Reduce boilerplate in wasmtime-wasi (#707)
This commit uses the `*.witx` files describing the current wasi API to reduce the boilerplate used to define implementations in the `wasmtime-wasi` crate. Eventually I'd like to remove lots of boilerplate in the `wasi-common` crate too, but this should at least be a good start! The boilerplate removed here is: * No need to list each function to add it to the `wasmtime_runtime::Module` being created * No need to list the signature of the function in a separate `syscalls.rs` file. Instead the `*.witx` file is processed in a single-use macro inside the `wasmtime-wasi` crate. This macro uses the signatures known from `*.witx` to automatically register with the right type in the wasm module as well as define a wrapper that the wasm module will call into. Functionally this is all the same as before, it's just defined in a different way now! The shim generated by this macro which wasmtime calls into only uses `i32`/`i64`/etc wasm types, and it internally uses `as` casts to convert to the right wasi types when delegating into the `wasi-common` crate. One change was necessary to get this implemented, however. The functions in `wasi-common` sometimes took `WasiCtx` and sometimes took a slice of memory. After this PR they uniformly all require both `WasiCtx` and memory so the wrappers can be auto-generated. The arguments are ignored if they weren't previously required.
This commit is contained in:
Alex Crichton
231
crates/wasi-common/wig/src/wasi.rs
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231
crates/wasi-common/wig/src/wasi.rs
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use crate::utils;
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use proc_macro2::{Ident, Span, TokenStream};
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use quote::{format_ident, quote};
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enum Abi {
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I32,
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I64,
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F32,
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F64,
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}
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/// This is a single-use macro intended to be used in the `wasmtime-wasi` crate.
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///
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/// This macro will generate a function, `add_wrappers_to_module`, which will
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/// use the input arguments to register all wasi functions inside of a `Module`
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/// instance. This will automatically assign the wasm underlying types and
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/// perform conversions from the wasm type to the underlying wasi type (often
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/// unsigned or of a smaller width).
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///
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/// The generated shim functions here will also `trace!` their arguments for
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/// logging purposes. Otherwise this is hopefully somewhat straightforward!
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///
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/// I'd recommend using `cargo +nightly expand` to explore the output of this
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/// macro some more.
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pub fn add_wrappers_to_module(args: TokenStream) -> TokenStream {
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let (path, _phase) = utils::witx_path_from_args(args);
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let doc = match witx::load(&[&path]) {
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Ok(doc) => doc,
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Err(e) => {
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panic!("error opening file {}: {}", path, e);
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}
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};
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let mut add = Vec::new();
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for module in doc.modules() {
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for func in module.funcs() {
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let name = func.name.as_str();
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let name_ident = Ident::new(func.name.as_str(), Span::call_site());
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let mut shim_arg_decls = Vec::new();
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let mut params = Vec::new();
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let mut formats = Vec::new();
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let mut format_args = Vec::new();
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let mut hostcall_args = Vec::new();
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for param in func.params.iter() {
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let name = format_ident!(
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"{}",
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match param.name.as_str() {
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"in" | "type" => format!("r#{}", param.name.as_str()),
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s => s.to_string(),
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}
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);
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// Registers a new parameter to the shim we're making with the
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// given `name`, the `abi_ty` wasm type and `hex` defines
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// whether it's debug-printed in a hex format or not.
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//
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// This will register a whole bunch of things:
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//
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// * The cranelift type for the parameter
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// * Syntax to specify the actual function parameter
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// * How to log the parameter value in a call to `trace!`
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// * How to actually pass this argument to the host
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// implementation, converting as necessary.
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let mut add_param = |name: &Ident, abi_ty: Abi, hex: bool| {
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match abi_ty {
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Abi::I32 => {
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params.push(quote! { types::I32 });
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shim_arg_decls.push(quote! { #name: i32 });
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}
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Abi::I64 => {
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params.push(quote! { types::I64 });
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shim_arg_decls.push(quote! { #name: i64 });
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}
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Abi::F32 => {
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params.push(quote! { types::F32 });
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shim_arg_decls.push(quote! { #name: f32 });
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}
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Abi::F64 => {
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params.push(quote! { types::F64 });
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shim_arg_decls.push(quote! { #name: f64 });
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}
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}
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formats.push(format!("{}={}", name, if hex { "{:#x}" } else { "{}" },));
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format_args.push(name.clone());
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hostcall_args.push(quote! { #name as _ });
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};
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match &*param.tref.type_() {
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witx::Type::Enum(e) => match e.repr {
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witx::IntRepr::U64 => add_param(&name, Abi::I64, false),
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_ => add_param(&name, Abi::I32, false),
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},
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witx::Type::Flags(f) => match f.repr {
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witx::IntRepr::U64 => add_param(&name, Abi::I64, true),
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_ => add_param(&name, Abi::I32, true),
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},
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witx::Type::Builtin(witx::BuiltinType::S8)
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| witx::Type::Builtin(witx::BuiltinType::U8)
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| witx::Type::Builtin(witx::BuiltinType::S16)
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| witx::Type::Builtin(witx::BuiltinType::U16)
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| witx::Type::Builtin(witx::BuiltinType::S32)
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| witx::Type::Builtin(witx::BuiltinType::U32) => {
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add_param(&name, Abi::I32, false);
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}
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witx::Type::Builtin(witx::BuiltinType::S64)
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| witx::Type::Builtin(witx::BuiltinType::U64) => {
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add_param(&name, Abi::I64, false);
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}
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witx::Type::Builtin(witx::BuiltinType::F32) => {
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add_param(&name, Abi::F32, false);
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}
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witx::Type::Builtin(witx::BuiltinType::F64) => {
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add_param(&name, Abi::F64, false);
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}
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// strings/arrays have an extra ABI parameter for the length
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// of the array passed.
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witx::Type::Builtin(witx::BuiltinType::String) | witx::Type::Array(_) => {
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add_param(&name, Abi::I32, true);
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let len = format_ident!("{}_len", name);
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add_param(&len, Abi::I32, false);
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}
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witx::Type::ConstPointer(_)
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| witx::Type::Handle(_)
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| witx::Type::Pointer(_) => {
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add_param(&name, Abi::I32, true);
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}
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witx::Type::Struct(_) | witx::Type::Union(_) => {
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panic!("unsupported argument type")
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}
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}
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}
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let mut results = func.results.iter();
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let mut ret_ty = quote! { () };
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let mut cvt_ret = quote! {};
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let mut returns = Vec::new();
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let mut handle_early_error = quote! { panic!("error: {:?}", e) };
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// The first result is returned bare right now...
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if let Some(ret) = results.next() {
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handle_early_error = quote! { return e.into() };
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match &*ret.tref.type_() {
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// Eventually we'll want to add support for more returned
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// types, but for now let's just conform to what `*.witx`
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// definitions currently use.
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witx::Type::Enum(e) => match e.repr {
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witx::IntRepr::U16 => {
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returns.push(quote! { types::I32 });
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ret_ty = quote! { i32 };
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cvt_ret = quote! { .into() }
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}
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other => panic!("unsupported ret enum repr {:?}", other),
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},
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other => panic!("unsupported first return {:?}", other),
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}
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}
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// ... and all remaining results are returned via out-poiners
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for result in results {
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let name = format_ident!("{}", result.name.as_str());
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params.push(quote! { types::I32 });
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shim_arg_decls.push(quote! { #name: i32 });
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formats.push(format!("{}={{:#x}}", name));
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format_args.push(name.clone());
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hostcall_args.push(quote! { #name as u32 });
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}
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let format_str = format!("{}({})", name, formats.join(", "));
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add.push(quote! {
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let sig = module.signatures.push(translate_signature(
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ir::Signature {
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params: vec![#(cranelift_codegen::ir::AbiParam::new(#params)),*],
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returns: vec![#(cranelift_codegen::ir::AbiParam::new(#returns)),*],
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call_conv,
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},
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pointer_type,
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));
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let func = module.functions.push(sig);
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module
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.exports
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.insert(#name.to_owned(), Export::Function(func));
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unsafe extern "C" fn #name_ident(
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ctx: *mut wasmtime_runtime::VMContext,
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#(#shim_arg_decls),*
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) -> #ret_ty {
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log::trace!(
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#format_str,
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#(#format_args),*
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);
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let wasi_ctx = match get_wasi_ctx(&mut *ctx) {
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Ok(e) => e,
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Err(e) => #handle_early_error,
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};
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let memory = match get_memory(&mut *ctx) {
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Ok(e) => e,
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Err(e) => #handle_early_error,
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};
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wasi_common::hostcalls::#name_ident(
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wasi_ctx,
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memory,
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#(#hostcall_args),*
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) #cvt_ret
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}
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finished_functions.push(#name_ident as *const _);
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});
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}
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}
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quote! {
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pub fn add_wrappers_to_module(
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module: &mut Module,
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finished_functions: &mut PrimaryMap<DefinedFuncIndex, *const wasmtime_runtime::VMFunctionBody>,
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call_conv: isa::CallConv,
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pointer_type: types::Type,
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) {
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#(#add)*
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}
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}
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}
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