std: move process implementations to `sys`

As per #117276, this moves the implementations of `Process` and friends out of the `pal` module and into the `sys` module, removing quite a lot of error-prone `#[path]` imports in the process (hah, get it ;-)). I've also made the `zircon` module a dedicated submodule of `pal::unix`, hopefully we can move some other definitions there as well (they are currently quite a lot of duplications in `sys`). Also, the `ensure_no_nuls` function on Windows now lives in `sys::pal::windows` – it's not specific to processes and shared by the argument implementation.

10 files changed, 3010 insertions, 0 deletions

diff --git a/library/std/src/sys/process/unix/common.rs b/library/std/src/sys/process/unix/common.rs
new file mode 100644
index 00000000000..8bc17f31491
--- /dev/null
+++ b/library/std/src/sys/process/unix/common.rs
@@ -0,0 +1,674 @@
+#[cfg(all(test, not(target_os = "emscripten")))]
+mod tests;
+
+use libc::{EXIT_FAILURE, EXIT_SUCCESS, c_char, c_int, gid_t, pid_t, uid_t};
+
+use crate::collections::BTreeMap;
+use crate::ffi::{CStr, CString, OsStr, OsString};
+use crate::os::unix::prelude::*;
+use crate::path::Path;
+use crate::sys::fd::FileDesc;
+use crate::sys::fs::File;
+#[cfg(not(target_os = "fuchsia"))]
+use crate::sys::fs::OpenOptions;
+use crate::sys::pipe::{self, AnonPipe};
+use crate::sys_common::process::{CommandEnv, CommandEnvs};
+use crate::sys_common::{FromInner, IntoInner};
+use crate::{fmt, io, ptr};
+
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "fuchsia")] {
+        // fuchsia doesn't have /dev/null
+    } else if #[cfg(target_os = "vxworks")] {
+        const DEV_NULL: &CStr = c"/null";
+    } else {
+        const DEV_NULL: &CStr = c"/dev/null";
+    }
+}
+
+// Android with api less than 21 define sig* functions inline, so it is not
+// available for dynamic link. Implementing sigemptyset and sigaddset allow us
+// to support older Android version (independent of libc version).
+// The following implementations are based on
+// https://github.com/aosp-mirror/platform_bionic/blob/ad8dcd6023294b646e5a8288c0ed431b0845da49/libc/include/android/legacy_signal_inlines.h
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "android")] {
+        #[allow(dead_code)]
+        pub unsafe fn sigemptyset(set: *mut libc::sigset_t) -> libc::c_int {
+            set.write_bytes(0u8, 1);
+            return 0;
+        }
+
+        #[allow(dead_code)]
+        pub unsafe fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int {
+            use crate::slice;
+            use libc::{c_ulong, sigset_t};
+
+            // The implementations from bionic (android libc) type pun `sigset_t` as an
+            // array of `c_ulong`. This works, but lets add a smoke check to make sure
+            // that doesn't change.
+            const _: () = assert!(
+                align_of::<c_ulong>() == align_of::<sigset_t>()
+                    && (size_of::<sigset_t>() % size_of::<c_ulong>()) == 0
+            );
+
+            let bit = (signum - 1) as usize;
+            if set.is_null() || bit >= (8 * size_of::<sigset_t>()) {
+                crate::sys::pal::os::set_errno(libc::EINVAL);
+                return -1;
+            }
+            let raw = slice::from_raw_parts_mut(
+                set as *mut c_ulong,
+                size_of::<sigset_t>() / size_of::<c_ulong>(),
+            );
+            const LONG_BIT: usize = size_of::<c_ulong>() * 8;
+            raw[bit / LONG_BIT] |= 1 << (bit % LONG_BIT);
+            return 0;
+        }
+    } else {
+        #[allow(unused_imports)]
+        pub use libc::{sigemptyset, sigaddset};
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Command
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct Command {
+    program: CString,
+    args: Vec<CString>,
+    /// Exactly what will be passed to `execvp`.
+    ///
+    /// First element is a pointer to `program`, followed by pointers to
+    /// `args`, followed by a `null`. Be careful when modifying `program` or
+    /// `args` to properly update this as well.
+    argv: Argv,
+    env: CommandEnv,
+
+    program_kind: ProgramKind,
+    cwd: Option<CString>,
+    uid: Option<uid_t>,
+    gid: Option<gid_t>,
+    saw_nul: bool,
+    closures: Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>>,
+    groups: Option<Box<[gid_t]>>,
+    stdin: Option<Stdio>,
+    stdout: Option<Stdio>,
+    stderr: Option<Stdio>,
+    #[cfg(target_os = "linux")]
+    create_pidfd: bool,
+    pgroup: Option<pid_t>,
+}
+
+// Create a new type for argv, so that we can make it `Send` and `Sync`
+struct Argv(Vec<*const c_char>);
+
+// It is safe to make `Argv` `Send` and `Sync`, because it contains
+// pointers to memory owned by `Command.args`
+unsafe impl Send for Argv {}
+unsafe impl Sync for Argv {}
+
+// passed back to std::process with the pipes connected to the child, if any
+// were requested
+pub struct StdioPipes {
+    pub stdin: Option<AnonPipe>,
+    pub stdout: Option<AnonPipe>,
+    pub stderr: Option<AnonPipe>,
+}
+
+// passed to do_exec() with configuration of what the child stdio should look
+// like
+#[cfg_attr(target_os = "vita", allow(dead_code))]
+pub struct ChildPipes {
+    pub stdin: ChildStdio,
+    pub stdout: ChildStdio,
+    pub stderr: ChildStdio,
+}
+
+pub enum ChildStdio {
+    Inherit,
+    Explicit(c_int),
+    Owned(FileDesc),
+
+    // On Fuchsia, null stdio is the default, so we simply don't specify
+    // any actions at the time of spawning.
+    #[cfg(target_os = "fuchsia")]
+    Null,
+}
+
+#[derive(Debug)]
+pub enum Stdio {
+    Inherit,
+    Null,
+    MakePipe,
+    Fd(FileDesc),
+    StaticFd(BorrowedFd<'static>),
+}
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum ProgramKind {
+    /// A program that would be looked up on the PATH (e.g. `ls`)
+    PathLookup,
+    /// A relative path (e.g. `my-dir/foo`, `../foo`, `./foo`)
+    Relative,
+    /// An absolute path.
+    Absolute,
+}
+
+impl ProgramKind {
+    fn new(program: &OsStr) -> Self {
+        if program.as_encoded_bytes().starts_with(b"/") {
+            Self::Absolute
+        } else if program.as_encoded_bytes().contains(&b'/') {
+            // If the program has more than one component in it, it is a relative path.
+            Self::Relative
+        } else {
+            Self::PathLookup
+        }
+    }
+}
+
+impl Command {
+    #[cfg(not(target_os = "linux"))]
+    pub fn new(program: &OsStr) -> Command {
+        let mut saw_nul = false;
+        let program_kind = ProgramKind::new(program.as_ref());
+        let program = os2c(program, &mut saw_nul);
+        Command {
+            argv: Argv(vec![program.as_ptr(), ptr::null()]),
+            args: vec![program.clone()],
+            program,
+            program_kind,
+            env: Default::default(),
+            cwd: None,
+            uid: None,
+            gid: None,
+            saw_nul,
+            closures: Vec::new(),
+            groups: None,
+            stdin: None,
+            stdout: None,
+            stderr: None,
+            pgroup: None,
+        }
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn new(program: &OsStr) -> Command {
+        let mut saw_nul = false;
+        let program_kind = ProgramKind::new(program.as_ref());
+        let program = os2c(program, &mut saw_nul);
+        Command {
+            argv: Argv(vec![program.as_ptr(), ptr::null()]),
+            args: vec![program.clone()],
+            program,
+            program_kind,
+            env: Default::default(),
+            cwd: None,
+            uid: None,
+            gid: None,
+            saw_nul,
+            closures: Vec::new(),
+            groups: None,
+            stdin: None,
+            stdout: None,
+            stderr: None,
+            create_pidfd: false,
+            pgroup: None,
+        }
+    }
+
+    pub fn set_arg_0(&mut self, arg: &OsStr) {
+        // Set a new arg0
+        let arg = os2c(arg, &mut self.saw_nul);
+        debug_assert!(self.argv.0.len() > 1);
+        self.argv.0[0] = arg.as_ptr();
+        self.args[0] = arg;
+    }
+
+    pub fn arg(&mut self, arg: &OsStr) {
+        // Overwrite the trailing null pointer in `argv` and then add a new null
+        // pointer.
+        let arg = os2c(arg, &mut self.saw_nul);
+        self.argv.0[self.args.len()] = arg.as_ptr();
+        self.argv.0.push(ptr::null());
+
+        // Also make sure we keep track of the owned value to schedule a
+        // destructor for this memory.
+        self.args.push(arg);
+    }
+
+    pub fn cwd(&mut self, dir: &OsStr) {
+        self.cwd = Some(os2c(dir, &mut self.saw_nul));
+    }
+    pub fn uid(&mut self, id: uid_t) {
+        self.uid = Some(id);
+    }
+    pub fn gid(&mut self, id: gid_t) {
+        self.gid = Some(id);
+    }
+    pub fn groups(&mut self, groups: &[gid_t]) {
+        self.groups = Some(Box::from(groups));
+    }
+    pub fn pgroup(&mut self, pgroup: pid_t) {
+        self.pgroup = Some(pgroup);
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn create_pidfd(&mut self, val: bool) {
+        self.create_pidfd = val;
+    }
+
+    #[cfg(not(target_os = "linux"))]
+    #[allow(dead_code)]
+    pub fn get_create_pidfd(&self) -> bool {
+        false
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn get_create_pidfd(&self) -> bool {
+        self.create_pidfd
+    }
+
+    pub fn saw_nul(&self) -> bool {
+        self.saw_nul
+    }
+
+    pub fn get_program(&self) -> &OsStr {
+        OsStr::from_bytes(self.program.as_bytes())
+    }
+
+    #[allow(dead_code)]
+    pub fn get_program_kind(&self) -> ProgramKind {
+        self.program_kind
+    }
+
+    pub fn get_args(&self) -> CommandArgs<'_> {
+        let mut iter = self.args.iter();
+        iter.next();
+        CommandArgs { iter }
+    }
+
+    pub fn get_envs(&self) -> CommandEnvs<'_> {
+        self.env.iter()
+    }
+
+    pub fn get_current_dir(&self) -> Option<&Path> {
+        self.cwd.as_ref().map(|cs| Path::new(OsStr::from_bytes(cs.as_bytes())))
+    }
+
+    pub fn get_argv(&self) -> &Vec<*const c_char> {
+        &self.argv.0
+    }
+
+    pub fn get_program_cstr(&self) -> &CStr {
+        &*self.program
+    }
+
+    #[allow(dead_code)]
+    pub fn get_cwd(&self) -> Option<&CStr> {
+        self.cwd.as_deref()
+    }
+    #[allow(dead_code)]
+    pub fn get_uid(&self) -> Option<uid_t> {
+        self.uid
+    }
+    #[allow(dead_code)]
+    pub fn get_gid(&self) -> Option<gid_t> {
+        self.gid
+    }
+    #[allow(dead_code)]
+    pub fn get_groups(&self) -> Option<&[gid_t]> {
+        self.groups.as_deref()
+    }
+    #[allow(dead_code)]
+    pub fn get_pgroup(&self) -> Option<pid_t> {
+        self.pgroup
+    }
+
+    pub fn get_closures(&mut self) -> &mut Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>> {
+        &mut self.closures
+    }
+
+    pub unsafe fn pre_exec(&mut self, f: Box<dyn FnMut() -> io::Result<()> + Send + Sync>) {
+        self.closures.push(f);
+    }
+
+    pub fn stdin(&mut self, stdin: Stdio) {
+        self.stdin = Some(stdin);
+    }
+
+    pub fn stdout(&mut self, stdout: Stdio) {
+        self.stdout = Some(stdout);
+    }
+
+    pub fn stderr(&mut self, stderr: Stdio) {
+        self.stderr = Some(stderr);
+    }
+
+    pub fn env_mut(&mut self) -> &mut CommandEnv {
+        &mut self.env
+    }
+
+    pub fn capture_env(&mut self) -> Option<CStringArray> {
+        let maybe_env = self.env.capture_if_changed();
+        maybe_env.map(|env| construct_envp(env, &mut self.saw_nul))
+    }
+
+    #[allow(dead_code)]
+    pub fn env_saw_path(&self) -> bool {
+        self.env.have_changed_path()
+    }
+
+    #[allow(dead_code)]
+    pub fn program_is_path(&self) -> bool {
+        self.program.to_bytes().contains(&b'/')
+    }
+
+    pub fn setup_io(
+        &self,
+        default: Stdio,
+        needs_stdin: bool,
+    ) -> io::Result<(StdioPipes, ChildPipes)> {
+        let null = Stdio::Null;
+        let default_stdin = if needs_stdin { &default } else { &null };
+        let stdin = self.stdin.as_ref().unwrap_or(default_stdin);
+        let stdout = self.stdout.as_ref().unwrap_or(&default);
+        let stderr = self.stderr.as_ref().unwrap_or(&default);
+        let (their_stdin, our_stdin) = stdin.to_child_stdio(true)?;
+        let (their_stdout, our_stdout) = stdout.to_child_stdio(false)?;
+        let (their_stderr, our_stderr) = stderr.to_child_stdio(false)?;
+        let ours = StdioPipes { stdin: our_stdin, stdout: our_stdout, stderr: our_stderr };
+        let theirs = ChildPipes { stdin: their_stdin, stdout: their_stdout, stderr: their_stderr };
+        Ok((ours, theirs))
+    }
+}
+
+fn os2c(s: &OsStr, saw_nul: &mut bool) -> CString {
+    CString::new(s.as_bytes()).unwrap_or_else(|_e| {
+        *saw_nul = true;
+        c"<string-with-nul>".to_owned()
+    })
+}
+
+// Helper type to manage ownership of the strings within a C-style array.
+pub struct CStringArray {
+    items: Vec<CString>,
+    ptrs: Vec<*const c_char>,
+}
+
+impl CStringArray {
+    pub fn with_capacity(capacity: usize) -> Self {
+        let mut result = CStringArray {
+            items: Vec::with_capacity(capacity),
+            ptrs: Vec::with_capacity(capacity + 1),
+        };
+        result.ptrs.push(ptr::null());
+        result
+    }
+    pub fn push(&mut self, item: CString) {
+        let l = self.ptrs.len();
+        self.ptrs[l - 1] = item.as_ptr();
+        self.ptrs.push(ptr::null());
+        self.items.push(item);
+    }
+    pub fn as_ptr(&self) -> *const *const c_char {
+        self.ptrs.as_ptr()
+    }
+}
+
+fn construct_envp(env: BTreeMap<OsString, OsString>, saw_nul: &mut bool) -> CStringArray {
+    let mut result = CStringArray::with_capacity(env.len());
+    for (mut k, v) in env {
+        // Reserve additional space for '=' and null terminator
+        k.reserve_exact(v.len() + 2);
+        k.push("=");
+        k.push(&v);
+
+        // Add the new entry into the array
+        if let Ok(item) = CString::new(k.into_vec()) {
+            result.push(item);
+        } else {
+            *saw_nul = true;
+        }
+    }
+
+    result
+}
+
+impl Stdio {
+    pub fn to_child_stdio(&self, readable: bool) -> io::Result<(ChildStdio, Option<AnonPipe>)> {
+        match *self {
+            Stdio::Inherit => Ok((ChildStdio::Inherit, None)),
+
+            // Make sure that the source descriptors are not an stdio
+            // descriptor, otherwise the order which we set the child's
+            // descriptors may blow away a descriptor which we are hoping to
+            // save. For example, suppose we want the child's stderr to be the
+            // parent's stdout, and the child's stdout to be the parent's
+            // stderr. No matter which we dup first, the second will get
+            // overwritten prematurely.
+            Stdio::Fd(ref fd) => {
+                if fd.as_raw_fd() >= 0 && fd.as_raw_fd() <= libc::STDERR_FILENO {
+                    Ok((ChildStdio::Owned(fd.duplicate()?), None))
+                } else {
+                    Ok((ChildStdio::Explicit(fd.as_raw_fd()), None))
+                }
+            }
+
+            Stdio::StaticFd(fd) => {
+                let fd = FileDesc::from_inner(fd.try_clone_to_owned()?);
+                Ok((ChildStdio::Owned(fd), None))
+            }
+
+            Stdio::MakePipe => {
+                let (reader, writer) = pipe::anon_pipe()?;
+                let (ours, theirs) = if readable { (writer, reader) } else { (reader, writer) };
+                Ok((ChildStdio::Owned(theirs.into_inner()), Some(ours)))
+            }
+
+            #[cfg(not(target_os = "fuchsia"))]
+            Stdio::Null => {
+                let mut opts = OpenOptions::new();
+                opts.read(readable);
+                opts.write(!readable);
+                let fd = File::open_c(DEV_NULL, &opts)?;
+                Ok((ChildStdio::Owned(fd.into_inner()), None))
+            }
+
+            #[cfg(target_os = "fuchsia")]
+            Stdio::Null => Ok((ChildStdio::Null, None)),
+        }
+    }
+}
+
+impl From<AnonPipe> for Stdio {
+    fn from(pipe: AnonPipe) -> Stdio {
+        Stdio::Fd(pipe.into_inner())
+    }
+}
+
+impl From<FileDesc> for Stdio {
+    fn from(fd: FileDesc) -> Stdio {
+        Stdio::Fd(fd)
+    }
+}
+
+impl From<File> for Stdio {
+    fn from(file: File) -> Stdio {
+        Stdio::Fd(file.into_inner())
+    }
+}
+
+impl From<io::Stdout> for Stdio {
+    fn from(_: io::Stdout) -> Stdio {
+        // This ought really to be is Stdio::StaticFd(input_argument.as_fd()).
+        // But AsFd::as_fd takes its argument by reference, and yields
+        // a bounded lifetime, so it's no use here. There is no AsStaticFd.
+        //
+        // Additionally AsFd is only implemented for the *locked* versions.
+        // We don't want to lock them here.  (The implications of not locking
+        // are the same as those for process::Stdio::inherit().)
+        //
+        // Arguably the hypothetical AsStaticFd and AsFd<'static>
+        // should be implemented for io::Stdout, not just for StdoutLocked.
+        Stdio::StaticFd(unsafe { BorrowedFd::borrow_raw(libc::STDOUT_FILENO) })
+    }
+}
+
+impl From<io::Stderr> for Stdio {
+    fn from(_: io::Stderr) -> Stdio {
+        Stdio::StaticFd(unsafe { BorrowedFd::borrow_raw(libc::STDERR_FILENO) })
+    }
+}
+
+impl ChildStdio {
+    pub fn fd(&self) -> Option<c_int> {
+        match *self {
+            ChildStdio::Inherit => None,
+            ChildStdio::Explicit(fd) => Some(fd),
+            ChildStdio::Owned(ref fd) => Some(fd.as_raw_fd()),
+
+            #[cfg(target_os = "fuchsia")]
+            ChildStdio::Null => None,
+        }
+    }
+}
+
+impl fmt::Debug for Command {
+    // show all attributes but `self.closures` which does not implement `Debug`
+    // and `self.argv` which is not useful for debugging
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if f.alternate() {
+            let mut debug_command = f.debug_struct("Command");
+            debug_command.field("program", &self.program).field("args", &self.args);
+            if !self.env.is_unchanged() {
+                debug_command.field("env", &self.env);
+            }
+
+            if self.cwd.is_some() {
+                debug_command.field("cwd", &self.cwd);
+            }
+            if self.uid.is_some() {
+                debug_command.field("uid", &self.uid);
+            }
+            if self.gid.is_some() {
+                debug_command.field("gid", &self.gid);
+            }
+
+            if self.groups.is_some() {
+                debug_command.field("groups", &self.groups);
+            }
+
+            if self.stdin.is_some() {
+                debug_command.field("stdin", &self.stdin);
+            }
+            if self.stdout.is_some() {
+                debug_command.field("stdout", &self.stdout);
+            }
+            if self.stderr.is_some() {
+                debug_command.field("stderr", &self.stderr);
+            }
+            if self.pgroup.is_some() {
+                debug_command.field("pgroup", &self.pgroup);
+            }
+
+            #[cfg(target_os = "linux")]
+            {
+                debug_command.field("create_pidfd", &self.create_pidfd);
+            }
+
+            debug_command.finish()
+        } else {
+            if let Some(ref cwd) = self.cwd {
+                write!(f, "cd {cwd:?} && ")?;
+            }
+            if self.env.does_clear() {
+                write!(f, "env -i ")?;
+                // Altered env vars will be printed next, that should exactly work as expected.
+            } else {
+                // Removed env vars need the command to be wrapped in `env`.
+                let mut any_removed = false;
+                for (key, value_opt) in self.get_envs() {
+                    if value_opt.is_none() {
+                        if !any_removed {
+                            write!(f, "env ")?;
+                            any_removed = true;
+                        }
+                        write!(f, "-u {} ", key.to_string_lossy())?;
+                    }
+                }
+            }
+            // Altered env vars can just be added in front of the program.
+            for (key, value_opt) in self.get_envs() {
+                if let Some(value) = value_opt {
+                    write!(f, "{}={value:?} ", key.to_string_lossy())?;
+                }
+            }
+            if self.program != self.args[0] {
+                write!(f, "[{:?}] ", self.program)?;
+            }
+            write!(f, "{:?}", self.args[0])?;
+
+            for arg in &self.args[1..] {
+                write!(f, " {:?}", arg)?;
+            }
+            Ok(())
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub struct ExitCode(u8);
+
+impl fmt::Debug for ExitCode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("unix_exit_status").field(&self.0).finish()
+    }
+}
+
+impl ExitCode {
+    pub const SUCCESS: ExitCode = ExitCode(EXIT_SUCCESS as _);
+    pub const FAILURE: ExitCode = ExitCode(EXIT_FAILURE as _);
+
+    #[inline]
+    pub fn as_i32(&self) -> i32 {
+        self.0 as i32
+    }
+}
+
+impl From<u8> for ExitCode {
+    fn from(code: u8) -> Self {
+        Self(code)
+    }
+}
+
+pub struct CommandArgs<'a> {
+    iter: crate::slice::Iter<'a, CString>,
+}
+
+impl<'a> Iterator for CommandArgs<'a> {
+    type Item = &'a OsStr;
+    fn next(&mut self) -> Option<&'a OsStr> {
+        self.iter.next().map(|cs| OsStr::from_bytes(cs.as_bytes()))
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a> ExactSizeIterator for CommandArgs<'a> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+impl<'a> fmt::Debug for CommandArgs<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter.clone()).finish()
+    }
+}
diff --git a/library/std/src/sys/process/unix/common/tests.rs b/library/std/src/sys/process/unix/common/tests.rs
new file mode 100644
index 00000000000..e5c8dd6e341
--- /dev/null
+++ b/library/std/src/sys/process/unix/common/tests.rs
@@ -0,0 +1,192 @@
+use super::*;
+use crate::ffi::OsStr;
+use crate::sys::{cvt, cvt_nz};
+use crate::{mem, ptr};
+
+macro_rules! t {
+    ($e:expr) => {
+        match $e {
+            Ok(t) => t,
+            Err(e) => panic!("received error for `{}`: {}", stringify!($e), e),
+        }
+    };
+}
+
+#[test]
+#[cfg_attr(
+    any(
+        // See #14232 for more information, but it appears that signal delivery to a
+        // newly spawned process may just be raced in the macOS, so to prevent this
+        // test from being flaky we ignore it on macOS.
+        target_os = "macos",
+        // When run under our current QEMU emulation test suite this test fails,
+        // although the reason isn't very clear as to why. For now this test is
+        // ignored there.
+        target_arch = "arm",
+        target_arch = "aarch64",
+        target_arch = "riscv64",
+    ),
+    ignore
+)]
+fn test_process_mask() {
+    // Test to make sure that a signal mask *does* get inherited.
+    fn test_inner(mut cmd: Command) {
+        unsafe {
+            let mut set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            let mut old_set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            t!(cvt(sigemptyset(set.as_mut_ptr())));
+            t!(cvt(sigaddset(set.as_mut_ptr(), libc::SIGINT)));
+            t!(cvt_nz(libc::pthread_sigmask(
+                libc::SIG_SETMASK,
+                set.as_ptr(),
+                old_set.as_mut_ptr()
+            )));
+
+            cmd.stdin(Stdio::MakePipe);
+            cmd.stdout(Stdio::MakePipe);
+
+            let (mut cat, mut pipes) = t!(cmd.spawn(Stdio::Null, true));
+            let stdin_write = pipes.stdin.take().unwrap();
+            let stdout_read = pipes.stdout.take().unwrap();
+
+            t!(cvt_nz(libc::pthread_sigmask(libc::SIG_SETMASK, old_set.as_ptr(), ptr::null_mut())));
+
+            t!(cvt(libc::kill(cat.id() as libc::pid_t, libc::SIGINT)));
+            // We need to wait until SIGINT is definitely delivered. The
+            // easiest way is to write something to cat, and try to read it
+            // back: if SIGINT is unmasked, it'll get delivered when cat is
+            // next scheduled.
+            let _ = stdin_write.write(b"Hello");
+            drop(stdin_write);
+
+            // Exactly 5 bytes should be read.
+            let mut buf = [0; 5];
+            let ret = t!(stdout_read.read(&mut buf));
+            assert_eq!(ret, 5);
+            assert_eq!(&buf, b"Hello");
+
+            t!(cat.wait());
+        }
+    }
+
+    // A plain `Command::new` uses the posix_spawn path on many platforms.
+    let cmd = Command::new(OsStr::new("cat"));
+    test_inner(cmd);
+
+    // Specifying `pre_exec` forces the fork/exec path.
+    let mut cmd = Command::new(OsStr::new("cat"));
+    unsafe { cmd.pre_exec(Box::new(|| Ok(()))) };
+    test_inner(cmd);
+}
+
+#[test]
+#[cfg_attr(
+    any(
+        // See test_process_mask
+        target_os = "macos",
+        target_arch = "arm",
+        target_arch = "aarch64",
+        target_arch = "riscv64",
+    ),
+    ignore
+)]
+fn test_process_group_posix_spawn() {
+    unsafe {
+        // Spawn a cat subprocess that's just going to hang since there is no I/O.
+        let mut cmd = Command::new(OsStr::new("cat"));
+        cmd.pgroup(0);
+        cmd.stdin(Stdio::MakePipe);
+        cmd.stdout(Stdio::MakePipe);
+        let (mut cat, _pipes) = t!(cmd.spawn(Stdio::Null, true));
+
+        // Check that we can kill its process group, which means there *is* one.
+        t!(cvt(libc::kill(-(cat.id() as libc::pid_t), libc::SIGINT)));
+
+        t!(cat.wait());
+    }
+}
+
+#[test]
+#[cfg_attr(
+    any(
+        // See test_process_mask
+        target_os = "macos",
+        target_arch = "arm",
+        target_arch = "aarch64",
+        target_arch = "riscv64",
+    ),
+    ignore
+)]
+fn test_process_group_no_posix_spawn() {
+    unsafe {
+        // Same as above, create hang-y cat. This time, force using the non-posix_spawnp path.
+        let mut cmd = Command::new(OsStr::new("cat"));
+        cmd.pgroup(0);
+        cmd.pre_exec(Box::new(|| Ok(()))); // pre_exec forces fork + exec
+        cmd.stdin(Stdio::MakePipe);
+        cmd.stdout(Stdio::MakePipe);
+        let (mut cat, _pipes) = t!(cmd.spawn(Stdio::Null, true));
+
+        // Check that we can kill its process group, which means there *is* one.
+        t!(cvt(libc::kill(-(cat.id() as libc::pid_t), libc::SIGINT)));
+
+        t!(cat.wait());
+    }
+}
+
+#[test]
+fn test_program_kind() {
+    let vectors = &[
+        ("foo", ProgramKind::PathLookup),
+        ("foo.out", ProgramKind::PathLookup),
+        ("./foo", ProgramKind::Relative),
+        ("../foo", ProgramKind::Relative),
+        ("dir/foo", ProgramKind::Relative),
+        // Note that paths on Unix can't contain / in them, so this is actually the directory "fo\\"
+        // followed by the file "o".
+        ("fo\\/o", ProgramKind::Relative),
+        ("/foo", ProgramKind::Absolute),
+        ("/dir/../foo", ProgramKind::Absolute),
+    ];
+
+    for (program, expected_kind) in vectors {
+        assert_eq!(
+            ProgramKind::new(program.as_ref()),
+            *expected_kind,
+            "actual != expected program kind for input {program}",
+        );
+    }
+}
+
+// Test that Rust std handles wait status values (`ExitStatus`) the way that Unix does,
+// at least for the values which represent a Unix exit status (`ExitCode`).
+// Should work on every #[cfg(unix)] platform.  However:
+#[cfg(not(any(
+    // Fuchsia is not Unix and has totally broken std::os::unix.
+    // https://github.com/rust-lang/rust/issues/58590#issuecomment-836535609
+    target_os = "fuchsia",
+)))]
+#[test]
+fn unix_exit_statuses() {
+    use crate::num::NonZero;
+    use crate::os::unix::process::ExitStatusExt;
+    use crate::process::*;
+
+    for exit_code in 0..=0xff {
+        // FIXME impl From<ExitCode> for ExitStatus and then test that here too;
+        // the two ExitStatus values should be the same
+        let raw_wait_status = exit_code << 8;
+        let exit_status = ExitStatus::from_raw(raw_wait_status);
+
+        assert_eq!(exit_status.code(), Some(exit_code));
+
+        if let Ok(nz) = NonZero::try_from(exit_code) {
+            assert!(!exit_status.success());
+            let es_error = exit_status.exit_ok().unwrap_err();
+            assert_eq!(es_error.code().unwrap(), i32::from(nz));
+        } else {
+            assert!(exit_status.success());
+            assert_eq!(exit_status.exit_ok(), Ok(()));
+        }
+    }
+}
diff --git a/library/std/src/sys/process/unix/fuchsia.rs b/library/std/src/sys/process/unix/fuchsia.rs
new file mode 100644
index 00000000000..0de32ecffd4
--- /dev/null
+++ b/library/std/src/sys/process/unix/fuchsia.rs
@@ -0,0 +1,318 @@
+use libc::{c_int, size_t};
+
+use super::common::*;
+use crate::num::NonZero;
+use crate::sys::pal::fuchsia::*;
+use crate::{fmt, io, mem, ptr};
+
+////////////////////////////////////////////////////////////////////////////////
+// Command
+////////////////////////////////////////////////////////////////////////////////
+
+impl Command {
+    pub fn spawn(
+        &mut self,
+        default: Stdio,
+        needs_stdin: bool,
+    ) -> io::Result<(Process, StdioPipes)> {
+        let envp = self.capture_env();
+
+        if self.saw_nul() {
+            return Err(io::const_error!(
+                io::ErrorKind::InvalidInput,
+                "nul byte found in provided data",
+            ));
+        }
+
+        let (ours, theirs) = self.setup_io(default, needs_stdin)?;
+
+        let process_handle = unsafe { self.do_exec(theirs, envp.as_ref())? };
+
+        Ok((Process { handle: Handle::new(process_handle) }, ours))
+    }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
+    pub fn exec(&mut self, default: Stdio) -> io::Error {
+        if self.saw_nul() {
+            return io::const_error!(
+                io::ErrorKind::InvalidInput,
+                "nul byte found in provided data",
+            );
+        }
+
+        match self.setup_io(default, true) {
+            Ok((_, _)) => {
+                // FIXME: This is tough because we don't support the exec syscalls
+                unimplemented!();
+            }
+            Err(e) => e,
+        }
+    }
+
+    unsafe fn do_exec(
+        &mut self,
+        stdio: ChildPipes,
+        maybe_envp: Option<&CStringArray>,
+    ) -> io::Result<zx_handle_t> {
+        let envp = match maybe_envp {
+            // None means to clone the current environment, which is done in the
+            // flags below.
+            None => ptr::null(),
+            Some(envp) => envp.as_ptr(),
+        };
+
+        let make_action = |local_io: &ChildStdio, target_fd| -> io::Result<fdio_spawn_action_t> {
+            if let Some(local_fd) = local_io.fd() {
+                Ok(fdio_spawn_action_t {
+                    action: FDIO_SPAWN_ACTION_TRANSFER_FD,
+                    local_fd,
+                    target_fd,
+                    ..Default::default()
+                })
+            } else {
+                if let ChildStdio::Null = local_io {
+                    // acts as no-op
+                    return Ok(Default::default());
+                }
+
+                let mut handle = ZX_HANDLE_INVALID;
+                let status = fdio_fd_clone(target_fd, &mut handle);
+                if status == ERR_INVALID_ARGS || status == ERR_NOT_SUPPORTED {
+                    // This descriptor is closed; skip it rather than generating an
+                    // error.
+                    return Ok(Default::default());
+                }
+                zx_cvt(status)?;
+
+                let mut cloned_fd = 0;
+                zx_cvt(fdio_fd_create(handle, &mut cloned_fd))?;
+
+                Ok(fdio_spawn_action_t {
+                    action: FDIO_SPAWN_ACTION_TRANSFER_FD,
+                    local_fd: cloned_fd as i32,
+                    target_fd,
+                    ..Default::default()
+                })
+            }
+        };
+
+        // Clone stdin, stdout, and stderr
+        let action1 = make_action(&stdio.stdin, 0)?;
+        let action2 = make_action(&stdio.stdout, 1)?;
+        let action3 = make_action(&stdio.stderr, 2)?;
+        let actions = [action1, action2, action3];
+
+        // We don't want FileDesc::drop to be called on any stdio. fdio_spawn_etc
+        // always consumes transferred file descriptors.
+        mem::forget(stdio);
+
+        for callback in self.get_closures().iter_mut() {
+            callback()?;
+        }
+
+        let mut process_handle: zx_handle_t = 0;
+        zx_cvt(fdio_spawn_etc(
+            ZX_HANDLE_INVALID,
+            FDIO_SPAWN_CLONE_JOB
+                | FDIO_SPAWN_CLONE_LDSVC
+                | FDIO_SPAWN_CLONE_NAMESPACE
+                | FDIO_SPAWN_CLONE_ENVIRON // this is ignored when envp is non-null
+                | FDIO_SPAWN_CLONE_UTC_CLOCK,
+            self.get_program_cstr().as_ptr(),
+            self.get_argv().as_ptr(),
+            envp,
+            actions.len() as size_t,
+            actions.as_ptr(),
+            &mut process_handle,
+            ptr::null_mut(),
+        ))?;
+        // FIXME: See if we want to do something with that err_msg
+
+        Ok(process_handle)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Processes
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct Process {
+    handle: Handle,
+}
+
+impl Process {
+    pub fn id(&self) -> u32 {
+        self.handle.raw() as u32
+    }
+
+    pub fn kill(&mut self) -> io::Result<()> {
+        unsafe {
+            zx_cvt(zx_task_kill(self.handle.raw()))?;
+        }
+
+        Ok(())
+    }
+
+    pub fn wait(&mut self) -> io::Result<ExitStatus> {
+        let mut proc_info: zx_info_process_t = Default::default();
+        let mut actual: size_t = 0;
+        let mut avail: size_t = 0;
+
+        unsafe {
+            zx_cvt(zx_object_wait_one(
+                self.handle.raw(),
+                ZX_TASK_TERMINATED,
+                ZX_TIME_INFINITE,
+                ptr::null_mut(),
+            ))?;
+            zx_cvt(zx_object_get_info(
+                self.handle.raw(),
+                ZX_INFO_PROCESS,
+                (&raw mut proc_info) as *mut libc::c_void,
+                size_of::<zx_info_process_t>(),
+                &mut actual,
+                &mut avail,
+            ))?;
+        }
+        if actual != 1 {
+            return Err(io::const_error!(
+                io::ErrorKind::InvalidData,
+                "failed to get exit status of process",
+            ));
+        }
+        Ok(ExitStatus(proc_info.return_code))
+    }
+
+    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        let mut proc_info: zx_info_process_t = Default::default();
+        let mut actual: size_t = 0;
+        let mut avail: size_t = 0;
+
+        unsafe {
+            let status =
+                zx_object_wait_one(self.handle.raw(), ZX_TASK_TERMINATED, 0, ptr::null_mut());
+            match status {
+                0 => {} // Success
+                x if x == ERR_TIMED_OUT => {
+                    return Ok(None);
+                }
+                _ => {
+                    panic!("Failed to wait on process handle: {status}");
+                }
+            }
+            zx_cvt(zx_object_get_info(
+                self.handle.raw(),
+                ZX_INFO_PROCESS,
+                (&raw mut proc_info) as *mut libc::c_void,
+                size_of::<zx_info_process_t>(),
+                &mut actual,
+                &mut avail,
+            ))?;
+        }
+        if actual != 1 {
+            return Err(io::const_error!(
+                io::ErrorKind::InvalidData,
+                "failed to get exit status of process",
+            ));
+        }
+        Ok(Some(ExitStatus(proc_info.return_code)))
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
+pub struct ExitStatus(i64);
+
+impl ExitStatus {
+    pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
+        match NonZero::try_from(self.0) {
+            /* was nonzero */ Ok(failure) => Err(ExitStatusError(failure)),
+            /* was zero, couldn't convert */ Err(_) => Ok(()),
+        }
+    }
+
+    pub fn code(&self) -> Option<i32> {
+        // FIXME: support extracting return code as an i64
+        self.0.try_into().ok()
+    }
+
+    pub fn signal(&self) -> Option<i32> {
+        None
+    }
+
+    // FIXME: The actually-Unix implementation in unix.rs uses WSTOPSIG, WCOREDUMP et al.
+    // I infer from the implementation of `success`, `code` and `signal` above that these are not
+    // available on Fuchsia.
+    //
+    // It does not appear that Fuchsia is Unix-like enough to implement ExitStatus (or indeed many
+    // other things from std::os::unix) properly. This veneer is always going to be a bodge. So
+    // while I don't know if these implementations are actually correct, I think they will do for
+    // now at least.
+    pub fn core_dumped(&self) -> bool {
+        false
+    }
+    pub fn stopped_signal(&self) -> Option<i32> {
+        None
+    }
+    pub fn continued(&self) -> bool {
+        false
+    }
+
+    pub fn into_raw(&self) -> c_int {
+        // We don't know what someone who calls into_raw() will do with this value, but it should
+        // have the conventional Unix representation. Despite the fact that this is not
+        // standardised in SuS or POSIX, all Unix systems encode the signal and exit status the
+        // same way. (Ie the WIFEXITED, WEXITSTATUS etc. macros have identical behavior on every
+        // Unix.)
+        //
+        // The caller of `std::os::unix::into_raw` is probably wanting a Unix exit status, and may
+        // do their own shifting and masking, or even pass the status to another computer running a
+        // different Unix variant.
+        //
+        // The other view would be to say that the caller on Fuchsia ought to know that `into_raw`
+        // will give a raw Fuchsia status (whatever that is - I don't know, personally). That is
+        // not possible here because we must return a c_int because that's what Unix (including
+        // SuS and POSIX) say a wait status is, but Fuchsia apparently uses a u64, so it won't
+        // necessarily fit.
+        //
+        // It seems to me that the right answer would be to provide std::os::fuchsia with its
+        // own ExitStatusExt, rather that trying to provide a not very convincing imitation of
+        // Unix. Ie, std::os::unix::process:ExitStatusExt ought not to exist on Fuchsia. But
+        // fixing this up that is beyond the scope of my efforts now.
+        let exit_status_as_if_unix: u8 = self.0.try_into().expect("Fuchsia process return code bigger than 8 bits, but std::os::unix::ExitStatusExt::into_raw() was called to try to convert the value into a traditional Unix-style wait status, which cannot represent values greater than 255.");
+        let wait_status_as_if_unix = (exit_status_as_if_unix as c_int) << 8;
+        wait_status_as_if_unix
+    }
+}
+
+/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
+impl From<c_int> for ExitStatus {
+    fn from(a: c_int) -> ExitStatus {
+        ExitStatus(a as i64)
+    }
+}
+
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "exit code: {}", self.0)
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ExitStatusError(NonZero<i64>);
+
+impl Into<ExitStatus> for ExitStatusError {
+    fn into(self) -> ExitStatus {
+        ExitStatus(self.0.into())
+    }
+}
+
+impl ExitStatusError {
+    pub fn code(self) -> Option<NonZero<i32>> {
+        // fixme: affected by the same bug as ExitStatus::code()
+        ExitStatus(self.0.into()).code().map(|st| st.try_into().unwrap())
+    }
+}
diff --git a/library/std/src/sys/process/unix/mod.rs b/library/std/src/sys/process/unix/mod.rs
new file mode 100644
index 00000000000..2e8b38f7de1
--- /dev/null
+++ b/library/std/src/sys/process/unix/mod.rs
@@ -0,0 +1,23 @@
+#[cfg_attr(any(target_os = "espidf", target_os = "horizon", target_os = "nuttx"), allow(unused))]
+mod common;
+
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "fuchsia")] {
+        mod fuchsia;
+        use fuchsia as imp;
+    } else if #[cfg(target_os = "vxworks")] {
+        mod vxworks;
+        use vxworks as imp;
+    } else if #[cfg(any(target_os = "espidf", target_os = "horizon", target_os = "vita", target_os = "nuttx"))] {
+        mod unsupported;
+        use unsupported as imp;
+    } else {
+        mod unix;
+        use unix as imp;
+    }
+}
+
+pub use imp::{ExitStatus, ExitStatusError, Process};
+
+pub use self::common::{Command, CommandArgs, ExitCode, Stdio, StdioPipes};
+pub use crate::ffi::OsString as EnvKey;
diff --git a/library/std/src/sys/process/unix/unix.rs b/library/std/src/sys/process/unix/unix.rs
new file mode 100644
index 00000000000..42542f81b65
--- /dev/null
+++ b/library/std/src/sys/process/unix/unix.rs
@@ -0,0 +1,1268 @@
+#[cfg(target_os = "vxworks")]
+use libc::RTP_ID as pid_t;
+#[cfg(not(target_os = "vxworks"))]
+use libc::{c_int, pid_t};
+#[cfg(not(any(
+    target_os = "vxworks",
+    target_os = "l4re",
+    target_os = "tvos",
+    target_os = "watchos",
+)))]
+use libc::{gid_t, uid_t};
+
+use super::common::*;
+use crate::io::{self, Error, ErrorKind};
+use crate::num::NonZero;
+use crate::sys::cvt;
+#[cfg(target_os = "linux")]
+use crate::sys::pal::linux::pidfd::PidFd;
+use crate::{fmt, mem, sys};
+
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "nto")] {
+        use crate::thread;
+        use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
+        use crate::time::Duration;
+        use crate::sync::LazyLock;
+        // Get smallest amount of time we can sleep.
+        // Return a common value if it cannot be determined.
+        fn get_clock_resolution() -> Duration {
+            static MIN_DELAY: LazyLock<Duration, fn() -> Duration> = LazyLock::new(|| {
+                let mut mindelay = libc::timespec { tv_sec: 0, tv_nsec: 0 };
+                if unsafe { libc::clock_getres(libc::CLOCK_MONOTONIC, &mut mindelay) } == 0
+                {
+                    Duration::from_nanos(mindelay.tv_nsec as u64)
+                } else {
+                    Duration::from_millis(1)
+                }
+            });
+            *MIN_DELAY
+        }
+        // Arbitrary minimum sleep duration for retrying fork/spawn
+        const MIN_FORKSPAWN_SLEEP: Duration = Duration::from_nanos(1);
+        // Maximum duration of sleeping before giving up and returning an error
+        const MAX_FORKSPAWN_SLEEP: Duration = Duration::from_millis(1000);
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Command
+////////////////////////////////////////////////////////////////////////////////
+
+impl Command {
+    pub fn spawn(
+        &mut self,
+        default: Stdio,
+        needs_stdin: bool,
+    ) -> io::Result<(Process, StdioPipes)> {
+        const CLOEXEC_MSG_FOOTER: [u8; 4] = *b"NOEX";
+
+        let envp = self.capture_env();
+
+        if self.saw_nul() {
+            return Err(io::const_error!(
+                ErrorKind::InvalidInput,
+                "nul byte found in provided data",
+            ));
+        }
+
+        let (ours, theirs) = self.setup_io(default, needs_stdin)?;
+
+        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
+        // look at the environment in one way or another (PATH in `execvp` or
+        // accessing the `environ` pointer ourselves). Make sure no other thread
+        // is accessing the environment when we do the fork itself.
+        //
+        // Note that as soon as we're done with the fork there's no need to hold
+        // a lock any more because the parent won't do anything and the child is
+        // in its own process. Thus the parent drops the lock guard immediately.
+        // 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 = 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();
+            let bytes = [
+                errno[0],
+                errno[1],
+                errno[2],
+                errno[3],
+                CLOEXEC_MSG_FOOTER[0],
+                CLOEXEC_MSG_FOOTER[1],
+                CLOEXEC_MSG_FOOTER[2],
+                CLOEXEC_MSG_FOOTER[3],
+            ];
+            // pipe I/O up to PIPE_BUF bytes should be atomic, and then
+            // we want to be sure we *don't* run at_exit destructors as
+            // we're being torn down regardless
+            rtassert!(output.write(&bytes).is_ok());
+            unsafe { libc::_exit(1) }
+        }
+
+        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 (on Linux) using SOCK_SEQPACKET, so it's valid.
+        let mut p = unsafe { Process::new(pid, pidfd) };
+        let mut bytes = [0; 8];
+
+        // loop to handle EINTR
+        loop {
+            match input.read(&mut bytes) {
+                Ok(0) => return Ok((p, ours)),
+                Ok(8) => {
+                    let (errno, footer) = bytes.split_at(4);
+                    assert_eq!(
+                        CLOEXEC_MSG_FOOTER, footer,
+                        "Validation on the CLOEXEC pipe failed: {:?}",
+                        bytes
+                    );
+                    let errno = i32::from_be_bytes(errno.try_into().unwrap());
+                    assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
+                    return Err(Error::from_raw_os_error(errno));
+                }
+                Err(ref e) if e.is_interrupted() => {}
+                Err(e) => {
+                    assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
+                    panic!("the CLOEXEC pipe failed: {e:?}")
+                }
+                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")
+                }
+            }
+        }
+    }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
+    // WatchOS and TVOS headers mark the `fork`/`exec*` functions with
+    // `__WATCHOS_PROHIBITED __TVOS_PROHIBITED`, and indicate that the
+    // `posix_spawn*` functions should be used instead. It isn't entirely clear
+    // what `PROHIBITED` means here (e.g. if calls to these functions are
+    // allowed to exist in dead code), but it sounds bad, so we go out of our
+    // way to avoid that all-together.
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    const ERR_APPLE_TV_WATCH_NO_FORK_EXEC: Error = io::const_error!(
+        ErrorKind::Unsupported,
+        "`fork`+`exec`-based process spawning is not supported on this target",
+    );
+
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    unsafe fn do_fork(&mut self) -> Result<pid_t, 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 = "watchos", target_os = "tvos", target_os = "nto")))]
+    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
+    // or closed a file descriptor while the fork() was occurring".
+    // 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(target_os = "nto")]
+    unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
+        use crate::sys::os::errno;
+
+        let mut delay = MIN_FORKSPAWN_SLEEP;
+
+        loop {
+            let r = libc::fork();
+            if r == -1 as libc::pid_t && errno() as libc::c_int == libc::EBADF {
+                if delay < get_clock_resolution() {
+                    // We cannot sleep this short (it would be longer).
+                    // Yield instead.
+                    thread::yield_now();
+                } else if delay < MAX_FORKSPAWN_SLEEP {
+                    thread::sleep(delay);
+                } else {
+                    return Err(io::const_error!(
+                        ErrorKind::WouldBlock,
+                        "forking returned EBADF too often",
+                    ));
+                }
+                delay *= 2;
+                continue;
+            } else {
+                return cvt(r);
+            }
+        }
+    }
+
+    pub fn exec(&mut self, default: Stdio) -> io::Error {
+        let envp = self.capture_env();
+
+        if self.saw_nul() {
+            return io::const_error!(ErrorKind::InvalidInput, "nul byte found in provided data");
+        }
+
+        match self.setup_io(default, true) {
+            Ok((_, theirs)) => {
+                unsafe {
+                    // Similar to when forking, we want to ensure that access to
+                    // the environment is synchronized, so make sure to grab the
+                    // environment lock before we try to exec.
+                    let _lock = sys::os::env_read_lock();
+
+                    let Err(e) = self.do_exec(theirs, envp.as_ref());
+                    e
+                }
+            }
+            Err(e) => e,
+        }
+    }
+
+    // And at this point we've reached a special time in the life of the
+    // child. The child must now be considered hamstrung and unable to
+    // do anything other than syscalls really. Consider the following
+    // scenario:
+    //
+    //      1. Thread A of process 1 grabs the malloc() mutex
+    //      2. Thread B of process 1 forks(), creating thread C
+    //      3. Thread C of process 2 then attempts to malloc()
+    //      4. The memory of process 2 is the same as the memory of
+    //         process 1, so the mutex is locked.
+    //
+    // This situation looks a lot like deadlock, right? It turns out
+    // that this is what pthread_atfork() takes care of, which is
+    // presumably implemented across platforms. The first thing that
+    // threads to *before* forking is to do things like grab the malloc
+    // mutex, and then after the fork they unlock it.
+    //
+    // Despite this information, libnative's spawn has been witnessed to
+    // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
+    // all collected backtraces point at malloc/free traffic in the
+    // child spawned process.
+    //
+    // For this reason, the block of code below should contain 0
+    // invocations of either malloc of free (or their related friends).
+    //
+    // As an example of not having malloc/free traffic, we don't close
+    // this file descriptor by dropping the FileDesc (which contains an
+    // allocation). Instead we just close it manually. This will never
+    // have the drop glue anyway because this code never returns (the
+    // child will either exec() or invoke libc::exit)
+    #[cfg(not(any(target_os = "tvos", target_os = "watchos")))]
+    unsafe fn do_exec(
+        &mut self,
+        stdio: ChildPipes,
+        maybe_envp: Option<&CStringArray>,
+    ) -> Result<!, io::Error> {
+        use crate::sys::{self, cvt_r};
+
+        if let Some(fd) = stdio.stdin.fd() {
+            cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))?;
+        }
+        if let Some(fd) = stdio.stdout.fd() {
+            cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))?;
+        }
+        if let Some(fd) = stdio.stderr.fd() {
+            cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))?;
+        }
+
+        #[cfg(not(target_os = "l4re"))]
+        {
+            if let Some(_g) = self.get_groups() {
+                //FIXME: Redox kernel does not support setgroups yet
+                #[cfg(not(target_os = "redox"))]
+                cvt(libc::setgroups(_g.len().try_into().unwrap(), _g.as_ptr()))?;
+            }
+            if let Some(u) = self.get_gid() {
+                cvt(libc::setgid(u as gid_t))?;
+            }
+            if let Some(u) = self.get_uid() {
+                // When dropping privileges from root, the `setgroups` call
+                // will remove any extraneous groups. We only drop groups
+                // if we have CAP_SETGID and we weren't given an explicit
+                // set of groups. If we don't call this, then even though our
+                // uid has dropped, we may still have groups that enable us to
+                // do super-user things.
+                //FIXME: Redox kernel does not support setgroups yet
+                #[cfg(not(target_os = "redox"))]
+                if self.get_groups().is_none() {
+                    let res = cvt(libc::setgroups(0, crate::ptr::null()));
+                    if let Err(e) = res {
+                        // Here we ignore the case of not having CAP_SETGID.
+                        // An alternative would be to require CAP_SETGID (in
+                        // addition to CAP_SETUID) for setting the UID.
+                        if e.raw_os_error() != Some(libc::EPERM) {
+                            return Err(e.into());
+                        }
+                    }
+                }
+                cvt(libc::setuid(u as uid_t))?;
+            }
+        }
+        if let Some(cwd) = self.get_cwd() {
+            cvt(libc::chdir(cwd.as_ptr()))?;
+        }
+
+        if let Some(pgroup) = self.get_pgroup() {
+            cvt(libc::setpgid(0, pgroup))?;
+        }
+
+        // emscripten has no signal support.
+        #[cfg(not(target_os = "emscripten"))]
+        {
+            // Inherit the signal mask from the parent rather than resetting it (i.e. do not call
+            // pthread_sigmask).
+
+            // If -Zon-broken-pipe is used, don't reset SIGPIPE to SIG_DFL.
+            // If -Zon-broken-pipe is not used, reset SIGPIPE to SIG_DFL for backward compatibility.
+            //
+            // -Zon-broken-pipe is an opportunity to change the default here.
+            if !crate::sys::pal::on_broken_pipe_flag_used() {
+                #[cfg(target_os = "android")] // see issue #88585
+                {
+                    let mut action: libc::sigaction = mem::zeroed();
+                    action.sa_sigaction = libc::SIG_DFL;
+                    cvt(libc::sigaction(libc::SIGPIPE, &action, crate::ptr::null_mut()))?;
+                }
+                #[cfg(not(target_os = "android"))]
+                {
+                    let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
+                    if ret == libc::SIG_ERR {
+                        return Err(io::Error::last_os_error());
+                    }
+                }
+                #[cfg(target_os = "hurd")]
+                {
+                    let ret = sys::signal(libc::SIGLOST, libc::SIG_DFL);
+                    if ret == libc::SIG_ERR {
+                        return Err(io::Error::last_os_error());
+                    }
+                }
+            }
+        }
+
+        for callback in self.get_closures().iter_mut() {
+            callback()?;
+        }
+
+        // Although we're performing an exec here we may also return with an
+        // error from this function (without actually exec'ing) in which case we
+        // want to be sure to restore the global environment back to what it
+        // once was, ensuring that our temporary override, when free'd, doesn't
+        // corrupt our process's environment.
+        let mut _reset = None;
+        if let Some(envp) = maybe_envp {
+            struct Reset(*const *const libc::c_char);
+
+            impl Drop for Reset {
+                fn drop(&mut self) {
+                    unsafe {
+                        *sys::os::environ() = self.0;
+                    }
+                }
+            }
+
+            _reset = Some(Reset(*sys::os::environ()));
+            *sys::os::environ() = envp.as_ptr();
+        }
+
+        libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
+        Err(io::Error::last_os_error())
+    }
+
+    #[cfg(any(target_os = "tvos", target_os = "watchos"))]
+    unsafe fn do_exec(
+        &mut self,
+        _stdio: ChildPipes,
+        _maybe_envp: Option<&CStringArray>,
+    ) -> Result<!, io::Error> {
+        return Err(Self::ERR_APPLE_TV_WATCH_NO_FORK_EXEC);
+    }
+
+    #[cfg(not(any(
+        target_os = "freebsd",
+        target_os = "illumos",
+        all(target_os = "linux", target_env = "gnu"),
+        all(target_os = "linux", target_env = "musl"),
+        target_os = "nto",
+        target_vendor = "apple",
+    )))]
+    fn posix_spawn(
+        &mut self,
+        _: &ChildPipes,
+        _: Option<&CStringArray>,
+    ) -> io::Result<Option<Process>> {
+        Ok(None)
+    }
+
+    // Only support platforms for which posix_spawn() can return ENOENT
+    // directly.
+    #[cfg(any(
+        target_os = "freebsd",
+        target_os = "illumos",
+        all(target_os = "linux", target_env = "gnu"),
+        all(target_os = "linux", target_env = "musl"),
+        target_os = "nto",
+        target_vendor = "apple",
+    ))]
+    // FIXME(#115199): Rust currently omits weak function definitions
+    // and its metadata from LLVM IR.
+    #[cfg_attr(target_os = "linux", no_sanitize(cfi))]
+    fn posix_spawn(
+        &mut self,
+        stdio: &ChildPipes,
+        envp: Option<&CStringArray>,
+    ) -> io::Result<Option<Process>> {
+        #[cfg(target_os = "linux")]
+        use core::sync::atomic::{AtomicU8, Ordering};
+
+        use crate::mem::MaybeUninit;
+        use crate::sys::{self, cvt_nz, on_broken_pipe_flag_used};
+
+        if self.get_gid().is_some()
+            || self.get_uid().is_some()
+            || (self.env_saw_path() && !self.program_is_path())
+            || !self.get_closures().is_empty()
+            || self.get_groups().is_some()
+        {
+            return Ok(None);
+        }
+
+        cfg_if::cfg_if! {
+            if #[cfg(target_os = "linux")] {
+                use crate::sys::weak::weak;
+
+                weak! {
+                    fn pidfd_spawnp(
+                        *mut libc::c_int,
+                        *const libc::c_char,
+                        *const libc::posix_spawn_file_actions_t,
+                        *const libc::posix_spawnattr_t,
+                        *const *mut libc::c_char,
+                        *const *mut libc::c_char
+                    ) -> libc::c_int
+                }
+
+                weak! { fn pidfd_getpid(libc::c_int) -> libc::c_int }
+
+                static PIDFD_SUPPORTED: AtomicU8 = AtomicU8::new(0);
+                const UNKNOWN: u8 = 0;
+                const SPAWN: u8 = 1;
+                // Obtaining a pidfd via the fork+exec path might work
+                const FORK_EXEC: u8 = 2;
+                // Neither pidfd_spawn nor fork/exec will get us a pidfd.
+                // Instead we'll just posix_spawn if the other preconditions are met.
+                const NO: u8 = 3;
+
+                if self.get_create_pidfd() {
+                    let mut support = PIDFD_SUPPORTED.load(Ordering::Relaxed);
+                    if support == FORK_EXEC {
+                        return Ok(None);
+                    }
+                    if support == UNKNOWN {
+                        support = NO;
+                        let our_pid = crate::process::id();
+                        let pidfd = cvt(unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) } as c_int);
+                        match pidfd {
+                            Ok(pidfd) => {
+                                support = FORK_EXEC;
+                                if let Some(Ok(pid)) = pidfd_getpid.get().map(|f| cvt(unsafe { f(pidfd) } as i32)) {
+                                    if pidfd_spawnp.get().is_some() && pid as u32 == our_pid {
+                                        support = SPAWN
+                                    }
+                                }
+                                unsafe { libc::close(pidfd) };
+                            }
+                            Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {
+                                // We're temporarily(?) out of file descriptors.  In this case obtaining a pidfd would also fail
+                                // Don't update the support flag so we can probe again later.
+                                return Err(e)
+                            }
+                            _ => {}
+                        }
+                        PIDFD_SUPPORTED.store(support, Ordering::Relaxed);
+                        if support == FORK_EXEC {
+                            return Ok(None);
+                        }
+                    }
+                    core::assert_matches::debug_assert_matches!(support, SPAWN | NO);
+                }
+            } else {
+                if self.get_create_pidfd() {
+                    unreachable!("only implemented on linux")
+                }
+            }
+        }
+
+        // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
+        #[cfg(all(target_os = "linux", target_env = "gnu"))]
+        {
+            if let Some(version) = sys::os::glibc_version() {
+                if version < (2, 24) {
+                    return Ok(None);
+                }
+            } else {
+                return Ok(None);
+            }
+        }
+
+        // On QNX Neutrino, posix_spawnp can fail with EBADF in case "another thread might have opened
+        // or closed a file descriptor while the posix_spawn() was occurring".
+        // Documentation says "... or try calling posix_spawn() again". This is what we do here.
+        // See also http://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/p/posix_spawn.html
+        #[cfg(target_os = "nto")]
+        unsafe fn retrying_libc_posix_spawnp(
+            pid: *mut pid_t,
+            file: *const c_char,
+            file_actions: *const posix_spawn_file_actions_t,
+            attrp: *const posix_spawnattr_t,
+            argv: *const *mut c_char,
+            envp: *const *mut c_char,
+        ) -> io::Result<i32> {
+            let mut delay = MIN_FORKSPAWN_SLEEP;
+            loop {
+                match libc::posix_spawnp(pid, file, file_actions, attrp, argv, envp) {
+                    libc::EBADF => {
+                        if delay < get_clock_resolution() {
+                            // We cannot sleep this short (it would be longer).
+                            // Yield instead.
+                            thread::yield_now();
+                        } else if delay < MAX_FORKSPAWN_SLEEP {
+                            thread::sleep(delay);
+                        } else {
+                            return Err(io::const_error!(
+                                ErrorKind::WouldBlock,
+                                "posix_spawnp returned EBADF too often",
+                            ));
+                        }
+                        delay *= 2;
+                        continue;
+                    }
+                    r => {
+                        return Ok(r);
+                    }
+                }
+            }
+        }
+
+        type PosixSpawnAddChdirFn = unsafe extern "C" fn(
+            *mut libc::posix_spawn_file_actions_t,
+            *const libc::c_char,
+        ) -> libc::c_int;
+
+        /// Get the function pointer for adding a chdir action to a
+        /// `posix_spawn_file_actions_t`, if available, assuming a dynamic libc.
+        ///
+        /// Some platforms can set a new working directory for a spawned process in the
+        /// `posix_spawn` path. This function looks up the function pointer for adding
+        /// such an action to a `posix_spawn_file_actions_t` struct.
+        #[cfg(not(all(target_os = "linux", target_env = "musl")))]
+        fn get_posix_spawn_addchdir() -> Option<PosixSpawnAddChdirFn> {
+            use crate::sys::weak::weak;
+
+            // POSIX.1-2024 standardizes this function:
+            // https://pubs.opengroup.org/onlinepubs/9799919799/functions/posix_spawn_file_actions_addchdir.html.
+            // The _np version is more widely available, though, so try that first.
+
+            weak! {
+                fn posix_spawn_file_actions_addchdir_np(
+                    *mut libc::posix_spawn_file_actions_t,
+                    *const libc::c_char
+                ) -> libc::c_int
+            }
+
+            weak! {
+                fn posix_spawn_file_actions_addchdir(
+                    *mut libc::posix_spawn_file_actions_t,
+                    *const libc::c_char
+                ) -> libc::c_int
+            }
+
+            posix_spawn_file_actions_addchdir_np
+                .get()
+                .or_else(|| posix_spawn_file_actions_addchdir.get())
+        }
+
+        /// Get the function pointer for adding a chdir action to a
+        /// `posix_spawn_file_actions_t`, if available, on platforms where the function
+        /// is known to exist.
+        ///
+        /// Weak symbol lookup doesn't work with statically linked libcs, so in cases
+        /// where static linking is possible we need to either check for the presence
+        /// of the symbol at compile time or know about it upfront.
+        #[cfg(all(target_os = "linux", target_env = "musl"))]
+        fn get_posix_spawn_addchdir() -> Option<PosixSpawnAddChdirFn> {
+            // Our minimum required musl supports this function, so we can just use it.
+            Some(libc::posix_spawn_file_actions_addchdir_np)
+        }
+
+        let addchdir = match self.get_cwd() {
+            Some(cwd) => {
+                if cfg!(target_vendor = "apple") {
+                    // There is a bug in macOS where a relative executable
+                    // path like "../myprogram" will cause `posix_spawn` to
+                    // successfully launch the program, but erroneously return
+                    // ENOENT when used with posix_spawn_file_actions_addchdir_np
+                    // which was introduced in macOS 10.15.
+                    if self.get_program_kind() == ProgramKind::Relative {
+                        return Ok(None);
+                    }
+                }
+                // Check for the availability of the posix_spawn addchdir
+                // function now. If it isn't available, bail and use the
+                // fork/exec path.
+                match get_posix_spawn_addchdir() {
+                    Some(f) => Some((f, cwd)),
+                    None => return Ok(None),
+                }
+            }
+            None => None,
+        };
+
+        let pgroup = self.get_pgroup();
+
+        struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);
+
+        impl Drop for PosixSpawnFileActions<'_> {
+            fn drop(&mut self) {
+                unsafe {
+                    libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
+                }
+            }
+        }
+
+        struct PosixSpawnattr<'a>(&'a mut MaybeUninit<libc::posix_spawnattr_t>);
+
+        impl Drop for PosixSpawnattr<'_> {
+            fn drop(&mut self) {
+                unsafe {
+                    libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
+                }
+            }
+        }
+
+        unsafe {
+            let mut attrs = MaybeUninit::uninit();
+            cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
+            let attrs = PosixSpawnattr(&mut attrs);
+
+            let mut flags = 0;
+
+            let mut file_actions = MaybeUninit::uninit();
+            cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
+            let file_actions = PosixSpawnFileActions(&mut file_actions);
+
+            if let Some(fd) = stdio.stdin.fd() {
+                cvt_nz(libc::posix_spawn_file_actions_adddup2(
+                    file_actions.0.as_mut_ptr(),
+                    fd,
+                    libc::STDIN_FILENO,
+                ))?;
+            }
+            if let Some(fd) = stdio.stdout.fd() {
+                cvt_nz(libc::posix_spawn_file_actions_adddup2(
+                    file_actions.0.as_mut_ptr(),
+                    fd,
+                    libc::STDOUT_FILENO,
+                ))?;
+            }
+            if let Some(fd) = stdio.stderr.fd() {
+                cvt_nz(libc::posix_spawn_file_actions_adddup2(
+                    file_actions.0.as_mut_ptr(),
+                    fd,
+                    libc::STDERR_FILENO,
+                ))?;
+            }
+            if let Some((f, cwd)) = addchdir {
+                cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
+            }
+
+            if let Some(pgroup) = pgroup {
+                flags |= libc::POSIX_SPAWN_SETPGROUP;
+                cvt_nz(libc::posix_spawnattr_setpgroup(attrs.0.as_mut_ptr(), pgroup))?;
+            }
+
+            // Inherit the signal mask from this process rather than resetting it (i.e. do not call
+            // posix_spawnattr_setsigmask).
+
+            // If -Zon-broken-pipe is used, don't reset SIGPIPE to SIG_DFL.
+            // If -Zon-broken-pipe is not used, reset SIGPIPE to SIG_DFL for backward compatibility.
+            //
+            // -Zon-broken-pipe is an opportunity to change the default here.
+            if !on_broken_pipe_flag_used() {
+                let mut default_set = MaybeUninit::<libc::sigset_t>::uninit();
+                cvt(sigemptyset(default_set.as_mut_ptr()))?;
+                cvt(sigaddset(default_set.as_mut_ptr(), libc::SIGPIPE))?;
+                #[cfg(target_os = "hurd")]
+                {
+                    cvt(sigaddset(default_set.as_mut_ptr(), libc::SIGLOST))?;
+                }
+                cvt_nz(libc::posix_spawnattr_setsigdefault(
+                    attrs.0.as_mut_ptr(),
+                    default_set.as_ptr(),
+                ))?;
+                flags |= libc::POSIX_SPAWN_SETSIGDEF;
+            }
+
+            cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
+
+            // Make sure we synchronize access to the global `environ` resource
+            let _env_lock = sys::os::env_read_lock();
+            let envp = envp.map(|c| c.as_ptr()).unwrap_or_else(|| *sys::os::environ() as *const _);
+
+            #[cfg(not(target_os = "nto"))]
+            let spawn_fn = libc::posix_spawnp;
+            #[cfg(target_os = "nto")]
+            let spawn_fn = retrying_libc_posix_spawnp;
+
+            #[cfg(target_os = "linux")]
+            if self.get_create_pidfd() && PIDFD_SUPPORTED.load(Ordering::Relaxed) == SPAWN {
+                let mut pidfd: libc::c_int = -1;
+                let spawn_res = pidfd_spawnp.get().unwrap()(
+                    &mut pidfd,
+                    self.get_program_cstr().as_ptr(),
+                    file_actions.0.as_ptr(),
+                    attrs.0.as_ptr(),
+                    self.get_argv().as_ptr() as *const _,
+                    envp as *const _,
+                );
+
+                let spawn_res = cvt_nz(spawn_res);
+                if let Err(ref e) = spawn_res
+                    && e.raw_os_error() == Some(libc::ENOSYS)
+                {
+                    PIDFD_SUPPORTED.store(FORK_EXEC, Ordering::Relaxed);
+                    return Ok(None);
+                }
+                spawn_res?;
+
+                let pid = match cvt(pidfd_getpid.get().unwrap()(pidfd)) {
+                    Ok(pid) => pid,
+                    Err(e) => {
+                        // The child has been spawned and we are holding its pidfd.
+                        // But we cannot obtain its pid even though pidfd_getpid support was verified earlier.
+                        // This might happen if libc can't open procfs because the file descriptor limit has been reached.
+                        libc::close(pidfd);
+                        return Err(Error::new(
+                            e.kind(),
+                            "pidfd_spawnp succeeded but the child's PID could not be obtained",
+                        ));
+                    }
+                };
+
+                return Ok(Some(Process::new(pid, pidfd)));
+            }
+
+            // Safety: -1 indicates we don't have a pidfd.
+            let mut p = Process::new(0, -1);
+
+            let spawn_res = spawn_fn(
+                &mut p.pid,
+                self.get_program_cstr().as_ptr(),
+                file_actions.0.as_ptr(),
+                attrs.0.as_ptr(),
+                self.get_argv().as_ptr() as *const _,
+                envp as *const _,
+            );
+
+            #[cfg(target_os = "nto")]
+            let spawn_res = spawn_res?;
+
+            cvt_nz(spawn_res)?;
+            Ok(Some(p))
+        }
+    }
+
+    #[cfg(target_os = "linux")]
+    fn send_pidfd(&self, sock: &crate::sys::net::Socket) {
+        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
+
+        use crate::io::IoSlice;
+        use crate::os::fd::RawFd;
+        use crate::sys::cvt_r;
+
+        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 = 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 = (&raw mut iov) as *mut _;
+            msg.msg_iovlen = 1;
+
+            // only attach cmsg if we successfully acquired the pidfd
+            if pidfd >= 0 {
+                msg.msg_controllen = size_of_val(&cmsg.buf) as _;
+                msg.msg_control = (&raw mut cmsg.buf) as *mut _;
+
+                let hdr = CMSG_FIRSTHDR((&raw mut msg) 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) => {}
+                other => rtabort!("failed to communicate with parent process. {:?}", other),
+            }
+        }
+    }
+
+    #[cfg(target_os = "linux")]
+    fn recv_pidfd(&self, sock: &crate::sys::net::Socket) -> pid_t {
+        use libc::{CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_SPACE, SCM_RIGHTS, SOL_SOCKET};
+
+        use crate::io::IoSliceMut;
+        use crate::sys::cvt_r;
+
+        unsafe {
+            const SCM_MSG_LEN: usize = 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 = (&raw mut iov) as *mut _;
+            msg.msg_iovlen = 1;
+            msg.msg_controllen = size_of::<Cmsg>() as _;
+            msg.msg_control = (&raw mut cmsg) as *mut _;
+
+            match cvt_r(|| libc::recvmsg(sock.as_raw(), &mut msg, libc::MSG_CMSG_CLOEXEC)) {
+                Err(_) => return -1,
+                Ok(_) => {}
+            }
+
+            let hdr = CMSG_FIRSTHDR((&raw mut msg) 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]
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Processes
+////////////////////////////////////////////////////////////////////////////////
+
+/// The unique ID of the process (this should never be negative).
+pub struct Process {
+    pid: pid_t,
+    status: Option<ExitStatus>,
+    // On Linux, stores the pidfd created for this child.
+    // This is None if the user did not request pidfd creation,
+    // or if the pidfd could not be created for some reason
+    // (e.g. the `pidfd_open` syscall was not available).
+    #[cfg(target_os = "linux")]
+    pidfd: Option<PidFd>,
+}
+
+impl Process {
+    #[cfg(target_os = "linux")]
+    /// # Safety
+    ///
+    /// `pidfd` must either be -1 (representing no file descriptor) or a valid, exclusively owned file
+    /// descriptor (See [I/O Safety]).
+    ///
+    /// [I/O Safety]: crate::io#io-safety
+    unsafe fn new(pid: pid_t, pidfd: pid_t) -> Self {
+        use crate::os::unix::io::FromRawFd;
+        use crate::sys_common::FromInner;
+        // Safety: If `pidfd` is nonnegative, we assume it's valid and otherwise unowned.
+        let pidfd = (pidfd >= 0).then(|| PidFd::from_inner(sys::fd::FileDesc::from_raw_fd(pidfd)));
+        Process { pid, status: None, pidfd }
+    }
+
+    #[cfg(not(target_os = "linux"))]
+    unsafe fn new(pid: pid_t, _pidfd: pid_t) -> Self {
+        Process { pid, status: None }
+    }
+
+    pub fn id(&self) -> u32 {
+        self.pid as u32
+    }
+
+    pub fn kill(&mut self) -> io::Result<()> {
+        // If we've already waited on this process then the pid can be recycled
+        // and used for another process, and we probably shouldn't be killing
+        // random processes, so return Ok because the process has exited already.
+        if self.status.is_some() {
+            return Ok(());
+        }
+        #[cfg(target_os = "linux")]
+        if let Some(pid_fd) = self.pidfd.as_ref() {
+            // pidfd_send_signal predates pidfd_open. so if we were able to get an fd then sending signals will work too
+            return pid_fd.kill();
+        }
+        cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
+    }
+
+    pub fn wait(&mut self) -> io::Result<ExitStatus> {
+        use crate::sys::cvt_r;
+        if let Some(status) = self.status {
+            return Ok(status);
+        }
+        #[cfg(target_os = "linux")]
+        if let Some(pid_fd) = self.pidfd.as_ref() {
+            let status = pid_fd.wait()?;
+            self.status = Some(status);
+            return Ok(status);
+        }
+        let mut status = 0 as c_int;
+        cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
+        self.status = Some(ExitStatus::new(status));
+        Ok(ExitStatus::new(status))
+    }
+
+    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        if let Some(status) = self.status {
+            return Ok(Some(status));
+        }
+        #[cfg(target_os = "linux")]
+        if let Some(pid_fd) = self.pidfd.as_ref() {
+            let status = pid_fd.try_wait()?;
+            if let Some(status) = status {
+                self.status = Some(status)
+            }
+            return Ok(status);
+        }
+        let mut status = 0 as c_int;
+        let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
+        if pid == 0 {
+            Ok(None)
+        } else {
+            self.status = Some(ExitStatus::new(status));
+            Ok(Some(ExitStatus::new(status)))
+        }
+    }
+}
+
+/// Unix exit statuses
+//
+// 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, Default)]
+pub struct ExitStatus(c_int);
+
+impl fmt::Debug for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("unix_wait_status").field(&self.0).finish()
+    }
+}
+
+impl ExitStatus {
+    pub fn new(status: c_int) -> ExitStatus {
+        ExitStatus(status)
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn from_waitid_siginfo(siginfo: libc::siginfo_t) -> ExitStatus {
+        let status = unsafe { siginfo.si_status() };
+
+        match siginfo.si_code {
+            libc::CLD_EXITED => ExitStatus((status & 0xff) << 8),
+            libc::CLD_KILLED => ExitStatus(status),
+            libc::CLD_DUMPED => ExitStatus(status | 0x80),
+            libc::CLD_CONTINUED => ExitStatus(0xffff),
+            libc::CLD_STOPPED | libc::CLD_TRAPPED => ExitStatus(((status & 0xff) << 8) | 0x7f),
+            _ => unreachable!("waitid() should only return the above codes"),
+        }
+    }
+
+    fn exited(&self) -> bool {
+        libc::WIFEXITED(self.0)
+    }
+
+    pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
+        // This assumes that WIFEXITED(status) && WEXITSTATUS==0 corresponds to status==0. This is
+        // true on all actual versions of Unix, is widely assumed, and is specified in SuS
+        // https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html. If it is not
+        // true for a platform pretending to be Unix, the tests (our doctests, and also
+        // unix/tests.rs) will spot it. `ExitStatusError::code` assumes this too.
+        match NonZero::try_from(self.0) {
+            /* was nonzero */ Ok(failure) => Err(ExitStatusError(failure)),
+            /* was zero, couldn't convert */ Err(_) => Ok(()),
+        }
+    }
+
+    pub fn code(&self) -> Option<i32> {
+        self.exited().then(|| libc::WEXITSTATUS(self.0))
+    }
+
+    pub fn signal(&self) -> Option<i32> {
+        libc::WIFSIGNALED(self.0).then(|| libc::WTERMSIG(self.0))
+    }
+
+    pub fn core_dumped(&self) -> bool {
+        libc::WIFSIGNALED(self.0) && libc::WCOREDUMP(self.0)
+    }
+
+    pub fn stopped_signal(&self) -> Option<i32> {
+        libc::WIFSTOPPED(self.0).then(|| libc::WSTOPSIG(self.0))
+    }
+
+    pub fn continued(&self) -> bool {
+        libc::WIFCONTINUED(self.0)
+    }
+
+    pub fn into_raw(&self) -> c_int {
+        self.0
+    }
+}
+
+/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
+impl From<c_int> for ExitStatus {
+    fn from(a: c_int) -> ExitStatus {
+        ExitStatus(a)
+    }
+}
+
+/// Converts a signal number to a readable, searchable name.
+///
+/// This string should be displayed right after the signal number.
+/// If a signal is unrecognized, it returns the empty string, so that
+/// you just get the number like "0". If it is recognized, you'll get
+/// something like "9 (SIGKILL)".
+fn signal_string(signal: i32) -> &'static str {
+    match signal {
+        libc::SIGHUP => " (SIGHUP)",
+        libc::SIGINT => " (SIGINT)",
+        libc::SIGQUIT => " (SIGQUIT)",
+        libc::SIGILL => " (SIGILL)",
+        libc::SIGTRAP => " (SIGTRAP)",
+        libc::SIGABRT => " (SIGABRT)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGBUS => " (SIGBUS)",
+        libc::SIGFPE => " (SIGFPE)",
+        libc::SIGKILL => " (SIGKILL)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGUSR1 => " (SIGUSR1)",
+        libc::SIGSEGV => " (SIGSEGV)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGUSR2 => " (SIGUSR2)",
+        libc::SIGPIPE => " (SIGPIPE)",
+        libc::SIGALRM => " (SIGALRM)",
+        libc::SIGTERM => " (SIGTERM)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGCHLD => " (SIGCHLD)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGCONT => " (SIGCONT)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGSTOP => " (SIGSTOP)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGTSTP => " (SIGTSTP)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGTTIN => " (SIGTTIN)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGTTOU => " (SIGTTOU)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGURG => " (SIGURG)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGXCPU => " (SIGXCPU)",
+        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
+        libc::SIGXFSZ => " (SIGXFSZ)",
+        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
+        libc::SIGVTALRM => " (SIGVTALRM)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGPROF => " (SIGPROF)",
+        #[cfg(not(any(target_os = "l4re", target_os = "rtems")))]
+        libc::SIGWINCH => " (SIGWINCH)",
+        #[cfg(not(any(target_os = "haiku", target_os = "l4re")))]
+        libc::SIGIO => " (SIGIO)",
+        #[cfg(target_os = "haiku")]
+        libc::SIGPOLL => " (SIGPOLL)",
+        #[cfg(not(target_os = "l4re"))]
+        libc::SIGSYS => " (SIGSYS)",
+        // For information on Linux signals, run `man 7 signal`
+        #[cfg(all(
+            target_os = "linux",
+            any(
+                target_arch = "x86_64",
+                target_arch = "x86",
+                target_arch = "arm",
+                target_arch = "aarch64"
+            )
+        ))]
+        libc::SIGSTKFLT => " (SIGSTKFLT)",
+        #[cfg(any(target_os = "linux", target_os = "nto", target_os = "cygwin"))]
+        libc::SIGPWR => " (SIGPWR)",
+        #[cfg(any(
+            target_os = "freebsd",
+            target_os = "netbsd",
+            target_os = "openbsd",
+            target_os = "dragonfly",
+            target_os = "nto",
+            target_vendor = "apple",
+            target_os = "cygwin",
+        ))]
+        libc::SIGEMT => " (SIGEMT)",
+        #[cfg(any(
+            target_os = "freebsd",
+            target_os = "netbsd",
+            target_os = "openbsd",
+            target_os = "dragonfly",
+            target_vendor = "apple",
+        ))]
+        libc::SIGINFO => " (SIGINFO)",
+        #[cfg(target_os = "hurd")]
+        libc::SIGLOST => " (SIGLOST)",
+        #[cfg(target_os = "freebsd")]
+        libc::SIGTHR => " (SIGTHR)",
+        #[cfg(target_os = "freebsd")]
+        libc::SIGLIBRT => " (SIGLIBRT)",
+        _ => "",
+    }
+}
+
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(code) = self.code() {
+            write!(f, "exit status: {code}")
+        } else if let Some(signal) = self.signal() {
+            let signal_string = signal_string(signal);
+            if self.core_dumped() {
+                write!(f, "signal: {signal}{signal_string} (core dumped)")
+            } else {
+                write!(f, "signal: {signal}{signal_string}")
+            }
+        } else if let Some(signal) = self.stopped_signal() {
+            let signal_string = signal_string(signal);
+            write!(f, "stopped (not terminated) by signal: {signal}{signal_string}")
+        } else if self.continued() {
+            write!(f, "continued (WIFCONTINUED)")
+        } else {
+            write!(f, "unrecognised wait status: {} {:#x}", self.0, self.0)
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub struct ExitStatusError(NonZero<c_int>);
+
+impl Into<ExitStatus> for ExitStatusError {
+    fn into(self) -> ExitStatus {
+        ExitStatus(self.0.into())
+    }
+}
+
+impl fmt::Debug for ExitStatusError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("unix_wait_status").field(&self.0).finish()
+    }
+}
+
+impl ExitStatusError {
+    pub fn code(self) -> Option<NonZero<i32>> {
+        ExitStatus(self.0.into()).code().map(|st| st.try_into().unwrap())
+    }
+}
+
+#[cfg(target_os = "linux")]
+mod linux_child_ext {
+    use crate::io::ErrorKind;
+    use crate::os::linux::process as os;
+    use crate::sys::pal::linux::pidfd as imp;
+    use crate::sys_common::FromInner;
+    use crate::{io, mem};
+
+    #[unstable(feature = "linux_pidfd", issue = "82971")]
+    impl crate::os::linux::process::ChildExt for crate::process::Child {
+        fn pidfd(&self) -> io::Result<&os::PidFd> {
+            self.handle
+                .pidfd
+                .as_ref()
+                // SAFETY: The os type is a transparent wrapper, therefore we can transmute references
+                .map(|fd| unsafe { mem::transmute::<&imp::PidFd, &os::PidFd>(fd) })
+                .ok_or_else(|| io::const_error!(ErrorKind::Uncategorized, "no pidfd was created."))
+        }
+
+        fn into_pidfd(mut self) -> Result<os::PidFd, Self> {
+            self.handle
+                .pidfd
+                .take()
+                .map(|fd| <os::PidFd as FromInner<imp::PidFd>>::from_inner(fd))
+                .ok_or_else(|| self)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;
+
+// See [`unsupported_wait_status::compare_with_linux`];
+#[cfg(all(test, target_os = "linux"))]
+#[path = "unsupported/wait_status.rs"]
+mod unsupported_wait_status;
diff --git a/library/std/src/sys/process/unix/unix/tests.rs b/library/std/src/sys/process/unix/unix/tests.rs
new file mode 100644
index 00000000000..f4d6ac6b4e3
--- /dev/null
+++ b/library/std/src/sys/process/unix/unix/tests.rs
@@ -0,0 +1,75 @@
+use crate::os::unix::process::{CommandExt, ExitStatusExt};
+use crate::panic::catch_unwind;
+use crate::process::Command;
+
+// Many of the other aspects of this situation, including heap alloc concurrency
+// safety etc., are tested in tests/ui/process/process-panic-after-fork.rs
+
+#[test]
+fn exitstatus_display_tests() {
+    // In practice this is the same on every Unix.
+    // If some weird platform turns out to be different, and this test fails, use #[cfg].
+    use crate::os::unix::process::ExitStatusExt;
+    use crate::process::ExitStatus;
+
+    let t = |v, s| assert_eq!(s, format!("{}", <ExitStatus as ExitStatusExt>::from_raw(v)));
+
+    t(0x0000f, "signal: 15 (SIGTERM)");
+    t(0x0008b, "signal: 11 (SIGSEGV) (core dumped)");
+    t(0x00000, "exit status: 0");
+    t(0x0ff00, "exit status: 255");
+
+    // On MacOS, 0x0137f is WIFCONTINUED, not WIFSTOPPED. Probably *BSD is similar.
+    //   https://github.com/rust-lang/rust/pull/82749#issuecomment-790525956
+    // The purpose of this test is to test our string formatting, not our understanding of the wait
+    // status magic numbers. So restrict these to Linux.
+    if cfg!(target_os = "linux") {
+        #[cfg(any(target_arch = "mips", target_arch = "mips64"))]
+        t(0x0137f, "stopped (not terminated) by signal: 19 (SIGPWR)");
+
+        #[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
+        t(0x0137f, "stopped (not terminated) by signal: 19 (SIGCONT)");
+
+        #[cfg(not(any(
+            target_arch = "mips",
+            target_arch = "mips64",
+            target_arch = "sparc",
+            target_arch = "sparc64"
+        )))]
+        t(0x0137f, "stopped (not terminated) by signal: 19 (SIGSTOP)");
+
+        t(0x0ffff, "continued (WIFCONTINUED)");
+    }
+
+    // Testing "unrecognised wait status" is hard because the wait.h macros typically
+    // assume that the value came from wait and isn't mad. With the glibc I have here
+    // this works:
+    if cfg!(all(target_os = "linux", target_env = "gnu")) {
+        t(0x000ff, "unrecognised wait status: 255 0xff");
+    }
+}
+
+#[test]
+#[cfg_attr(target_os = "emscripten", ignore)]
+fn test_command_fork_no_unwind() {
+    let got = catch_unwind(|| {
+        let mut c = Command::new("echo");
+        c.arg("hi");
+        unsafe {
+            c.pre_exec(|| panic!("{}", "crash now!"));
+        }
+        let st = c.status().expect("failed to get command status");
+        dbg!(st);
+        st
+    });
+    dbg!(&got);
+    let status = got.expect("panic unexpectedly propagated");
+    dbg!(status);
+    let signal = status.signal().expect("expected child process to die of signal");
+    assert!(
+        signal == libc::SIGABRT
+            || signal == libc::SIGILL
+            || signal == libc::SIGTRAP
+            || signal == libc::SIGSEGV
+    );
+}
diff --git a/library/std/src/sys/process/unix/unsupported.rs b/library/std/src/sys/process/unix/unsupported.rs
new file mode 100644
index 00000000000..78d270923cf
--- /dev/null
+++ b/library/std/src/sys/process/unix/unsupported.rs
@@ -0,0 +1,72 @@
+use libc::{c_int, pid_t};
+
+use super::common::*;
+use crate::io;
+use crate::num::NonZero;
+use crate::sys::pal::unsupported::*;
+
+////////////////////////////////////////////////////////////////////////////////
+// Command
+////////////////////////////////////////////////////////////////////////////////
+
+impl Command {
+    pub fn spawn(
+        &mut self,
+        _default: Stdio,
+        _needs_stdin: bool,
+    ) -> io::Result<(Process, StdioPipes)> {
+        unsupported()
+    }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        unsupported()
+    }
+
+    pub fn exec(&mut self, _default: Stdio) -> io::Error {
+        unsupported_err()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Processes
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct Process {
+    _handle: pid_t,
+}
+
+impl Process {
+    pub fn id(&self) -> u32 {
+        0
+    }
+
+    pub fn kill(&mut self) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn wait(&mut self) -> io::Result<ExitStatus> {
+        unsupported()
+    }
+
+    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        unsupported()
+    }
+}
+
+mod wait_status;
+pub use wait_status::ExitStatus;
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ExitStatusError(NonZero<c_int>);
+
+impl Into<ExitStatus> for ExitStatusError {
+    fn into(self) -> ExitStatus {
+        ExitStatus::from(c_int::from(self.0))
+    }
+}
+
+impl ExitStatusError {
+    pub fn code(self) -> Option<NonZero<i32>> {
+        ExitStatus::from(c_int::from(self.0)).code().map(|st| st.try_into().unwrap())
+    }
+}
diff --git a/library/std/src/sys/process/unix/unsupported/wait_status.rs b/library/std/src/sys/process/unix/unsupported/wait_status.rs
new file mode 100644
index 00000000000..f348d557e4b
--- /dev/null
+++ b/library/std/src/sys/process/unix/unsupported/wait_status.rs
@@ -0,0 +1,84 @@
+//! Emulated wait status for non-Unix #[cfg(unix) platforms
+//!
+//! Separate module to facilitate testing against a real Unix implementation.
+
+use super::ExitStatusError;
+use crate::ffi::c_int;
+use crate::fmt;
+use crate::num::NonZero;
+
+/// Emulated wait status for use by `unsupported.rs`
+///
+/// Uses the "traditional unix" encoding.  For use on platfors which are `#[cfg(unix)]`
+/// but do not actually support subprocesses at all.
+///
+/// These platforms aren't Unix, but are simply pretending to be for porting convenience.
+/// So, we provide a faithful pretence here.
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
+pub struct ExitStatus {
+    wait_status: c_int,
+}
+
+/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it
+impl From<c_int> for ExitStatus {
+    fn from(wait_status: c_int) -> ExitStatus {
+        ExitStatus { wait_status }
+    }
+}
+
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "emulated wait status: {}", self.wait_status)
+    }
+}
+
+impl ExitStatus {
+    pub fn code(&self) -> Option<i32> {
+        // Linux and FreeBSD both agree that values linux 0x80
+        // count as "WIFEXITED" even though this is quite mad.
+        // Likewise the macros disregard all the high bits, so are happy to declare
+        // out-of-range values to be WIFEXITED, WIFSTOPPED, etc.
+        let w = self.wait_status;
+        if (w & 0x7f) == 0 { Some((w & 0xff00) >> 8) } else { None }
+    }
+
+    #[allow(unused)]
+    pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
+        // This assumes that WIFEXITED(status) && WEXITSTATUS==0 corresponds to status==0. This is
+        // true on all actual versions of Unix, is widely assumed, and is specified in SuS
+        // https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html. If it is not
+        // true for a platform pretending to be Unix, the tests (our doctests, and also
+        // unix/tests.rs) will spot it. `ExitStatusError::code` assumes this too.
+        match NonZero::try_from(self.wait_status) {
+            /* was nonzero */ Ok(failure) => Err(ExitStatusError(failure)),
+            /* was zero, couldn't convert */ Err(_) => Ok(()),
+        }
+    }
+
+    pub fn signal(&self) -> Option<i32> {
+        let signal = self.wait_status & 0x007f;
+        if signal > 0 && signal < 0x7f { Some(signal) } else { None }
+    }
+
+    pub fn core_dumped(&self) -> bool {
+        self.signal().is_some() && (self.wait_status & 0x80) != 0
+    }
+
+    pub fn stopped_signal(&self) -> Option<i32> {
+        let w = self.wait_status;
+        if (w & 0xff) == 0x7f { Some((w & 0xff00) >> 8) } else { None }
+    }
+
+    pub fn continued(&self) -> bool {
+        self.wait_status == 0xffff
+    }
+
+    pub fn into_raw(&self) -> c_int {
+        self.wait_status
+    }
+}
+
+#[cfg(test)]
+#[path = "wait_status/tests.rs"]
+// needed because this module is also imported through #[path] for testing purposes
+mod tests;
diff --git a/library/std/src/sys/process/unix/unsupported/wait_status/tests.rs b/library/std/src/sys/process/unix/unsupported/wait_status/tests.rs
new file mode 100644
index 00000000000..0d9232fac5e
--- /dev/null
+++ b/library/std/src/sys/process/unix/unsupported/wait_status/tests.rs
@@ -0,0 +1,36 @@
+// Note that tests in this file are run on Linux as well as on platforms using unsupported
+
+// Test that our emulation exactly matches Linux
+//
+// This test runs *on Linux* but it tests
+// the implementation used on non-Unix `#[cfg(unix)]` platforms.
+//
+// I.e. we're using Linux as a proxy for "trad unix".
+#[cfg(target_os = "linux")]
+#[test]
+fn compare_with_linux() {
+    use super::ExitStatus as Emulated;
+    use crate::os::unix::process::ExitStatusExt as _;
+    use crate::process::ExitStatus as Real;
+
+    // Check that we handle out-of-range values similarly, too.
+    for wstatus in -0xf_ffff..0xf_ffff {
+        let emulated = Emulated::from(wstatus);
+        let real = Real::from_raw(wstatus);
+
+        macro_rules! compare { { $method:ident } => {
+            assert_eq!(
+                emulated.$method(),
+                real.$method(),
+                "{wstatus:#x}.{}()",
+                stringify!($method),
+            );
+        } }
+        compare!(code);
+        compare!(signal);
+        compare!(core_dumped);
+        compare!(stopped_signal);
+        compare!(continued);
+        compare!(into_raw);
+    }
+}
diff --git a/library/std/src/sys/process/unix/vxworks.rs b/library/std/src/sys/process/unix/vxworks.rs
new file mode 100644
index 00000000000..5f1727789a1
--- /dev/null
+++ b/library/std/src/sys/process/unix/vxworks.rs
@@ -0,0 +1,268 @@
+#![forbid(unsafe_op_in_unsafe_fn)]
+use libc::{self, RTP_ID, c_char, c_int};
+
+use super::common::*;
+use crate::io::{self, ErrorKind};
+use crate::num::NonZero;
+use crate::sys::cvt;
+use crate::sys::pal::thread;
+use crate::{fmt, sys};
+
+////////////////////////////////////////////////////////////////////////////////
+// Command
+////////////////////////////////////////////////////////////////////////////////
+
+impl Command {
+    pub fn spawn(
+        &mut self,
+        default: Stdio,
+        needs_stdin: bool,
+    ) -> io::Result<(Process, StdioPipes)> {
+        use crate::sys::cvt_r;
+        let envp = self.capture_env();
+
+        if self.saw_nul() {
+            return Err(io::const_error!(
+                ErrorKind::InvalidInput,
+                "nul byte found in provided data",
+            ));
+        }
+        let (ours, theirs) = self.setup_io(default, needs_stdin)?;
+        let mut p = Process { pid: 0, status: None };
+
+        unsafe {
+            macro_rules! t {
+                ($e:expr) => {
+                    match $e {
+                        Ok(e) => e,
+                        Err(e) => return Err(e.into()),
+                    }
+                };
+            }
+
+            let mut orig_stdin = libc::STDIN_FILENO;
+            let mut orig_stdout = libc::STDOUT_FILENO;
+            let mut orig_stderr = libc::STDERR_FILENO;
+
+            if let Some(fd) = theirs.stdin.fd() {
+                orig_stdin = t!(cvt_r(|| libc::dup(libc::STDIN_FILENO)));
+                t!(cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO)));
+            }
+            if let Some(fd) = theirs.stdout.fd() {
+                orig_stdout = t!(cvt_r(|| libc::dup(libc::STDOUT_FILENO)));
+                t!(cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO)));
+            }
+            if let Some(fd) = theirs.stderr.fd() {
+                orig_stderr = t!(cvt_r(|| libc::dup(libc::STDERR_FILENO)));
+                t!(cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO)));
+            }
+
+            if let Some(cwd) = self.get_cwd() {
+                t!(cvt(libc::chdir(cwd.as_ptr())));
+            }
+
+            // pre_exec closures are ignored on VxWorks
+            let _ = self.get_closures();
+
+            let c_envp = envp
+                .as_ref()
+                .map(|c| c.as_ptr())
+                .unwrap_or_else(|| *sys::os::environ() as *const _);
+            let stack_size = crate::cmp::max(
+                crate::env::var_os("RUST_MIN_STACK")
+                    .and_then(|s| s.to_str().and_then(|s| s.parse().ok()))
+                    .unwrap_or(thread::DEFAULT_MIN_STACK_SIZE),
+                libc::PTHREAD_STACK_MIN,
+            );
+
+            // ensure that access to the environment is synchronized
+            let _lock = sys::os::env_read_lock();
+
+            let ret = libc::rtpSpawn(
+                self.get_program_cstr().as_ptr(),
+                self.get_argv().as_ptr() as *mut *const c_char, // argv
+                c_envp as *mut *const c_char,
+                100 as c_int, // initial priority
+                stack_size,   // initial stack size.
+                0,            // options
+                0,            // task options
+            );
+
+            // Because FileDesc was not used, each duplicated file descriptor
+            // needs to be closed manually
+            if orig_stdin != libc::STDIN_FILENO {
+                t!(cvt_r(|| libc::dup2(orig_stdin, libc::STDIN_FILENO)));
+                libc::close(orig_stdin);
+            }
+            if orig_stdout != libc::STDOUT_FILENO {
+                t!(cvt_r(|| libc::dup2(orig_stdout, libc::STDOUT_FILENO)));
+                libc::close(orig_stdout);
+            }
+            if orig_stderr != libc::STDERR_FILENO {
+                t!(cvt_r(|| libc::dup2(orig_stderr, libc::STDERR_FILENO)));
+                libc::close(orig_stderr);
+            }
+
+            if ret != libc::RTP_ID_ERROR {
+                p.pid = ret;
+                Ok((p, ours))
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
+    pub fn exec(&mut self, default: Stdio) -> io::Error {
+        let ret = Command::spawn(self, default, false);
+        match ret {
+            Ok(t) => unsafe {
+                let mut status = 0 as c_int;
+                libc::waitpid(t.0.pid, &mut status, 0);
+                libc::exit(0);
+            },
+            Err(e) => e,
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Processes
+////////////////////////////////////////////////////////////////////////////////
+
+/// The unique id of the process (this should never be negative).
+pub struct Process {
+    pid: RTP_ID,
+    status: Option<ExitStatus>,
+}
+
+impl Process {
+    pub fn id(&self) -> u32 {
+        self.pid as u32
+    }
+
+    pub fn kill(&mut self) -> io::Result<()> {
+        // If we've already waited on this process then the pid can be recycled
+        // and used for another process, and we probably shouldn't be killing
+        // random processes, so return Ok because the process has exited already.
+        if self.status.is_some() {
+            Ok(())
+        } else {
+            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
+        }
+    }
+
+    pub fn wait(&mut self) -> io::Result<ExitStatus> {
+        use crate::sys::cvt_r;
+        if let Some(status) = self.status {
+            return Ok(status);
+        }
+        let mut status = 0 as c_int;
+        cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
+        self.status = Some(ExitStatus::new(status));
+        Ok(ExitStatus::new(status))
+    }
+
+    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        if let Some(status) = self.status {
+            return Ok(Some(status));
+        }
+        let mut status = 0 as c_int;
+        let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
+        if pid == 0 {
+            Ok(None)
+        } else {
+            self.status = Some(ExitStatus::new(status));
+            Ok(Some(ExitStatus::new(status)))
+        }
+    }
+}
+
+/// Unix exit statuses
+#[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
+pub struct ExitStatus(c_int);
+
+impl ExitStatus {
+    pub fn new(status: c_int) -> ExitStatus {
+        ExitStatus(status)
+    }
+
+    fn exited(&self) -> bool {
+        libc::WIFEXITED(self.0)
+    }
+
+    pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
+        // This assumes that WIFEXITED(status) && WEXITSTATUS==0 corresponds to status==0. This is
+        // true on all actual versions of Unix, is widely assumed, and is specified in SuS
+        // https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html. If it is not
+        // true for a platform pretending to be Unix, the tests (our doctests, and also
+        // unix/tests.rs) will spot it. `ExitStatusError::code` assumes this too.
+        match NonZero::try_from(self.0) {
+            Ok(failure) => Err(ExitStatusError(failure)),
+            Err(_) => Ok(()),
+        }
+    }
+
+    pub fn code(&self) -> Option<i32> {
+        if self.exited() { Some(libc::WEXITSTATUS(self.0)) } else { None }
+    }
+
+    pub fn signal(&self) -> Option<i32> {
+        if !self.exited() { Some(libc::WTERMSIG(self.0)) } else { None }
+    }
+
+    pub fn core_dumped(&self) -> bool {
+        // This method is not yet properly implemented on VxWorks
+        false
+    }
+
+    pub fn stopped_signal(&self) -> Option<i32> {
+        if libc::WIFSTOPPED(self.0) { Some(libc::WSTOPSIG(self.0)) } else { None }
+    }
+
+    pub fn continued(&self) -> bool {
+        // This method is not yet properly implemented on VxWorks
+        false
+    }
+
+    pub fn into_raw(&self) -> c_int {
+        self.0
+    }
+}
+
+/// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
+impl From<c_int> for ExitStatus {
+    fn from(a: c_int) -> ExitStatus {
+        ExitStatus(a)
+    }
+}
+
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(code) = self.code() {
+            write!(f, "exit code: {code}")
+        } else {
+            let signal = self.signal().unwrap();
+            write!(f, "signal: {signal}")
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ExitStatusError(NonZero<c_int>);
+
+impl Into<ExitStatus> for ExitStatusError {
+    fn into(self) -> ExitStatus {
+        ExitStatus(self.0.into())
+    }
+}
+
+impl ExitStatusError {
+    pub fn code(self) -> Option<NonZero<i32>> {
+        ExitStatus(self.0.into()).code().map(|st| st.try_into().unwrap())
+    }
+}