wasmtime/runtime/component/func/
host.rs

1use crate::component::concurrent;
2#[cfg(feature = "component-model-async")]
3use crate::component::concurrent::{Accessor, Status};
4use crate::component::func::{LiftContext, LowerContext};
5use crate::component::matching::InstanceType;
6use crate::component::storage::slice_to_storage_mut;
7use crate::component::types::ComponentFunc;
8use crate::component::{ComponentNamedList, ComponentType, Instance, Lift, Lower, Val};
9use crate::prelude::*;
10use crate::runtime::vm::component::{
11    ComponentInstance, VMComponentContext, VMLowering, VMLoweringCallee,
12};
13use crate::runtime::vm::{SendSyncPtr, VMOpaqueContext, VMStore};
14use crate::{AsContextMut, CallHook, StoreContextMut, ValRaw};
15use alloc::sync::Arc;
16use core::any::Any;
17use core::future::Future;
18use core::mem::{self, MaybeUninit};
19use core::pin::Pin;
20use core::ptr::NonNull;
21use wasmtime_environ::component::{
22    CanonicalAbiInfo, ComponentTypes, InterfaceType, MAX_FLAT_ASYNC_PARAMS, MAX_FLAT_PARAMS,
23    MAX_FLAT_RESULTS, OptionsIndex, TypeFuncIndex, TypeTuple,
24};
25
26pub struct HostFunc {
27    entrypoint: VMLoweringCallee,
28    typecheck: Box<dyn (Fn(TypeFuncIndex, &InstanceType<'_>) -> Result<()>) + Send + Sync>,
29    func: Box<dyn Any + Send + Sync>,
30}
31
32impl core::fmt::Debug for HostFunc {
33    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
34        f.debug_struct("HostFunc").finish_non_exhaustive()
35    }
36}
37
38enum HostResult<T> {
39    Done(Result<T>),
40    #[cfg(feature = "component-model-async")]
41    Future(Pin<Box<dyn Future<Output = Result<T>> + Send>>),
42}
43
44impl HostFunc {
45    fn from_canonical<T, F, P, R>(func: F) -> Arc<HostFunc>
46    where
47        F: Fn(StoreContextMut<'_, T>, P) -> HostResult<R> + Send + Sync + 'static,
48        P: ComponentNamedList + Lift + 'static,
49        R: ComponentNamedList + Lower + 'static,
50        T: 'static,
51    {
52        let entrypoint = Self::entrypoint::<T, F, P, R>;
53        Arc::new(HostFunc {
54            entrypoint,
55            typecheck: Box::new(typecheck::<P, R>),
56            func: Box::new(func),
57        })
58    }
59
60    pub(crate) fn from_closure<T, F, P, R>(func: F) -> Arc<HostFunc>
61    where
62        T: 'static,
63        F: Fn(StoreContextMut<T>, P) -> Result<R> + Send + Sync + 'static,
64        P: ComponentNamedList + Lift + 'static,
65        R: ComponentNamedList + Lower + 'static,
66    {
67        Self::from_canonical::<T, _, _, _>(move |store, params| {
68            HostResult::Done(func(store, params))
69        })
70    }
71
72    #[cfg(feature = "component-model-async")]
73    pub(crate) fn from_concurrent<T, F, P, R>(func: F) -> Arc<HostFunc>
74    where
75        T: 'static,
76        F: Fn(&Accessor<T>, P) -> Pin<Box<dyn Future<Output = Result<R>> + Send + '_>>
77            + Send
78            + Sync
79            + 'static,
80        P: ComponentNamedList + Lift + 'static,
81        R: ComponentNamedList + Lower + 'static,
82    {
83        let func = Arc::new(func);
84        Self::from_canonical::<T, _, _, _>(move |store, params| {
85            let func = func.clone();
86            HostResult::Future(Box::pin(
87                store.wrap_call(move |accessor| func(accessor, params)),
88            ))
89        })
90    }
91
92    extern "C" fn entrypoint<T, F, P, R>(
93        cx: NonNull<VMOpaqueContext>,
94        data: NonNull<u8>,
95        ty: u32,
96        options: u32,
97        storage: NonNull<MaybeUninit<ValRaw>>,
98        storage_len: usize,
99    ) -> bool
100    where
101        F: Fn(StoreContextMut<'_, T>, P) -> HostResult<R> + Send + Sync + 'static,
102        P: ComponentNamedList + Lift,
103        R: ComponentNamedList + Lower + 'static,
104        T: 'static,
105    {
106        let data = SendSyncPtr::new(NonNull::new(data.as_ptr() as *mut F).unwrap());
107        unsafe {
108            call_host_and_handle_result::<T>(cx, |store, instance| {
109                call_host(
110                    store,
111                    instance,
112                    TypeFuncIndex::from_u32(ty),
113                    OptionsIndex::from_u32(options),
114                    NonNull::slice_from_raw_parts(storage, storage_len).as_mut(),
115                    move |store, args| (*data.as_ptr())(store, args),
116                )
117            })
118        }
119    }
120
121    fn new_dynamic_canonical<T, F>(func: F) -> Arc<HostFunc>
122    where
123        F: Fn(
124                StoreContextMut<'_, T>,
125                ComponentFunc,
126                Vec<Val>,
127                usize,
128            ) -> Pin<Box<dyn Future<Output = Result<Vec<Val>>> + Send + 'static>>
129            + Send
130            + Sync
131            + 'static,
132        T: 'static,
133    {
134        Arc::new(HostFunc {
135            entrypoint: dynamic_entrypoint::<T, F>,
136            // This function performs dynamic type checks and subsequently does
137            // not need to perform up-front type checks. Instead everything is
138            // dynamically managed at runtime.
139            typecheck: Box::new(move |_expected_index, _expected_types| Ok(())),
140            func: Box::new(func),
141        })
142    }
143
144    pub(crate) fn new_dynamic<T: 'static, F>(func: F) -> Arc<HostFunc>
145    where
146        F: Fn(StoreContextMut<'_, T>, ComponentFunc, &[Val], &mut [Val]) -> Result<()>
147            + Send
148            + Sync
149            + 'static,
150    {
151        Self::new_dynamic_canonical::<T, _>(
152            move |store, ty, mut params_and_results, result_start| {
153                let (params, results) = params_and_results.split_at_mut(result_start);
154                let result = func(store, ty, params, results).map(move |()| params_and_results);
155                Box::pin(async move { result })
156            },
157        )
158    }
159
160    #[cfg(feature = "component-model-async")]
161    pub(crate) fn new_dynamic_concurrent<T, F>(func: F) -> Arc<HostFunc>
162    where
163        T: 'static,
164        F: for<'a> Fn(
165                &'a Accessor<T>,
166                ComponentFunc,
167                &'a [Val],
168                &'a mut [Val],
169            ) -> Pin<Box<dyn Future<Output = Result<()>> + Send + 'a>>
170            + Send
171            + Sync
172            + 'static,
173    {
174        let func = Arc::new(func);
175        Self::new_dynamic_canonical::<T, _>(
176            move |store, ty, mut params_and_results, result_start| {
177                let func = func.clone();
178                Box::pin(store.wrap_call(move |accessor| {
179                    Box::pin(async move {
180                        let (params, results) = params_and_results.split_at_mut(result_start);
181                        func(accessor, ty, params, results).await?;
182                        Ok(params_and_results)
183                    })
184                }))
185            },
186        )
187    }
188
189    pub fn typecheck(&self, ty: TypeFuncIndex, types: &InstanceType<'_>) -> Result<()> {
190        (self.typecheck)(ty, types)
191    }
192
193    pub fn lowering(&self) -> VMLowering {
194        let data = NonNull::from(&*self.func).cast();
195        VMLowering {
196            callee: NonNull::new(self.entrypoint as *mut _).unwrap().into(),
197            data: data.into(),
198        }
199    }
200}
201
202fn typecheck<P, R>(ty: TypeFuncIndex, types: &InstanceType<'_>) -> Result<()>
203where
204    P: ComponentNamedList + Lift,
205    R: ComponentNamedList + Lower,
206{
207    let ty = &types.types[ty];
208    P::typecheck(&InterfaceType::Tuple(ty.params), types)
209        .context("type mismatch with parameters")?;
210    R::typecheck(&InterfaceType::Tuple(ty.results), types).context("type mismatch with results")?;
211    Ok(())
212}
213
214/// The "meat" of calling a host function from wasm.
215///
216/// This function is delegated to from implementations of
217/// `HostFunc::from_closure`. Most of the arguments from the `entrypoint` are
218/// forwarded here except for the `data` pointer which is encapsulated in the
219/// `closure` argument here.
220///
221/// This function is parameterized over:
222///
223/// * `T` - the type of store this function works with (an unsafe assertion)
224/// * `Params` - the parameters to the host function, viewed as a tuple
225/// * `Return` - the result of the host function
226/// * `F` - the `closure` to actually receive the `Params` and return the
227///   `Return`
228///
229/// It's expected that `F` will "un-tuple" the arguments to pass to a host
230/// closure.
231///
232/// This function is in general `unsafe` as the validity of all the parameters
233/// must be upheld. Generally that's done by ensuring this is only called from
234/// the select few places it's intended to be called from.
235unsafe fn call_host<T, Params, Return, F>(
236    store: StoreContextMut<'_, T>,
237    instance: Instance,
238    ty: TypeFuncIndex,
239    options: OptionsIndex,
240    storage: &mut [MaybeUninit<ValRaw>],
241    closure: F,
242) -> Result<()>
243where
244    F: Fn(StoreContextMut<'_, T>, Params) -> HostResult<Return> + Send + Sync + 'static,
245    Params: Lift,
246    Return: Lower + 'static,
247{
248    let (component, store) = instance.component_and_store_mut(store.0);
249    let mut store = StoreContextMut(store);
250    let vminstance = instance.id().get(store.0);
251    let opts = &vminstance.component().env_component().options[options];
252    let async_ = opts.async_;
253    let caller_instance = opts.instance;
254    let mut flags = vminstance.instance_flags(caller_instance);
255
256    // Perform a dynamic check that this instance can indeed be left. Exiting
257    // the component is disallowed, for example, when the `realloc` function
258    // calls a canonical import.
259    if unsafe { !flags.may_leave() } {
260        return Err(anyhow!(crate::Trap::CannotLeaveComponent));
261    }
262
263    let types = component.types();
264    let ty = &types[ty];
265    let param_tys = InterfaceType::Tuple(ty.params);
266    let result_tys = InterfaceType::Tuple(ty.results);
267
268    if async_ {
269        #[cfg(feature = "component-model-async")]
270        {
271            let mut storage = unsafe { Storage::<'_, Params, u32>::new_async::<Return>(storage) };
272
273            // Lift the parameters, either from flat storage or from linear
274            // memory.
275            let lift = &mut LiftContext::new(store.0.store_opaque_mut(), options, instance);
276            lift.enter_call();
277            let params = storage.lift_params(lift, param_tys)?;
278
279            // Load the return pointer, if present.
280            let retptr = match storage.async_retptr() {
281                Some(ptr) => {
282                    let mut lower = LowerContext::new(store.as_context_mut(), options, instance);
283                    validate_inbounds::<Return>(lower.as_slice_mut(), ptr)?
284                }
285                // If there's no return pointer then `Return` should have an
286                // empty flat representation. In this situation pretend the
287                // return pointer was 0 so we have something to shepherd along
288                // into the closure below.
289                None => {
290                    assert_eq!(Return::flatten_count(), 0);
291                    0
292                }
293            };
294
295            let host_result = closure(store.as_context_mut(), params);
296
297            let mut lower_result = {
298                move |store: StoreContextMut<T>, ret: Return| {
299                    unsafe {
300                        flags.set_may_leave(false);
301                    }
302                    let mut lower = LowerContext::new(store, options, instance);
303                    ret.linear_lower_to_memory(&mut lower, result_tys, retptr)?;
304                    unsafe {
305                        flags.set_may_leave(true);
306                    }
307                    lower.exit_call()?;
308                    Ok(())
309                }
310            };
311            let task = match host_result {
312                HostResult::Done(result) => {
313                    lower_result(store.as_context_mut(), result?)?;
314                    None
315                }
316                #[cfg(feature = "component-model-async")]
317                HostResult::Future(future) => instance.first_poll(
318                    store.as_context_mut(),
319                    future,
320                    caller_instance,
321                    lower_result,
322                )?,
323            };
324
325            let status = if let Some(task) = task {
326                Status::Started.pack(Some(task))
327            } else {
328                Status::Returned.pack(None)
329            };
330
331            let mut lower = LowerContext::new(store, options, instance);
332            storage.lower_results(&mut lower, InterfaceType::U32, status)?;
333        }
334        #[cfg(not(feature = "component-model-async"))]
335        {
336            let _ = caller_instance;
337            unreachable!(
338                "async-lowered imports should have failed validation \
339                 when `component-model-async` feature disabled"
340            );
341        }
342    } else {
343        let mut storage = unsafe { Storage::<'_, Params, Return>::new_sync(storage) };
344        let mut lift = LiftContext::new(store.0.store_opaque_mut(), options, instance);
345        lift.enter_call();
346        let params = storage.lift_params(&mut lift, param_tys)?;
347
348        let ret = match closure(store.as_context_mut(), params) {
349            HostResult::Done(result) => result?,
350            #[cfg(feature = "component-model-async")]
351            HostResult::Future(future) => {
352                concurrent::poll_and_block(store.0, future, caller_instance)?
353            }
354        };
355
356        unsafe {
357            flags.set_may_leave(false);
358        }
359        let mut lower = LowerContext::new(store, options, instance);
360        storage.lower_results(&mut lower, result_tys, ret)?;
361        unsafe {
362            flags.set_may_leave(true);
363        }
364        lower.exit_call()?;
365    }
366
367    return Ok(());
368
369    /// Type-level representation of the matrix of possibilities of how
370    /// WebAssembly parameters and results are handled in the canonical ABI.
371    ///
372    /// Wasmtime's ABI here always works with `&mut [MaybeUninit<ValRaw>]` as the
373    /// base representation of params/results. Parameters are passed
374    /// sequentially and results are returned by overwriting the parameters.
375    /// That means both params/results start from index 0.
376    ///
377    /// The type-level representation here involves working with the typed
378    /// `P::Lower` and `R::Lower` values which is a type-level representation of
379    /// a lowered value. All lowered values are in essence a sequence of
380    /// `ValRaw` values one after the other to fit within this original array
381    /// that is the basis of Wasmtime's ABI.
382    ///
383    /// The various combinations here are cryptic, but only used in this file.
384    /// This in theory cuts down on the verbosity below, but an explanation of
385    /// the various acronyms here are:
386    ///
387    /// * Pd - params direct - means that parameters are passed directly in
388    ///   their flat representation via `P::Lower`.
389    ///
390    /// * Pi - params indirect - means that parameters are passed indirectly in
391    ///   linear memory and the argument here is `ValRaw` to store the pointer.
392    ///
393    /// * Rd - results direct - means that results are returned directly in
394    ///   their flat representation via `R::Lower`. Note that this is always
395    ///   represented as `MaybeUninit<R::Lower>` as well because the return
396    ///   values may point to uninitialized memory if there were no parameters
397    ///   for example.
398    ///
399    /// * Ri - results indirect - means that results are returned indirectly in
400    ///   linear memory through the pointer specified. Note that this is
401    ///   specified as a `ValRaw` to represent the argument that's being given
402    ///   to the host from WebAssembly.
403    ///
404    /// * Ar - async results - means that the parameters to this call
405    ///   additionally include an async result pointer. Async results are always
406    ///   transmitted via a pointer so this is always a `ValRaw`.
407    ///
408    /// Internally this type makes liberal use of `Union` and `Pair` helpers
409    /// below which are simple `#[repr(C)]` wrappers around a pair of types that
410    /// are a union or a pair.
411    ///
412    /// Note that for any combination of `P` and `R` this `enum` is actually
413    /// pointless as a single variant will be used. In theory we should be able
414    /// to monomorphize based on `P` and `R` to a specific type. This
415    /// monomorphization depends on conditionals like `flatten_count() <= N`,
416    /// however, and I don't know how to encode that in Rust easily. In lieu of
417    /// that we assume LLVM will figure things out and boil away the actual enum
418    /// and runtime dispatch.
419    enum Storage<'a, P: ComponentType, R: ComponentType> {
420        /// Params: direct, Results: direct
421        ///
422        /// The lowered representation of params/results are overlaid on top of
423        /// each other.
424        PdRd(&'a mut Union<P::Lower, MaybeUninit<R::Lower>>),
425
426        /// Params: direct, Results: indirect
427        ///
428        /// The return pointer comes after the params so this is sequentially
429        /// laid out with one after the other.
430        PdRi(&'a Pair<P::Lower, ValRaw>),
431
432        /// Params: indirect, Results: direct
433        ///
434        /// Here the return values are overlaid on top of the pointer parameter.
435        PiRd(&'a mut Union<ValRaw, MaybeUninit<R::Lower>>),
436
437        /// Params: indirect, Results: indirect
438        ///
439        /// Here the two parameters are laid out sequentially one after the
440        /// other.
441        PiRi(&'a Pair<ValRaw, ValRaw>),
442
443        /// Params: direct + async result, Results: direct
444        ///
445        /// This is like `PdRd` except that the parameters additionally include
446        /// a pointer for where to store the result.
447        #[cfg(feature = "component-model-async")]
448        PdArRd(&'a mut Union<Pair<P::Lower, ValRaw>, MaybeUninit<R::Lower>>),
449
450        /// Params: indirect + async result, Results: direct
451        ///
452        /// This is like `PiRd` except that the parameters additionally include
453        /// a pointer for where to store the result.
454        #[cfg(feature = "component-model-async")]
455        PiArRd(&'a mut Union<Pair<ValRaw, ValRaw>, MaybeUninit<R::Lower>>),
456    }
457
458    // Helper structure used above in `Storage` to represent two consecutive
459    // values.
460    #[repr(C)]
461    #[derive(Copy, Clone)]
462    struct Pair<T, U> {
463        a: T,
464        b: U,
465    }
466
467    // Helper structure used above in `Storage` to represent two values overlaid
468    // on each other.
469    #[repr(C)]
470    union Union<T: Copy, U: Copy> {
471        a: T,
472        b: U,
473    }
474
475    /// Representation of where parameters are lifted from.
476    enum Src<'a, T> {
477        /// Parameters are directly lifted from `T`, which is under the hood a
478        /// sequence of `ValRaw`. This is `P::Lower` for example.
479        Direct(&'a T),
480
481        /// Parameters are loaded from linear memory, and this is the wasm
482        /// parameter representing the pointer into linear memory to load from.
483        Indirect(&'a ValRaw),
484    }
485
486    /// Dual of [`Src`], where to store results.
487    enum Dst<'a, T> {
488        /// Results are stored directly in this pointer.
489        ///
490        /// Note that this is a mutable pointer but it's specifically
491        /// `MaybeUninit` as trampolines do not initialize it. The `T` here will
492        /// be `R::Lower` for example.
493        Direct(&'a mut MaybeUninit<T>),
494
495        /// Results are stored in linear memory, and this value is the wasm
496        /// parameter given which represents the pointer into linear memory.
497        ///
498        /// Note that this is not mutable as the parameter is not mutated, but
499        /// memory will be mutated.
500        Indirect(&'a ValRaw),
501    }
502
503    impl<P, R> Storage<'_, P, R>
504    where
505        P: ComponentType + Lift,
506        R: ComponentType + Lower,
507    {
508        /// Classifies a new `Storage` suitable for use with sync functions.
509        ///
510        /// There's a 2x2 matrix of whether parameters and results are stored on the
511        /// stack or on the heap. Each of the 4 branches here have a different
512        /// representation of the storage of arguments/returns.
513        ///
514        /// Also note that while four branches are listed here only one is taken for
515        /// any particular `Params` and `Return` combination. This should be
516        /// trivially DCE'd by LLVM. Perhaps one day with enough const programming in
517        /// Rust we can make monomorphizations of this function codegen only one
518        /// branch, but today is not that day.
519        ///
520        /// # Safety
521        ///
522        /// Requires that the `storage` provided does indeed match an wasm
523        /// function with the signature of `P` and `R` as params/results.
524        unsafe fn new_sync(storage: &mut [MaybeUninit<ValRaw>]) -> Storage<'_, P, R> {
525            // SAFETY: this `unsafe` is due to the `slice_to_storage_*` helpers
526            // used which view the slice provided as a different type. This
527            // safety should be upheld by the contract of the `ComponentType`
528            // trait and its `Lower` type parameter meaning they're valid to
529            // view as a sequence of `ValRaw` types. Additionally the
530            // `ComponentType` trait ensures that the matching of the runtime
531            // length of `storage` should match the actual size of `P::Lower`
532            // and `R::Lower` or such as needed.
533            unsafe {
534                if P::flatten_count() <= MAX_FLAT_PARAMS {
535                    if R::flatten_count() <= MAX_FLAT_RESULTS {
536                        Storage::PdRd(slice_to_storage_mut(storage).assume_init_mut())
537                    } else {
538                        Storage::PdRi(slice_to_storage_mut(storage).assume_init_ref())
539                    }
540                } else {
541                    if R::flatten_count() <= MAX_FLAT_RESULTS {
542                        Storage::PiRd(slice_to_storage_mut(storage).assume_init_mut())
543                    } else {
544                        Storage::PiRi(slice_to_storage_mut(storage).assume_init_ref())
545                    }
546                }
547            }
548        }
549
550        fn lift_params(&self, cx: &mut LiftContext<'_>, ty: InterfaceType) -> Result<P> {
551            match self.lift_src() {
552                Src::Direct(storage) => P::linear_lift_from_flat(cx, ty, storage),
553                Src::Indirect(ptr) => {
554                    let ptr = validate_inbounds::<P>(cx.memory(), ptr)?;
555                    P::linear_lift_from_memory(cx, ty, &cx.memory()[ptr..][..P::SIZE32])
556                }
557            }
558        }
559
560        fn lift_src(&self) -> Src<'_, P::Lower> {
561            match self {
562                // SAFETY: these `unsafe` blocks are due to accessing union
563                // fields. The safety here relies on the contract of the
564                // `ComponentType` trait which should ensure that the types
565                // projected onto a list of wasm parameters are indeed correct.
566                // That means that the projections here, if the types are
567                // correct, all line up to initialized memory that's well-typed
568                // to access.
569                Storage::PdRd(storage) => unsafe { Src::Direct(&storage.a) },
570                Storage::PdRi(storage) => Src::Direct(&storage.a),
571                #[cfg(feature = "component-model-async")]
572                Storage::PdArRd(storage) => unsafe { Src::Direct(&storage.a.a) },
573                Storage::PiRd(storage) => unsafe { Src::Indirect(&storage.a) },
574                Storage::PiRi(storage) => Src::Indirect(&storage.a),
575                #[cfg(feature = "component-model-async")]
576                Storage::PiArRd(storage) => unsafe { Src::Indirect(&storage.a.a) },
577            }
578        }
579
580        fn lower_results<T>(
581            &mut self,
582            cx: &mut LowerContext<'_, T>,
583            ty: InterfaceType,
584            ret: R,
585        ) -> Result<()> {
586            match self.lower_dst() {
587                Dst::Direct(storage) => ret.linear_lower_to_flat(cx, ty, storage),
588                Dst::Indirect(ptr) => {
589                    let ptr = validate_inbounds::<R>(cx.as_slice_mut(), ptr)?;
590                    ret.linear_lower_to_memory(cx, ty, ptr)
591                }
592            }
593        }
594
595        fn lower_dst(&mut self) -> Dst<'_, R::Lower> {
596            match self {
597                // SAFETY: these unsafe blocks are due to accessing fields of a
598                // `union` which is not safe in Rust. The returned value is
599                // `MaybeUninit<R::Lower>` in all cases, however, which should
600                // safely model how `union` memory is possibly uninitialized.
601                // Additionally `R::Lower` has the `unsafe` contract that all
602                // its bit patterns must be sound, which additionally should
603                // help make this safe.
604                Storage::PdRd(storage) => unsafe { Dst::Direct(&mut storage.b) },
605                Storage::PiRd(storage) => unsafe { Dst::Direct(&mut storage.b) },
606                #[cfg(feature = "component-model-async")]
607                Storage::PdArRd(storage) => unsafe { Dst::Direct(&mut storage.b) },
608                #[cfg(feature = "component-model-async")]
609                Storage::PiArRd(storage) => unsafe { Dst::Direct(&mut storage.b) },
610                Storage::PdRi(storage) => Dst::Indirect(&storage.b),
611                Storage::PiRi(storage) => Dst::Indirect(&storage.b),
612            }
613        }
614
615        #[cfg(feature = "component-model-async")]
616        fn async_retptr(&self) -> Option<&ValRaw> {
617            match self {
618                // SAFETY: like above these are `unsafe` due to accessing a
619                // `union` field. This should be safe via the construction of
620                // `Storage` which should correctly determine whether or not an
621                // async return pointer is provided and classify the args/rets
622                // appropriately.
623                Storage::PdArRd(storage) => unsafe { Some(&storage.a.b) },
624                Storage::PiArRd(storage) => unsafe { Some(&storage.a.b) },
625                Storage::PdRd(_) | Storage::PiRd(_) | Storage::PdRi(_) | Storage::PiRi(_) => None,
626            }
627        }
628    }
629
630    #[cfg(feature = "component-model-async")]
631    impl<P> Storage<'_, P, u32>
632    where
633        P: ComponentType + Lift,
634    {
635        /// Classifies a new `Storage` suitable for use with async functions.
636        ///
637        /// # Safety
638        ///
639        /// Requires that the `storage` provided does indeed match an `async`
640        /// wasm function with the signature of `P` and `R` as params/results.
641        unsafe fn new_async<R>(storage: &mut [MaybeUninit<ValRaw>]) -> Storage<'_, P, u32>
642        where
643            R: ComponentType + Lower,
644        {
645            // SAFETY: see `Storage::new` for discussion on why this should be
646            // safe given the unsafe contract of the `ComponentType` trait.
647            unsafe {
648                if P::flatten_count() <= wasmtime_environ::component::MAX_FLAT_ASYNC_PARAMS {
649                    if R::flatten_count() == 0 {
650                        Storage::PdRd(slice_to_storage_mut(storage).assume_init_mut())
651                    } else {
652                        Storage::PdArRd(slice_to_storage_mut(storage).assume_init_mut())
653                    }
654                } else {
655                    if R::flatten_count() == 0 {
656                        Storage::PiRd(slice_to_storage_mut(storage).assume_init_mut())
657                    } else {
658                        Storage::PiArRd(slice_to_storage_mut(storage).assume_init_mut())
659                    }
660                }
661            }
662        }
663    }
664}
665
666pub(crate) fn validate_inbounds<T: ComponentType>(memory: &[u8], ptr: &ValRaw) -> Result<usize> {
667    // FIXME(#4311): needs memory64 support
668    let ptr = usize::try_from(ptr.get_u32())?;
669    if ptr % usize::try_from(T::ALIGN32)? != 0 {
670        bail!("pointer not aligned");
671    }
672    let end = match ptr.checked_add(T::SIZE32) {
673        Some(n) => n,
674        None => bail!("pointer size overflow"),
675    };
676    if end > memory.len() {
677        bail!("pointer out of bounds")
678    }
679    Ok(ptr)
680}
681
682unsafe fn call_host_and_handle_result<T>(
683    cx: NonNull<VMOpaqueContext>,
684    func: impl FnOnce(StoreContextMut<'_, T>, Instance) -> Result<()>,
685) -> bool
686where
687    T: 'static,
688{
689    let cx = unsafe { VMComponentContext::from_opaque(cx) };
690    unsafe {
691        ComponentInstance::enter_host_from_wasm(cx, |store, instance| {
692            let mut store = store.unchecked_context_mut();
693            store.0.call_hook(CallHook::CallingHost)?;
694            let res = func(store.as_context_mut(), instance);
695            store.0.call_hook(CallHook::ReturningFromHost)?;
696            res
697        })
698    }
699}
700
701unsafe fn call_host_dynamic<T, F>(
702    store: StoreContextMut<'_, T>,
703    instance: Instance,
704    ty: TypeFuncIndex,
705    options: OptionsIndex,
706    storage: &mut [MaybeUninit<ValRaw>],
707    closure: F,
708) -> Result<()>
709where
710    F: Fn(
711            StoreContextMut<'_, T>,
712            ComponentFunc,
713            Vec<Val>,
714            usize,
715        ) -> Pin<Box<dyn Future<Output = Result<Vec<Val>>> + Send + 'static>>
716        + Send
717        + Sync
718        + 'static,
719    T: 'static,
720{
721    let (component, store) = instance.component_and_store_mut(store.0);
722    let mut store = StoreContextMut(store);
723    let vminstance = instance.id().get(store.0);
724    let opts = &component.env_component().options[options];
725    let async_ = opts.async_;
726    let caller_instance = opts.instance;
727    let mut flags = vminstance.instance_flags(caller_instance);
728
729    // Perform a dynamic check that this instance can indeed be left. Exiting
730    // the component is disallowed, for example, when the `realloc` function
731    // calls a canonical import.
732    if unsafe { !flags.may_leave() } {
733        return Err(anyhow!(crate::Trap::CannotLeaveComponent));
734    }
735
736    let types = component.types();
737    let func_ty = &types[ty];
738    let param_tys = &types[func_ty.params];
739    let result_tys = &types[func_ty.results];
740
741    let mut params_and_results = Vec::new();
742    let mut lift = &mut LiftContext::new(store.0.store_opaque_mut(), options, instance);
743    lift.enter_call();
744    let max_flat = if async_ {
745        MAX_FLAT_ASYNC_PARAMS
746    } else {
747        MAX_FLAT_PARAMS
748    };
749    let ty = ComponentFunc::from(ty, &lift.instance_type());
750
751    let ret_index = unsafe {
752        dynamic_params_load(
753            &mut lift,
754            types,
755            storage,
756            param_tys,
757            &mut params_and_results,
758            max_flat,
759        )?
760    };
761    let result_start = params_and_results.len();
762    for _ in 0..result_tys.types.len() {
763        params_and_results.push(Val::Bool(false));
764    }
765
766    if async_ {
767        #[cfg(feature = "component-model-async")]
768        {
769            let retptr = if result_tys.types.len() == 0 {
770                0
771            } else {
772                let retptr = unsafe { storage[ret_index].assume_init() };
773                let mut lower = LowerContext::new(store.as_context_mut(), options, instance);
774                validate_inbounds_dynamic(&result_tys.abi, lower.as_slice_mut(), &retptr)?
775            };
776
777            let future = closure(store.as_context_mut(), ty, params_and_results, result_start);
778
779            let task = instance.first_poll(store, future, caller_instance, {
780                let result_tys = func_ty.results;
781                move |store: StoreContextMut<T>, result_vals: Vec<Val>| {
782                    unsafe {
783                        flags.set_may_leave(false);
784                    }
785
786                    let mut lower = LowerContext::new(store, options, instance);
787                    let result_tys = &lower.types[result_tys];
788                    let result_vals = &result_vals[result_start..];
789                    assert_eq!(result_vals.len(), result_tys.types.len());
790                    let mut ptr = retptr;
791                    for (val, ty) in result_vals.iter().zip(result_tys.types.iter()) {
792                        let offset = lower.types.canonical_abi(ty).next_field32_size(&mut ptr);
793                        val.store(&mut lower, *ty, offset)?;
794                    }
795
796                    unsafe {
797                        flags.set_may_leave(true);
798                    }
799
800                    lower.exit_call()?;
801
802                    Ok(())
803                }
804            })?;
805
806            let status = if let Some(task) = task {
807                Status::Started.pack(Some(task))
808            } else {
809                Status::Returned.pack(None)
810            };
811
812            storage[0] = MaybeUninit::new(ValRaw::i32(status as i32));
813        }
814        #[cfg(not(feature = "component-model-async"))]
815        {
816            unreachable!(
817                "async-lowered imports should have failed validation \
818                 when `component-model-async` feature disabled"
819            );
820        }
821    } else {
822        let future = closure(store.as_context_mut(), ty, params_and_results, result_start);
823        let result_vals = concurrent::poll_and_block(store.0, future, caller_instance)?;
824        let result_vals = &result_vals[result_start..];
825
826        unsafe {
827            flags.set_may_leave(false);
828        }
829
830        let mut cx = LowerContext::new(store, options, instance);
831        if let Some(cnt) = result_tys.abi.flat_count(MAX_FLAT_RESULTS) {
832            let mut dst = storage[..cnt].iter_mut();
833            for (val, ty) in result_vals.iter().zip(result_tys.types.iter()) {
834                val.lower(&mut cx, *ty, &mut dst)?;
835            }
836            assert!(dst.next().is_none());
837        } else {
838            let ret_ptr = unsafe { storage[ret_index].assume_init_ref() };
839            let mut ptr = validate_inbounds_dynamic(&result_tys.abi, cx.as_slice_mut(), ret_ptr)?;
840            for (val, ty) in result_vals.iter().zip(result_tys.types.iter()) {
841                let offset = types.canonical_abi(ty).next_field32_size(&mut ptr);
842                val.store(&mut cx, *ty, offset)?;
843            }
844        }
845
846        unsafe {
847            flags.set_may_leave(true);
848        }
849
850        cx.exit_call()?;
851    }
852
853    Ok(())
854}
855
856/// Loads the parameters for a dynamic host function call into `params`
857///
858/// Returns the number of flat `storage` values consumed.
859///
860/// # Safety
861///
862/// Requires that `param_tys` matches the type signature of the `storage` that
863/// was passed in.
864unsafe fn dynamic_params_load(
865    cx: &mut LiftContext<'_>,
866    types: &ComponentTypes,
867    storage: &[MaybeUninit<ValRaw>],
868    param_tys: &TypeTuple,
869    params: &mut Vec<Val>,
870    max_flat_params: usize,
871) -> Result<usize> {
872    if let Some(param_count) = param_tys.abi.flat_count(max_flat_params) {
873        // NB: can use `MaybeUninit::slice_assume_init_ref` when that's stable
874        let storage =
875            unsafe { mem::transmute::<&[MaybeUninit<ValRaw>], &[ValRaw]>(&storage[..param_count]) };
876        let mut iter = storage.iter();
877        for ty in param_tys.types.iter() {
878            params.push(Val::lift(cx, *ty, &mut iter)?);
879        }
880        assert!(iter.next().is_none());
881        Ok(param_count)
882    } else {
883        let mut offset = validate_inbounds_dynamic(&param_tys.abi, cx.memory(), unsafe {
884            storage[0].assume_init_ref()
885        })?;
886        for ty in param_tys.types.iter() {
887            let abi = types.canonical_abi(ty);
888            let size = usize::try_from(abi.size32).unwrap();
889            let memory = &cx.memory()[abi.next_field32_size(&mut offset)..][..size];
890            params.push(Val::load(cx, *ty, memory)?);
891        }
892        Ok(1)
893    }
894}
895
896pub(crate) fn validate_inbounds_dynamic(
897    abi: &CanonicalAbiInfo,
898    memory: &[u8],
899    ptr: &ValRaw,
900) -> Result<usize> {
901    // FIXME(#4311): needs memory64 support
902    let ptr = usize::try_from(ptr.get_u32())?;
903    if ptr % usize::try_from(abi.align32)? != 0 {
904        bail!("pointer not aligned");
905    }
906    let end = match ptr.checked_add(usize::try_from(abi.size32).unwrap()) {
907        Some(n) => n,
908        None => bail!("pointer size overflow"),
909    };
910    if end > memory.len() {
911        bail!("pointer out of bounds")
912    }
913    Ok(ptr)
914}
915
916extern "C" fn dynamic_entrypoint<T, F>(
917    cx: NonNull<VMOpaqueContext>,
918    data: NonNull<u8>,
919    ty: u32,
920    options: u32,
921    storage: NonNull<MaybeUninit<ValRaw>>,
922    storage_len: usize,
923) -> bool
924where
925    F: Fn(
926            StoreContextMut<'_, T>,
927            ComponentFunc,
928            Vec<Val>,
929            usize,
930        ) -> Pin<Box<dyn Future<Output = Result<Vec<Val>>> + Send + 'static>>
931        + Send
932        + Sync
933        + 'static,
934    T: 'static,
935{
936    let data = SendSyncPtr::new(NonNull::new(data.as_ptr() as *mut F).unwrap());
937    unsafe {
938        call_host_and_handle_result(cx, |store, instance| {
939            call_host_dynamic::<T, _>(
940                store,
941                instance,
942                TypeFuncIndex::from_u32(ty),
943                OptionsIndex::from_u32(options),
944                NonNull::slice_from_raw_parts(storage, storage_len).as_mut(),
945                &*data.as_ptr(),
946            )
947        })
948    }
949}
wasmtime/runtime/component/func/host.rs

wasmtime/runtime/component/func/
host.rs
