native globals

spec/src/run.rs

@@ -110,7 +110,7 @@ fn run_action(program: &ProgramInstance, action: &test::Action)
                     elements::Internal::Global(global_index) => Ok(ItemIndex::IndexSpace(global_index)),
                     _ => Err(InterpreterError::Global(format!("Expected to have exported global with name {}", field))),
                 })
-                .and_then(|g| module.global(g, None).map(|g| Some(g.get())))
+                .and_then(|g| module.global(g, None, None).map(|g| Some(g.get())))
         }
     }
 }

src/interpreter/env.rs

@@ -116,8 +116,8 @@ impl ModuleInstanceInterface for EnvModuleInstance {
 		self.instance.memory(index)
 	}
 
-	fn global(&self, index: ItemIndex, variable_type: Option<VariableType>) -> Result<Arc<VariableInstance>, Error> {
-		self.instance.global(index, variable_type)
+	fn global<'a>(&self, index: ItemIndex, variable_type: Option<VariableType>, externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>) -> Result<Arc<VariableInstance>, Error> {
+		self.instance.global(index, variable_type, externals)
 	}
 
 	fn function_type(&self, function_index: ItemIndex) -> Result<FunctionSignature, Error> {
@@ -143,19 +143,19 @@ impl ModuleInstanceInterface for EnvModuleInstance {
 	fn call_internal_function(&self, outer: CallerContext, index: u32) -> Result<Option<RuntimeValue>, Error> {
 		// to make interpreter independent of *SCRIPTEN runtime, just make abort/assert = interpreter Error
 		match index {
-			INDEX_FUNC_ABORT => self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_ABORT), Some(VariableType::I32))
+			INDEX_FUNC_ABORT => self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_ABORT), Some(VariableType::I32), None)
 				.and_then(|g| g.set(RuntimeValue::I32(1)))
 				.and_then(|_| Err(Error::Trap("abort".into()))),
 			INDEX_FUNC_ASSERT => outer.value_stack.pop_as::<i32>()
 				.and_then(|condition| if condition == 0 {
-					self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_ABORT), Some(VariableType::I32))
+					self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_ABORT), Some(VariableType::I32), None)
 						.and_then(|g| g.set(RuntimeValue::I32(1)))
 						.and_then(|_| Err(Error::Trap("assertion failed".into())))
 				} else {
 					Ok(None)
 				}),
 			INDEX_FUNC_ENLARGE_MEMORY => Ok(Some(RuntimeValue::I32(0))), // TODO: support memory enlarge
-			INDEX_FUNC_GET_TOTAL_MEMORY => self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_TOTAL_MEMORY), Some(VariableType::I32))
+			INDEX_FUNC_GET_TOTAL_MEMORY => self.global(ItemIndex::IndexSpace(INDEX_GLOBAL_TOTAL_MEMORY), Some(VariableType::I32), None)
 				.map(|g| g.get())
 				.map(Some),
 			INDEX_FUNC_MIN_NONUSED ... INDEX_FUNC_MAX => Err(Error::Trap("unimplemented".into())),

src/interpreter/env_native.rs

@@ -13,6 +13,8 @@ use interpreter::variable::{VariableInstance, VariableType};
 
 /// Min index of native function.
 pub const NATIVE_INDEX_FUNC_MIN: u32 = 10001;
+/// Min index of native global.
+pub const NATIVE_INDEX_GLOBAL_MIN: u32 = 20001;
 
 /// User functions executor.
 pub trait UserFunctionExecutor {
@@ -65,12 +67,14 @@ impl UserFunctionDescriptor {
 	}
 }
 
-/// Set of user-defined functions
-pub struct UserFunctions<'a> {
-	/// Functions list.
+/// Set of user-defined module elements.
+pub struct UserDefinedElements<'a> {
+	/// User globals list.
+	pub globals: HashMap<String, Arc<VariableInstance>>,
+	/// User functions list.
 	pub functions: Cow<'static, [UserFunctionDescriptor]>,
 	/// Functions executor.
-	pub executor: &'a mut UserFunctionExecutor,
+	pub executor: Option<&'a mut UserFunctionExecutor>,
 }
 
 /// Native module instance.
@@ -78,21 +82,31 @@ pub struct NativeModuleInstance<'a> {
 	/// Underllying module reference.
 	env: Arc<ModuleInstanceInterface>,
 	/// User function executor.
-	executor: RwLock<&'a mut UserFunctionExecutor>,
+	executor: RwLock<Option<&'a mut UserFunctionExecutor>>,
 	/// By-name functions index.
-	by_name: HashMap<String, u32>,
+	functions_by_name: HashMap<String, u32>,
 	/// User functions list.
 	functions: Cow<'static, [UserFunctionDescriptor]>,
+	/// By-name functions index.
+	globals_by_name: HashMap<String, u32>,
+	/// User globals list.
+	globals: Vec<Arc<VariableInstance>>,
 }
 
 impl<'a> NativeModuleInstance<'a> {
 	/// Create new native module
-	pub fn new(env: Arc<ModuleInstanceInterface>, functions: UserFunctions<'a>) -> Result<Self, Error> {
+	pub fn new(env: Arc<ModuleInstanceInterface>, elements: UserDefinedElements<'a>) -> Result<Self, Error> {
+		if !elements.functions.is_empty() && elements.executor.is_none() {
+			return Err(Error::Function("trying to construct native env module with functions, but without executor".into()));
+		}
+
 		Ok(NativeModuleInstance {
 			env: env,
-			executor: RwLock::new(functions.executor),
-			by_name: functions.functions.iter().enumerate().map(|(i, f)| (f.name().to_owned(), i as u32)).collect(),
-			functions: functions.functions,
+			executor: RwLock::new(elements.executor),
+			functions_by_name: elements.functions.iter().enumerate().map(|(i, f)| (f.name().to_owned(), i as u32)).collect(),
+			functions: elements.functions,
+			globals_by_name: elements.globals.iter().enumerate().map(|(i, (g_name, _))| (g_name.to_owned(), i as u32)).collect(),
+			globals: elements.globals.into_iter().map(|(_, g)| g).collect(),
 		})
 	}
 }
@@ -107,9 +121,10 @@ impl<'a> ModuleInstanceInterface for NativeModuleInstance<'a> {
 	}
 
 	fn export_entry<'b>(&self, name: &str, required_type: &ExportEntryType) -> Result<Internal, Error> {
-		if let Some(index) = self.by_name.get(name) {
+		if let Some(index) = self.functions_by_name.get(name) {
 			let composite_index = NATIVE_INDEX_FUNC_MIN + *index;
 			match required_type {
+				&ExportEntryType::Any => return Ok(Internal::Function(composite_index)),
 				&ExportEntryType::Function(ref required_type)
 					if self.function_type(ItemIndex::Internal(composite_index))
 						.expect("by_name contains index; function_type succeeds for all functions from by_name; qed") == *required_type
@@ -117,6 +132,17 @@ impl<'a> ModuleInstanceInterface for NativeModuleInstance<'a> {
 				_ => (),
 			}
 		}
+		if let Some(index) = self.globals_by_name.get(name) {
+			match required_type {
+				&ExportEntryType::Any => return Ok(Internal::Global(NATIVE_INDEX_GLOBAL_MIN + *index)),
+				&ExportEntryType::Global(ref required_type)
+					if self.globals.get(*index as usize)
+						.expect("globals_by_name maps to indexes of globals; index read from globals_by_name; qed")
+						.variable_type() == *required_type
+					=> return Ok(Internal::Global(NATIVE_INDEX_GLOBAL_MIN + *index)),
+				_ => (),
+			}
+		}
 
 		self.env.export_entry(name, required_type)
 	}
@@ -129,8 +155,20 @@ impl<'a> ModuleInstanceInterface for NativeModuleInstance<'a> {
 		self.env.memory(index)
 	}
 
-	fn global(&self, index: ItemIndex, variable_type: Option<VariableType>) -> Result<Arc<VariableInstance>, Error> {
-		self.env.global(index, variable_type)
+	fn global<'b>(&self, global_index: ItemIndex, variable_type: Option<VariableType>, externals: Option<&'b HashMap<String, Arc<ModuleInstanceInterface + 'b>>>) -> Result<Arc<VariableInstance>, Error> {
+		let index = match global_index {
+			ItemIndex::IndexSpace(index) | ItemIndex::Internal(index) => index,
+			ItemIndex::External(_) => unreachable!("trying to get global, exported by native env module"),
+		};
+
+		if index < NATIVE_INDEX_GLOBAL_MIN {
+			return self.env.global(global_index, variable_type, externals);
+		}
+
+		self.globals
+			.get((index - NATIVE_INDEX_GLOBAL_MIN) as usize)
+			.cloned()
+			.ok_or(Error::Native(format!("trying to get native global with index {}", index)))
 	}
 
 	fn function_type(&self, function_index: ItemIndex) -> Result<FunctionSignature, Error> {
@@ -139,7 +177,7 @@ impl<'a> ModuleInstanceInterface for NativeModuleInstance<'a> {
 			ItemIndex::External(_) => unreachable!("trying to call function, exported by native env module"),
 		};
 
-		if index < NATIVE_INDEX_FUNC_MIN {
+		if index < NATIVE_INDEX_FUNC_MIN || index >= NATIVE_INDEX_GLOBAL_MIN {
 			return self.env.function_type(function_index);
 		}
 
@@ -165,20 +203,23 @@ impl<'a> ModuleInstanceInterface for NativeModuleInstance<'a> {
 	}
 
 	fn call_internal_function(&self, outer: CallerContext, index: u32) -> Result<Option<RuntimeValue>, Error> {
-		if index < NATIVE_INDEX_FUNC_MIN {
+		if index < NATIVE_INDEX_FUNC_MIN || index >= NATIVE_INDEX_GLOBAL_MIN {
 			return self.env.call_internal_function(outer, index);
 		}
 
 		self.functions
 			.get((index - NATIVE_INDEX_FUNC_MIN) as usize)
 			.ok_or(Error::Native(format!("trying to call native function with index {}", index)))
-			.and_then(|f| self.executor.write().execute(&f.name(), outer))
+			.and_then(|f| self.executor.write()
+				.as_mut()
+				.expect("function existss; if function exists, executor must also exists [checked in constructor]; qed")
+				.execute(&f.name(), outer))
 	}
 }
 
 /// Create wrapper for env module with given native user functions.
-pub fn env_native_module<'a>(env: Arc<ModuleInstanceInterface>, user_functions: UserFunctions<'a>) -> Result<NativeModuleInstance, Error> {
-	NativeModuleInstance::new(env, user_functions)
+pub fn env_native_module<'a>(env: Arc<ModuleInstanceInterface>, user_elements: UserDefinedElements<'a>) -> Result<NativeModuleInstance, Error> {
+	NativeModuleInstance::new(env, user_elements)
 }
 
 impl<'a> PartialEq for UserFunctionDescriptor {

src/interpreter/imports.rs

@@ -151,7 +151,7 @@ impl ModuleImports {
 	pub fn global<'a>(&self, externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>, import: &ImportEntry, required_type: Option<VariableType>) -> Result<Arc<VariableInstance>, Error> {
 		let (module, export) = self.external_export(externals, import, &required_type.clone().map(|rt| ExportEntryType::Global(rt)).unwrap_or(ExportEntryType::Any))?;
 		if let Internal::Global(external_index) = export {
-			return module.global(ItemIndex::Internal(external_index), required_type);
+			return module.global(ItemIndex::Internal(external_index), required_type, externals);
 		}
 
 		Err(Error::Program(format!("wrong import {} from module {} (expecting global)", import.field(), import.module())))

src/interpreter/mod.rs

@@ -78,6 +78,6 @@ pub use self::module::{ModuleInstance, ModuleInstanceInterface, ItemIndex, Expor
 pub use self::table::TableInstance;
 pub use self::program::ProgramInstance;
 pub use self::value::RuntimeValue;
-pub use self::variable::VariableInstance;
-pub use self::env_native::{env_native_module, UserFunctions, UserFunctionExecutor, UserFunctionDescriptor};
+pub use self::variable::{VariableInstance, VariableType, ExternalVariableValue};
+pub use self::env_native::{env_native_module, UserDefinedElements, UserFunctionExecutor, UserFunctionDescriptor};
 pub use self::env::EnvParams;

src/interpreter/module.rs

@@ -62,7 +62,7 @@ pub trait ModuleInstanceInterface {
 	/// Get memory reference.
 	fn memory(&self, index: ItemIndex) -> Result<Arc<MemoryInstance>, Error>;
 	/// Get global reference.
-	fn global(&self, index: ItemIndex, variable_type: Option<VariableType>) -> Result<Arc<VariableInstance>, Error>;
+	fn global<'a>(&self, index: ItemIndex, variable_type: Option<VariableType>, externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>) -> Result<Arc<VariableInstance>, Error>;
 	/// Get function type for given function index.
 	fn function_type(&self, function_index: ItemIndex) -> Result<FunctionSignature, Error>;
 	/// Get function type for given function index.
@@ -241,7 +241,7 @@ impl ModuleInstance {
 						self.exports.entry(export.field().into()).or_insert_with(Default::default).push(Internal::Function(function_index));
 					},
 					&Internal::Global(global_index) => {
-						self.global(ItemIndex::IndexSpace(global_index), None)
+						self.global(ItemIndex::IndexSpace(global_index), None, externals)
 							.and_then(|g| if g.is_mutable() {
 								Err(Error::Validation(format!("trying to export mutable global {}", export.field())))
 							} else {
@@ -337,6 +337,7 @@ impl ModuleInstance {
 
 					let mut context = FunctionValidationContext::new(
 						self,
+						externals,
 						&locals, 
 						DEFAULT_VALUE_STACK_LIMIT, 
 						DEFAULT_FRAME_STACK_LIMIT, 
@@ -430,7 +431,7 @@ impl ModuleInstanceInterface for ModuleInstance {
 
 	fn execute_export(&self, name: &str, params: ExecutionParams) -> Result<Option<RuntimeValue>, Error> {
 		let index = self.exports.get(name)
-			.ok_or(Error::Function(format!("missing exports with name {}", name)))
+			.ok_or(Error::Function(format!("missing executable export with name {}", name)))
 			.and_then(|l| l.iter()
 				.find(|i| match i {
 					&&Internal::Function(_) => true,
@@ -447,12 +448,12 @@ impl ModuleInstanceInterface for ModuleInstance {
 
 	fn export_entry<'a>(&self, name: &str, required_type: &ExportEntryType) -> Result<Internal, Error> {
 		self.exports.get(name)
-			.ok_or(Error::Function(format!("missing exports with name {}", name)))
+			.ok_or(Error::Function(format!("missing export entry with name {}", name)))
 			.and_then(|l| l.iter()
 				.find(|i| match required_type {
 					&ExportEntryType::Any => true,
 					&ExportEntryType::Global(global_type) => match i {
-						&&Internal::Global(global_index) => self.global(ItemIndex::IndexSpace(global_index), Some(global_type)).map(|_| true).unwrap_or(false),
+						&&Internal::Global(global_index) => self.global(ItemIndex::IndexSpace(global_index), Some(global_type), None).map(|_| true).unwrap_or(false),
 						_ => false,
 					},
 					&ExportEntryType::Function(ref required_type) => match i {
@@ -493,7 +494,7 @@ impl ModuleInstanceInterface for ModuleInstance {
 		}
 	}
 
-	fn global(&self, index: ItemIndex, variable_type: Option<VariableType>) -> Result<Arc<VariableInstance>, Error> {
+	fn global<'a>(&self, index: ItemIndex, variable_type: Option<VariableType>, externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>) -> Result<Arc<VariableInstance>, Error> {
 		match self.imports.parse_global_index(index) {
 			ItemIndex::IndexSpace(_) => unreachable!("parse_global_index resolves IndexSpace option"),
 			ItemIndex::Internal(index) => self.globals.get(index as usize).cloned()
@@ -502,7 +503,7 @@ impl ModuleInstanceInterface for ModuleInstance {
 				.ok_or(Error::Global(format!("trying to access external global with index {} in module without import section", index)))
 				.and_then(|s| s.entries().get(index as usize)
 					.ok_or(Error::Global(format!("trying to access external global with index {} in module with {}-entries import section", index, s.entries().len()))))
-				.and_then(|e| self.imports.global(None, e, variable_type)),
+				.and_then(|e| self.imports.global(externals, e, variable_type)),
 		}
 	}
 

src/interpreter/runner.rs

@@ -477,7 +477,7 @@ impl Interpreter {
 
 	fn run_get_global<'a>(context: &mut FunctionContext, index: u32) -> Result<InstructionOutcome<'a>, Error> {
 		context.module()
-			.global(ItemIndex::IndexSpace(index), None)
+			.global(ItemIndex::IndexSpace(index), None, Some(context.externals))
 			.and_then(|g| context.value_stack_mut().push(g.get()))
 			.map(|_| InstructionOutcome::RunNextInstruction)
 	}
@@ -486,7 +486,7 @@ impl Interpreter {
 		context
 			.value_stack_mut()
 			.pop()
-			.and_then(|v| context.module().global(ItemIndex::IndexSpace(index), None).and_then(|g| g.set(v)))
+			.and_then(|v| context.module().global(ItemIndex::IndexSpace(index), None, Some(context.externals)).and_then(|g| g.set(v)))
 			.map(|_| InstructionOutcome::RunNextInstruction)
 	}
 

src/interpreter/table.rs

@@ -12,7 +12,12 @@ pub struct TableInstance {
 	/// Table variables type.
 	variable_type: VariableType,
 	/// Table memory buffer.
-	buffer: RwLock<Vec<VariableInstance>>,
+	buffer: RwLock<Vec<TableElement>>,
+}
+
+/// Table element. Cloneable wrapper around VariableInstance.
+struct TableElement {
+	pub var: VariableInstance,
 }
 
 impl TableInstance {
@@ -24,7 +29,7 @@ impl TableInstance {
 		Ok(Arc::new(TableInstance {
 			variable_type: variable_type,
 			buffer: RwLock::new(
-				vec![VariableInstance::new(true, variable_type, RuntimeValue::Null)?; table_type.limits().initial() as usize]
+				vec![TableElement::new(VariableInstance::new(true, variable_type, RuntimeValue::Null)?); table_type.limits().initial() as usize]
 			),
 		}))
 	}
@@ -39,7 +44,7 @@ impl TableInstance {
 		let buffer = self.buffer.read();
 		let buffer_len = buffer.len();
 		buffer.get(offset as usize)
-			.map(|v| v.get())
+			.map(|v| v.var.get())
 			.ok_or(Error::Table(format!("trying to read table item with index {} when there are only {} items", offset, buffer_len)))
 	}
 
@@ -61,6 +66,21 @@ impl TableInstance {
 		let buffer_len = buffer.len();
 		buffer.get_mut(offset as usize)
 			.ok_or(Error::Table(format!("trying to update table item with index {} when there are only {} items", offset, buffer_len)))
-			.and_then(|v| v.set(value))
+			.and_then(|v| v.var.set(value))
+	}
+}
+
+impl TableElement {
+	pub fn new(var: VariableInstance) -> Self {
+		TableElement {
+			var: var,
+		}
+	}
+}
+
+impl Clone for TableElement {
+	fn clone(&self) -> Self {
+		TableElement::new(VariableInstance::new(self.var.is_mutable(), self.var.variable_type(), self.var.get())
+			.expect("it only fails when variable_type() != passed variable value; both are read from already constructed var; qed"))
 	}
 }

src/interpreter/tests/basics.rs

@@ -1,16 +1,18 @@
 ///! Basic tests for instructions/constructions, missing in wabt tests
 
 use std::sync::{Arc, Weak};
+use std::collections::HashMap;
 use builder::module;
 use elements::{ExportEntry, Internal, ImportEntry, External, GlobalEntry, GlobalType,
 	InitExpr, ValueType, BlockType, Opcodes, Opcode, FunctionType};
 use interpreter::Error;
-use interpreter::env_native::{env_native_module, UserFunctions, UserFunctionExecutor, UserFunctionDescriptor};
+use interpreter::env_native::{env_native_module, UserDefinedElements, UserFunctionExecutor, UserFunctionDescriptor};
 use interpreter::memory::MemoryInstance;
 use interpreter::module::{ModuleInstance, ModuleInstanceInterface, CallerContext, ItemIndex, ExecutionParams, ExportEntryType, FunctionSignature};
 use interpreter::program::ProgramInstance;
 use interpreter::validator::{FunctionValidationContext, Validator};
-use interpreter::value::RuntimeValue;
+use interpreter::value::{RuntimeValue, TryInto};
+use interpreter::variable::{VariableInstance, ExternalVariableValue, VariableType};
 
 #[test]
 fn import_function() {
@@ -115,6 +117,24 @@ const SIGNATURES: &'static [UserFunctionDescriptor] = &[
 	),
 ];
 
+const NO_SIGNATURES: &'static [UserFunctionDescriptor] = &[];
+
+// 'external' variable
+struct MeasuredVariable {
+	pub val: i32,
+}
+
+impl ExternalVariableValue for MeasuredVariable {
+	fn get(&self) -> RuntimeValue {
+		RuntimeValue::I32(self.val)
+	}
+
+	fn set(&mut self, val: RuntimeValue) -> Result<(), Error> {
+		self.val = val.try_into()?;
+		Ok(())
+	}
+}
+
 // user function executor
 struct FunctionExecutor {
 	pub memory: Arc<MemoryInstance>,
@@ -152,7 +172,7 @@ impl UserFunctionExecutor for FunctionExecutor {
 }
 
 #[test]
-fn single_program_different_modules() {
+fn native_env_function() {
 	// create new program
 	let program = ProgramInstance::new().unwrap();
 	// => env module is created
@@ -166,8 +186,9 @@ fn single_program_different_modules() {
 		values: Vec::new(),
 	};
 	{
-		let functions: UserFunctions = UserFunctions {
-			executor: &mut executor,
+		let functions: UserDefinedElements = UserDefinedElements {
+			executor: Some(&mut executor),
+			globals: HashMap::new(),
 			functions: ::std::borrow::Cow::from(SIGNATURES),
 		};
 		let native_env_instance = Arc::new(env_native_module(env_instance, functions).unwrap());
@@ -210,6 +231,57 @@ fn single_program_different_modules() {
 	assert_eq!(executor.values, vec![7, 57, 42]);
 }
 
+#[test]
+fn native_env_global() {
+	// module constructor
+	let module_constructor = |elements| {
+		let program = ProgramInstance::new().unwrap();
+		let env_instance = program.module("env").unwrap();
+		let native_env_instance = Arc::new(env_native_module(env_instance.clone(), elements).unwrap());
+		let params = ExecutionParams::with_external("env".into(), native_env_instance);
+
+		let module = module()
+			.with_import(ImportEntry::new("env".into(), "ext_global".into(), External::Global(GlobalType::new(ValueType::I32, false))))
+			.function()
+				.signature().return_type().i32().build()
+				.body().with_opcodes(Opcodes::new(vec![
+					Opcode::GetGlobal(0),
+					Opcode::End,
+				])).build()
+				.build()
+			.build();
+		program.add_module("main", module, Some(&params.externals))?
+			.execute_index(0, params.clone())
+	};
+
+	// try to add module, exporting non-existant env' variable => error
+	{
+		assert!(module_constructor(UserDefinedElements {
+			executor: None,
+			globals: HashMap::new(),
+			functions: ::std::borrow::Cow::from(NO_SIGNATURES),
+		}).is_err());
+	}
+
+	// now add simple variable natively => ok
+	{
+		assert_eq!(module_constructor(UserDefinedElements {
+			executor: None,
+			globals: vec![("ext_global".into(), Arc::new(VariableInstance::new(false, VariableType::I32, RuntimeValue::I32(777)).unwrap()))].into_iter().collect(),
+			functions: ::std::borrow::Cow::from(NO_SIGNATURES),
+		}).unwrap().unwrap(), RuntimeValue::I32(777));
+	}
+
+	// now add 'getter+setter' variable natively => ok
+	{
+		assert_eq!(module_constructor(UserDefinedElements {
+			executor: None,
+			globals: vec![("ext_global".into(), Arc::new(VariableInstance::new_external_global(false, VariableType::I32, Box::new(MeasuredVariable { val: 345 })).unwrap()))].into_iter().collect(),
+			functions: ::std::borrow::Cow::from(NO_SIGNATURES),
+		}).unwrap().unwrap(), RuntimeValue::I32(345));
+	}
+}
+
 #[test]
 fn import_env_mutable_global() {
 	let program = ProgramInstance::new().unwrap();
@@ -228,8 +300,9 @@ fn env_native_export_entry_type_check() {
 		memory: program.module("env").unwrap().memory(ItemIndex::Internal(0)).unwrap(),
 		values: Vec::new(),
 	};
-	let native_env_instance = Arc::new(env_native_module(program.module("env").unwrap(), UserFunctions {
-		executor: &mut function_executor,
+	let native_env_instance = Arc::new(env_native_module(program.module("env").unwrap(), UserDefinedElements {
+		executor: Some(&mut function_executor),
+		globals: HashMap::new(),
 		functions: ::std::borrow::Cow::from(SIGNATURES),
 	}).unwrap());
 
@@ -242,7 +315,7 @@ fn env_native_export_entry_type_check() {
 #[test]
 fn if_else_with_return_type_validation() {
 	let module_instance = ModuleInstance::new(Weak::default(), "test".into(), module().build()).unwrap();
-	let mut context = FunctionValidationContext::new(&module_instance, &[], 1024, 1024, FunctionSignature::Module(&FunctionType::default()));
+	let mut context = FunctionValidationContext::new(&module_instance, None, &[], 1024, 1024, FunctionSignature::Module(&FunctionType::default()));
 
 	Validator::validate_function(&mut context, BlockType::NoResult, &[
 		Opcode::I32Const(1),

src/interpreter/validator.rs

@@ -1,4 +1,5 @@
 use std::u32;
+use std::sync::Arc;
 use std::collections::HashMap;
 use elements::{Opcode, BlockType, ValueType};
 use interpreter::Error;
@@ -14,6 +15,8 @@ const NATURAL_ALIGNMENT: u32 = 0xFFFFFFFF;
 pub struct FunctionValidationContext<'a> {
 	/// Wasm module instance (in process of instantiation).
 	module_instance: &'a ModuleInstance,
+	/// Native externals.
+	externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>,
 	/// Current instruction position.
 	position: usize,
 	/// Local variables.
@@ -569,6 +572,7 @@ impl Validator {
 impl<'a> FunctionValidationContext<'a> {
 	pub fn new(
 		module_instance: &'a ModuleInstance, 
+		externals: Option<&'a HashMap<String, Arc<ModuleInstanceInterface + 'a>>>,
 		locals: &'a [ValueType], 
 		value_stack_limit: usize, 
 		frame_stack_limit: usize, 
@@ -576,6 +580,7 @@ impl<'a> FunctionValidationContext<'a> {
 	) -> Self {
 		FunctionValidationContext {
 			module_instance: module_instance,
+			externals: externals,
 			position: 0,
 			locals: locals,
 			value_stack: StackWithLimit::with_limit(value_stack_limit),
@@ -688,7 +693,7 @@ impl<'a> FunctionValidationContext<'a> {
 
 	pub fn require_global(&self, idx: u32, mutability: Option<bool>) -> Result<StackValueType, Error> {
 		self.module_instance
-			.global(ItemIndex::IndexSpace(idx), None)
+			.global(ItemIndex::IndexSpace(idx), None, self.externals.clone())
 			.and_then(|g| match mutability {
 				Some(true) if !g.is_mutable() => Err(Error::Validation(format!("Expected global {} to be mutable", idx))),
 				Some(false) if g.is_mutable() => Err(Error::Validation(format!("Expected global {} to be immutable", idx))),

src/interpreter/variable.rs

@@ -1,3 +1,4 @@
+use std::fmt;
 use parking_lot::RwLock;
 use elements::{GlobalType, ValueType, TableElementType};
 use interpreter::Error;
@@ -18,6 +19,14 @@ pub enum VariableType {
 	F64,
 }
 
+/// Externally stored variable value.
+pub trait ExternalVariableValue {
+	/// Get variable value.
+	fn get(&self) -> RuntimeValue;
+	/// Set variable value.
+	fn set(&mut self, value: RuntimeValue) -> Result<(), Error>;
+}
+
 /// Variable instance.
 #[derive(Debug)]
 pub struct VariableInstance {
@@ -26,7 +35,15 @@ pub struct VariableInstance {
 	/// Variable type.
 	variable_type: VariableType,
 	/// Global value.
-	value: RwLock<RuntimeValue>,
+	value: RwLock<VariableValue>,
+}
+
+/// Enum variable value.
+enum VariableValue {
+	/// Internal value.
+	Internal(RuntimeValue),
+	/// External value.
+	External(Box<ExternalVariableValue>),
 }
 
 impl VariableInstance {
@@ -40,7 +57,7 @@ impl VariableInstance {
 		Ok(VariableInstance {
 			is_mutable: is_mutable,
 			variable_type: variable_type,
-			value: RwLock::new(value),
+			value: RwLock::new(VariableValue::Internal(value)),
 		})
 	}
 
@@ -49,6 +66,21 @@ impl VariableInstance {
 		Self::new(global_type.is_mutable(), global_type.content_type().into(), value)
 	}
 
+	/// New global with externally stored value.
+	pub fn new_external_global(is_mutable: bool, variable_type: VariableType, value: Box<ExternalVariableValue>) -> Result<Self, Error> {
+		// TODO: there is nothing about null value in specification + there is nothing about initializing missing table elements? => runtime check for nulls
+		let current_value = value.get();
+		if !current_value.is_null() && current_value.variable_type() != Some(variable_type) {
+			return Err(Error::Variable(format!("trying to initialize variable of type {:?} with value of type {:?}", variable_type, current_value.variable_type())));
+		}
+
+		Ok(VariableInstance {
+			is_mutable: is_mutable,
+			variable_type: variable_type,
+			value: RwLock::new(VariableValue::External(value)),
+		})
+	}
+
 	/// Is mutable
 	pub fn is_mutable(&self) -> bool {
 		self.is_mutable
@@ -61,7 +93,7 @@ impl VariableInstance {
 
 	/// Get the value of the variable instance
 	pub fn get(&self) -> RuntimeValue {
-		self.value.read().clone()
+		self.value.read().get()
 	}
 
 	/// Set the value of the variable instance
@@ -73,17 +105,25 @@ impl VariableInstance {
 			return Err(Error::Variable(format!("trying to update variable of type {:?} with value of type {:?}", self.variable_type, value.variable_type())));
 		}
 
-		*self.value.write() = value;
-		Ok(())
+		self.value.write().set(value)
 	}
 }
 
-impl Clone for VariableInstance {
-	fn clone(&self) -> Self {
-		VariableInstance {
-			is_mutable: self.is_mutable,
-			variable_type: self.variable_type,
-			value: RwLock::new(self.value.read().clone()),
+impl VariableValue {
+	fn get(&self) -> RuntimeValue {
+		match *self {
+			VariableValue::Internal(ref value) => value.clone(),
+			VariableValue::External(ref value) => value.get(),
+		}
+	}
+
+	fn set(&mut self, new_value: RuntimeValue) -> Result<(), Error> {
+		match *self {
+			VariableValue::Internal(ref mut value) => {
+				*value = new_value;
+				Ok(())
+			},
+			VariableValue::External(ref mut value) => value.set(new_value),
 		}
 	}
 }
@@ -106,3 +146,12 @@ impl From<TableElementType> for VariableType {
 		}
 	}
 }
+
+impl fmt::Debug for VariableValue {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		match *self {
+			VariableValue::Internal(ref value) => write!(f, "Variable.Internal({:?})", value),
+			VariableValue::External(ref value) => write!(f, "Variable.External({:?})", value.get()),
+		}
+	}
+}