wasmtime/src/values.rs

use crate::r#ref::ExternRef;
use crate::{Func, Store, ValType};
use anyhow::{bail, Result};
use std::ptr;
use wasmtime_runtime::VMExternRef;

/// Possible runtime values that a WebAssembly module can either consume or
/// produce.
#[derive(Debug, Clone)]
pub enum Val {
    /// A 32-bit integer
    I32(i32),

    /// A 64-bit integer
    I64(i64),

    /// A 32-bit float.
    ///
    /// Note that the raw bits of the float are stored here, and you can use
    /// `f32::from_bits` to create an `f32` value.
    F32(u32),

    /// A 64-bit float.
    ///
    /// Note that the raw bits of the float are stored here, and you can use
    /// `f64::from_bits` to create an `f64` value.
    F64(u64),

    /// An `externref` value which can hold opaque data to the wasm instance itself.
    ExternRef(Option<ExternRef>),

    /// A first-class reference to a WebAssembly function.
    FuncRef(Func),

    /// A 128-bit number
    V128(u128),
}

macro_rules! accessors {
    ($bind:ident $(($variant:ident($ty:ty) $get:ident $unwrap:ident $cvt:expr))*) => ($(
        /// Attempt to access the underlying value of this `Val`, returning
        /// `None` if it is not the correct type.
        pub fn $get(&self) -> Option<$ty> {
            if let Val::$variant($bind) = self {
                Some($cvt)
            } else {
                None
            }
        }

        /// Returns the underlying value of this `Val`, panicking if it's the
        /// wrong type.
        ///
        /// # Panics
        ///
        /// Panics if `self` is not of the right type.
        pub fn $unwrap(&self) -> $ty {
            self.$get().expect(concat!("expected ", stringify!($ty)))
        }
    )*)
}

impl Val {
    /// Returns a null `externref` value.
    pub fn null() -> Val {
        Val::ExternRef(None)
    }

    /// Returns the corresponding [`ValType`] for this `Val`.
    pub fn ty(&self) -> ValType {
        match self {
            Val::I32(_) => ValType::I32,
            Val::I64(_) => ValType::I64,
            Val::F32(_) => ValType::F32,
            Val::F64(_) => ValType::F64,
            Val::ExternRef(_) => ValType::ExternRef,
            Val::FuncRef(_) => ValType::FuncRef,
            Val::V128(_) => ValType::V128,
        }
    }

    pub(crate) unsafe fn write_value_to(&self, p: *mut u128) {
        match self {
            Val::I32(i) => ptr::write(p as *mut i32, *i),
            Val::I64(i) => ptr::write(p as *mut i64, *i),
            Val::F32(u) => ptr::write(p as *mut u32, *u),
            Val::F64(u) => ptr::write(p as *mut u64, *u),
            Val::V128(b) => ptr::write(p as *mut u128, *b),
            Val::ExternRef(None) => ptr::write(p, 0),
            Val::ExternRef(Some(x)) => ptr::write(p as *mut *mut u8, x.inner.clone().into_raw()),
            _ => unimplemented!("Val::write_value_to"),
        }
    }

    pub(crate) unsafe fn read_value_from(store: &Store, p: *const u128, ty: &ValType) -> Val {
        match ty {
            ValType::I32 => Val::I32(ptr::read(p as *const i32)),
            ValType::I64 => Val::I64(ptr::read(p as *const i64)),
            ValType::F32 => Val::F32(ptr::read(p as *const u32)),
            ValType::F64 => Val::F64(ptr::read(p as *const u64)),
            ValType::V128 => Val::V128(ptr::read(p as *const u128)),
            ValType::ExternRef => {
                let raw = ptr::read(p as *const *mut u8);
                if raw.is_null() {
                    Val::ExternRef(None)
                } else {
                    Val::ExternRef(Some(ExternRef {
                        inner: VMExternRef::from_raw(raw),
                        store: store.weak(),
                    }))
                }
            }
            _ => unimplemented!("Val::read_value_from: {:?}", ty),
        }
    }

    accessors! {
        e
        (I32(i32) i32 unwrap_i32 *e)
        (I64(i64) i64 unwrap_i64 *e)
        (F32(f32) f32 unwrap_f32 f32::from_bits(*e))
        (F64(f64) f64 unwrap_f64 f64::from_bits(*e))
        (FuncRef(&Func) funcref unwrap_funcref e)
        (V128(u128) v128 unwrap_v128 *e)
    }

    /// Attempt to access the underlying `externref` value of this `Val`.
    ///
    /// If this is not an `externref`, then `None` is returned.
    ///
    /// If this is a null `externref`, then `Some(None)` is returned.
    ///
    /// If this is a non-null `externref`, then `Some(Some(..))` is returned.
    pub fn externref(&self) -> Option<Option<ExternRef>> {
        match self {
            Val::ExternRef(e) => Some(e.clone()),
            _ => None,
        }
    }

    /// Returns the underlying `externref` value of this `Val`, panicking if it's the
    /// wrong type.
    ///
    /// If this is a null `externref`, then `None` is returned.
    ///
    /// If this is a non-null `externref`, then `Some(..)` is returned.
    ///
    /// # Panics
    ///
    /// Panics if `self` is not a (nullable) `externref`.
    pub fn unwrap_externref(&self) -> Option<ExternRef> {
        self.externref().expect("expected externref")
    }

    pub(crate) fn comes_from_same_store(&self, store: &Store) -> bool {
        match self {
            Val::FuncRef(f) => Store::same(store, f.store()),

            // TODO: need to implement this once we actually finalize what
            // `externref` will look like and it's actually implemented to pass it
            // to compiled wasm as well.
            Val::ExternRef(Some(e)) => e.store.ptr_eq(&store.weak()),
            Val::ExternRef(None) => true,

            // Integers have no association with any particular store, so
            // they're always considered as "yes I came from that store",
            Val::I32(_) | Val::I64(_) | Val::F32(_) | Val::F64(_) | Val::V128(_) => true,
        }
    }
}

impl From<i32> for Val {
    fn from(val: i32) -> Val {
        Val::I32(val)
    }
}

impl From<i64> for Val {
    fn from(val: i64) -> Val {
        Val::I64(val)
    }
}

impl From<f32> for Val {
    fn from(val: f32) -> Val {
        Val::F32(val.to_bits())
    }
}

impl From<f64> for Val {
    fn from(val: f64) -> Val {
        Val::F64(val.to_bits())
    }
}

impl From<ExternRef> for Val {
    fn from(val: ExternRef) -> Val {
        Val::ExternRef(Some(val))
    }
}

impl From<Option<ExternRef>> for Val {
    fn from(val: Option<ExternRef>) -> Val {
        Val::ExternRef(val)
    }
}

impl From<Func> for Val {
    fn from(val: Func) -> Val {
        Val::FuncRef(val)
    }
}

pub(crate) fn into_checked_anyfunc(
    val: Val,
    store: &Store,
) -> Result<wasmtime_runtime::VMCallerCheckedAnyfunc> {
    if !val.comes_from_same_store(store) {
        bail!("cross-`Store` values are not supported");
    }
    Ok(match val {
        Val::ExternRef(None) => wasmtime_runtime::VMCallerCheckedAnyfunc {
            func_ptr: ptr::null(),
            type_index: wasmtime_runtime::VMSharedSignatureIndex::default(),
            vmctx: ptr::null_mut(),
        },
        Val::FuncRef(f) => {
            let f = f.wasmtime_function();
            wasmtime_runtime::VMCallerCheckedAnyfunc {
                func_ptr: f.address,
                type_index: f.signature,
                vmctx: f.vmctx,
            }
        }
        _ => bail!("val is not funcref"),
    })
}

pub(crate) fn from_checked_anyfunc(
    item: wasmtime_runtime::VMCallerCheckedAnyfunc,
    store: &Store,
) -> Val {
    if item.type_index == wasmtime_runtime::VMSharedSignatureIndex::default() {
        return Val::ExternRef(None);
    }
    let instance_handle = unsafe { wasmtime_runtime::InstanceHandle::from_vmctx(item.vmctx) };
    let export = wasmtime_runtime::ExportFunction {
        address: item.func_ptr,
        signature: item.type_index,
        vmctx: item.vmctx,
    };
    let instance = store.existing_instance_handle(instance_handle);
    let f = Func::from_wasmtime_function(export, instance);
    Val::FuncRef(f)
}