diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6f1a9923f1..6042581405 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -21,6 +21,8 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v1
+      with:
+        submodules: recursive
     - name: Install Rust
       uses: actions-rs/toolchain@v1
       with:
@@ -52,6 +54,8 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v1
+      with:
+        submodules: recursive
     - name: Install Rust
       uses: actions-rs/toolchain@v1
       with:
@@ -99,6 +103,8 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v1
+      with:
+        submodules: recursive
     - name: Install Rust
       uses: actions-rs/toolchain@v1
       with:
diff --git a/.gitmodules b/.gitmodules
index 23fd919b97..137cc0e19b 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "misc_testsuite"]
 	path = misc_testsuite
 	url = https://github.com/cranestation/wasi-misc-tests
+[submodule "WASI"]
+	path = WASI
+	url = https://github.com/WebAssembly/WASI
diff --git a/Cargo.toml b/Cargo.toml
index 970cd8f58f..8383a9df18 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,6 +29,7 @@ log = "0.4"
 filetime = "0.2.7"
 lazy_static = "1.4.0"
 num = { version = "0.2.0", default-features = false }
+wig = { path = "wig", version = "0.0.0" }
 
 [target.'cfg(unix)'.dependencies]
 nix = "0.15"
diff --git a/WASI b/WASI
new file mode 160000
index 0000000000..7a5f477fe4
--- /dev/null
+++ b/WASI
@@ -0,0 +1 @@
+Subproject commit 7a5f477fe411c2887d0689184d4aadbfc4892c0f
diff --git a/src/fs/file.rs b/src/fs/file.rs
index 1266f331b0..86090b2c3a 100644
--- a/src/fs/file.rs
+++ b/src/fs/file.rs
@@ -83,7 +83,7 @@ impl<'ctx> io::Read for File<'ctx> {
     /// TODO: Not yet implemented. See the comment in `Dir::open_file`.
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let iov = [host::__wasi_iovec_t {
-            buf: buf.as_mut_ptr() as *mut core::ffi::c_void,
+            buf: buf.as_mut_ptr() as *mut u8,
             buf_len: buf.len(),
         }];
         let mut nread = 0;
diff --git a/src/host.rs b/src/host.rs
index ac9a4efa81..d2378e1a48 100644
--- a/src/host.rs
+++ b/src/host.rs
@@ -6,60 +6,15 @@
 
 use crate::wasi::*;
 use std::{io, slice};
+use wig::witx_host_types;
 
-pub(crate) type void = ::std::os::raw::c_void;
+witx_host_types!("unstable" "wasi_unstable_preview0");
 
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub(crate) struct __wasi_prestat_t {
-    pub(crate) pr_type: __wasi_preopentype_t,
-    pub(crate) u: __wasi_prestat_t___wasi_prestat_u,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub(crate) union __wasi_prestat_t___wasi_prestat_u {
-    pub(crate) dir: __wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t,
-    _bindgen_union_align: u64,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub(crate) struct __wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t {
-    pub(crate) pr_name_len: usize,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub(crate) struct __wasi_ciovec_t {
-    pub(crate) buf: *const void,
-    pub(crate) buf_len: usize,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub(crate) struct __wasi_iovec_t {
-    pub(crate) buf: *mut void,
-    pub(crate) buf_len: usize,
-}
-
-#[allow(unused)]
 pub(crate) unsafe fn ciovec_to_host(ciovec: &__wasi_ciovec_t) -> io::IoSlice {
     let slice = slice::from_raw_parts(ciovec.buf as *const u8, ciovec.buf_len);
     io::IoSlice::new(slice)
 }
 
-#[allow(unused)]
-pub(crate) unsafe fn ciovec_to_host_mut(ciovec: &mut __wasi_ciovec_t) -> io::IoSliceMut {
-    let slice = slice::from_raw_parts_mut(ciovec.buf as *mut u8, ciovec.buf_len);
-    io::IoSliceMut::new(slice)
-}
-
-pub(crate) unsafe fn iovec_to_host(iovec: &__wasi_iovec_t) -> io::IoSlice {
-    let slice = slice::from_raw_parts(iovec.buf as *const u8, iovec.buf_len);
-    io::IoSlice::new(slice)
-}
-
 pub(crate) unsafe fn iovec_to_host_mut(iovec: &mut __wasi_iovec_t) -> io::IoSliceMut {
     let slice = slice::from_raw_parts_mut(iovec.buf as *mut u8, iovec.buf_len);
     io::IoSliceMut::new(slice)
@@ -105,30 +60,23 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>(),
+            ::std::mem::size_of::<__wasi_prestat_dir>(),
             8usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t)
-            )
+            concat!("Size of: ", stringify!(__wasi_prestat_dir))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>(),
+            ::std::mem::align_of::<__wasi_prestat_dir>(),
             8usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t)
-            )
+            concat!("Alignment of ", stringify!(__wasi_prestat_dir))
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>()))
-                    .pr_name_len as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_prestat_dir>())).pr_name_len as *const _ as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t),
+                stringify!(__wasi_prestat_dir),
                 "::",
                 stringify!(pr_name_len)
             )
@@ -138,27 +86,21 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_prestat_t___wasi_prestat_u() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_prestat_t___wasi_prestat_u>(),
+            ::std::mem::size_of::<__wasi_prestat_u>(),
             8usize,
-            concat!("Size of: ", stringify!(__wasi_prestat_t___wasi_prestat_u))
+            concat!("Size of: ", stringify!(__wasi_prestat_u))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_prestat_t___wasi_prestat_u>(),
+            ::std::mem::align_of::<__wasi_prestat_u>(),
             8usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u)
-            )
+            concat!("Alignment of ", stringify!(__wasi_prestat_u))
         );
         assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_prestat_t___wasi_prestat_u>())).dir as *const _
-                    as usize
-            },
+            unsafe { &(*(::std::ptr::null::<__wasi_prestat_u>())).dir as *const _ as usize },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u),
+                stringify!(__wasi_prestat_u),
                 "::",
                 stringify!(dir)
             )
diff --git a/src/hostcalls_impl/fs.rs b/src/hostcalls_impl/fs.rs
index 6b07a1a207..6f6d8027cb 100644
--- a/src/hostcalls_impl/fs.rs
+++ b/src/hostcalls_impl/fs.rs
@@ -110,7 +110,7 @@ pub(crate) unsafe fn fd_pwrite(
         .get_fd_entry(fd)?
         .as_descriptor(wasi::__WASI_RIGHT_FD_WRITE, 0)?
         .as_file()?;
-    let iovs = dec_iovec_slice(memory, iovs_ptr, iovs_len)?;
+    let iovs = dec_ciovec_slice(memory, iovs_ptr, iovs_len)?;
 
     if offset > i64::max_value() as u64 {
         return Err(Error::EIO);
@@ -352,8 +352,8 @@ pub(crate) unsafe fn fd_write(
         nwritten
     );
 
-    let iovs = dec_iovec_slice(memory, iovs_ptr, iovs_len)?;
-    let iovs: Vec<io::IoSlice> = iovs.iter().map(|vec| host::iovec_to_host(vec)).collect();
+    let iovs = dec_ciovec_slice(memory, iovs_ptr, iovs_len)?;
+    let iovs: Vec<io::IoSlice> = iovs.iter().map(|vec| host::ciovec_to_host(vec)).collect();
 
     // perform unbuffered writes
     let host_nwritten = match wasi_ctx
@@ -986,8 +986,8 @@ pub(crate) unsafe fn fd_prestat_get(
         prestat_ptr,
         host::__wasi_prestat_t {
             pr_type: wasi::__WASI_PREOPENTYPE_DIR,
-            u: host::__wasi_prestat_t___wasi_prestat_u {
-                dir: host::__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t {
+            u: host::__wasi_prestat_u {
+                dir: host::__wasi_prestat_dir {
                     pr_name_len: path.len(),
                 },
             },
diff --git a/src/hostcalls_impl/misc.rs b/src/hostcalls_impl/misc.rs
index b6005b7ccf..5ad1f73b0e 100644
--- a/src/hostcalls_impl/misc.rs
+++ b/src/hostcalls_impl/misc.rs
@@ -217,7 +217,7 @@ pub(crate) fn poll_oneoff(
     let mut timeout: Option<ClockEventData> = None;
     let mut fd_events = Vec::new();
     for subscription in subscriptions {
-        match subscription.type_ {
+        match subscription.r#type {
             wasi::__WASI_EVENTTYPE_CLOCK => {
                 let clock = unsafe { subscription.u.clock };
                 let delay = wasi_clock_to_relative_ns_delay(clock)?;
@@ -234,12 +234,12 @@ pub(crate) fn poll_oneoff(
                     *timeout = current;
                 }
             }
-            type_
-                if type_ == wasi::__WASI_EVENTTYPE_FD_READ
-                    || type_ == wasi::__WASI_EVENTTYPE_FD_WRITE =>
+            r#type
+                if r#type == wasi::__WASI_EVENTTYPE_FD_READ
+                    || r#type == wasi::__WASI_EVENTTYPE_FD_WRITE =>
             {
-                let wasi_fd = unsafe { subscription.u.fd_readwrite.fd };
-                let rights = if type_ == wasi::__WASI_EVENTTYPE_FD_READ {
+                let wasi_fd = unsafe { subscription.u.fd_readwrite.file_descriptor };
+                let rights = if r#type == wasi::__WASI_EVENTTYPE_FD_READ {
                     wasi::__WASI_RIGHT_FD_READ
                 } else {
                     wasi::__WASI_RIGHT_FD_WRITE
@@ -252,22 +252,20 @@ pub(crate) fn poll_oneoff(
                 } {
                     Ok(descriptor) => fd_events.push(FdEventData {
                         descriptor,
-                        type_: subscription.type_,
+                        r#type: subscription.r#type,
                         userdata: subscription.userdata,
                     }),
                     Err(err) => {
                         let event = wasi::__wasi_event_t {
                             userdata: subscription.userdata,
-                            type_,
+                            r#type,
                             error: err.as_wasi_errno(),
-                            u: wasi::__wasi_event_t___wasi_event_u {
-                                fd_readwrite: wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
+                            u: wasi::__wasi_event_u {
+                                fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
                                     nbytes: 0,
                                     flags: 0,
-                                    __bindgen_padding_0: [0, 0, 0],
                                 },
                             },
-                            __bindgen_padding_0: 0,
                         };
                         events.push(event);
                     }
@@ -291,9 +289,7 @@ pub(crate) fn poll_oneoff(
     enc_int_byref(memory, nevents, events_count)
 }
 
-fn wasi_clock_to_relative_ns_delay(
-    wasi_clock: wasi::__wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-) -> Result<u128> {
+fn wasi_clock_to_relative_ns_delay(wasi_clock: wasi::__wasi_subscription_clock_t) -> Result<u128> {
     use std::time::SystemTime;
 
     if wasi_clock.flags != wasi::__WASI_SUBSCRIPTION_CLOCK_ABSTIME {
@@ -316,6 +312,6 @@ pub(crate) struct ClockEventData {
 #[derive(Debug)]
 pub(crate) struct FdEventData<'a> {
     pub(crate) descriptor: &'a Descriptor,
-    pub(crate) type_: wasi::__wasi_eventtype_t,
+    pub(crate) r#type: wasi::__wasi_eventtype_t,
     pub(crate) userdata: wasi::__wasi_userdata_t,
 }
diff --git a/src/memory.rs b/src/memory.rs
index 90efebbf4e..9f1173a8fb 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -209,7 +209,7 @@ pub(crate) fn dec_ciovec_slice(
             let len = dec_usize(PrimInt::from_le(raw_iov.buf_len));
             let buf = PrimInt::from_le(raw_iov.buf);
             Ok(host::__wasi_ciovec_t {
-                buf: dec_ptr(memory, buf, len)? as *const host::void,
+                buf: dec_ptr(memory, buf, len)? as *const u8,
                 buf_len: len,
             })
         })
@@ -229,7 +229,7 @@ pub(crate) fn dec_iovec_slice(
             let len = dec_usize(PrimInt::from_le(raw_iov.buf_len));
             let buf = PrimInt::from_le(raw_iov.buf);
             Ok(host::__wasi_iovec_t {
-                buf: dec_ptr(memory, buf, len)? as *mut host::void,
+                buf: dec_ptr(memory, buf, len)? as *mut u8,
                 buf_len: len,
             })
         })
@@ -293,7 +293,6 @@ pub(crate) fn dec_fdstat_byref(
         fs_flags: PrimInt::from_le(raw.fs_flags),
         fs_rights_base: PrimInt::from_le(raw.fs_rights_base),
         fs_rights_inheriting: PrimInt::from_le(raw.fs_rights_inheriting),
-        __bindgen_padding_0: 0,
     })
 }
 
@@ -305,7 +304,6 @@ pub(crate) fn enc_fdstat_byref(
     let raw = wasi::__wasi_fdstat_t {
         fs_filetype: PrimInt::to_le(fdstat.fs_filetype),
         fs_flags: PrimInt::to_le(fdstat.fs_flags),
-        __bindgen_padding_0: 0,
         fs_rights_base: PrimInt::to_le(fdstat.fs_rights_base),
         fs_rights_inheriting: PrimInt::to_le(fdstat.fs_rights_inheriting),
     };
@@ -334,8 +332,8 @@ pub(crate) fn dec_prestat_byref(
     match PrimInt::from_le(raw.pr_type) {
         wasi::__WASI_PREOPENTYPE_DIR => Ok(host::__wasi_prestat_t {
             pr_type: wasi::__WASI_PREOPENTYPE_DIR,
-            u: host::__wasi_prestat_t___wasi_prestat_u {
-                dir: host::__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t {
+            u: host::__wasi_prestat_u {
+                dir: host::__wasi_prestat_dir {
                     pr_name_len: dec_usize(PrimInt::from_le(unsafe { raw.u.dir.pr_name_len })),
                 },
             },
@@ -352,8 +350,8 @@ pub(crate) fn enc_prestat_byref(
     let raw = match prestat.pr_type {
         wasi::__WASI_PREOPENTYPE_DIR => Ok(wasi32::__wasi_prestat_t {
             pr_type: PrimInt::to_le(wasi::__WASI_PREOPENTYPE_DIR),
-            u: wasi32::__wasi_prestat_t___wasi_prestat_u {
-                dir: wasi32::__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t {
+            u: wasi32::__wasi_prestat_u {
+                dir: wasi32::__wasi_prestat_dir {
                     pr_name_len: enc_usize(unsafe { prestat.u.dir.pr_name_len }),
                 },
             },
@@ -410,39 +408,40 @@ pub(crate) fn dec_subscriptions(
 
     raw_input_slice
         .into_iter()
-        .map(|raw_subscription|{
+        .map(|raw_subscription| {
             let userdata = PrimInt::from_le(raw_subscription.userdata);
-            let type_ = PrimInt::from_le(raw_subscription.type_);
+            let r#type = PrimInt::from_le(raw_subscription.r#type);
             let raw_u = raw_subscription.u;
-            let u = match type_ {
-                wasi::__WASI_EVENTTYPE_CLOCK => wasi::__wasi_subscription_t___wasi_subscription_u {
+            let u = match r#type {
+                wasi::__WASI_EVENTTYPE_CLOCK => wasi::__wasi_subscription_u {
                     clock: unsafe {
-                        wasi::__wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t {
+                        wasi::__wasi_subscription_clock_t {
                             identifier: PrimInt::from_le(raw_u.clock.identifier),
                             clock_id: PrimInt::from_le(raw_u.clock.clock_id),
                             timeout: PrimInt::from_le(raw_u.clock.timeout),
                             precision: PrimInt::from_le(raw_u.clock.precision),
                             flags: PrimInt::from_le(raw_u.clock.flags),
-                            __bindgen_padding_0: 0,
-                            __bindgen_padding_1: [0,0,0],
                         }
                     },
                 },
-                wasi::__WASI_EVENTTYPE_FD_READ | wasi::__WASI_EVENTTYPE_FD_WRITE => wasi::__wasi_subscription_t___wasi_subscription_u {
-                    fd_readwrite:  wasi::__wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t {
-                        fd: PrimInt::from_le(unsafe{raw_u.fd_readwrite.fd})
+                wasi::__WASI_EVENTTYPE_FD_READ | wasi::__WASI_EVENTTYPE_FD_WRITE => {
+                    wasi::__wasi_subscription_u {
+                        fd_readwrite: wasi::__wasi_subscription_fd_readwrite_t {
+                            file_descriptor: PrimInt::from_le(unsafe {
+                                raw_u.fd_readwrite.file_descriptor
+                            }),
+                        },
                     }
-                },
-                _  => return Err(Error::EINVAL)
+                }
+                _ => return Err(Error::EINVAL),
             };
             Ok(wasi::__wasi_subscription_t {
                 userdata,
-                type_,
+                r#type,
                 u,
-                __bindgen_padding_0: 0,
             })
         })
-    .collect::<Result<Vec<_>>>()
+        .collect::<Result<Vec<_>>>()
 }
 
 pub(crate) fn enc_events(
@@ -461,17 +460,14 @@ pub(crate) fn enc_events(
             let fd_readwrite = unsafe { event.u.fd_readwrite };
             wasi::__wasi_event_t {
                 userdata: PrimInt::to_le(event.userdata),
-                type_: PrimInt::to_le(event.type_),
+                r#type: PrimInt::to_le(event.r#type),
                 error: PrimInt::to_le(event.error),
-                u: wasi::__wasi_event_t___wasi_event_u {
-                    fd_readwrite:
-                        wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-                            nbytes: PrimInt::to_le(fd_readwrite.nbytes),
-                            flags: PrimInt::to_le(fd_readwrite.flags),
-                            __bindgen_padding_0: [0; 3],
-                        },
+                u: wasi::__wasi_event_u {
+                    fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
+                        nbytes: PrimInt::to_le(fd_readwrite.nbytes),
+                        flags: PrimInt::to_le(fd_readwrite.flags),
+                    },
                 },
-                __bindgen_padding_0: 0,
             }
         };
     }
diff --git a/src/sys/unix/hostcalls_impl/misc.rs b/src/sys/unix/hostcalls_impl/misc.rs
index 3ed78ffec6..98d81db8d1 100644
--- a/src/sys/unix/hostcalls_impl/misc.rs
+++ b/src/sys/unix/hostcalls_impl/misc.rs
@@ -86,7 +86,7 @@ pub(crate) fn poll_oneoff(
         .iter()
         .map(|event| {
             let mut flags = PollFlags::empty();
-            match event.type_ {
+            match event.r#type {
                 wasi::__WASI_EVENTTYPE_FD_READ => flags.insert(PollFlags::POLLIN),
                 wasi::__WASI_EVENTTYPE_FD_WRITE => flags.insert(PollFlags::POLLOUT),
                 // An event on a file descriptor can currently only be of type FD_READ or FD_WRITE
@@ -133,16 +133,14 @@ fn poll_oneoff_handle_timeout_event(
 ) {
     events.push(wasi::__wasi_event_t {
         userdata: timeout.userdata,
-        type_: wasi::__WASI_EVENTTYPE_CLOCK,
+        r#type: wasi::__WASI_EVENTTYPE_CLOCK,
         error: wasi::__WASI_ESUCCESS,
-        u: wasi::__wasi_event_t___wasi_event_u {
-            fd_readwrite: wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
+        u: wasi::__wasi_event_u {
+            fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
                 nbytes: 0,
                 flags: 0,
-                __bindgen_padding_0: [0, 0, 0],
             },
         },
-        __bindgen_padding_0: 0,
     });
 }
 
@@ -165,69 +163,57 @@ fn poll_oneoff_handle_fd_event<'a>(
         log::debug!("poll_oneoff_handle_fd_event revents = {:?}", revents);
 
         let mut nbytes = 0;
-        if fd_event.type_ == wasi::__WASI_EVENTTYPE_FD_READ {
+        if fd_event.r#type == wasi::__WASI_EVENTTYPE_FD_READ {
             let _ = unsafe { fionread(fd_event.descriptor.as_raw_fd(), &mut nbytes) };
         }
 
         let output_event = if revents.contains(PollFlags::POLLNVAL) {
             wasi::__wasi_event_t {
                 userdata: fd_event.userdata,
-                type_: fd_event.type_,
+                r#type: fd_event.r#type,
                 error: wasi::__WASI_EBADF,
-                u: wasi::__wasi_event_t___wasi_event_u {
-                    fd_readwrite:
-                        wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-                            nbytes: 0,
-                            flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
-                            __bindgen_padding_0: [0, 0, 0],
-                        },
+                u: wasi::__wasi_event_u {
+                    fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
+                        nbytes: 0,
+                        flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
+                    },
                 },
-                __bindgen_padding_0: 0,
             }
         } else if revents.contains(PollFlags::POLLERR) {
             wasi::__wasi_event_t {
                 userdata: fd_event.userdata,
-                type_: fd_event.type_,
+                r#type: fd_event.r#type,
                 error: wasi::__WASI_EIO,
-                u: wasi::__wasi_event_t___wasi_event_u {
-                    fd_readwrite:
-                        wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-                            nbytes: 0,
-                            flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
-                            __bindgen_padding_0: [0, 0, 0],
-                        },
+                u: wasi::__wasi_event_u {
+                    fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
+                        nbytes: 0,
+                        flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
+                    },
                 },
-                __bindgen_padding_0: 0,
             }
         } else if revents.contains(PollFlags::POLLHUP) {
             wasi::__wasi_event_t {
                 userdata: fd_event.userdata,
-                type_: fd_event.type_,
+                r#type: fd_event.r#type,
                 error: wasi::__WASI_ESUCCESS,
-                u: wasi::__wasi_event_t___wasi_event_u {
-                    fd_readwrite:
-                        wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-                            nbytes: 0,
-                            flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
-                            __bindgen_padding_0: [0, 0, 0],
-                        },
+                u: wasi::__wasi_event_u {
+                    fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
+                        nbytes: 0,
+                        flags: wasi::__WASI_EVENT_FD_READWRITE_HANGUP,
+                    },
                 },
-                __bindgen_padding_0: 0,
             }
         } else if revents.contains(PollFlags::POLLIN) | revents.contains(PollFlags::POLLOUT) {
             wasi::__wasi_event_t {
                 userdata: fd_event.userdata,
-                type_: fd_event.type_,
+                r#type: fd_event.r#type,
                 error: wasi::__WASI_ESUCCESS,
-                u: wasi::__wasi_event_t___wasi_event_u {
-                    fd_readwrite:
-                        wasi::__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-                            nbytes: nbytes.try_into()?,
-                            flags: 0,
-                            __bindgen_padding_0: [0, 0, 0],
-                        },
+                u: wasi::__wasi_event_u {
+                    fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
+                        nbytes: nbytes.try_into()?,
+                        flags: 0,
+                    },
                 },
-                __bindgen_padding_0: 0,
             }
         } else {
             continue;
diff --git a/src/wasi.rs b/src/wasi.rs
index 8dccc67559..21e230fcfd 100644
--- a/src/wasi.rs
+++ b/src/wasi.rs
@@ -6,117 +6,9 @@
 #![allow(non_snake_case)]
 #![allow(dead_code)]
 
-// C types
-pub type char = i8;
-pub type schar = i8;
-pub type uchar = u8;
-pub type short = i16;
-pub type ushort = u16;
-pub type int = i32;
-pub type uint = u32;
-pub type longlong = i64;
-pub type ulonglong = u64;
+use wig::witx_wasi_types;
 
-// libc stdint types
-pub type int8_t = i8;
-pub type uint8_t = u8;
-pub type int16_t = i16;
-pub type uint16_t = u16;
-pub type int32_t = i32;
-pub type uint32_t = u32;
-pub type int64_t = i64;
-pub type uint64_t = u64;
-pub type intmax_t = i64;
-pub type uintmax_t = u64;
-pub type int_least8_t = i8;
-pub type int_least16_t = i16;
-pub type int_least32_t = i32;
-pub type int_least64_t = i64;
-pub type uint_least8_t = u8;
-pub type uint_least16_t = u16;
-pub type uint_least32_t = u32;
-pub type uint_least64_t = u64;
-pub type int_fast8_t = i8;
-pub type int_fast16_t = i32;
-pub type int_fast32_t = i32;
-pub type int_fast64_t = i64;
-pub type uint_fast8_t = u8;
-pub type uint_fast16_t = u32;
-pub type uint_fast32_t = u32;
-pub type uint_fast64_t = u64;
-pub type wchar_t = i32;
-
-// libc types
-pub type dev_t = u64;
-pub type uid_t = u32;
-pub type gid_t = u32;
-pub type ino_t = u64;
-pub type ino64_t = u64;
-pub type mode_t = u32;
-pub type nlink_t = u64;
-pub type off_t = i64;
-pub type off64_t = i64;
-pub type pid_t = i32;
-pub type clock_t = i64;
-pub type rlim_t = u64;
-pub type rlim64_t = u64;
-pub type id_t = u32;
-pub type time_t = i64;
-pub type useconds_t = u32;
-pub type suseconds_t = i64;
-pub type daddr_t = i32;
-pub type key_t = i32;
-pub type clockid_t = i32;
-pub type blksize_t = i64;
-pub type blkcnt_t = i64;
-pub type blkcnt64_t = i64;
-pub type fsblkcnt_t = u64;
-pub type fsblkcnt64_t = u64;
-pub type fsfilcnt_t = u64;
-pub type fsfilcnt64_t = u64;
-pub type fsword_t = i64;
-pub type ssize_t = i32;
-pub type loff_t = off64_t;
-pub type socklen_t = u32;
-pub type sig_atomic_t = i32;
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct fsid_t {
-    pub __val: [i32; 2usize],
-}
-
-// WASI types
-pub type __wasi_advice_t = u8;
-pub type __wasi_clockid_t = u32;
-pub type __wasi_device_t = u64;
-pub type __wasi_dircookie_t = u64;
-pub type __wasi_errno_t = u16;
-pub type __wasi_eventrwflags_t = u16;
-pub type __wasi_eventtype_t = u8;
-pub type __wasi_exitcode_t = u32;
-pub type __wasi_fd_t = u32;
-pub type __wasi_fdflags_t = u16;
-pub type __wasi_fdsflags_t = u16;
-pub type __wasi_filedelta_t = i64;
-pub type __wasi_filesize_t = u64;
-pub type __wasi_filetype_t = u8;
-pub type __wasi_preopentype_t = u8;
-pub type __wasi_fstflags_t = u16;
-pub type __wasi_inode_t = u64;
-pub type __wasi_linkcount_t = u32;
-pub type __wasi_lookupflags_t = u32;
-pub type __wasi_oflags_t = u16;
-pub type __wasi_riflags_t = u16;
-pub type __wasi_rights_t = u64;
-pub type __wasi_roflags_t = u16;
-pub type __wasi_sdflags_t = u8;
-pub type __wasi_siflags_t = u16;
-pub type __wasi_signal_t = u8;
-pub type __wasi_subclockflags_t = u16;
-pub type __wasi_timestamp_t = u64;
-pub type __wasi_userdata_t = u64;
-pub type __wasi_whence_t = u8;
+witx_wasi_types!("unstable" "wasi_unstable_preview0");
 
 pub(crate) const RIGHTS_ALL: __wasi_rights_t = __WASI_RIGHT_FD_DATASYNC
     | __WASI_RIGHT_FD_READ
@@ -215,122 +107,6 @@ pub(crate) const RIGHTS_TTY_BASE: __wasi_rights_t = __WASI_RIGHT_FD_READ
 #[allow(unused)]
 pub(crate) const RIGHTS_TTY_INHERITING: __wasi_rights_t = 0;
 
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_dirent_t {
-    pub d_next: __wasi_dircookie_t,
-    pub d_ino: __wasi_inode_t,
-    pub d_namlen: u32,
-    pub d_type: __wasi_filetype_t,
-    pub __bindgen_padding_0: [u8; 3usize],
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct __wasi_event_t {
-    pub userdata: __wasi_userdata_t,
-    pub error: __wasi_errno_t,
-    pub type_: __wasi_eventtype_t,
-    pub __bindgen_padding_0: u32,
-    pub u: __wasi_event_t___wasi_event_u,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub union __wasi_event_t___wasi_event_u {
-    pub fd_readwrite: __wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t,
-    _bindgen_union_align: [u64; 2usize],
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t {
-    pub nbytes: __wasi_filesize_t,
-    pub flags: __wasi_eventrwflags_t,
-    pub __bindgen_padding_0: [u16; 3usize],
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub union __wasi_event_t__bindgen_ty_1 {
-    pub fd_readwrite: __wasi_event_t__bindgen_ty_1__bindgen_ty_1,
-    _bindgen_union_align: [u64; 2usize],
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_event_t__bindgen_ty_1__bindgen_ty_1 {
-    pub nbytes: __wasi_filesize_t,
-    pub flags: __wasi_eventrwflags_t,
-    pub __bindgen_padding_0: [u16; 3usize],
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_event_t__bindgen_ty_1__bindgen_ty_2 {
-    pub signal: __wasi_signal_t,
-    pub exitcode: __wasi_exitcode_t,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_fdstat_t {
-    pub fs_filetype: __wasi_filetype_t,
-    pub fs_flags: __wasi_fdflags_t,
-    pub __bindgen_padding_0: u32,
-    pub fs_rights_base: __wasi_rights_t,
-    pub fs_rights_inheriting: __wasi_rights_t,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_filestat_t {
-    pub st_dev: __wasi_device_t,
-    pub st_ino: __wasi_inode_t,
-    pub st_filetype: __wasi_filetype_t,
-    pub st_nlink: __wasi_linkcount_t,
-    pub st_size: __wasi_filesize_t,
-    pub st_atim: __wasi_timestamp_t,
-    pub st_mtim: __wasi_timestamp_t,
-    pub st_ctim: __wasi_timestamp_t,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct __wasi_subscription_t {
-    pub userdata: __wasi_userdata_t,
-    pub type_: __wasi_eventtype_t,
-    pub __bindgen_padding_0: u32,
-    pub u: __wasi_subscription_t___wasi_subscription_u,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub union __wasi_subscription_t___wasi_subscription_u {
-    pub clock: __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-    pub fd_readwrite:
-        __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t,
-    _bindgen_union_align: [u64; 5usize],
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t {
-    pub identifier: __wasi_userdata_t,
-    pub clock_id: __wasi_clockid_t,
-    pub __bindgen_padding_0: u32,
-    pub timeout: __wasi_timestamp_t,
-    pub precision: __wasi_timestamp_t,
-    pub flags: __wasi_subclockflags_t,
-    pub __bindgen_padding_1: [u16; 3usize],
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t {
-    pub fd: __wasi_fd_t,
-}
-
 pub fn strerror(errno: __wasi_errno_t) -> &'static str {
     match errno {
         __WASI_ESUCCESS => "__WASI_ESUCCESS",
@@ -423,250 +199,12 @@ pub fn whence_to_str(whence: __wasi_whence_t) -> &'static str {
     }
 }
 
-// libc constants
-pub const INT8_MIN: i32 = -128;
-pub const INT16_MIN: i32 = -32768;
-pub const INT32_MIN: i32 = -2147483648;
-pub const INT8_MAX: u32 = 127;
-pub const INT16_MAX: u32 = 32767;
-pub const INT32_MAX: u32 = 2147483647;
-pub const UINT8_MAX: u32 = 255;
-pub const UINT16_MAX: u32 = 65535;
-pub const UINT32_MAX: u32 = 4294967295;
-pub const INT_LEAST8_MIN: i32 = -128;
-pub const INT_LEAST16_MIN: i32 = -32768;
-pub const INT_LEAST32_MIN: i32 = -2147483648;
-pub const INT_LEAST8_MAX: u32 = 127;
-pub const INT_LEAST16_MAX: u32 = 32767;
-pub const INT_LEAST32_MAX: u32 = 2147483647;
-pub const UINT_LEAST8_MAX: u32 = 255;
-pub const UINT_LEAST16_MAX: u32 = 65535;
-pub const UINT_LEAST32_MAX: u32 = 4294967295;
-pub const INT_FAST8_MIN: i32 = -128;
-pub const INT_FAST16_MIN: i32 = -2147483648;
-pub const INT_FAST32_MIN: i32 = -2147483648;
-pub const INT_FAST8_MAX: u32 = 127;
-pub const INT_FAST16_MAX: u32 = 2147483647;
-pub const INT_FAST32_MAX: u32 = 2147483647;
-pub const UINT_FAST8_MAX: u32 = 255;
-pub const UINT_FAST16_MAX: u32 = 4294967295;
-pub const UINT_FAST32_MAX: u32 = 4294967295;
-pub const WINT_MIN: i32 = -2147483648;
-pub const WINT_MAX: i32 = 2147483647;
-
-// WASI constants
-pub const __WASI_ADVICE_NORMAL: __wasi_advice_t = 0;
-pub const __WASI_ADVICE_SEQUENTIAL: __wasi_advice_t = 1;
-pub const __WASI_ADVICE_RANDOM: __wasi_advice_t = 2;
-pub const __WASI_ADVICE_WILLNEED: __wasi_advice_t = 3;
-pub const __WASI_ADVICE_DONTNEED: __wasi_advice_t = 4;
-pub const __WASI_ADVICE_NOREUSE: __wasi_advice_t = 5;
-pub const __WASI_CLOCK_REALTIME: __wasi_clockid_t = 0;
-pub const __WASI_CLOCK_MONOTONIC: __wasi_clockid_t = 1;
-pub const __WASI_CLOCK_PROCESS_CPUTIME_ID: __wasi_clockid_t = 2;
-pub const __WASI_CLOCK_THREAD_CPUTIME_ID: __wasi_clockid_t = 3;
 pub const __WASI_DIRCOOKIE_START: __wasi_dircookie_t = 0;
-pub const __WASI_ESUCCESS: __wasi_errno_t = 0;
-pub const __WASI_E2BIG: __wasi_errno_t = 1;
-pub const __WASI_EACCES: __wasi_errno_t = 2;
-pub const __WASI_EADDRINUSE: __wasi_errno_t = 3;
-pub const __WASI_EADDRNOTAVAIL: __wasi_errno_t = 4;
-pub const __WASI_EAFNOSUPPORT: __wasi_errno_t = 5;
-pub const __WASI_EAGAIN: __wasi_errno_t = 6;
-pub const __WASI_EALREADY: __wasi_errno_t = 7;
-pub const __WASI_EBADF: __wasi_errno_t = 8;
-pub const __WASI_EBADMSG: __wasi_errno_t = 9;
-pub const __WASI_EBUSY: __wasi_errno_t = 10;
-pub const __WASI_ECANCELED: __wasi_errno_t = 11;
-pub const __WASI_ECHILD: __wasi_errno_t = 12;
-pub const __WASI_ECONNABORTED: __wasi_errno_t = 13;
-pub const __WASI_ECONNREFUSED: __wasi_errno_t = 14;
-pub const __WASI_ECONNRESET: __wasi_errno_t = 15;
-pub const __WASI_EDEADLK: __wasi_errno_t = 16;
-pub const __WASI_EDESTADDRREQ: __wasi_errno_t = 17;
-pub const __WASI_EDOM: __wasi_errno_t = 18;
-pub const __WASI_EDQUOT: __wasi_errno_t = 19;
-pub const __WASI_EEXIST: __wasi_errno_t = 20;
-pub const __WASI_EFAULT: __wasi_errno_t = 21;
-pub const __WASI_EFBIG: __wasi_errno_t = 22;
-pub const __WASI_EHOSTUNREACH: __wasi_errno_t = 23;
-pub const __WASI_EIDRM: __wasi_errno_t = 24;
-pub const __WASI_EILSEQ: __wasi_errno_t = 25;
-pub const __WASI_EINPROGRESS: __wasi_errno_t = 26;
-pub const __WASI_EINTR: __wasi_errno_t = 27;
-pub const __WASI_EINVAL: __wasi_errno_t = 28;
-pub const __WASI_EIO: __wasi_errno_t = 29;
-pub const __WASI_EISCONN: __wasi_errno_t = 30;
-pub const __WASI_EISDIR: __wasi_errno_t = 31;
-pub const __WASI_ELOOP: __wasi_errno_t = 32;
-pub const __WASI_EMFILE: __wasi_errno_t = 33;
-pub const __WASI_EMLINK: __wasi_errno_t = 34;
-pub const __WASI_EMSGSIZE: __wasi_errno_t = 35;
-pub const __WASI_EMULTIHOP: __wasi_errno_t = 36;
-pub const __WASI_ENAMETOOLONG: __wasi_errno_t = 37;
-pub const __WASI_ENETDOWN: __wasi_errno_t = 38;
-pub const __WASI_ENETRESET: __wasi_errno_t = 39;
-pub const __WASI_ENETUNREACH: __wasi_errno_t = 40;
-pub const __WASI_ENFILE: __wasi_errno_t = 41;
-pub const __WASI_ENOBUFS: __wasi_errno_t = 42;
-pub const __WASI_ENODEV: __wasi_errno_t = 43;
-pub const __WASI_ENOENT: __wasi_errno_t = 44;
-pub const __WASI_ENOEXEC: __wasi_errno_t = 45;
-pub const __WASI_ENOLCK: __wasi_errno_t = 46;
-pub const __WASI_ENOLINK: __wasi_errno_t = 47;
-pub const __WASI_ENOMEM: __wasi_errno_t = 48;
-pub const __WASI_ENOMSG: __wasi_errno_t = 49;
-pub const __WASI_ENOPROTOOPT: __wasi_errno_t = 50;
-pub const __WASI_ENOSPC: __wasi_errno_t = 51;
-pub const __WASI_ENOSYS: __wasi_errno_t = 52;
-pub const __WASI_ENOTCONN: __wasi_errno_t = 53;
-pub const __WASI_ENOTDIR: __wasi_errno_t = 54;
-pub const __WASI_ENOTEMPTY: __wasi_errno_t = 55;
-pub const __WASI_ENOTRECOVERABLE: __wasi_errno_t = 56;
-pub const __WASI_ENOTSOCK: __wasi_errno_t = 57;
-pub const __WASI_ENOTSUP: __wasi_errno_t = 58;
-pub const __WASI_ENOTTY: __wasi_errno_t = 59;
-pub const __WASI_ENXIO: __wasi_errno_t = 60;
-pub const __WASI_EOVERFLOW: __wasi_errno_t = 61;
-pub const __WASI_EOWNERDEAD: __wasi_errno_t = 62;
-pub const __WASI_EPERM: __wasi_errno_t = 63;
-pub const __WASI_EPIPE: __wasi_errno_t = 64;
-pub const __WASI_EPROTO: __wasi_errno_t = 65;
-pub const __WASI_EPROTONOSUPPORT: __wasi_errno_t = 66;
-pub const __WASI_EPROTOTYPE: __wasi_errno_t = 67;
-pub const __WASI_ERANGE: __wasi_errno_t = 68;
-pub const __WASI_EROFS: __wasi_errno_t = 69;
-pub const __WASI_ESPIPE: __wasi_errno_t = 70;
-pub const __WASI_ESRCH: __wasi_errno_t = 71;
-pub const __WASI_ESTALE: __wasi_errno_t = 72;
-pub const __WASI_ETIMEDOUT: __wasi_errno_t = 73;
-pub const __WASI_ETXTBSY: __wasi_errno_t = 74;
-pub const __WASI_EXDEV: __wasi_errno_t = 75;
-pub const __WASI_ENOTCAPABLE: __wasi_errno_t = 76;
-pub const __WASI_EVENT_FD_READWRITE_HANGUP: __wasi_eventrwflags_t = 1;
-pub const __WASI_EVENTTYPE_CLOCK: __wasi_eventtype_t = 0;
-pub const __WASI_EVENTTYPE_FD_READ: __wasi_eventtype_t = 1;
-pub const __WASI_EVENTTYPE_FD_WRITE: __wasi_eventtype_t = 2;
-pub const __WASI_FDFLAG_APPEND: __wasi_fdflags_t = 1;
-pub const __WASI_FDFLAG_DSYNC: __wasi_fdflags_t = 2;
-pub const __WASI_FDFLAG_NONBLOCK: __wasi_fdflags_t = 4;
-pub const __WASI_FDFLAG_RSYNC: __wasi_fdflags_t = 8;
-pub const __WASI_FDFLAG_SYNC: __wasi_fdflags_t = 16;
-pub const __WASI_PREOPENTYPE_DIR: __wasi_preopentype_t = 0;
-pub const __WASI_FILETYPE_UNKNOWN: __wasi_filetype_t = 0;
-pub const __WASI_FILETYPE_BLOCK_DEVICE: __wasi_filetype_t = 1;
-pub const __WASI_FILETYPE_CHARACTER_DEVICE: __wasi_filetype_t = 2;
-pub const __WASI_FILETYPE_DIRECTORY: __wasi_filetype_t = 3;
-pub const __WASI_FILETYPE_REGULAR_FILE: __wasi_filetype_t = 4;
-pub const __WASI_FILETYPE_SOCKET_DGRAM: __wasi_filetype_t = 5;
-pub const __WASI_FILETYPE_SOCKET_STREAM: __wasi_filetype_t = 6;
-pub const __WASI_FILETYPE_SYMBOLIC_LINK: __wasi_filetype_t = 7;
-pub const __WASI_FILESTAT_SET_ATIM: __wasi_fstflags_t = 1;
-pub const __WASI_FILESTAT_SET_ATIM_NOW: __wasi_fstflags_t = 2;
-pub const __WASI_FILESTAT_SET_MTIM: __wasi_fstflags_t = 4;
-pub const __WASI_FILESTAT_SET_MTIM_NOW: __wasi_fstflags_t = 8;
-pub const __WASI_LOOKUP_SYMLINK_FOLLOW: __wasi_lookupflags_t = 1;
-pub const __WASI_O_CREAT: __wasi_oflags_t = 1;
-pub const __WASI_O_DIRECTORY: __wasi_oflags_t = 2;
-pub const __WASI_O_EXCL: __wasi_oflags_t = 4;
-pub const __WASI_O_TRUNC: __wasi_oflags_t = 8;
-pub const __WASI_SOCK_RECV_PEEK: __wasi_riflags_t = 1;
-pub const __WASI_SOCK_RECV_WAITALL: __wasi_riflags_t = 2;
-pub const __WASI_RIGHT_FD_DATASYNC: __wasi_rights_t = 1;
-pub const __WASI_RIGHT_FD_READ: __wasi_rights_t = 2;
-pub const __WASI_RIGHT_FD_SEEK: __wasi_rights_t = 4;
-pub const __WASI_RIGHT_FD_FDSTAT_SET_FLAGS: __wasi_rights_t = 8;
-pub const __WASI_RIGHT_FD_SYNC: __wasi_rights_t = 16;
-pub const __WASI_RIGHT_FD_TELL: __wasi_rights_t = 32;
-pub const __WASI_RIGHT_FD_WRITE: __wasi_rights_t = 64;
-pub const __WASI_RIGHT_FD_ADVISE: __wasi_rights_t = 128;
-pub const __WASI_RIGHT_FD_ALLOCATE: __wasi_rights_t = 256;
-pub const __WASI_RIGHT_PATH_CREATE_DIRECTORY: __wasi_rights_t = 512;
-pub const __WASI_RIGHT_PATH_CREATE_FILE: __wasi_rights_t = 1024;
-pub const __WASI_RIGHT_PATH_LINK_SOURCE: __wasi_rights_t = 2048;
-pub const __WASI_RIGHT_PATH_LINK_TARGET: __wasi_rights_t = 4096;
-pub const __WASI_RIGHT_PATH_OPEN: __wasi_rights_t = 8192;
-pub const __WASI_RIGHT_FD_READDIR: __wasi_rights_t = 16384;
-pub const __WASI_RIGHT_PATH_READLINK: __wasi_rights_t = 32768;
-pub const __WASI_RIGHT_PATH_RENAME_SOURCE: __wasi_rights_t = 65536;
-pub const __WASI_RIGHT_PATH_RENAME_TARGET: __wasi_rights_t = 131072;
-pub const __WASI_RIGHT_PATH_FILESTAT_GET: __wasi_rights_t = 262144;
-pub const __WASI_RIGHT_PATH_FILESTAT_SET_SIZE: __wasi_rights_t = 524288;
-pub const __WASI_RIGHT_PATH_FILESTAT_SET_TIMES: __wasi_rights_t = 1048576;
-pub const __WASI_RIGHT_FD_FILESTAT_GET: __wasi_rights_t = 2097152;
-pub const __WASI_RIGHT_FD_FILESTAT_SET_SIZE: __wasi_rights_t = 4194304;
-pub const __WASI_RIGHT_FD_FILESTAT_SET_TIMES: __wasi_rights_t = 8388608;
-pub const __WASI_RIGHT_PATH_SYMLINK: __wasi_rights_t = 16777216;
-pub const __WASI_RIGHT_PATH_REMOVE_DIRECTORY: __wasi_rights_t = 33554432;
-pub const __WASI_RIGHT_PATH_UNLINK_FILE: __wasi_rights_t = 67108864;
-pub const __WASI_RIGHT_POLL_FD_READWRITE: __wasi_rights_t = 134217728;
-pub const __WASI_RIGHT_SOCK_SHUTDOWN: __wasi_rights_t = 268435456;
-pub const __WASI_SOCK_RECV_DATA_TRUNCATED: __wasi_roflags_t = 1;
-pub const __WASI_SHUT_RD: __wasi_sdflags_t = 1;
-pub const __WASI_SHUT_WR: __wasi_sdflags_t = 2;
-pub const __WASI_SIGHUP: __wasi_signal_t = 1;
-pub const __WASI_SIGINT: __wasi_signal_t = 2;
-pub const __WASI_SIGQUIT: __wasi_signal_t = 3;
-pub const __WASI_SIGILL: __wasi_signal_t = 4;
-pub const __WASI_SIGTRAP: __wasi_signal_t = 5;
-pub const __WASI_SIGABRT: __wasi_signal_t = 6;
-pub const __WASI_SIGBUS: __wasi_signal_t = 7;
-pub const __WASI_SIGFPE: __wasi_signal_t = 8;
-pub const __WASI_SIGKILL: __wasi_signal_t = 9;
-pub const __WASI_SIGUSR1: __wasi_signal_t = 10;
-pub const __WASI_SIGSEGV: __wasi_signal_t = 11;
-pub const __WASI_SIGUSR2: __wasi_signal_t = 12;
-pub const __WASI_SIGPIPE: __wasi_signal_t = 13;
-pub const __WASI_SIGALRM: __wasi_signal_t = 14;
-pub const __WASI_SIGTERM: __wasi_signal_t = 15;
-pub const __WASI_SIGCHLD: __wasi_signal_t = 16;
-pub const __WASI_SIGCONT: __wasi_signal_t = 17;
-pub const __WASI_SIGSTOP: __wasi_signal_t = 18;
-pub const __WASI_SIGTSTP: __wasi_signal_t = 19;
-pub const __WASI_SIGTTIN: __wasi_signal_t = 20;
-pub const __WASI_SIGTTOU: __wasi_signal_t = 21;
-pub const __WASI_SIGURG: __wasi_signal_t = 22;
-pub const __WASI_SIGXCPU: __wasi_signal_t = 23;
-pub const __WASI_SIGXFSZ: __wasi_signal_t = 24;
-pub const __WASI_SIGVTALRM: __wasi_signal_t = 25;
-pub const __WASI_SIGPROF: __wasi_signal_t = 26;
-pub const __WASI_SIGWINCH: __wasi_signal_t = 27;
-pub const __WASI_SIGPOLL: __wasi_signal_t = 28;
-pub const __WASI_SIGPWR: __wasi_signal_t = 29;
-pub const __WASI_SIGSYS: __wasi_signal_t = 30;
-pub const __WASI_SUBSCRIPTION_CLOCK_ABSTIME: __wasi_subclockflags_t = 1;
-pub const __WASI_WHENCE_CUR: __wasi_whence_t = 0;
-pub const __WASI_WHENCE_END: __wasi_whence_t = 1;
-pub const __WASI_WHENCE_SET: __wasi_whence_t = 2;
 
 #[cfg(test)]
 mod test {
     use super::*;
 
-    #[test]
-    fn bindgen_test_layout_fsid_t() {
-        assert_eq!(
-            ::std::mem::size_of::<fsid_t>(),
-            8usize,
-            concat!("Size of: ", stringify!(fsid_t))
-        );
-        assert_eq!(
-            ::std::mem::align_of::<fsid_t>(),
-            4usize,
-            concat!("Alignment of ", stringify!(fsid_t))
-        );
-        assert_eq!(
-            unsafe { &(*(::std::ptr::null::<fsid_t>())).__val as *const _ as usize },
-            0usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(fsid_t),
-                "::",
-                stringify!(__val)
-            )
-        );
-    }
-
     #[test]
     fn bindgen_test_layout_wasi_dirent_t() {
         assert_eq!(
@@ -719,45 +257,35 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t>(),
+            ::std::mem::size_of::<__wasi_event_fd_readwrite_t>(),
             16usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t)
-            )
+            concat!("Size of: ", stringify!(__wasi_event_fd_readwrite_t))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t>(),
+            ::std::mem::align_of::<__wasi_event_fd_readwrite_t>(),
             8usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t)
-            )
+            concat!("Alignment of ", stringify!(__wasi_event_fd_readwrite_t))
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t>(
-                )))
-                .nbytes as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_event_fd_readwrite_t>())).nbytes as *const _ as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t),
+                stringify!(__wasi_event_fd_readwrite_t),
                 "::",
                 stringify!(nbytes)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t>(
-                )))
-                .flags as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_event_fd_readwrite_t>())).flags as *const _ as usize
             },
             8usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t),
+                stringify!(__wasi_event_fd_readwrite_t),
                 "::",
                 stringify!(flags)
             )
@@ -767,24 +295,21 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_event_t___wasi_event_u() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_event_t___wasi_event_u>(),
+            ::std::mem::size_of::<__wasi_event_u>(),
             16usize,
-            concat!("Size of: ", stringify!(__wasi_event_t___wasi_event_u))
+            concat!("Size of: ", stringify!(__wasi_event_u))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_event_t___wasi_event_u>(),
+            ::std::mem::align_of::<__wasi_event_u>(),
             8usize,
-            concat!("Alignment of ", stringify!(__wasi_event_t___wasi_event_u))
+            concat!("Alignment of ", stringify!(__wasi_event_u))
         );
         assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t___wasi_event_u>())).fd_readwrite as *const _
-                    as usize
-            },
+            unsafe { &(*(::std::ptr::null::<__wasi_event_u>())).fd_readwrite as *const _ as usize },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_event_t___wasi_event_u),
+                stringify!(__wasi_event_u),
                 "::",
                 stringify!(fd_readwrite)
             )
@@ -824,13 +349,13 @@ mod test {
             )
         );
         assert_eq!(
-            unsafe { &(*(::std::ptr::null::<__wasi_event_t>())).type_ as *const _ as usize },
+            unsafe { &(*(::std::ptr::null::<__wasi_event_t>())).r#type as *const _ as usize },
             10usize,
             concat!(
                 "Offset of field: ",
                 stringify!(__wasi_event_t),
                 "::",
-                stringify!(type_)
+                stringify!(r#type)
             )
         );
         assert_eq!(
@@ -845,112 +370,6 @@ mod test {
         );
     }
 
-    #[test]
-    fn bindgen_test_layout_wasi_event_t__bindgen_ty_1__bindgen_ty_1() {
-        assert_eq!(
-            ::std::mem::size_of::<__wasi_event_t__bindgen_ty_1__bindgen_ty_1>(),
-            16usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_1)
-            )
-        );
-        assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t__bindgen_ty_1__bindgen_ty_1>())).nbytes
-                    as *const _ as usize
-            },
-            0usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_1),
-                "::",
-                stringify!(nbytes)
-            )
-        );
-        assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t__bindgen_ty_1__bindgen_ty_1>())).flags
-                    as *const _ as usize
-            },
-            8usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_1),
-                "::",
-                stringify!(flags)
-            )
-        );
-    }
-
-    #[test]
-    fn bindgen_test_layout_wasi_event_t__bindgen_ty_1__bindgen_ty_2() {
-        assert_eq!(
-            ::std::mem::size_of::<__wasi_event_t__bindgen_ty_1__bindgen_ty_2>(),
-            8usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_2)
-            )
-        );
-        assert_eq!(
-            ::std::mem::align_of::<__wasi_event_t__bindgen_ty_1__bindgen_ty_2>(),
-            4usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_2)
-            )
-        );
-        assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t__bindgen_ty_1__bindgen_ty_2>())).signal
-                    as *const _ as usize
-            },
-            0usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_2),
-                "::",
-                stringify!(signal)
-            )
-        );
-        assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t__bindgen_ty_1__bindgen_ty_2>())).exitcode
-                    as *const _ as usize
-            },
-            4usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(__wasi_event_t__bindgen_ty_1__bindgen_ty_2),
-                "::",
-                stringify!(exitcode)
-            )
-        );
-    }
-
-    #[test]
-    fn bindgen_test_layout_wasi_event_t__bindgen_ty_1() {
-        assert_eq!(
-            ::std::mem::size_of::<__wasi_event_t__bindgen_ty_1>(),
-            16usize,
-            concat!("Size of: ", stringify!(__wasi_event_t__bindgen_ty_1))
-        );
-        assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_event_t__bindgen_ty_1>())).fd_readwrite as *const _
-                    as usize
-            },
-            0usize,
-            concat!(
-                "Offset of field: ",
-                stringify!(__wasi_event_t__bindgen_ty_1),
-                "::",
-                stringify!(fd_readwrite)
-            )
-        );
-    }
-
     #[test]
     fn bindgen_test_layout_wasi_event_t() {
         assert_eq!(
@@ -979,13 +398,13 @@ mod test {
             )
         );
         assert_eq!(
-            unsafe { &(*(::std::ptr::null::<__wasi_event_t>())).type_ as *const _ as usize },
+            unsafe { &(*(::std::ptr::null::<__wasi_event_t>())).r#type as *const _ as usize },
             10usize,
             concat!(
                 "Offset of field: ",
                 stringify!(__wasi_event_t),
                 "::",
-                stringify!(type_)
+                stringify!(r#type)
             )
         );
     }
@@ -1136,113 +555,76 @@ mod test {
     }
 
     #[test]
-    fn bindgen_test_layout___wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t(
-    ) {
+    fn bindgen_test_layout___wasi_subscription_clock_t() {
         assert_eq!(
-            ::std::mem::size_of::<
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-            >(),
+            ::std::mem::size_of::<__wasi_subscription_clock_t>(),
             40usize,
-            concat!(
-                "Size of: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                )
-            )
+            concat!("Size of: ", stringify!(__wasi_subscription_clock_t))
         );
         assert_eq!(
-            ::std::mem::align_of::<
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-            >(),
+            ::std::mem::align_of::<__wasi_subscription_clock_t>(),
             8usize,
-            concat!(
-                "Alignment of ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                )
-            )
+            concat!("Alignment of ", stringify!(__wasi_subscription_clock_t))
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-                >()))
-                .identifier as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_clock_t>())).identifier as *const _
+                    as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                ),
+                stringify!(__wasi_subscription_clock_t),
                 "::",
                 stringify!(identifier)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-                >()))
-                .clock_id as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_clock_t>())).clock_id as *const _
+                    as usize
             },
             8usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                ),
+                stringify!(__wasi_subscription_clock_t),
                 "::",
                 stringify!(clock_id)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-                >()))
-                .timeout as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_clock_t>())).timeout as *const _ as usize
             },
             16usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                ),
+                stringify!(__wasi_subscription_clock_t),
                 "::",
                 stringify!(timeout)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-                >()))
-                .precision as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_clock_t>())).precision as *const _
+                    as usize
             },
             24usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                ),
+                stringify!(__wasi_subscription_clock_t),
                 "::",
                 stringify!(precision)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t,
-                >()))
-                .flags as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_clock_t>())).flags as *const _ as usize
             },
             32usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                    __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_clock_t
-                ),
+                stringify!(__wasi_subscription_clock_t),
                 "::",
                 stringify!(flags)
             )
@@ -1253,42 +635,27 @@ mod test {
     fn bindgen_test_layout___wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t(
     ) {
         assert_eq!(
-            ::std::mem::size_of::<
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t,
-            >(),
+            ::std::mem::size_of::<__wasi_subscription_fd_readwrite_t>(),
             4usize,
-            concat!(
-                "Size of: ",
-                stringify!(
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t
-            )
-            )
+            concat!("Size of: ", stringify!(__wasi_subscription_fd_readwrite_t))
         );
         assert_eq!(
-            ::std::mem::align_of::<
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t,
-            >(),
+            ::std::mem::align_of::<__wasi_subscription_fd_readwrite_t>(),
             4usize,
             concat!(
                 "Alignment of ",
-                stringify!(
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t
-            )
+                stringify!(__wasi_subscription_fd_readwrite_t)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t,
-            >()))
-            .fd as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_fd_readwrite_t>())).file_descriptor
+                    as *const _ as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(
-                __wasi_subscription_t___wasi_subscription_u___wasi_subscription_u_fd_readwrite_t
-            ),
+                stringify!(__wasi_subscription_fd_readwrite_t),
                 "::",
                 stringify!(fd)
             )
@@ -1298,43 +665,33 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_subscription_t___wasi_subscription_u() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_subscription_t___wasi_subscription_u>(),
+            ::std::mem::size_of::<__wasi_subscription_u>(),
             40usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_subscription_t___wasi_subscription_u)
-            )
+            concat!("Size of: ", stringify!(__wasi_subscription_u))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_subscription_t___wasi_subscription_u>(),
+            ::std::mem::align_of::<__wasi_subscription_u>(),
             8usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_subscription_t___wasi_subscription_u)
-            )
+            concat!("Alignment of ", stringify!(__wasi_subscription_u))
         );
         assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_subscription_t___wasi_subscription_u>())).clock
-                    as *const _ as usize
-            },
+            unsafe { &(*(::std::ptr::null::<__wasi_subscription_u>())).clock as *const _ as usize },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_subscription_t___wasi_subscription_u),
+                stringify!(__wasi_subscription_u),
                 "::",
                 stringify!(clock)
             )
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<__wasi_subscription_t___wasi_subscription_u>())).fd_readwrite
-                    as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_subscription_u>())).fd_readwrite as *const _ as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_subscription_t___wasi_subscription_u),
+                stringify!(__wasi_subscription_u),
                 "::",
                 stringify!(fd_readwrite)
             )
@@ -1366,13 +723,15 @@ mod test {
             )
         );
         assert_eq!(
-            unsafe { &(*(::std::ptr::null::<__wasi_subscription_t>())).type_ as *const _ as usize },
+            unsafe {
+                &(*(::std::ptr::null::<__wasi_subscription_t>())).r#type as *const _ as usize
+            },
             8usize,
             concat!(
                 "Offset of field: ",
                 stringify!(__wasi_subscription_t),
                 "::",
-                stringify!(type_)
+                stringify!(r#type)
             )
         );
         assert_eq!(
diff --git a/src/wasi32.rs b/src/wasi32.rs
index 52821d97fd..c46d4f6141 100644
--- a/src/wasi32.rs
+++ b/src/wasi32.rs
@@ -6,60 +6,14 @@
 #![allow(non_snake_case)]
 #![allow(dead_code)]
 
+use wig::witx_wasi32_types;
+
 use crate::wasi::*;
 
-// C types
-pub type long = i32;
-pub type ulong = u32;
+pub type uintptr_t = u32;
+pub type size_t = u32;
 
-// libc types
-pub type size_t = ulong;
-pub type intptr_t = long;
-pub type uintptr_t = ulong;
-pub type timer_t = uintptr_t; // *mut ::std::os::raw::c_void
-pub type caddr_t = uintptr_t; // *mut i8
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_ciovec_t {
-    pub buf: uintptr_t, // *const ::std::os::raw::c_void
-    pub buf_len: size_t,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_iovec_t {
-    pub buf: uintptr_t, // *mut ::std::os::raw::c_void
-    pub buf_len: size_t,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct __wasi_prestat_t {
-    pub pr_type: __wasi_preopentype_t,
-    pub u: __wasi_prestat_t___wasi_prestat_u,
-}
-
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub union __wasi_prestat_t___wasi_prestat_u {
-    pub dir: __wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t,
-}
-
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct __wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t {
-    pub pr_name_len: size_t,
-}
-
-pub const INTPTR_MIN: i32 = -2147483648;
-pub const INTPTR_MAX: u32 = 2147483647;
-pub const UINTPTR_MAX: u32 = 4294967295;
-pub const PTRDIFF_MIN: i32 = -2147483648;
-pub const PTRDIFF_MAX: u32 = 2147483647;
-pub const SIG_ATOMIC_MIN: i32 = -2147483648;
-pub const SIG_ATOMIC_MAX: u32 = 2147483647;
-pub const SIZE_MAX: u32 = 4294967295;
+witx_wasi32_types!("unstable" "wasi_unstable_preview0");
 
 #[cfg(test)]
 mod test {
@@ -136,30 +90,23 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>(),
+            ::std::mem::size_of::<__wasi_prestat_dir>(),
             4usize,
-            concat!(
-                "Size of: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t)
-            )
+            concat!("Size of: ", stringify!(__wasi_prestat_dir))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>(),
+            ::std::mem::align_of::<__wasi_prestat_dir>(),
             4usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t)
-            )
+            concat!("Alignment of ", stringify!(__wasi_prestat_dir))
         );
         assert_eq!(
             unsafe {
-                &(*(::std::ptr::null::<__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t>()))
-                    .pr_name_len as *const _ as usize
+                &(*(::std::ptr::null::<__wasi_prestat_dir>())).pr_name_len as *const _ as usize
             },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u___wasi_prestat_u_dir_t),
+                stringify!(__wasi_prestat_dir),
                 "::",
                 stringify!(pr_name_len)
             )
@@ -169,27 +116,21 @@ mod test {
     #[test]
     fn bindgen_test_layout___wasi_prestat_t___wasi_prestat_u() {
         assert_eq!(
-            ::std::mem::size_of::<__wasi_prestat_t___wasi_prestat_u>(),
+            ::std::mem::size_of::<__wasi_prestat_u>(),
             4usize,
-            concat!("Size of: ", stringify!(__wasi_prestat_t___wasi_prestat_u))
+            concat!("Size of: ", stringify!(__wasi_prestat_u))
         );
         assert_eq!(
-            ::std::mem::align_of::<__wasi_prestat_t___wasi_prestat_u>(),
+            ::std::mem::align_of::<__wasi_prestat_u>(),
             4usize,
-            concat!(
-                "Alignment of ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u)
-            )
+            concat!("Alignment of ", stringify!(__wasi_prestat_u))
         );
         assert_eq!(
-            unsafe {
-                &(*(::std::ptr::null::<__wasi_prestat_t___wasi_prestat_u>())).dir as *const _
-                    as usize
-            },
+            unsafe { &(*(::std::ptr::null::<__wasi_prestat_u>())).dir as *const _ as usize },
             0usize,
             concat!(
                 "Offset of field: ",
-                stringify!(__wasi_prestat_t___wasi_prestat_u),
+                stringify!(__wasi_prestat_u),
                 "::",
                 stringify!(dir)
             )
diff --git a/wig/Cargo.toml b/wig/Cargo.toml
new file mode 100644
index 0000000000..4c71a738c5
--- /dev/null
+++ b/wig/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "wig"
+version = "0.0.0"
+authors = ["Dan Gohman <sunfish@mozilla.com>"]
+edition = "2018"
+categories = ["wasm"]
+keywords = ["webassembly", "wasm"]
+license = "Apache-2.0 WITH LLVM-exception"
+repository = "https://github.com/CraneStation/wasi-common"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0.2"
+proc-macro2 = "1.0.6"
+# We include the WASI repo primarily for the witx files, but it's also useful
+# to use the witx parser it contains, rather than the witx crate from
+# crates.io, so that it always matches the version of the witx files.
+witx = { path = "../WASI/tools/witx" }
diff --git a/wig/LICENSE b/wig/LICENSE
new file mode 100644
index 0000000000..f9d81955f4
--- /dev/null
+++ b/wig/LICENSE
@@ -0,0 +1,220 @@
+
+                                 Apache License
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+
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diff --git a/wig/src/lib.rs b/wig/src/lib.rs
new file mode 100644
index 0000000000..ec4b3371c9
--- /dev/null
+++ b/wig/src/lib.rs
@@ -0,0 +1,34 @@
+extern crate proc_macro;
+extern crate proc_macro2;
+extern crate quote;
+extern crate witx;
+
+mod raw_types;
+mod utils;
+
+use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
+
+#[proc_macro]
+pub fn witx_host_types(args: TokenStream) -> TokenStream {
+    TokenStream::from(raw_types::gen(
+        TokenStream2::from(args),
+        raw_types::Mode::Host,
+    ))
+}
+
+#[proc_macro]
+pub fn witx_wasi_types(args: TokenStream) -> TokenStream {
+    TokenStream::from(raw_types::gen(
+        TokenStream2::from(args),
+        raw_types::Mode::Wasi,
+    ))
+}
+
+#[proc_macro]
+pub fn witx_wasi32_types(args: TokenStream) -> TokenStream {
+    TokenStream::from(raw_types::gen(
+        TokenStream2::from(args),
+        raw_types::Mode::Wasi32,
+    ))
+}
diff --git a/wig/src/raw_types.rs b/wig/src/raw_types.rs
new file mode 100644
index 0000000000..8068054794
--- /dev/null
+++ b/wig/src/raw_types.rs
@@ -0,0 +1,250 @@
+//! Translate witx types to Rust.
+
+use crate::utils;
+use proc_macro2::{Delimiter, Group, Literal, TokenStream, TokenTree};
+use quote::{format_ident, quote};
+use std::convert::TryFrom;
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Mode {
+    Host,
+    Wasi32,
+    Wasi,
+}
+
+impl Mode {
+    pub fn include_target_types(&self) -> bool {
+        match self {
+            Mode::Host | Mode::Wasi32 => true,
+            Mode::Wasi => false,
+        }
+    }
+}
+
+pub fn gen(args: TokenStream, mode: Mode) -> TokenStream {
+    let mut output = TokenStream::new();
+
+    let (path, _phase) = utils::witx_path_from_args(args);
+    let doc = match witx::load(&path) {
+        Ok(doc) => doc,
+        Err(e) => {
+            panic!("error opening file {}: {}", path, e);
+        }
+    };
+
+    gen_datatypes(&mut output, &doc, mode);
+
+    output
+}
+
+fn gen_datatypes(output: &mut TokenStream, doc: &witx::Document, mode: Mode) {
+    for datatype in doc.datatypes() {
+        if mode.include_target_types() != type_has_target_size(doc, &datatype) {
+            continue;
+        }
+
+        gen_datatype(output, doc, mode, &datatype);
+    }
+}
+
+fn gen_datatype(
+    output: &mut TokenStream,
+    doc: &witx::Document,
+    mode: Mode,
+    datatype: &witx::Datatype,
+) {
+    match &datatype.variant {
+        witx::DatatypeVariant::Alias(a) => {
+            if a.name.as_str() == "size_t" {
+                let wasi_name = format_ident!("__wasi_{}", a.name.as_str());
+                match mode {
+                    Mode::Host => output.extend(quote!(pub type #wasi_name = usize;)),
+                    Mode::Wasi => panic!("size_t has target-specific size"),
+                    Mode::Wasi32 => output.extend(quote!(pub type #wasi_name = u32;)),
+                }
+            } else {
+                let wasi_name = format_ident!("__wasi_{}", a.name.as_str());
+                let to = ident_tokens(mode, &a.to);
+                output.extend(quote!(pub type #wasi_name = #to;));
+            }
+        }
+        witx::DatatypeVariant::Enum(e) => {
+            let wasi_name = format_ident!("__wasi_{}", e.name.as_str());
+            let repr = int_repr_tokens(e.repr);
+            output.extend(quote!(pub type #wasi_name = #repr;));
+            for (index, variant) in e.variants.iter().enumerate() {
+                let value_name = format_ident!("__WASI_{}", variant.as_str());
+                let index_name = Literal::usize_unsuffixed(index);
+                output.extend(quote!(pub const #value_name: #wasi_name = #index_name;));
+            }
+        }
+        witx::DatatypeVariant::Flags(f) => {
+            let wasi_name = format_ident!("__wasi_{}", f.name.as_str());
+            let repr = int_repr_tokens(f.repr);
+            output.extend(quote!(pub type #wasi_name = #repr;));
+            for (index, flag) in f.flags.iter().enumerate() {
+                let value_name = format_ident!("__WASI_{}", flag.as_str());
+                let flag_value = Literal::u128_unsuffixed(
+                    1u128
+                        .checked_shl(u32::try_from(index).expect("flag value overflow"))
+                        .expect("flag value overflow"),
+                );
+                output.extend(quote!(pub const #value_name: #wasi_name = #flag_value;));
+            }
+        }
+        witx::DatatypeVariant::Struct(s) => {
+            output.extend(quote!(#[repr(C)]));
+
+            // Types which contain unions can't trivially implement Debug,
+            // Hash, or Eq, because the type itself doesn't record which
+            // union member is active.
+            if struct_has_union(&doc, s) {
+                output.extend(quote!(#[derive(Copy, Clone)]));
+                output.extend(quote!(#[allow(missing_debug_implementations)]));
+            } else {
+                output.extend(quote!(#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq)]));
+            }
+
+            let wasi_name = format_ident!("__wasi_{}", s.name.as_str());
+            output.extend(quote!(pub struct #wasi_name));
+
+            let mut inner = TokenStream::new();
+            for member in &s.members {
+                let member_name = format_ident!("r#{}", member.name.as_str());
+                let member_type = ident_tokens(mode, &member.type_);
+                inner.extend(quote!(pub #member_name: #member_type,));
+            }
+            let braced = Group::new(Delimiter::Brace, inner);
+            output.extend(TokenStream::from(TokenTree::Group(braced)));
+        }
+        witx::DatatypeVariant::Union(u) => {
+            output.extend(quote!(#[repr(C)]));
+            output.extend(quote!(#[derive(Copy, Clone)]));
+            output.extend(quote!(#[allow(missing_debug_implementations)]));
+
+            let wasi_name = format_ident!("__wasi_{}", u.name.as_str());
+            output.extend(quote!(pub union #wasi_name));
+
+            let mut inner = TokenStream::new();
+            for variant in &u.variants {
+                let variant_name = format_ident!("r#{}", variant.name.as_str());
+                let variant_type = ident_tokens(mode, &variant.type_);
+                inner.extend(quote!(pub #variant_name: #variant_type,));
+            }
+            let braced = Group::new(Delimiter::Brace, inner);
+            output.extend(TokenStream::from(TokenTree::Group(braced)));
+        }
+    }
+}
+
+fn int_repr_tokens(int_repr: witx::IntRepr) -> TokenStream {
+    match int_repr {
+        witx::IntRepr::U8 => quote!(u8),
+        witx::IntRepr::U16 => quote!(u16),
+        witx::IntRepr::U32 => quote!(u32),
+        witx::IntRepr::U64 => quote!(u64),
+    }
+}
+
+fn builtin_tokens(mode: Mode, builtin: witx::BuiltinType) -> TokenStream {
+    match builtin {
+        witx::BuiltinType::String => match mode {
+            Mode::Host => quote!((*const u8, usize)),
+            Mode::Wasi => panic!("strings have target-specific size"),
+            Mode::Wasi32 => quote!((u32, u32)),
+        },
+        witx::BuiltinType::U8 => quote!(u8),
+        witx::BuiltinType::U16 => quote!(u16),
+        witx::BuiltinType::U32 => quote!(u32),
+        witx::BuiltinType::U64 => quote!(u64),
+        witx::BuiltinType::S8 => quote!(i8),
+        witx::BuiltinType::S16 => quote!(i16),
+        witx::BuiltinType::S32 => quote!(i32),
+        witx::BuiltinType::S64 => quote!(i64),
+        witx::BuiltinType::F32 => quote!(f32),
+        witx::BuiltinType::F64 => quote!(f64),
+    }
+}
+
+fn ident_tokens(mode: Mode, ident: &witx::DatatypeIdent) -> TokenStream {
+    match ident {
+        witx::DatatypeIdent::Builtin(builtin) => builtin_tokens(mode, *builtin),
+        witx::DatatypeIdent::Ident(ident) => TokenStream::from(TokenTree::Ident(format_ident!(
+            "__wasi_{}",
+            ident.name.as_str()
+        ))),
+        witx::DatatypeIdent::Pointer(pointee) => {
+            let pointee = ident_tokens(mode, pointee);
+            match mode {
+                Mode::Host => quote!(*mut #pointee),
+                Mode::Wasi => panic!("pointers have target-specific size"),
+                Mode::Wasi32 => quote!(u32),
+            }
+        }
+        witx::DatatypeIdent::ConstPointer(pointee) => {
+            let pointee = ident_tokens(mode, pointee);
+            match mode {
+                Mode::Host => quote!(*const #pointee),
+                Mode::Wasi => panic!("pointers have target-specific size"),
+                Mode::Wasi32 => quote!(u32),
+            }
+        }
+        witx::DatatypeIdent::Array(element) => {
+            let element_name = ident_tokens(mode, element);
+            match mode {
+                Mode::Host => quote!((*const #element_name, usize)),
+                Mode::Wasi => panic!("arrays have target-specific size"),
+                Mode::Wasi32 => quote!((u32, u32)),
+            }
+        }
+    }
+}
+
+/// Test whether the given struct contains any union members.
+fn struct_has_union(doc: &witx::Document, s: &witx::StructDatatype) -> bool {
+    s.members.iter().any(|member| match &member.type_ {
+        witx::DatatypeIdent::Ident(ident) => match &doc.datatype(&ident.name).unwrap().variant {
+            witx::DatatypeVariant::Union(_) => true,
+            witx::DatatypeVariant::Struct(s) => struct_has_union(doc, &s),
+            _ => false,
+        },
+        _ => false,
+    })
+}
+
+/// Test whether the given type has a target-specific size.
+fn type_has_target_size(doc: &witx::Document, type_: &witx::Datatype) -> bool {
+    match &type_.variant {
+        witx::DatatypeVariant::Alias(a) => {
+            a.name.as_str() == "size_t" || ident_has_target_size(doc, &a.to)
+        }
+        witx::DatatypeVariant::Enum(_) => false,
+        witx::DatatypeVariant::Flags(_) => false,
+        witx::DatatypeVariant::Struct(s) => s
+            .members
+            .iter()
+            .any(|m| ident_has_target_size(doc, &m.type_)),
+        witx::DatatypeVariant::Union(u) => u
+            .variants
+            .iter()
+            .any(|v| ident_has_target_size(doc, &v.type_)),
+    }
+}
+
+/// Test whether the given type ident has a target-specific size.
+fn ident_has_target_size(doc: &witx::Document, ident: &witx::DatatypeIdent) -> bool {
+    match ident {
+        witx::DatatypeIdent::Ident(ident) => {
+            type_has_target_size(doc, &doc.datatype(&ident.name).unwrap())
+        }
+        witx::DatatypeIdent::Builtin(builtin) => {
+            if let witx::BuiltinType::String = builtin {
+                true
+            } else {
+                false
+            }
+        }
+        witx::DatatypeIdent::Pointer(_) | witx::DatatypeIdent::ConstPointer(_) => true,
+        witx::DatatypeIdent::Array(element) => ident_has_target_size(doc, element),
+    }
+}
diff --git a/wig/src/utils.rs b/wig/src/utils.rs
new file mode 100644
index 0000000000..283cbd2d1a
--- /dev/null
+++ b/wig/src/utils.rs
@@ -0,0 +1,54 @@
+use proc_macro2::{Literal, TokenStream, TokenTree};
+/// Given the input tokens to a macro invocation, return the path to the
+/// witx file to process.
+pub(crate) fn witx_path_from_args(args: TokenStream) -> (String, String) {
+    let mut strings = Vec::new();
+
+    for arg in args {
+        if let TokenTree::Literal(literal) = arg {
+            let parsed = parse_string_literal(literal);
+
+            strings.push(parsed);
+        } else {
+            panic!("arguments must be string literals");
+        }
+    }
+
+    if strings.len() != 2 {
+        panic!("expected two string literals");
+    }
+
+    let phase = &strings[0];
+    let id = &strings[1];
+    let path = witx_path(phase, id);
+
+    (path, phase.clone())
+}
+
+fn witx_path(phase: &str, id: &str) -> String {
+    let root = std::env::var("CARGO_MANIFEST_DIR").unwrap_or(".".into());
+    format!("{}/WASI/phases/{}/witx/{}.witx", root, phase, id)
+}
+
+// Convert a `Literal` holding a string literal into the `String`.
+//
+// FIXME: It feels like there should be an easier way to do this.
+fn parse_string_literal(literal: Literal) -> String {
+    let s = literal.to_string();
+    assert!(
+        s.starts_with('"') && s.ends_with('"'),
+        "string literal must be enclosed in double-quotes"
+    );
+
+    let trimmed = s[1..s.len() - 1].to_owned();
+    assert!(
+        !trimmed.contains('"'),
+        "string literal must not contain embedded quotes for now"
+    );
+    assert!(
+        !trimmed.contains('\\'),
+        "string literal must not contain embedded backslashes for now"
+    );
+
+    trimmed
+}