diff_wasmi.rs

//! Evaluate an exported Wasm function using the wasmi interpreter.

use crate::generators::{Config, DiffValue, DiffValueType};
use crate::oracles::engine::{DiffEngine, DiffInstance};
use wasmtime::{Error, Result, Trap, error::Context as _};

/// A wrapper for `wasmi` as a [`DiffEngine`].
pub struct WasmiEngine {
    engine: wasmi::Engine,
}

impl WasmiEngine {
    pub(crate) fn new(config: &mut Config) -> Self {
        let config = &mut config.module_config.config;
        // Force generated Wasm modules to never have features that Wasmi doesn't support.
        config.relaxed_simd_enabled = false;
        config.threads_enabled = false;
        config.exceptions_enabled = false;
        config.gc_enabled = false;

        let mut wasmi_config = wasmi::Config::default();
        wasmi_config
            .consume_fuel(false)
            .floats(true)
            .wasm_mutable_global(true)
            .wasm_sign_extension(config.sign_extension_ops_enabled)
            .wasm_saturating_float_to_int(config.saturating_float_to_int_enabled)
            .wasm_multi_value(config.multi_value_enabled)
            .wasm_bulk_memory(config.bulk_memory_enabled)
            .wasm_reference_types(config.reference_types_enabled)
            .wasm_tail_call(config.tail_call_enabled)
            .wasm_multi_memory(config.max_memories > 1)
            .wasm_extended_const(config.extended_const_enabled)
            .wasm_custom_page_sizes(config.custom_page_sizes_enabled)
            .wasm_memory64(config.memory64_enabled)
            .wasm_simd(config.simd_enabled)
            .wasm_wide_arithmetic(config.wide_arithmetic_enabled);
        Self {
            engine: wasmi::Engine::new(&wasmi_config),
        }
    }

    fn trap_code(&self, err: &Error) -> Option<wasmi::TrapCode> {
        let err = err.downcast_ref::<wasmi::Error>()?;
        if let Some(code) = err.as_trap_code() {
            return Some(code);
        }

        match err.kind() {
            wasmi::errors::ErrorKind::Instantiation(
                wasmi::errors::InstantiationError::ElementSegmentDoesNotFit { .. },
            ) => Some(wasmi::TrapCode::TableOutOfBounds),
            wasmi::errors::ErrorKind::Memory(wasmi::errors::MemoryError::OutOfBoundsAccess) => {
                Some(wasmi::TrapCode::MemoryOutOfBounds)
            }
            wasmi::errors::ErrorKind::Table(wasmi::errors::TableError::CopyOutOfBounds) => {
                Some(wasmi::TrapCode::TableOutOfBounds)
            }
            _ => {
                log::trace!("unknown wasmi error: {:?}", err.kind());
                None
            }
        }
    }
}

impl DiffEngine for WasmiEngine {
    fn name(&self) -> &'static str {
        "wasmi"
    }

    fn instantiate(&mut self, wasm: &[u8]) -> Result<Box<dyn DiffInstance>> {
        let module =
            wasmi::Module::new(&self.engine, wasm).context("unable to validate Wasm module")?;
        let mut store = wasmi::Store::new(&self.engine, ());
        let instance = wasmi::Linker::<()>::new(&self.engine)
            .instantiate_and_start(&mut store, &module)
            .context("unable to instantiate module in wasmi")?;
        Ok(Box::new(WasmiInstance { store, instance }))
    }

    fn assert_error_match(&self, lhs: &Error, rhs: &Trap) {
        match self.trap_code(lhs) {
            Some(code) => assert_eq!(wasmi_to_wasmtime_trap_code(code), *rhs),
            None => panic!("unexpected wasmi error {lhs:?}"),
        }
    }

    fn is_non_deterministic_error(&self, err: &Error) -> bool {
        matches!(self.trap_code(err), Some(wasmi::TrapCode::StackOverflow))
    }
}

/// Converts `wasmi` trap code to `wasmtime` trap code.
fn wasmi_to_wasmtime_trap_code(trap: wasmi::TrapCode) -> Trap {
    use wasmi::TrapCode;
    match trap {
        TrapCode::UnreachableCodeReached => Trap::UnreachableCodeReached,
        TrapCode::MemoryOutOfBounds => Trap::MemoryOutOfBounds,
        TrapCode::TableOutOfBounds => Trap::TableOutOfBounds,
        TrapCode::IndirectCallToNull => Trap::IndirectCallToNull,
        TrapCode::IntegerDivisionByZero => Trap::IntegerDivisionByZero,
        TrapCode::IntegerOverflow => Trap::IntegerOverflow,
        TrapCode::BadConversionToInteger => Trap::BadConversionToInteger,
        TrapCode::StackOverflow => Trap::StackOverflow,
        TrapCode::BadSignature => Trap::BadSignature,
        TrapCode::OutOfFuel => unimplemented!("built-in fuel metering is unused"),
        TrapCode::GrowthOperationLimited => unimplemented!("resource limiter is unused"),
    }
}

/// A wrapper for `wasmi` Wasm instances.
struct WasmiInstance {
    store: wasmi::Store<()>,
    instance: wasmi::Instance,
}

impl DiffInstance for WasmiInstance {
    fn name(&self) -> &'static str {
        "wasmi"
    }

    fn evaluate(
        &mut self,
        function_name: &str,
        arguments: &[DiffValue],
        result_tys: &[DiffValueType],
    ) -> Result<Option<Vec<DiffValue>>> {
        let function = self
            .instance
            .get_export(&self.store, function_name)
            .and_then(wasmi::Extern::into_func)
            .unwrap();
        let arguments: Vec<_> = arguments.iter().map(|x| x.into()).collect();
        let mut results = vec![wasmi::Val::I32(0); result_tys.len()];
        function
            .call(&mut self.store, &arguments, &mut results)
            .context("wasmi function trap")?;
        Ok(Some(results.into_iter().map(Into::into).collect()))
    }

    fn get_global(&mut self, name: &str, _ty: DiffValueType) -> Option<DiffValue> {
        Some(
            self.instance
                .get_export(&self.store, name)
                .unwrap()
                .into_global()
                .unwrap()
                .get(&self.store)
                .into(),
        )
    }

    fn get_memory(&mut self, name: &str, shared: bool) -> Option<Vec<u8>> {
        assert!(!shared);
        Some(
            self.instance
                .get_export(&self.store, name)
                .unwrap()
                .into_memory()
                .unwrap()
                .data(&self.store)
                .to_vec(),
        )
    }
}

impl From<&DiffValue> for wasmi::Val {
    fn from(v: &DiffValue) -> Self {
        use wasmi::Val as WasmiValue;
        match *v {
            DiffValue::I32(n) => WasmiValue::I32(n),
            DiffValue::I64(n) => WasmiValue::I64(n),
            DiffValue::F32(n) => WasmiValue::F32(wasmi::F32::from_bits(n)),
            DiffValue::F64(n) => WasmiValue::F64(wasmi::F64::from_bits(n)),
            DiffValue::V128(n) => WasmiValue::V128(wasmi::V128::from(n)),
            DiffValue::FuncRef { null } => {
                assert!(null);
                WasmiValue::default(wasmi::ValType::FuncRef)
            }
            DiffValue::ExternRef { null } => {
                assert!(null);
                WasmiValue::default(wasmi::ValType::ExternRef)
            }
            DiffValue::AnyRef { .. } => unimplemented!(),
            DiffValue::ExnRef { .. } => unimplemented!(),
            DiffValue::ContRef { .. } => unimplemented!(),
        }
    }
}

impl From<wasmi::Val> for DiffValue {
    fn from(value: wasmi::Val) -> Self {
        use wasmi::Val as WasmiValue;
        match value {
            WasmiValue::I32(n) => DiffValue::I32(n),
            WasmiValue::I64(n) => DiffValue::I64(n),
            WasmiValue::F32(n) => DiffValue::F32(n.to_bits()),
            WasmiValue::F64(n) => DiffValue::F64(n.to_bits()),
            WasmiValue::V128(n) => DiffValue::V128(n.as_u128()),
            WasmiValue::FuncRef(f) => DiffValue::FuncRef { null: f.is_null() },
            WasmiValue::ExternRef(e) => DiffValue::ExternRef { null: e.is_null() },
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn smoke() {
        crate::oracles::engine::smoke_test_engine(|_, config| Ok(WasmiEngine::new(config)))
    }
}