diff --git a/src/libstd/sys/wasi/args.rs b/src/libstd/sys/wasi/args.rs
index 8b4b354d9fc20..679bb1b2cbe30 100644
--- a/src/libstd/sys/wasi/args.rs
+++ b/src/libstd/sys/wasi/args.rs
@@ -27,14 +27,24 @@ pub fn args() -> Args {
     })
 }
 
+fn cvt_wasi(r: u16) -> crate::io::Result<()> {
+    if r != 0 {
+        Err(Error::from_raw_os_error(r as i32))
+    } else {
+        Ok(())
+    }
+}
+
 fn maybe_args() -> io::Result<Args> {
+    // FIXME: replace with safe functions
+    use wasi::wasi_unstable::raw::{__wasi_args_sizes_get, __wasi_args_get};
     unsafe {
         let (mut argc, mut argv_buf_size) = (0, 0);
-        cvt_wasi(libc::__wasi_args_sizes_get(&mut argc, &mut argv_buf_size))?;
+        cvt_wasi(__wasi_args_sizes_get(&mut argc, &mut argv_buf_size))?;
 
-        let mut argc = vec![core::ptr::null_mut::<libc::c_char>(); argc];
+        let mut argc = vec![core::ptr::null_mut::<u8>(); argc];
         let mut argv_buf = vec![0; argv_buf_size];
-        cvt_wasi(libc::__wasi_args_get(argc.as_mut_ptr(), argv_buf.as_mut_ptr()))?;
+        cvt_wasi(__wasi_args_get(argc.as_mut_ptr(), argv_buf.as_mut_ptr()))?;
 
         let args = argc.into_iter()
             .map(|ptr| CStr::from_ptr(ptr).to_bytes().to_vec())
diff --git a/src/libstd/sys/wasi/ext/fs.rs b/src/libstd/sys/wasi/ext/fs.rs
index 0ec4122f385da..ecd509f01dabd 100644
--- a/src/libstd/sys/wasi/ext/fs.rs
+++ b/src/libstd/sys/wasi/ext/fs.rs
@@ -336,16 +336,16 @@ pub trait FileTypeExt {
 
 impl FileTypeExt for fs::FileType {
     fn is_block_device(&self) -> bool {
-        self.as_inner().bits() == libc::__WASI_FILETYPE_BLOCK_DEVICE
+        self.as_inner().bits() == wasi::FILETYPE_BLOCK_DEVICE
     }
     fn is_character_device(&self) -> bool {
-        self.as_inner().bits() == libc::__WASI_FILETYPE_CHARACTER_DEVICE
+        self.as_inner().bits() == wasi::FILETYPE_CHARACTER_DEVICE
     }
     fn is_socket_dgram(&self) -> bool {
-        self.as_inner().bits() == libc::__WASI_FILETYPE_SOCKET_DGRAM
+        self.as_inner().bits() == wasi::FILETYPE_SOCKET_DGRAM
     }
     fn is_socket_stream(&self) -> bool {
-        self.as_inner().bits() == libc::__WASI_FILETYPE_SOCKET_STREAM
+        self.as_inner().bits() == wasi::FILETYPE_SOCKET_STREAM
     }
 }
 
diff --git a/src/libstd/sys/wasi/ext/io.rs b/src/libstd/sys/wasi/ext/io.rs
index 12afd1d42dc19..c843144f0c406 100644
--- a/src/libstd/sys/wasi/ext/io.rs
+++ b/src/libstd/sys/wasi/ext/io.rs
@@ -8,6 +8,8 @@ use crate::sys;
 use crate::net;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 
+use wasi::wasi_unstable as wasi;
+
 /// Raw file descriptors.
 pub type RawFd = u32;
 
@@ -125,18 +127,18 @@ impl IntoRawFd for fs::File {
 
 impl AsRawFd for io::Stdin {
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDIN_FILENO as u32
+        wasi::STDIN_FD
     }
 }
 
 impl AsRawFd for io::Stdout {
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDOUT_FILENO as u32
+        wasi::STDOUT_FD
     }
 }
 
 impl AsRawFd for io::Stderr {
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDERR_FILENO as u32
+        wasi::STDERR_FD
     }
 }
diff --git a/src/libstd/sys/wasi/fd.rs b/src/libstd/sys/wasi/fd.rs
index 25692ec086801..93fe8add326c8 100644
--- a/src/libstd/sys/wasi/fd.rs
+++ b/src/libstd/sys/wasi/fd.rs
@@ -3,348 +3,240 @@
 use crate::io::{self, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
 use crate::net::Shutdown;
-use crate::sys::cvt_wasi;
-use libc::{self, c_char, c_void};
+use wasi::wasi_unstable as wasi;
 
 #[derive(Debug)]
 pub struct WasiFd {
-    fd: libc::__wasi_fd_t,
+    fd: wasi::Fd,
 }
 
-// FIXME: these should probably all be fancier structs, builders, enums, etc
-pub type LookupFlags = u32;
-pub type FdFlags = u16;
-pub type Advice = u8;
-pub type Rights = u64;
-pub type Oflags = u16;
-pub type DirCookie = u64;
-pub type Timestamp = u64;
-pub type FstFlags = u16;
-pub type RiFlags = u16;
-pub type RoFlags = u16;
-pub type SiFlags = u16;
-
-fn iovec(a: &mut [IoSliceMut<'_>]) -> (*const libc::__wasi_iovec_t, usize) {
+fn iovec(a: &mut [IoSliceMut<'_>]) -> &[wasi::IoVec] {
     assert_eq!(
         mem::size_of::<IoSliceMut<'_>>(),
-        mem::size_of::<libc::__wasi_iovec_t>()
+        mem::size_of::<wasi::IoVec>()
     );
     assert_eq!(
         mem::align_of::<IoSliceMut<'_>>(),
-        mem::align_of::<libc::__wasi_iovec_t>()
+        mem::align_of::<wasi::IoVec>()
     );
-    (a.as_ptr() as *const libc::__wasi_iovec_t, a.len())
+    /// SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout
+    unsafe { mem::transmute(a) }
 }
 
-fn ciovec(a: &[IoSlice<'_>]) -> (*const libc::__wasi_ciovec_t, usize) {
+fn ciovec(a: &[IoSlice<'_>]) -> &[wasi::CIoVec] {
     assert_eq!(
         mem::size_of::<IoSlice<'_>>(),
-        mem::size_of::<libc::__wasi_ciovec_t>()
+        mem::size_of::<wasi::CIoVec>()
     );
     assert_eq!(
         mem::align_of::<IoSlice<'_>>(),
-        mem::align_of::<libc::__wasi_ciovec_t>()
+        mem::align_of::<wasi::CIoVec>()
     );
-    (a.as_ptr() as *const libc::__wasi_ciovec_t, a.len())
+    /// SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout
+    unsafe { mem::transmute(a) }
 }
 
 impl WasiFd {
-    pub unsafe fn from_raw(fd: libc::__wasi_fd_t) -> WasiFd {
+    pub unsafe fn from_raw(fd: wasi::Fd) -> WasiFd {
         WasiFd { fd }
     }
 
-    pub fn into_raw(self) -> libc::__wasi_fd_t {
+    pub fn into_raw(self) -> wasi::Fd {
         let ret = self.fd;
         mem::forget(self);
         ret
     }
 
-    pub fn as_raw(&self) -> libc::__wasi_fd_t {
+    pub fn as_raw(&self) -> wasi::Fd {
         self.fd
     }
 
     pub fn datasync(&self) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_datasync(self.fd) })
+        wasi::fd_datasync(self.fd).map_err(From::from)
     }
 
     pub fn pread(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
-        let mut read = 0;
-        let (ptr, len) = iovec(bufs);
-        cvt_wasi(unsafe { libc::__wasi_fd_pread(self.fd, ptr, len, offset, &mut read) })?;
-        Ok(read)
+        wasi::fd_pread(self.fd, iovec(bufs), offset).map_err(From::from)
     }
 
     pub fn pwrite(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
-        let mut read = 0;
-        let (ptr, len) = ciovec(bufs);
-        cvt_wasi(unsafe { libc::__wasi_fd_pwrite(self.fd, ptr, len, offset, &mut read) })?;
-        Ok(read)
+        wasi::fd_pwrite(self.fd, ciovec(bufs), offset).map_err(From::from)
     }
 
     pub fn read(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        let mut read = 0;
-        let (ptr, len) = iovec(bufs);
-        cvt_wasi(unsafe { libc::__wasi_fd_read(self.fd, ptr, len, &mut read) })?;
-        Ok(read)
+        wasi::fd_read(self.fd, iovec(bufs)).map_err(From::from)
     }
 
     pub fn write(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        let mut read = 0;
-        let (ptr, len) = ciovec(bufs);
-        cvt_wasi(unsafe { libc::__wasi_fd_write(self.fd, ptr, len, &mut read) })?;
-        Ok(read)
+        wasi::fd_write(self.fd, ciovec(bufs)).map_err(From::from)
     }
 
     pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
         let (whence, offset) = match pos {
-            SeekFrom::Start(pos) => (libc::__WASI_WHENCE_SET, pos as i64),
-            SeekFrom::End(pos) => (libc::__WASI_WHENCE_END, pos),
-            SeekFrom::Current(pos) => (libc::__WASI_WHENCE_CUR, pos),
+            SeekFrom::Start(pos) => (wasi::WHENCE_SET, pos as i64),
+            SeekFrom::End(pos) => (wasi::WHENCE_END, pos),
+            SeekFrom::Current(pos) => (wasi::WHENCE_CUR, pos),
         };
-        let mut pos = 0;
-        cvt_wasi(unsafe { libc::__wasi_fd_seek(self.fd, offset, whence, &mut pos) })?;
-        Ok(pos)
+        wasi::fd_seek(self.fd, offset, whence).map_err(From::from)
     }
 
     pub fn tell(&self) -> io::Result<u64> {
-        let mut pos = 0;
-        cvt_wasi(unsafe { libc::__wasi_fd_tell(self.fd, &mut pos) })?;
-        Ok(pos)
+        wasi::fd_tell(self.fd).map_err(From::from)
     }
 
     // FIXME: __wasi_fd_fdstat_get
 
-    pub fn set_flags(&self, flags: FdFlags) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_fdstat_set_flags(self.fd, flags) })
+    pub fn set_flags(&self, flags: wasi::FdFlags) -> io::Result<()> {
+        wasi::fd_fdstat_set_flags(self.fd, flags).map_err(From::from)
     }
 
-    pub fn set_rights(&self, base: Rights, inheriting: Rights) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_fdstat_set_rights(self.fd, base, inheriting) })
+    pub fn set_rights(&self, base: wasi::Rights, inheriting: wasi::Rights) -> io::Result<()> {
+        wasi::fd_fdstat_set_rights(self.fd, base, inheriting).map_err(From::from)
     }
 
     pub fn sync(&self) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_sync(self.fd) })
+        wasi::fd_sync(self.fd).map_err(From::from)
     }
 
-    pub fn advise(&self, offset: u64, len: u64, advice: Advice) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_advise(self.fd, offset, len, advice as u8) })
+    pub fn advise(&self, offset: u64, len: u64, advice: wasi::Advice) -> io::Result<()> {
+        wasi::fd_advise(self.fd, offset, len, advice).map_err(From::from)
     }
 
     pub fn allocate(&self, offset: u64, len: u64) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_allocate(self.fd, offset, len) })
+        wasi::fd_allocate(self.fd, offset, len).map_err(From::from)
     }
 
     pub fn create_directory(&self, path: &[u8]) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_create_directory(self.fd, path.as_ptr() as *const c_char, path.len())
-        })
+        wasi::path_create_directory(self.fd, path).map_err(From::from)
     }
 
     pub fn link(
         &self,
-        old_flags: LookupFlags,
+        old_flags: wasi::LookupFlags,
         old_path: &[u8],
         new_fd: &WasiFd,
         new_path: &[u8],
     ) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_link(
-                self.fd,
-                old_flags,
-                old_path.as_ptr() as *const c_char,
-                old_path.len(),
-                new_fd.fd,
-                new_path.as_ptr() as *const c_char,
-                new_path.len(),
-            )
-        })
+        wasi::path_link(self.fd, old_flags, old_path, new_fd.fd, new_path)
+            .map_err(From::from)
     }
 
     pub fn open(
         &self,
-        dirflags: LookupFlags,
+        dirflags: wasi::LookupFlags,
         path: &[u8],
-        oflags: Oflags,
-        fs_rights_base: Rights,
-        fs_rights_inheriting: Rights,
-        fs_flags: FdFlags,
+        oflags: wasi::OFlags,
+        fs_rights_base: wasi::Rights,
+        fs_rights_inheriting: wasi::Rights,
+        fs_flags: wasi::FdFlags,
     ) -> io::Result<WasiFd> {
-        unsafe {
-            let mut fd = 0;
-            cvt_wasi(libc::__wasi_path_open(
-                self.fd,
-                dirflags,
-                path.as_ptr() as *const c_char,
-                path.len(),
-                oflags,
-                fs_rights_base,
-                fs_rights_inheriting,
-                fs_flags,
-                &mut fd,
-            ))?;
-            Ok(WasiFd::from_raw(fd))
-        }
-    }
-
-    pub fn readdir(&self, buf: &mut [u8], cookie: DirCookie) -> io::Result<usize> {
-        let mut used = 0;
-        cvt_wasi(unsafe {
-            libc::__wasi_fd_readdir(
-                self.fd,
-                buf.as_mut_ptr() as *mut c_void,
-                buf.len(),
-                cookie,
-                &mut used,
-            )
-        })?;
-        Ok(used)
+        let fd = wasi_path_open(
+            self.fd,
+            dirflags,
+            path,
+            oflags,
+            fs_rights_base,
+            fs_rights_inheriting,
+            fs_flags,
+        )?;
+        Ok(WasiFd::from_raw(fd))
+    }
+
+    pub fn readdir(&self, buf: &mut [u8], cookie: wasi::DirCookie) -> io::Result<usize> {
+        wasi::fd_readdir(self.fd, buf, cookie).map_err(From::from)
     }
 
     pub fn readlink(&self, path: &[u8], buf: &mut [u8]) -> io::Result<usize> {
-        let mut used = 0;
-        cvt_wasi(unsafe {
-            libc::__wasi_path_readlink(
-                self.fd,
-                path.as_ptr() as *const c_char,
-                path.len(),
-                buf.as_mut_ptr() as *mut c_char,
-                buf.len(),
-                &mut used,
-            )
-        })?;
-        Ok(used)
+        wasi::path_readlink(self.fd, path, buf).map_err(From::from)
     }
 
     pub fn rename(&self, old_path: &[u8], new_fd: &WasiFd, new_path: &[u8]) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_rename(
-                self.fd,
-                old_path.as_ptr() as *const c_char,
-                old_path.len(),
-                new_fd.fd,
-                new_path.as_ptr() as *const c_char,
-                new_path.len(),
-            )
-        })
+        wasi::path_rename(self.fd, old_path, new_fd.fd, new_path)
+            .map_err(From::from)
     }
 
-    pub fn filestat_get(&self, buf: *mut libc::__wasi_filestat_t) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_filestat_get(self.fd, buf) })
+    pub fn filestat_get(&self) -> io::Result<wasi::Filestat> {
+        wasi::fd_filestat_get(self.fd, buf).map_err(From::from)
     }
 
     pub fn filestat_set_times(
         &self,
-        atim: Timestamp,
-        mtim: Timestamp,
-        fstflags: FstFlags,
+        atim: wasi::Timestamp,
+        mtim: wasi::Timestamp,
+        fstflags: wasi::FstFlags,
     ) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_filestat_set_times(self.fd, atim, mtim, fstflags) })
+        wasi::fd_filestat_set_times(self.fd, atim, mtim, fstflags)
+            .map_err(From::from)
     }
 
     pub fn filestat_set_size(&self, size: u64) -> io::Result<()> {
-        cvt_wasi(unsafe { libc::__wasi_fd_filestat_set_size(self.fd, size) })
+        wasi::fd_filestat_set_size(self.fd, size).map_err(From::from)
     }
 
     pub fn path_filestat_get(
         &self,
-        flags: LookupFlags,
+        flags: wasi::LookupFlags,
         path: &[u8],
-        buf: *mut libc::__wasi_filestat_t,
-    ) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_filestat_get(
-                self.fd,
-                flags,
-                path.as_ptr() as *const c_char,
-                path.len(),
-                buf,
-            )
-        })
+    ) -> io::Result<wasi::FileStat> {
+        wasi::path_filestat_get(self.fd, flags, path).map_err(From::from)
     }
 
     pub fn path_filestat_set_times(
         &self,
-        flags: LookupFlags,
+        flags: wasi::LookupFlags,
         path: &[u8],
-        atim: Timestamp,
-        mtim: Timestamp,
-        fstflags: FstFlags,
+        atim: wasi::Timestamp,
+        mtim: wasi::Timestamp,
+        fstflags: wasi::FstFlags,
     ) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_filestat_set_times(
-                self.fd,
-                flags,
-                path.as_ptr() as *const c_char,
-                path.len(),
-                atim,
-                mtim,
-                fstflags,
-            )
-        })
+        wasi::path_filestat_set_times(
+            self.fd,
+            flags,
+            path,
+            atim,
+            mtim,
+            fstflags,
+        ).map_err(From::from)
     }
 
     pub fn symlink(&self, old_path: &[u8], new_path: &[u8]) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_symlink(
-                old_path.as_ptr() as *const c_char,
-                old_path.len(),
-                self.fd,
-                new_path.as_ptr() as *const c_char,
-                new_path.len(),
-            )
-        })
+        wasi::path_symlink(old_path, self.fd, new_path).map_err(From::from)
     }
 
     pub fn unlink_file(&self, path: &[u8]) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_unlink_file(self.fd, path.as_ptr() as *const c_char, path.len())
-        })
+        wasi::path_unlink_file(self.fd, path).map_err(From::from)
     }
 
     pub fn remove_directory(&self, path: &[u8]) -> io::Result<()> {
-        cvt_wasi(unsafe {
-            libc::__wasi_path_remove_directory(self.fd, path.as_ptr() as *const c_char, path.len())
-        })
+        wasi::path_remove_directory(self.fd, path).map_err(From::from)
     }
 
     pub fn sock_recv(
         &self,
         ri_data: &mut [IoSliceMut<'_>],
-        ri_flags: RiFlags,
-    ) -> io::Result<(usize, RoFlags)> {
-        let mut ro_datalen = 0;
-        let mut ro_flags = 0;
-        let (ptr, len) = iovec(ri_data);
-        cvt_wasi(unsafe {
-            libc::__wasi_sock_recv(self.fd, ptr, len, ri_flags, &mut ro_datalen, &mut ro_flags)
-        })?;
-        Ok((ro_datalen, ro_flags))
+        ri_flags: wasi::RiFlags,
+    ) -> io::Result<(usize, wasi::RoFlags)> {
+        wasi::sock_recv(self.fd, iovec(ri_data), ri_flags).map_err(From::from)
     }
 
-    pub fn sock_send(&self, si_data: &[IoSlice<'_>], si_flags: SiFlags) -> io::Result<usize> {
-        let mut so_datalen = 0;
-        let (ptr, len) = ciovec(si_data);
-        cvt_wasi(unsafe { libc::__wasi_sock_send(self.fd, ptr, len, si_flags, &mut so_datalen) })?;
-        Ok(so_datalen)
+    pub fn sock_send(&self, si_data: &[IoSlice<'_>], si_flags: wasi::SiFlags) -> io::Result<usize> {
+        wasi::sock_send(self.fd, ciovec(si_data), si_flags).map_err(From::from)
     }
 
     pub fn sock_shutdown(&self, how: Shutdown) -> io::Result<()> {
         let how = match how {
-            Shutdown::Read => libc::__WASI_SHUT_RD,
-            Shutdown::Write => libc::__WASI_SHUT_WR,
-            Shutdown::Both => libc::__WASI_SHUT_WR | libc::__WASI_SHUT_RD,
+            Shutdown::Read => WASI::SHUT_RD,
+            Shutdown::Write => WASI::SHUT_WR,
+            Shutdown::Both => WASI::SHUT_WR | WASI::SHUT_RD,
         };
-        cvt_wasi(unsafe { libc::__wasi_sock_shutdown(self.fd, how) })?;
-        Ok(())
+        wasi::sock_shutdown(self.fd, how).map_err(From::from)
     }
 }
 
 impl Drop for WasiFd {
     fn drop(&mut self) {
-        unsafe {
-            // FIXME: can we handle the return code here even though we can't on
-            // unix?
-            libc::__wasi_fd_close(self.fd);
-        }
+        // FIXME: can we handle the return code here even though we can't on
+        // unix?
+        let _ = wasi::fd_close(self.fd);
     }
 }
diff --git a/src/libstd/sys/wasi/fs.rs b/src/libstd/sys/wasi/fs.rs
index 172c60385b317..f23ecfc2bcd22 100644
--- a/src/libstd/sys/wasi/fs.rs
+++ b/src/libstd/sys/wasi/fs.rs
@@ -15,13 +15,15 @@ use crate::sys_common::FromInner;
 pub use crate::sys_common::fs::copy;
 pub use crate::sys_common::fs::remove_dir_all;
 
+use wasi::wasi_unstable as wasi;
+
 pub struct File {
     fd: WasiFd,
 }
 
 #[derive(Clone)]
 pub struct FileAttr {
-    meta: libc::__wasi_filestat_t,
+    meta: wasi::FileStat,
 }
 
 pub struct ReadDir {
@@ -38,7 +40,7 @@ struct ReadDirInner {
 }
 
 pub struct DirEntry {
-    meta: libc::__wasi_dirent_t,
+    meta: wasi::Dirent,
     name: Vec<u8>,
     inner: Arc<ReadDirInner>,
 }
@@ -47,11 +49,11 @@ pub struct DirEntry {
 pub struct OpenOptions {
     read: bool,
     write: bool,
-    dirflags: libc::__wasi_lookupflags_t,
-    fdflags: libc::__wasi_fdflags_t,
-    oflags: libc::__wasi_oflags_t,
-    rights_base: Option<libc::__wasi_rights_t>,
-    rights_inheriting: Option<libc::__wasi_rights_t>,
+    dirflags: wasi::LookupFlags,
+    fdflags: wasi::FdFlags,
+    oflags: wasi::OFlags,
+    rights_base: Option<wasi::Rights>,
+    rights_inheriting: Option<wasi::Rights>,
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -61,7 +63,7 @@ pub struct FilePermissions {
 
 #[derive(PartialEq, Eq, Hash, Debug, Copy, Clone)]
 pub struct FileType {
-    bits: libc::__wasi_filetype_t,
+    bits: wasi::FileType,
 }
 
 #[derive(Debug)]
@@ -101,7 +103,7 @@ impl FileAttr {
         Ok(SystemTime::from_wasi_timestamp(self.meta.st_ctim))
     }
 
-    pub fn as_wasi(&self) -> &libc::__wasi_filestat_t {
+    pub fn as_wasi(&self) -> &wasi::FileStat {
         &self.meta
     }
 }
@@ -118,18 +120,18 @@ impl FilePermissions {
 
 impl FileType {
     pub fn is_dir(&self) -> bool {
-        self.bits == libc::__WASI_FILETYPE_DIRECTORY
+        self.bits == wasi::FILETYPE_DIRECTORY
     }
 
     pub fn is_file(&self) -> bool {
-        self.bits == libc::__WASI_FILETYPE_REGULAR_FILE
+        self.bits == wasi::FILETYPE_REGULAR_FILE
     }
 
     pub fn is_symlink(&self) -> bool {
-        self.bits == libc::__WASI_FILETYPE_SYMBOLIC_LINK
+        self.bits == wasi::FILETYPE_SYMBOLIC_LINK
     }
 
-    pub fn bits(&self) -> libc::__wasi_filetype_t {
+    pub fn bits(&self) -> wasi::FileType {
         self.bits
     }
 }
@@ -173,7 +175,7 @@ impl Iterator for ReadDir {
             // must have been truncated at the end of the buffer, so reset our
             // offset so we can go back and reread into the buffer, picking up
             // where we last left off.
-            let dirent_size = mem::size_of::<libc::__wasi_dirent_t>();
+            let dirent_size = mem::size_of::<wasi::Dirent>();
             if data.len() < dirent_size {
                 assert!(self.cookie.is_some());
                 assert!(self.buf.len() >= dirent_size);
@@ -182,7 +184,7 @@ impl Iterator for ReadDir {
             }
             let (dirent, data) = data.split_at(dirent_size);
             let dirent =
-                unsafe { ptr::read_unaligned(dirent.as_ptr() as *const libc::__wasi_dirent_t) };
+                unsafe { ptr::read_unaligned(dirent.as_ptr() as *const wasi::Dirent) };
 
             // If the file name was truncated, then we need to reinvoke
             // `readdir` so we truncate our buffer to start over and reread this
@@ -241,7 +243,7 @@ impl DirEntry {
         })
     }
 
-    pub fn ino(&self) -> libc::__wasi_inode_t {
+    pub fn ino(&self) -> wasi::Inode {
         self.meta.d_ino
     }
 }
@@ -249,7 +251,7 @@ impl DirEntry {
 impl OpenOptions {
     pub fn new() -> OpenOptions {
         let mut base = OpenOptions::default();
-        base.dirflags = libc::__WASI_LOOKUP_SYMLINK_FOLLOW;
+        base.dirflags = wasi::LOOKUP_SYMLINK_FOLLOW;
         return base;
     }
 
@@ -262,23 +264,23 @@ impl OpenOptions {
     }
 
     pub fn truncate(&mut self, truncate: bool) {
-        self.oflag(libc::__WASI_O_TRUNC, truncate);
+        self.oflag(wasi::O_TRUNC, truncate);
     }
 
     pub fn create(&mut self, create: bool) {
-        self.oflag(libc::__WASI_O_CREAT, create);
+        self.oflag(wasi::O_CREAT, create);
     }
 
     pub fn create_new(&mut self, create_new: bool) {
-        self.oflag(libc::__WASI_O_EXCL, create_new);
-        self.oflag(libc::__WASI_O_CREAT, create_new);
+        self.oflag(wasi::O_EXCL, create_new);
+        self.oflag(wasi::O_CREAT, create_new);
     }
 
     pub fn directory(&mut self, directory: bool) {
-        self.oflag(libc::__WASI_O_DIRECTORY, directory);
+        self.oflag(wasi::O_DIRECTORY, directory);
     }
 
-    fn oflag(&mut self, bit: libc::__wasi_oflags_t, set: bool) {
+    fn oflag(&mut self, bit: wasi::OFlags, set: bool) {
         if set {
             self.oflags |= bit;
         } else {
@@ -287,26 +289,26 @@ impl OpenOptions {
     }
 
     pub fn append(&mut self, set: bool) {
-        self.fdflag(libc::__WASI_FDFLAG_APPEND, set);
+        self.fdflag(wasi::FDFLAG_APPEND, set);
     }
 
     pub fn dsync(&mut self, set: bool) {
-        self.fdflag(libc::__WASI_FDFLAG_DSYNC, set);
+        self.fdflag(wasi::FDFLAG_DSYNC, set);
     }
 
     pub fn nonblock(&mut self, set: bool) {
-        self.fdflag(libc::__WASI_FDFLAG_NONBLOCK, set);
+        self.fdflag(wasi::FDFLAG_NONBLOCK, set);
     }
 
     pub fn rsync(&mut self, set: bool) {
-        self.fdflag(libc::__WASI_FDFLAG_RSYNC, set);
+        self.fdflag(wasi::FDFLAG_RSYNC, set);
     }
 
     pub fn sync(&mut self, set: bool) {
-        self.fdflag(libc::__WASI_FDFLAG_SYNC, set);
+        self.fdflag(wasi::FDFLAG_SYNC, set);
     }
 
-    fn fdflag(&mut self, bit: libc::__wasi_fdflags_t, set: bool) {
+    fn fdflag(&mut self, bit: wasi::FdFlags, set: bool) {
         if set {
             self.fdflags |= bit;
         } else {
@@ -314,15 +316,15 @@ impl OpenOptions {
         }
     }
 
-    pub fn fs_rights_base(&mut self, rights: libc::__wasi_rights_t) {
+    pub fn fs_rights_base(&mut self, rights: wasi::Rights) {
         self.rights_base = Some(rights);
     }
 
-    pub fn fs_rights_inheriting(&mut self, rights: libc::__wasi_rights_t) {
+    pub fn fs_rights_inheriting(&mut self, rights: wasi::Rights) {
         self.rights_inheriting = Some(rights);
     }
 
-    fn rights_base(&self) -> libc::__wasi_rights_t {
+    fn rights_base(&self) -> wasi::Rights {
         if let Some(rights) = self.rights_base {
             return rights;
         }
@@ -334,52 +336,52 @@ impl OpenOptions {
         // based on that.
         let mut base = 0;
         if self.read {
-            base |= libc::__WASI_RIGHT_FD_READ;
-            base |= libc::__WASI_RIGHT_FD_READDIR;
+            base |= wasi::RIGHT_FD_READ;
+            base |= wasi::RIGHT_FD_READDIR;
         }
         if self.write {
-            base |= libc::__WASI_RIGHT_FD_WRITE;
-            base |= libc::__WASI_RIGHT_FD_DATASYNC;
-            base |= libc::__WASI_RIGHT_FD_ALLOCATE;
-            base |= libc::__WASI_RIGHT_FD_FILESTAT_SET_SIZE;
+            base |= wasi::RIGHT_FD_WRITE;
+            base |= wasi::RIGHT_FD_DATASYNC;
+            base |= wasi::RIGHT_FD_ALLOCATE;
+            base |= wasi::RIGHT_FD_FILESTAT_SET_SIZE;
         }
 
         // FIXME: some of these should probably be read-only or write-only...
-        base |= libc::__WASI_RIGHT_FD_ADVISE;
-        base |= libc::__WASI_RIGHT_FD_FDSTAT_SET_FLAGS;
-        base |= libc::__WASI_RIGHT_FD_FILESTAT_SET_TIMES;
-        base |= libc::__WASI_RIGHT_FD_SEEK;
-        base |= libc::__WASI_RIGHT_FD_SYNC;
-        base |= libc::__WASI_RIGHT_FD_TELL;
-        base |= libc::__WASI_RIGHT_PATH_CREATE_DIRECTORY;
-        base |= libc::__WASI_RIGHT_PATH_CREATE_FILE;
-        base |= libc::__WASI_RIGHT_PATH_FILESTAT_GET;
-        base |= libc::__WASI_RIGHT_PATH_LINK_SOURCE;
-        base |= libc::__WASI_RIGHT_PATH_LINK_TARGET;
-        base |= libc::__WASI_RIGHT_PATH_OPEN;
-        base |= libc::__WASI_RIGHT_PATH_READLINK;
-        base |= libc::__WASI_RIGHT_PATH_REMOVE_DIRECTORY;
-        base |= libc::__WASI_RIGHT_PATH_RENAME_SOURCE;
-        base |= libc::__WASI_RIGHT_PATH_RENAME_TARGET;
-        base |= libc::__WASI_RIGHT_PATH_SYMLINK;
-        base |= libc::__WASI_RIGHT_PATH_UNLINK_FILE;
-        base |= libc::__WASI_RIGHT_POLL_FD_READWRITE;
+        base |= wasi::RIGHT_FD_ADVISE;
+        base |= wasi::RIGHT_FD_FDSTAT_SET_FLAGS;
+        base |= wasi::RIGHT_FD_FILESTAT_SET_TIMES;
+        base |= wasi::RIGHT_FD_SEEK;
+        base |= wasi::RIGHT_FD_SYNC;
+        base |= wasi::RIGHT_FD_TELL;
+        base |= wasi::RIGHT_PATH_CREATE_DIRECTORY;
+        base |= wasi::RIGHT_PATH_CREATE_FILE;
+        base |= wasi::RIGHT_PATH_FILESTAT_GET;
+        base |= wasi::RIGHT_PATH_LINK_SOURCE;
+        base |= wasi::RIGHT_PATH_LINK_TARGET;
+        base |= wasi::RIGHT_PATH_OPEN;
+        base |= wasi::RIGHT_PATH_READLINK;
+        base |= wasi::RIGHT_PATH_REMOVE_DIRECTORY;
+        base |= wasi::RIGHT_PATH_RENAME_SOURCE;
+        base |= wasi::RIGHT_PATH_RENAME_TARGET;
+        base |= wasi::RIGHT_PATH_SYMLINK;
+        base |= wasi::RIGHT_PATH_UNLINK_FILE;
+        base |= wasi::RIGHT_POLL_FD_READWRITE;
 
         return base;
     }
 
-    fn rights_inheriting(&self) -> libc::__wasi_rights_t {
+    fn rights_inheriting(&self) -> wasi::Rights {
         self.rights_inheriting.unwrap_or_else(|| self.rights_base())
     }
 
-    pub fn lookup_flags(&mut self, flags: libc::__wasi_lookupflags_t) {
+    pub fn lookup_flags(&mut self, flags: wasi::LookupFlags) {
         self.dirflags = flags;
     }
 }
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
-        let (dir, file) = open_parent(path, libc::__WASI_RIGHT_PATH_OPEN)?;
+        let (dir, file) = open_parent(path, wasi::RIGHT_PATH_OPEN)?;
         open_at(&dir, &file, opts)
     }
 
@@ -388,14 +390,12 @@ impl File {
     }
 
     pub fn file_attr(&self) -> io::Result<FileAttr> {
-        let mut ret = FileAttr::zero();
-        self.fd.filestat_get(&mut ret.meta)?;
-        Ok(ret)
+        self.fd.filestat_get().map_ok(|meta| FileAttr { meta })
     }
 
     pub fn metadata_at(
         &self,
-        flags: libc::__wasi_lookupflags_t,
+        flags: wasi::LookupFlags,
         path: &Path,
     ) -> io::Result<FileAttr> {
         metadata_at(&self.fd, flags, path)
@@ -477,7 +477,7 @@ impl DirBuilder {
     }
 
     pub fn mkdir(&self, p: &Path) -> io::Result<()> {
-        let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_CREATE_DIRECTORY)?;
+        let (dir, file) = open_parent(p, wasi::RIGHT_PATH_CREATE_DIRECTORY)?;
         dir.create_directory(file.as_os_str().as_bytes())
     }
 }
@@ -508,13 +508,13 @@ pub fn readdir(p: &Path) -> io::Result<ReadDir> {
 }
 
 pub fn unlink(p: &Path) -> io::Result<()> {
-    let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_UNLINK_FILE)?;
+    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_UNLINK_FILE)?;
     dir.unlink_file(file.as_os_str().as_bytes())
 }
 
 pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
-    let (old, old_file) = open_parent(old, libc::__WASI_RIGHT_PATH_RENAME_SOURCE)?;
-    let (new, new_file) = open_parent(new, libc::__WASI_RIGHT_PATH_RENAME_TARGET)?;
+    let (old, old_file) = open_parent(old, wasi::RIGHT_PATH_RENAME_SOURCE)?;
+    let (new, new_file) = open_parent(new, wasi::RIGHT_PATH_RENAME_TARGET)?;
     old.rename(
         old_file.as_os_str().as_bytes(),
         &new,
@@ -529,12 +529,12 @@ pub fn set_perm(_p: &Path, _perm: FilePermissions) -> io::Result<()> {
 }
 
 pub fn rmdir(p: &Path) -> io::Result<()> {
-    let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_REMOVE_DIRECTORY)?;
+    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_REMOVE_DIRECTORY)?;
     dir.remove_directory(file.as_os_str().as_bytes())
 }
 
 pub fn readlink(p: &Path) -> io::Result<PathBuf> {
-    let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_READLINK)?;
+    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_READLINK)?;
     read_link(&dir, &file)
 }
 
@@ -570,15 +570,15 @@ fn read_link(fd: &WasiFd, file: &Path) -> io::Result<PathBuf> {
 }
 
 pub fn symlink(src: &Path, dst: &Path) -> io::Result<()> {
-    let (dst, dst_file) = open_parent(dst, libc::__WASI_RIGHT_PATH_SYMLINK)?;
+    let (dst, dst_file) = open_parent(dst, wasi::RIGHT_PATH_SYMLINK)?;
     dst.symlink(src.as_os_str().as_bytes(), dst_file.as_os_str().as_bytes())
 }
 
 pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
-    let (src, src_file) = open_parent(src, libc::__WASI_RIGHT_PATH_LINK_SOURCE)?;
-    let (dst, dst_file) = open_parent(dst, libc::__WASI_RIGHT_PATH_LINK_TARGET)?;
+    let (src, src_file) = open_parent(src, wasi::RIGHT_PATH_LINK_SOURCE)?;
+    let (dst, dst_file) = open_parent(dst, wasi::RIGHT_PATH_LINK_TARGET)?;
     src.link(
-        libc::__WASI_LOOKUP_SYMLINK_FOLLOW,
+        wasi::LOOKUP_SYMLINK_FOLLOW,
         src_file.as_os_str().as_bytes(),
         &dst,
         dst_file.as_os_str().as_bytes(),
@@ -586,23 +586,22 @@ pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
 }
 
 pub fn stat(p: &Path) -> io::Result<FileAttr> {
-    let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_FILESTAT_GET)?;
-    metadata_at(&dir, libc::__WASI_LOOKUP_SYMLINK_FOLLOW, &file)
+    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_FILESTAT_GET)?;
+    metadata_at(&dir, wasi::LOOKUP_SYMLINK_FOLLOW, &file)
 }
 
 pub fn lstat(p: &Path) -> io::Result<FileAttr> {
-    let (dir, file) = open_parent(p, libc::__WASI_RIGHT_PATH_FILESTAT_GET)?;
+    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_FILESTAT_GET)?;
     metadata_at(&dir, 0, &file)
 }
 
 fn metadata_at(
     fd: &WasiFd,
-    flags: libc::__wasi_lookupflags_t,
+    flags: wasi::LookupFlags,
     path: &Path,
 ) -> io::Result<FileAttr> {
-    let mut ret = FileAttr::zero();
-    fd.path_filestat_get(flags, path.as_os_str().as_bytes(), &mut ret.meta)?;
-    Ok(ret)
+    fd.path_filestat_get(flags, path.as_os_str().as_bytes())
+        .map_ok(|meta| FileAttr { meta })
 }
 
 pub fn canonicalize(_p: &Path) -> io::Result<PathBuf> {
@@ -652,12 +651,12 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 /// to any preopened file descriptor.
 fn open_parent(
     p: &Path,
-    rights: libc::__wasi_rights_t,
+    rights: wasi::Rights,
 ) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
     let p = CString::new(p.as_os_str().as_bytes())?;
     unsafe {
         let mut ret = ptr::null();
-        let fd = __wasilibc_find_relpath(p.as_ptr(), rights, 0, &mut ret);
+        let fd = libc::__wasilibc_find_relpath(p.as_ptr(), rights, 0, &mut ret);
         if fd == -1 {
             let msg = format!(
                 "failed to find a preopened file descriptor \
@@ -677,15 +676,4 @@ fn open_parent(
 
         return Ok((ManuallyDrop::new(WasiFd::from_raw(fd as u32)), path));
     }
-
-    // FIXME(rust-lang/libc#1314) use the `libc` crate for this when the API
-    // there is published
-    extern "C" {
-        pub fn __wasilibc_find_relpath(
-            path: *const libc::c_char,
-            rights_base: libc::__wasi_rights_t,
-            rights_inheriting: libc::__wasi_rights_t,
-            relative_path: *mut *const libc::c_char,
-        ) -> libc::c_int;
-    }
 }
diff --git a/src/libstd/sys/wasi/io.rs b/src/libstd/sys/wasi/io.rs
index ffecca5d1b6ff..ebea3a03e439f 100644
--- a/src/libstd/sys/wasi/io.rs
+++ b/src/libstd/sys/wasi/io.rs
@@ -1,11 +1,12 @@
 use crate::marker::PhantomData;
 use crate::slice;
 
-use libc::{__wasi_ciovec_t, __wasi_iovec_t, c_void};
+use wasi::wasi_unstable as wasi;
+use core::ffi::c_void;
 
 #[repr(transparent)]
 pub struct IoSlice<'a> {
-    vec: __wasi_ciovec_t,
+    vec: wasi::CIoVec,
     _p: PhantomData<&'a [u8]>,
 }
 
@@ -13,7 +14,7 @@ impl<'a> IoSlice<'a> {
     #[inline]
     pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
         IoSlice {
-            vec: __wasi_ciovec_t {
+            vec: wasi::CIoVec {
                 buf: buf.as_ptr() as *const c_void,
                 buf_len: buf.len(),
             },
@@ -43,7 +44,7 @@ impl<'a> IoSlice<'a> {
 
 #[repr(transparent)]
 pub struct IoSliceMut<'a> {
-    vec: __wasi_iovec_t,
+    vec: wasi::IoVec,
     _p: PhantomData<&'a mut [u8]>,
 }
 
@@ -51,7 +52,7 @@ impl<'a> IoSliceMut<'a> {
     #[inline]
     pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
         IoSliceMut {
-            vec: __wasi_iovec_t {
+            vec: wasi::IoVec {
                 buf: buf.as_mut_ptr() as *mut c_void,
                 buf_len: buf.len()
             },
diff --git a/src/libstd/sys/wasi/mod.rs b/src/libstd/sys/wasi/mod.rs
index f842869e08ee6..0a16c29e5af53 100644
--- a/src/libstd/sys/wasi/mod.rs
+++ b/src/libstd/sys/wasi/mod.rs
@@ -14,10 +14,10 @@
 //! compiling for wasm. That way it's a compile time error for something that's
 //! guaranteed to be a runtime error!
 
-use libc;
-use crate::io::{Error, ErrorKind};
+use crate::io;
 use crate::mem;
 use crate::os::raw::c_char;
+use wasi::wasi_unstable as wasi;
 
 pub mod alloc;
 pub mod args;
@@ -60,12 +60,12 @@ pub fn unsupported<T>() -> crate::io::Result<T> {
     Err(unsupported_err())
 }
 
-pub fn unsupported_err() -> Error {
-    Error::new(ErrorKind::Other, "operation not supported on wasm yet")
+pub fn unsupported_err() -> io::Error {
+    io::Error::new(io::ErrorKind::Other, "operation not supported on wasm yet")
 }
 
-pub fn decode_error_kind(_code: i32) -> ErrorKind {
-    ErrorKind::Other
+pub fn decode_error_kind(_code: i32) -> io::ErrorKind {
+    io::ErrorKind::Other
 }
 
 // This enum is used as the storage for a bunch of types which can't actually
@@ -83,15 +83,18 @@ pub unsafe fn strlen(mut s: *const c_char) -> usize {
 }
 
 pub unsafe fn abort_internal() -> ! {
-    libc::abort()
+    wasi::proc_exit(127)
 }
 
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut ret = (0u64, 0u64);
     unsafe {
-        let base = &mut ret as *mut (u64, u64) as *mut libc::c_void;
+        let base = &mut ret as *mut (u64, u64) as *mut core::ffi::c_void;
         let len = mem::size_of_val(&ret);
-        cvt_wasi(libc::__wasi_random_get(base, len)).unwrap();
+        let ret = wasi::raw::__wasi_random_get(base, len);
+        if ret != 0 {
+            panic!("__wasi_random_get failure")
+        }
     }
     return ret
 }
@@ -113,16 +116,14 @@ impl_is_minus_one! { i8 i16 i32 i64 isize }
 
 pub fn cvt<T: IsMinusOne>(t: T) -> crate::io::Result<T> {
     if t.is_minus_one() {
-        Err(Error::last_os_error())
+        Err(io::Error::last_os_error())
     } else {
         Ok(t)
     }
 }
 
-pub fn cvt_wasi(r: u16) -> crate::io::Result<()> {
-    if r != libc::__WASI_ESUCCESS {
-        Err(Error::from_raw_os_error(r as i32))
-    } else {
-        Ok(())
+impl From<wasi::Error> for io::Error {
+    fn from(err: wasi::Error) -> Self {
+        Self::from_raw_os_error(err as i32)
     }
 }
diff --git a/src/libstd/sys/wasi/os.rs b/src/libstd/sys/wasi/os.rs
index 822ea02a11b89..026ff71de345b 100644
--- a/src/libstd/sys/wasi/os.rs
+++ b/src/libstd/sys/wasi/os.rs
@@ -12,6 +12,8 @@ use crate::sys::memchr;
 use crate::sys::{cvt, unsupported, Void};
 use crate::vec;
 
+use wasi::wasi_unstable as wasi;
+
 #[cfg(not(target_feature = "atomics"))]
 pub unsafe fn env_lock() -> impl Any {
     // No need for a lock if we're single-threaded, but this function will need
@@ -19,29 +21,11 @@ pub unsafe fn env_lock() -> impl Any {
 }
 
 pub fn errno() -> i32 {
-    extern {
-        #[thread_local]
-        static errno: libc::c_int;
-    }
-
-    unsafe { errno as i32 }
+    panic!("unsupported")
 }
 
 pub fn error_string(errno: i32) -> String {
-    extern {
-        fn strerror_r(errnum: libc::c_int, buf: *mut libc::c_char,
-                      buflen: libc::size_t) -> libc::c_int;
-    }
-
-    let mut buf = [0 as libc::c_char; 1024];
-
-    let p = buf.as_mut_ptr();
-    unsafe {
-        if strerror_r(errno as libc::c_int, p, buf.len()) < 0 {
-            panic!("strerror_r failure");
-        }
-        str::from_utf8(CStr::from_ptr(p).to_bytes()).unwrap().to_owned()
-    }
+    wasi::error_string(errno).to_string()
 }
 
 pub fn getcwd() -> io::Result<PathBuf> {
@@ -105,6 +89,7 @@ impl Iterator for Env {
 pub fn env() -> Env {
     unsafe {
         let _guard = env_lock();
+        // FIXME: replace with wasi::environ_get
         let mut environ = libc::environ;
         let mut result = Vec::new();
         while environ != ptr::null_mut() && *environ != ptr::null_mut() {
@@ -174,9 +159,7 @@ pub fn home_dir() -> Option<PathBuf> {
 }
 
 pub fn exit(code: i32) -> ! {
-    unsafe {
-        libc::exit(code)
-    }
+    unsafe { wasi::proc_exit(code as u32) }
 }
 
 pub fn getpid() -> u32 {
diff --git a/src/libstd/sys/wasi/stdio.rs b/src/libstd/sys/wasi/stdio.rs
index 2bf8d803c01bb..dc6a6ef375a1c 100644
--- a/src/libstd/sys/wasi/stdio.rs
+++ b/src/libstd/sys/wasi/stdio.rs
@@ -1,8 +1,9 @@
 use crate::io::{self, IoSlice, IoSliceMut};
-use crate::libc;
 use crate::mem::ManuallyDrop;
 use crate::sys::fd::WasiFd;
 
+use wasi::wasi_unstable as wasi;
+
 pub struct Stdin;
 pub struct Stdout;
 pub struct Stderr;
@@ -17,7 +18,7 @@ impl Stdin {
     }
 
     pub fn read_vectored(&self, data: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(libc::STDIN_FILENO as u32) })
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDIN_FD) })
             .read(data)
     }
 }
@@ -32,7 +33,7 @@ impl Stdout {
     }
 
     pub fn write_vectored(&self, data: &[IoSlice<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(libc::STDOUT_FILENO as u32) })
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDOUT_FD) })
             .write(data)
     }
 
@@ -51,7 +52,7 @@ impl Stderr {
     }
 
     pub fn write_vectored(&self, data: &[IoSlice<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(libc::STDERR_FILENO as u32) })
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDERR_FD) })
             .write(data)
     }
 
@@ -73,7 +74,7 @@ impl io::Write for Stderr {
 pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
 
 pub fn is_ebadf(err: &io::Error) -> bool {
-    err.raw_os_error() == Some(libc::__WASI_EBADF as i32)
+    err.raw_os_error() == Some(wasi::EBADF as i32)
 }
 
 pub fn panic_output() -> Option<impl io::Write> {
diff --git a/src/libstd/sys/wasi/thread.rs b/src/libstd/sys/wasi/thread.rs
index 5e69e4d948fee..9e0726432d9c4 100644
--- a/src/libstd/sys/wasi/thread.rs
+++ b/src/libstd/sys/wasi/thread.rs
@@ -19,8 +19,8 @@ impl Thread {
     }
 
     pub fn yield_now() {
-        let ret = unsafe { libc::__wasi_sched_yield() };
-        debug_assert_eq!(ret, 0);
+        let ret = wasi::sched_yield();
+        debug_assert_eq!(ret, Ok(()));
     }
 
     pub fn set_name(_name: &CStr) {
diff --git a/src/libstd/sys/wasi/time.rs b/src/libstd/sys/wasi/time.rs
index 3f14c80928c67..4c89a1781b9ef 100644
--- a/src/libstd/sys/wasi/time.rs
+++ b/src/libstd/sys/wasi/time.rs
@@ -1,7 +1,6 @@
 use crate::time::Duration;
 use crate::mem;
-use crate::sys::cvt_wasi;
-use libc;
+use wasi::wasi_unstable as wasi;
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 pub struct Instant(Duration);
@@ -12,23 +11,19 @@ pub struct SystemTime(Duration);
 pub const UNIX_EPOCH: SystemTime = SystemTime(Duration::from_secs(0));
 
 fn current_time(clock: u32) -> Duration {
-    unsafe {
-        let mut ts = mem::zeroed();
-        cvt_wasi(libc::__wasi_clock_time_get(
-            clock,
-            1, // precision... seems ignored though?
-            &mut ts,
-        )).unwrap();
-        Duration::new(
-            (ts / 1_000_000_000) as u64,
-            (ts % 1_000_000_000) as u32,
-        )
-    }
+    let ts = wasi::clock_time_get(
+        clock,
+        1, // precision... seems ignored though?
+    ).unwrap();
+    Duration::new(
+        (ts / 1_000_000_000) as u64,
+        (ts % 1_000_000_000) as u32,
+    )
 }
 
 impl Instant {
     pub fn now() -> Instant {
-        Instant(current_time(libc::__WASI_CLOCK_MONOTONIC))
+        Instant(current_time(wasi::CLOCK_MONOTONIC))
     }
 
     pub const fn zero() -> Instant {
@@ -54,10 +49,10 @@ impl Instant {
 
 impl SystemTime {
     pub fn now() -> SystemTime {
-        SystemTime(current_time(libc::__WASI_CLOCK_REALTIME))
+        SystemTime(current_time(wasi::CLOCK_REALTIME))
     }
 
-    pub fn from_wasi_timestamp(ts: libc::__wasi_timestamp_t) -> SystemTime {
+    pub fn from_wasi_timestamp(ts: wasi::Timestamp) -> SystemTime {
         SystemTime(Duration::from_nanos(ts))
     }