Panic if channel in other function

[Duslia]

I write the code below. And use tinygo build -o wasm.wasm -target wasi . to compile

package main

func main() {}

//export start
func start() {
	ch := make(chan int32, 1)

	go func() {
		ch <- 1
	}()
	<-ch
}

And I use wasmtime to call start function. It will panic

panic: runtime error: nil pointer dereference
Error: wasm trap: wasm `unreachable` instruction executed
wasm backtrace:
    0: 0x61ce - runtime.abort
                    at /usr/local/Cellar/tinygo/0.26.0/src/runtime/runtime_tinygowasm.go:73:6
              - runtime.runtimePanic
                    at /usr/local/Cellar/tinygo/0.26.0/src/runtime/panic.go:59:7
    1: 0x27a0 - runtime.nilPanic
                    at /usr/local/Cellar/tinygo/0.26.0/src/runtime/panic.go:122:14
    2: 0x1569b - runtime.chanRecv
                    at /usr/local/Cellar/tinygo/0.26.0/src/runtime/chan.go:533:11
    3: 0x58f70 - start
                    at /Users/bytedance/go/src/wasm/lego_client/client/main.go:22:2

If these code in main function, it won't panic.

[dgryski]

My guess is that by overriding the start function, the Go runtime is not able to properly set itself up. Can you reproduce this with a different function not named start ?

[Duslia]

I have tried another function name but it still cannot work.

[fgsch]

Which tinygo version are you using?
I cannot reproduce this with tinygo 0.26.0.

[Duslia]

Which tinygo version are you using? I cannot reproduce this with tinygo 0.26.0.

I use v0.26.0. I'll improve the demo

[Duslia]

wasmtime runtime code:

use wasmtime::{Config, Engine, Linker, Module, Store};

pub struct StoreData {
    pub wasi_context: wasmtime_wasi::WasiCtx,
}

impl StoreData {
    pub(crate) fn new(
        wasi_context: wasmtime_wasi::WasiCtx,
    ) -> Self {
        Self {
            wasi_context,
        }
    }
}

pub fn new_store(
    engine: Engine,
    wasi_context: wasmtime_wasi::WasiCtx,
) -> Store<StoreData> {
    Store::new(
        &engine,
        StoreData::new(wasi_context),
    )
}

fn main() {
    let rt: tokio::runtime::Runtime = tokio::runtime::Builder::new_multi_thread()
        .enable_all()
        .worker_threads(1)
        .build()
        .unwrap();

    std::thread::sleep(std::time::Duration::from_secs(1));
    rt.spawn(async {
        let mut cfg = Config::new();
        cfg.async_support(true);
        cfg.consume_fuel(false);
        let engine = Engine::new(&cfg).unwrap();
        let key =
            "{path to your}/wasm.wasm";

        let ins = Module::from_file(&engine, key).unwrap();
        let mut linker = Linker::new(&engine);
        let wasi_context_builder = wasmtime_wasi::WasiCtxBuilder::new()
            .inherit_stdio()
            .inherit_args()
            .unwrap()
            .inherit_env()
            .unwrap();
        let mut wasi_context = wasi_context_builder.build();
        let mut store = new_store(engine, wasi_context);
        store.set_epoch_deadline(10000000);
        wasmtime_wasi::tokio::add_to_linker(&mut linker, |state: &mut StoreData| &mut state.wasi_context).unwrap();
        let ins = linker
            .instantiate_async(&mut store, &ins)
            .await.unwrap();
        let func = ins.get_typed_func::<(), (), _>(&mut store, "test");
        let _ = func.unwrap().call_async(&mut store, ()).await.unwrap();
    });
    std::thread::sleep(tokio::time::Duration::from_secs(1));
}

Cargo.toml

[package]
name = "hello-world"
version = "0.1.0"
edition = "2018"

[dependencies]
futures = { version = "0.3.*" }
log = "*"
tokio = { version = "1", features = ["full"] }
tokio-util = { version = "0.7.0", features = ["compat", "io"] }
futures-util = "0.3.21"
wasmtime = { version = "0.37" }
wasmtime-wasi = { version = "0.37", features = ["tokio"] }

wasm:

package main

func main() {
	ch := make(chan int32, 1)

	go func() {
		ch <- 1
	}()
	<-ch
}

//export test
func test() {
	ch := make(chan int32, 1)

	go func() {
		ch <- 1
	}()
	<-ch
}

output:

panic: runtime error: nil pointer dereference
thread 'tokio-runtime-worker' panicked at 'called `Result::unwrap()` on an `Err` value: Trap { reason: InstructionTrap(UnreachableCodeReached), wasm_trace: [FrameInfo { module_name: None, func_index: 9, func_name: Some("runtime.runtimePanic"), func_start: FilePos(2747), instr: Some(FilePos(2911)), symbols: [] }, FrameInfo { module_name: None, func_index: 3, func_name: Some("runtime.nilPanic"), func_start: FilePos(542), instr: Some(FilePos(593)), symbols: [] }, FrameInfo { module_name: None, func_index: 44, func_name: Some("runtime.chanRecv"), func_start: FilePos(16177), instr: Some(FilePos(16973)), symbols: [] }, FrameInfo { module_name: None, func_index: 51, func_name: Some("test"), func_start: FilePos(19173), instr: Some(FilePos(19560)), symbols: [] }], native_trace: Backtrace { trace:    0: <unknown>

[dgryski]

The problem with calling arbitrary functions without going through main is that the runtime is not properly initialized. In this case, the channel logic requires that the scheduler has been initialized, but by calling test directly, it hasn't been.

[Duslia]

So what can I do to avoid this problem?

[dgryski]

@aykevl I wonder if we can export a user-callable runtime init function somehow or otherwise check that the required setup has happened?

[Duslia]

@dgryski @aykevl Is there any progress?

[dgryski]

Closing as dupe of #2735