Support reference types in the C API

.github/workflows/main.yml

@@ -231,6 +231,8 @@ jobs:
 
     # Ensure all our examples build and execute
     - run: cargo run -p run-examples
+      env:
+        RUST_BACKTRACE: 1
 
     # Build and test all features except for lightbeam
     - run: |

.gitignore

@@ -15,3 +15,4 @@ rusty-tags.*
 tags
 target
 .z3-trace
+foo

crates/c-api/include/doc-wasm.h

@@ -1147,19 +1147,22 @@
 
 /**
  * \struct wasm_ref_t
- * \brief Unimplemented and used in Wasmtime right now.
+ * \brief A reference type: either a funcref or an externref.
  *
  * \typedef wasm_ref_t
  * \brief Convenience alias for #wasm_ref_t
  *
  * \fn void wasm_ref_delete(own wasm_ref_t *v);
- * \brief Deletes a reference.
+ * \brief Delete a reference.
  *
  * \fn own wasm_ref_t *wasm_ref_copy(const wasm_ref_t *)
- * \brief Unimplemented in Wasmtime, aborts the process if called.
+ * \brief Copy a reference.
  *
  * \fn bool wasm_ref_same(const wasm_ref_t *, const wasm_ref_t *)
- * \brief Unimplemented in Wasmtime, aborts the process if called.
+ * \brief Are the given references pointing to the same externref?
+ *
+ * > Note: Wasmtime does not support checking funcrefs for equality, and this
+ * > function will always return false for funcrefs.
  *
  * \fn void* wasm_ref_get_host_info(const wasm_ref_t *);
  * \brief Unimplemented in Wasmtime, always returns `NULL`.
@@ -1614,6 +1617,9 @@
  * If a trap happens during execution or some other error then a non-`NULL` trap
  * is returned. In this situation the `results` are is unmodified.
  *
+ * Does not take ownership of `wasm_val_t` arguments. Gives ownership of
+ * `wasm_val_t` results.
+ *
  * > Note: to avoid the UB associated with passing the wrong number of results
  * > or parameters by accident, or to distinguish between traps and other
  * > errors, it's recommended to use #wasmtime_func_call.
@@ -1758,10 +1764,9 @@
  * Returns an error if the #wasm_ref_t does not match the element type of the
  * table provided or if it comes from a different store than the one provided.
  *
+ * Does not take ownship of the `init` value.
+ *
  * > Note: for funcref tables you can use #wasmtime_funcref_table_new as well.
- * >
- * > Additionally the #wasm_ref_t does not have much support in Wasmtime, so you
- * > may not be able to create an appropriate initial value.
  *
  * \fn wasm_tabletype_t *wasm_table_type(const wasm_table_t *);
  * \brief Returns the type of this table.
@@ -1774,12 +1779,10 @@
  * Attempts to get a value at an index in this table. This function returns
  * `NULL` if the index is out of bounds.
  *
+ * Gives ownership of the resulting `wasm_ref_t*`.
+ *
  * > Note: for funcref tables you can use #wasmtime_funcref_table_get to learn
  * > about out-of-bounds errors.
- * >
- * > Additionally the #wasm_ref_t does not have much
- * > support in Wasmtime, so you may not be able to do much with the returned
- * > value.
  *
  * \fn void wasm_table_set(wasm_table_t *, wasm_table_size_t index, wasm_ref_t *);
  * \brief Sets an element in this table.
@@ -1791,11 +1794,10 @@
  * * The #wasm_ref_t comes from a different store than the table provided.
  * * The #wasm_ref_t does not have an appropriate type to store in this table.
  *
+ * Does not take ownership of the given `wasm_ref_t*`.
+ *
  * > Note: for funcref tables you can use #wasmtime_funcref_table_set to learn
  * > about errors.
- * >
- * > Additionally the #wasm_ref_t does not have much support in Wasmtime, so you
- * > may not be able to create an appropriate initial value.
  *
  * \fn wasm_table_size_t wasm_table_size(const wasm_table_t *);
  * \brief Gets the current size, in elements, of this table.
@@ -1813,10 +1815,9 @@
  * * The #wasm_ref_t comes from a different store than the table provided.
  * * The #wasm_ref_t does not have an appropriate type to store in this table.
  *
+ * Does not take ownership of the givein `init` value.
+ *
  * > Note: for funcref tables you can use #wasmtime_funcref_table_grow as well.
- * >
- * > Additionally the #wasm_ref_t does not have much support in Wasmtime, so you
- * > may not be able to create an appropriate initial value.
  */
 
 /**

crates/c-api/include/wasmtime.h

@@ -651,6 +651,9 @@ WASM_API_EXTERN const wasm_name_t *wasmtime_frame_module_name(const wasm_frame_t
  *
  * The `trap` pointer cannot be `NULL`. The `args` and `results` pointers may be
  * `NULL` if the corresponding length is zero.
+ *
+ * Does not take ownership of `wasm_val_t` arguments. Gives ownership of
+ * `wasm_val_t` results.
  */
 WASM_API_EXTERN own wasmtime_error_t *wasmtime_func_call(
     wasm_func_t *func,
@@ -833,6 +836,63 @@ WASM_API_EXTERN wasmtime_error_t *wasmtime_funcref_table_grow(
     wasm_table_size_t *prev_size
 );
 
+/**
+ * \brief Create a new `externref` value.
+ *
+ * Creates a new `externref` value wrapping the provided data, and writes it to
+ * `valp`.
+ *
+ * This function does not take an associated finalizer to clean up the data when
+ * the reference is reclaimed. If you need a finalizer to clean up the data,
+ * then use #wasmtime_externref_new_with_finalizer.
+ */
+WASM_API_EXTERN void wasmtime_externref_new(void *data, wasm_val_t *valp);
+
+/**
+ * \brief A finalizer for an `externref`'s wrapped data.
+ *
+ * A finalizer callback to clean up an `externref`'s wrapped data after the
+ * `externref` has been reclaimed. This is an opportunity to run destructors,
+ * free dynamically allocated memory, close file handles, etc.
+ */
+typedef void (*wasmtime_externref_finalizer_t)(void*);
+
+/**
+ * \brief Create a new `externref` value with a finalizer.
+ *
+ * Creates a new `externref` value wrapping the provided data, and writes it to
+ * `valp`.
+ *
+ * When the reference is reclaimed, the wrapped data is cleaned up with the
+ * provided finalizer. If you do not need to clean up the wrapped data, then use
+ * #wasmtime_externref_new.
+ */
+WASM_API_EXTERN void wasmtime_externref_new_with_finalizer(
+    void *data,
+    wasmtime_externref_finalizer_t finalizer,
+    wasm_val_t *valp
+);
+
+/**
+ * \brief Get an `externref`'s wrapped data
+ *
+ * If the given value is a reference to a non-null `externref`, writes the
+ * wrapped data that was passed into #wasmtime_externref_new or
+ * #wasmtime_externref_new_with_finalizer when creating the given `externref` to
+ * `datap`, and returns `true`.
+ *
+ * If the value is a reference to a null `externref`, writes `NULL` to `datap`
+ * and returns `true`.
+ *
+ * If the given value is not an `externref`, returns `false` and leaves `datap`
+ * unmodified.
+ *
+ * Does not take ownership of `val`.
+ *
+ * Both `val` and `datap` must not be `NULL`.
+ */
+WASM_API_EXTERN bool wasmtime_externref_data(wasm_val_t* val, void** datap);
+
 #undef own
 
 #ifdef __cplusplus

crates/c-api/src/func.rs

@@ -2,6 +2,7 @@ use crate::{wasm_extern_t, wasm_functype_t, wasm_store_t, wasm_val_t};
 use crate::{wasm_name_t, wasm_trap_t, wasmtime_error_t};
 use anyhow::anyhow;
 use std::ffi::c_void;
+use std::mem::MaybeUninit;
 use std::panic::{self, AssertUnwindSafe};
 use std::ptr;
 use std::str;
@@ -89,6 +90,7 @@ fn create_function(
     let func = Func::new(store, ty, move |caller, params, results| {
         let params = params
             .iter()
+            .cloned()
             .map(|p| wasm_val_t::from_val(p))
             .collect::<Vec<_>>();
         let mut out_results = vec![wasm_val_t::default(); results.len()];
@@ -163,7 +165,7 @@ pub extern "C" fn wasmtime_func_new_with_env(
 pub unsafe extern "C" fn wasm_func_call(
     wasm_func: &wasm_func_t,
     args: *const wasm_val_t,
-    results: *mut wasm_val_t,
+    results: *mut MaybeUninit<wasm_val_t>,
 ) -> *mut wasm_trap_t {
     let func = wasm_func.func();
     let mut trap = ptr::null_mut();
@@ -186,7 +188,7 @@ pub unsafe extern "C" fn wasmtime_func_call(
     func: &wasm_func_t,
     args: *const wasm_val_t,
     num_args: usize,
-    results: *mut wasm_val_t,
+    results: *mut MaybeUninit<wasm_val_t>,
     num_results: usize,
     trap_ptr: &mut *mut wasm_trap_t,
 ) -> Option<Box<wasmtime_error_t>> {
@@ -201,7 +203,7 @@ pub unsafe extern "C" fn wasmtime_func_call(
 fn _wasmtime_func_call(
     func: &wasm_func_t,
     args: &[wasm_val_t],
-    results: &mut [wasm_val_t],
+    results: &mut [MaybeUninit<wasm_val_t>],
     trap_ptr: &mut *mut wasm_trap_t,
 ) -> Option<Box<wasmtime_error_t>> {
     let func = func.func();
@@ -217,8 +219,8 @@ fn _wasmtime_func_call(
     let result = panic::catch_unwind(AssertUnwindSafe(|| func.call(&params)));
     match result {
         Ok(Ok(out)) => {
-            for (slot, val) in results.iter_mut().zip(out.iter()) {
-                *slot = wasm_val_t::from_val(val);
+            for (slot, val) in results.iter_mut().zip(out.into_vec().into_iter()) {
+                crate::initialize(slot, wasm_val_t::from_val(val));
             }
             None
         }

crates/c-api/src/global.rs

@@ -1,5 +1,6 @@
 use crate::{handle_result, wasmtime_error_t};
 use crate::{wasm_extern_t, wasm_globaltype_t, wasm_store_t, wasm_val_t};
+use std::mem::MaybeUninit;
 use std::ptr;
 use wasmtime::{Extern, Global};
 
@@ -72,8 +73,8 @@ pub extern "C" fn wasm_global_type(g: &wasm_global_t) -> Box<wasm_globaltype_t>
 }
 
 #[no_mangle]
-pub extern "C" fn wasm_global_get(g: &wasm_global_t, out: &mut wasm_val_t) {
-    out.set(g.global().get());
+pub extern "C" fn wasm_global_get(g: &wasm_global_t, out: &mut MaybeUninit<wasm_val_t>) {
+    crate::initialize(out, wasm_val_t::from_val(g.global().get()));
 }
 
 #[no_mangle]

crates/c-api/src/lib.rs

@@ -63,15 +63,13 @@ pub struct wasm_shared_module_t {
     _unused: [u8; 0],
 }
 
-struct HostInfoState {
-    info: *mut std::ffi::c_void,
-    finalizer: Option<extern "C" fn(arg1: *mut std::ffi::c_void)>,
-}
-
-impl Drop for HostInfoState {
-    fn drop(&mut self) {
-        if let Some(f) = &self.finalizer {
-            f(self.info);
-        }
+/// Initialize a `MaybeUninit<T>`
+///
+/// TODO: Replace calls to this function with
+/// https://doc.rust-lang.org/nightly/std/mem/union.MaybeUninit.html#method.write
+/// once it is stable.
+pub(crate) fn initialize<T>(dst: &mut std::mem::MaybeUninit<T>, val: T) {
+    unsafe {
+        std::ptr::write(dst.as_mut_ptr(), val);
     }
 }