wasmer/lib/llvm-backend/src/trampolines.rs

use crate::intrinsics::Intrinsics;
use inkwell::{
    builder::Builder,
    context::Context,
    module::{Linkage, Module},
    types::{BasicType, FunctionType},
    values::FunctionValue,
    AddressSpace,
};
use wasmer_runtime_core::{
    module::ModuleInfo,
    structures::{SliceMap, TypedIndex},
    types::{FuncSig, SigIndex, Type},
};

pub fn generate_trampolines(
    info: &ModuleInfo,
    signatures: &SliceMap<SigIndex, FunctionType>,
    module: &Module,
    context: &Context,
    builder: &Builder,
    intrinsics: &Intrinsics,
) {
    for (sig_index, sig) in info.signatures.iter() {
        let func_type = signatures[sig_index];

        let trampoline_sig = intrinsics.void_ty.fn_type(
            &[
                intrinsics.ctx_ptr_ty.as_basic_type_enum(), // vmctx ptr
                func_type
                    .ptr_type(AddressSpace::Generic)
                    .as_basic_type_enum(), // func ptr
                intrinsics.i64_ptr_ty.as_basic_type_enum(), // args ptr
                intrinsics.i64_ptr_ty.as_basic_type_enum(), // returns ptr
            ],
            false,
        );

        let trampoline_func = module.add_function(
            &format!("trmp{}", sig_index.index()),
            trampoline_sig,
            Some(Linkage::External),
        );

        generate_trampoline(trampoline_func, sig, context, builder, intrinsics);
    }
}

fn generate_trampoline(
    trampoline_func: FunctionValue,
    func_sig: &FuncSig,
    context: &Context,
    builder: &Builder,
    intrinsics: &Intrinsics,
) {
    let entry_block = context.append_basic_block(&trampoline_func, "entry");
    builder.position_at_end(&entry_block);

    let (vmctx_ptr, func_ptr, args_ptr, returns_ptr) = match trampoline_func.get_params().as_slice()
    {
        &[vmctx_ptr, func_ptr, args_ptr, returns_ptr] => (
            vmctx_ptr,
            func_ptr.into_pointer_value(),
            args_ptr.into_pointer_value(),
            returns_ptr.into_pointer_value(),
        ),
        _ => unimplemented!(),
    };

    let cast_ptr_ty = |wasmer_ty| match wasmer_ty {
        Type::I32 => intrinsics.i32_ptr_ty,
        Type::I64 => intrinsics.i64_ptr_ty,
        Type::F32 => intrinsics.f32_ptr_ty,
        Type::F64 => intrinsics.f64_ptr_ty,
    };

    let mut args_vec = Vec::with_capacity(func_sig.params().len() + 1);
    args_vec.push(vmctx_ptr);

    for (i, param_ty) in func_sig.params().iter().enumerate() {
        let index = intrinsics.i32_ty.const_int(i as _, false);
        let item_pointer = unsafe { builder.build_in_bounds_gep(args_ptr, &[index], "arg_ptr") };

        let casted_pointer_type = cast_ptr_ty(*param_ty);

        let typed_item_pointer =
            builder.build_pointer_cast(item_pointer, casted_pointer_type, "typed_arg_pointer");

        let arg = builder.build_load(typed_item_pointer, "arg");
        args_vec.push(arg);
    }

    let call_site = builder.build_call(func_ptr, &args_vec, "call");

    match func_sig.returns() {
        &[] => {}
        &[one_ret] => {
            let ret_ptr_type = cast_ptr_ty(one_ret);

            let typed_ret_ptr =
                builder.build_pointer_cast(returns_ptr, ret_ptr_type, "typed_ret_ptr");
            builder.build_store(
                typed_ret_ptr,
                call_site.try_as_basic_value().left().unwrap(),
            );
        }
        _ => unimplemented!("multi-value returns"),
    }

    builder.build_return(None);
}