diff --git a/Cargo.lock b/Cargo.lock
index 8fd0285a7e6..5a56bf03f4d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1294,7 +1294,7 @@ checksum = "473a1265acc8ff1e808cd0a1af8cee3c2ee5200916058a2ca113c29f2d903571"
 dependencies = [
  "cfg-if",
  "libc",
- "wasi",
+ "wasi 0.7.0",
 ]
 
 [[package]]
@@ -4301,7 +4301,7 @@ dependencies = [
  "rustc_msan",
  "rustc_tsan",
  "unwind",
- "wasi",
+ "wasi 0.9.0+wasi-snapshot-preview1",
 ]
 
 [[package]]
@@ -5172,6 +5172,12 @@ name = "wasi"
 version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b89c3ce4ce14bdc6fb6beaf9ec7928ca331de5df7e5ea278375642a2f478570d"
+
+[[package]]
+name = "wasi"
+version = "0.9.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
 dependencies = [
  "compiler_builtins",
  "rustc-std-workspace-alloc",
diff --git a/src/libstd/Cargo.toml b/src/libstd/Cargo.toml
index c55911a33f5..a22e162bbff 100644
--- a/src/libstd/Cargo.toml
+++ b/src/libstd/Cargo.toml
@@ -54,7 +54,7 @@ fortanix-sgx-abi = { version = "0.3.2", features = ['rustc-dep-of-std'] }
 hermit-abi = { version = "0.1", features = ['rustc-dep-of-std'] }
 
 [target.wasm32-wasi.dependencies]
-wasi = { version = "0.7.0", features = ['rustc-dep-of-std', 'alloc'] }
+wasi = { version = "0.9.0", features = ['rustc-dep-of-std'], default-features = false }
 
 [features]
 default = ["std_detect_file_io", "std_detect_dlsym_getauxval"]
diff --git a/src/libstd/sys/wasi/args.rs b/src/libstd/sys/wasi/args.rs
index 3280c4990dc..3db36f5e132 100644
--- a/src/libstd/sys/wasi/args.rs
+++ b/src/libstd/sys/wasi/args.rs
@@ -1,15 +1,11 @@
-use crate::ffi::OsString;
+use crate::ffi::{CStr, OsStr, OsString};
 use crate::marker::PhantomData;
-use crate::os::wasi::ffi::OsStringExt;
+use crate::os::wasi::ffi::OsStrExt;
 use crate::vec;
 
-use ::wasi::wasi_unstable as wasi;
+pub unsafe fn init(_argc: isize, _argv: *const *const u8) {}
 
-pub unsafe fn init(_argc: isize, _argv: *const *const u8) {
-}
-
-pub unsafe fn cleanup() {
-}
+pub unsafe fn cleanup() {}
 
 pub struct Args {
     iter: vec::IntoIter<OsString>,
@@ -18,17 +14,24 @@ pub struct Args {
 
 /// Returns the command line arguments
 pub fn args() -> Args {
-    let buf = wasi::args_sizes_get().and_then(|args_sizes| {
-        let mut buf = Vec::with_capacity(args_sizes.get_count());
-        wasi::args_get(args_sizes, |arg| {
-            let arg = OsString::from_vec(arg.to_vec());
-            buf.push(arg);
-        })?;
-        Ok(buf)
-    }).unwrap_or(vec![]);
     Args {
-        iter: buf.into_iter(),
-        _dont_send_or_sync_me: PhantomData
+        iter: maybe_args().unwrap_or(Vec::new()).into_iter(),
+        _dont_send_or_sync_me: PhantomData,
+    }
+}
+
+fn maybe_args() -> Option<Vec<OsString>> {
+    unsafe {
+        let (argc, buf_size) = wasi::args_sizes_get().ok()?;
+        let mut argv = Vec::with_capacity(argc);
+        let mut buf = Vec::with_capacity(buf_size);
+        wasi::args_get(argv.as_mut_ptr(), buf.as_mut_ptr()).ok()?;
+        let mut ret = Vec::with_capacity(argc);
+        for ptr in argv {
+            let s = CStr::from_ptr(ptr.cast());
+            ret.push(OsStr::from_bytes(s.to_bytes()).to_owned());
+        }
+        Some(ret)
     }
 }
 
diff --git a/src/libstd/sys/wasi/ext/fs.rs b/src/libstd/sys/wasi/ext/fs.rs
index 9fa4abfd171..92d0e60c07e 100644
--- a/src/libstd/sys/wasi/ext/fs.rs
+++ b/src/libstd/sys/wasi/ext/fs.rs
@@ -4,12 +4,10 @@
 
 use crate::fs::{self, File, Metadata, OpenOptions};
 use crate::io::{self, IoSlice, IoSliceMut};
-use crate::os::wasi::ffi::OsStrExt;
 use crate::path::{Path, PathBuf};
+use crate::sys::fs::osstr2str;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner};
 
-use ::wasi::wasi_unstable as wasi;
-
 /// WASI-specific extensions to [`File`].
 ///
 /// [`File`]: ../../../../std/fs/struct.File.html
@@ -49,62 +47,62 @@ pub trait FileExt {
 
     /// Returns the current position within the file.
     ///
-    /// This corresponds to the `__wasi_fd_tell` syscall and is similar to
+    /// This corresponds to the `fd_tell` syscall and is similar to
     /// `seek` where you offset 0 bytes from the current position.
     fn tell(&self) -> io::Result<u64>;
 
     /// Adjust the flags associated with this file.
     ///
-    /// This corresponds to the `__wasi_fd_fdstat_set_flags` syscall.
+    /// This corresponds to the `fd_fdstat_set_flags` syscall.
     fn fdstat_set_flags(&self, flags: u16) -> io::Result<()>;
 
     /// Adjust the rights associated with this file.
     ///
-    /// This corresponds to the `__wasi_fd_fdstat_set_rights` syscall.
+    /// This corresponds to the `fd_fdstat_set_rights` syscall.
     fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> io::Result<()>;
 
     /// Provide file advisory information on a file descriptor.
     ///
-    /// This corresponds to the `__wasi_fd_advise` syscall.
+    /// This corresponds to the `fd_advise` syscall.
     fn advise(&self, offset: u64, len: u64, advice: u8) -> io::Result<()>;
 
     /// Force the allocation of space in a file.
     ///
-    /// This corresponds to the `__wasi_fd_allocate` syscall.
+    /// This corresponds to the `fd_allocate` syscall.
     fn allocate(&self, offset: u64, len: u64) -> io::Result<()>;
 
     /// Create a directory.
     ///
-    /// This corresponds to the `__wasi_path_create_directory` syscall.
+    /// This corresponds to the `path_create_directory` syscall.
     fn create_directory<P: AsRef<Path>>(&self, dir: P) -> io::Result<()>;
 
     /// Read the contents of a symbolic link.
     ///
-    /// This corresponds to the `__wasi_path_readlink` syscall.
+    /// This corresponds to the `path_readlink` syscall.
     fn read_link<P: AsRef<Path>>(&self, path: P) -> io::Result<PathBuf>;
 
     /// Return the attributes of a file or directory.
     ///
-    /// This corresponds to the `__wasi_path_filestat_get` syscall.
+    /// This corresponds to the `path_filestat_get` syscall.
     fn metadata_at<P: AsRef<Path>>(&self, lookup_flags: u32, path: P) -> io::Result<Metadata>;
 
     /// Unlink a file.
     ///
-    /// This corresponds to the `__wasi_path_unlink_file` syscall.
+    /// This corresponds to the `path_unlink_file` syscall.
     fn remove_file<P: AsRef<Path>>(&self, path: P) -> io::Result<()>;
 
     /// Remove a directory.
     ///
-    /// This corresponds to the `__wasi_path_remove_directory` syscall.
+    /// This corresponds to the `path_remove_directory` syscall.
     fn remove_directory<P: AsRef<Path>>(&self, path: P) -> io::Result<()>;
 }
 
-// FIXME: bind __wasi_fd_fdstat_get - need to define a custom return type
-// FIXME: bind __wasi_fd_readdir - can't return `ReadDir` since we only have entry name
-// FIXME: bind __wasi_fd_filestat_set_times maybe? - on crates.io for unix
-// FIXME: bind __wasi_path_filestat_set_times maybe? - on crates.io for unix
-// FIXME: bind __wasi_poll_oneoff maybe? - probably should wait for I/O to settle
-// FIXME: bind __wasi_random_get maybe? - on crates.io for unix
+// FIXME: bind fd_fdstat_get - need to define a custom return type
+// FIXME: bind fd_readdir - can't return `ReadDir` since we only have entry name
+// FIXME: bind fd_filestat_set_times maybe? - on crates.io for unix
+// FIXME: bind path_filestat_set_times maybe? - on crates.io for unix
+// FIXME: bind poll_oneoff maybe? - probably should wait for I/O to settle
+// FIXME: bind random_get maybe? - on crates.io for unix
 
 impl FileExt for fs::File {
     fn read_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
@@ -136,9 +134,7 @@ impl FileExt for fs::File {
     }
 
     fn create_directory<P: AsRef<Path>>(&self, dir: P) -> io::Result<()> {
-        self.as_inner()
-            .fd()
-            .create_directory(dir.as_ref().as_os_str().as_bytes())
+        self.as_inner().fd().create_directory(osstr2str(dir.as_ref().as_ref())?)
     }
 
     fn read_link<P: AsRef<Path>>(&self, path: P) -> io::Result<PathBuf> {
@@ -151,15 +147,11 @@ impl FileExt for fs::File {
     }
 
     fn remove_file<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
-        self.as_inner()
-            .fd()
-            .unlink_file(path.as_ref().as_os_str().as_bytes())
+        self.as_inner().fd().unlink_file(osstr2str(path.as_ref().as_ref())?)
     }
 
     fn remove_directory<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
-        self.as_inner()
-            .fd()
-            .remove_directory(path.as_ref().as_os_str().as_bytes())
+        self.as_inner().fd().remove_directory(osstr2str(path.as_ref().as_ref())?)
     }
 }
 
@@ -167,10 +159,10 @@ impl FileExt for fs::File {
 ///
 /// [`fs::OpenOptions`]: ../../../../std/fs/struct.OpenOptions.html
 pub trait OpenOptionsExt {
-    /// Pass custom `dirflags` argument to `__wasi_path_open`.
+    /// Pass custom `dirflags` argument to `path_open`.
     ///
     /// This option configures the `dirflags` argument to the
-    /// `__wasi_path_open` syscall which `OpenOptions` will eventually call. The
+    /// `path_open` syscall which `OpenOptions` will eventually call. The
     /// `dirflags` argument configures how the file is looked up, currently
     /// primarily affecting whether symlinks are followed or not.
     ///
@@ -188,31 +180,31 @@ pub trait OpenOptionsExt {
     fn directory(&mut self, dir: bool) -> &mut Self;
 
     /// Indicates whether `__WASI_FDFLAG_DSYNC` is passed in the `fs_flags`
-    /// field of `__wasi_path_open`.
+    /// field of `path_open`.
     ///
     /// This option is by default `false`
     fn dsync(&mut self, dsync: bool) -> &mut Self;
 
     /// Indicates whether `__WASI_FDFLAG_NONBLOCK` is passed in the `fs_flags`
-    /// field of `__wasi_path_open`.
+    /// field of `path_open`.
     ///
     /// This option is by default `false`
     fn nonblock(&mut self, nonblock: bool) -> &mut Self;
 
     /// Indicates whether `__WASI_FDFLAG_RSYNC` is passed in the `fs_flags`
-    /// field of `__wasi_path_open`.
+    /// field of `path_open`.
     ///
     /// This option is by default `false`
     fn rsync(&mut self, rsync: bool) -> &mut Self;
 
     /// Indicates whether `__WASI_FDFLAG_SYNC` is passed in the `fs_flags`
-    /// field of `__wasi_path_open`.
+    /// field of `path_open`.
     ///
     /// This option is by default `false`
     fn sync(&mut self, sync: bool) -> &mut Self;
 
     /// Indicates the value that should be passed in for the `fs_rights_base`
-    /// parameter of `__wasi_path_open`.
+    /// parameter of `path_open`.
     ///
     /// This option defaults based on the `read` and `write` configuration of
     /// this `OpenOptions` builder. If this method is called, however, the
@@ -220,7 +212,7 @@ pub trait OpenOptionsExt {
     fn fs_rights_base(&mut self, rights: u64) -> &mut Self;
 
     /// Indicates the value that should be passed in for the
-    /// `fs_rights_inheriting` parameter of `__wasi_path_open`.
+    /// `fs_rights_inheriting` parameter of `path_open`.
     ///
     /// The default for this option is the same value as what will be passed
     /// for the `fs_rights_base` parameter but if this method is called then
@@ -229,7 +221,7 @@ pub trait OpenOptionsExt {
 
     /// Open a file or directory.
     ///
-    /// This corresponds to the `__wasi_path_open` syscall.
+    /// This corresponds to the `path_open` syscall.
     fn open_at<P: AsRef<Path>>(&self, file: &File, path: P) -> io::Result<File>;
 }
 
@@ -284,38 +276,38 @@ impl OpenOptionsExt for OpenOptions {
 ///
 /// [`fs::Metadata`]: ../../../../std/fs/struct.Metadata.html
 pub trait MetadataExt {
-    /// Returns the `st_dev` field of the internal `__wasi_filestat_t`
+    /// Returns the `st_dev` field of the internal `filestat_t`
     fn dev(&self) -> u64;
-    /// Returns the `st_ino` field of the internal `__wasi_filestat_t`
+    /// Returns the `st_ino` field of the internal `filestat_t`
     fn ino(&self) -> u64;
-    /// Returns the `st_nlink` field of the internal `__wasi_filestat_t`
-    fn nlink(&self) -> u32;
-    /// Returns the `st_atim` field of the internal `__wasi_filestat_t`
+    /// Returns the `st_nlink` field of the internal `filestat_t`
+    fn nlink(&self) -> u64;
+    /// Returns the `st_atim` field of the internal `filestat_t`
     fn atim(&self) -> u64;
-    /// Returns the `st_mtim` field of the internal `__wasi_filestat_t`
+    /// Returns the `st_mtim` field of the internal `filestat_t`
     fn mtim(&self) -> u64;
-    /// Returns the `st_ctim` field of the internal `__wasi_filestat_t`
+    /// Returns the `st_ctim` field of the internal `filestat_t`
     fn ctim(&self) -> u64;
 }
 
 impl MetadataExt for fs::Metadata {
     fn dev(&self) -> u64 {
-        self.as_inner().as_wasi().st_dev
+        self.as_inner().as_wasi().dev
     }
     fn ino(&self) -> u64 {
-        self.as_inner().as_wasi().st_ino
+        self.as_inner().as_wasi().ino
     }
-    fn nlink(&self) -> u32 {
-        self.as_inner().as_wasi().st_nlink
+    fn nlink(&self) -> u64 {
+        self.as_inner().as_wasi().nlink
     }
     fn atim(&self) -> u64 {
-        self.as_inner().as_wasi().st_atim
+        self.as_inner().as_wasi().atim
     }
     fn mtim(&self) -> u64 {
-        self.as_inner().as_wasi().st_mtim
+        self.as_inner().as_wasi().mtim
     }
     fn ctim(&self) -> u64 {
-        self.as_inner().as_wasi().st_ctim
+        self.as_inner().as_wasi().ctim
     }
 }
 
@@ -355,7 +347,7 @@ impl FileTypeExt for fs::FileType {
 ///
 /// [`fs::DirEntry`]: ../../../../std/fs/struct.DirEntry.html
 pub trait DirEntryExt {
-    /// Returns the underlying `d_ino` field of the `__wasi_dirent_t`
+    /// Returns the underlying `d_ino` field of the `dirent_t`
     fn ino(&self) -> u64;
 }
 
@@ -367,7 +359,7 @@ impl DirEntryExt for fs::DirEntry {
 
 /// Create a hard link.
 ///
-/// This corresponds to the `__wasi_path_link` syscall.
+/// This corresponds to the `path_link` syscall.
 pub fn link<P: AsRef<Path>, U: AsRef<Path>>(
     old_fd: &File,
     old_flags: u32,
@@ -377,15 +369,15 @@ pub fn link<P: AsRef<Path>, U: AsRef<Path>>(
 ) -> io::Result<()> {
     old_fd.as_inner().fd().link(
         old_flags,
-        old_path.as_ref().as_os_str().as_bytes(),
+        osstr2str(old_path.as_ref().as_ref())?,
         new_fd.as_inner().fd(),
-        new_path.as_ref().as_os_str().as_bytes(),
+        osstr2str(new_path.as_ref().as_ref())?,
     )
 }
 
 /// Rename a file or directory.
 ///
-/// This corresponds to the `__wasi_path_rename` syscall.
+/// This corresponds to the `path_rename` syscall.
 pub fn rename<P: AsRef<Path>, U: AsRef<Path>>(
     old_fd: &File,
     old_path: P,
@@ -393,22 +385,21 @@ pub fn rename<P: AsRef<Path>, U: AsRef<Path>>(
     new_path: U,
 ) -> io::Result<()> {
     old_fd.as_inner().fd().rename(
-        old_path.as_ref().as_os_str().as_bytes(),
+        osstr2str(old_path.as_ref().as_ref())?,
         new_fd.as_inner().fd(),
-        new_path.as_ref().as_os_str().as_bytes(),
+        osstr2str(new_path.as_ref().as_ref())?,
     )
 }
 
 /// Create a symbolic link.
 ///
-/// This corresponds to the `__wasi_path_symlink` syscall.
+/// This corresponds to the `path_symlink` syscall.
 pub fn symlink<P: AsRef<Path>, U: AsRef<Path>>(
     old_path: P,
     fd: &File,
     new_path: U,
 ) -> io::Result<()> {
-    fd.as_inner().fd().symlink(
-        old_path.as_ref().as_os_str().as_bytes(),
-        new_path.as_ref().as_os_str().as_bytes(),
-    )
+    fd.as_inner()
+        .fd()
+        .symlink(osstr2str(old_path.as_ref().as_ref())?, osstr2str(new_path.as_ref().as_ref())?)
 }
diff --git a/src/libstd/sys/wasi/ext/io.rs b/src/libstd/sys/wasi/ext/io.rs
index f1839df3801..f678b71a2b9 100644
--- a/src/libstd/sys/wasi/ext/io.rs
+++ b/src/libstd/sys/wasi/ext/io.rs
@@ -8,8 +8,6 @@ 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;
 
@@ -127,18 +125,18 @@ impl IntoRawFd for fs::File {
 
 impl AsRawFd for io::Stdin {
     fn as_raw_fd(&self) -> RawFd {
-        wasi::STDIN_FD
+        sys::stdio::Stdin.as_raw_fd()
     }
 }
 
 impl AsRawFd for io::Stdout {
     fn as_raw_fd(&self) -> RawFd {
-        wasi::STDOUT_FD
+        sys::stdio::Stdout.as_raw_fd()
     }
 }
 
 impl AsRawFd for io::Stderr {
     fn as_raw_fd(&self) -> RawFd {
-        wasi::STDERR_FD
+        sys::stdio::Stderr.as_raw_fd()
     }
 }
diff --git a/src/libstd/sys/wasi/fd.rs b/src/libstd/sys/wasi/fd.rs
index 5b7a8678b66..00327c1743c 100644
--- a/src/libstd/sys/wasi/fd.rs
+++ b/src/libstd/sys/wasi/fd.rs
@@ -1,40 +1,31 @@
 #![allow(dead_code)]
 
+use super::err2io;
 use crate::io::{self, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
 use crate::net::Shutdown;
-use super::err2io;
-use ::wasi::wasi_unstable as wasi;
 
 #[derive(Debug)]
 pub struct WasiFd {
     fd: wasi::Fd,
 }
 
-fn iovec<'a>(a: &'a mut [IoSliceMut<'_>]) -> &'a [wasi::IoVec] {
-    assert_eq!(
-        mem::size_of::<IoSliceMut<'_>>(),
-        mem::size_of::<wasi::IoVec>()
-    );
-    assert_eq!(
-        mem::align_of::<IoSliceMut<'_>>(),
-        mem::align_of::<wasi::IoVec>()
-    );
+fn iovec<'a>(a: &'a mut [IoSliceMut<'_>]) -> &'a [wasi::Iovec] {
+    assert_eq!(mem::size_of::<IoSliceMut<'_>>(), mem::size_of::<wasi::Iovec>());
+    assert_eq!(mem::align_of::<IoSliceMut<'_>>(), mem::align_of::<wasi::Iovec>());
     /// SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout
-    unsafe { mem::transmute(a) }
+    unsafe {
+        mem::transmute(a)
+    }
 }
 
-fn ciovec<'a>(a: &'a [IoSlice<'_>]) -> &'a [wasi::CIoVec] {
-    assert_eq!(
-        mem::size_of::<IoSlice<'_>>(),
-        mem::size_of::<wasi::CIoVec>()
-    );
-    assert_eq!(
-        mem::align_of::<IoSlice<'_>>(),
-        mem::align_of::<wasi::CIoVec>()
-    );
+fn ciovec<'a>(a: &'a [IoSlice<'_>]) -> &'a [wasi::Ciovec] {
+    assert_eq!(mem::size_of::<IoSlice<'_>>(), mem::size_of::<wasi::Ciovec>());
+    assert_eq!(mem::align_of::<IoSlice<'_>>(), mem::align_of::<wasi::Ciovec>());
     /// SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout
-    unsafe { mem::transmute(a) }
+    unsafe {
+        mem::transmute(a)
+    }
 }
 
 impl WasiFd {
@@ -87,7 +78,7 @@ impl WasiFd {
 
     // FIXME: __wasi_fd_fdstat_get
 
-    pub fn set_flags(&self, flags: wasi::FdFlags) -> io::Result<()> {
+    pub fn set_flags(&self, flags: wasi::Fdflags) -> io::Result<()> {
         unsafe { wasi::fd_fdstat_set_flags(self.fd, flags).map_err(err2io) }
     }
 
@@ -107,31 +98,30 @@ impl WasiFd {
         unsafe { wasi::fd_allocate(self.fd, offset, len).map_err(err2io) }
     }
 
-    pub fn create_directory(&self, path: &[u8]) -> io::Result<()> {
+    pub fn create_directory(&self, path: &str) -> io::Result<()> {
         unsafe { wasi::path_create_directory(self.fd, path).map_err(err2io) }
     }
 
     pub fn link(
         &self,
-        old_flags: wasi::LookupFlags,
-        old_path: &[u8],
+        old_flags: wasi::Lookupflags,
+        old_path: &str,
         new_fd: &WasiFd,
-        new_path: &[u8],
+        new_path: &str,
     ) -> io::Result<()> {
         unsafe {
-            wasi::path_link(self.fd, old_flags, old_path, new_fd.fd, new_path)
-                .map_err(err2io)
+            wasi::path_link(self.fd, old_flags, old_path, new_fd.fd, new_path).map_err(err2io)
         }
     }
 
     pub fn open(
         &self,
-        dirflags: wasi::LookupFlags,
-        path: &[u8],
-        oflags: wasi::OFlags,
+        dirflags: wasi::Lookupflags,
+        path: &str,
+        oflags: wasi::Oflags,
         fs_rights_base: wasi::Rights,
         fs_rights_inheriting: wasi::Rights,
-        fs_flags: wasi::FdFlags,
+        fs_flags: wasi::Fdflags,
     ) -> io::Result<WasiFd> {
         unsafe {
             wasi::path_open(
@@ -142,25 +132,25 @@ impl WasiFd {
                 fs_rights_base,
                 fs_rights_inheriting,
                 fs_flags,
-            ).map(|fd| WasiFd::from_raw(fd)).map_err(err2io)
+            )
+            .map(|fd| WasiFd::from_raw(fd))
+            .map_err(err2io)
         }
     }
 
-    pub fn readdir(&self, buf: &mut [u8], cookie: wasi::DirCookie) -> io::Result<usize> {
-        unsafe { wasi::fd_readdir(self.fd, buf, cookie).map_err(err2io) }
+    pub fn readdir(&self, buf: &mut [u8], cookie: wasi::Dircookie) -> io::Result<usize> {
+        unsafe { wasi::fd_readdir(self.fd, buf.as_mut_ptr(), buf.len(), cookie).map_err(err2io) }
     }
 
-    pub fn readlink(&self, path: &[u8], buf: &mut [u8]) -> io::Result<usize> {
-        unsafe { wasi::path_readlink(self.fd, path, buf).map_err(err2io) }
+    pub fn readlink(&self, path: &str, buf: &mut [u8]) -> io::Result<usize> {
+        unsafe { wasi::path_readlink(self.fd, path, buf.as_mut_ptr(), buf.len()).map_err(err2io) }
     }
 
-    pub fn rename(&self, old_path: &[u8], new_fd: &WasiFd, new_path: &[u8]) -> io::Result<()> {
-        unsafe {
-            wasi::path_rename(self.fd, old_path, new_fd.fd, new_path).map_err(err2io)
-        }
+    pub fn rename(&self, old_path: &str, new_fd: &WasiFd, new_path: &str) -> io::Result<()> {
+        unsafe { wasi::path_rename(self.fd, old_path, new_fd.fd, new_path).map_err(err2io) }
     }
 
-    pub fn filestat_get(&self) -> io::Result<wasi::FileStat> {
+    pub fn filestat_get(&self) -> io::Result<wasi::Filestat> {
         unsafe { wasi::fd_filestat_get(self.fd).map_err(err2io) }
     }
 
@@ -168,11 +158,9 @@ impl WasiFd {
         &self,
         atim: wasi::Timestamp,
         mtim: wasi::Timestamp,
-        fstflags: wasi::FstFlags,
+        fstflags: wasi::Fstflags,
     ) -> io::Result<()> {
-        unsafe {
-            wasi::fd_filestat_set_times(self.fd, atim, mtim, fstflags).map_err(err2io)
-        }
+        unsafe { wasi::fd_filestat_set_times(self.fd, atim, mtim, fstflags).map_err(err2io) }
     }
 
     pub fn filestat_set_size(&self, size: u64) -> io::Result<()> {
@@ -181,61 +169,55 @@ impl WasiFd {
 
     pub fn path_filestat_get(
         &self,
-        flags: wasi::LookupFlags,
-        path: &[u8],
-    ) -> io::Result<wasi::FileStat> {
+        flags: wasi::Lookupflags,
+        path: &str,
+    ) -> io::Result<wasi::Filestat> {
         unsafe { wasi::path_filestat_get(self.fd, flags, path).map_err(err2io) }
     }
 
     pub fn path_filestat_set_times(
         &self,
-        flags: wasi::LookupFlags,
-        path: &[u8],
+        flags: wasi::Lookupflags,
+        path: &str,
         atim: wasi::Timestamp,
         mtim: wasi::Timestamp,
-        fstflags: wasi::FstFlags,
+        fstflags: wasi::Fstflags,
     ) -> io::Result<()> {
         unsafe {
-            wasi::path_filestat_set_times(
-                self.fd,
-                flags,
-                path,
-                atim,
-                mtim,
-                fstflags,
-            ).map_err(err2io)
+            wasi::path_filestat_set_times(self.fd, flags, path, atim, mtim, fstflags)
+                .map_err(err2io)
         }
     }
 
-    pub fn symlink(&self, old_path: &[u8], new_path: &[u8]) -> io::Result<()> {
+    pub fn symlink(&self, old_path: &str, new_path: &str) -> io::Result<()> {
         unsafe { wasi::path_symlink(old_path, self.fd, new_path).map_err(err2io) }
     }
 
-    pub fn unlink_file(&self, path: &[u8]) -> io::Result<()> {
+    pub fn unlink_file(&self, path: &str) -> io::Result<()> {
         unsafe { wasi::path_unlink_file(self.fd, path).map_err(err2io) }
     }
 
-    pub fn remove_directory(&self, path: &[u8]) -> io::Result<()> {
+    pub fn remove_directory(&self, path: &str) -> io::Result<()> {
         unsafe { wasi::path_remove_directory(self.fd, path).map_err(err2io) }
     }
 
     pub fn sock_recv(
         &self,
         ri_data: &mut [IoSliceMut<'_>],
-        ri_flags: wasi::RiFlags,
-    ) -> io::Result<(usize, wasi::RoFlags)> {
+        ri_flags: wasi::Riflags,
+    ) -> io::Result<(usize, wasi::Roflags)> {
         unsafe { wasi::sock_recv(self.fd, iovec(ri_data), ri_flags).map_err(err2io) }
     }
 
-    pub fn sock_send(&self, si_data: &[IoSlice<'_>], si_flags: wasi::SiFlags) -> io::Result<usize> {
+    pub fn sock_send(&self, si_data: &[IoSlice<'_>], si_flags: wasi::Siflags) -> io::Result<usize> {
         unsafe { wasi::sock_send(self.fd, ciovec(si_data), si_flags).map_err(err2io) }
     }
 
     pub fn sock_shutdown(&self, how: Shutdown) -> io::Result<()> {
         let how = match how {
-            Shutdown::Read => wasi::SHUT_RD,
-            Shutdown::Write => wasi::SHUT_WR,
-            Shutdown::Both => wasi::SHUT_WR | wasi::SHUT_RD,
+            Shutdown::Read => wasi::SDFLAGS_RD,
+            Shutdown::Write => wasi::SDFLAGS_WR,
+            Shutdown::Both => wasi::SDFLAGS_WR | wasi::SDFLAGS_RD,
         };
         unsafe { wasi::sock_shutdown(self.fd, how).map_err(err2io) }
     }
diff --git a/src/libstd/sys/wasi/fs.rs b/src/libstd/sys/wasi/fs.rs
index 4113f6a2e09..fad092e35c3 100644
--- a/src/libstd/sys/wasi/fs.rs
+++ b/src/libstd/sys/wasi/fs.rs
@@ -15,20 +15,18 @@ 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: wasi::FileStat,
+    meta: wasi::Filestat,
 }
 
 pub struct ReadDir {
     inner: Arc<ReadDirInner>,
-    cookie: Option<wasi::DirCookie>,
+    cookie: Option<wasi::Dircookie>,
     buf: Vec<u8>,
     offset: usize,
     cap: usize,
@@ -49,9 +47,9 @@ pub struct DirEntry {
 pub struct OpenOptions {
     read: bool,
     write: bool,
-    dirflags: wasi::LookupFlags,
-    fdflags: wasi::FdFlags,
-    oflags: wasi::OFlags,
+    dirflags: wasi::Lookupflags,
+    fdflags: wasi::Fdflags,
+    oflags: wasi::Oflags,
     rights_base: Option<wasi::Rights>,
     rights_inheriting: Option<wasi::Rights>,
 }
@@ -63,7 +61,7 @@ pub struct FilePermissions {
 
 #[derive(PartialEq, Eq, Hash, Debug, Copy, Clone)]
 pub struct FileType {
-    bits: wasi::FileType,
+    bits: wasi::Filetype,
 }
 
 #[derive(Debug)]
@@ -71,7 +69,7 @@ pub struct DirBuilder {}
 
 impl FileAttr {
     pub fn size(&self) -> u64 {
-        self.meta.st_size
+        self.meta.size
     }
 
     pub fn perm(&self) -> FilePermissions {
@@ -80,24 +78,22 @@ impl FileAttr {
     }
 
     pub fn file_type(&self) -> FileType {
-        FileType {
-            bits: self.meta.st_filetype,
-        }
+        FileType { bits: self.meta.filetype }
     }
 
     pub fn modified(&self) -> io::Result<SystemTime> {
-        Ok(SystemTime::from_wasi_timestamp(self.meta.st_mtim))
+        Ok(SystemTime::from_wasi_timestamp(self.meta.mtim))
     }
 
     pub fn accessed(&self) -> io::Result<SystemTime> {
-        Ok(SystemTime::from_wasi_timestamp(self.meta.st_atim))
+        Ok(SystemTime::from_wasi_timestamp(self.meta.atim))
     }
 
     pub fn created(&self) -> io::Result<SystemTime> {
-        Ok(SystemTime::from_wasi_timestamp(self.meta.st_ctim))
+        Ok(SystemTime::from_wasi_timestamp(self.meta.ctim))
     }
 
-    pub fn as_wasi(&self) -> &wasi::FileStat {
+    pub fn as_wasi(&self) -> &wasi::Filestat {
         &self.meta
     }
 }
@@ -125,7 +121,7 @@ impl FileType {
         self.bits == wasi::FILETYPE_SYMBOLIC_LINK
     }
 
-    pub fn bits(&self) -> wasi::FileType {
+    pub fn bits(&self) -> wasi::Filetype {
         self.bits
     }
 }
@@ -177,8 +173,7 @@ impl Iterator for ReadDir {
                 continue;
             }
             let (dirent, data) = data.split_at(dirent_size);
-            let dirent =
-                unsafe { ptr::read_unaligned(dirent.as_ptr() as *const wasi::Dirent) };
+            let dirent = 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
@@ -224,17 +219,11 @@ impl DirEntry {
     }
 
     pub fn metadata(&self) -> io::Result<FileAttr> {
-        metadata_at(
-            &self.inner.dir.fd,
-            0,
-            OsStr::from_bytes(&self.name).as_ref(),
-        )
+        metadata_at(&self.inner.dir.fd, 0, OsStr::from_bytes(&self.name).as_ref())
     }
 
     pub fn file_type(&self) -> io::Result<FileType> {
-        Ok(FileType {
-            bits: self.meta.d_type,
-        })
+        Ok(FileType { bits: self.meta.d_type })
     }
 
     pub fn ino(&self) -> wasi::Inode {
@@ -245,7 +234,7 @@ impl DirEntry {
 impl OpenOptions {
     pub fn new() -> OpenOptions {
         let mut base = OpenOptions::default();
-        base.dirflags = wasi::LOOKUP_SYMLINK_FOLLOW;
+        base.dirflags = wasi::LOOKUPFLAGS_SYMLINK_FOLLOW;
         return base;
     }
 
@@ -258,23 +247,23 @@ impl OpenOptions {
     }
 
     pub fn truncate(&mut self, truncate: bool) {
-        self.oflag(wasi::O_TRUNC, truncate);
+        self.oflag(wasi::OFLAGS_TRUNC, truncate);
     }
 
     pub fn create(&mut self, create: bool) {
-        self.oflag(wasi::O_CREAT, create);
+        self.oflag(wasi::OFLAGS_CREAT, create);
     }
 
     pub fn create_new(&mut self, create_new: bool) {
-        self.oflag(wasi::O_EXCL, create_new);
-        self.oflag(wasi::O_CREAT, create_new);
+        self.oflag(wasi::OFLAGS_EXCL, create_new);
+        self.oflag(wasi::OFLAGS_CREAT, create_new);
     }
 
     pub fn directory(&mut self, directory: bool) {
-        self.oflag(wasi::O_DIRECTORY, directory);
+        self.oflag(wasi::OFLAGS_DIRECTORY, directory);
     }
 
-    fn oflag(&mut self, bit: wasi::OFlags, set: bool) {
+    fn oflag(&mut self, bit: wasi::Oflags, set: bool) {
         if set {
             self.oflags |= bit;
         } else {
@@ -283,26 +272,26 @@ impl OpenOptions {
     }
 
     pub fn append(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAG_APPEND, set);
+        self.fdflag(wasi::FDFLAGS_APPEND, set);
     }
 
     pub fn dsync(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAG_DSYNC, set);
+        self.fdflag(wasi::FDFLAGS_DSYNC, set);
     }
 
     pub fn nonblock(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAG_NONBLOCK, set);
+        self.fdflag(wasi::FDFLAGS_NONBLOCK, set);
     }
 
     pub fn rsync(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAG_RSYNC, set);
+        self.fdflag(wasi::FDFLAGS_RSYNC, set);
     }
 
     pub fn sync(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAG_SYNC, set);
+        self.fdflag(wasi::FDFLAGS_SYNC, set);
     }
 
-    fn fdflag(&mut self, bit: wasi::FdFlags, set: bool) {
+    fn fdflag(&mut self, bit: wasi::Fdflags, set: bool) {
         if set {
             self.fdflags |= bit;
         } else {
@@ -330,36 +319,36 @@ impl OpenOptions {
         // based on that.
         let mut base = 0;
         if self.read {
-            base |= wasi::RIGHT_FD_READ;
-            base |= wasi::RIGHT_FD_READDIR;
+            base |= wasi::RIGHTS_FD_READ;
+            base |= wasi::RIGHTS_FD_READDIR;
         }
         if self.write {
-            base |= wasi::RIGHT_FD_WRITE;
-            base |= wasi::RIGHT_FD_DATASYNC;
-            base |= wasi::RIGHT_FD_ALLOCATE;
-            base |= wasi::RIGHT_FD_FILESTAT_SET_SIZE;
+            base |= wasi::RIGHTS_FD_WRITE;
+            base |= wasi::RIGHTS_FD_DATASYNC;
+            base |= wasi::RIGHTS_FD_ALLOCATE;
+            base |= wasi::RIGHTS_FD_FILESTAT_SET_SIZE;
         }
 
         // FIXME: some of these should probably be read-only or write-only...
-        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;
+        base |= wasi::RIGHTS_FD_ADVISE;
+        base |= wasi::RIGHTS_FD_FDSTAT_SET_FLAGS;
+        base |= wasi::RIGHTS_FD_FILESTAT_SET_TIMES;
+        base |= wasi::RIGHTS_FD_SEEK;
+        base |= wasi::RIGHTS_FD_SYNC;
+        base |= wasi::RIGHTS_FD_TELL;
+        base |= wasi::RIGHTS_PATH_CREATE_DIRECTORY;
+        base |= wasi::RIGHTS_PATH_CREATE_FILE;
+        base |= wasi::RIGHTS_PATH_FILESTAT_GET;
+        base |= wasi::RIGHTS_PATH_LINK_SOURCE;
+        base |= wasi::RIGHTS_PATH_LINK_TARGET;
+        base |= wasi::RIGHTS_PATH_OPEN;
+        base |= wasi::RIGHTS_PATH_READLINK;
+        base |= wasi::RIGHTS_PATH_REMOVE_DIRECTORY;
+        base |= wasi::RIGHTS_PATH_RENAME_SOURCE;
+        base |= wasi::RIGHTS_PATH_RENAME_TARGET;
+        base |= wasi::RIGHTS_PATH_SYMLINK;
+        base |= wasi::RIGHTS_PATH_UNLINK_FILE;
+        base |= wasi::RIGHTS_POLL_FD_READWRITE;
 
         return base;
     }
@@ -368,14 +357,14 @@ impl OpenOptions {
         self.rights_inheriting.unwrap_or_else(|| self.rights_base())
     }
 
-    pub fn lookup_flags(&mut self, flags: wasi::LookupFlags) {
+    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, wasi::RIGHT_PATH_OPEN)?;
+        let (dir, file) = open_parent(path, wasi::RIGHTS_PATH_OPEN)?;
         open_at(&dir, &file, opts)
     }
 
@@ -387,11 +376,7 @@ impl File {
         self.fd.filestat_get().map(|meta| FileAttr { meta })
     }
 
-    pub fn metadata_at(
-        &self,
-        flags: wasi::LookupFlags,
-        path: &Path,
-    ) -> io::Result<FileAttr> {
+    pub fn metadata_at(&self, flags: wasi::Lookupflags, path: &Path) -> io::Result<FileAttr> {
         metadata_at(&self.fd, flags, path)
     }
 
@@ -457,11 +442,7 @@ impl File {
 
 impl FromInner<u32> for File {
     fn from_inner(fd: u32) -> File {
-        unsafe {
-            File {
-                fd: WasiFd::from_raw(fd),
-            }
-        }
+        unsafe { File { fd: WasiFd::from_raw(fd) } }
     }
 }
 
@@ -471,16 +452,14 @@ impl DirBuilder {
     }
 
     pub fn mkdir(&self, p: &Path) -> io::Result<()> {
-        let (dir, file) = open_parent(p, wasi::RIGHT_PATH_CREATE_DIRECTORY)?;
-        dir.create_directory(file.as_os_str().as_bytes())
+        let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_CREATE_DIRECTORY)?;
+        dir.create_directory(osstr2str(file.as_ref())?)
     }
 }
 
 impl fmt::Debug for File {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("File")
-            .field("fd", &self.fd.as_raw())
-            .finish()
+        f.debug_struct("File").field("fd", &self.fd.as_raw()).finish()
     }
 }
 
@@ -494,26 +473,19 @@ pub fn readdir(p: &Path) -> io::Result<ReadDir> {
         buf: vec![0; 128],
         offset: 0,
         cap: 0,
-        inner: Arc::new(ReadDirInner {
-            dir,
-            root: p.to_path_buf(),
-        }),
+        inner: Arc::new(ReadDirInner { dir, root: p.to_path_buf() }),
     })
 }
 
 pub fn unlink(p: &Path) -> io::Result<()> {
-    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_UNLINK_FILE)?;
-    dir.unlink_file(file.as_os_str().as_bytes())
+    let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_UNLINK_FILE)?;
+    dir.unlink_file(osstr2str(file.as_ref())?)
 }
 
 pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
-    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,
-        new_file.as_os_str().as_bytes(),
-    )
+    let (old, old_file) = open_parent(old, wasi::RIGHTS_PATH_RENAME_SOURCE)?;
+    let (new, new_file) = open_parent(new, wasi::RIGHTS_PATH_RENAME_TARGET)?;
+    old.rename(osstr2str(old_file.as_ref())?, &new, osstr2str(new_file.as_ref())?)
 }
 
 pub fn set_perm(_p: &Path, _perm: FilePermissions) -> io::Result<()> {
@@ -523,12 +495,12 @@ pub fn set_perm(_p: &Path, _perm: FilePermissions) -> io::Result<()> {
 }
 
 pub fn rmdir(p: &Path) -> io::Result<()> {
-    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_REMOVE_DIRECTORY)?;
-    dir.remove_directory(file.as_os_str().as_bytes())
+    let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_REMOVE_DIRECTORY)?;
+    dir.remove_directory(osstr2str(file.as_ref())?)
 }
 
 pub fn readlink(p: &Path) -> io::Result<PathBuf> {
-    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_READLINK)?;
+    let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_READLINK)?;
     read_link(&dir, &file)
 }
 
@@ -549,7 +521,7 @@ fn read_link(fd: &WasiFd, file: &Path) -> io::Result<PathBuf> {
     // Now that we have an initial guess of how big to make our buffer, call
     // `readlink` in a loop until it fails or reports it filled fewer bytes than
     // we asked for, indicating we got everything.
-    let file = file.as_os_str().as_bytes();
+    let file = osstr2str(file.as_ref())?;
     let mut destination = vec![0u8; initial_size];
     loop {
         let len = fd.readlink(file, &mut destination)?;
@@ -564,38 +536,34 @@ 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, wasi::RIGHT_PATH_SYMLINK)?;
-    dst.symlink(src.as_os_str().as_bytes(), dst_file.as_os_str().as_bytes())
+    let (dst, dst_file) = open_parent(dst, wasi::RIGHTS_PATH_SYMLINK)?;
+    dst.symlink(osstr2str(src.as_ref())?, osstr2str(dst_file.as_ref())?)
 }
 
 pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
-    let (src, src_file) = open_parent(src, wasi::RIGHT_PATH_LINK_SOURCE)?;
-    let (dst, dst_file) = open_parent(dst, wasi::RIGHT_PATH_LINK_TARGET)?;
+    let (src, src_file) = open_parent(src, wasi::RIGHTS_PATH_LINK_SOURCE)?;
+    let (dst, dst_file) = open_parent(dst, wasi::RIGHTS_PATH_LINK_TARGET)?;
     src.link(
-        wasi::LOOKUP_SYMLINK_FOLLOW,
-        src_file.as_os_str().as_bytes(),
+        wasi::LOOKUPFLAGS_SYMLINK_FOLLOW,
+        osstr2str(src_file.as_ref())?,
         &dst,
-        dst_file.as_os_str().as_bytes(),
+        osstr2str(dst_file.as_ref())?,
     )
 }
 
 pub fn stat(p: &Path) -> io::Result<FileAttr> {
-    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_FILESTAT_GET)?;
-    metadata_at(&dir, wasi::LOOKUP_SYMLINK_FOLLOW, &file)
+    let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_FILESTAT_GET)?;
+    metadata_at(&dir, wasi::LOOKUPFLAGS_SYMLINK_FOLLOW, &file)
 }
 
 pub fn lstat(p: &Path) -> io::Result<FileAttr> {
-    let (dir, file) = open_parent(p, wasi::RIGHT_PATH_FILESTAT_GET)?;
+    let (dir, file) = open_parent(p, wasi::RIGHTS_PATH_FILESTAT_GET)?;
     metadata_at(&dir, 0, &file)
 }
 
-fn metadata_at(
-    fd: &WasiFd,
-    flags: wasi::LookupFlags,
-    path: &Path,
-) -> io::Result<FileAttr> {
-    fd.path_filestat_get(flags, path.as_os_str().as_bytes())
-        .map(|meta| FileAttr { meta })
+fn metadata_at(fd: &WasiFd, flags: wasi::Lookupflags, path: &Path) -> io::Result<FileAttr> {
+    let meta = fd.path_filestat_get(flags, osstr2str(path.as_ref())?)?;
+    Ok(FileAttr { meta })
 }
 
 pub fn canonicalize(_p: &Path) -> io::Result<PathBuf> {
@@ -607,7 +575,7 @@ pub fn canonicalize(_p: &Path) -> io::Result<PathBuf> {
 fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
     let fd = fd.open(
         opts.dirflags,
-        path.as_os_str().as_bytes(),
+        osstr2str(path.as_ref())?,
         opts.oflags,
         opts.rights_base(),
         opts.rights_inheriting(),
@@ -643,10 +611,7 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 ///
 /// Note that this can fail if `p` doesn't look like it can be opened relative
 /// to any preopened file descriptor.
-fn open_parent(
-    p: &Path,
-    rights: wasi::Rights,
-) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
+fn open_parent(p: &Path, rights: wasi::Rights) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
     let p = CString::new(p.as_os_str().as_bytes())?;
     unsafe {
         let mut ret = ptr::null();
@@ -671,3 +636,7 @@ fn open_parent(
         return Ok((ManuallyDrop::new(WasiFd::from_raw(fd as u32)), path));
     }
 }
+
+pub fn osstr2str(f: &OsStr) -> io::Result<&str> {
+    f.to_str().ok_or_else(|| io::Error::new(io::ErrorKind::Other, "input must be utf-8"))
+}
diff --git a/src/libstd/sys/wasi/io.rs b/src/libstd/sys/wasi/io.rs
index 4be92faed30..41a6e9783c0 100644
--- a/src/libstd/sys/wasi/io.rs
+++ b/src/libstd/sys/wasi/io.rs
@@ -1,12 +1,9 @@
 use crate::marker::PhantomData;
 use crate::slice;
 
-use ::wasi::wasi_unstable as wasi;
-use core::ffi::c_void;
-
 #[repr(transparent)]
 pub struct IoSlice<'a> {
-    vec: wasi::CIoVec,
+    vec: wasi::Ciovec,
     _p: PhantomData<&'a [u8]>,
 }
 
@@ -14,8 +11,8 @@ impl<'a> IoSlice<'a> {
     #[inline]
     pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
         IoSlice {
-            vec: wasi::CIoVec {
-                buf: buf.as_ptr() as *const c_void,
+            vec: wasi::Ciovec {
+                buf: buf.as_ptr(),
                 buf_len: buf.len(),
             },
             _p: PhantomData,
@@ -44,7 +41,7 @@ impl<'a> IoSlice<'a> {
 
 #[repr(transparent)]
 pub struct IoSliceMut<'a> {
-    vec: wasi::IoVec,
+    vec: wasi::Iovec,
     _p: PhantomData<&'a mut [u8]>,
 }
 
@@ -52,8 +49,8 @@ impl<'a> IoSliceMut<'a> {
     #[inline]
     pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
         IoSliceMut {
-            vec: wasi::IoVec {
-                buf: buf.as_mut_ptr() as *mut c_void,
+            vec: wasi::Iovec {
+                buf: buf.as_mut_ptr(),
                 buf_len: buf.len()
             },
             _p: PhantomData,
diff --git a/src/libstd/sys/wasi/mod.rs b/src/libstd/sys/wasi/mod.rs
index 517e3be9cb5..83f98a19f47 100644
--- a/src/libstd/sys/wasi/mod.rs
+++ b/src/libstd/sys/wasi/mod.rs
@@ -17,7 +17,6 @@
 use crate::io as std_io;
 use crate::mem;
 use crate::os::raw::c_char;
-use ::wasi::wasi_unstable as wasi;
 
 pub mod alloc;
 pub mod args;
@@ -72,25 +71,21 @@ pub fn decode_error_kind(errno: i32) -> std_io::ErrorKind {
     if errno > u16::max_value() as i32 || errno < 0 {
         return Other;
     }
-    let code = match wasi::Error::new(errno as u16) {
-        Some(code) => code,
-        None => return Other,
-    };
-    match code {
-        wasi::ECONNREFUSED => ConnectionRefused,
-        wasi::ECONNRESET => ConnectionReset,
-        wasi::EPERM | wasi::EACCES => PermissionDenied,
-        wasi::EPIPE => BrokenPipe,
-        wasi::ENOTCONN => NotConnected,
-        wasi::ECONNABORTED => ConnectionAborted,
-        wasi::EADDRNOTAVAIL => AddrNotAvailable,
-        wasi::EADDRINUSE => AddrInUse,
-        wasi::ENOENT => NotFound,
-        wasi::EINTR => Interrupted,
-        wasi::EINVAL => InvalidInput,
-        wasi::ETIMEDOUT => TimedOut,
-        wasi::EEXIST => AlreadyExists,
-        wasi::EAGAIN => WouldBlock,
+    match errno as u16 {
+        wasi::ERRNO_CONNREFUSED => ConnectionRefused,
+        wasi::ERRNO_CONNRESET => ConnectionReset,
+        wasi::ERRNO_PERM | wasi::ERRNO_ACCES => PermissionDenied,
+        wasi::ERRNO_PIPE => BrokenPipe,
+        wasi::ERRNO_NOTCONN => NotConnected,
+        wasi::ERRNO_CONNABORTED => ConnectionAborted,
+        wasi::ERRNO_ADDRNOTAVAIL => AddrNotAvailable,
+        wasi::ERRNO_ADDRINUSE => AddrInUse,
+        wasi::ERRNO_NOENT => NotFound,
+        wasi::ERRNO_INTR => Interrupted,
+        wasi::ERRNO_INVAL => InvalidInput,
+        wasi::ERRNO_TIMEDOUT => TimedOut,
+        wasi::ERRNO_EXIST => AlreadyExists,
+        wasi::ERRNO_AGAIN => WouldBlock,
         _ => Other,
     }
 }
@@ -116,16 +111,13 @@ pub unsafe fn abort_internal() -> ! {
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut ret = (0u64, 0u64);
     unsafe {
-        let base = &mut ret as *mut (u64, u64) as *mut core::ffi::c_void;
+        let base = &mut ret as *mut (u64, u64) as *mut u8;
         let len = mem::size_of_val(&ret);
-        let ret = wasi::raw::__wasi_random_get(base, len);
-        if ret != 0 {
-            panic!("__wasi_random_get failure")
-        }
+        wasi::random_get(base, len).expect("random_get failure");
     }
     return ret
 }
 
 fn err2io(err: wasi::Error) -> std_io::Error {
-    std_io::Error::from_raw_os_error(err.get() as i32)
+    std_io::Error::from_raw_os_error(err.raw_error().into())
 }
diff --git a/src/libstd/sys/wasi/stdio.rs b/src/libstd/sys/wasi/stdio.rs
index 1d57b9922e5..1d53884f2d6 100644
--- a/src/libstd/sys/wasi/stdio.rs
+++ b/src/libstd/sys/wasi/stdio.rs
@@ -2,8 +2,6 @@ use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
 use crate::sys::fd::WasiFd;
 
-use ::wasi::wasi_unstable as wasi;
-
 pub struct Stdin;
 pub struct Stdout;
 pub struct Stderr;
@@ -18,8 +16,11 @@ impl Stdin {
     }
 
     pub fn read_vectored(&self, data: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDIN_FD) })
-            .read(data)
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(self.as_raw_fd()) }).read(data)
+    }
+
+    pub fn as_raw_fd(&self) -> u32 {
+        0
     }
 }
 
@@ -33,13 +34,16 @@ impl Stdout {
     }
 
     pub fn write_vectored(&self, data: &[IoSlice<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDOUT_FD) })
-            .write(data)
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(self.as_raw_fd()) }).write(data)
     }
 
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }
+
+    pub fn as_raw_fd(&self) -> u32 {
+        1
+    }
 }
 
 impl Stderr {
@@ -52,13 +56,16 @@ impl Stderr {
     }
 
     pub fn write_vectored(&self, data: &[IoSlice<'_>]) -> io::Result<usize> {
-        ManuallyDrop::new(unsafe { WasiFd::from_raw(wasi::STDERR_FD) })
-            .write(data)
+        ManuallyDrop::new(unsafe { WasiFd::from_raw(self.as_raw_fd()) }).write(data)
     }
 
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }
+
+    pub fn as_raw_fd(&self) -> u32 {
+        2
+    }
 }
 
 impl io::Write for Stderr {
@@ -74,7 +81,7 @@ 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(wasi::EBADF.get() as i32)
+    err.raw_os_error() == Some(wasi::ERRNO_BADF.into())
 }
 
 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 6ce41420284..0986759b89b 100644
--- a/src/libstd/sys/wasi/thread.rs
+++ b/src/libstd/sys/wasi/thread.rs
@@ -4,22 +4,18 @@ use crate::mem;
 use crate::sys::{unsupported, Void};
 use crate::time::Duration;
 
-use ::wasi::wasi_unstable as wasi;
-
 pub struct Thread(Void);
 
 pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>)
-        -> io::Result<Thread>
-    {
+    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
         unsupported()
     }
 
     pub fn yield_now() {
-        let ret = wasi::sched_yield();
+        let ret = unsafe { wasi::sched_yield() };
         debug_assert_eq!(ret, Ok(()));
     }
 
@@ -33,32 +29,30 @@ impl Thread {
 
         const USERDATA: wasi::Userdata = 0x0123_45678;
 
-        let clock = wasi::raw::__wasi_subscription_u_clock_t {
-            identifier: 0,
-            clock_id: wasi::CLOCK_MONOTONIC,
+        let clock = wasi::SubscriptionClock {
+            id: wasi::CLOCKID_MONOTONIC,
             timeout: nanos as u64,
             precision: 0,
             flags: 0,
         };
 
-        let in_ = [wasi::Subscription {
+        let in_ = wasi::Subscription {
             userdata: USERDATA,
-            type_: wasi::EVENTTYPE_CLOCK,
-            u: wasi::raw::__wasi_subscription_u { clock: clock },
-        }];
-        let (res, event) = unsafe {
-            let mut out: [wasi::Event; 1] = mem::zeroed();
-            let res = wasi::poll_oneoff(&in_, &mut out);
-            (res, out[0])
+            r#type: wasi::EVENTTYPE_CLOCK,
+            u: wasi::SubscriptionU { clock },
         };
-        match (res, event) {
-            (Ok(1), wasi::Event {
-                userdata: USERDATA,
-                error: 0,
-                type_: wasi::EVENTTYPE_CLOCK,
-                ..
-            }) => {}
-            _ => panic!("thread::sleep(): unexpected result of poll_oneoff"),
+        unsafe {
+            let mut event: wasi::Event = mem::zeroed();
+            let res = wasi::poll_oneoff(&in_, &mut event, 1);
+            match (res, event) {
+                (
+                    Ok(1),
+                    wasi::Event {
+                        userdata: USERDATA, error: 0, r#type: wasi::EVENTTYPE_CLOCK, ..
+                    },
+                ) => {}
+                _ => panic!("thread::sleep(): unexpected result of poll_oneoff"),
+            }
         }
     }
 
@@ -69,6 +63,10 @@ impl Thread {
 
 pub mod guard {
     pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> { None }
-    pub unsafe fn init() -> Option<Guard> { None }
+    pub unsafe fn current() -> Option<Guard> {
+        None
+    }
+    pub unsafe fn init() -> Option<Guard> {
+        None
+    }
 }
diff --git a/src/libstd/sys/wasi/time.rs b/src/libstd/sys/wasi/time.rs
index 4394a22f9c2..80ec317b5a2 100644
--- a/src/libstd/sys/wasi/time.rs
+++ b/src/libstd/sys/wasi/time.rs
@@ -1,5 +1,4 @@
 use crate::time::Duration;
-use ::wasi::wasi_unstable as wasi;
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 pub struct Instant(Duration);
@@ -10,19 +9,18 @@ pub struct SystemTime(Duration);
 pub const UNIX_EPOCH: SystemTime = SystemTime(Duration::from_secs(0));
 
 fn current_time(clock: u32) -> Duration {
-    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,
-    )
+    let ts = unsafe {
+        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(wasi::CLOCK_MONOTONIC))
+        Instant(current_time(wasi::CLOCKID_MONOTONIC))
     }
 
     pub const fn zero() -> Instant {
@@ -48,15 +46,14 @@ impl Instant {
 
 impl SystemTime {
     pub fn now() -> SystemTime {
-        SystemTime(current_time(wasi::CLOCK_REALTIME))
+        SystemTime(current_time(wasi::CLOCKID_REALTIME))
     }
 
     pub fn from_wasi_timestamp(ts: wasi::Timestamp) -> SystemTime {
         SystemTime(Duration::from_nanos(ts))
     }
 
-    pub fn sub_time(&self, other: &SystemTime)
-                    -> Result<Duration, Duration> {
+    pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
         self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
     }