wasmtime/runtime/externals/global.rs
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use crate::prelude::*;
use crate::runtime::vm::{GcRootsList, SendSyncPtr};
use crate::{
store::{AutoAssertNoGc, StoreData, StoreOpaque, Stored},
trampoline::generate_global_export,
AnyRef, AsContext, AsContextMut, ExternRef, Func, GlobalType, HeapType, Mutability, Ref,
RootedGcRefImpl, Val, ValType,
};
use core::ptr;
use core::ptr::NonNull;
use wasmtime_environ::TypeTrace;
/// A WebAssembly `global` value which can be read and written to.
///
/// A `global` in WebAssembly is sort of like a global variable within an
/// [`Instance`](crate::Instance). The `global.get` and `global.set`
/// instructions will modify and read global values in a wasm module. Globals
/// can either be imported or exported from wasm modules.
///
/// A [`Global`] "belongs" to the store that it was originally created within
/// (either via [`Global::new`] or via instantiating a
/// [`Module`](crate::Module)). Operations on a [`Global`] 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(transparent)] // here for the C API
pub struct Global(pub(super) Stored<crate::runtime::vm::ExportGlobal>);
impl Global {
/// Creates a new WebAssembly `global` value with the provide type `ty` and
/// initial value `val`.
///
/// The `store` argument will be the owner of the [`Global`] returned. Using
/// the returned [`Global`] other items in the store may access this global.
/// For example this could be provided as an argument to
/// [`Instance::new`](crate::Instance::new) or
/// [`Linker::define`](crate::Linker::define).
///
/// # Errors
///
/// Returns an error if the `ty` provided does not match the type of the
/// value `val`, or if `val` comes from a different store than `store`.
///
/// # Examples
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let engine = Engine::default();
/// let mut store = Store::new(&engine, ());
///
/// let ty = GlobalType::new(ValType::I32, Mutability::Const);
/// let i32_const = Global::new(&mut store, ty, 1i32.into())?;
/// let ty = GlobalType::new(ValType::F64, Mutability::Var);
/// let f64_mut = Global::new(&mut store, ty, 2.0f64.into())?;
///
/// let module = Module::new(
/// &engine,
/// "(module
/// (global (import \"\" \"i32-const\") i32)
/// (global (import \"\" \"f64-mut\") (mut f64))
/// )"
/// )?;
///
/// let mut linker = Linker::new(&engine);
/// linker.define(&store, "", "i32-const", i32_const)?;
/// linker.define(&store, "", "f64-mut", f64_mut)?;
///
/// let instance = linker.instantiate(&mut store, &module)?;
/// // ...
/// # Ok(())
/// # }
/// ```
pub fn new(mut store: impl AsContextMut, ty: GlobalType, val: Val) -> Result<Global> {
Global::_new(store.as_context_mut().0, ty, val)
}
fn _new(store: &mut StoreOpaque, ty: GlobalType, val: Val) -> Result<Global> {
val.ensure_matches_ty(store, ty.content()).context(
"type mismatch: initial value provided does not match the type of this global",
)?;
unsafe {
let wasmtime_export = generate_global_export(store, ty, val)?;
Ok(Global::from_wasmtime_global(wasmtime_export, store))
}
}
/// Returns the underlying type of this `global`.
///
/// # Panics
///
/// Panics if `store` does not own this global.
pub fn ty(&self, store: impl AsContext) -> GlobalType {
self._ty(store.as_context().0)
}
pub(crate) fn _ty(&self, store: &StoreOpaque) -> GlobalType {
let ty = &store[self.0].global;
GlobalType::from_wasmtime_global(store.engine(), &ty)
}
/// Returns the current [`Val`] of this global.
///
/// # Panics
///
/// Panics if `store` does not own this global.
pub fn get(&self, mut store: impl AsContextMut) -> Val {
unsafe {
let store = store.as_context_mut();
let mut store = AutoAssertNoGc::new(store.0);
let definition = &*store[self.0].definition;
match self._ty(&store).content() {
ValType::I32 => Val::from(*definition.as_i32()),
ValType::I64 => Val::from(*definition.as_i64()),
ValType::F32 => Val::F32(*definition.as_u32()),
ValType::F64 => Val::F64(*definition.as_u64()),
ValType::V128 => Val::V128((*definition.as_u128()).into()),
ValType::Ref(ref_ty) => {
let reference: Ref = match ref_ty.heap_type() {
HeapType::Func | HeapType::ConcreteFunc(_) => {
Func::_from_raw(&mut store, definition.as_func_ref().cast()).into()
}
HeapType::NoFunc => Ref::Func(None),
HeapType::Extern => Ref::Extern(
definition
.as_gc_ref()
.map(|r| {
let r = store.unwrap_gc_store_mut().clone_gc_ref(r);
ExternRef::from_cloned_gc_ref(&mut store, r)
})
.into(),
),
HeapType::NoExtern => Ref::Extern(None),
HeapType::Any
| HeapType::Eq
| HeapType::I31
| HeapType::Struct
| HeapType::ConcreteStruct(_)
| HeapType::Array
| HeapType::ConcreteArray(_) => definition
.as_gc_ref()
.map(|r| {
let r = store.unwrap_gc_store_mut().clone_gc_ref(r);
AnyRef::from_cloned_gc_ref(&mut store, r)
})
.into(),
HeapType::None => Ref::Any(None),
};
debug_assert!(
ref_ty.is_nullable() || !reference.is_null(),
"if the type is non-nullable, we better have a non-null reference"
);
reference.into()
}
}
}
}
/// Attempts to set the current value of this global to [`Val`].
///
/// # Errors
///
/// Returns an error if this global has a different type than `Val`, if
/// it's not a mutable global, or if `val` comes from a different store than
/// the one provided.
///
/// # Panics
///
/// Panics if `store` does not own this global.
pub fn set(&self, mut store: impl AsContextMut, val: Val) -> Result<()> {
let mut store = AutoAssertNoGc::new(store.as_context_mut().0);
let global_ty = self._ty(&store);
if global_ty.mutability() != Mutability::Var {
bail!("immutable global cannot be set");
}
val.ensure_matches_ty(&store, global_ty.content())
.context("type mismatch: attempt to set global to value of wrong type")?;
unsafe {
let definition = &mut *store[self.0].definition;
match val {
Val::I32(i) => *definition.as_i32_mut() = i,
Val::I64(i) => *definition.as_i64_mut() = i,
Val::F32(f) => *definition.as_u32_mut() = f,
Val::F64(f) => *definition.as_u64_mut() = f,
Val::V128(i) => *definition.as_u128_mut() = i.into(),
Val::FuncRef(f) => {
*definition.as_func_ref_mut() = f.map_or(ptr::null_mut(), |f| {
f.vm_func_ref(&mut store).as_ptr().cast()
});
}
Val::ExternRef(e) => {
let new = match e {
None => None,
#[cfg_attr(not(feature = "gc"), allow(unreachable_patterns))]
Some(e) => Some(e.try_gc_ref(&store)?.unchecked_copy()),
};
let new = new.as_ref();
definition.write_gc_ref(store.unwrap_gc_store_mut(), new);
}
Val::AnyRef(a) => {
let new = match a {
None => None,
#[cfg_attr(not(feature = "gc"), allow(unreachable_patterns))]
Some(a) => Some(a.try_gc_ref(&store)?.unchecked_copy()),
};
let new = new.as_ref();
definition.write_gc_ref(store.unwrap_gc_store_mut(), new);
}
}
}
Ok(())
}
pub(crate) fn trace_root(&self, store: &mut StoreOpaque, gc_roots_list: &mut GcRootsList) {
if let Some(ref_ty) = self._ty(store).content().as_ref() {
if !ref_ty.is_vmgcref_type_and_points_to_object() {
return;
}
if let Some(gc_ref) = unsafe { (*store[self.0].definition).as_gc_ref() } {
let gc_ref = NonNull::from(gc_ref);
let gc_ref = SendSyncPtr::new(gc_ref);
unsafe {
gc_roots_list.add_root(gc_ref, "Wasm global");
}
}
}
}
pub(crate) unsafe fn from_wasmtime_global(
mut wasmtime_export: crate::runtime::vm::ExportGlobal,
store: &mut StoreOpaque,
) -> Global {
wasmtime_export
.global
.wasm_ty
.canonicalize_for_runtime_usage(&mut |module_index| {
crate::runtime::vm::Instance::from_vmctx(wasmtime_export.vmctx, |instance| {
instance.engine_type_index(module_index)
})
});
Global(store.store_data_mut().insert(wasmtime_export))
}
pub(crate) fn wasmtime_ty<'a>(&self, data: &'a StoreData) -> &'a wasmtime_environ::Global {
&data[self.0].global
}
pub(crate) fn vmimport(&self, store: &StoreOpaque) -> crate::runtime::vm::VMGlobalImport {
crate::runtime::vm::VMGlobalImport {
from: store[self.0].definition,
}
}
/// Get a stable hash key for this global.
///
/// Even if the same underlying global definition is added to the
/// `StoreData` multiple times and becomes multiple `wasmtime::Global`s,
/// this hash key will be consistent across all of these globals.
pub(crate) fn hash_key(&self, store: &StoreOpaque) -> impl core::hash::Hash + Eq {
store[self.0].definition as usize
}
}
#[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
(global (export "g") (mut i32) (i32.const 0))
)
"#,
)?;
let instance = Instance::new(&mut store, &module, &[])?;
// Each time we `get_global`, we call `Global::from_wasmtime` which adds
// a new entry to `StoreData`, so `g1` and `g2` will have different
// indices into `StoreData`.
let g1 = instance.get_global(&mut store, "g").unwrap();
let g2 = instance.get_global(&mut store, "g").unwrap();
// That said, they really point to the same global.
assert_eq!(g1.get(&mut store).unwrap_i32(), 0);
assert_eq!(g2.get(&mut store).unwrap_i32(), 0);
g1.set(&mut store, Val::I32(42))?;
assert_eq!(g1.get(&mut store).unwrap_i32(), 42);
assert_eq!(g2.get(&mut store).unwrap_i32(), 42);
// And therefore their hash keys are the same.
assert!(g1.hash_key(&store.as_context().0) == g2.hash_key(&store.as_context().0));
// But the hash keys are different from different globals.
let instance2 = Instance::new(&mut store, &module, &[])?;
let g3 = instance2.get_global(&mut store, "g").unwrap();
assert!(g1.hash_key(&store.as_context().0) != g3.hash_key(&store.as_context().0));
Ok(())
}
}