wasmtime/runtime/externals/

table.rs

use crate::prelude::*;
use crate::runtime::vm::{self as runtime, GcStore};
use crate::store::{AutoAssertNoGc, StoreInstanceId, StoreOpaque};
use crate::trampoline::generate_table_export;
use crate::{AnyRef, AsContext, AsContextMut, ExternRef, Func, HeapType, Ref, TableType, Trap};
use core::iter;
use wasmtime_environ::DefinedTableIndex;

/// A WebAssembly `table`, or an array of values.
///
/// Like [`Memory`][crate::Memory] a table is an indexed array of values, but
/// unlike [`Memory`][crate::Memory] it's an array of WebAssembly reference type
/// values rather than bytes. One of the most common usages of a table is a
/// function table for wasm modules (a `funcref` table), where each element has
/// the `ValType::FuncRef` type.
///
/// A [`Table`] "belongs" to the store that it was originally created within
/// (either via [`Table::new`] or via instantiating a
/// [`Module`](crate::Module)). Operations on a [`Table`] only work with the
/// store it belongs to, and if another store is passed in by accident then
/// methods will panic.
#[derive(Copy, Clone, Debug)]
#[repr(C)] // here for the C API
pub struct Table {
    instance: StoreInstanceId,
    index: DefinedTableIndex,
}

// Double-check that the C representation in `extern.h` matches our in-Rust
// representation here in terms of size/alignment/etc.
const _: () = {
    #[repr(C)]
    struct Tmp(u64, u32);
    #[repr(C)]
    struct C(Tmp, u32);
    assert!(core::mem::size_of::<C>() == core::mem::size_of::<Table>());
    assert!(core::mem::align_of::<C>() == core::mem::align_of::<Table>());
    assert!(core::mem::offset_of!(Table, instance) == 0);
};

impl Table {
    /// Creates a new [`Table`] with the given parameters.
    ///
    /// * `store` - the owner of the resulting [`Table`]
    /// * `ty` - the type of this table, containing both the element type as
    ///   well as the initial size and maximum size, if any.
    /// * `init` - the initial value to fill all table entries with, if the
    ///   table starts with an initial size.
    ///
    /// # Errors
    ///
    /// Returns an error if `init` does not match the element type of the table,
    /// or if `init` does not belong to the `store` provided.
    ///
    /// # Panics
    ///
    /// This function will panic when used with a [`Store`](`crate::Store`)
    /// which has a [`ResourceLimiterAsync`](`crate::ResourceLimiterAsync`)
    /// (see also: [`Store::limiter_async`](`crate::Store::limiter_async`).
    /// When using an async resource limiter, use [`Table::new_async`]
    /// instead.
    ///
    /// # Examples
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// let engine = Engine::default();
    /// let mut store = Store::new(&engine, ());
    ///
    /// let ty = TableType::new(RefType::FUNCREF, 2, None);
    /// let table = Table::new(&mut store, ty, Ref::Func(None))?;
    ///
    /// let module = Module::new(
    ///     &engine,
    ///     "(module
    ///         (table (import \"\" \"\") 2 funcref)
    ///         (func $f (result i32)
    ///             i32.const 10)
    ///         (elem (i32.const 0) $f)
    ///     )"
    /// )?;
    ///
    /// let instance = Instance::new(&mut store, &module, &[table.into()])?;
    /// // ...
    /// # Ok(())
    /// # }
    /// ```
    pub fn new(mut store: impl AsContextMut, ty: TableType, init: Ref) -> Result<Table> {
        Table::_new(store.as_context_mut().0, ty, init)
    }

    /// Async variant of [`Table::new`]. You must use this variant with
    /// [`Store`](`crate::Store`)s which have a
    /// [`ResourceLimiterAsync`](`crate::ResourceLimiterAsync`).
    ///
    /// # Panics
    ///
    /// This function will panic when used with a non-async
    /// [`Store`](`crate::Store`)
    #[cfg(feature = "async")]
    pub async fn new_async(
        mut store: impl AsContextMut<Data: Send>,
        ty: TableType,
        init: Ref,
    ) -> Result<Table> {
        let mut store = store.as_context_mut();
        assert!(
            store.0.async_support(),
            "cannot use `new_async` without enabling async support on the config"
        );
        store
            .on_fiber(|store| Table::_new(store.0, ty, init))
            .await?
    }

    fn _new(store: &mut StoreOpaque, ty: TableType, init: Ref) -> Result<Table> {
        let table = generate_table_export(store, &ty)?;
        let init = init.into_table_element(store, ty.element())?;
        let (wasmtime_table, gc_store) = table.wasmtime_table(store, iter::empty());
        wasmtime_table.fill(gc_store, 0, init, ty.minimum())?;
        Ok(table)
    }

    /// Returns the underlying type of this table, including its element type as
    /// well as the maximum/minimum lower bounds.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this table.
    pub fn ty(&self, store: impl AsContext) -> TableType {
        self._ty(store.as_context().0)
    }

    fn _ty(&self, store: &StoreOpaque) -> TableType {
        TableType::from_wasmtime_table(store.engine(), self.wasmtime_ty(store))
    }

    /// Returns the `runtime::Table` within `store` as well as the optional
    /// `GcStore` in use within `store`.
    ///
    /// # Panics
    ///
    /// Panics if this table does not belong to `store`.
    fn wasmtime_table<'a>(
        &self,
        store: &'a mut StoreOpaque,
        lazy_init_range: impl Iterator<Item = u64>,
    ) -> (&'a mut runtime::Table, Option<&'a mut GcStore>) {
        self.instance.assert_belongs_to(store.id());
        let (store, instance) = store.optional_gc_store_and_instance_mut(self.instance.instance());

        (
            instance.get_defined_table_with_lazy_init(self.index, lazy_init_range),
            store,
        )
    }

    /// Returns the table element value at `index`.
    ///
    /// Returns `None` if `index` is out of bounds.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this table.
    pub fn get(&self, mut store: impl AsContextMut, index: u64) -> Option<Ref> {
        let mut store = AutoAssertNoGc::new(store.as_context_mut().0);
        let (table, gc_store) = self.wasmtime_table(&mut store, iter::once(index));
        match table.get(gc_store, index)? {
            runtime::TableElement::FuncRef(f) => {
                // SAFETY: the `table` belongs to `store`, so elements within
                // the table must also belong to the store.
                let func = unsafe { f.map(|f| Func::from_vm_func_ref(store.id(), f)) };
                Some(func.into())
            }

            runtime::TableElement::UninitFunc => {
                unreachable!("lazy init above should have converted UninitFunc")
            }

            runtime::TableElement::GcRef(None) => {
                Some(Ref::null(self._ty(&store).element().heap_type()))
            }

            #[cfg_attr(
                not(feature = "gc"),
                expect(unreachable_code, unused_variables, reason = "definitions cfg'd off")
            )]
            runtime::TableElement::GcRef(Some(x)) => {
                match self._ty(&store).element().heap_type().top() {
                    HeapType::Any => {
                        let x = AnyRef::from_cloned_gc_ref(&mut store, x);
                        Some(x.into())
                    }
                    HeapType::Extern => {
                        let x = ExternRef::from_cloned_gc_ref(&mut store, x);
                        Some(x.into())
                    }
                    HeapType::Func => {
                        unreachable!("never have TableElement::GcRef for func tables")
                    }
                    ty => unreachable!("not a top type: {ty:?}"),
                }
            }

            runtime::TableElement::ContRef(_c) => {
                // TODO(#10248) Required to support stack switching in the embedder API.
                unimplemented!()
            }
        }
    }

    /// Writes the `val` provided into `index` within this table.
    ///
    /// # Errors
    ///
    /// Returns an error if `index` is out of bounds, if `val` does not have
    /// the right type to be stored in this table, or if `val` belongs to a
    /// different store.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this table.
    pub fn set(&self, mut store: impl AsContextMut, index: u64, val: Ref) -> Result<()> {
        let store = store.as_context_mut().0;
        let ty = self.ty(&store);
        let val = val.into_table_element(store, ty.element())?;
        let (table, _) = self.wasmtime_table(store, iter::empty());
        table
            .set(index, val)
            .map_err(|()| anyhow!("table element index out of bounds"))
    }

    /// Returns the current size of this table.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this table.
    pub fn size(&self, store: impl AsContext) -> u64 {
        self.internal_size(store.as_context().0)
    }

    pub(crate) fn internal_size(&self, store: &StoreOpaque) -> u64 {
        // unwrap here should be ok because the runtime should always guarantee
        // that we can fit the number of elements in a 64-bit integer.
        u64::try_from(store[self.instance].table(self.index).current_elements).unwrap()
    }

    /// Grows the size of this table by `delta` more elements, initialization
    /// all new elements to `init`.
    ///
    /// Returns the previous size of this table if successful.
    ///
    /// # Errors
    ///
    /// Returns an error if the table cannot be grown by `delta`, for example
    /// if it would cause the table to exceed its maximum size. Also returns an
    /// error if `init` is not of the right type or if `init` does not belong to
    /// `store`.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this table.
    ///
    /// This function will panic when used with a [`Store`](`crate::Store`)
    /// which has a [`ResourceLimiterAsync`](`crate::ResourceLimiterAsync`)
    /// (see also: [`Store::limiter_async`](`crate::Store::limiter_async`)).
    /// When using an async resource limiter, use [`Table::grow_async`]
    /// instead.
    pub fn grow(&self, mut store: impl AsContextMut, delta: u64, init: Ref) -> Result<u64> {
        let store = store.as_context_mut().0;
        let ty = self.ty(&store);
        let init = init.into_table_element(store, ty.element())?;
        let (table, _gc_store) = self.wasmtime_table(store, iter::empty());
        // FIXME(#11179) shouldn't need to subvert the borrow checker
        let table: *mut _ = table;
        unsafe {
            match (*table).grow(delta, init, store)? {
                Some(size) => {
                    let vm = (*table).vmtable();
                    store[self.instance].table_ptr(self.index).write(vm);
                    // unwrap here should be ok because the runtime should always guarantee
                    // that we can fit the table size in a 64-bit integer.
                    Ok(u64::try_from(size).unwrap())
                }
                None => bail!("failed to grow table by `{}`", delta),
            }
        }
    }

    /// Async variant of [`Table::grow`]. Required when using a
    /// [`ResourceLimiterAsync`](`crate::ResourceLimiterAsync`).
    ///
    /// # Panics
    ///
    /// This function will panic when used with a non-async
    /// [`Store`](`crate::Store`).
    #[cfg(feature = "async")]
    pub async fn grow_async(
        &self,
        mut store: impl AsContextMut<Data: Send>,
        delta: u64,
        init: Ref,
    ) -> Result<u64> {
        let mut store = store.as_context_mut();
        assert!(
            store.0.async_support(),
            "cannot use `grow_async` without enabling async support on the config"
        );
        store
            .on_fiber(|store| self.grow(store, delta, init))
            .await?
    }

    /// Copy `len` elements from `src_table[src_index..]` into
    /// `dst_table[dst_index..]`.
    ///
    /// # Errors
    ///
    /// Returns an error if the range is out of bounds of either the source or
    /// destination tables, or if the source table's element type does not match
    /// the destination table's element type.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own either `dst_table` or `src_table`.
    pub fn copy(
        mut store: impl AsContextMut,
        dst_table: &Table,
        dst_index: u64,
        src_table: &Table,
        src_index: u64,
        len: u64,
    ) -> Result<()> {
        let store = store.as_context_mut().0;

        let dst_ty = dst_table.ty(&store);
        let src_ty = src_table.ty(&store);
        src_ty
            .element()
            .ensure_matches(store.engine(), dst_ty.element())
            .context(
                "type mismatch: source table's element type does not match \
                 destination table's element type",
            )?;

        // SAFETY: the the two tables have the same type, as type-checked above.
        unsafe {
            Self::copy_raw(store, dst_table, dst_index, src_table, src_index, len)?;
        }
        Ok(())
    }

    /// Copies the elements of `src_table` to `dst_table`.
    ///
    /// # Panics
    ///
    /// Panics if the either table doesn't belong to `store`.
    ///
    /// # Safety
    ///
    /// Requires that the two tables have previously been type-checked to have
    /// the same type.
    pub(crate) unsafe fn copy_raw(
        store: &mut StoreOpaque,
        dst_table: &Table,
        dst_index: u64,
        src_table: &Table,
        src_index: u64,
        len: u64,
    ) -> Result<(), Trap> {
        // Handle lazy initialization of the source table first before doing
        // anything else.
        let src_range = src_index..(src_index.checked_add(len).unwrap_or(u64::MAX));
        src_table.wasmtime_table(store, src_range);

        // validate `dst_table` belongs to `store`.
        dst_table.wasmtime_table(store, iter::empty());

        // Figure out which of the three cases we're in:
        //
        // 1. Cross-instance table copy.
        // 2. Intra-instance table copy.
        // 3. Intra-table copy.
        //
        // We handle each of them slightly differently.
        let src_instance = src_table.instance.instance();
        let dst_instance = dst_table.instance.instance();
        match (
            src_instance == dst_instance,
            src_table.index == dst_table.index,
        ) {
            // 1. Cross-instance table copy: split the mutable store borrow into
            // two mutable instance borrows, get each instance's defined table,
            // and do the copy.
            (false, _) => {
                // SAFETY: accessing two instances mutably at the same time
                // requires only accessing defined entities on each instance
                // which is done below with `get_defined_*` methods.
                let (gc_store, [src_instance, dst_instance]) = unsafe {
                    store.optional_gc_store_and_instances_mut([src_instance, dst_instance])
                };
                src_instance.get_defined_table(src_table.index).copy_to(
                    dst_instance.get_defined_table(dst_table.index),
                    gc_store,
                    dst_index,
                    src_index,
                    len,
                )
            }

            // 2. Intra-instance, distinct-tables copy: split the mutable
            // instance borrow into two distinct mutable table borrows and do
            // the copy.
            (true, false) => {
                let (gc_store, instance) = store.optional_gc_store_and_instance_mut(src_instance);
                let [(_, src_table), (_, dst_table)] = instance
                    .tables_mut()
                    .get_disjoint_mut([src_table.index, dst_table.index])
                    .unwrap();
                src_table.copy_to(dst_table, gc_store, dst_index, src_index, len)
            }

            // 3. Intra-table copy: get the table and copy within it!
            (true, true) => {
                let (gc_store, instance) = store.optional_gc_store_and_instance_mut(src_instance);
                instance
                    .get_defined_table(src_table.index)
                    .copy_within(gc_store, dst_index, src_index, len)
            }
        }
    }

    /// Fill `table[dst..(dst + len)]` with the given value.
    ///
    /// # Errors
    ///
    /// Returns an error if
    ///
    /// * `val` is not of the same type as this table's
    ///   element type,
    ///
    /// * the region to be filled is out of bounds, or
    ///
    /// * `val` comes from a different `Store` from this table.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own either `dst_table` or `src_table`.
    pub fn fill(&self, mut store: impl AsContextMut, dst: u64, val: Ref, len: u64) -> Result<()> {
        let store = store.as_context_mut().0;
        let ty = self.ty(&store);
        let val = val.into_table_element(store, ty.element())?;

        let (table, gc_store) = self.wasmtime_table(store, iter::empty());
        table.fill(gc_store, dst, val, len)?;

        Ok(())
    }

    #[cfg(feature = "gc")]
    pub(crate) fn trace_roots(
        &self,
        store: &mut StoreOpaque,
        gc_roots_list: &mut crate::runtime::vm::GcRootsList,
    ) {
        if !self
            ._ty(store)
            .element()
            .is_vmgcref_type_and_points_to_object()
        {
            return;
        }

        let (table, _) = self.wasmtime_table(store, iter::empty());
        for gc_ref in table.gc_refs_mut() {
            if let Some(gc_ref) = gc_ref {
                unsafe {
                    gc_roots_list.add_root(gc_ref.into(), "Wasm table element");
                }
            }
        }
    }

    pub(crate) fn from_raw(instance: StoreInstanceId, index: DefinedTableIndex) -> Table {
        Table { instance, index }
    }

    pub(crate) fn wasmtime_ty<'a>(&self, store: &'a StoreOpaque) -> &'a wasmtime_environ::Table {
        let module = store[self.instance].env_module();
        let index = module.table_index(self.index);
        &module.tables[index]
    }

    pub(crate) fn vmimport(&self, store: &StoreOpaque) -> crate::runtime::vm::VMTableImport {
        let instance = &store[self.instance];
        crate::runtime::vm::VMTableImport {
            from: instance.table_ptr(self.index).into(),
            vmctx: instance.vmctx().into(),
            index: self.index,
        }
    }

    pub(crate) fn comes_from_same_store(&self, store: &StoreOpaque) -> bool {
        store.id() == self.instance.store_id()
    }

    /// Get a stable hash key for this table.
    ///
    /// Even if the same underlying table definition is added to the
    /// `StoreData` multiple times and becomes multiple `wasmtime::Table`s,
    /// this hash key will be consistent across all of these tables.
    #[cfg_attr(
        not(test),
        expect(dead_code, reason = "Not used yet, but added for consistency")
    )]
    pub(crate) fn hash_key(&self, store: &StoreOpaque) -> impl core::hash::Hash + Eq + use<'_> {
        store[self.instance].table_ptr(self.index).as_ptr().addr()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{Instance, Module, Store};

    #[test]
    fn hash_key_is_stable_across_duplicate_store_data_entries() -> Result<()> {
        let mut store = Store::<()>::default();
        let module = Module::new(
            store.engine(),
            r#"
                (module
                    (table (export "t") 1 1 externref)
                )
            "#,
        )?;
        let instance = Instance::new(&mut store, &module, &[])?;

        // Each time we `get_table`, we call `Table::from_wasmtime` which adds
        // a new entry to `StoreData`, so `t1` and `t2` will have different
        // indices into `StoreData`.
        let t1 = instance.get_table(&mut store, "t").unwrap();
        let t2 = instance.get_table(&mut store, "t").unwrap();

        // That said, they really point to the same table.
        assert!(t1.get(&mut store, 0).unwrap().unwrap_extern().is_none());
        assert!(t2.get(&mut store, 0).unwrap().unwrap_extern().is_none());
        let e = ExternRef::new(&mut store, 42)?;
        t1.set(&mut store, 0, e.into())?;
        assert!(t1.get(&mut store, 0).unwrap().unwrap_extern().is_some());
        assert!(t2.get(&mut store, 0).unwrap().unwrap_extern().is_some());

        // And therefore their hash keys are the same.
        assert!(t1.hash_key(&store.as_context().0) == t2.hash_key(&store.as_context().0));

        // But the hash keys are different from different tables.
        let instance2 = Instance::new(&mut store, &module, &[])?;
        let t3 = instance2.get_table(&mut store, "t").unwrap();
        assert!(t1.hash_key(&store.as_context().0) != t3.hash_key(&store.as_context().0));

        Ok(())
    }
}