wasmer/lib/middleware-common/src/metering.rs

131 lines
4.9 KiB
Rust

use wasmer_runtime_core::{
codegen::{Event, EventSink, FunctionMiddleware, InternalEvent},
module::ModuleInfo,
vm::{Ctx, InternalField},
wasmparser::{Operator, Type as WpType, TypeOrFuncType as WpTypeOrFuncType},
Instance,
};
static INTERNAL_FIELD: InternalField = InternalField::allocate();
/// Metering is a compiler middleware that calculates the cost of WebAssembly instructions at compile
/// time and will count the cost of executed instructions at runtime. Within the Metering functionality,
/// this instruction cost is called `points`.
///
/// The Metering struct takes a `limit` parameter which is the maximum number of points which can be
/// used by an instance during a function call. If this limit is exceeded, the function call will
/// trap. Each instance has a `points_used` field which can be used to track points used during
/// a function call and should be set back to zero after a function call.
///
/// Each compiler backend with Metering enabled should produce the same cost used at runtime for
/// the same function calls so we can say that the metering is deterministic.
///
pub struct Metering {
limit: u64,
current_block: u64,
}
impl Metering {
pub fn new(limit: u64) -> Metering {
Metering {
limit,
current_block: 0,
}
}
}
#[derive(Copy, Clone, Debug)]
pub struct ExecutionLimitExceededError;
impl FunctionMiddleware for Metering {
type Error = String;
fn feed_event<'a, 'b: 'a>(
&mut self,
op: Event<'a, 'b>,
_module_info: &ModuleInfo,
sink: &mut EventSink<'a, 'b>,
) -> Result<(), Self::Error> {
match op {
Event::Internal(InternalEvent::FunctionBegin(_)) => {
self.current_block = 0;
}
Event::Wasm(&ref op) | Event::WasmOwned(ref op) => {
self.current_block += 1;
match *op {
Operator::Loop { .. }
| Operator::Block { .. }
| Operator::End
| Operator::If { .. }
| Operator::Else
| Operator::Unreachable
| Operator::Br { .. }
| Operator::BrTable { .. }
| Operator::BrIf { .. }
| Operator::Call { .. }
| Operator::CallIndirect { .. }
| Operator::Return => {
sink.push(Event::Internal(InternalEvent::GetInternal(
INTERNAL_FIELD.index() as _,
)));
sink.push(Event::WasmOwned(Operator::I64Const {
value: self.current_block as i64,
}));
sink.push(Event::WasmOwned(Operator::I64Add));
sink.push(Event::Internal(InternalEvent::SetInternal(
INTERNAL_FIELD.index() as _,
)));
self.current_block = 0;
}
_ => {}
}
match *op {
Operator::Br { .. }
| Operator::BrTable { .. }
| Operator::BrIf { .. }
| Operator::Call { .. }
| Operator::CallIndirect { .. } => {
sink.push(Event::Internal(InternalEvent::GetInternal(
INTERNAL_FIELD.index() as _,
)));
sink.push(Event::WasmOwned(Operator::I64Const {
value: self.limit as i64,
}));
sink.push(Event::WasmOwned(Operator::I64GeU));
sink.push(Event::WasmOwned(Operator::If {
ty: WpTypeOrFuncType::Type(WpType::EmptyBlockType),
}));
sink.push(Event::Internal(InternalEvent::Breakpoint(Box::new(|_| {
Err(Box::new(ExecutionLimitExceededError))
}))));
sink.push(Event::WasmOwned(Operator::End));
}
_ => {}
}
}
_ => {}
}
sink.push(op);
Ok(())
}
}
/// Returns the number of points used by an Instance.
pub fn get_points_used(instance: &Instance) -> u64 {
instance.get_internal(&INTERNAL_FIELD)
}
/// Sets the number of points used by an Instance.
pub fn set_points_used(instance: &mut Instance, value: u64) {
instance.set_internal(&INTERNAL_FIELD, value);
}
/// Returns the number of points used in a Ctx.
pub fn get_points_used_ctx(ctx: &Ctx) -> u64 {
ctx.get_internal(&INTERNAL_FIELD)
}
/// Sets the number of points used in a Ctx.
pub fn set_points_used_ctx(ctx: &mut Ctx, value: u64) {
ctx.set_internal(&INTERNAL_FIELD, value);
}