wasmtime 0.28.0

//! Support for a calling of an imported function.

use crate::{Engine, FuncType, Trap};
use anyhow::Result;
use std::any::Any;
use std::cmp;
use std::mem;
use std::panic::{self, AssertUnwindSafe};
use std::sync::Arc;
use wasmtime_environ::entity::PrimaryMap;
use wasmtime_environ::isa::TargetIsa;
use wasmtime_environ::wasm::SignatureIndex;
use wasmtime_environ::{ir, wasm, CompiledFunction, Module, ModuleType};
use wasmtime_jit::trampoline::ir::{
    ExternalName, Function, InstBuilder, MemFlags, StackSlotData, StackSlotKind,
};
use wasmtime_jit::trampoline::{
    self, binemit, pretty_error, Context, FunctionBuilder, FunctionBuilderContext,
};
use wasmtime_jit::CodeMemory;
use wasmtime_jit::{blank_sig, wasmtime_call_conv};
use wasmtime_runtime::{
    Imports, InstanceAllocationRequest, InstanceAllocator, InstanceHandle,
    OnDemandInstanceAllocator, VMContext, VMFunctionBody, VMSharedSignatureIndex, VMTrampoline,
};

struct TrampolineState {
    func: Box<dyn Fn(*mut VMContext, *mut u128) -> Result<(), Trap> + Send + Sync>,
    #[allow(dead_code)]
    code_memory: CodeMemory,
}

unsafe extern "C" fn stub_fn(
    vmctx: *mut VMContext,
    caller_vmctx: *mut VMContext,
    values_vec: *mut u128,
) {
    // Here we are careful to use `catch_unwind` to ensure Rust panics don't
    // unwind past us. The primary reason for this is that Rust considers it UB
    // to unwind past an `extern "C"` function. Here we are in an `extern "C"`
    // function and the cross into wasm was through an `extern "C"` function at
    // the base of the stack as well. We'll need to wait for assorted RFCs and
    // language features to enable this to be done in a sound and stable fashion
    // before avoiding catching the panic here.
    //
    // Also note that there are intentionally no local variables on this stack
    // frame. The reason for that is that some of the "raise" functions we have
    // below will trigger a longjmp, which won't run local destructors if we
    // have any. To prevent leaks we avoid having any local destructors by
    // avoiding local variables.
    let result = panic::catch_unwind(AssertUnwindSafe(|| {
        call_stub(vmctx, caller_vmctx, values_vec)
    }));

    match result {
        Ok(Ok(())) => {}

        // If a trap was raised (an error returned from the imported function)
        // then we smuggle the trap through `Box<dyn Error>` through to the
        // call-site, which gets unwrapped in `Trap::from_runtime` later on as we
        // convert from the internal `Trap` type to our own `Trap` type in this
        // crate.
        Ok(Err(trap)) => wasmtime_runtime::raise_user_trap(Box::new(trap)),

        // And finally if the imported function panicked, then we trigger the
        // form of unwinding that's safe to jump over wasm code on all
        // platforms.
        Err(panic) => wasmtime_runtime::resume_panic(panic),
    }

    unsafe fn call_stub(
        vmctx: *mut VMContext,
        caller_vmctx: *mut VMContext,
        values_vec: *mut u128,
    ) -> Result<(), Trap> {
        let instance = InstanceHandle::from_vmctx(vmctx);
        let state = &instance
            .host_state()
            .downcast_ref::<TrampolineState>()
            .expect("state");
        (state.func)(caller_vmctx, values_vec)
    }
}

/// Create a trampoline for invoking a function.
fn make_trampoline(
    isa: &dyn TargetIsa,
    code_memory: &mut CodeMemory,
    fn_builder_ctx: &mut FunctionBuilderContext,
    signature: &ir::Signature,
) -> *mut [VMFunctionBody] {
    // Mostly reverse copy of the similar method from wasmtime's
    // wasmtime-jit/src/compiler.rs.
    let pointer_type = isa.pointer_type();
    let mut stub_sig = blank_sig(isa, wasmtime_call_conv(isa));

    // Add the `values_vec` parameter.
    stub_sig.params.push(ir::AbiParam::new(pointer_type));

    // Compute the size of the values vector. The vmctx and caller vmctx are passed separately.
    let value_size = mem::size_of::<u128>();
    let values_vec_len = ((value_size as usize)
        * cmp::max(signature.params.len() - 2, signature.returns.len()))
        as u32;

    let mut context = Context::new();
    context.func = Function::with_name_signature(ExternalName::user(0, 0), signature.clone());

    let ss = context.func.create_stack_slot(StackSlotData::new(
        StackSlotKind::ExplicitSlot,
        values_vec_len,
    ));

    {
        let mut builder = FunctionBuilder::new(&mut context.func, fn_builder_ctx);
        let block0 = builder.create_block();

        builder.append_block_params_for_function_params(block0);
        builder.switch_to_block(block0);
        builder.seal_block(block0);

        let values_vec_ptr_val = builder.ins().stack_addr(pointer_type, ss, 0);
        let mflags = MemFlags::trusted();
        for i in 2..signature.params.len() {
            let val = builder.func.dfg.block_params(block0)[i];
            builder.ins().store(
                mflags,
                val,
                values_vec_ptr_val,
                ((i - 2) * value_size) as i32,
            );
        }

        let block_params = builder.func.dfg.block_params(block0);
        let vmctx_ptr_val = block_params[0];
        let caller_vmctx_ptr_val = block_params[1];

        let callee_args = vec![vmctx_ptr_val, caller_vmctx_ptr_val, values_vec_ptr_val];

        let new_sig = builder.import_signature(stub_sig);

        let callee_value = builder
            .ins()
            .iconst(pointer_type, stub_fn as *const VMFunctionBody as i64);
        builder
            .ins()
            .call_indirect(new_sig, callee_value, &callee_args);

        let mflags = MemFlags::trusted();
        let mut results = Vec::new();
        for (i, r) in signature.returns.iter().enumerate() {
            let load = builder.ins().load(
                r.value_type,
                mflags,
                values_vec_ptr_val,
                (i * value_size) as i32,
            );
            results.push(load);
        }
        builder.ins().return_(&results);
        builder.finalize()
    }

    let mut code_buf: Vec<u8> = Vec::new();
    let mut reloc_sink = trampoline::TrampolineRelocSink::default();
    let mut trap_sink = binemit::NullTrapSink {};
    let mut stack_map_sink = binemit::NullStackMapSink {};
    context
        .compile_and_emit(
            isa,
            &mut code_buf,
            &mut reloc_sink,
            &mut trap_sink,
            &mut stack_map_sink,
        )
        .map_err(|error| pretty_error(&context.func, Some(isa), error))
        .expect("compile_and_emit");

    let unwind_info = context
        .create_unwind_info(isa)
        .map_err(|error| pretty_error(&context.func, Some(isa), error))
        .expect("create unwind information");

    assert!(reloc_sink.relocs().is_empty());
    code_memory
        .allocate_for_function(&CompiledFunction {
            body: code_buf,
            jt_offsets: context.func.jt_offsets,
            unwind_info,
            relocations: Default::default(),
            address_map: Default::default(),
            stack_maps: Default::default(),
            stack_slots: Default::default(),
            traps: Default::default(),
            value_labels_ranges: Default::default(),
        })
        .expect("allocate_for_function")
}

pub fn create_function(
    ft: &FuncType,
    func: Box<dyn Fn(*mut VMContext, *mut u128) -> Result<(), Trap> + Send + Sync>,
    engine: &Engine,
) -> Result<(InstanceHandle, VMTrampoline)> {
    // Note that we specifically enable reference types here in our ISA because
    // `Func::new` is intended to be infallible, but our signature may use
    // reference types which requires safepoints.
    let isa = engine.config().target_isa_with_reference_types();

    let mut sig = blank_sig(&*isa, wasmtime_call_conv(&*isa));
    sig.params.extend(
        ft.params()
            .map(|p| ir::AbiParam::new(p.get_wasmtime_type())),
    );
    sig.returns.extend(
        ft.results()
            .map(|p| ir::AbiParam::new(p.get_wasmtime_type())),
    );

    let mut fn_builder_ctx = FunctionBuilderContext::new();
    let mut code_memory = CodeMemory::new();

    let wasm_trampoline =
        make_trampoline(isa.as_ref(), &mut code_memory, &mut fn_builder_ctx, &sig);

    // ... and then we also need a trampoline with the standard "trampoline ABI"
    // which enters into the ABI specified by `ft`. Note that this is only used
    // if `Func::call` is called on an object created by `Func::new`.
    let host_trampoline = trampoline::make_trampoline(
        &*isa,
        &mut code_memory,
        &mut fn_builder_ctx,
        &sig,
        mem::size_of::<u128>(),
    )?;

    code_memory.publish(isa.as_ref());

    let sig = engine.signatures().register(ft.as_wasm_func_type());

    unsafe {
        let instance = create_raw_function(
            wasm_trampoline,
            sig,
            Box::new(TrampolineState { func, code_memory }),
        )?;
        Ok((instance, host_trampoline))
    }
}

pub unsafe fn create_raw_function(
    func: *mut [VMFunctionBody],
    sig: VMSharedSignatureIndex,
    host_state: Box<dyn Any + Send + Sync>,
) -> Result<InstanceHandle> {
    let mut module = Module::new();
    let mut finished_functions = PrimaryMap::new();

    let sig_id = SignatureIndex::from_u32(u32::max_value() - 1);
    module.types.push(ModuleType::Function(sig_id));
    let func_id = module.functions.push(sig_id);
    module
        .exports
        .insert(String::new(), wasm::EntityIndex::Function(func_id));
    finished_functions.push(func);

    Ok(
        OnDemandInstanceAllocator::default().allocate(InstanceAllocationRequest {
            module: Arc::new(module),
            finished_functions: &finished_functions,
            imports: Imports::default(),
            shared_signatures: sig.into(),
            host_state,
            store: None,
        })?,
    )
}