn lgamma_r(n: f64, s: &mut i32) -> f64;
+    pub fn lgammaf_r(n: f32, s: &mut i32) -> f32;
 }
diff --git a/library/std/src/sys/unix/fs.rs b/library/std/src/sys/unix/fs.rs
index fbc7f04ce..a5604c92a 100644
--- a/library/std/src/sys/unix/fs.rs
+++ b/library/std/src/sys/unix/fs.rs
@@ -7,17 +7,6 @@ use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
-#[cfg(any(
-    target_os = "android",
-    target_os = "linux",
-    target_os = "solaris",
-    target_os = "fuchsia",
-    target_os = "redox",
-    target_os = "illumos",
-    target_os = "nto",
-    target_os = "vita",
-))]
-use crate::mem::MaybeUninit;
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd};
 use crate::path::{Path, PathBuf};
 use crate::ptr;
@@ -712,22 +701,10 @@ impl Iterator for ReadDir {
                 // requires the full extent of *entry_ptr to be in bounds of the same
                 // allocation, which is not necessarily the case here.
                 //
-                // Absent any other way to obtain a pointer to `(*entry_ptr).d_name`
-                // legally in Rust analogously to how it would be done in C, we instead
-                // need to make our own non-libc allocation that conforms to the weird
-                // imaginary definition of dirent64, and use that for a field offset
-                // computation.
+                // Instead we must access fields individually through their offsets.
                 macro_rules! offset_ptr {
                     ($entry_ptr:expr, $field:ident) => {{
-                        const OFFSET: isize = {
-                            let delusion = MaybeUninit::<dirent64>::uninit();
-                            let entry_ptr = delusion.as_ptr();
-                            unsafe {
-                                ptr::addr_of!((*entry_ptr).$field)
-                                    .cast::<u8>()
-                                    .offset_from(entry_ptr.cast::<u8>())
-                            }
-                        };
+                        const OFFSET: isize = mem::offset_of!(dirent64, $field) as isize;
                         if true {
                             // Cast to the same type determined by the else branch.
                             $entry_ptr.byte_offset(OFFSET).cast::<_>()
@@ -1227,6 +1204,7 @@ impl File {
         self.0.write_vectored_at(bufs, offset)
     }
 
+    #[inline]
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }
diff --git a/library/std/src/sys/unix/kernel_copy.rs b/library/std/src/sys/unix/kernel_copy.rs
index 7d49bbdcb..4d17a1b00 100644
--- a/library/std/src/sys/unix/kernel_copy.rs
+++ b/library/std/src/sys/unix/kernel_copy.rs
@@ -89,6 +89,12 @@ enum FdMeta {
     NoneObtained,
 }
 
+#[derive(PartialEq)]
+enum FdHandle {
+    Input,
+    Output,
+}
+
 impl FdMeta {
     fn maybe_fifo(&self) -> bool {
         match self {
@@ -114,12 +120,14 @@ impl FdMeta {
         }
     }
 
-    fn copy_file_range_candidate(&self) -> bool {
+    fn copy_file_range_candidate(&self, f: FdHandle) -> bool {
         match self {
             // copy_file_range will fail on empty procfs files. `read` can determine whether EOF has been reached
             // without extra cost and skip the write, thus there is no benefit in attempting copy_file_range
-            FdMeta::Metadata(meta) if meta.is_file() && meta.len() > 0 => true,
-            FdMeta::NoneObtained => true,
+            FdMeta::Metadata(meta) if f == FdHandle::Input && meta.is_file() && meta.len() > 0 => {
+                true
+            }
+            FdMeta::Metadata(meta) if f == FdHandle::Output && meta.is_file() => true,
             _ => false,
         }
     }
@@ -197,7 +205,9 @@ impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> {
             written += flush()?;
             let max_write = reader.min_limit();
 
-            if input_meta.copy_file_range_candidate() && output_meta.copy_file_range_candidate() {
+            if input_meta.copy_file_range_candidate(FdHandle::Input)
+                && output_meta.copy_file_range_candidate(FdHandle::Output)
+            {
                 let result = copy_regular_files(readfd, writefd, max_write);
                 result.update_take(reader);
 
diff --git a/library/std/src/sys/unix/mod.rs b/library/std/src/sys/unix/mod.rs
index 326f1481e..77ef086f2 100644
--- a/library/std/src/sys/unix/mod.rs
+++ b/library/std/src/sys/unix/mod.rs
@@ -110,6 +110,11 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
             while libc::poll(pfds.as_mut_ptr(), 3, 0) == -1 {
                 match errno() {
                     libc::EINTR => continue,
+                    #[cfg(target_vendor = "unikraft")]
+                    libc::ENOSYS => {
+                        // Not all configurations of Unikraft enable `LIBPOSIX_EVENT`.
+                        break 'poll;
+                    }
                     libc::EINVAL | libc::EAGAIN | libc::ENOMEM => {
                         // RLIMIT_NOFILE or temporary allocation failures
                         // may be preventing use of poll(), fall back to fcntl
@@ -165,7 +170,14 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     }
 
     unsafe fn reset_sigpipe(#[allow(unused_variables)] sigpipe: u8) {
-        #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia", target_os = "horizon")))]
+        #[cfg(not(any(
+            target_os = "emscripten",
+            target_os = "fuchsia",
+            target_os = "horizon",
+            // Unikraft's `signal` implementation is currently broken:
+            // https://github.com/unikraft/lib-musl/issues/57
+            target_vendor = "unikraft",
+        )))]
         {
             // We don't want to add this as a public type to std, nor do we
             // want to `include!` a file from the compiler (which would break
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index a68c14758..57e1a36da 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -495,6 +495,34 @@ pub struct Env {
     iter: vec::IntoIter<(OsString, OsString)>,
 }
 
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
 impl !Send for Env {}
 impl !Sync for Env {}
 
@@ -566,16 +594,21 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    let s = run_with_cstr(k.as_bytes(), |k| {
+    run_with_cstr(k.as_bytes(), |k| {
         let _guard = env_read_lock();
-        Ok(unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char)
+        let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
+
+        if v.is_null() {
+            Ok(None)
+        } else {
+            // SAFETY: `v` cannot be mutated while executing this line since we've a read lock
+            let bytes = unsafe { CStr::from_ptr(v) }.to_bytes().to_vec();
+
+            Ok(Some(OsStringExt::from_vec(bytes)))
+        }
     })
-    .ok()?;
-    if s.is_null() {
-        None
-    } else {
-        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
-    }
+    .ok()
+    .flatten()
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
diff --git a/library/std/src/sys/unix/os_str.rs b/library/std/src/sys/unix/os_str.rs
index f7333fd5a..463b0a275 100644
--- a/library/std/src/sys/unix/os_str.rs
+++ b/library/std/src/sys/unix/os_str.rs
@@ -96,6 +96,16 @@ impl AsInner<[u8]> for Buf {
 }
 
 impl Buf {
+    #[inline]
+    pub fn into_os_str_bytes(self) -> Vec<u8> {
+        self.inner
+    }
+
+    #[inline]
+    pub unsafe fn from_os_str_bytes_unchecked(s: Vec<u8>) -> Self {
+        Self { inner: s }
+    }
+
     pub fn from_string(s: String) -> Buf {
         Buf { inner: s.into_bytes() }
     }
diff --git a/library/std/src/sys/unix/process/process_fuchsia.rs b/library/std/src/sys/unix/process/process_fuchsia.rs
index e45c380a0..9931c2af2 100644
--- a/library/std/src/sys/unix/process/process_fuchsia.rs
+++ b/library/std/src/sys/unix/process/process_fuchsia.rs
@@ -235,7 +235,7 @@ impl Process {
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
 pub struct ExitStatus(i64);
 
 impl ExitStatus {
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index 0ce93af66..3963e7f52 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -10,9 +10,6 @@ use core::ffi::NonZero_c_int;
 #[cfg(target_os = "linux")]
 use crate::os::linux::process::PidFd;
 
-#[cfg(target_os = "linux")]
-use crate::sys::weak::raw_syscall;
-
 #[cfg(any(
     target_os = "macos",
     target_os = "watchos",
@@ -91,6 +88,11 @@ impl Command {
         if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
             return Ok((ret, ours));
         }
+
+        #[cfg(target_os = "linux")]
+        let (input, output) = sys::net::Socket::new_pair(libc::AF_UNIX, libc::SOCK_SEQPACKET)?;
+
+        #[cfg(not(target_os = "linux"))]
         let (input, output) = sys::pipe::anon_pipe()?;
 
         // Whatever happens after the fork is almost for sure going to touch or
@@ -104,12 +106,16 @@ impl Command {
         // The child calls `mem::forget` to leak the lock, which is crucial because
         // releasing a lock is not async-signal-safe.
         let env_lock = sys::os::env_read_lock();
-        let (pid, pidfd) = unsafe { self.do_fork()? };
+        let pid = unsafe { self.do_fork()? };
 
         if pid == 0 {
             crate::panic::always_abort();
             mem::forget(env_lock); // avoid non-async-signal-safe unlocking
             drop(input);
+            #[cfg(target_os = "linux")]
+            if self.get_create_pidfd() {
+                self.send_pidfd(&output);
+            }
             let Err(err) = unsafe { self.do_exec(theirs, envp.as_ref()) };
             let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
             let errno = errno.to_be_bytes();
@@ -133,6 +139,12 @@ impl Command {
         drop(env_lock);
         drop(output);
 
+        #[cfg(target_os = "linux")]
+        let pidfd = if self.get_create_pidfd() { self.recv_pidfd(&input) } else { -1 };
+
+        #[cfg(not(target_os = "linux"))]
+        let pidfd = -1;
+
         // Safety: We obtained the pidfd from calling `clone3` with
         // `CLONE_PIDFD` so it's valid an otherwise unowned.
         let mut p = unsafe { Process::new(pid, pidfd) };
@@ -160,6 +172,7 @@ impl Command {
                 }
                 Ok(..) => {
                     // pipe I/O up to PIPE_BUF bytes should be atomic
+                    // similarly SOCK_SEQPACKET messages should arrive whole
                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
                     panic!("short read on the CLOEXEC pipe")
                 }
@@ -185,20 +198,19 @@ impl Command {
     );
 
     #[cfg(any(target_os = "tvos", target_os = "watchos"))]
-    unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
+    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
     }
 
     // Attempts to fork the process. If successful, returns Ok((0, -1))
     // in the child, and Ok((child_pid, -1)) in the parent.
     #[cfg(not(any(
-        target_os = "linux",
         target_os = "watchos",
         target_os = "tvos",
         all(target_os = "nto", target_env = "nto71"),
     )))]
-    unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
-        cvt(libc::fork()).map(|res| (res, -1))
+    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
+        cvt(libc::fork())
     }
 
     // On QNX Neutrino, fork can fail with EBADF in case "another thread might have opened
@@ -206,7 +218,7 @@ impl Command {
     // Documentation says "... or try calling fork() again". This is what we do here.
     // See also https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/f/fork.html
     #[cfg(all(target_os = "nto", target_env = "nto71"))]
-    unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
+    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         use crate::sys::os::errno;
 
         let mut delay = MIN_FORKSPAWN_SLEEP;
@@ -229,91 +241,11 @@ impl Command {
                 delay *= 2;
                 continue;
             } else {
-                return cvt(r).map(|res| (res, -1));
+                return cvt(r);
             }
         }
     }
 
-    // Attempts to fork the process. If successful, returns Ok((0, -1))
-    // in the child, and Ok((child_pid, child_pidfd)) in the parent.
-    #[cfg(target_os = "linux")]
-    unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> {
-        use crate::sync::atomic::{AtomicBool, Ordering};
-
-        static HAS_CLONE3: AtomicBool = AtomicBool::new(true);
-        const CLONE_PIDFD: u64 = 0x00001000;
-
-        #[repr(C)]
-        struct clone_args {
-            flags: u64,
-            pidfd: u64,
-            child_tid: u64,
-            parent_tid: u64,
-            exit_signal: u64,
-            stack: u64,
-            stack_size: u64,
-            tls: u64,
-            set_tid: u64,
-            set_tid_size: u64,
-            cgroup: u64,
-        }
-
-        raw_syscall! {
-            fn clone3(cl_args: *mut clone_args, len: libc::size_t) -> libc::c_long
-        }
-
-        // Bypassing libc for `clone3` can make further libc calls unsafe,
-        // so we use it sparingly for now. See #89522 for details.
-        // Some tools (e.g. sandboxing tools) may also expect `fork`
-        // rather than `clone3`.
-        let want_clone3_pidfd = self.get_create_pidfd();
-
-        // If we fail to create a pidfd for any reason, this will
-        // stay as -1, which indicates an error.
-        let mut pidfd: pid_t = -1;
-
-        // Attempt to use the `clone3` syscall, which supports more arguments
-        // (in particular, the ability to create a pidfd). If this fails,
-        // we will fall through this block to a call to `fork()`
-        if want_clone3_pidfd && HAS_CLONE3.load(Ordering::Relaxed) {
-            let mut args = clone_args {
-                flags: CLONE_PIDFD,
-                pidfd: &mut pidfd as *mut pid_t as u64,
-                child_tid: 0,
-                parent_tid: 0,
-                exit_signal: libc::SIGCHLD as u64,
-                stack: 0,
-                stack_size: 0,
-                tls: 0,
-                set_tid: 0,
-                set_tid_size: 0,
-                cgroup: 0,
-            };
-
-            let args_ptr = &mut args as *mut clone_args;
-            let args_size = crate::mem::size_of::<clone_args>();
-
-            let res = cvt(clone3(args_ptr, args_size));
-            match res {
-                Ok(n) => return Ok((n as pid_t, pidfd)),
-                Err(e) => match e.raw_os_error() {
-                    // Multiple threads can race to execute this store,
-                    // but that's fine - that just means that multiple threads
-                    // will have tried and failed to execute the same syscall,
-                    // with no other side effects.
-                    Some(libc::ENOSYS) => HAS_CLONE3.store(false, Ordering::Relaxed),
-                    // Fallback to fork if `EPERM` is returned. (e.g. blocked by seccomp)
-                    Some(libc::EPERM) => {}
-                    _ => return Err(e),
-                },
-            }
-        }
-
-        // Generally, we just call `fork`. If we get here after wanting `clone3`,
-        // then the syscall does not exist or we do not have permission to call it.
-        cvt(libc::fork()).map(|res| (res, pidfd))
-    }
-
     pub fn exec(&mut self, default: Stdio) -> io::Error {
         let envp = self.capture_env();
 
@@ -722,6 +654,115 @@ impl Command {
             Ok(Some(p))
         }
     }
+
+    #[cfg(target_os = "linux")]
+    fn send_pidfd(&self, sock: &crate::sys::net::Socket) {
+        use crate::io::IoSlice;
+        use crate::os::fd::RawFd;
+        use crate::sys::cvt_r;
+        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
+
+        unsafe {
+            let child_pid = libc::getpid();
+            // pidfd_open sets CLOEXEC by default
+            let pidfd = libc::syscall(libc::SYS_pidfd_open, child_pid, 0);
+
+            let fds: [c_int; 1] = [pidfd as RawFd];
+
+            const SCM_MSG_LEN: usize = mem::size_of::<[c_int; 1]>();
+
+            #[repr(C)]
+            union Cmsg {
+                buf: [u8; unsafe { CMSG_SPACE(SCM_MSG_LEN as u32) as usize }],
+                _align: libc::cmsghdr,
+            }
+
+            let mut cmsg: Cmsg = mem::zeroed();
+
+            // 0-length message to send through the socket so we can pass along the fd
+            let mut iov = [IoSlice::new(b"")];
+            let mut msg: libc::msghdr = mem::zeroed();
+
+            msg.msg_iov = &mut iov as *mut _ as *mut _;
+            msg.msg_iovlen = 1;
+            msg.msg_controllen = mem::size_of_val(&cmsg.buf) as _;
+            msg.msg_control = &mut cmsg.buf as *mut _ as *mut _;
+
+            // only attach cmsg if we successfully acquired the pidfd
+            if pidfd >= 0 {
+                let hdr = CMSG_FIRSTHDR(&mut msg as *mut _ as *mut _);
+                (*hdr).cmsg_level = SOL_SOCKET;
+                (*hdr).cmsg_type = SCM_RIGHTS;
+                (*hdr).cmsg_len = CMSG_LEN(SCM_MSG_LEN as _) as _;
+                let data = CMSG_DATA(hdr);
+                crate::ptr::copy_nonoverlapping(
+                    fds.as_ptr().cast::<u8>(),
+                    data as *mut _,
+                    SCM_MSG_LEN,
+                );
+            }
+
+            // we send the 0-length message even if we failed to acquire the pidfd
+            // so we get a consistent SEQPACKET order
+            match cvt_r(|| libc::sendmsg(sock.as_raw(), &msg, 0)) {
+                Ok(0) => {}
+                _ => rtabort!("failed to communicate with parent process"),
+            }
+        }
+    }
+
+    #[cfg(target_os = "linux")]
+    fn recv_pidfd(&self, sock: &crate::sys::net::Socket) -> pid_t {
+        use crate::io::IoSliceMut;
+        use crate::sys::cvt_r;
+
+        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
+
+        unsafe {
+            const SCM_MSG_LEN: usize = mem::size_of::<[c_int; 1]>();
+
+            #[repr(C)]
+            union Cmsg {
+                _buf: [u8; unsafe { CMSG_SPACE(SCM_MSG_LEN as u32) as usize }],
+                _align: libc::cmsghdr,
+            }
+            let mut cmsg: Cmsg = mem::zeroed();
+            // 0-length read to get the fd
+            let mut iov = [IoSliceMut::new(&mut [])];
+
+            let mut msg: libc::msghdr = mem::zeroed();
+
+            msg.msg_iov = &mut iov as *mut _ as *mut _;
+            msg.msg_iovlen = 1;
+            msg.msg_controllen = mem::size_of::<Cmsg>() as _;
+            msg.msg_control = &mut cmsg as *mut _ as *mut _;
+
+            match cvt_r(|| libc::recvmsg(sock.as_raw(), &mut msg, 0)) {
+                Err(_) => return -1,
+                Ok(_) => {}
+            }
+
+            let hdr = CMSG_FIRSTHDR(&mut msg as *mut _ as *mut _);
+            if hdr.is_null()
+                || (*hdr).cmsg_level != SOL_SOCKET
+                || (*hdr).cmsg_type != SCM_RIGHTS
+                || (*hdr).cmsg_len != CMSG_LEN(SCM_MSG_LEN as _) as _
+            {
+                return -1;
+            }
+            let data = CMSG_DATA(hdr);
+
+            let mut fds = [-1 as c_int];
+
+            crate::ptr::copy_nonoverlapping(
+                data as *const _,
+                fds.as_mut_ptr().cast::<u8>(),
+                SCM_MSG_LEN,
+            );
+
+            fds[0]
+        }
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -800,7 +841,7 @@ impl Process {
 //
 // This is not actually an "exit status" in Unix terminology.  Rather, it is a "wait status".
 // See the discussion in comments and doc comments for `std::process::ExitStatus`.
-#[derive(PartialEq, Eq, Clone, Copy)]
+#[derive(PartialEq, Eq, Clone, Copy, Default)]
 pub struct ExitStatus(c_int);
 
 impl fmt::Debug for ExitStatus {
diff --git a/library/std/src/sys/unix/process/process_unix/tests.rs b/library/std/src/sys/unix/process/process_unix/tests.rs
index e5e1f956b..6aa79e7f9 100644
--- a/library/std/src/sys/unix/process/process_unix/tests.rs
+++ b/library/std/src/sys/unix/process/process_unix/tests.rs
@@ -60,3 +60,28 @@ fn test_command_fork_no_unwind() {
             || signal == libc::SIGSEGV
     );
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_command_pidfd() {
+    use crate::os::fd::RawFd;
+    use crate::os::linux::process::{ChildExt, CommandExt};
+    use crate::process::Command;
+
+    let our_pid = crate::process::id();
+    let pidfd = unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) };
+    let pidfd_open_available = if pidfd >= 0 {
+        unsafe { libc::close(pidfd as RawFd) };
+        true
+    } else {
+        false
+    };
+
+    // always exercise creation attempts
+    let child = Command::new("echo").create_pidfd(true).spawn().unwrap();
+
+    // but only check if we know that the kernel supports pidfds
+    if pidfd_open_available {
+        assert!(child.pidfd().is_ok())
+    }
+}
diff --git a/library/std/src/sys/unix/process/process_unsupported.rs b/library/std/src/sys/unix/process/process_unsupported.rs
index f28ca58d0..8e0b971af 100644
--- a/library/std/src/sys/unix/process/process_unsupported.rs
+++ b/library/std/src/sys/unix/process/process_unsupported.rs
@@ -55,7 +55,7 @@ impl Process {
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
 pub struct ExitStatus(c_int);
 
 impl ExitStatus {
diff --git a/library/std/src/sys/unix/process/process_vxworks.rs b/library/std/src/sys/unix/process/process_vxworks.rs
index f70d3cb39..1ff2b2fb3 100644
--- a/library/std/src/sys/unix/process/process_vxworks.rs
+++ b/library/std/src/sys/unix/process/process_vxworks.rs
@@ -179,7 +179,7 @@ impl Process {
 }
 
 /// Unix exit statuses
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
 pub struct ExitStatus(c_int);
 
 impl ExitStatus {
diff --git a/library/std/src/sys/unix/rand.rs b/library/std/src/sys/unix/rand.rs
index d471be33e..fbf158f56 100644
--- a/library/std/src/sys/unix/rand.rs
+++ b/library/std/src/sys/unix/rand.rs
@@ -17,7 +17,6 @@ pub fn hashmap_random_keys() -> (u64, u64) {
     not(target_os = "tvos"),
     not(target_os = "watchos"),
     not(target_os = "openbsd"),
-    not(target_os = "freebsd"),
     not(target_os = "netbsd"),
     not(target_os = "fuchsia"),
     not(target_os = "redox"),
@@ -68,11 +67,25 @@ mod imp {
         unsafe { libc::getrandom(buf.as_mut_ptr().cast(), buf.len(), 0) }
     }
 
+    #[cfg(target_os = "freebsd")]
+    fn getrandom(buf: &mut [u8]) -> libc::ssize_t {
+        // FIXME: using the above when libary std's libc is updated
+        extern "C" {
+            fn getrandom(
+                buffer: *mut libc::c_void,
+                length: libc::size_t,
+                flags: libc::c_uint,
+            ) -> libc::ssize_t;
+        }
+        unsafe { getrandom(buf.as_mut_ptr().cast(), buf.len(), 0) }
+    }
+
     #[cfg(not(any(
         target_os = "linux",
         target_os = "android",
         target_os = "espidf",
-        target_os = "horizon"
+        target_os = "horizon",
+        target_os = "freebsd"
     )))]
     fn getrandom_fill_bytes(_buf: &mut [u8]) -> bool {
         false
@@ -82,7 +95,8 @@ mod imp {
         target_os = "linux",
         target_os = "android",
         target_os = "espidf",
-        target_os = "horizon"
+        target_os = "horizon",
+        target_os = "freebsd"
     ))]
     fn getrandom_fill_bytes(v: &mut [u8]) -> bool {
         use crate::sync::atomic::{AtomicBool, Ordering};
@@ -222,7 +236,7 @@ mod imp {
     }
 }
 
-#[cfg(any(target_os = "freebsd", target_os = "netbsd"))]
+#[cfg(target_os = "netbsd")]
 mod imp {
     use crate::ptr;
 
diff --git a/library/std/src/sys/unix/stdio.rs b/library/std/src/sys/unix/stdio.rs
index a26f20795..97e75f1b5 100644
--- a/library/std/src/sys/unix/stdio.rs
+++ b/library/std/src/sys/unix/stdio.rs
@@ -54,6 +54,7 @@ impl io::Write for Stdout {
         true
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }
@@ -81,6 +82,7 @@ impl io::Write for Stderr {
         true
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }
diff --git a/library/std/src/sys/unsupported/os.rs b/library/std/src/sys/unsupported/os.rs
index e150ae143..248b34829 100644
--- a/library/std/src/sys/unsupported/os.rs
+++ b/library/std/src/sys/unsupported/os.rs
@@ -65,10 +65,26 @@ pub fn current_exe() -> io::Result<PathBuf> {
 
 pub struct Env(!);
 
+impl Env {
+    // FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self(inner) = self;
+        match *inner {}
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self(inner) = self;
+        match *inner {}
+    }
+}
+
 impl Iterator for Env {
     type Item = (OsString, OsString);
     fn next(&mut self) -> Option<(OsString, OsString)> {
-        self.0
+        let Self(inner) = self;
+        match *inner {}
     }
 }
 
diff --git a/library/std/src/sys/unsupported/process.rs b/library/std/src/sys/unsupported/process.rs
index a494f2d6b..77b675aaa 100644
--- a/library/std/src/sys/unsupported/process.rs
+++ b/library/std/src/sys/unsupported/process.rs
@@ -99,58 +99,59 @@ impl fmt::Debug for Command {
     }
 }
 
-pub struct ExitStatus(!);
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
+#[non_exhaustive]
+pub struct ExitStatus();
 
 impl ExitStatus {
     pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
-        self.0
+        Ok(())
     }
 
     pub fn code(&self) -> Option<i32> {
-        self.0
+        Some(0)
     }
 }
 
-impl Clone for ExitStatus {
-    fn clone(&self) -> ExitStatus {
-        self.0
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "<dummy exit status>")
     }
 }
 
-impl Copy for ExitStatus {}
+pub struct ExitStatusError(!);
 
-impl PartialEq for ExitStatus {
-    fn eq(&self, _other: &ExitStatus) -> bool {
+impl Clone for ExitStatusError {
+    fn clone(&self) -> ExitStatusError {
         self.0
     }
 }
 
-impl Eq for ExitStatus {}
+impl Copy for ExitStatusError {}
 
-impl fmt::Debug for ExitStatus {
-    fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl PartialEq for ExitStatusError {
+    fn eq(&self, _other: &ExitStatusError) -> bool {
         self.0
     }
 }
 
-impl fmt::Display for ExitStatus {
+impl Eq for ExitStatusError {}
+
+impl fmt::Debug for ExitStatusError {
     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.0
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
-pub struct ExitStatusError(ExitStatus);
-
 impl Into<ExitStatus> for ExitStatusError {
     fn into(self) -> ExitStatus {
-        self.0.0
+        self.0
     }
 }
 
 impl ExitStatusError {
     pub fn code(self) -> Option<NonZeroI32> {
-        self.0.0
+        self.0
     }
 }
 
diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index 1b50c2ea6..d7295a799 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -16,14 +16,20 @@ pub struct WasiFd {
 fn iovec<'a>(a: &'a mut [IoSliceMut<'_>]) -> &'a [wasi::Iovec] {
     assert_eq!(mem::size_of::<IoSliceMut<'_>>(), mem::size_of::<wasi::Iovec>());
     assert_eq!(mem::align_of::<IoSliceMut<'_>>(), mem::align_of::<wasi::Iovec>());
-    // SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout
+    // SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout.
+    // We decorate our `IoSliceMut` with `repr(transparent)` (see `io.rs`), and
+    // `crate::io::IoSliceMut` is a `repr(transparent)` wrapper around our type, so this is
+    // guaranteed.
     unsafe { mem::transmute(a) }
 }
 
 fn ciovec<'a>(a: &'a [IoSlice<'_>]) -> &'a [wasi::Ciovec] {
     assert_eq!(mem::size_of::<IoSlice<'_>>(), mem::size_of::<wasi::Ciovec>());
     assert_eq!(mem::align_of::<IoSlice<'_>>(), mem::align_of::<wasi::Ciovec>());
-    // SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout
+    // SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout.
+    // We decorate our `IoSlice` with `repr(transparent)` (see `io.rs`), and
+    // `crate::io::IoSlice` is a `repr(transparent)` wrapper around our type, so this is
+    // guaranteed.
     unsafe { mem::transmute(a) }
 }
 
diff --git a/library/std/src/sys/wasi/mod.rs b/library/std/src/sys/wasi/mod.rs
index a22237080..98517da1d 100644
--- a/library/std/src/sys/wasi/mod.rs
+++ b/library/std/src/sys/wasi/mod.rs
@@ -29,8 +29,7 @@ pub mod fs;
 #[path = "../wasm/atomics/futex.rs"]
 pub mod futex;
 pub mod io;
-#[path = "../unsupported/locks/mod.rs"]
-pub mod locks;
+
 pub mod net;
 pub mod os;
 #[path = "../unix/os_str.rs"]
@@ -47,14 +46,27 @@ pub mod thread;
 pub mod thread_local_dtor;
 #[path = "../unsupported/thread_local_key.rs"]
 pub mod thread_local_key;
-#[path = "../unsupported/thread_parking.rs"]
-pub mod thread_parking;
 pub mod time;
 
 cfg_if::cfg_if! {
-    if #[cfg(not(target_feature = "atomics"))] {
+    if #[cfg(target_feature = "atomics")] {
+        #[path = "../unix/locks"]
+        pub mod locks {
+            #![allow(unsafe_op_in_unsafe_fn)]
+            mod futex_condvar;
+            mod futex_mutex;
+            mod futex_rwlock;
+            pub(crate) use futex_condvar::Condvar;
+            pub(crate) use futex_mutex::Mutex;
+            pub(crate) use futex_rwlock::RwLock;
+        }
+    } else {
+        #[path = "../unsupported/locks/mod.rs"]
+        pub mod locks;
         #[path = "../unsupported/once.rs"]
         pub mod once;
+        #[path = "../unsupported/thread_parking.rs"]
+        pub mod thread_parking;
     }
 }
 
diff --git a/library/std/src/sys/wasi/os.rs b/library/std/src/sys/wasi/os.rs
index 9919dc708..d53bddd8e 100644
--- a/library/std/src/sys/wasi/os.rs
+++ b/library/std/src/sys/wasi/os.rs
@@ -142,10 +142,39 @@ impl StdError for JoinPathsError {
 pub fn current_exe() -> io::Result<PathBuf> {
     unsupported()
 }
+
 pub struct Env {
     iter: vec::IntoIter<(OsString, OsString)>,
 }
 
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
 impl !Send for Env {}
 impl !Sync for Env {}
 
@@ -196,16 +225,23 @@ pub fn env() -> Env {
 }
 
 pub fn getenv(k: &OsStr) -> Option<OsString> {
-    let s = run_with_cstr(k.as_bytes(), |k| unsafe {
+    // environment variables with a nul byte can't be set, so their value is
+    // always None as well
+    run_with_cstr(k.as_bytes(), |k| {
         let _guard = env_read_lock();
-        Ok(libc::getenv(k.as_ptr()) as *const libc::c_char)
+        let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
+
+        if v.is_null() {
+            Ok(None)
+        } else {
+            // SAFETY: `v` cannot be mutated while executing this line since we've a read lock
+            let bytes = unsafe { CStr::from_ptr(v) }.to_bytes().to_vec();
+
+            Ok(Some(OsStringExt::from_vec(bytes)))
+        }
     })
-    .ok()?;
-    if s.is_null() {
-        None
-    } else {
-        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
-    }
+    .ok()
+    .flatten()
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
@@ -224,6 +260,11 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     })
 }
 
+#[allow(dead_code)]
+pub fn page_size() -> usize {
+    unsafe { libc::sysconf(libc::_SC_PAGESIZE) as usize }
+}
+
 pub fn temp_dir() -> PathBuf {
     panic!("no filesystem on wasm")
 }
diff --git a/library/std/src/sys/wasi/thread.rs b/library/std/src/sys/wasi/thread.rs
index e7a6ab4be..a0eefa881 100644
--- a/library/std/src/sys/wasi/thread.rs
+++ b/library/std/src/sys/wasi/thread.rs
@@ -1,5 +1,3 @@
-#![deny(unsafe_op_in_unsafe_fn)]
-
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
@@ -7,14 +5,124 @@ use crate::num::NonZeroUsize;
 use crate::sys::unsupported;
 use crate::time::Duration;
 
-pub struct Thread(!);
+cfg_if::cfg_if! {
+    if #[cfg(target_feature = "atomics")] {
+        use crate::cmp;
+        use crate::ptr;
+        use crate::sys::os;
+        // Add a few symbols not in upstream `libc` just yet.
+        mod libc {
+            pub use crate::ffi;
+            pub use crate::mem;
+            pub use libc::*;
+
+            // defined in wasi-libc
+            // https://github.com/WebAssembly/wasi-libc/blob/a6f871343313220b76009827ed0153586361c0d5/libc-top-half/musl/include/alltypes.h.in#L108
+            #[repr(C)]
+            union pthread_attr_union {
+                __i: [ffi::c_int; if mem::size_of::<ffi::c_long>() == 8 { 14 } else { 9 }],
+                __vi: [ffi::c_int; if mem::size_of::<ffi::c_long>() == 8 { 14 } else { 9 }],
+                __s: [ffi::c_ulong; if mem::size_of::<ffi::c_long>() == 8 { 7 } else { 9 }],
+            }
+
+            #[repr(C)]
+            pub struct pthread_attr_t {
+                __u: pthread_attr_union,
+            }
+
+            #[allow(non_camel_case_types)]
+            pub type pthread_t = *mut ffi::c_void;
+
+            extern "C" {
+                pub fn pthread_create(
+                    native: *mut pthread_t,
+                    attr: *const pthread_attr_t,
+                    f: extern "C" fn(*mut ffi::c_void) -> *mut ffi::c_void,
+                    value: *mut ffi::c_void,
+                ) -> ffi::c_int;
+                pub fn pthread_join(native: pthread_t, value: *mut *mut ffi::c_void) -> ffi::c_int;
+                pub fn pthread_attr_init(attrp: *mut pthread_attr_t) -> ffi::c_int;
+                pub fn pthread_attr_setstacksize(
+                    attr: *mut pthread_attr_t,
+                    stack_size: libc::size_t,
+                ) -> ffi::c_int;
+                pub fn pthread_attr_destroy(attr: *mut pthread_attr_t) -> ffi::c_int;
+                pub fn pthread_detach(thread: pthread_t) -> ffi::c_int;
+            }
+        }
+
+        pub struct Thread {
+            id: libc::pthread_t,
+        }
+
+        impl Drop for Thread {
+            fn drop(&mut self) {
+                let ret = unsafe { libc::pthread_detach(self.id) };
+                debug_assert_eq!(ret, 0);
+            }
+        }
+    } else {
+        pub struct Thread(!);
+    }
+}
 
 pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
-        unsupported()
+    cfg_if::cfg_if! {
+        if #[cfg(target_feature = "atomics")] {
+            pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+                let p = Box::into_raw(Box::new(p));
+                let mut native: libc::pthread_t = mem::zeroed();
+                let mut attr: libc::pthread_attr_t = mem::zeroed();
+                assert_eq!(libc::pthread_attr_init(&mut attr), 0);
+
+                let stack_size = cmp::max(stack, DEFAULT_MIN_STACK_SIZE);
+
+                match libc::pthread_attr_setstacksize(&mut attr, stack_size) {
+                    0 => {}
+                    n => {
+                        assert_eq!(n, libc::EINVAL);
+                        // EINVAL means |stack_size| is either too small or not a
+                        // multiple of the system page size. Because it's definitely
+                        // >= PTHREAD_STACK_MIN, it must be an alignment issue.
+                        // Round up to the nearest page and try again.
+                        let page_size = os::page_size();
+                        let stack_size =
+                            (stack_size + page_size - 1) & (-(page_size as isize - 1) as usize - 1);
+                        assert_eq!(libc::pthread_attr_setstacksize(&mut attr, stack_size), 0);
+                    }
+                };
+
+                let ret = libc::pthread_create(&mut native, &attr, thread_start, p as *mut _);
+                // Note: if the thread creation fails and this assert fails, then p will
+                // be leaked. However, an alternative design could cause double-free
+                // which is clearly worse.
+                assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+
+                return if ret != 0 {
+                    // The thread failed to start and as a result p was not consumed. Therefore, it is
+                    // safe to reconstruct the box so that it gets deallocated.
+                    drop(Box::from_raw(p));
+                    Err(io::Error::from_raw_os_error(ret))
+                } else {
+                    Ok(Thread { id: native })
+                };
+
+                extern "C" fn thread_start(main: *mut libc::c_void) -> *mut libc::c_void {
+                    unsafe {
+                        // Finally, let's run some code.
+                        Box::from_raw(main as *mut Box<dyn FnOnce()>)();
+                    }
+                    ptr::null_mut()
+                }
+            }
+        } else {
+            pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+                unsupported()
+            }
+        }
     }
 
     pub fn yield_now() {
@@ -62,7 +170,19 @@ impl Thread {
     }
 
     pub fn join(self) {
-        self.0
+        cfg_if::cfg_if! {
+            if #[cfg(target_feature = "atomics")] {
+                unsafe {
+                    let ret = libc::pthread_join(self.id, ptr::null_mut());
+                    mem::forget(self);
+                    if ret != 0 {
+                        rtabort!("failed to join thread: {}", io::Error::from_raw_os_error(ret));
+                    }
+                }
+            } else {
+                self.0
+            }
+        }
     }
 }
 
diff --git a/library/std/src/sys/windows/cmath.rs b/library/std/src/sys/windows/cmath.rs
index 43ab8c7ee..1b2a86f3c 100644
--- a/library/std/src/sys/windows/cmath.rs
+++ b/library/std/src/sys/windows/cmath.rs
@@ -1,6 +1,6 @@
 #![cfg(not(test))]
 
-use libc::{c_double, c_float};
+use libc::{c_double, c_float, c_int};
 
 extern "C" {
     pub fn acos(n: c_double) -> c_double;
@@ -23,6 +23,10 @@ extern "C" {
     pub fn sinh(n: c_double) -> c_double;
     pub fn tan(n: c_double) -> c_double;
     pub fn tanh(n: c_double) -> c_double;
+    pub fn tgamma(n: c_double) -> c_double;
+    pub fn tgammaf(n: c_float) -> c_float;
+    pub fn lgamma_r(n: c_double, s: &mut c_int) -> c_double;
+    pub fn lgammaf_r(n: c_float, s: &mut c_int) -> c_float;
 }
 
 pub use self::shims::*;
diff --git a/library/std/src/sys/windows/compat.rs b/library/std/src/sys/windows/compat.rs
index 4fe95d411..e28dd4935 100644
--- a/library/std/src/sys/windows/compat.rs
+++ b/library/std/src/sys/windows/compat.rs
@@ -69,10 +69,7 @@ unsafe extern "C" fn init() {
 
 /// Helper macro for creating CStrs from literals and symbol names.
 macro_rules! ansi_str {
-    (sym $ident:ident) => {{
-        #[allow(unused_unsafe)]
-        crate::sys::compat::const_cstr_from_bytes(concat!(stringify!($ident), "\0").as_bytes())
-    }};
+    (sym $ident:ident) => {{ crate::sys::compat::const_cstr_from_bytes(concat!(stringify!($ident), "\0").as_bytes()) }};
     ($lit:literal) => {{ crate::sys::compat::const_cstr_from_bytes(concat!($lit, "\0").as_bytes()) }};
 }
 
diff --git a/library/std/src/sys/windows/os.rs b/library/std/src/sys/windows/os.rs
index d7adeb266..58afca088 100644
--- a/library/std/src/sys/windows/os.rs
+++ b/library/std/src/sys/windows/os.rs
@@ -25,10 +25,6 @@ pub fn errno() -> i32 {
 
 /// Gets a detailed string description for the given error number.
 pub fn error_string(mut errnum: i32) -> String {
-    // This value is calculated from the macro
-    // MAKELANGID(LANG_SYSTEM_DEFAULT, SUBLANG_SYS_DEFAULT)
-    let langId = 0x0800 as c::DWORD;
-
     let mut buf = [0 as c::WCHAR; 2048];
 
     unsafe {
@@ -56,13 +52,13 @@ pub fn error_string(mut errnum: i32) -> String {
             flags | c::FORMAT_MESSAGE_FROM_SYSTEM | c::FORMAT_MESSAGE_IGNORE_INSERTS,
             module,
             errnum as c::DWORD,
-            langId,
+            0,
             buf.as_mut_ptr(),
             buf.len() as c::DWORD,
             ptr::null(),
         ) as usize;
         if res == 0 {
-            // Sometimes FormatMessageW can fail e.g., system doesn't like langId,
+            // Sometimes FormatMessageW can fail e.g., system doesn't like 0 as langId,
             let fm_err = errno();
             return format!("OS Error {errnum} (FormatMessageW() returned error {fm_err})");
         }
@@ -85,25 +81,69 @@ pub fn error_string(mut errnum: i32) -> String {
 
 pub struct Env {
     base: c::LPWCH,
-    cur: c::LPWCH,
+    iter: EnvIterator,
+}
+
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    iter: &'a EnvIterator,
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        let iter: EnvIterator = (*iter).clone();
+        let mut list = f.debug_list();
+        for (a, b) in iter {
+            list.entry(&(a.to_str().unwrap(), b.to_str().unwrap()));
+        }
+        list.finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { base: _, iter } = self;
+        EnvStrDebug { iter }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { base: _, iter } = self;
+        f.debug_list().entries(iter.clone()).finish()
+    }
 }
 
 impl Iterator for Env {
     type Item = (OsString, OsString);
 
     fn next(&mut self) -> Option<(OsString, OsString)> {
+        let Self { base: _, iter } = self;
+        iter.next()
+    }
+}
+
+#[derive(Clone)]
+struct EnvIterator(c::LPWCH);
+
+impl Iterator for EnvIterator {
+    type Item = (OsString, OsString);
+
+    fn next(&mut self) -> Option<(OsString, OsString)> {
+        let Self(cur) = self;
         loop {
             unsafe {
-                if *self.cur == 0 {
+                if **cur == 0 {
                     return None;
                 }
-                let p = self.cur as *const u16;
+                let p = *cur as *const u16;
                 let mut len = 0;
                 while *p.add(len) != 0 {
                     len += 1;
                 }
                 let s = slice::from_raw_parts(p, len);
-                self.cur = self.cur.add(len + 1);
+                *cur = cur.add(len + 1);
 
                 // Windows allows environment variables to start with an equals
                 // symbol (in any other position, this is the separator between
@@ -137,7 +177,7 @@ pub fn env() -> Env {
         if ch.is_null() {
             panic!("failure getting env string from OS: {}", io::Error::last_os_error());
         }
-        Env { base: ch, cur: ch }
+        Env { base: ch, iter: EnvIterator(ch) }
     }
 }
 
diff --git a/library/std/src/sys/windows/os_str.rs b/library/std/src/sys/windows/os_str.rs
index 16c4f55c6..4708657a9 100644
--- a/library/std/src/sys/windows/os_str.rs
+++ b/library/std/src/sys/windows/os_str.rs
@@ -63,6 +63,16 @@ impl fmt::Display for Slice {
 }
 
 impl Buf {
+    #[inline]
+    pub fn into_os_str_bytes(self) -> Vec<u8> {
+        self.inner.into_bytes()
+    }
+
+    #[inline]
+    pub unsafe fn from_os_str_bytes_unchecked(s: Vec<u8>) -> Self {
+        Self { inner: Wtf8Buf::from_bytes_unchecked(s) }
+    }
+
     pub fn with_capacity(capacity: usize) -> Buf {
         Buf { inner: Wtf8Buf::with_capacity(capacity) }
     }
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index e3493cbb8..2dd0c67ac 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -652,7 +652,7 @@ impl Process {
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
 pub struct ExitStatus(c::DWORD);
 
 impl ExitStatus {
diff --git a/library/std/src/sys/windows/thread_local_dtor.rs b/library/std/src/sys/windows/thread_local_dtor.rs
index 9707a95df..cf542d2bf 100644
--- a/library/std/src/sys/windows/thread_local_dtor.rs
+++ b/library/std/src/sys/windows/thread_local_dtor.rs
@@ -4,29 +4,4 @@
 #![unstable(feature = "thread_local_internals", issue = "none")]
 #![cfg(target_thread_local)]
 
-// Using a per-thread list avoids the problems in synchronizing global state.
-#[thread_local]
-static mut DESTRUCTORS: Vec<(*mut u8, unsafe extern "C" fn(*mut u8))> = Vec::new();
-
-// Ensure this can never be inlined because otherwise this may break in dylibs.
-// See #44391.
-#[inline(never)]
-pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
-    DESTRUCTORS.push((t, dtor));
-}
-
-#[inline(never)] // See comment above
-/// Runs destructors. This should not be called until thread exit.
-pub unsafe fn run_keyless_dtors() {
-    // Drop all the destructors.
-    //
-    // Note: While this is potentially an infinite loop, it *should* be
-    // the case that this loop always terminates because we provide the
-    // guarantee that a TLS key cannot be set after it is flagged for
-    // destruction.
-    while let Some((ptr, dtor)) = DESTRUCTORS.pop() {
-        (dtor)(ptr);
-    }
-    // We're done so free the memory.
-    DESTRUCTORS = Vec::new();
-}
+pub use super::thread_local_key::register_keyless_dtor as register_dtor;
diff --git a/library/std/src/sys/windows/thread_local_key.rs b/library/std/src/sys/windows/thread_local_key.rs
index 17628b757..036d96596 100644
--- a/library/std/src/sys/windows/thread_local_key.rs
+++ b/library/std/src/sys/windows/thread_local_key.rs
@@ -1,7 +1,7 @@
 use crate::cell::UnsafeCell;
 use crate::ptr;
 use crate::sync::atomic::{
-    AtomicPtr, AtomicU32,
+    AtomicBool, AtomicPtr, AtomicU32,
     Ordering::{AcqRel, Acquire, Relaxed, Release},
 };
 use crate::sys::c;
@@ -9,6 +9,41 @@ use crate::sys::c;
 #[cfg(test)]
 mod tests;
 
+/// An optimization hint. The compiler is often smart enough to know if an atomic
+/// is never set and can remove dead code based on that fact.
+static HAS_DTORS: AtomicBool = AtomicBool::new(false);
+
+// Using a per-thread list avoids the problems in synchronizing global state.
+#[thread_local]
+#[cfg(target_thread_local)]
+static mut DESTRUCTORS: Vec<(*mut u8, unsafe extern "C" fn(*mut u8))> = Vec::new();
+
+// Ensure this can never be inlined because otherwise this may break in dylibs.
+// See #44391.
+#[inline(never)]
+#[cfg(target_thread_local)]
+pub unsafe fn register_keyless_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
+    DESTRUCTORS.push((t, dtor));
+    HAS_DTORS.store(true, Relaxed);
+}
+
+#[inline(never)] // See comment above
+#[cfg(target_thread_local)]
+/// Runs destructors. This should not be called until thread exit.
+unsafe fn run_keyless_dtors() {
+    // Drop all the destructors.
+    //
+    // Note: While this is potentially an infinite loop, it *should* be
+    // the case that this loop always terminates because we provide the
+    // guarantee that a TLS key cannot be set after it is flagged for
+    // destruction.
+    while let Some((ptr, dtor)) = DESTRUCTORS.pop() {
+        (dtor)(ptr);
+    }
+    // We're done so free the memory.
+    DESTRUCTORS = Vec::new();
+}
+
 type Key = c::DWORD;
 type Dtor = unsafe extern "C" fn(*mut u8);
 
@@ -156,6 +191,8 @@ static DTORS: AtomicPtr<StaticKey> = AtomicPtr::new(ptr::null_mut());
 /// Should only be called once per key, otherwise loops or breaks may occur in
 /// the linked list.
 unsafe fn register_dtor(key: &'static StaticKey) {
+    // Ensure this is never run when native thread locals are available.
+    assert_eq!(false, cfg!(target_thread_local));
     let this = <*const StaticKey>::cast_mut(key);
     // Use acquire ordering to pass along the changes done by the previously
     // registered keys when we store the new head with release ordering.
@@ -167,6 +204,7 @@ unsafe fn register_dtor(key: &'static StaticKey) {
             Err(new) => head = new,
         }
     }
+    HAS_DTORS.store(true, Release);
 }
 
 // -------------------------------------------------------------------------
@@ -240,10 +278,14 @@ pub static p_thread_callback: unsafe extern "system" fn(c::LPVOID, c::DWORD, c::
 
 #[allow(dead_code, unused_variables)]
 unsafe extern "system" fn on_tls_callback(h: c::LPVOID, dwReason: c::DWORD, pv: c::LPVOID) {
+    if !HAS_DTORS.load(Acquire) {
+        return;
+    }
     if dwReason == c::DLL_THREAD_DETACH || dwReason == c::DLL_PROCESS_DETACH {
+        #[cfg(not(target_thread_local))]
         run_dtors();
         #[cfg(target_thread_local)]
-        super::thread_local_dtor::run_keyless_dtors();
+        run_keyless_dtors();
     }
 
     // See comments above for what this is doing. Note that we don't need this
diff --git a/library/std/src/sys/windows/thread_local_key/tests.rs b/library/std/src/sys/windows/thread_local_key/tests.rs
index c95f383fb..c739f0caf 100644
--- a/library/std/src/sys/windows/thread_local_key/tests.rs
+++ b/library/std/src/sys/windows/thread_local_key/tests.rs
@@ -1,3 +1,7 @@
+// This file only tests the thread local key fallback.
+// Windows targets with native thread local support do not use this.
+#![cfg(not(target_thread_local))]
+
 use super::StaticKey;
 use crate::ptr;