platform/redox/mod.rs

use core::{mem, ptr, result::Result as CoreResult, slice, str};
use syscall::{
    self,
    data::{Map, Stat as redox_stat, StatVfs as redox_statvfs, TimeSpec as redox_timespec},
    PtraceEvent, Result,
};

use crate::{
    c_str::{CStr, CString},
    fs::File,
    header::{
        dirent::dirent,
        errno::{EINVAL, EIO, ENOMEM, EPERM, ERANGE},
        fcntl,
        sys_mman::{MAP_ANONYMOUS, PROT_READ, PROT_WRITE},
        sys_random,
        sys_resource::{rlimit, RLIM_INFINITY},
        sys_stat::stat,
        sys_statvfs::statvfs,
        sys_time::{timeval, timezone},
        sys_utsname::{utsname, UTSLENGTH},
        sys_wait,
        time::timespec,
        unistd::{F_OK, R_OK, W_OK, X_OK},
    },
    io::{self, prelude::*, BufReader, SeekFrom},
};

use super::{errno, types::*, Pal, Read};

static mut BRK_CUR: *mut c_void = ptr::null_mut();
static mut BRK_END: *mut c_void = ptr::null_mut();

mod epoll;
mod extra;
mod ptrace;
mod signal;
mod socket;

macro_rules! path_from_c_str {
    ($c_str:expr) => {{
        match $c_str.to_str() {
            Ok(ok) => ok,
            Err(err) => {
                unsafe {
                    errno = EINVAL;
                }
                return -1;
            }
        }
    }};
}

pub fn e(sys: Result<usize>) -> usize {
    match sys {
        Ok(ok) => ok,
        Err(err) => {
            unsafe {
                errno = err.errno as c_int;
            }
            !0
        }
    }
}

pub struct Sys;

impl Pal for Sys {
    fn access(path: &CStr, mode: c_int) -> c_int {
        let fd = match File::open(path, fcntl::O_PATH | fcntl::O_CLOEXEC) {
            Ok(fd) => fd,
            Err(_) => return -1,
        };

        if mode == F_OK {
            return 0;
        }

        let mut stat = syscall::Stat::default();

        if e(syscall::fstat(*fd as usize, &mut stat)) == !0 {
            return -1;
        }

        let uid = e(syscall::getuid());
        if uid == !0 {
            return -1;
        }
        let gid = e(syscall::getgid());
        if gid == !0 {
            return -1;
        }

        let perms = if stat.st_uid as usize == uid {
            stat.st_mode >> (3 * 2 & 0o7)
        } else if stat.st_gid as usize == gid {
            stat.st_mode >> (3 * 1 & 0o7)
        } else {
            stat.st_mode & 0o7
        };
        if (mode & R_OK == R_OK && perms & 0o4 != 0o4)
            || (mode & W_OK == W_OK && perms & 0o2 != 0o2)
            || (mode & X_OK == X_OK && perms & 0o1 != 0o1)
        {
            unsafe {
                errno = EINVAL;
            }
            return -1;
        }

        0
    }

    fn brk(addr: *mut c_void) -> *mut c_void {
        unsafe {
            // On first invocation, allocate a buffer for brk
            if BRK_CUR.is_null() {
                // 4 megabytes of RAM ought to be enough for anybody
                const BRK_MAX_SIZE: usize = 4 * 1024 * 1024;

                let allocated = Self::mmap(
                    ptr::null_mut(),
                    BRK_MAX_SIZE,
                    PROT_READ | PROT_WRITE,
                    MAP_ANONYMOUS,
                    0,
                    0,
                );
                if allocated == !0 as *mut c_void
                /* MAP_FAILED */
                {
                    return !0 as *mut c_void;
                }

                BRK_CUR = allocated;
                BRK_END = (allocated as *mut u8).add(BRK_MAX_SIZE) as *mut c_void;
            }

            if addr.is_null() {
                // Lookup what previous brk() invocations have set the address to
                BRK_CUR
            } else if BRK_CUR <= addr && addr < BRK_END {
                // It's inside buffer, return
                BRK_CUR = addr;
                addr
            } else {
                // It was outside of valid range
                errno = ENOMEM;
                ptr::null_mut()
            }
        }
    }

    fn chdir(path: &CStr) -> c_int {
        let path = path_from_c_str!(path);
        e(syscall::chdir(path)) as c_int
    }

    fn chmod(path: &CStr, mode: mode_t) -> c_int {
        match File::open(path, fcntl::O_PATH | fcntl::O_CLOEXEC) {
            Ok(file) => Self::fchmod(*file, mode),
            Err(_) => -1,
        }
    }

    fn chown(path: &CStr, owner: uid_t, group: gid_t) -> c_int {
        match File::open(path, fcntl::O_PATH | fcntl::O_CLOEXEC) {
            Ok(file) => Self::fchown(*file, owner, group),
            Err(_) => -1,
        }
    }

    fn clock_gettime(clk_id: clockid_t, tp: *mut timespec) -> c_int {
        let mut redox_tp = unsafe { redox_timespec::from(&*tp) };
        match e(syscall::clock_gettime(clk_id as usize, &mut redox_tp)) as c_int {
            -1 => -1,
            _ => {
                unsafe {
                    (*tp).tv_sec = redox_tp.tv_sec;
                    (*tp).tv_nsec = redox_tp.tv_nsec as i64;
                };
                0
            }
        }
    }

    fn close(fd: c_int) -> c_int {
        e(syscall::close(fd as usize)) as c_int
    }

    fn dup(fd: c_int) -> c_int {
        e(syscall::dup(fd as usize, &[])) as c_int
    }

    fn dup2(fd1: c_int, fd2: c_int) -> c_int {
        e(syscall::dup2(fd1 as usize, fd2 as usize, &[])) as c_int
    }

    fn exit(status: c_int) -> ! {
        let _ = syscall::exit(status as usize);
        loop {}
    }

    unsafe fn execve(
        path: &CStr,
        mut argv: *const *mut c_char,
        mut envp: *const *mut c_char,
    ) -> c_int {
        let mut file = match File::open(path, fcntl::O_RDONLY | fcntl::O_CLOEXEC) {
            Ok(file) => file,
            Err(_) => return -1,
        };
        let fd = *file as usize;

        // Count arguments
        let mut len = 0;
        while !(*argv.offset(len)).is_null() {
            len += 1;
        }

        let mut args: Vec<[usize; 2]> = Vec::with_capacity(len as usize);

        // Read shebang (for example #!/bin/sh)
        let interpreter = {
            let mut reader = BufReader::new(&mut file);

            let mut shebang = [0; 2];
            let mut read = 0;

            while read < 2 {
                match reader.read(&mut shebang) {
                    Ok(0) => break,
                    Ok(i) => read += i,
                    Err(_) => return -1,
                }
            }

            if &shebang == b"#!" {
                // So, this file is interpreted.
                // That means the actual file descriptor passed to `fexec` won't be this file.
                // So we need to check ourselves that this file is actually be executable.

                let mut stat = redox_stat::default();
                if e(syscall::fstat(fd, &mut stat)) == !0 {
                    return -1;
                }
                let uid = e(syscall::getuid());
                if uid == !0 {
                    return -1;
                }
                let gid = e(syscall::getuid());
                if gid == !0 {
                    return -1;
                }

                let mode = if uid == stat.st_uid as usize {
                    (stat.st_mode >> 3 * 2) & 0o7
                } else if gid == stat.st_gid as usize {
                    (stat.st_mode >> 3 * 1) & 0o7
                } else {
                    stat.st_mode & 0o7
                };

                if mode & 0o1 == 0o0 {
                    errno = EPERM;
                    return -1;
                }

                // Then, read the actual interpreter:
                let mut interpreter = Vec::new();
                match reader.read_until(b'\n', &mut interpreter) {
                    Err(_) => return -1,
                    Ok(_) => {
                        if interpreter.ends_with(&[b'\n']) {
                            interpreter.pop().unwrap();
                        }
                        // TODO: Returning the interpreter here is actually a
                        // hack. Preferrably we should reassign `file =`
                        // directly from here. Just wait until NLL comes
                        // around...
                        Some(interpreter)
                    }
                }
            } else {
                None
            }
        };
        let mut _interpreter_path = None;
        if let Some(interpreter) = interpreter {
            let cstring = match CString::new(interpreter) {
                Ok(cstring) => cstring,
                Err(_) => return -1,
            };
            file = match File::open(&cstring, fcntl::O_RDONLY | fcntl::O_CLOEXEC) {
                Ok(file) => file,
                Err(_) => return -1,
            };

            // Make sure path is kept alive long enough, and push it to the arguments
            _interpreter_path = Some(cstring);
            let path_ref = _interpreter_path.as_ref().unwrap();
            args.push([path_ref.as_ptr() as usize, path_ref.to_bytes().len()]);
        } else {
            if file.seek(SeekFrom::Start(0)).is_err() {
                return -1;
            }
        }

        // Arguments
        while !(*argv).is_null() {
            let arg = *argv;

            let mut len = 0;
            while *arg.offset(len) != 0 {
                len += 1;
            }
            args.push([arg as usize, len as usize]);
            argv = argv.offset(1);
        }

        // Environment variables
        let mut len = 0;
        while !(*envp.offset(len)).is_null() {
            len += 1;
        }

        let mut envs: Vec<[usize; 2]> = Vec::with_capacity(len as usize);
        while !(*envp).is_null() {
            let env = *envp;

            let mut len = 0;
            while *env.offset(len) != 0 {
                len += 1;
            }
            envs.push([env as usize, len as usize]);
            envp = envp.offset(1);
        }

        e(syscall::fexec(*file as usize, &args, &envs)) as c_int
    }

    fn fchdir(fd: c_int) -> c_int {
        let mut buf = [0; 4096];
        let res = e(syscall::fpath(fd as usize, &mut buf));
        if res == !0 {
            !0
        } else {
            match str::from_utf8(&buf[..res]) {
                Ok(path) => e(syscall::chdir(&path)) as c_int,
                Err(_) => {
                    unsafe { errno = EINVAL };
                    return -1;
                }
            }
        }
    }

    fn fchmod(fd: c_int, mode: mode_t) -> c_int {
        e(syscall::fchmod(fd as usize, mode as u16)) as c_int
    }

    fn fchown(fd: c_int, owner: uid_t, group: gid_t) -> c_int {
        e(syscall::fchown(fd as usize, owner as u32, group as u32)) as c_int
    }

    fn fcntl(fd: c_int, cmd: c_int, args: c_int) -> c_int {
        e(syscall::fcntl(fd as usize, cmd as usize, args as usize)) as c_int
    }

    fn flock(_fd: c_int, _operation: c_int) -> c_int {
        // TODO: Redox does not have file locking yet
        0
    }

    fn fork() -> pid_t {
        e(unsafe { syscall::clone(syscall::CloneFlags::empty()) }) as pid_t
    }

    fn fstat(fildes: c_int, buf: *mut stat) -> c_int {
        let mut redox_buf: redox_stat = redox_stat::default();
        match e(syscall::fstat(fildes as usize, &mut redox_buf)) {
            0 => {
                if let Some(buf) = unsafe { buf.as_mut() } {
                    buf.st_dev = redox_buf.st_dev as dev_t;
                    buf.st_ino = redox_buf.st_ino as ino_t;
                    buf.st_nlink = redox_buf.st_nlink as nlink_t;
                    buf.st_mode = redox_buf.st_mode as mode_t;
                    buf.st_uid = redox_buf.st_uid as uid_t;
                    buf.st_gid = redox_buf.st_gid as gid_t;
                    // TODO st_rdev
                    buf.st_rdev = 0;
                    buf.st_size = redox_buf.st_size as off_t;
                    buf.st_blksize = redox_buf.st_blksize as blksize_t;
                    buf.st_atim = timespec {
                        tv_sec: redox_buf.st_atime as time_t,
                        tv_nsec: redox_buf.st_atime_nsec as c_long,
                    };
                    buf.st_mtim = timespec {
                        tv_sec: redox_buf.st_mtime as time_t,
                        tv_nsec: redox_buf.st_mtime_nsec as c_long,
                    };
                    buf.st_ctim = timespec {
                        tv_sec: redox_buf.st_ctime as time_t,
                        tv_nsec: redox_buf.st_ctime_nsec as c_long,
                    };
                }
                0
            }
            _ => -1,
        }
    }

    fn fstatvfs(fildes: c_int, buf: *mut statvfs) -> c_int {
        let mut kbuf: redox_statvfs = redox_statvfs::default();
        match e(syscall::fstatvfs(fildes as usize, &mut kbuf)) {
            0 => {
                unsafe {
                    if !buf.is_null() {
                        (*buf).f_bsize = kbuf.f_bsize as c_ulong;
                        (*buf).f_frsize = kbuf.f_bsize as c_ulong;
                        (*buf).f_blocks = kbuf.f_blocks;
                        (*buf).f_bfree = kbuf.f_bfree;
                        (*buf).f_bavail = kbuf.f_bavail;
                        //TODO
                        (*buf).f_files = 0;
                        (*buf).f_ffree = 0;
                        (*buf).f_favail = 0;
                        (*buf).f_fsid = 0;
                        (*buf).f_flag = 0;
                        (*buf).f_namemax = 0;
                    }
                }
                0
            }
            _ => -1,
        }
    }

    fn fsync(fd: c_int) -> c_int {
        e(syscall::fsync(fd as usize)) as c_int
    }

    fn ftruncate(fd: c_int, len: off_t) -> c_int {
        e(syscall::ftruncate(fd as usize, len as usize)) as c_int
    }

    fn futex(addr: *mut c_int, op: c_int, val: c_int) -> c_int {
        match unsafe {
            syscall::futex(
                addr as *mut i32,
                op as usize,
                val as i32,
                0,
                ptr::null_mut(),
            )
        } {
            Ok(success) => success as c_int,
            Err(err) => -(err.errno as c_int),
        }
    }

    fn futimens(fd: c_int, times: *const timespec) -> c_int {
        let times = [unsafe { redox_timespec::from(&*times) }, unsafe {
            redox_timespec::from(&*times.offset(1))
        }];
        e(syscall::futimens(fd as usize, &times)) as c_int
    }

    fn utimens(path: &CStr, times: *const timespec) -> c_int {
        match File::open(path, fcntl::O_PATH | fcntl::O_CLOEXEC) {
            Ok(file) => Self::futimens(*file, times),
            Err(_) => -1,
        }
    }

    fn getcwd(buf: *mut c_char, size: size_t) -> *mut c_char {
        let buf_slice = unsafe { slice::from_raw_parts_mut(buf as *mut u8, size as usize) };
        if !buf_slice.is_empty() {
            let nonnull_size = buf_slice.len() - 1;
            let read = e(syscall::getcwd(&mut buf_slice[..nonnull_size]));
            if read == !0 {
                ptr::null_mut()
            } else if read == nonnull_size {
                unsafe {
                    errno = ERANGE;
                }
                ptr::null_mut()
            } else {
                for b in &mut buf_slice[read..] {
                    *b = 0;
                }
                buf
            }
        } else {
            unsafe {
                errno = EINVAL;
            }
            ptr::null_mut()
        }
    }

    fn getdents(fd: c_int, mut dirents: *mut dirent, max_bytes: usize) -> c_int {
        //TODO: rewrite this code. Originally the *dirents = dirent { ... } stuff below caused
        // massive issues. This has been hacked around, but it still isn't perfect

        // Get initial reading position
        let mut read = match syscall::lseek(fd as usize, 0, syscall::SEEK_CUR) {
            Ok(pos) => pos as isize,
            Err(err) => return -err.errno,
        };

        let mut written = 0;
        let mut buf = [0; 1024];

        let mut name = [0; 256];
        let mut i = 0;

        let mut flush = |written: &mut usize, i: &mut usize, name: &mut [c_char; 256]| {
            if *i < name.len() {
                // Set NUL byte
                name[*i] = 0;
            }
            // Get size: full size - unused bytes
            if *written + mem::size_of::<dirent>() > max_bytes {
                // Seek back to after last read entry and return
                match syscall::lseek(fd as usize, read, syscall::SEEK_SET) {
                    Ok(_) => return Some(*written as c_int),
                    Err(err) => return Some(-err.errno),
                }
            }
            let size = mem::size_of::<dirent>() - name.len().saturating_sub(*i + 1);
            unsafe {
                //This is the offending code mentioned above
                *dirents = dirent {
                    d_ino: 0,
                    d_off: read as off_t,
                    d_reclen: size as c_ushort,
                    d_type: 0,
                    d_name: *name,
                };
                dirents = (dirents as *mut u8).offset(size as isize) as *mut dirent;
            }
            read += *i as isize + /* newline */ 1;
            *written += size;
            *i = 0;
            None
        };

        loop {
            // Read a chunk from the directory
            let len = match syscall::read(fd as usize, &mut buf) {
                Ok(0) => {
                    if i > 0 {
                        if let Some(value) = flush(&mut written, &mut i, &mut name) {
                            return value;
                        }
                    }
                    return written as c_int;
                }
                Ok(n) => n,
                Err(err) => return -err.errno,
            };

            // Handle everything
            let mut start = 0;
            while start < len {
                let buf = &buf[start..len];

                // Copy everything up until a newline
                let newline = buf.iter().position(|&c| c == b'\n');
                let pre_len = newline.unwrap_or(buf.len());
                let post_len = newline.map(|i| i + 1).unwrap_or(buf.len());
                if i < pre_len {
                    // Reserve space for NUL byte
                    let name_len = name.len() - 1;
                    let name = &mut name[i..name_len];
                    let copy = pre_len.min(name.len());
                    let buf = unsafe { slice::from_raw_parts(buf.as_ptr() as *const c_char, copy) };
                    name[..copy].copy_from_slice(buf);
                }

                i += pre_len;
                start += post_len;

                // Write the directory entry
                if newline.is_some() {
                    if let Some(value) = flush(&mut written, &mut i, &mut name) {
                        return value;
                    }
                }
            }
        }
    }

    fn getegid() -> gid_t {
        e(syscall::getegid()) as gid_t
    }

    fn geteuid() -> uid_t {
        e(syscall::geteuid()) as uid_t
    }

    fn getgid() -> gid_t {
        e(syscall::getgid()) as gid_t
    }

    fn getpagesize() -> usize {
        4096
    }

    fn getpgid(pid: pid_t) -> pid_t {
        e(syscall::getpgid(pid as usize)) as pid_t
    }

    fn getpid() -> pid_t {
        e(syscall::getpid()) as pid_t
    }

    fn getppid() -> pid_t {
        e(syscall::getppid()) as pid_t
    }

    fn getrandom(buf: &mut [u8], flags: c_uint) -> ssize_t {
        //TODO: make this a system call?

        let path = if flags & sys_random::GRND_RANDOM != 0 {
            //TODO: /dev/random equivalent
            "rand:"
        } else {
            "rand:"
        };

        let mut open_flags = syscall::O_RDONLY | syscall::O_CLOEXEC;
        if flags & sys_random::GRND_NONBLOCK != 0 {
            open_flags |= syscall::O_NONBLOCK;
        }

        let fd = e(syscall::open(path, open_flags));
        if fd == !0 {
            return -1;
        }

        let res = e(syscall::read(fd, buf)) as ssize_t;

        let _ = syscall::close(fd);

        res
    }

    unsafe fn getrlimit(resource: c_int, rlim: *mut rlimit) -> c_int {
        //TODO
        if !rlim.is_null() {
            (*rlim).rlim_cur = RLIM_INFINITY;
            (*rlim).rlim_max = RLIM_INFINITY;
        }
        0
    }

    fn gettid() -> pid_t {
        //TODO
        Self::getpid()
    }

    fn gettimeofday(tp: *mut timeval, tzp: *mut timezone) -> c_int {
        let mut redox_tp = redox_timespec::default();
        let err = e(syscall::clock_gettime(
            syscall::CLOCK_REALTIME,
            &mut redox_tp,
        )) as c_int;
        if err < 0 {
            return err;
        }
        unsafe {
            (*tp).tv_sec = redox_tp.tv_sec as time_t;
            (*tp).tv_usec = (redox_tp.tv_nsec / 1000) as suseconds_t;

            if !tzp.is_null() {
                (*tzp).tz_minuteswest = 0;
                (*tzp).tz_dsttime = 0;
            }
        }
        0
    }

    fn getuid() -> uid_t {
        e(syscall::getuid()) as pid_t
    }

    fn link(path1: &CStr, path2: &CStr) -> c_int {
        e(unsafe { syscall::link(path1.as_ptr() as *const u8, path2.as_ptr() as *const u8) })
            as c_int
    }

    fn lseek(fd: c_int, offset: off_t, whence: c_int) -> off_t {
        e(syscall::lseek(
            fd as usize,
            offset as isize,
            whence as usize,
        )) as off_t
    }

    fn mkdir(path: &CStr, mode: mode_t) -> c_int {
        match File::create(
            path,
            fcntl::O_DIRECTORY | fcntl::O_EXCL | fcntl::O_CLOEXEC,
            0o777,
        ) {
            Ok(_fd) => 0,
            Err(_) => -1,
        }
    }

    fn mkfifo(path: &CStr, mode: mode_t) -> c_int {
        match File::create(
            path,
            fcntl::O_CREAT | fcntl::O_CLOEXEC,
            syscall::MODE_FIFO as mode_t | (mode & 0o777),
        ) {
            Ok(fd) => 0,
            Err(_) => -1,
        }
    }

    unsafe fn mmap(
        addr: *mut c_void,
        len: usize,
        prot: c_int,
        flags: c_int,
        fildes: c_int,
        off: off_t,
    ) -> *mut c_void {
        let map = Map {
            offset: off as usize,
            size: len,
            flags: syscall::MapFlags::from_bits_truncate(
                ((prot as usize) << 16) | ((flags as usize) & 0xFFFF),
            ),
            address: addr as usize,
        };

        if flags & MAP_ANONYMOUS == MAP_ANONYMOUS {
            e(syscall::fmap(!0, &map)) as *mut c_void
        } else {
            e(syscall::fmap(fildes as usize, &map)) as *mut c_void
        }
    }

    unsafe fn mprotect(addr: *mut c_void, len: usize, prot: c_int) -> c_int {
        e(syscall::mprotect(
            addr as usize,
            len,
            syscall::MapFlags::from_bits((prot as usize) << 16)
                .expect("mprotect: invalid bit pattern"),
        )) as c_int
    }

    unsafe fn msync(addr: *mut c_void, len: usize, flags: c_int) -> c_int {
        eprintln!("msync {:p} {:x} {:x}", addr, len, flags);
        e(Err(syscall::Error::new(syscall::ENOSYS))) as c_int
        /* TODO
        e(syscall::msync(
            addr as usize,
            len,
            flags
        )) as c_int
        */
    }

    unsafe fn munmap(addr: *mut c_void, len: usize) -> c_int {
        if e(syscall::funmap(addr as usize, len)) == !0 {
            return !0;
        }
        0
    }

    fn nanosleep(rqtp: *const timespec, rmtp: *mut timespec) -> c_int {
        let redox_rqtp = unsafe { redox_timespec::from(&*rqtp) };
        let mut redox_rmtp: redox_timespec;
        if rmtp.is_null() {
            redox_rmtp = redox_timespec::default();
        } else {
            redox_rmtp = unsafe { redox_timespec::from(&*rmtp) };
        }
        match e(syscall::nanosleep(&redox_rqtp, &mut redox_rmtp)) as c_int {
            -1 => -1,
            _ => {
                unsafe {
                    if !rmtp.is_null() {
                        (*rmtp).tv_sec = redox_rmtp.tv_sec;
                        (*rmtp).tv_nsec = redox_rmtp.tv_nsec as i64;
                    }
                }
                0
            }
        }
    }

    fn open(path: &CStr, oflag: c_int, mode: mode_t) -> c_int {
        let path = path_from_c_str!(path);
        e(syscall::open(
            path,
            ((oflag as usize) & 0xFFFF_0000) | ((mode as usize) & 0xFFFF),
        )) as c_int
    }

    fn pipe2(fds: &mut [c_int], flags: c_int) -> c_int {
        let mut usize_fds: [usize; 2] = [0; 2];
        let res = e(syscall::pipe2(&mut usize_fds, flags as usize));
        fds[0] = usize_fds[0] as c_int;
        fds[1] = usize_fds[1] as c_int;
        res as c_int
    }

    #[cfg(target_arch = "aarch64")]
    unsafe fn pte_clone(stack: *mut usize) -> pid_t {
        //TODO: aarch64
        unimplemented!("pte_clone not implemented on aarch64");
    }

    #[cfg(target_arch = "x86_64")]
    unsafe fn pte_clone(stack: *mut usize) -> pid_t {
        let flags = syscall::CLONE_VM
            | syscall::CLONE_FS
            | syscall::CLONE_FILES
            | syscall::CLONE_SIGHAND
            | syscall::CLONE_STACK;
        let pid;
        llvm_asm!("
            # Call clone syscall
            syscall

            # Check if child or parent
            test rax, rax
            jnz .parent

            # Load registers
            pop rax
            pop rdi
            pop rsi
            pop rdx
            pop rcx
            pop r8
            pop r9

            # Call entry point
            call rax

            # Exit
            mov rax, 1
            xor rdi, rdi
            syscall

            # Invalid instruction on failure to exit
            ud2

            # Return PID if parent
            .parent:
            "
            : "={rax}"(pid)
            : "{rax}"(syscall::SYS_CLONE), "{rdi}"(flags), "{rsi}"(stack)
            : "memory", "rbx", "rcx", "rdx", "rsi", "rdi", "r8",
              "r9", "r10", "r11", "r12", "r13", "r14", "r15"
            : "intel", "volatile"
        );
        e(syscall::Error::demux(pid)) as pid_t
    }

    fn read(fd: c_int, buf: &mut [u8]) -> ssize_t {
        e(syscall::read(fd as usize, buf)) as ssize_t
    }

    fn fpath(fildes: c_int, out: &mut [u8]) -> ssize_t {
        e(syscall::fpath(fildes as usize, out)) as ssize_t
    }

    fn readlink(pathname: &CStr, out: &mut [u8]) -> ssize_t {
        let file = match File::open(
            pathname,
            fcntl::O_PATH | fcntl::O_SYMLINK | fcntl::O_CLOEXEC,
        ) {
            Ok(ok) => ok,
            Err(_) => return -1,
        };

        if out.is_empty() {
            return 0;
        }

        let len = out.len();
        let read = e(syscall::fpath(*file as usize, &mut out[..len - 1]));
        if (read as c_int) < 0 {
            return -1;
        }
        out[read as usize] = 0;

        0
    }

    fn rename(oldpath: &CStr, newpath: &CStr) -> c_int {
        let newpath = path_from_c_str!(newpath);
        match File::open(oldpath, fcntl::O_PATH | fcntl::O_CLOEXEC) {
            Ok(file) => e(syscall::frename(*file as usize, newpath)) as c_int,
            Err(_) => -1,
        }
    }

    fn rmdir(path: &CStr) -> c_int {
        let path = path_from_c_str!(path);
        e(syscall::rmdir(path)) as c_int
    }

    fn sched_yield() -> c_int {
        e(syscall::sched_yield()) as c_int
    }

    fn setpgid(pid: pid_t, pgid: pid_t) -> c_int {
        e(syscall::setpgid(pid as usize, pgid as usize)) as c_int
    }

    fn setregid(rgid: gid_t, egid: gid_t) -> c_int {
        e(syscall::setregid(rgid as usize, egid as usize)) as c_int
    }

    fn setreuid(ruid: uid_t, euid: uid_t) -> c_int {
        e(syscall::setreuid(ruid as usize, euid as usize)) as c_int
    }

    fn symlink(path1: &CStr, path2: &CStr) -> c_int {
        let mut file = match File::create(
            path2,
            fcntl::O_WRONLY | fcntl::O_SYMLINK | fcntl::O_CLOEXEC,
            0o777,
        ) {
            Ok(ok) => ok,
            Err(_) => return -1,
        };

        if file.write(path1.to_bytes()).is_err() {
            return -1;
        }

        0
    }

    fn umask(mask: mode_t) -> mode_t {
        e(syscall::umask(mask as usize)) as mode_t
    }

    fn uname(utsname: *mut utsname) -> c_int {
        fn gethostname(name: &mut [u8]) -> io::Result<()> {
            if name.is_empty() {
                return Ok(());
            }

            let mut file = File::open(
                &CString::new("/etc/hostname").unwrap(),
                fcntl::O_RDONLY | fcntl::O_CLOEXEC,
            )?;

            let mut read = 0;
            let name_len = name.len();
            loop {
                match file.read(&mut name[read..name_len - 1])? {
                    0 => break,
                    n => read += n,
                }
            }
            name[read] = 0;
            Ok(())
        }

        fn inner(utsname: *mut utsname) -> CoreResult<(), i32> {
            match gethostname(unsafe {
                slice::from_raw_parts_mut(
                    (*utsname).nodename.as_mut_ptr() as *mut u8,
                    (*utsname).nodename.len(),
                )
            }) {
                Ok(_) => (),
                Err(_) => return Err(EIO),
            }

            let file_path = c_str!("sys:uname");
            let mut file = match File::open(file_path, fcntl::O_RDONLY | fcntl::O_CLOEXEC) {
                Ok(ok) => ok,
                Err(_) => return Err(EIO),
            };
            let mut lines = BufReader::new(&mut file).lines();

            let mut read_line = |dst: &mut [c_char]| {
                let line = match lines.next() {
                    Some(Ok(l)) => match CString::new(l) {
                        Ok(l) => l,
                        Err(_) => return Err(EIO),
                    },
                    None | Some(Err(_)) => return Err(EIO),
                };

                let line_slice: &[c_char] = unsafe { mem::transmute(line.as_bytes_with_nul()) };

                if line_slice.len() <= UTSLENGTH {
                    dst[..line_slice.len()].copy_from_slice(line_slice);
                    Ok(())
                } else {
                    Err(EIO)
                }
            };

            unsafe {
                read_line(&mut (*utsname).sysname)?;
                read_line(&mut (*utsname).release)?;
                read_line(&mut (*utsname).machine)?;

                // Version is not provided
                ptr::write_bytes((*utsname).version.as_mut_ptr(), 0, UTSLENGTH);

                // Redox doesn't provide domainname in sys:uname
                //read_line(&mut (*utsname).domainname)?;
                ptr::write_bytes((*utsname).domainname.as_mut_ptr(), 0, UTSLENGTH);
            }

            Ok(())
        }

        match inner(utsname) {
            Ok(()) => 0,
            Err(err) => unsafe {
                errno = err;
                -1
            },
        }
    }

    fn unlink(path: &CStr) -> c_int {
        let path = path_from_c_str!(path);
        e(syscall::unlink(path)) as c_int
    }

    fn waitpid(mut pid: pid_t, stat_loc: *mut c_int, options: c_int) -> pid_t {
        if pid == !0 {
            pid = 0;
        }
        let mut res = None;
        let mut status = 0;

        let inner = |status: &mut usize, flags| {
            syscall::waitpid(
                pid as usize,
                status,
                syscall::WaitFlags::from_bits(flags as usize)
                    .expect("waitpid: invalid bit pattern"),
            )
        };

        // First, allow ptrace to handle waitpid
        // TODO: Handle special PIDs here (such as -1)
        let state = ptrace::init_state();
        let mut sessions = state.sessions.lock();
        if let Ok(session) = ptrace::get_session(&mut sessions, pid) {
            if options & sys_wait::WNOHANG != sys_wait::WNOHANG {
                let mut _event = PtraceEvent::default();
                let _ = (&mut &session.tracer).read(&mut _event);

                res = Some(e(inner(
                    &mut status,
                    options | sys_wait::WNOHANG | sys_wait::WUNTRACED,
                )));
                if res == Some(0) {
                    // WNOHANG, just pretend ptrace SIGSTOP:ped this
                    status = (syscall::SIGSTOP << 8) | 0x7f;
                    assert!(syscall::wifstopped(status));
                    assert_eq!(syscall::wstopsig(status), syscall::SIGSTOP);
                    res = Some(pid as usize);
                }
            }
        }

        // If ptrace didn't impact this waitpid, proceed *almost* as
        // normal: We still need to add WUNTRACED, but we only return
        // it if (and only if) a ptrace traceme was activated during
        // the wait.
        let res = res.unwrap_or_else(|| loop {
            let res = e(inner(&mut status, options | sys_wait::WUNTRACED));

            // TODO: Also handle special PIDs here
            if !syscall::wifstopped(res) || ptrace::is_traceme(pid) {
                break res;
            }
        });

        // If stat_loc is non-null, set that and the return
        unsafe {
            if !stat_loc.is_null() {
                *stat_loc = status as c_int;
            }
        }
        res as pid_t
    }

    fn write(fd: c_int, buf: &[u8]) -> ssize_t {
        e(syscall::write(fd as usize, buf)) as ssize_t
    }

    fn verify() -> bool {
        // GETPID on Redox is 20, which is WRITEV on Linux
        e(unsafe { syscall::syscall5(syscall::number::SYS_GETPID, !0, !0, !0, !0, !0) }) != !0
    }
}