Support useTicks host function

src/main.rs

@@ -9,7 +9,7 @@ use wasmi::memory_units::Pages;
 use wasmi::{
  Error as InterpreterError, Externals, FuncInstance, FuncRef, ImportsBuilder, MemoryInstance,
  MemoryRef, Module, ModuleImportResolver, ModuleInstance, NopExternals, RuntimeArgs,
- RuntimeValue, Signature, Trap, ValueType,
+ RuntimeValue, Signature, Trap, TrapKind, ValueType,
 };
 
 mod types;
@@ -20,8 +20,10 @@ const BLOCKDATASIZE_FUNC_INDEX: usize = 1;
 const BLOCKDATACOPY_FUNC_INDEX: usize = 2;
 const SAVEPOSTSTATEROOT_FUNC_INDEX: usize = 3;
 const PUSHNEWDEPOSIT_FUNC_INDEX: usize = 4;
+const USETICKS_FUNC_INDEX: usize = 5;
 
 struct Runtime<'a> {
+ ticks_left: u32,
  memory: Option<MemoryRef>,
  pre_state: &'a Bytes32,
  block_data: &'a ShardBlockBody,
@@ -35,6 +37,7 @@ impl<'a> Runtime<'a> {
  memory: Option<MemoryRef>,
  ) -> Runtime<'a> {
  Runtime {
+ ticks_left: 10_000_000, // FIXME: make this configurable
  memory: if memory.is_some() {
  memory
  } else {
@@ -59,6 +62,15 @@ impl<'a> Externals for Runtime<'a> {
  args: RuntimeArgs,
  ) -> Result<Option<RuntimeValue>, Trap> {
  match index {
+ USETICKS_FUNC_INDEX => {
+ let ticks: u32 = args.nth(0);
+ if self.ticks_left < ticks {
+ // FIXME: use TrapKind::Host
+ return Err(Trap::new(TrapKind::Unreachable));
+ }
+ self.ticks_left -= ticks;
+ Ok(None)
+ }
  LOADPRESTATEROOT_FUNC_INDEX => {
  let ptr: u32 = args.nth(0);
  println!("loadprestateroot to {}", ptr);
@@ -124,6 +136,10 @@ impl<'a> ModuleImportResolver for RuntimeModuleImportResolver {
  _signature: &Signature,
  ) -> Result<FuncRef, InterpreterError> {
  let func_ref = match field_name {
+ "eth2_useTicks" => FuncInstance::alloc_host(
+ Signature::new(&[ValueType::I32][..], None),
+ USETICKS_FUNC_INDEX,
+ ),
  "eth2_loadPreStateRoot" => FuncInstance::alloc_host(
  Signature::new(&[ValueType::I32][..], None),
  LOADPRESTATEROOT_FUNC_INDEX,