wasmtime/runtime/externals/
global.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
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(())
    }
}