Enable copy-on-write memories for components

crates/wasmtime/src/compiler.rs

@@ -28,7 +28,7 @@ use std::collections::{btree_map, BTreeMap, BTreeSet};
 use std::{any::Any, collections::HashMap};
 use wasmtime_environ::{
     Compiler, DefinedFuncIndex, FuncIndex, FunctionBodyData, ModuleTranslation, ModuleType,
-    ModuleTypes, PrimaryMap, SignatureIndex, StaticModuleIndex, Tunables, WasmFunctionInfo,
+    ModuleTypes, PrimaryMap, SignatureIndex, StaticModuleIndex, WasmFunctionInfo,
 };
 use wasmtime_jit::{CompiledFunctionInfo, CompiledModuleInfo};
 
@@ -447,8 +447,7 @@ impl FunctionIndices {
     pub fn link_and_append_code<'a>(
         mut self,
         mut obj: object::write::Object<'static>,
-        tunables: &'a Tunables,
-        compiler: &dyn Compiler,
+        engine: &'a Engine,
         compiled_funcs: Vec<(String, Box<dyn Any + Send>)>,
         translations: PrimaryMap<StaticModuleIndex, ModuleTranslation<'_>>,
     ) -> Result<(wasmtime_jit::ObjectBuilder<'a>, Artifacts)> {
@@ -457,6 +456,8 @@ impl FunctionIndices {
         // The result is a vector parallel to `compiled_funcs` where
         // `symbol_ids_and_locs[i]` is the symbol ID and function location of
         // `compiled_funcs[i]`.
+        let compiler = engine.compiler();
+        let tunables = &engine.config().tunables;
         let symbol_ids_and_locs = compiler.append_code(
             &mut obj,
             &compiled_funcs,
@@ -559,7 +560,22 @@ impl FunctionIndices {
 
         artifacts.modules = translations
             .into_iter()
-            .map(|(module, translation)| {
+            .map(|(module, mut translation)| {
+                // If configured attempt to use static memory initialization which
+                // can either at runtime be implemented as a single memcpy to
+                // initialize memory or otherwise enabling virtual-memory-tricks
+                // such as mmap'ing from a file to get copy-on-write.
+                if engine.config().memory_init_cow {
+                    let align = compiler.page_size_align();
+                    let max_always_allowed = engine.config().memory_guaranteed_dense_image_size;
+                    translation.try_static_init(align, max_always_allowed);
+                }
+
+                // Attempt to convert table initializer segments to
+                // FuncTable representation where possible, to enable
+                // table lazy init.
+                translation.try_func_table_init();
+
                 let funcs: PrimaryMap<DefinedFuncIndex, CompiledFunctionInfo> =
                     wasm_functions_for_module(&mut wasm_functions, module)
                         .map(|(key, wasm_func_index)| {

crates/wasmtime/src/component/component.rs

@@ -206,8 +206,7 @@ impl Component {
 
         let (mut object, compilation_artifacts) = function_indices.link_and_append_code(
             object,
-            &engine.config().tunables,
-            compiler,
+            engine,
             compiled_funcs,
             module_translations,
         )?;
@@ -473,3 +472,34 @@ impl ComponentRuntimeInfo for ComponentInner {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::component::Component;
+    use crate::{Config, Engine};
+    use wasmtime_environ::MemoryInitialization;
+
+    #[test]
+    fn cow_on_by_default() {
+        let mut config = Config::new();
+        config.wasm_component_model(true);
+        let engine = Engine::new(&config).unwrap();
+        let component = Component::new(
+            &engine,
+            r#"
+                (component
+                    (core module
+                        (memory 1)
+                        (data (i32.const 100) "abcd")
+                    )
+                )
+            "#,
+        )
+        .unwrap();
+
+        for (_, module) in component.inner.static_modules.iter() {
+            let init = &module.env_module().memory_initialization;
+            assert!(matches!(init, MemoryInitialization::Static { .. }));
+        }
+    }
+}

crates/wasmtime/src/module.rs

@@ -402,7 +402,6 @@ impl Module {
         use crate::compiler::CompileInputs;
 
         let tunables = &engine.config().tunables;
-        let compiler = engine.compiler();
 
         // First a `ModuleEnvironment` is created which records type information
         // about the wasm module. This is where the WebAssembly is parsed and
@@ -437,25 +436,9 @@ impl Module {
         engine.append_compiler_info(&mut object);
         engine.append_bti(&mut object);
 
-        // If configured attempt to use static memory initialization which
-        // can either at runtime be implemented as a single memcpy to
-        // initialize memory or otherwise enabling virtual-memory-tricks
-        // such as mmap'ing from a file to get copy-on-write.
-        if engine.config().memory_init_cow {
-            let align = engine.compiler().page_size_align();
-            let max_always_allowed = engine.config().memory_guaranteed_dense_image_size;
-            translation.try_static_init(align, max_always_allowed);
-        }
-
-        // Attempt to convert table initializer segments to
-        // FuncTable representation where possible, to enable
-        // table lazy init.
-        translation.try_func_table_init();
-
         let (mut object, compilation_artifacts) = function_indices.link_and_append_code(
             object,
-            tunables,
-            compiler,
+            engine,
             compiled_funcs,
             std::iter::once(translation).collect(),
         )?;
@@ -1361,3 +1344,27 @@ fn memory_images(engine: &Engine, module: &CompiledModule) -> Result<Option<Modu
     };
     ModuleMemoryImages::new(module.module(), module.code_memory().wasm_data(), mmap)
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{Engine, Module};
+    use wasmtime_environ::MemoryInitialization;
+
+    #[test]
+    fn cow_on_by_default() {
+        let engine = Engine::default();
+        let module = Module::new(
+            &engine,
+            r#"
+                (module
+                    (memory 1)
+                    (data (i32.const 100) "abcd")
+                )
+            "#,
+        )
+        .unwrap();
+
+        let init = &module.env_module().memory_initialization;
+        assert!(matches!(init, MemoryInitialization::Static { .. }));
+    }
+}