runtime: gc does not work with `wasmexport` and "void" functions

ajwerner commented 1 month ago

Go version

go version devel go1.24-c208b91 Fri Sep 20 13:54:44 2024 +0000 linux/amd64

Output of `go env` in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/ajwerner/.cache/go-build'
GOENV='/home/ajwerner/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/ajwerner/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/ajwerner/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/ajwerner/sdk/gotip'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/ajwerner/sdk/gotip/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.24-c208b91 Fri Sep 20 13:54:44 2024 +0000'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/ajwerner/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/ajwerner/src/wasmexport-test/go-runner/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build899058900=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I attempted to use the new functionality introduced in https://github.com/golang/go/issues/65199 which allows for greatly reducing the cost to call a go function compiled to webassembly. At first it worked great, but then I noticed it failing whenever it needed to grow the stack. I also notice that if you just call runtime.GC, similar bad stuff happens.

Consider the following program:

//go:build wasm

package main

import (
    "runtime"
)

func main() {
}

//go:wasmexport void-gc
func voidGc() {
    runtime.GC()
}

//go:wasmexport not-void-gc
func notVoidGc() int32 {
    runtime.GC()
    return 0
}

You can compile this program like:

GOOS=wasip1 GOARCH=wasm gotip build -buildmode=c-shared -o test.wasm ./test_wasm.go

Then you can have a runner program like:

package main

import (
    "context"
    _ "embed"
    "log"
    "os"

    "github.com/tetratelabs/wazero"
    "github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
)

//go:embed test.wasm
var wasm []byte

func main() {
    ctx := context.Background()
    r := wazero.NewRuntime(ctx)
    defer r.Close(ctx) // This closes everything this Runtime created.
    wasi_snapshot_preview1.MustInstantiate(ctx, r)
    mod, err := r.InstantiateWithConfig(ctx, wasm, wazero.NewModuleConfig().
        WithStartFunctions("_initialize").
        WithArgs("arg0").
        WithStderr(os.Stderr).
        WithStdout(os.Stdout).
        WithSysNanosleep())
    if err != nil {
        log.Panicln(err)
    }
    _, err = mod.ExportedFunction("void-gc").Call(ctx)
    if err != nil {
        log.Panicln(err)
    }
}

which can be run with go run ./main.go

go run ./main.go

What did you see happen?

I saw the runtime crash inside wasm, see output. I'll note that in my initial issue, I was not calling runtime.GC, I just happened to see similar failures inside things like growstack and background gc assist. I also noticed that if I add a return value to the entrypoint function, the problems seem to go away.

What did you expect to see?

I expected to not see it crash.

ajwerner commented 1 month ago

@johanbrandhorst this one is likely to interest you.

gabyhelp commented 1 month ago

Related Issues and Documentation

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

johanbrandhorst commented 1 month ago

CC @golang/wasm @cherrymui

gopherbot commented 5 days ago

Change https://go.dev/cl/624000 mentions this issue: cmd/internal/obj/wasm: correct return PC for frameless wasmexport wrappers

golang / go