Backward compatibility and tracing

.gitignore

@@ -4,4 +4,3 @@ target
 .DS_Store
 .idea
 .vscode
-*~

BENCHMARKS.md

@@ -1,91 +0,0 @@
-# Benchmarks
-
-## Table of Contents
-
-- [Benchmark Results](#benchmark-results)
-    - [coremark, instrumented](#coremark,-instrumented)
-    - [recursive_ok, instrumented](#recursive_ok,-instrumented)
-    - [fibonacci_recursive, instrumented](#fibonacci_recursive,-instrumented)
-    - [factorial_recursive, instrumented](#factorial_recursive,-instrumented)
-    - [count_until, instrumented](#count_until,-instrumented)
-    - [memory_vec_add, instrumented](#memory_vec_add,-instrumented)
-    - [wasm_kernel::tiny_keccak, instrumented](#wasm_kernel::tiny_keccak,-instrumented)
-    - [global_bump, instrumented](#global_bump,-instrumented)
-
-## Instrumented Modules sizes
-
-| fixture                      |  original size   | gas metered/host fn | gas metered/mut global | size diff |
-|------------------------------|------------------|---------------------|------------------------|-----------|
-| recursive_ok.wat             |             0 kb |         0 kb (137%) |            0 kb (177%) |      +29% |
-| count_until.wat              |             0 kb |         0 kb (125%) |            0 kb (153%) |      +21% |
-| global_bump.wat              |             0 kb |         0 kb (123%) |            0 kb (145%) |      +18% |
-| memory-vec-add.wat           |             0 kb |         0 kb (116%) |            0 kb (134%) |      +15% |
-| factorial.wat                |             0 kb |         0 kb (125%) |            0 kb (145%) |      +15% |
-| fibonacci.wat                |             0 kb |         0 kb (121%) |            0 kb (134%) |      +10% |
-| contract_terminate.wasm      |             1 kb |         1 kb (110%) |            1 kb (112%) |       +2% |
-| coremark_minimal.wasm        |             7 kb |         8 kb (114%) |            8 kb (115%) |       +0% |
-| trait_erc20.wasm             |            10 kb |        11 kb (108%) |           11 kb (108%) |       +0% |
-| rand_extension.wasm          |             4 kb |         5 kb (109%) |            5 kb (109%) |       +0% |
-| multisig.wasm                |            27 kb |        30 kb (110%) |           30 kb (110%) |       +0% |
-| wasm_kernel.wasm             |           779 kb |       787 kb (100%) |          795 kb (101%) |       +0% |
-| many_blocks.wasm             |          1023 kb |      2389 kb (233%) |         2389 kb (233%) |       +0% |
-| contract_transfer.wasm       |             7 kb |         8 kb (113%) |            8 kb (113%) |       +0% |
-| erc1155.wasm                 |            26 kb |        29 kb (111%) |           29 kb (111%) |       +0% |
-| erc20.wasm                   |             9 kb |        10 kb (108%) |           10 kb (109%) |       +0% |
-| dns.wasm                     |            10 kb |        11 kb (108%) |           11 kb (108%) |       +0% |
-| proxy.wasm                   |             3 kb |         4 kb (108%) |            4 kb (109%) |       +0% |
-| erc721.wasm                  |            13 kb |        14 kb (108%) |           14 kb (108%) |       +0% |
-
-## Benchmark Results
-
-### coremark, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `20.81 s` (✅ **1.00x**)                 | `20.20 s` (✅ **1.03x faster**)            |
-
-### recursive_ok, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `367.11 us` (✅ **1.00x**)               | `585.39 us` (❌ *1.59x slower*)            |
-
-### fibonacci_recursive, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `9.15 us` (✅ **1.00x**)                 | `13.56 us` (❌ *1.48x slower*)             |
-
-### factorial_recursive, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `1.50 us` (✅ **1.00x**)                 | `1.98 us` (❌ *1.32x slower*)              |
-
-### count_until, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `5.03 ms` (✅ **1.00x**)                 | `8.13 ms` (❌ *1.62x slower*)              |
-
-### memory_vec_add, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `6.21 ms` (✅ **1.00x**)                 | `8.45 ms` (❌ *1.36x slower*)              |
-
-### wasm_kernel::tiny_keccak, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `925.22 us` (✅ **1.00x**)               | `1.08 ms` (❌ *1.17x slower*)              |
-
-### global_bump, instrumented
-
-|        | `with host_function::Injector`          | `with mutable_global::Injector`           |
-|:-------|:----------------------------------------|:----------------------------------------- |
-|        | `3.79 ms` (✅ **1.00x**)                 | `7.03 ms` (❌ *1.86x slower*)              |
-
----
-Made with [criterion-table](https://github.com/nu11ptr/criterion-table)
-

CHANGELOG.md

@@ -16,26 +16,7 @@ The interface provided to smart contracts will adhere to semver with one excepti
 major version bumps will be backwards compatible with regard to already deployed contracts.
 In other words: Upgrading this pallet will not break pre-existing contracts.
 
-## [Unreleased]
-
-### New
-
-- Add new gas metering method: mutable global + local gas function
-[#34](https://github.com/paritytech/wasm-instrument/pull/34)
-- Account for locals initialization costs
-[#38](https://github.com/paritytech/wasm-instrument/pull/38)
-
-## [v0.3.0]
-
-### Changed
-
-- Use 64bit arithmetic for per-block gas counter
-[#30](https://github.com/paritytech/wasm-instrument/pull/30)
-
 ## [v0.2.0] 2022-06-06
-
-### Changed
-
 - Adjust debug information (if already parsed) when injecting gas metering
 [#16](https://github.com/paritytech/wasm-instrument/pull/16)
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "wasm-instrument"
-version = "0.4.0"
+version = "0.2.0"
 edition = "2021"
 rust-version = "1.56.1"
 authors = ["Parity Technologies <admin@parity.io>"]
@@ -22,22 +22,21 @@ codegen-units = 1
 
 [dependencies]
 parity-wasm = { version = "0.45", default-features = false }
+log = { version = "0.4.8", default-features = false, optional = true }
+test-log = { version = "0.2", optional = true }
+env_logger = { version = "0.9", optional = true }
 
 [dev-dependencies]
 binaryen = "0.12"
-criterion = "0.4"
+criterion = "0.3"
 diff = "0.1"
-pretty_assertions = "1"
 rand = "0.8"
 wat = "1"
-wasmparser = "0.95"
+wasmparser = "0.87"
 wasmprinter = "0.2"
-wasmi = "0.20"
 
 [features]
 default = ["std"]
 std = ["parity-wasm/std"]
 sign_ext = ["parity-wasm/sign_ext"]
-
+trace-log = ["dep:log", "dep:test-log", "dep:env_logger"]
-[lib]
-bench = false

benches/benches.rs

@@ -1,23 +1,20 @@
 use criterion::{
-	criterion_group, criterion_main, measurement::Measurement, Bencher, BenchmarkGroup, Criterion,
+	criterion_group, criterion_main, measurement::Measurement, BenchmarkGroup, Criterion,
 	Throughput,
 };
 use std::{
 	fs::{read, read_dir},
 	path::PathBuf,
-	slice,
 };
 use wasm_instrument::{
-	gas_metering::{self, host_function, mutable_global, Backend, ConstantCostRules},
+	gas_metering, inject_stack_limiter,
-	inject_stack_limiter,
+	parity_wasm::{deserialize_buffer, elements::Module},
-	parity_wasm::{deserialize_buffer, elements::Module, serialize},
 };
 
 fn fixture_dir() -> PathBuf {
 	let mut path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
 	path.push("benches");
 	path.push("fixtures");
-	path.push("wasm");
 	path
 }
 
@@ -39,12 +36,7 @@ where
 fn gas_metering(c: &mut Criterion) {
 	let mut group = c.benchmark_group("Gas Metering");
 	any_fixture(&mut group, |module| {
-		gas_metering::inject(
+		gas_metering::inject(module, &gas_metering::ConstantCostRules::default(), "env").unwrap();
-			module,
-			host_function::Injector::new("env", "gas"),
-			&ConstantCostRules::default(),
-		)
-		.unwrap();
 	});
 }
 
@@ -55,520 +47,5 @@ fn stack_height_limiter(c: &mut Criterion) {
 	});
 }
 
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
-use wasmi::{
-	self,
-	core::{Pages, Value, F32},
-	Caller, Config, Engine, Extern, Func, Instance, Linker, Memory, StackLimits, Store,
-};
-fn prepare_module<P: Backend>(backend: P, input: &[u8]) -> (wasmi::Module, Store<u64>) {
-	let module = deserialize_buffer(input).unwrap();
-	let instrumented_module =
-		gas_metering::inject(module, backend, &ConstantCostRules::default()).unwrap();
-	let input = serialize(instrumented_module).unwrap();
-	// Prepare wasmi
-	let engine = Engine::new(&bench_config());
-	let module = wasmi::Module::new(&engine, &mut &input[..]).unwrap();
-	// Init host state with maximum gas_left
-	let store = Store::new(&engine, u64::MAX);
-
-	(module, store)
-}
-
-fn add_gas_host_func(linker: &mut Linker<u64>, store: &mut Store<u64>) {
-	// Create gas host function
-	let host_gas = Func::wrap(store, |mut caller: Caller<'_, u64>, param: u64| {
-		*caller.host_data_mut() -= param;
-	});
-	// Link the gas host function
-	linker.define("env", "gas", host_gas).unwrap();
-}
-
-fn add_gas_left_global(instance: &Instance, mut store: Store<u64>) -> Store<u64> {
-	instance
-		.get_export(&mut store, "gas_left")
-		.and_then(Extern::into_global)
-		.unwrap()
-		.set(&mut store, Value::I64(-1i64)) // the same as u64::MAX
-		.unwrap();
-	store
-}
-
-fn gas_metered_coremark(c: &mut Criterion) {
-	let mut group = c.benchmark_group("coremark, instrumented");
-	// Benchmark host_function::Injector
-	let wasm_filename = "coremark_minimal.wasm";
-	let bytes = read(fixture_dir().join(wasm_filename)).unwrap();
-	group.bench_function("with host_function::Injector", |bench| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &bytes);
-		// Link the host functions with the imported ones
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		// Create clock_ms host function.
-		let host_clock_ms = Func::wrap(&mut store, || {
-			SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_millis() as u64
-		});
-		// Link the time measurer for the coremark wasm
-		linker.define("env", "clock_ms", host_clock_ms).unwrap();
-
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-
-		bench.iter(|| {
-			let run = instance
-				.get_export(&mut store, "run")
-				.and_then(Extern::into_func)
-				.unwrap()
-				.typed::<(), F32>(&mut store)
-				.unwrap();
-			// Call the wasm!
-			run.call(&mut store, ()).unwrap();
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |bench| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &bytes);
-		// Add the gas_left mutable global
-		let mut linker = <Linker<u64>>::new();
-		// Create clock_ms host function.
-		let host_clock_ms = Func::wrap(&mut store, || {
-			SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_millis() as u64
-		});
-		// Link the time measurer for the coremark wasm
-		linker.define("env", "clock_ms", host_clock_ms).unwrap();
-
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-
-		bench.iter(|| {
-			let run = instance
-				.get_export(&mut store, "run")
-				.and_then(Extern::into_func)
-				.unwrap()
-				.typed::<(), F32>(&mut store)
-				.unwrap();
-			// Call the wasm!
-			run.call(&mut store, ()).unwrap();
-		})
-	});
-}
-
-/// Converts the `.wat` encoded `bytes` into `.wasm` encoded bytes.
-pub fn wat2wasm(bytes: &[u8]) -> Vec<u8> {
-	wat::parse_bytes(bytes).unwrap().into_owned()
-}
-
-/// Returns a [`Config`] useful for benchmarking.
-fn bench_config() -> Config {
-	let mut config = Config::default();
-	config.set_stack_limits(StackLimits::new(1024, 1024 * 1024, 64 * 1024).unwrap());
-	config
-}
-
-fn gas_metered_recursive_ok(c: &mut Criterion) {
-	let mut group = c.benchmark_group("recursive_ok, instrumented");
-	const RECURSIVE_DEPTH: i32 = 8000;
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/recursive_ok.wat"));
-
-	group.bench_function("with host_function::Injector", |bench| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-
-		let bench_call = instance.get_export(&store, "call").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		bench.iter(|| {
-			bench_call
-				.call(&mut store, &[Value::I32(RECURSIVE_DEPTH)], &mut result)
-				.unwrap();
-			assert_eq!(result, [Value::I32(0)]);
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |bench| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-
-		let bench_call = instance.get_export(&store, "call").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		bench.iter(|| {
-			bench_call
-				.call(&mut store, &[Value::I32(RECURSIVE_DEPTH)], &mut result)
-				.unwrap();
-			assert_eq!(result, [Value::I32(0)]);
-		})
-	});
-}
-
-fn gas_metered_fibonacci_recursive(c: &mut Criterion) {
-	let mut group = c.benchmark_group("fibonacci_recursive, instrumented");
-	const FIBONACCI_REC_N: i64 = 10;
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/fibonacci.wat"));
-
-	group.bench_function("with host_function::Injector", |bench| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-
-		let bench_call = instance
-			.get_export(&store, "fib_recursive")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut result = [Value::I32(0)];
-
-		bench.iter(|| {
-			bench_call
-				.call(&mut store, &[Value::I64(FIBONACCI_REC_N)], &mut result)
-				.unwrap();
-		});
-	});
-
-	group.bench_function("with mutable_global::Injector", |bench| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-
-		let bench_call = instance
-			.get_export(&store, "fib_recursive")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut result = [Value::I32(0)];
-
-		bench.iter(|| {
-			bench_call
-				.call(&mut store, &[Value::I64(FIBONACCI_REC_N)], &mut result)
-				.unwrap();
-		});
-	});
-}
-
-fn gas_metered_fac_recursive(c: &mut Criterion) {
-	let mut group = c.benchmark_group("factorial_recursive, instrumented");
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/factorial.wat"));
-
-	group.bench_function("with host_function::Injector", |b| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let fac = instance
-			.get_export(&store, "recursive_factorial")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut result = [Value::I64(0)];
-
-		b.iter(|| {
-			fac.call(&mut store, &[Value::I64(25)], &mut result).unwrap();
-			assert_eq!(result, [Value::I64(7034535277573963776)]);
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |b| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-		let fac = instance
-			.get_export(&store, "recursive_factorial")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut result = [Value::I64(0)];
-
-		b.iter(|| {
-			fac.call(&mut store, &[Value::I64(25)], &mut result).unwrap();
-			assert_eq!(result, [Value::I64(7034535277573963776)]);
-		})
-	});
-}
-
-fn gas_metered_count_until(c: &mut Criterion) {
-	const COUNT_UNTIL: i32 = 100_000;
-	let mut group = c.benchmark_group("count_until, instrumented");
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/count_until.wat"));
-
-	group.bench_function("with host_function::Injector", |b| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let count_until =
-			instance.get_export(&store, "count_until").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		b.iter(|| {
-			count_until.call(&mut store, &[Value::I32(COUNT_UNTIL)], &mut result).unwrap();
-			assert_eq!(result, [Value::I32(COUNT_UNTIL)]);
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |b| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-		let count_until =
-			instance.get_export(&store, "count_until").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		b.iter(|| {
-			count_until.call(&mut store, &[Value::I32(COUNT_UNTIL)], &mut result).unwrap();
-			assert_eq!(result, [Value::I32(COUNT_UNTIL)]);
-		})
-	});
-}
-
-fn gas_metered_vec_add(c: &mut Criterion) {
-	fn test_for<A, B>(
-		b: &mut Bencher,
-		vec_add: Func,
-		mut store: &mut Store<u64>,
-		mem: Memory,
-		len: usize,
-		vec_a: A,
-		vec_b: B,
-	) where
-		A: IntoIterator<Item = i32>,
-		B: IntoIterator<Item = i32>,
-	{
-		use core::mem::size_of;
-
-		let ptr_result = 10;
-		let len_result = len * size_of::<i64>();
-		let ptr_a = ptr_result + len_result;
-		let len_a = len * size_of::<i32>();
-		let ptr_b = ptr_a + len_a;
-
-		// Reset `result` buffer to zeros:
-		mem.data_mut(&mut store)[ptr_result..ptr_result + (len * size_of::<i32>())].fill(0);
-		// Initialize `a` buffer:
-		for (n, a) in vec_a.into_iter().take(len).enumerate() {
-			mem.write(&mut store, ptr_a + (n * size_of::<i32>()), &a.to_le_bytes()).unwrap();
-		}
-		// Initialize `b` buffer:
-		for (n, b) in vec_b.into_iter().take(len).enumerate() {
-			mem.write(&mut store, ptr_b + (n * size_of::<i32>()), &b.to_le_bytes()).unwrap();
-		}
-
-		// Prepare parameters and all Wasm `vec_add`:
-		let params = [
-			Value::I32(ptr_result as i32),
-			Value::I32(ptr_a as i32),
-			Value::I32(ptr_b as i32),
-			Value::I32(len as i32),
-		];
-		b.iter(|| {
-			vec_add.call(&mut store, &params, &mut []).unwrap();
-		});
-
-		// Validate the result buffer:
-		for n in 0..len {
-			let mut buffer4 = [0x00; 4];
-			let mut buffer8 = [0x00; 8];
-			let a = {
-				mem.read(&store, ptr_a + (n * size_of::<i32>()), &mut buffer4).unwrap();
-				i32::from_le_bytes(buffer4)
-			};
-			let b = {
-				mem.read(&store, ptr_b + (n * size_of::<i32>()), &mut buffer4).unwrap();
-				i32::from_le_bytes(buffer4)
-			};
-			let actual_result = {
-				mem.read(&store, ptr_result + (n * size_of::<i64>()), &mut buffer8).unwrap();
-				i64::from_le_bytes(buffer8)
-			};
-			let expected_result = (a as i64) + (b as i64);
-			assert_eq!(
-				expected_result, actual_result,
-				"given a = {a} and b = {b}, results diverge at index {n}"
-			);
-		}
-	}
-
-	let mut group = c.benchmark_group("memory_vec_add, instrumented");
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/memory-vec-add.wat"));
-	const LEN: usize = 100_000;
-
-	group.bench_function("with host_function::Injector", |b| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let vec_add = instance.get_export(&store, "vec_add").and_then(Extern::into_func).unwrap();
-		let mem = instance.get_export(&store, "mem").and_then(Extern::into_memory).unwrap();
-		mem.grow(&mut store, Pages::new(25).unwrap()).unwrap();
-		test_for(
-			b,
-			vec_add,
-			&mut store,
-			mem,
-			LEN,
-			(0..LEN).map(|i| (i * i) as i32),
-			(0..LEN).map(|i| (i * 10) as i32),
-		)
-	});
-
-	group.bench_function("with mutable_global::Injector", |b| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-		let vec_add = instance.get_export(&store, "vec_add").and_then(Extern::into_func).unwrap();
-		let mem = instance.get_export(&store, "mem").and_then(Extern::into_memory).unwrap();
-		mem.grow(&mut store, Pages::new(25).unwrap()).unwrap();
-		test_for(
-			b,
-			vec_add,
-			&mut store,
-			mem,
-			LEN,
-			(0..LEN).map(|i| (i * i) as i32),
-			(0..LEN).map(|i| (i * 10) as i32),
-		)
-	});
-}
-
-fn gas_metered_tiny_keccak(c: &mut Criterion) {
-	let mut group = c.benchmark_group("wasm_kernel::tiny_keccak, instrumented");
-	let wasm_filename = "wasm_kernel.wasm";
-	let wasm_bytes = read(fixture_dir().join(wasm_filename)).unwrap();
-
-	group.bench_function("with host_function::Injector", |b| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let prepare = instance
-			.get_export(&store, "prepare_tiny_keccak")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let keccak = instance
-			.get_export(&store, "bench_tiny_keccak")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut test_data_ptr = Value::I32(0);
-		prepare.call(&mut store, &[], slice::from_mut(&mut test_data_ptr)).unwrap();
-		b.iter(|| {
-			keccak.call(&mut store, slice::from_ref(&test_data_ptr), &mut []).unwrap();
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |b| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-		let prepare = instance
-			.get_export(&store, "prepare_tiny_keccak")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let keccak = instance
-			.get_export(&store, "bench_tiny_keccak")
-			.and_then(Extern::into_func)
-			.unwrap();
-		let mut test_data_ptr = Value::I32(0);
-		prepare.call(&mut store, &[], slice::from_mut(&mut test_data_ptr)).unwrap();
-		b.iter(|| {
-			keccak.call(&mut store, slice::from_ref(&test_data_ptr), &mut []).unwrap();
-		})
-	});
-}
-
-fn gas_metered_global_bump(c: &mut Criterion) {
-	const BUMP_AMOUNT: i32 = 100_000;
-	let mut group = c.benchmark_group("global_bump, instrumented");
-	let wasm_bytes = wat2wasm(include_bytes!("fixtures/wat/global_bump.wat"));
-
-	group.bench_function("with host_function::Injector", |b| {
-		let backend = host_function::Injector::new("env", "gas");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Link the host function with the imported one
-		let mut linker = <Linker<u64>>::new();
-		add_gas_host_func(&mut linker, &mut store);
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let bump = instance.get_export(&store, "bump").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		b.iter(|| {
-			bump.call(&mut store, &[Value::I32(BUMP_AMOUNT)], &mut result).unwrap();
-			assert_eq!(result, [Value::I32(BUMP_AMOUNT)]);
-		})
-	});
-
-	group.bench_function("with mutable_global::Injector", |b| {
-		let backend = mutable_global::Injector::new("gas_left");
-		let (module, mut store) = prepare_module(backend, &wasm_bytes);
-		// Add the gas_left mutable global
-		let linker = <Linker<u64>>::new();
-		let instance = linker.instantiate(&mut store, &module).unwrap().start(&mut store).unwrap();
-		let mut store = add_gas_left_global(&instance, store);
-		let bump = instance.get_export(&store, "bump").and_then(Extern::into_func).unwrap();
-		let mut result = [Value::I32(0)];
-
-		b.iter(|| {
-			bump.call(&mut store, &[Value::I32(BUMP_AMOUNT)], &mut result).unwrap();
-			assert_eq!(result, [Value::I32(BUMP_AMOUNT)]);
-		})
-	});
-}
-
 criterion_group!(benches, gas_metering, stack_height_limiter);
-criterion_group!(
+criterion_main!(benches);
-	name = coremark;
-	config = Criterion::default()
-		.sample_size(10)
-		.measurement_time(Duration::from_millis(275000))
-		.warm_up_time(Duration::from_millis(1000));
-	targets =
-		 gas_metered_coremark,
-);
-criterion_group!(
-	name = wasmi_fixtures;
-	config = Criterion::default()
-		.sample_size(10)
-		.measurement_time(Duration::from_millis(250000))
-	.warm_up_time(Duration::from_millis(1000));
-	targets =
-		gas_metered_recursive_ok,
-		gas_metered_fibonacci_recursive,
-		gas_metered_fac_recursive,
-		gas_metered_count_until,
-		gas_metered_vec_add,
-		gas_metered_tiny_keccak,
-		gas_metered_global_bump,
-);
-criterion_main!(coremark, wasmi_fixtures);

benches/fixtures/wat/count_until.wat

@@ -1,25 +0,0 @@
-;; Exports a function `count_until` that takes an input `n`.
-;; The exported function counts an integer `n` times and then returns `n`.
-(module
-  (func $count_until (export "count_until") (param $limit i32) (result i32)
-    (local $counter i32)
-    (block
-        (loop
-            (br_if
-                1
-                (i32.eq
-                    (local.tee $counter
-                        (i32.add
-                            (local.get $counter)
-                            (i32.const 1)
-                        )
-                    )
-                    (local.get $limit)
-                )
-            )
-            (br 0)
-        )
-    )
-    (return (local.get $counter))
-  )
-)

benches/fixtures/wat/factorial.wat

@@ -1,35 +0,0 @@
-(module
-    ;; Iterative factorial function, does not use recursion.
-    (func (export "iterative_factorial") (param i64) (result i64)
-        (local i64)
-        (local.set 1 (i64.const 1))
-        (block
-            (br_if 0 (i64.lt_s (local.get 0) (i64.const 2)))
-            (loop
-                (local.set 1 (i64.mul (local.get 1) (local.get 0)))
-                (local.set 0 (i64.add (local.get 0) (i64.const -1)))
-                (br_if 0 (i64.gt_s (local.get 0) (i64.const 1)))
-            )
-        )
-        (local.get 1)
-    )
-
-    ;; Recursive trivial factorial function.
-    (func $rec_fac (export "recursive_factorial") (param i64) (result i64)
-        (if (result i64)
-            (i64.eq (local.get 0) (i64.const 0))
-            (then (i64.const 1))
-            (else
-                (i64.mul
-                    (local.get 0)
-                    (call $rec_fac
-                        (i64.sub
-                            (local.get 0)
-                            (i64.const 1)
-                        )
-                    )
-                )
-            )
-        )
-    )
-)

benches/fixtures/wat/fibonacci.wat

@@ -1,47 +0,0 @@
-(module
-    (func $fib_recursive (export "fib_recursive") (param $N i64) (result i64)
-        (if
-            (i64.le_s (local.get $N) (i64.const 1))
-            (then (return (local.get $N)))
-        )
-        (return
-            (i64.add
-                (call $fib_recursive
-                  (i64.sub (local.get $N) (i64.const 1))
-                )
-                (call $fib_recursive
-                  (i64.sub (local.get $N) (i64.const 2))
-                )
-            )
-        )
-    )
-
-    (func $fib_iterative (export "fib_iterative") (param $N i64) (result i64)
-        (local $n1 i64)
-        (local $n2 i64)
-        (local $tmp i64)
-        (local $i i64)
-        ;; return $N for N <= 1
-        (if
-            (i64.le_s (local.get $N) (i64.const 1))
-            (then (return (local.get $N)))
-        )
-        (local.set $n1 (i64.const 1))
-        (local.set $n2 (i64.const 1))
-        (local.set $i (i64.const 2))
-        ;;since we normally return n2, handle n=1 case specially
-        (loop $again
-            (if
-                (i64.lt_s (local.get $i) (local.get $N))
-                (then
-                    (local.set $tmp (i64.add (local.get $n1) (local.get $n2)))
-                    (local.set $n1 (local.get $n2))
-                    (local.set $n2 (local.get $tmp))
-                    (local.set $i (i64.add (local.get $i) (i64.const 1)))
-                    (br $again)
-                )
-            )
-        )
-        (local.get $n2)
-    )
-)

benches/fixtures/wat/global_bump.wat

@@ -1,27 +0,0 @@
-;; Exports a function `bump` that takes an input `n`.
-;; The exported function bumps a global variable `n` times and then returns it.
-(module
-    (global $g (mut i32) (i32.const 0))
-    (func $bump (export "bump") (param $n i32) (result i32)
-        (global.set $g (i32.const 0))
-        (block $break
-            (loop $continue
-                (br_if ;; if $g == $n then break
-                    $break
-                    (i32.eq
-                        (global.get $g)
-                        (local.get $n)
-                    )
-                )
-                (global.set $g ;; $g += 1
-                    (i32.add
-                        (global.get $g)
-                        (i32.const 1)
-                    )
-                )
-                (br $continue)
-            )
-        )
-        (return (global.get $g))
-    )
-)

benches/fixtures/wat/memory-vec-add.wat

@@ -1,58 +0,0 @@
-;; Exports a function `vec_add` that computes the addition of 2 vectors
-;; of length `len` starting at `ptr_a` and `ptr_b` and stores the result
-;; into a buffer of the same length starting at `ptr_result`.
-(module
-    (memory (export "mem") 1)
-    (func (export "vec_add")
-        (param $ptr_result i32)
-        (param $ptr_a i32)
-        (param $ptr_b i32)
-        (param $len i32)
-        (local $n i32)
-        (block $exit
-            (loop $loop
-                (br_if ;; exit loop if $n == $len
-                    $exit
-                    (i32.eq
-                        (local.get $n)
-                        (local.get $len)
-                    )
-                )
-                (i64.store offset=0 ;; ptr_result[n] = ptr_a[n] + ptr_b[n]
-                    (i32.add
-                        (local.get $ptr_result)
-                        (i32.mul
-                            (local.get $n)
-                            (i32.const 8)
-                        )
-                    )
-                    (i64.add
-                        (i64.load32_s offset=0 ;; load ptr_a[n]
-                            (i32.add
-                                (local.get $ptr_a)
-                                (i32.mul
-                                    (local.get $n)
-                                    (i32.const 4)
-                                )
-                            )
-                        )
-                        (i64.load32_s offset=0 ;; load ptr_b[n]
-                            (i32.add
-                                (local.get $ptr_b)
-                                (i32.mul
-                                    (local.get $n)
-                                    (i32.const 4)
-                                )
-                            )
-                        )
-                    )
-                )
-                (local.set $n ;; increment n
-                    (i32.add (local.get $n) (i32.const 1))
-                 )
-                (br $loop) ;; continue loop
-            )
-        )
-        (return)
-    )
-)

benches/fixtures/wat/recursive_ok.wat

@@ -1,22 +0,0 @@
-;; Exports a function `call` that takes an input `n`.
-;; The exported function calls itself `n` times.
-(module
-    (func $call (export "call") (param $n i32) (result i32)
-        (if (result i32)
-            (local.get $n)
-            (then
-                (return
-                    (call $call
-                        (i32.sub
-                            (local.get $n)
-                            (i32.const 1)
-                        )
-                    )
-                )
-            )
-            (else
-                (return (local.get $n))
-            )
-        )
-    )
-)

src/gas_metering/backend.rs

@@ -1,138 +0,0 @@
-//! Provides backends for the gas metering instrumentation
-use parity_wasm::elements;
-
-/// Implementation details of the specific method of the gas metering.
-#[derive(Clone)]
-pub enum GasMeter {
-	/// Gas metering with an external function.
-	External {
-		/// Name of the module to import the gas function from.
-		module: &'static str,
-		/// Name of the external gas function to be imported.
-		function: &'static str,
-	},
-	/// Gas metering with a local function and a mutable global.
-	Internal {
-		/// Name of the mutable global to be exported.
-		global: &'static str,
-		/// Body of the local gas counting function to be injected.
-		func_instructions: elements::Instructions,
-		/// Cost of the gas function execution.
-		cost: u64,
-	},
-}
-
-use super::Rules;
-/// Under the hood part of the gas metering mechanics.
-pub trait Backend {
-	/// Provides the gas metering implementation details.  
-	fn gas_meter<R: Rules>(self, module: &elements::Module, rules: &R) -> GasMeter;
-}
-
-/// Gas metering with an external host function.
-pub mod host_function {
-	use super::{Backend, GasMeter, Rules};
-	use parity_wasm::elements::Module;
-	/// Injects invocations of the gas charging host function into each metering block.
-	pub struct Injector {
-		/// The name of the module to import the gas function from.
-		module: &'static str,
-		/// The name of the gas function to import.
-		name: &'static str,
-	}
-
-	impl Injector {
-		pub fn new(module: &'static str, name: &'static str) -> Self {
-			Self { module, name }
-		}
-	}
-
-	impl Backend for Injector {
-		fn gas_meter<R: Rules>(self, _module: &Module, _rules: &R) -> GasMeter {
-			GasMeter::External { module: self.module, function: self.name }
-		}
-	}
-}
-
-/// Gas metering with a mutable global.
-///
-/// # Note
-///
-/// Not for all execution engines this method gives performance wins compared to using an [external
-/// host function](host_function). See benchmarks and size overhead tests for examples of how to
-/// make measurements needed to decide which gas metering method is better for your particular case.
-///
-/// # Warning
-///
-/// It is not recommended to apply [stack limiter](crate::inject_stack_limiter) instrumentation to a
-/// module instrumented with this type of gas metering. This could lead to a massive module size
-/// bloat. This is a known issue to be fixed in upcoming versions.
-pub mod mutable_global {
-	use super::{Backend, GasMeter, Rules};
-	use alloc::vec;
-	use parity_wasm::elements::{self, Instruction, Module};
-	/// Injects a mutable global variable and a local function to the module to track
-	/// current gas left.
-	///
-	/// The function is called in every metering block. In case of falling out of gas, the global is
-	/// set to the sentinel value `U64::MAX` and `unreachable` instruction is called. The execution
-	/// engine should take care of getting the current global value and setting it back in order to
-	/// sync the gas left value during an execution.
-	pub struct Injector {
-		/// The export name of the gas tracking global.
-		pub global_name: &'static str,
-	}
-
-	impl Injector {
-		pub fn new(global_name: &'static str) -> Self {
-			Self { global_name }
-		}
-	}
-
-	impl Backend for Injector {
-		fn gas_meter<R: Rules>(self, module: &Module, rules: &R) -> GasMeter {
-			let gas_global_idx = module.globals_space() as u32;
-
-			let func_instructions = vec![
-				Instruction::GetGlobal(gas_global_idx),
-				Instruction::GetLocal(0),
-				Instruction::I64GeU,
-				Instruction::If(elements::BlockType::NoResult),
-				Instruction::GetGlobal(gas_global_idx),
-				Instruction::GetLocal(0),
-				Instruction::I64Sub,
-				Instruction::SetGlobal(gas_global_idx),
-				Instruction::Else,
-				// sentinel val u64::MAX
-				Instruction::I64Const(-1i64),           // non-charged instruction
-				Instruction::SetGlobal(gas_global_idx), // non-charged instruction
-				Instruction::Unreachable,               // non-charged instruction
-				Instruction::End,
-				Instruction::End,
-			];
-
-			// calculate gas used for the gas charging func execution itself
-			let mut gas_fn_cost = func_instructions.iter().fold(0, |cost, instruction| {
-				cost + (rules.instruction_cost(instruction).unwrap_or(0) as u64)
-			});
-			// don't charge for the instructions used to fail when out of gas
-			let fail_cost = vec![
-				Instruction::I64Const(-1i64),           // non-charged instruction
-				Instruction::SetGlobal(gas_global_idx), // non-charged instruction
-				Instruction::Unreachable,               // non-charged instruction
-			]
-			.iter()
-			.fold(0, |cost, instruction| {
-				cost + (rules.instruction_cost(instruction).unwrap_or(0) as u64)
-			});
-
-			gas_fn_cost -= fail_cost;
-
-			GasMeter::Internal {
-				global: self.global_name,
-				func_instructions: elements::Instructions::new(func_instructions),
-				cost: gas_fn_cost,
-			}
-		}
-	}
-}

src/gas_metering/mod.rs

@@ -1,13 +1,9 @@
-//! This module is used to instrument a Wasm module with the gas metering code.
+//! This module is used to instrument a Wasm module with gas metering code.
 //!
 //! The primary public interface is the [`inject`] function which transforms a given
 //! module into one that charges gas for code to be executed. See function documentation for usage
 //! and details.
 
-mod backend;
-
-pub use backend::{host_function, mutable_global, Backend, GasMeter};
-
 #[cfg(test)]
 mod validation;
 
@@ -36,9 +32,6 @@ pub trait Rules {
 	/// code into the function calling `memory.grow`. Therefore returning anything but
 	/// [`MemoryGrowCost::Free`] introduces some overhead to the `memory.grow` instruction.
 	fn memory_grow_cost(&self) -> MemoryGrowCost;
-
-	/// A surcharge cost to calling a function that is added per local of that function.
-	fn call_per_local_cost(&self) -> u32;
 }
 
 /// Dynamic costs for memory growth.
@@ -74,12 +67,11 @@ impl MemoryGrowCost {
 /// # Note
 ///
 /// In a production environment it usually makes no sense to assign every instruction
-/// the same cost. A proper implemention of [`Rules`] should be provided that is probably
+/// the same cost. A proper implemention of [`Rules`] should be prived that is probably
 /// created by benchmarking.
 pub struct ConstantCostRules {
 	instruction_cost: u32,
 	memory_grow_cost: u32,
-	call_per_local_cost: u32,
 }
 
 impl ConstantCostRules {
@@ -87,15 +79,15 @@ impl ConstantCostRules {
 	///
 	/// Uses `instruction_cost` for every instruction and `memory_grow_cost` to dynamically
 	/// meter the memory growth instruction.
-	pub fn new(instruction_cost: u32, memory_grow_cost: u32, call_per_local_cost: u32) -> Self {
+	pub fn new(instruction_cost: u32, memory_grow_cost: u32) -> Self {
-		Self { instruction_cost, memory_grow_cost, call_per_local_cost }
+		Self { instruction_cost, memory_grow_cost }
 	}
 }
 
 impl Default for ConstantCostRules {
 	/// Uses instruction cost of `1` and disables memory growth instrumentation.
 	fn default() -> Self {
-		Self { instruction_cost: 1, memory_grow_cost: 0, call_per_local_cost: 1 }
+		Self { instruction_cost: 1, memory_grow_cost: 0 }
 	}
 }
 
@@ -107,167 +99,86 @@ impl Rules for ConstantCostRules {
 	fn memory_grow_cost(&self) -> MemoryGrowCost {
 		NonZeroU32::new(self.memory_grow_cost).map_or(MemoryGrowCost::Free, MemoryGrowCost::Linear)
 	}
-
-	fn call_per_local_cost(&self) -> u32 {
-		self.call_per_local_cost
-	}
 }
 
-/// Transforms a given module into one that tracks the gas charged during its execution.
+/// Transforms a given module into one that charges gas for code to be executed by proxy of an
+/// imported gas metering function.
 ///
-/// The output module uses the `gas` function to track the gas spent. The function could be either
+/// The output module imports a function "gas" from the specified module with type signature
-/// an imported or a local one modifying a mutable global. The argument is the amount of gas
+/// [i32] -> []. The argument is the amount of gas required to continue execution. The external
-/// required to continue execution. The execution engine is meant to keep track of the total amount
+/// function is meant to keep track of the total amount of gas used and trap or otherwise halt
-/// of gas used and trap or otherwise halt execution of the runtime if the gas usage exceeds some
+/// execution of the runtime if the gas usage exceeds some allowed limit.
-/// allowed limit.
 ///
-/// The body of each function of the original module is divided into metered blocks, and the calls
+/// The body of each function is divided into metered blocks, and the calls to charge gas are
-/// to charge gas are inserted at the beginning of every such block of code. A metered block is
+/// inserted at the beginning of every such block of code. A metered block is defined so that,
-/// defined so that, unless there is a trap, either all of the instructions are executed or none
+/// unless there is a trap, either all of the instructions are executed or none are. These are
-/// are. These are similar to basic blocks in a control flow graph, except that in some cases
+/// similar to basic blocks in a control flow graph, except that in some cases multiple basic
-/// multiple basic blocks can be merged into a single metered block. This is the case if any path
+/// blocks can be merged into a single metered block. This is the case if any path through the
-/// through the control flow graph containing one basic block also contains another.
+/// control flow graph containing one basic block also contains another.
 ///
-/// Charging gas at the beginning of each metered block ensures that 1) all instructions
+/// Charging gas is at the beginning of each metered block ensures that 1) all instructions
 /// executed are already paid for, 2) instructions that will not be executed are not charged for
-/// unless execution traps, and 3) the number of calls to `gas` is minimized. The corollary is
+/// unless execution traps, and 3) the number of calls to "gas" is minimized. The corollary is that
-/// that modules instrumented with this metering code may charge gas for instructions not
+/// modules instrumented with this metering code may charge gas for instructions not executed in
-/// executed in the event of a trap.
+/// the event of a trap.
 ///
-/// Additionally, each `memory.grow` instruction found in the module is instrumented to first
+/// Additionally, each `memory.grow` instruction found in the module is instrumented to first make
-/// make a call to charge gas for the additional pages requested. This cannot be done as part of
+/// a call to charge gas for the additional pages requested. This cannot be done as part of the
-/// the block level gas charges as the gas cost is not static and depends on the stack argument
+/// block level gas charges as the gas cost is not static and depends on the stack argument to
-/// to `memory.grow`.
+/// `memory.grow`.
 ///
 /// The above transformations are performed for every function body defined in the module. This
 /// function also rewrites all function indices references by code, table elements, etc., since
-/// the addition of an imported functions changes the indices of module-defined functions. If
+/// the addition of an imported functions changes the indices of module-defined functions. If the
-/// the module has a `NameSection`, added by calling `parse_names`, the indices will also be
+/// the module has a NameSection, added by calling `parse_names`, the indices will also be updated.
-/// updated.
-///
-/// Syncronizing the amount of gas charged with the execution engine can be done in two ways. The
-/// first way is by calling the imported `gas` host function, see [`host_function`] for details. The
-/// second way is by using a local `gas` function together with a mutable global, see
-/// [`mutable_global`] for details.
 ///
 /// This routine runs in time linear in the size of the input module.
 ///
 /// The function fails if the module contains any operation forbidden by gas rule set, returning
-/// the original module as an `Err`.
+/// the original module as an Err.
-pub fn inject<R: Rules, B: Backend>(
+pub fn inject<R: Rules>(
 	module: elements::Module,
-	backend: B,
 	rules: &R,
+	gas_module_name: &str,
 ) -> Result<elements::Module, elements::Module> {
-	// Prepare module and return the gas function
+	// Injecting gas counting external
-	let gas_meter = backend.gas_meter(&module, rules);
-
-	let import_count = module.import_count(elements::ImportCountType::Function) as u32;
-	let functions_space = module.functions_space() as u32;
-	let gas_global_idx = module.globals_space() as u32;
-
 	let mut mbuilder = builder::from_module(module);
+	let import_sig =
+		mbuilder.push_signature(builder::signature().with_param(ValueType::I32).build_sig());
 
-	// Calculate the indexes and gas function cost,
+	mbuilder.push_import(
-	// for external gas function the cost is counted on the host side
+		builder::import()
-	let (gas_func_idx, total_func, gas_fn_cost) = match gas_meter {
+			.module(gas_module_name)
-		GasMeter::External { module: gas_module, function } => {
+			.field("gas")
-			// Inject the import of the gas function
+			.external()
-			let import_sig = mbuilder
+			.func(import_sig)
-				.push_signature(builder::signature().with_param(ValueType::I64).build_sig());
+			.build(),
-			mbuilder.push_import(
+	);
-				builder::import()
-					.module(gas_module)
-					.field(function)
-					.external()
-					.func(import_sig)
-					.build(),
-			);
 
-			(import_count, functions_space + 1, 0)
+	// back to plain module
-		},
-		GasMeter::Internal { global, ref func_instructions, cost } => {
-			// Inject the gas counting global
-			mbuilder.push_global(
-				builder::global()
-					.with_type(ValueType::I64)
-					.mutable()
-					.init_expr(Instruction::I64Const(0))
-					.build(),
-			);
-			// Inject the export entry for the gas counting global
-			let ebuilder = builder::ExportBuilder::new();
-			let global_export = ebuilder
-				.field(global)
-				.with_internal(elements::Internal::Global(gas_global_idx))
-				.build();
-			mbuilder.push_export(global_export);
-
-			let func_idx = functions_space;
-
-			// Build local gas function
-			let gas_func_sig =
-				builder::SignatureBuilder::new().with_param(ValueType::I64).build_sig();
-
-			let function = builder::FunctionBuilder::new()
-				.with_signature(gas_func_sig)
-				.body()
-				.with_instructions(func_instructions.clone())
-				.build()
-				.build();
-
-			// Inject local gas function
-			mbuilder.push_function(function);
-
-			(func_idx, func_idx + 1, cost)
-		},
-	};
-
-	// We need the built the module for making injections to its blocks
 	let mut module = mbuilder.build();
 
+	// calculate actual function index of the imported definition
+	//    (subtract all imports that are NOT functions)
+
+	let gas_func = module.import_count(elements::ImportCountType::Function) as u32 - 1;
+	let total_func = module.functions_space() as u32;
 	let mut need_grow_counter = false;
 	let mut error = false;
 
-	// Iterate over module sections and perform needed transformations.
+	// Updating calling addresses (all calls to function index >= `gas_func` should be incremented)
-	// Indexes are needed to be fixed up in `GasMeter::External` case, as it adds an imported
-	// function, which goes to the beginning of the module's functions space.
 	for section in module.sections_mut() {
 		match section {
-			elements::Section::Code(code_section) => {
+			elements::Section::Code(code_section) =>
-				let injection_targets = match gas_meter {
+				for func_body in code_section.bodies_mut() {
-					GasMeter::External { .. } => code_section.bodies_mut().as_mut_slice(),
+					for instruction in func_body.code_mut().elements_mut().iter_mut() {
-					// Don't inject counters to the local gas function, which is the last one as
+						if let Instruction::Call(call_index) = instruction {
-					// it's just added. Cost for its execution is added statically before each
+							if *call_index >= gas_func {
-					// invocation (see `inject_counter()`).
+								*call_index += 1
-					GasMeter::Internal { .. } => {
-						let len = code_section.bodies().len();
-						&mut code_section.bodies_mut()[..len - 1]
-					},
-				};
-
-				for func_body in injection_targets {
-					// Increment calling addresses if needed
-					if let GasMeter::External { .. } = gas_meter {
-						for instruction in func_body.code_mut().elements_mut().iter_mut() {
-							if let Instruction::Call(call_index) = instruction {
-								if *call_index >= gas_func_idx {
-									*call_index += 1
-								}
 							}
 						}
 					}
-					let locals_count =
+					if inject_counter(func_body.code_mut(), rules, gas_func).is_err() {
-						func_body.locals().iter().map(|val_type| val_type.count()).sum();
-					if inject_counter(
-						func_body.code_mut(),
-						gas_fn_cost,
-						locals_count,
-						rules,
-						gas_func_idx,
-					)
-					.is_err()
-					{
 						error = true;
 						break
 					}
@@ -276,50 +187,42 @@ pub fn inject<R: Rules, B: Backend>(
 					{
 						need_grow_counter = true;
 					}
-				}
+				},
-			},
+			elements::Section::Export(export_section) => {
-			elements::Section::Export(export_section) =>
+				for export in export_section.entries_mut() {
-				if let GasMeter::External { module: _, function: _ } = gas_meter {
+					if let elements::Internal::Function(func_index) = export.internal_mut() {
-					for export in export_section.entries_mut() {
+						if *func_index >= gas_func {
-						if let elements::Internal::Function(func_index) = export.internal_mut() {
+							*func_index += 1
-							if *func_index >= gas_func_idx {
-								*func_index += 1
-							}
 						}
 					}
-				},
+				}
+			},
 			elements::Section::Element(elements_section) => {
 				// Note that we do not need to check the element type referenced because in the
 				// WebAssembly 1.0 spec, the only allowed element type is funcref.
-				if let GasMeter::External { .. } = gas_meter {
+				for segment in elements_section.entries_mut() {
-					for segment in elements_section.entries_mut() {
+					// update all indirect call addresses initial values
-						// update all indirect call addresses initial values
+					for func_index in segment.members_mut() {
-						for func_index in segment.members_mut() {
+						if *func_index >= gas_func {
-							if *func_index >= gas_func_idx {
+							*func_index += 1
-								*func_index += 1
-							}
 						}
 					}
 				}
 			},
 			elements::Section::Start(start_idx) =>
-				if let GasMeter::External { .. } = gas_meter {
+				if *start_idx >= gas_func {
-					if *start_idx >= gas_func_idx {
+					*start_idx += 1
-						*start_idx += 1
-					}
 				},
 			elements::Section::Name(s) =>
-				if let GasMeter::External { .. } = gas_meter {
+				for functions in s.functions_mut() {
-					for functions in s.functions_mut() {
+					*functions.names_mut() =
-						*functions.names_mut() =
+						IndexMap::from_iter(functions.names().iter().map(|(mut idx, name)| {
-							IndexMap::from_iter(functions.names().iter().map(|(mut idx, name)| {
+							if idx >= gas_func {
-								if idx >= gas_func_idx {
+								idx += 1;
-									idx += 1;
+							}
-								}
 
-								(idx, name.clone())
+							(idx, name.clone())
-							}));
+						}));
-					}
 				},
 			_ => {},
 		}
@@ -330,7 +233,7 @@ pub fn inject<R: Rules, B: Backend>(
 	}
 
 	if need_grow_counter {
-		Ok(add_grow_counter(module, rules, gas_func_idx))
+		Ok(add_grow_counter(module, rules, gas_func))
 	} else {
 		Ok(module)
 	}
@@ -381,7 +284,7 @@ struct MeteredBlock {
 	/// Index of the first instruction (aka `Opcode`) in the block.
 	start_pos: usize,
 	/// Sum of costs of all instructions until end of the block.
-	cost: u64,
+	cost: u32,
 }
 
 /// Counter is used to manage state during the gas metering algorithm implemented by
@@ -472,8 +375,7 @@ impl Counter {
 				.expect("last_index is greater than 0; last_index is stack size - 1; qed");
 			let prev_metered_block = &mut prev_control_block.active_metered_block;
 			if closing_metered_block.start_pos == prev_metered_block.start_pos {
-				prev_metered_block.cost =
+				prev_metered_block.cost += closing_metered_block.cost;
-					prev_metered_block.cost.checked_add(closing_metered_block.cost).ok_or(())?;
 				return Ok(())
 			}
 		}
@@ -523,7 +425,7 @@ impl Counter {
 	/// Increment the cost of the current block by the specified value.
 	fn increment(&mut self, val: u32) -> Result<(), ()> {
 		let top_block = self.active_metered_block()?;
-		top_block.cost = top_block.cost.checked_add(val.into()).ok_or(())?;
+		top_block.cost = top_block.cost.checked_add(val).ok_or(())?;
 		Ok(())
 	}
 }
@@ -563,9 +465,8 @@ fn add_grow_counter<R: Rules>(
 			.with_instructions(elements::Instructions::new(vec![
 				GetLocal(0),
 				GetLocal(0),
-				I64ExtendUI32,
+				I32Const(cost as i32),
-				I64Const(i64::from(cost)),
+				I32Mul,
-				I64Mul,
 				// todo: there should be strong guarantee that it does not return anything on
 				// stack?
 				Call(gas_func),
@@ -582,7 +483,6 @@ fn add_grow_counter<R: Rules>(
 fn determine_metered_blocks<R: Rules>(
 	instructions: &elements::Instructions,
 	rules: &R,
-	locals_count: u32,
 ) -> Result<Vec<MeteredBlock>, ()> {
 	use parity_wasm::elements::Instruction::*;
 
@@ -590,9 +490,6 @@ fn determine_metered_blocks<R: Rules>(
 
 	// Begin an implicit function (i.e. `func...end`) block.
 	counter.begin_control_block(0, false);
-	// Add locals initialization cost to the function block.
-	let locals_init_cost = rules.call_per_local_cost().checked_mul(locals_count).ok_or(())?;
-	counter.increment(locals_init_cost)?;
 
 	for cursor in 0..instructions.elements().len() {
 		let instruction = &instructions.elements()[cursor];
@@ -659,19 +556,16 @@ fn determine_metered_blocks<R: Rules>(
 
 fn inject_counter<R: Rules>(
 	instructions: &mut elements::Instructions,
-	gas_function_cost: u64,
-	locals_count: u32,
 	rules: &R,
 	gas_func: u32,
 ) -> Result<(), ()> {
-	let blocks = determine_metered_blocks(instructions, rules, locals_count)?;
+	let blocks = determine_metered_blocks(instructions, rules)?;
-	insert_metering_calls(instructions, gas_function_cost, blocks, gas_func)
+	insert_metering_calls(instructions, blocks, gas_func)
 }
 
 // Then insert metering calls into a sequence of instructions given the block locations and costs.
 fn insert_metering_calls(
 	instructions: &mut elements::Instructions,
-	gas_function_cost: u64,
 	blocks: Vec<MeteredBlock>,
 	gas_func: u32,
 ) -> Result<(), ()> {
@@ -689,8 +583,7 @@ fn insert_metering_calls(
 		// If there the next block starts at this position, inject metering instructions.
 		let used_block = if let Some(block) = block_iter.peek() {
 			if block.start_pos == original_pos {
-				new_instrs
+				new_instrs.push(I32Const(block.cost as i32));
-					.push(I64Const((block.cost.checked_add(gas_function_cost).ok_or(())?) as i64));
 				new_instrs.push(Call(gas_func));
 				true
 			} else {
@@ -719,7 +612,6 @@ fn insert_metering_calls(
 mod tests {
 	use super::*;
 	use parity_wasm::{builder, elements, elements::Instruction::*, serialize};
-	use pretty_assertions::assert_eq;
 
 	fn get_function_body(
 		module: &elements::Module,
@@ -732,7 +624,7 @@ mod tests {
 	}
 
 	#[test]
-	fn simple_grow_host_fn() {
+	fn simple_grow() {
 		let module = parse_wat(
 			r#"(module
 			(func (result i32)
@@ -742,26 +634,17 @@ mod tests {
 			(memory 0 1)
 			)"#,
 		);
-		let backend = host_function::Injector::new("env", "gas");
+
-		let injected_module =
+		let injected_module = inject(module, &ConstantCostRules::new(1, 10_000), "env").unwrap();
-			super::inject(module, backend, &ConstantCostRules::new(1, 10_000, 1)).unwrap();
 
 		assert_eq!(
 			get_function_body(&injected_module, 0).unwrap(),
-			&vec![I64Const(2), Call(0), GetGlobal(0), Call(2), End][..]
+			&vec![I32Const(2), Call(0), GetGlobal(0), Call(2), End][..]
 		);
 		assert_eq!(
 			get_function_body(&injected_module, 1).unwrap(),
-			&vec![
+			&vec![GetLocal(0), GetLocal(0), I32Const(10000), I32Mul, Call(0), GrowMemory(0), End,]
-				GetLocal(0),
+				[..]
-				GetLocal(0),
-				I64ExtendUI32,
-				I64Const(10000),
-				I64Mul,
-				Call(0),
-				GrowMemory(0),
-				End,
-			][..]
 		);
 
 		let binary = serialize(injected_module).expect("serialization failed");
@@ -769,64 +652,7 @@ mod tests {
 	}
 
 	#[test]
-	fn simple_grow_mut_global() {
+	fn grow_no_gas_no_track() {
-		let module = parse_wat(
-			r#"(module
-			(func (result i32)
-			  global.get 0
-			  memory.grow)
-			(global i32 (i32.const 42))
-			(memory 0 1)
-			)"#,
-		);
-		let backend = mutable_global::Injector::new("gas_left");
-		let injected_module =
-			super::inject(module, backend, &ConstantCostRules::new(1, 10_000, 1)).unwrap();
-
-		assert_eq!(
-			get_function_body(&injected_module, 0).unwrap(),
-			&vec![I64Const(13), Call(1), GetGlobal(0), Call(2), End][..]
-		);
-		assert_eq!(
-			get_function_body(&injected_module, 1).unwrap(),
-			&vec![
-				Instruction::GetGlobal(1),
-				Instruction::GetLocal(0),
-				Instruction::I64GeU,
-				Instruction::If(elements::BlockType::NoResult),
-				Instruction::GetGlobal(1),
-				Instruction::GetLocal(0),
-				Instruction::I64Sub,
-				Instruction::SetGlobal(1),
-				Instruction::Else,
-				// sentinel val u64::MAX
-				Instruction::I64Const(-1i64), // non-charged instruction
-				Instruction::SetGlobal(1),    // non-charged instruction
-				Instruction::Unreachable,     // non-charged instruction
-				Instruction::End,
-				Instruction::End,
-			][..]
-		);
-		assert_eq!(
-			get_function_body(&injected_module, 2).unwrap(),
-			&vec![
-				GetLocal(0),
-				GetLocal(0),
-				I64ExtendUI32,
-				I64Const(10000),
-				I64Mul,
-				Call(1),
-				GrowMemory(0),
-				End,
-			][..]
-		);
-
-		let binary = serialize(injected_module).expect("serialization failed");
-		wasmparser::validate(&binary).unwrap();
-	}
-
-	#[test]
-	fn grow_no_gas_no_track_host_fn() {
 		let module = parse_wat(
 			r"(module
 			(func (result i32)
@@ -836,13 +662,12 @@ mod tests {
 			(memory 0 1)
 			)",
 		);
-		let backend = host_function::Injector::new("env", "gas");
+
-		let injected_module =
+		let injected_module = inject(module, &ConstantCostRules::default(), "env").unwrap();
-			super::inject(module, backend, &ConstantCostRules::default()).unwrap();
 
 		assert_eq!(
 			get_function_body(&injected_module, 0).unwrap(),
-			&vec![I64Const(2), Call(0), GetGlobal(0), GrowMemory(0), End][..]
+			&vec![I32Const(2), Call(0), GetGlobal(0), GrowMemory(0), End][..]
 		);
 
 		assert_eq!(injected_module.functions_space(), 2);
@@ -852,33 +677,7 @@ mod tests {
 	}
 
 	#[test]
-	fn grow_no_gas_no_track_mut_global() {
+	fn call_index() {
-		let module = parse_wat(
-			r"(module
-			(func (result i32)
-			  global.get 0
-			  memory.grow)
-			(global i32 (i32.const 42))
-			(memory 0 1)
-			)",
-		);
-		let backend = mutable_global::Injector::new("gas_left");
-		let injected_module =
-			super::inject(module, backend, &ConstantCostRules::default()).unwrap();
-
-		assert_eq!(
-			get_function_body(&injected_module, 0).unwrap(),
-			&vec![I64Const(13), Call(1), GetGlobal(0), GrowMemory(0), End][..]
-		);
-
-		assert_eq!(injected_module.functions_space(), 2);
-
-		let binary = serialize(injected_module).expect("serialization failed");
-		wasmparser::validate(&binary).unwrap();
-	}
-
-	#[test]
-	fn call_index_host_fn() {
 		let module = builder::module()
 			.global()
 			.value_type()
@@ -915,24 +714,22 @@ mod tests {
 			.build()
 			.build();
 
-		let backend = host_function::Injector::new("env", "gas");
+		let injected_module = inject(module, &ConstantCostRules::default(), "env").unwrap();
-		let injected_module =
-			super::inject(module, backend, &ConstantCostRules::default()).unwrap();
 
 		assert_eq!(
 			get_function_body(&injected_module, 1).unwrap(),
 			&vec![
-				I64Const(3),
+				I32Const(3),
 				Call(0),
 				Call(1),
 				If(elements::BlockType::NoResult),
-				I64Const(3),
+				I32Const(3),
 				Call(0),
 				Call(1),
 				Call(1),
 				Call(1),
 				Else,
-				I64Const(2),
+				I32Const(2),
 				Call(0),
 				Call(1),
 				Call(1),
@@ -943,89 +740,20 @@ mod tests {
 		);
 	}
 
-	#[test]
-	fn call_index_mut_global() {
-		let module = builder::module()
-			.global()
-			.value_type()
-			.i32()
-			.build()
-			.function()
-			.signature()
-			.param()
-			.i32()
-			.build()
-			.body()
-			.build()
-			.build()
-			.function()
-			.signature()
-			.param()
-			.i32()
-			.build()
-			.body()
-			.with_instructions(elements::Instructions::new(vec![
-				Call(0),
-				If(elements::BlockType::NoResult),
-				Call(0),
-				Call(0),
-				Call(0),
-				Else,
-				Call(0),
-				Call(0),
-				End,
-				Call(0),
-				End,
-			]))
-			.build()
-			.build()
-			.build();
-
-		let backend = mutable_global::Injector::new("gas_left");
-		let injected_module =
-			super::inject(module, backend, &ConstantCostRules::default()).unwrap();
-
-		assert_eq!(
-			get_function_body(&injected_module, 1).unwrap(),
-			&vec![
-				I64Const(14),
-				Call(2),
-				Call(0),
-				If(elements::BlockType::NoResult),
-				I64Const(14),
-				Call(2),
-				Call(0),
-				Call(0),
-				Call(0),
-				Else,
-				I64Const(13),
-				Call(2),
-				Call(0),
-				Call(0),
-				End,
-				Call(0),
-				End
-			][..]
-		);
-	}
-
 	fn parse_wat(source: &str) -> elements::Module {
 		let module_bytes = wat::parse_str(source).unwrap();
 		elements::deserialize_buffer(module_bytes.as_ref()).unwrap()
 	}
 
 	macro_rules! test_gas_counter_injection {
-		(names = ($name1:ident, $name2:ident); input = $input:expr; expected = $expected:expr) => {
+		(name = $name:ident; input = $input:expr; expected = $expected:expr) => {
 			#[test]
-			fn $name1() {
+			fn $name() {
 				let input_module = parse_wat($input);
 				let expected_module = parse_wat($expected);
-				let injected_module = super::inject(
+
-					input_module,
+				let injected_module = inject(input_module, &ConstantCostRules::default(), "env")
-					host_function::Injector::new("env", "gas"),
+					.expect("inject_gas_counter call failed");
-					&ConstantCostRules::default(),
-				)
-				.expect("inject_gas_counter call failed");
 
 				let actual_func_body = get_function_body(&injected_module, 0)
 					.expect("injected module must have a function body");
@@ -1034,51 +762,11 @@ mod tests {
 
 				assert_eq!(actual_func_body, expected_func_body);
 			}
-
-			#[test]
-			fn $name2() {
-				let input_module = parse_wat($input);
-				let draft_module = parse_wat($expected);
-				let gas_fun_cost = match mutable_global::Injector::new("gas_left")
-					.gas_meter(&input_module, &ConstantCostRules::default())
-				{
-					GasMeter::Internal { cost, .. } => cost as i64,
-					_ => 0i64,
-				};
-
-				let injected_module = super::inject(
-					input_module,
-					mutable_global::Injector::new("gas_left"),
-					&ConstantCostRules::default(),
-				)
-				.expect("inject_gas_counter call failed");
-
-				let actual_func_body = get_function_body(&injected_module, 0)
-					.expect("injected module must have a function body");
-				let mut expected_func_body = get_function_body(&draft_module, 0)
-					.expect("post-module must have a function body")
-					.to_vec();
-
-				// modify expected instructions set for gas_metering::mutable_global
-				let mut iter = expected_func_body.iter_mut();
-				while let Some(ins) = iter.next() {
-					if let I64Const(cost) = ins {
-						if let Some(ins_next) = iter.next() {
-							if let Call(0) = ins_next {
-								*cost += gas_fun_cost;
-								*ins_next = Call(1);
-							}
-						}
-					}
-				}
-
-				assert_eq!(actual_func_body, &expected_func_body);
-			}
 		};
 	}
 
 	test_gas_counter_injection! {
-		names = (simple_host_fn, simple_mut_global);
+		name = simple;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1087,13 +775,13 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 1))
+				(call 0 (i32.const 1))
 				(get_global 0)))
 		"#
 	}
 
 	test_gas_counter_injection! {
-		names = (nested_host_fn, nested_mut_global);
+		name = nested;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1107,7 +795,7 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 6))
+				(call 0 (i32.const 6))
 				(get_global 0)
 				(block
 					(get_global 0)
@@ -1118,7 +806,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (ifelse_host_fn, ifelse_mut_global);
+		name = ifelse;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1136,16 +824,16 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 3))
+				(call 0 (i32.const 3))
 				(get_global 0)
 				(if
 					(then
-						(call 0 (i64.const 3))
+						(call 0 (i32.const 3))
 						(get_global 0)
 						(get_global 0)
 						(get_global 0))
 					(else
-						(call 0 (i64.const 2))
+						(call 0 (i32.const 2))
 						(get_global 0)
 						(get_global 0)))
 				(get_global 0)))
@@ -1153,7 +841,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (branch_innermost_host_fn, branch_innermost_mut_global);
+		name = branch_innermost;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1169,13 +857,13 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 6))
+				(call 0 (i32.const 6))
 				(get_global 0)
 				(block
 					(get_global 0)
 					(drop)
 					(br 0)
-					(call 0 (i64.const 2))
+					(call 0 (i32.const 2))
 					(get_global 0)
 					(drop))
 				(get_global 0)))
@@ -1183,7 +871,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (branch_outer_block_host_fn, branch_outer_block_mut_global);
+		name = branch_outer_block;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1203,18 +891,18 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 5))
+				(call 0 (i32.const 5))
 				(get_global 0)
 				(block
 					(get_global 0)
 					(if
 						(then
-							(call 0 (i64.const 4))
+							(call 0 (i32.const 4))
 							(get_global 0)
 							(get_global 0)
 							(drop)
 							(br_if 1)))
-					(call 0 (i64.const 2))
+					(call 0 (i32.const 2))
 					(get_global 0)
 					(drop))
 				(get_global 0)))
@@ -1222,7 +910,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (branch_outer_loop_host_fn, branch_outer_loop_mut_global);
+		name = branch_outer_loop;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1245,18 +933,18 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 3))
+				(call 0 (i32.const 3))
 				(get_global 0)
 				(loop
-					(call 0 (i64.const 4))
+					(call 0 (i32.const 4))
 					(get_global 0)
 					(if
 						(then
-							(call 0 (i64.const 2))
+							(call 0 (i32.const 2))
 							(get_global 0)
 							(br_if 0))
 						(else
-							(call 0 (i64.const 4))
+							(call 0 (i32.const 4))
 							(get_global 0)
 							(get_global 0)
 							(drop)
@@ -1268,7 +956,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (return_from_func_host_fn, return_from_func_mut_global);
+		name = return_from_func;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1281,19 +969,19 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 2))
+				(call 0 (i32.const 2))
 				(get_global 0)
 				(if
 					(then
-						(call 0 (i64.const 1))
+						(call 0 (i32.const 1))
 						(return)))
-				(call 0 (i64.const 1))
+				(call 0 (i32.const 1))
 				(get_global 0)))
 		"#
 	}
 
 	test_gas_counter_injection! {
-		names = (branch_from_if_not_else_host_fn, branch_from_if_not_else_mut_global);
+		name = branch_from_if_not_else;
 		input = r#"
 		(module
 			(func (result i32)
@@ -1310,18 +998,18 @@ mod tests {
 		expected = r#"
 		(module
 			(func (result i32)
-				(call 0 (i64.const 5))
+				(call 0 (i32.const 5))
 				(get_global 0)
 				(block
 					(get_global 0)
 					(if
 						(then
-							(call 0 (i64.const 1))
+							(call 0 (i32.const 1))
 							(br 1))
 						(else
-							(call 0 (i64.const 1))
+							(call 0 (i32.const 1))
 							(br 0)))
-					(call 0 (i64.const 2))
+					(call 0 (i32.const 2))
 					(get_global 0)
 					(drop))
 				(get_global 0)))
@@ -1329,7 +1017,7 @@ mod tests {
 	}
 
 	test_gas_counter_injection! {
-		names = (empty_loop_host_fn, empty_loop_mut_global);
+		name = empty_loop;
 		input = r#"
 		(module
 			(func
@@ -1343,9 +1031,9 @@ mod tests {
 		expected = r#"
 		(module
 			(func
-				(call 0 (i64.const 2))
+				(call 0 (i32.const 2))
 				(loop
-					(call 0 (i64.const 1))
+					(call 0 (i32.const 1))
 					(br 0)
 				)
 				unreachable

src/gas_metering/validation.rs

@@ -23,10 +23,10 @@ struct ControlFlowNode {
 	first_instr_pos: Option<usize>,
 
 	/// The actual gas cost of executing all instructions in the basic block.
-	actual_cost: u64,
+	actual_cost: u32,
 
 	/// The amount of gas charged by the injected metering instructions within this basic block.
-	charged_cost: u64,
+	charged_cost: u32,
 
 	/// Whether there are any other nodes in the graph that loop back to this one. Every cycle in
 	/// the control flow graph contains at least one node with this flag set.
@@ -68,10 +68,10 @@ impl ControlFlowGraph {
 	}
 
 	fn increment_actual_cost(&mut self, node_id: NodeId, cost: u32) {
-		self.get_node_mut(node_id).actual_cost += u64::from(cost);
+		self.get_node_mut(node_id).actual_cost += cost;
 	}
 
-	fn increment_charged_cost(&mut self, node_id: NodeId, cost: u64) {
+	fn increment_charged_cost(&mut self, node_id: NodeId, cost: u32) {
 		self.get_node_mut(node_id).charged_cost += cost;
 	}
 
@@ -134,10 +134,6 @@ fn build_control_flow_graph(
 
 	let mut stack = vec![ControlFrame::new(entry_node_id, terminal_node_id, false)];
 	let mut metered_blocks_iter = blocks.iter().peekable();
-
-	let locals_count = body.locals().iter().fold(0, |count, val_type| count + val_type.count());
-	let locals_init_cost = (rules.call_per_local_cost()).checked_mul(locals_count).ok_or(())?;
-
 	for (cursor, instruction) in body.code().elements().iter().enumerate() {
 		let active_node_id = stack
 			.last()
@@ -153,10 +149,6 @@ fn build_control_flow_graph(
 			graph.increment_charged_cost(active_node_id, next_metered_block.cost);
 		}
 
-		// Add locals initialization cost to the function block.
-		if cursor == 0 {
-			graph.increment_actual_cost(active_node_id, locals_init_cost);
-		}
 		let instruction_cost = rules.instruction_cost(instruction).ok_or(())?;
 		match instruction {
 			Instruction::Block(_) => {
@@ -275,9 +267,9 @@ fn validate_graph_gas_costs(graph: &ControlFlowGraph) -> bool {
 	fn visit(
 		graph: &ControlFlowGraph,
 		node_id: NodeId,
-		mut total_actual: u64,
+		mut total_actual: u32,
-		mut total_charged: u64,
+		mut total_charged: u32,
-		loop_costs: &mut Map<NodeId, (u64, u64)>,
+		loop_costs: &mut Map<NodeId, (u32, u32)>,
 	) -> bool {
 		let node = graph.get_node(node_id);
 
@@ -350,11 +342,8 @@ mod tests {
 
 			for func_body in module.code_section().iter().flat_map(|section| section.bodies()) {
 				let rules = ConstantCostRules::default();
-				let locals_count =
-					func_body.locals().iter().fold(0, |count, val_type| count + val_type.count());
 
-				let metered_blocks =
+				let metered_blocks = determine_metered_blocks(func_body.code(), &rules).unwrap();
-					determine_metered_blocks(func_body.code(), &rules, locals_count).unwrap();
 				let success =
 					validate_metering_injections(func_body, &rules, &metered_blocks).unwrap();
 				assert!(success);

src/lib.rs

@@ -8,4 +8,6 @@ mod stack_limiter;
 
 pub use export_globals::export_mutable_globals;
 pub use parity_wasm;
-pub use stack_limiter::inject as inject_stack_limiter;
+pub use stack_limiter::{
+	compute_stack_cost, compute_stack_height_weight, inject as inject_stack_limiter,
+};

src/stack_limiter/max_height.rs

@@ -1,15 +1,30 @@
 use super::resolve_func_type;
-use alloc::vec::Vec;
+use alloc::{vec, vec::Vec};
-use parity_wasm::elements::{self, BlockType, Type};
+use parity_wasm::elements::{self, BlockType, Type, ValueType};
 
 #[cfg(feature = "sign_ext")]
 use parity_wasm::elements::SignExtInstruction;
 
+#[cfg(feature = "trace-log")]
+macro_rules! trace {
+    ($($tt:tt)*) => {
+      ::log::trace!($($tt)*);
+    };
+}
+
+#[cfg(not(feature = "trace-log"))]
+macro_rules! trace {
+	($($tt:tt)*) => {};
+}
+
 // The cost in stack items that should be charged per call of a function. This is
 // is a static cost that is added to each function call. This makes sense because even
 // if a function does not use any parameters or locals some stack space on the host
 // machine might be consumed to hold some context.
-const ACTIVATION_FRAME_COST: u32 = 2;
+const ACTIVATION_FRAME_HEIGHT: u32 = 2;
+
+// Weight of an activation frame.
+const ACTIVATION_FRAME_WEIGHT: u32 = 32;
 
 /// Control stack frame.
 #[derive(Debug)]
@@ -18,36 +33,41 @@ struct Frame {
 	/// never passes control further was executed.
 	is_polymorphic: bool,
 
-	/// Count of values which will be pushed after the exit
+	/// Type of value which will be pushed after exiting
-	/// from the current block.
+	/// the current block or `None` if block does not return a result.
-	end_arity: u32,
+	result_type: Option<ValueType>,
 
-	/// Count of values which should be poped upon a branch to
+	/// Type of value which should be poped upon a branch to
-	/// this frame.
+	/// this frame or `None` if branching shouldn't affect the stack.
 	///
-	/// This might be diffirent from `end_arity` since branch
+	/// This might be diffirent from `result_type` since branch
 	/// to the loop header can't take any values.
-	branch_arity: u32,
+	branch_type: Option<ValueType>,
 
 	/// Stack height before entering in the block.
-	start_height: u32,
+	start_height: usize,
 }
 
-/// This is a compound stack that abstracts tracking height of the value stack
+/// This is a compound stack that abstracts tracking height and weight of the value stack
 /// and manipulation of the control stack.
 struct Stack {
-	height: u32,
+	values: Vec<ValueType>,
 	control_stack: Vec<Frame>,
 }
 
 impl Stack {
 	fn new() -> Stack {
-		Stack { height: ACTIVATION_FRAME_COST, control_stack: Vec::new() }
+		Stack { values: Vec::new(), control_stack: Vec::new() }
+	}
+
+	/// Returns current weight of the value stack.
+	fn weight(&self) -> u32 {
+		self.values.iter().map(|v| value_cost(*v)).sum()
 	}
 
 	/// Returns current height of the value stack.
-	fn height(&self) -> u32 {
+	fn height(&self) -> usize {
-		self.height
+		self.values.len()
 	}
 
 	/// Returns a reference to a frame by specified depth relative to the top of
@@ -70,59 +90,71 @@ impl Stack {
 
 	/// Push control frame into the control stack.
 	fn push_frame(&mut self, frame: Frame) {
+		trace!("  Push control frame {:?}", frame);
 		self.control_stack.push(frame);
 	}
 
 	/// Pop control frame from the control stack.
 	///
 	/// Returns `Err` if the control stack is empty.
+
+	#[allow(clippy::let_and_return)]
 	fn pop_frame(&mut self) -> Result<Frame, &'static str> {
-		self.control_stack.pop().ok_or("stack must be non-empty")
+		trace!("  Pop control frame");
+		let frame = self.control_stack.pop().ok_or("stack must be non-empty");
+		trace!("    {:?}", frame);
+		frame
 	}
 
 	/// Truncate the height of value stack to the specified height.
-	fn trunc(&mut self, new_height: u32) {
+	fn trunc(&mut self, new_height: usize) {
-		self.height = new_height;
+		trace!("  Truncate value stack to {}", new_height);
+		self.values.truncate(new_height);
 	}
 
-	/// Push specified number of values into the value stack.
+	/// Push a value into the value stack.
-	///
+	fn push_value(&mut self, value: ValueType) -> Result<(), &'static str> {
-	/// Returns `Err` if the height overflow usize value.
+		trace!("  Push {:?} to value stack", value);
-	fn push_values(&mut self, value_count: u32) -> Result<(), &'static str> {
+		self.values.push(value);
-		self.height = self.height.checked_add(value_count).ok_or("stack overflow")?;
+		if self.values.len() >= u32::MAX as usize {
+			return Err("stack overflow")
+		}
 		Ok(())
 	}
 
-	/// Pop specified number of values from the value stack.
+	/// Pop a value from the value stack.
 	///
 	/// Returns `Err` if the stack happen to be negative value after
-	/// values popped.
+	/// value popped.
-	fn pop_values(&mut self, value_count: u32) -> Result<(), &'static str> {
+	fn pop_value(&mut self) -> Result<Option<ValueType>, &'static str> {
-		if value_count == 0 {
+		let top_frame = self.frame(0)?;
-			return Ok(())
+		if self.height() == top_frame.start_height {
-		}
+			return if top_frame.is_polymorphic {
-		{
+				Ok(None)
-			let top_frame = self.frame(0)?;
+			} else {
-			if self.height == top_frame.start_height {
+				Err("trying to pop more values than pushed")
-				// It is an error to pop more values than was pushed in the current frame
-				// (ie pop values pushed in the parent frame), unless the frame became
-				// polymorphic.
-				return if top_frame.is_polymorphic {
-					Ok(())
-				} else {
-					return Err("trying to pop more values than pushed")
-				}
 			}
 		}
 
-		self.height = self.height.checked_sub(value_count).ok_or("stack underflow")?;
+		if self.height() > 0 {
+			let vt = self.values.pop();
+			trace!("Pop {:?} from value stack", vt);
+			Ok(vt)
+		} else {
+			Err("trying to pop more values than pushed")
+		}
+	}
+}
 
-		Ok(())
+fn value_cost(val: ValueType) -> u32 {
+	match val {
+		ValueType::I32 | ValueType::F32 => 4,
+		ValueType::I64 | ValueType::F64 => 8,
 	}
 }
 
 /// This function expects the function to be validated.
-pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static str> {
+pub fn compute(func_idx: u32, module: &elements::Module) -> Result<(u32, u32), &'static str> {
 	use parity_wasm::elements::Instruction::*;
 
 	let func_section = module.function_section().ok_or("No function section")?;
@@ -145,47 +177,55 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 		.ok_or("Function body for the index isn't found")?;
 	let instructions = body.code();
 
+	// Get globals to resove their types
+	let globals: Vec<ValueType> = if let Some(global_section) = module.global_section() {
+		global_section
+			.entries()
+			.iter()
+			.map(|g| g.global_type().content_type())
+			.collect()
+	} else {
+		Vec::new()
+	};
+
+	let mut locals = func_signature.params().to_vec();
+	locals.extend(body.locals().iter().flat_map(|l| vec![l.value_type(); l.count() as usize]));
+
 	let mut stack = Stack::new();
-	let mut max_height: u32 = 0;
+	let mut max_weight: u32 = 0;
-	let mut pc = 0;
+	let mut max_height: usize = 0;
 
 	// Add implicit frame for the function. Breaks to this frame and execution of
 	// the last end should deal with this frame.
-	let func_arity = func_signature.results().len() as u32;
+	let func_results = func_signature.results();
+	let param_weight: u32 = func_signature.params().iter().map(|v| value_cost(*v)).sum();
+
+	let func_result_type = if func_results.is_empty() { None } else { Some(func_results[0]) };
+
 	stack.push_frame(Frame {
 		is_polymorphic: false,
-		end_arity: func_arity,
+		result_type: func_result_type,
-		branch_arity: func_arity,
+		branch_type: func_result_type,
 		start_height: 0,
 	});
 
-	loop {
+	for opcode in instructions.elements() {
-		if pc >= instructions.elements().len() {
+		trace!("Processing opcode {:?}", opcode);
-			break
-		}
-
-		// If current value stack is higher than maximal height observed so far,
-		// save the new height.
-		// However, we don't increase maximal value in unreachable code.
-		if stack.height() > max_height && !stack.frame(0)?.is_polymorphic {
-			max_height = stack.height();
-		}
-
-		let opcode = &instructions.elements()[pc];
 
 		match opcode {
 			Nop => {},
 			Block(ty) | Loop(ty) | If(ty) => {
-				let end_arity = if *ty == BlockType::NoResult { 0 } else { 1 };
-				let branch_arity = if let Loop(_) = *opcode { 0 } else { end_arity };
 				if let If(_) = *opcode {
-					stack.pop_values(1)?;
+					stack.pop_value()?;
 				}
 				let height = stack.height();
+				let end_result = if let BlockType::Value(vt) = *ty { Some(vt) } else { None };
 				stack.push_frame(Frame {
-					is_polymorphic: false,
+					is_polymorphic: stack.frame(0)?.is_polymorphic, /* Block inside unreachable
-					end_arity,
+					                                                 * code is
-					branch_arity,
+					                                                 * unreachable */
+					result_type: end_result,
+					branch_type: if let Loop(_) = *opcode { None } else { end_result },
 					start_height: height,
 				});
 			},
@@ -196,45 +236,56 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			End => {
 				let frame = stack.pop_frame()?;
 				stack.trunc(frame.start_height);
-				stack.push_values(frame.end_arity)?;
+				if let Some(vt) = frame.result_type {
+					stack.push_value(vt)?;
+				}
+				// Push the frame back for now to allow for stack calculations. We'll get rid of it
+				// later
+				stack.push_frame(frame);
 			},
 			Unreachable => {
 				stack.mark_unreachable()?;
 			},
 			Br(target) => {
 				// Pop values for the destination block result.
-				let target_arity = stack.frame(*target)?.branch_arity;
+				if stack.frame(*target)?.branch_type.is_some() {
-				stack.pop_values(target_arity)?;
+					stack.pop_value()?;
+				}
 
 				// This instruction unconditionally transfers control to the specified block,
 				// thus all instruction until the end of the current block is deemed unreachable
 				stack.mark_unreachable()?;
 			},
 			BrIf(target) => {
+				let target_type = stack.frame(*target)?.branch_type;
 				// Pop values for the destination block result.
-				let target_arity = stack.frame(*target)?.branch_arity;
+				if target_type.is_some() {
-				stack.pop_values(target_arity)?;
+					stack.pop_value()?;
+				}
 
 				// Pop condition value.
-				stack.pop_values(1)?;
+				stack.pop_value()?;
 
 				// Push values back.
-				stack.push_values(target_arity)?;
+				if let Some(vt) = target_type {
+					stack.push_value(vt)?;
+				}
 			},
 			BrTable(br_table_data) => {
-				let arity_of_default = stack.frame(br_table_data.default)?.branch_arity;
+				let default_type = stack.frame(br_table_data.default)?.branch_type;
 
 				// Check that all jump targets have an equal arities.
 				for target in &*br_table_data.table {
-					let arity = stack.frame(*target)?.branch_arity;
+					if stack.frame(*target)?.branch_type != default_type {
-					if arity != arity_of_default {
+						return Err("Types of all jump-targets must be equal")
-						return Err("Arity of all jump-targets must be equal")
 					}
 				}
 
-				// Because all jump targets have an equal arities, we can just take arity of
+				// Because all jump targets have equal types, we can just take type of
 				// the default branch.
-				stack.pop_values(arity_of_default)?;
+				if default_type.is_some() {
+					stack.pop_value()?;
+				}
 
 				// This instruction doesn't let control flow to go further, since the control flow
 				// should take either one of branches depending on the value or the default branch.
@@ -243,80 +294,114 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			Return => {
 				// Pop return values of the function. Mark successive instructions as unreachable
 				// since this instruction doesn't let control flow to go further.
-				stack.pop_values(func_arity)?;
+				if func_result_type.is_some() {
+					stack.pop_value()?;
+				}
 				stack.mark_unreachable()?;
 			},
 			Call(idx) => {
 				let ty = resolve_func_type(*idx, module)?;
 
 				// Pop values for arguments of the function.
-				stack.pop_values(ty.params().len() as u32)?;
+				for _ in ty.params() {
+					stack.pop_value()?;
+				}
 
 				// Push result of the function execution to the stack.
-				let callee_arity = ty.results().len() as u32;
+				let callee_results = ty.results();
-				stack.push_values(callee_arity)?;
+				if !callee_results.is_empty() {
+					stack.push_value(callee_results[0])?;
+				}
 			},
 			CallIndirect(x, _) => {
 				let Type::Function(ty) =
 					type_section.types().get(*x as usize).ok_or("Type not found")?;
 
 				// Pop the offset into the function table.
-				stack.pop_values(1)?;
+				stack.pop_value()?;
 
 				// Pop values for arguments of the function.
-				stack.pop_values(ty.params().len() as u32)?;
+				for _ in ty.params() {
+					stack.pop_value()?;
+				}
 
 				// Push result of the function execution to the stack.
-				let callee_arity = ty.results().len() as u32;
+				let callee_results = ty.results();
-				stack.push_values(callee_arity)?;
+				if !callee_results.is_empty() {
+					stack.push_value(callee_results[0])?;
+				}
 			},
 			Drop => {
-				stack.pop_values(1)?;
+				stack.pop_value()?;
 			},
 			Select => {
 				// Pop two values and one condition.
-				stack.pop_values(2)?;
+				let val = stack.pop_value()?;
-				stack.pop_values(1)?;
+				stack.pop_value()?;
+				stack.pop_value()?;
 
 				// Push the selected value.
-				stack.push_values(1)?;
+				if let Some(vt) = val {
+					stack.push_value(vt)?;
+				}
 			},
-			GetLocal(_) => {
+			GetLocal(idx) => {
-				stack.push_values(1)?;
+				let idx = *idx as usize;
+				if idx >= locals.len() {
+					return Err("Reference to a global is out of bounds")
+				}
+				stack.push_value(locals[idx])?;
 			},
 			SetLocal(_) => {
-				stack.pop_values(1)?;
+				stack.pop_value()?;
 			},
-			TeeLocal(_) => {
+			TeeLocal(idx) => {
 				// This instruction pops and pushes the value, so
 				// effectively it doesn't modify the stack height.
-				stack.pop_values(1)?;
+				let idx = *idx as usize;
-				stack.push_values(1)?;
+				if idx >= locals.len() {
+					return Err("Reference to a local is out of bounds")
+				}
+				stack.pop_value()?;
+				stack.push_value(locals[idx])?;
 			},
-			GetGlobal(_) => {
+			GetGlobal(idx) => {
-				stack.push_values(1)?;
+				let idx = *idx as usize;
+				if idx >= globals.len() {
+					return Err("Reference to a global is out of bounds")
+				}
+				stack.push_value(globals[idx])?;
 			},
 			SetGlobal(_) => {
-				stack.pop_values(1)?;
+				stack.pop_value()?;
 			},
+
+			// These instructions pop the address and pushes the result
 			I32Load(_, _) |
-			I64Load(_, _) |
-			F32Load(_, _) |
-			F64Load(_, _) |
 			I32Load8S(_, _) |
 			I32Load8U(_, _) |
 			I32Load16S(_, _) |
-			I32Load16U(_, _) |
+			I32Load16U(_, _) => {
+				stack.pop_value()?;
+				stack.push_value(ValueType::I32)?;
+			},
+			I64Load(_, _) |
 			I64Load8S(_, _) |
 			I64Load8U(_, _) |
 			I64Load16S(_, _) |
 			I64Load16U(_, _) |
 			I64Load32S(_, _) |
 			I64Load32U(_, _) => {
-				// These instructions pop the address and pushes the result,
+				stack.pop_value()?;
-				// which effictively don't modify the stack height.
+				stack.push_value(ValueType::I64)?;
-				stack.pop_values(1)?;
+			},
-				stack.push_values(1)?;
+			F32Load(_, _) => {
+				stack.pop_value()?;
+				stack.push_value(ValueType::F32)?;
+			},
+			F64Load(_, _) => {
+				stack.pop_value()?;
+				stack.push_value(ValueType::F64)?;
 			},
 
 			I32Store(_, _) |
@@ -329,29 +414,38 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			I64Store16(_, _) |
 			I64Store32(_, _) => {
 				// These instructions pop the address and the value.
-				stack.pop_values(2)?;
+				stack.pop_value()?;
+				stack.pop_value()?;
 			},
 
 			CurrentMemory(_) => {
 				// Pushes current memory size
-				stack.push_values(1)?;
+				stack.push_value(ValueType::I32)?;
 			},
 			GrowMemory(_) => {
 				// Grow memory takes the value of pages to grow and pushes
-				stack.pop_values(1)?;
+				stack.pop_value()?;
-				stack.push_values(1)?;
+				stack.push_value(ValueType::I32)?;
 			},
 
-			I32Const(_) | I64Const(_) | F32Const(_) | F64Const(_) => {
+			I32Const(_) => {
-				// These instructions just push the single literal value onto the stack.
+				stack.push_value(ValueType::I32)?;
-				stack.push_values(1)?;
+			},
+			I64Const(_) => {
+				stack.push_value(ValueType::I64)?;
+			},
+			F32Const(_) => {
+				stack.push_value(ValueType::F32)?;
+			},
+			F64Const(_) => {
+				stack.push_value(ValueType::F64)?;
 			},
 
 			I32Eqz | I64Eqz => {
 				// These instructions pop the value and compare it against zero, and pushes
 				// the result of the comparison.
-				stack.pop_values(1)?;
+				stack.pop_value()?;
-				stack.push_values(1)?;
+				stack.push_value(ValueType::I32)?;
 			},
 
 			I32Eq | I32Ne | I32LtS | I32LtU | I32GtS | I32GtU | I32LeS | I32LeU | I32GeS |
@@ -359,16 +453,18 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			I64GeS | I64GeU | F32Eq | F32Ne | F32Lt | F32Gt | F32Le | F32Ge | F64Eq | F64Ne |
 			F64Lt | F64Gt | F64Le | F64Ge => {
 				// Comparison operations take two operands and produce one result.
-				stack.pop_values(2)?;
+				stack.pop_value()?;
-				stack.push_values(1)?;
+				stack.pop_value()?;
+				stack.push_value(ValueType::I32)?;
 			},
 
 			I32Clz | I32Ctz | I32Popcnt | I64Clz | I64Ctz | I64Popcnt | F32Abs | F32Neg |
 			F32Ceil | F32Floor | F32Trunc | F32Nearest | F32Sqrt | F64Abs | F64Neg | F64Ceil |
 			F64Floor | F64Trunc | F64Nearest | F64Sqrt => {
 				// Unary operators take one operand and produce one result.
-				stack.pop_values(1)?;
+				if let Some(vt) = stack.pop_value()? {
-				stack.push_values(1)?;
+					stack.push_value(vt)?;
+				}
 			},
 
 			I32Add | I32Sub | I32Mul | I32DivS | I32DivU | I32RemS | I32RemU | I32And | I32Or |
@@ -378,19 +474,34 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			F32Min | F32Max | F32Copysign | F64Add | F64Sub | F64Mul | F64Div | F64Min |
 			F64Max | F64Copysign => {
 				// Binary operators take two operands and produce one result.
-				stack.pop_values(2)?;
+				let val = stack.pop_value()?;
-				stack.push_values(1)?;
+				stack.pop_value()?;
+				if let Some(vt) = val {
+					stack.push_value(vt)?;
+				}
 			},
 
+			// Conversion operators take one value and produce one result.
 			I32WrapI64 | I32TruncSF32 | I32TruncUF32 | I32TruncSF64 | I32TruncUF64 |
+			I32ReinterpretF32 => {
+				stack.pop_value()?;
+				stack.push_value(ValueType::I32)?;
+			},
 			I64ExtendSI32 | I64ExtendUI32 | I64TruncSF32 | I64TruncUF32 | I64TruncSF64 |
-			I64TruncUF64 | F32ConvertSI32 | F32ConvertUI32 | F32ConvertSI64 | F32ConvertUI64 |
+			I64TruncUF64 | I64ReinterpretF64 => {
-			F32DemoteF64 | F64ConvertSI32 | F64ConvertUI32 | F64ConvertSI64 | F64ConvertUI64 |
+				stack.pop_value()?;
-			F64PromoteF32 | I32ReinterpretF32 | I64ReinterpretF64 | F32ReinterpretI32 |
+				stack.push_value(ValueType::I64)?;
+			},
+			F32ConvertSI32 | F32ConvertUI32 | F32ConvertSI64 | F32ConvertUI64 | F32DemoteF64 |
+			F32ReinterpretI32 => {
+				stack.pop_value()?;
+				stack.push_value(ValueType::F32)?;
+			},
+
+			F64ConvertSI32 | F64ConvertUI32 | F64ConvertSI64 | F64ConvertUI64 | F64PromoteF32 |
 			F64ReinterpretI64 => {
-				// Conversion operators take one value and produce one result.
+				stack.pop_value()?;
-				stack.pop_values(1)?;
+				stack.push_value(ValueType::F64)?;
-				stack.push_values(1)?;
 			},
 
 			#[cfg(feature = "sign_ext")]
@@ -398,15 +509,45 @@ pub fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, &'static
 			SignExt(SignExtInstruction::I32Extend16S) |
 			SignExt(SignExtInstruction::I64Extend8S) |
 			SignExt(SignExtInstruction::I64Extend16S) |
-			SignExt(SignExtInstruction::I64Extend32S) => {
+			SignExt(SignExtInstruction::I64Extend32S) =>
-				stack.pop_values(1)?;
+				if let Some(vt) = stack.pop_value()? {
-				stack.push_values(1)?;
+					stack.push_value(vt)?;
-			},
+				},
+		}
+
+		// If current value stack is heavier than maximal weight observed so far,
+		// save the new weight.
+		// However, we don't increase maximal value in unreachable code.
+		if !stack.frame(0)?.is_polymorphic {
+			let (cur_weight, cur_height) = (stack.weight(), stack.height());
+			if cur_weight > max_weight {
+				max_weight = cur_weight;
+				trace!("Max weight is now {}", max_weight);
+			}
+			if cur_height > max_height {
+				max_height = cur_height;
+				trace!("Max height is now {}", max_height);
+			}
+		}
+
+		// Post-execution stage: pop a control frame if block is ended
+		if *opcode == End {
+			stack.pop_frame()?;
 		}
-		pc += 1;
 	}
 
-	Ok(max_height)
+	trace!("Final max stack height: {} + {}", ACTIVATION_FRAME_HEIGHT, max_height);
+	trace!(
+		"Final max stack weight: {} + {} + {}",
+		ACTIVATION_FRAME_WEIGHT,
+		max_weight,
+		param_weight
+	);
+
+	Ok((
+		ACTIVATION_FRAME_HEIGHT + max_height as u32,
+		ACTIVATION_FRAME_WEIGHT + max_weight + param_weight,
+	))
 }
 
 #[cfg(test)]
@@ -414,6 +555,9 @@ mod tests {
 	use super::*;
 	use parity_wasm::elements;
 
+	#[cfg(feature = "trace-log")]
+	use test_log::test;
+
 	fn parse_wat(source: &str) -> elements::Module {
 		elements::deserialize_buffer(&wat::parse_str(source).expect("Failed to wat2wasm"))
 			.expect("Failed to deserialize the module")
@@ -436,8 +580,8 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 3 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 3, ACTIVATION_FRAME_WEIGHT + 12));
 	}
 
 	#[test]
@@ -446,15 +590,15 @@ mod tests {
 			r#"
 (module
 	(func (result i32)
-		i32.const 0
+		i64.const 0
 		return
 	)
 )
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 1 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 1, ACTIVATION_FRAME_WEIGHT + 8));
 	}
 
 	#[test]
@@ -471,8 +615,8 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT, ACTIVATION_FRAME_WEIGHT));
 	}
 
 	#[test]
@@ -500,8 +644,8 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 2 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 2, ACTIVATION_FRAME_WEIGHT + 8));
 	}
 
 	#[test]
@@ -524,8 +668,8 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 1 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 1, ACTIVATION_FRAME_WEIGHT + 4));
 	}
 
 	#[test]
@@ -546,8 +690,8 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 1 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 1, ACTIVATION_FRAME_WEIGHT + 4));
 	}
 
 	#[test]
@@ -572,7 +716,7 @@ mod tests {
 "#,
 		);
 
-		let height = compute(0, &module).unwrap();
+		let res = compute(0, &module).unwrap();
-		assert_eq!(height, 3 + ACTIVATION_FRAME_COST);
+		assert_eq!(res, (ACTIVATION_FRAME_HEIGHT + 3, ACTIVATION_FRAME_WEIGHT + 12));
 	}
 }

src/stack_limiter/mod.rs

@@ -154,7 +154,7 @@ fn generate_stack_height_global(module: &mut elements::Module) -> u32 {
 /// Calculate stack costs for all functions.
 ///
 /// Returns a vector with a stack cost for each function, including imports.
-fn compute_stack_costs(module: &elements::Module) -> Result<Vec<u32>, &'static str> {
+pub fn compute_stack_costs(module: &elements::Module) -> Result<Vec<u32>, &'static str> {
 	let func_imports = module.import_count(elements::ImportCountType::Function);
 
 	// TODO: optimize!
@@ -173,7 +173,7 @@ fn compute_stack_costs(module: &elements::Module) -> Result<Vec<u32>, &'static s
 /// Stack cost of the given *defined* function is the sum of it's locals count (that is,
 /// number of arguments plus number of local variables) and the maximal stack
 /// height.
-fn compute_stack_cost(func_idx: u32, module: &elements::Module) -> Result<u32, &'static str> {
+pub fn compute_stack_cost(func_idx: u32, module: &elements::Module) -> Result<u32, &'static str> {
 	// To calculate the cost of a function we need to convert index from
 	// function index space to defined function spaces.
 	let func_imports = module.import_count(elements::ImportCountType::Function) as u32;
@@ -194,13 +194,27 @@ fn compute_stack_cost(func_idx: u32, module: &elements::Module) -> Result<u32, &
 			locals_count.checked_add(local_group.count()).ok_or("Overflow in local count")?;
 	}
 
-	let max_stack_height = max_height::compute(defined_func_idx, module)?;
+	let (max_stack_height, _max_stack_weight) = max_height::compute(defined_func_idx, module)?;
 
 	locals_count
 		.checked_add(max_stack_height)
 		.ok_or("Overflow in adding locals_count and max_stack_height")
 }
 
+/// Stack height is the measurement maximum wasm stack height reached during function execution.
+/// Stack weight is weighted value which approximates a real stack size on x64 architecture.
+pub fn compute_stack_height_weight(
+	func_idx: u32,
+	module: &elements::Module,
+) -> Result<(u32, u32), &'static str> {
+	let func_imports = module.import_count(elements::ImportCountType::Function) as u32;
+	let defined_func_idx = func_idx
+		.checked_sub(func_imports)
+		.ok_or("This should be a index of a defined function")?;
+
+	max_height::compute(defined_func_idx, module)
+}
+
 fn instrument_functions(
 	ctx: &mut Context,
 	module: &mut elements::Module,

tests/diff.rs

@@ -1,9 +1,10 @@
+use parity_wasm::elements::Module;
 use std::{
 	fs,
 	io::{self, Read, Write},
 	path::{Path, PathBuf},
 };
-use wasm_instrument::{self as instrument, gas_metering, parity_wasm::elements};
+use wasm_instrument::{self as instrument, parity_wasm::elements};
 use wasmparser::validate;
 
 fn slurp<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
@@ -19,23 +20,18 @@ fn dump<P: AsRef<Path>>(path: P, buf: &[u8]) -> io::Result<()> {
 	Ok(())
 }
 
-fn run_diff_test<F: FnOnce(&[u8]) -> Vec<u8>>(
+fn run_diff_test<F: FnOnce(&[u8]) -> Vec<u8>>(test_dir: &str, name: &str, test: F) {
-	test_dir: &str,
-	in_name: &str,
-	out_name: &str,
-	test: F,
-) {
 	let mut fixture_path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
 	fixture_path.push("tests");
 	fixture_path.push("fixtures");
 	fixture_path.push(test_dir);
-	fixture_path.push(in_name);
+	fixture_path.push(name);
 
 	let mut expected_path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
 	expected_path.push("tests");
 	expected_path.push("expectations");
 	expected_path.push(test_dir);
-	expected_path.push(out_name);
+	expected_path.push(name);
 
 	let fixture_wasm = wat::parse_file(&fixture_path).expect("Failed to read fixture");
 	validate(&fixture_wasm).expect("Fixture is invalid");
@@ -52,7 +48,7 @@ fn run_diff_test<F: FnOnce(&[u8]) -> Vec<u8>>(
 	if actual_wat != expected_wat {
 		println!("difference!");
 		println!("--- {}", expected_path.display());
-		println!("+++ {} test {}", test_dir, out_name);
+		println!("+++ {} test {}", test_dir, name);
 		for diff in diff::lines(expected_wat, &actual_wat) {
 			match diff {
 				diff::Result::Left(l) => println!("-{}", l),
@@ -76,18 +72,13 @@ mod stack_height {
 		( $name:ident ) => {
 			#[test]
 			fn $name() {
-				run_diff_test(
+				run_diff_test("stack-height", concat!(stringify!($name), ".wat"), |input| {
-					"stack-height",
+					let module =
-					concat!(stringify!($name), ".wat"),
+						elements::deserialize_buffer(input).expect("Failed to deserialize");
-					concat!(stringify!($name), ".wat"),
+					let instrumented = instrument::inject_stack_limiter(module, 1024)
-					|input| {
+						.expect("Failed to instrument with stack counter");
-						let module =
+					elements::serialize(instrumented).expect("Failed to serialize")
-							elements::deserialize_buffer(input).expect("Failed to deserialize");
+				});
-						let instrumented = instrument::inject_stack_limiter(module, 1024)
-							.expect("Failed to instrument with stack counter");
-						elements::serialize(instrumented).expect("Failed to serialize")
-					},
-				);
 			}
 		};
 	}
@@ -105,53 +96,27 @@ mod gas {
 	use super::*;
 
 	macro_rules! def_gas_test {
-		( ($input:ident, $name1:ident, $name2:ident) ) => {
+		( $name:ident ) => {
 			#[test]
-			fn $name1() {
+			fn $name() {
-				run_diff_test(
+				run_diff_test("gas", concat!(stringify!($name), ".wat"), |input| {
-					"gas",
+					let rules = instrument::gas_metering::ConstantCostRules::default();
-					concat!(stringify!($input), ".wat"),
-					concat!(stringify!($name1), ".wat"),
-					|input| {
-						let rules = gas_metering::ConstantCostRules::default();
 
-						let module: elements::Module =
+					let module: Module =
-							elements::deserialize_buffer(input).expect("Failed to deserialize");
+						elements::deserialize_buffer(input).expect("Failed to deserialize");
-						let module = module.parse_names().expect("Failed to parse names");
+					let module = module.parse_names().expect("Failed to parse names");
-						let backend = gas_metering::host_function::Injector::new("env", "gas");
 
-						let instrumented = gas_metering::inject(module, backend, &rules)
+					let instrumented = instrument::gas_metering::inject(module, &rules, "env")
-							.expect("Failed to instrument with gas metering");
+						.expect("Failed to instrument with gas metering");
-						elements::serialize(instrumented).expect("Failed to serialize")
+					elements::serialize(instrumented).expect("Failed to serialize")
-					},
+				});
-				);
-			}
-
-			#[test]
-			fn $name2() {
-				run_diff_test(
-					"gas",
-					concat!(stringify!($input), ".wat"),
-					concat!(stringify!($name2), ".wat"),
-					|input| {
-						let rules = gas_metering::ConstantCostRules::default();
-
-						let module: elements::Module =
-							elements::deserialize_buffer(input).expect("Failed to deserialize");
-						let module = module.parse_names().expect("Failed to parse names");
-						let backend = gas_metering::mutable_global::Injector::new("gas_left");
-						let instrumented = gas_metering::inject(module, backend, &rules)
-							.expect("Failed to instrument with gas metering");
-						elements::serialize(instrumented).expect("Failed to serialize")
-					},
-				);
 			}
 		};
 	}
 
-	def_gas_test!((ifs, ifs_host_fn, ifs_mut_global));
+	def_gas_test!(ifs);
-	def_gas_test!((simple, simple_host_fn, simple_mut_global));
+	def_gas_test!(simple);
-	def_gas_test!((start, start_host_fn, start_mut_global));
+	def_gas_test!(start);
-	def_gas_test!((call, call_host_fn, call_mut_global));
+	def_gas_test!(call);
-	def_gas_test!((branch, branch_host_fn, branch_mut_global));
+	def_gas_test!(branch);
 }

tests/expectations/gas/branch.wat

@@ -1,12 +1,12 @@
 (module
   (type (;0;) (func (result i32)))
-  (type (;1;) (func (param i64)))
+  (type (;1;) (func (param i32)))
   (import "env" "gas" (func (;0;) (type 1)))
   (func $fibonacci_with_break (;1;) (type 0) (result i32)
     (local i32 i32)
-    i64.const 15
+    i32.const 13
     call 0
-    block ;; label = @1
+    block  ;; label = @1
       i32.const 0
       local.set 0
       i32.const 1
@@ -18,7 +18,7 @@
       local.set 1
       i32.const 1
       br_if 0 (;@1;)
-      i64.const 5
+      i32.const 5
       call 0
       local.get 0
       local.get 1

tests/expectations/gas/branch_mut_global.wat

@@ -1,47 +0,0 @@
-(module
-  (type (;0;) (func (result i32)))
-  (type (;1;) (func (param i64)))
-  (func $fibonacci_with_break (;0;) (type 0) (result i32)
-    (local $x i32) (local $y i32)
-    i64.const 26
-    call 1
-    block ;; label = @1
-      i32.const 0
-      local.set $x
-      i32.const 1
-      local.set $y
-      local.get $x
-      local.get $y
-      local.tee $x
-      i32.add
-      local.set $y
-      i32.const 1
-      br_if 0 (;@1;)
-      i64.const 16
-      call 1
-      local.get $x
-      local.get $y
-      local.tee $x
-      i32.add
-      local.set $y
-    end
-    local.get $y
-  )
-  (func (;1;) (type 1) (param i64)
-    global.get 0
-    local.get 0
-    i64.ge_u
-    if ;; label = @1
-      global.get 0
-      local.get 0
-      i64.sub
-      global.set 0
-    else
-      i64.const -1
-      global.set 0
-      unreachable
-    end
-  )
-  (global (;0;) (mut i64) i64.const 0)
-  (export "gas_left" (global 0))
-)

tests/expectations/gas/call.wat

@@ -1,10 +1,10 @@
 (module
   (type (;0;) (func (param i32 i32) (result i32)))
-  (type (;1;) (func (param i64)))
+  (type (;1;) (func (param i32)))
   (import "env" "gas" (func (;0;) (type 1)))
   (func $add_locals (;1;) (type 0) (param $x i32) (param $y i32) (result i32)
     (local i32)
-    i64.const 6
+    i32.const 5
     call 0
     local.get $x
     local.get $y
@@ -13,7 +13,7 @@
     local.get 2
   )
   (func $add (;2;) (type 0) (param i32 i32) (result i32)
-    i64.const 3
+    i32.const 3
     call 0
     local.get 0
     local.get 1

tests/expectations/gas/call_mut_global.wat

@@ -1,38 +0,0 @@
-(module
-  (type (;0;) (func (param i32 i32) (result i32)))
-  (type (;1;) (func (param i64)))
-  (func $add_locals (;0;) (type 0) (param $x i32) (param $y i32) (result i32)
-    (local $t i32)
-    i64.const 17
-    call 2
-    local.get $x
-    local.get $y
-    call $add
-    local.set $t
-    local.get $t
-  )
-  (func $add (;1;) (type 0) (param $x i32) (param $y i32) (result i32)
-    i64.const 14
-    call 2
-    local.get $x
-    local.get $y
-    i32.add
-  )
-  (func (;2;) (type 1) (param i64)
-    global.get 0
-    local.get 0
-    i64.ge_u
-    if ;; label = @1
-      global.get 0
-      local.get 0
-      i64.sub
-      global.set 0
-    else
-      i64.const -1
-      global.set 0
-      unreachable
-    end
-  )
-  (global (;0;) (mut i64) i64.const 0)
-  (export "gas_left" (global 0))
-)

tests/expectations/gas/ifs.wat

@@ -1,19 +1,19 @@
 (module
   (type (;0;) (func (param i32) (result i32)))
-  (type (;1;) (func (param i64)))
+  (type (;1;) (func (param i32)))
   (import "env" "gas" (func (;0;) (type 1)))
   (func (;1;) (type 0) (param i32) (result i32)
-    i64.const 2
+    i32.const 2
     call 0
     i32.const 1
-    if (result i32) ;; label = @1
+    if (result i32)  ;; label = @1
-      i64.const 3
+      i32.const 3
       call 0
       local.get 0
       i32.const 1
       i32.add
     else
-      i64.const 2
+      i32.const 2
       call 0
       local.get 0
       i32.popcnt

tests/expectations/gas/ifs_mut_global.wat

@@ -1,38 +0,0 @@
-(module
-  (type (;0;) (func (param i32) (result i32)))
-  (type (;1;) (func (param i64)))
-  (func (;0;) (type 0) (param $x i32) (result i32)
-    i64.const 13
-    call 1
-    i32.const 1
-    if (result i32) ;; label = @1
-      i64.const 14
-      call 1
-      local.get $x
-      i32.const 1
-      i32.add
-    else
-      i64.const 13
-      call 1
-      local.get $x
-      i32.popcnt
-    end
-  )
-  (func (;1;) (type 1) (param i64)
-    global.get 0
-    local.get 0
-    i64.ge_u
-    if ;; label = @1
-      global.get 0
-      local.get 0
-      i64.sub
-      global.set 0
-    else
-      i64.const -1
-      global.set 0
-      unreachable
-    end
-  )
-  (global (;0;) (mut i64) i64.const 0)
-  (export "gas_left" (global 0))
-)

tests/expectations/gas/simple.wat

@@ -1,16 +1,16 @@
 (module
   (type (;0;) (func))
-  (type (;1;) (func (param i64)))
+  (type (;1;) (func (param i32)))
   (import "env" "gas" (func (;0;) (type 1)))
   (func (;1;) (type 0)
-    i64.const 2
+    i32.const 2
     call 0
     i32.const 1
-    if ;; label = @1
+    if  ;; label = @1
-      i64.const 1
+      i32.const 1
       call 0
-      loop ;; label = @2
+      loop  ;; label = @2
-        i64.const 2
+        i32.const 2
         call 0
         i32.const 123
         drop
@@ -18,9 +18,9 @@
     end
   )
   (func (;2;) (type 0)
-    i64.const 1
+    i32.const 1
     call 0
-    block ;; label = @1
+    block  ;; label = @1
     end
   )
   (export "simple" (func 1))

tests/expectations/gas/simple_mut_global.wat

@@ -1,43 +0,0 @@
-(module
-  (type (;0;) (func))
-  (type (;1;) (func (param i64)))
-  (func (;0;) (type 0)
-    i64.const 13
-    call 2
-    i32.const 1
-    if ;; label = @1
-      i64.const 12
-      call 2
-      loop ;; label = @2
-        i64.const 13
-        call 2
-        i32.const 123
-        drop
-      end
-    end
-  )
-  (func (;1;) (type 0)
-    i64.const 12
-    call 2
-    block ;; label = @1
-    end
-  )
-  (func (;2;) (type 1) (param i64)
-    global.get 0
-    local.get 0
-    i64.ge_u
-    if ;; label = @1
-      global.get 0
-      local.get 0
-      i64.sub
-      global.set 0
-    else
-      i64.const -1
-      global.set 0
-      unreachable
-    end
-  )
-  (global (;0;) (mut i64) i64.const 0)
-  (export "simple" (func 0))
-  (export "gas_left" (global 0))
-)

tests/expectations/gas/start.wat

@@ -1,12 +1,12 @@
 (module
   (type (;0;) (func (param i32 i32)))
   (type (;1;) (func))
-  (type (;2;) (func (param i64)))
+  (type (;2;) (func (param i32)))
   (import "env" "ext_return" (func $ext_return (;0;) (type 0)))
   (import "env" "memory" (memory (;0;) 1 1))
   (import "env" "gas" (func (;1;) (type 2)))
   (func $start (;2;) (type 1)
-    i64.const 4
+    i32.const 4
     call 1
     i32.const 8
     i32.const 4

tests/expectations/gas/start_mut_global.wat

@@ -1,36 +0,0 @@
-(module
-  (type (;0;) (func (param i32 i32)))
-  (type (;1;) (func))
-  (type (;2;) (func (param i64)))
-  (import "env" "ext_return" (func $ext_return (;0;) (type 0)))
-  (import "env" "memory" (memory (;0;) 1 1))
-  (func $start (;1;) (type 1)
-    i64.const 15
-    call 3
-    i32.const 8
-    i32.const 4
-    call $ext_return
-    unreachable
-  )
-  (func (;2;) (type 1))
-  (func (;3;) (type 2) (param i64)
-    global.get 0
-    local.get 0
-    i64.ge_u
-    if ;; label = @1
-      global.get 0
-      local.get 0
-      i64.sub
-      global.set 0
-    else
-      i64.const -1
-      global.set 0
-      unreachable
-    end
-  )
-  (global (;0;) (mut i64) i64.const 0)
-  (export "call" (func 2))
-  (export "gas_left" (global 0))
-  (start $start)
-  (data (;0;) (i32.const 8) "\01\02\03\04")
-)

tests/expectations/stack-height/empty_functions.wat

@@ -8,7 +8,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 0
@@ -25,7 +25,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 0
@@ -42,7 +42,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 1

tests/expectations/stack-height/global.wat

@@ -24,7 +24,7 @@
     global.get 1
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $i32.add
@@ -44,7 +44,7 @@
     global.get 1
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $i32.add

tests/expectations/stack-height/imports.wat

@@ -20,7 +20,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 2

tests/expectations/stack-height/many_locals.wat

@@ -11,7 +11,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $one-group-many-locals

tests/expectations/stack-height/simple.wat

@@ -12,7 +12,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 0

tests/expectations/stack-height/start.wat

@@ -15,7 +15,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $start
@@ -32,7 +32,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 2

tests/expectations/stack-height/table.wat

@@ -13,7 +13,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $i32.add
@@ -37,7 +37,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call 1
@@ -56,7 +56,7 @@
     global.get 0
     i32.const 1024
     i32.gt_u
-    if ;; label = @1
+    if  ;; label = @1
       unreachable
     end
     call $i32.add

tests/overhead.rs

@@ -1,10 +1,9 @@
 use std::{
-	fs::{read, read_dir, ReadDir},
+	fs::{read, read_dir},
 	path::PathBuf,
 };
 use wasm_instrument::{
-	gas_metering::{self, host_function, mutable_global, ConstantCostRules},
+	gas_metering, inject_stack_limiter,
-	inject_stack_limiter,
 	parity_wasm::{deserialize_buffer, elements::Module, serialize},
 };
 
@@ -15,157 +14,60 @@ fn fixture_dir() -> PathBuf {
 	path
 }
 
-use gas_metering::Backend;
+/// Print the overhead of applying gas metering, stack height limiting or both.
-fn gas_metered_mod_len<B: Backend>(orig_module: Module, backend: B) -> (Module, usize) {
+///
-	let module = gas_metering::inject(orig_module, backend, &ConstantCostRules::default()).unwrap();
+/// Use `cargo test print_overhead -- --nocapture`.
-	let bytes = serialize(module.clone()).unwrap();
+#[test]
-	let len = bytes.len();
+fn print_size_overhead() {
-	(module, len)
+	let mut results: Vec<_> = read_dir(fixture_dir())
-}
+		.unwrap()
-
-fn stack_limited_mod_len(module: Module) -> (Module, usize) {
-	let module = inject_stack_limiter(module, 128).unwrap();
-	let bytes = serialize(module.clone()).unwrap();
-	let len = bytes.len();
-	(module, len)
-}
-
-struct InstrumentedWasmResults {
-	filename: String,
-	original_module_len: usize,
-	stack_limited_len: usize,
-	gas_metered_host_fn_len: usize,
-	gas_metered_mut_glob_len: usize,
-	gas_metered_host_fn_then_stack_limited_len: usize,
-	gas_metered_mut_glob_then_stack_limited_len: usize,
-}
-
-fn size_overheads_all(files: ReadDir) -> Vec<InstrumentedWasmResults> {
-	files
 		.map(|entry| {
 			let entry = entry.unwrap();
-			let filename = entry.file_name().into_string().unwrap();
+			let (orig_len, orig_module) = {
-
+				let bytes = read(&entry.path()).unwrap();
-			let (original_module_len, orig_module) = {
-				let bytes = match entry.path().extension().unwrap().to_str() {
-					Some("wasm") => read(&entry.path()).unwrap(),
-					Some("wat") =>
-						wat::parse_bytes(&read(&entry.path()).unwrap()).unwrap().into_owned(),
-					_ => panic!("expected fixture_dir containing .wasm or .wat files only"),
-				};
-
 				let len = bytes.len();
 				let module: Module = deserialize_buffer(&bytes).unwrap();
 				(len, module)
 			};
+			let (gas_metering_len, gas_module) = {
+				let module = gas_metering::inject(
+					orig_module.clone(),
+					&gas_metering::ConstantCostRules::default(),
+					"env",
+				)
+				.unwrap();
+				let bytes = serialize(module.clone()).unwrap();
+				let len = bytes.len();
+				(len, module)
+			};
+			let stack_height_len = {
+				let module = inject_stack_limiter(orig_module, 128).unwrap();
+				let bytes = serialize(module).unwrap();
+				bytes.len()
+			};
+			let both_len = {
+				let module = inject_stack_limiter(gas_module, 128).unwrap();
+				let bytes = serialize(module).unwrap();
+				bytes.len()
+			};
 
-			let (gm_host_fn_module, gas_metered_host_fn_len) = gas_metered_mod_len(
+			let overhead = both_len * 100 / orig_len;
-				orig_module.clone(),
-				host_function::Injector::new("env", "gas"),
-			);
 
-			let (gm_mut_global_module, gas_metered_mut_glob_len) =
+			(
-				gas_metered_mod_len(orig_module.clone(), mutable_global::Injector::new("gas_left"));
+				overhead,
-
+				format!(
-			let stack_limited_len = stack_limited_mod_len(orig_module).1;
+					"{:30}: orig = {:4} kb, gas_metering = {} %, stack_limiter = {} %, both = {} %",
-
+					entry.file_name().to_str().unwrap(),
-			let (_gm_hf_sl_mod, gas_metered_host_fn_then_stack_limited_len) =
+					orig_len / 1024,
-				stack_limited_mod_len(gm_host_fn_module);
+					gas_metering_len * 100 / orig_len,
-
+					stack_height_len * 100 / orig_len,
-			let (_gm_mg_sl_module, gas_metered_mut_glob_then_stack_limited_len) =
+					overhead,
-				stack_limited_mod_len(gm_mut_global_module);
+				),
-
+			)
-			InstrumentedWasmResults {
-				filename,
-				original_module_len,
-				stack_limited_len,
-				gas_metered_host_fn_len,
-				gas_metered_mut_glob_len,
-				gas_metered_host_fn_then_stack_limited_len,
-				gas_metered_mut_glob_then_stack_limited_len,
-			}
 		})
-		.collect()
+		.collect();
-}
-
-fn calc_size_overheads() -> Vec<InstrumentedWasmResults> {
-	let mut wasm_path = fixture_dir();
-	wasm_path.push("wasm");
-
-	let mut wat_path = fixture_dir();
-	wat_path.push("wat");
-
-	let mut results = size_overheads_all(read_dir(wasm_path).unwrap());
-	let results_wat = size_overheads_all(read_dir(wat_path).unwrap());
-
-	results.extend(results_wat);
-
-	results
-}
-
-/// Print the overhead of applying gas metering, stack
-/// height limiting or both.
-///
-/// Use `cargo test print_size_overhead -- --nocapture`.
-#[test]
-fn print_size_overhead() {
-	let mut results = calc_size_overheads();
-	results.sort_unstable_by(|a, b| {
-		b.gas_metered_mut_glob_then_stack_limited_len
-			.cmp(&a.gas_metered_mut_glob_then_stack_limited_len)
-	});
-
-	for r in results {
-		let filename = r.filename;
-		let original_size = r.original_module_len / 1024;
-		let stack_limit = r.stack_limited_len * 100 / r.original_module_len;
-		let host_fn = r.gas_metered_host_fn_len * 100 / r.original_module_len;
-		let mut_glob = r.gas_metered_mut_glob_len * 100 / r.original_module_len;
-		let host_fn_sl = r.gas_metered_host_fn_then_stack_limited_len * 100 / r.original_module_len;
-		let mut_glob_sl =
-			r.gas_metered_mut_glob_then_stack_limited_len * 100 / r.original_module_len;
-
-		println!(
-			"{filename:30}: orig = {original_size:4} kb, stack_limiter = {stack_limit} %, \
-			  gas_metered_host_fn =    {host_fn} %, both = {host_fn_sl} %,\n \
-			 {:69} gas_metered_mut_global = {mut_glob} %, both = {mut_glob_sl} %",
-			""
-		);
-	}
-}
-
-/// Compare module size overhead of applying gas metering with two methods.
-///
-/// Use `cargo test print_gas_metered_sizes -- --nocapture`.
-#[test]
-fn print_gas_metered_sizes() {
-	let overheads = calc_size_overheads();
-	let mut results = overheads
-		.iter()
-		.map(|r| {
-			let diff = (r.gas_metered_mut_glob_len * 100 / r.gas_metered_host_fn_len) as i32 - 100;
-			(diff, r)
-		})
-		.collect::<Vec<(i32, &InstrumentedWasmResults)>>();
 	results.sort_unstable_by(|a, b| b.0.cmp(&a.0));
-
+	for entry in results {
-	println!(
+		println!("{}", entry.1);
-		"| {:28} | {:^16} | gas metered/host fn | gas metered/mut global | size diff |",
-		"fixture", "original size",
-	);
-	println!("|{:-^30}|{:-^18}|{:-^21}|{:-^24}|{:-^11}|", "", "", "", "", "",);
-	for r in results {
-		let filename = &r.1.filename;
-		let original_size = &r.1.original_module_len / 1024;
-		let host_fn = &r.1.gas_metered_host_fn_len / 1024;
-		let mut_glob = &r.1.gas_metered_mut_glob_len / 1024;
-		let host_fn_percent = &r.1.gas_metered_host_fn_len * 100 / r.1.original_module_len;
-		let mut_glob_percent = &r.1.gas_metered_mut_glob_len * 100 / r.1.original_module_len;
-		let host_fn = format!("{host_fn} kb ({host_fn_percent:}%)");
-		let mut_glob = format!("{mut_glob} kb ({mut_glob_percent:}%)");
-		let diff = &r.0;
-		println!(
-			"| {filename:28} | {original_size:13} kb | {host_fn:>19} | {mut_glob:>22} | {diff:+8}% |"
-		);
 	}
 }