wasm: add `//go:wasmexport` support (#4451)

This adds support for the `//go:wasmexport` pragma as proposed here:
https://github.com/golang/go/issues/65199

It is currently implemented only for wasip1 and wasm-unknown, but it is
certainly possible to extend it to other targets like GOOS=js and
wasip2.

22 files changed, 765 insertions, 67 deletions

diff --git a/builder/build.go b/builder/build.go
index 3f12b9991..4c49fe13c 100644
--- a/builder/build.go
+++ b/builder/build.go
@@ -197,6 +197,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		ABI:             config.ABI(),
 		GOOS:            config.GOOS(),
 		GOARCH:          config.GOARCH(),
+		BuildMode:       config.BuildMode(),
 		CodeModel:       config.CodeModel(),
 		RelocationModel: config.RelocationModel(),
 		SizeLevel:       sizeLevel,
@@ -649,6 +650,13 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	result.Binary = result.Executable // final file
 	ldflags := append(config.LDFlags(), "-o", result.Executable)
 
+	if config.Options.BuildMode == "c-shared" {
+		if !strings.HasPrefix(config.Triple(), "wasm32-") {
+			return result, fmt.Errorf("buildmode c-shared is only supported on wasm at the moment")
+		}
+		ldflags = append(ldflags, "--no-entry")
+	}
+
 	// Add compiler-rt dependency if needed. Usually this is a simple load from
 	// a cache.
 	if config.Target.RTLib == "compiler-rt" {
@@ -880,7 +888,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 
 				err := cmd.Run()
 				if err != nil {
-					return fmt.Errorf("wasm-tools failed: %w", err)
+					return fmt.Errorf("`wasm-tools component embed` failed: %w", err)
 				}
 
 				// wasm-tools component new embedded.wasm -o component.wasm
@@ -902,7 +910,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 
 				err = cmd.Run()
 				if err != nil {
-					return fmt.Errorf("wasm-tools failed: %w", err)
+					return fmt.Errorf("`wasm-tools component new` failed: %w", err)
 				}
 			}
 
diff --git a/compileopts/config.go b/compileopts/config.go
index cc1f4d61c..44d3b005c 100644
--- a/compileopts/config.go
+++ b/compileopts/config.go
@@ -33,6 +33,17 @@ func (c *Config) CPU() string {
 	return c.Target.CPU
 }
 
+// The current build mode (like the `-buildmode` command line flag).
+func (c *Config) BuildMode() string {
+	if c.Options.BuildMode != "" {
+		return c.Options.BuildMode
+	}
+	if c.Target.BuildMode != "" {
+		return c.Target.BuildMode
+	}
+	return "default"
+}
+
 // Features returns a list of features this CPU supports. For example, for a
 // RISC-V processor, that could be "+a,+c,+m". For many targets, an empty list
 // will be returned.
diff --git a/compileopts/options.go b/compileopts/options.go
index 980097200..b83f6f63b 100644
--- a/compileopts/options.go
+++ b/compileopts/options.go
@@ -8,6 +8,7 @@ import (
 )
 
 var (
+	validBuildModeOptions     = []string{"default", "c-shared"}
 	validGCOptions            = []string{"none", "leaking", "conservative", "custom", "precise"}
 	validSchedulerOptions     = []string{"none", "tasks", "asyncify"}
 	validSerialOptions        = []string{"none", "uart", "usb", "rtt"}
@@ -26,6 +27,7 @@ type Options struct {
 	GOMIPS          string // environment variable (only used with GOARCH=mips and GOARCH=mipsle)
 	Directory       string // working dir, leave it unset to use the current working dir
 	Target          string
+	BuildMode       string // -buildmode flag
 	Opt             string
 	GC              string
 	PanicStrategy   string
@@ -61,6 +63,14 @@ type Options struct {
 
 // Verify performs a validation on the given options, raising an error if options are not valid.
 func (o *Options) Verify() error {
+	if o.BuildMode != "" {
+		valid := isInArray(validBuildModeOptions, o.BuildMode)
+		if !valid {
+			return fmt.Errorf(`invalid buildmode option '%s': valid values are %s`,
+				o.BuildMode,
+				strings.Join(validBuildModeOptions, ", "))
+		}
+	}
 	if o.GC != "" {
 		valid := isInArray(validGCOptions, o.GC)
 		if !valid {
diff --git a/compileopts/target.go b/compileopts/target.go
index 41a7babd9..ab9f871f3 100644
--- a/compileopts/target.go
+++ b/compileopts/target.go
@@ -32,6 +32,7 @@ type TargetSpec struct {
 	GOARCH           string   `json:"goarch,omitempty"`
 	SoftFloat        bool     // used for non-baremetal systems (GOMIPS=softfloat etc)
 	BuildTags        []string `json:"build-tags,omitempty"`
+	BuildMode        string   `json:"buildmode,omitempty"` // default build mode (if nothing specified)
 	GC               string   `json:"gc,omitempty"`
 	Scheduler        string   `json:"scheduler,omitempty"`
 	Serial           string   `json:"serial,omitempty"` // which serial output to use (uart, usb, none)
diff --git a/compiler/compiler.go b/compiler/compiler.go
index 6756fe969..752e4a5c6 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -44,6 +44,7 @@ type Config struct {
 	ABI             string
 	GOOS            string
 	GOARCH          string
+	BuildMode       string
 	CodeModel       string
 	RelocationModel string
 	SizeLevel       int
@@ -1384,6 +1385,11 @@ func (b *builder) createFunction() {
 		b.llvmFn.SetLinkage(llvm.InternalLinkage)
 		b.createFunction()
 	}
+
+	// Create wrapper function that can be called externally.
+	if b.info.wasmExport != "" {
+		b.createWasmExport()
+	}
 }
 
 // posser is an interface that's implemented by both ssa.Value and
diff --git a/compiler/goroutine.go b/compiler/goroutine.go
index a23556345..701797152 100644
--- a/compiler/goroutine.go
+++ b/compiler/goroutine.go
@@ -7,6 +7,7 @@ import (
 	"go/token"
 	"go/types"
 
+	"github.com/tinygo-org/tinygo/compiler/llvmutil"
 	"golang.org/x/tools/go/ssa"
 	"tinygo.org/x/go-llvm"
 )
@@ -101,7 +102,7 @@ func (b *builder) createGo(instr *ssa.Go) {
 
 	paramBundle := b.emitPointerPack(params)
 	var stackSize llvm.Value
-	callee := b.createGoroutineStartWrapper(funcType, funcPtr, prefix, hasContext, instr.Pos())
+	callee := b.createGoroutineStartWrapper(funcType, funcPtr, prefix, hasContext, false, instr.Pos())
 	if b.AutomaticStackSize {
 		// The stack size is not known until after linking. Call a dummy
 		// function that will be replaced with a load from a special ELF
@@ -121,6 +122,147 @@ func (b *builder) createGo(instr *ssa.Go) {
 	b.createCall(fnType, start, []llvm.Value{callee, paramBundle, stackSize, llvm.Undef(b.dataPtrType)}, "")
 }
 
+// Create an exported wrapper function for functions with the //go:wasmexport
+// pragma. This wrapper function is quite complex when the scheduler is enabled:
+// it needs to start a new goroutine each time the exported function is called.
+func (b *builder) createWasmExport() {
+	pos := b.info.wasmExportPos
+	if b.info.exported {
+		// //export really shouldn't be used anymore when //go:wasmexport is
+		// available, because //go:wasmexport is much better defined.
+		b.addError(pos, "cannot use //export and //go:wasmexport at the same time")
+		return
+	}
+
+	const suffix = "#wasmexport"
+
+	// Declare the exported function.
+	paramTypes := b.llvmFnType.ParamTypes()
+	exportedFnType := llvm.FunctionType(b.llvmFnType.ReturnType(), paramTypes[:len(paramTypes)-1], false)
+	exportedFn := llvm.AddFunction(b.mod, b.fn.RelString(nil)+suffix, exportedFnType)
+	b.addStandardAttributes(exportedFn)
+	llvmutil.AppendToGlobal(b.mod, "llvm.used", exportedFn)
+	exportedFn.AddFunctionAttr(b.ctx.CreateStringAttribute("wasm-export-name", b.info.wasmExport))
+
+	// Create a builder for this wrapper function.
+	builder := newBuilder(b.compilerContext, b.ctx.NewBuilder(), b.fn)
+	defer builder.Dispose()
+
+	// Define this function as a separate function in DWARF
+	if b.Debug {
+		if b.fn.Syntax() != nil {
+			// Create debug info file if needed.
+			pos := b.program.Fset.Position(pos)
+			builder.difunc = builder.attachDebugInfoRaw(b.fn, exportedFn, suffix, pos.Filename, pos.Line)
+		}
+		builder.setDebugLocation(pos)
+	}
+
+	// Create a single basic block inside of it.
+	bb := llvm.AddBasicBlock(exportedFn, "entry")
+	builder.SetInsertPointAtEnd(bb)
+
+	// Insert an assertion to make sure this //go:wasmexport function is not
+	// called at a time when it is not allowed (for example, before the runtime
+	// is initialized).
+	builder.createRuntimeCall("wasmExportCheckRun", nil, "")
+
+	if b.Scheduler == "none" {
+		// When the scheduler has been disabled, this is really trivial: just
+		// call the function.
+		params := exportedFn.Params()
+		params = append(params, llvm.ConstNull(b.dataPtrType)) // context parameter
+		retval := builder.CreateCall(b.llvmFnType, b.llvmFn, params, "")
+		if b.fn.Signature.Results() == nil {
+			builder.CreateRetVoid()
+		} else {
+			builder.CreateRet(retval)
+		}
+
+	} else {
+		// The scheduler is enabled, so we need to start a new goroutine, wait
+		// for it to complete, and read the result value.
+
+		// Build a function that looks like this:
+		//
+		//   func foo#wasmexport(param0, param1, ..., paramN) {
+		//       var state *stateStruct
+		//
+		//       // 'done' must be explicitly initialized ('state' is not zeroed)
+		//       state.done = false
+		//
+		//       // store the parameters in the state object
+		//       state.param0 = param0
+		//       state.param1 = param1
+		//       ...
+		//       state.paramN = paramN
+		//
+		//       // create a goroutine and push it to the runqueue
+		//       task.start(uintptr(gowrapper), &state)
+		//
+		//       // run the scheduler
+		//       runtime.wasmExportRun(&state.done)
+		//
+		//       // if there is a return value, load it and return
+		//       return state.result
+		//   }
+
+		hasReturn := b.fn.Signature.Results() != nil
+
+		// Build the state struct type.
+		// It stores the function parameters, the 'done' flag, and reserves
+		// space for a return value if needed.
+		stateFields := exportedFnType.ParamTypes()
+		numParams := len(stateFields)
+		stateFields = append(stateFields, b.ctx.Int1Type()) // 'done' field
+		if hasReturn {
+			stateFields = append(stateFields, b.llvmFnType.ReturnType())
+		}
+		stateStruct := b.ctx.StructType(stateFields, false)
+
+		// Allocate the state struct on the stack.
+		statePtr := builder.CreateAlloca(stateStruct, "status")
+
+		// Initialize the 'done' field.
+		doneGEP := builder.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(b.ctx.Int32Type(), uint64(numParams), false),
+		}, "done.gep")
+		builder.CreateStore(llvm.ConstNull(b.ctx.Int1Type()), doneGEP)
+
+		// Store all parameters in the state object.
+		for i, param := range exportedFn.Params() {
+			gep := builder.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+				llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false),
+			}, "")
+			builder.CreateStore(param, gep)
+		}
+
+		// Create a new goroutine and add it to the runqueue.
+		wrapper := b.createGoroutineStartWrapper(b.llvmFnType, b.llvmFn, "", false, true, pos)
+		stackSize := llvm.ConstInt(b.uintptrType, b.DefaultStackSize, false)
+		taskStartFnType, taskStartFn := builder.getFunction(b.program.ImportedPackage("internal/task").Members["start"].(*ssa.Function))
+		builder.createCall(taskStartFnType, taskStartFn, []llvm.Value{wrapper, statePtr, stackSize, llvm.Undef(b.dataPtrType)}, "")
+
+		// Run the scheduler.
+		builder.createRuntimeCall("wasmExportRun", []llvm.Value{doneGEP}, "")
+
+		// Read the return value (if any) and return to the caller of the
+		// //go:wasmexport function.
+		if hasReturn {
+			gep := builder.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+				llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(b.ctx.Int32Type(), uint64(numParams)+1, false),
+			}, "")
+			retval := builder.CreateLoad(b.llvmFnType.ReturnType(), gep, "retval")
+			builder.CreateRet(retval)
+		} else {
+			builder.CreateRetVoid()
+		}
+	}
+}
+
 // createGoroutineStartWrapper creates a wrapper for the task-based
 // implementation of goroutines. For example, to call a function like this:
 //
@@ -144,7 +286,7 @@ func (b *builder) createGo(instr *ssa.Go) {
 // to last parameter of the function) is used for this wrapper. If hasContext is
 // false, the parameter bundle is assumed to have no context parameter and undef
 // is passed instead.
-func (c *compilerContext) createGoroutineStartWrapper(fnType llvm.Type, fn llvm.Value, prefix string, hasContext bool, pos token.Pos) llvm.Value {
+func (c *compilerContext) createGoroutineStartWrapper(fnType llvm.Type, fn llvm.Value, prefix string, hasContext, isWasmExport bool, pos token.Pos) llvm.Value {
 	var wrapper llvm.Value
 
 	b := &builder{
@@ -162,14 +304,18 @@ func (c *compilerContext) createGoroutineStartWrapper(fnType llvm.Type, fn llvm.
 	if !fn.IsAFunction().IsNil() {
 		// See whether this wrapper has already been created. If so, return it.
 		name := fn.Name()
-		wrapper = c.mod.NamedFunction(name + "$gowrapper")
+		wrapperName := name + "$gowrapper"
+		if isWasmExport {
+			wrapperName += "-wasmexport"
+		}
+		wrapper = c.mod.NamedFunction(wrapperName)
 		if !wrapper.IsNil() {
 			return llvm.ConstPtrToInt(wrapper, c.uintptrType)
 		}
 
 		// Create the wrapper.
 		wrapperType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{c.dataPtrType}, false)
-		wrapper = llvm.AddFunction(c.mod, name+"$gowrapper", wrapperType)
+		wrapper = llvm.AddFunction(c.mod, wrapperName, wrapperType)
 		c.addStandardAttributes(wrapper)
 		wrapper.SetLinkage(llvm.LinkOnceODRLinkage)
 		wrapper.SetUnnamedAddr(true)
@@ -199,23 +345,110 @@ func (c *compilerContext) createGoroutineStartWrapper(fnType llvm.Type, fn llvm.
 			b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
 		}
 
-		// Create the list of params for the call.
-		paramTypes := fnType.ParamTypes()
-		if !hasContext {
-			paramTypes = paramTypes[:len(paramTypes)-1] // strip context parameter
-		}
-		params := b.emitPointerUnpack(wrapper.Param(0), paramTypes)
-		if !hasContext {
-			params = append(params, llvm.Undef(c.dataPtrType)) // add dummy context parameter
-		}
+		if !isWasmExport {
+			// Regular 'go' instruction.
 
-		// Create the call.
-		b.CreateCall(fnType, fn, params, "")
+			// Create the list of params for the call.
+			paramTypes := fnType.ParamTypes()
+			if !hasContext {
+				paramTypes = paramTypes[:len(paramTypes)-1] // strip context parameter
+			}
 
-		if c.Scheduler == "asyncify" {
-			b.CreateCall(deadlockType, deadlock, []llvm.Value{
-				llvm.Undef(c.dataPtrType),
-			}, "")
+			params := b.emitPointerUnpack(wrapper.Param(0), paramTypes)
+			if !hasContext {
+				params = append(params, llvm.Undef(c.dataPtrType)) // add dummy context parameter
+			}
+
+			// Create the call.
+			b.CreateCall(fnType, fn, params, "")
+
+			if c.Scheduler == "asyncify" {
+				b.CreateCall(deadlockType, deadlock, []llvm.Value{
+					llvm.Undef(c.dataPtrType),
+				}, "")
+			}
+		} else {
+			// Goroutine started from a //go:wasmexport pragma.
+			// The function looks like this:
+			//
+			//   func foo$gowrapper-wasmexport(state *stateStruct) {
+			//       // load values
+			//       param0 := state.params[0]
+			//       param1 := state.params[1]
+			//
+			//       // call wrapped functions
+			//       result := foo(param0, param1, ...)
+			//
+			//       // store result value (if there is any)
+			//       state.result = result
+			//
+			//       // finish exported function
+			//       state.done = true
+			//       runtime.wasmExportExit()
+			//   }
+			//
+			// The state object here looks like:
+			//
+			//   struct state {
+			//       param0
+			//       param1
+			//       param* // etc
+			//       done bool
+			//       result returnType
+			//   }
+
+			returnType := fnType.ReturnType()
+			hasReturn := returnType != b.ctx.VoidType()
+			statePtr := wrapper.Param(0)
+
+			// Create the state struct (it must match the type in createWasmExport).
+			stateFields := fnType.ParamTypes()
+			numParams := len(stateFields) - 1
+			stateFields = stateFields[:numParams:numParams]     // strip 'context' parameter
+			stateFields = append(stateFields, c.ctx.Int1Type()) // 'done' bool
+			if hasReturn {
+				stateFields = append(stateFields, returnType)
+			}
+			stateStruct := b.ctx.StructType(stateFields, false)
+
+			// Extract parameters from the state object, and call the function
+			// that's being wrapped.
+			var callParams []llvm.Value
+			for i := 0; i < numParams; i++ {
+				gep := b.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+					llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+					llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false),
+				}, "")
+				param := b.CreateLoad(stateFields[i], gep, "")
+				callParams = append(callParams, param)
+			}
+			callParams = append(callParams, llvm.ConstNull(c.dataPtrType)) // add 'context' parameter
+			result := b.CreateCall(fnType, fn, callParams, "")
+
+			// Store the return value back into the shared state.
+			// Unlike regular goroutines, these special //go:wasmexport
+			// goroutines can return a value.
+			if hasReturn {
+				gep := b.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+					llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+					llvm.ConstInt(c.ctx.Int32Type(), uint64(numParams)+1, false),
+				}, "result.ptr")
+				b.CreateStore(result, gep)
+			}
+
+			// Mark this function as having finished executing.
+			// This is important so the runtime knows the exported function
+			// didn't block.
+			doneGEP := b.CreateInBoundsGEP(stateStruct, statePtr, []llvm.Value{
+				llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(c.ctx.Int32Type(), uint64(numParams), false),
+			}, "done.gep")
+			b.CreateStore(llvm.ConstInt(b.ctx.Int1Type(), 1, false), doneGEP)
+
+			// Call back into the runtime. This will exit the goroutine, switch
+			// back to the scheduler, which will in turn return from the
+			// //go:wasmexport function.
+			b.createRuntimeCall("wasmExportExit", nil, "")
 		}
 
 	} else {
@@ -297,5 +530,5 @@ func (c *compilerContext) createGoroutineStartWrapper(fnType llvm.Type, fn llvm.
 	}
 
 	// Return a ptrtoint of the wrapper, not the function itself.
-	return b.CreatePtrToInt(wrapper, c.uintptrType, "")
+	return llvm.ConstPtrToInt(wrapper, c.uintptrType)
 }
diff --git a/compiler/symbol.go b/compiler/symbol.go
index 32eb55107..4a080cbbc 100644
--- a/compiler/symbol.go
+++ b/compiler/symbol.go
@@ -23,15 +23,17 @@ import (
 // The linkName value contains a valid link name, even if //go:linkname is not
 // present.
 type functionInfo struct {
-	wasmModule string     // go:wasm-module
-	wasmName   string     // wasm-export-name or wasm-import-name in the IR
-	linkName   string     // go:linkname, go:export - the IR function name
-	section    string     // go:section - object file section name
-	exported   bool       // go:export, CGo
-	interrupt  bool       // go:interrupt
-	nobounds   bool       // go:nobounds
-	variadic   bool       // go:variadic (CGo only)
-	inline     inlineType // go:inline
+	wasmModule    string     // go:wasm-module
+	wasmName      string     // wasm-export-name or wasm-import-name in the IR
+	wasmExport    string     // go:wasmexport is defined (export is unset, this adds an exported wrapper)
+	wasmExportPos token.Pos  // position of //go:wasmexport comment
+	linkName      string     // go:linkname, go:export - the IR function name
+	section       string     // go:section - object file section name
+	exported      bool       // go:export, CGo
+	interrupt     bool       // go:interrupt
+	nobounds      bool       // go:nobounds
+	variadic      bool       // go:variadic (CGo only)
+	inline        inlineType // go:inline
 }
 
 type inlineType int
@@ -241,8 +243,22 @@ func (c *compilerContext) getFunctionInfo(f *ssa.Function) functionInfo {
 		// Pick the default linkName.
 		linkName: f.RelString(nil),
 	}
+
+	// Check for a few runtime functions that are treated specially.
+	if info.linkName == "runtime.wasmEntryReactor" && c.BuildMode == "c-shared" {
+		info.linkName = "_initialize"
+		info.wasmName = "_initialize"
+		info.exported = true
+	}
+	if info.linkName == "runtime.wasmEntryCommand" && c.BuildMode == "default" {
+		info.linkName = "_start"
+		info.wasmName = "_start"
+		info.exported = true
+	}
+
 	// Check for //go: pragmas, which may change the link name (among others).
 	c.parsePragmas(&info, f)
+
 	c.functionInfos[f] = info
 	return info
 }
@@ -296,10 +312,39 @@ func (c *compilerContext) parsePragmas(info *functionInfo, f *ssa.Function) {
 				if len(parts) != 3 {
 					continue
 				}
-				c.checkWasmImport(f, comment.Text)
+				if f.Blocks != nil {
+					// Defined functions cannot be exported.
+					c.addError(f.Pos(), "can only use //go:wasmimport on declarations")
+					continue
+				}
+				c.checkWasmImportExport(f, comment.Text)
 				info.exported = true
 				info.wasmModule = parts[1]
 				info.wasmName = parts[2]
+			case "//go:wasmexport":
+				if f.Blocks == nil {
+					c.addError(f.Pos(), "can only use //go:wasmexport on definitions")
+					continue
+				}
+				if len(parts) != 2 {
+					c.addError(f.Pos(), fmt.Sprintf("expected one parameter to //go:wasmimport, not %d", len(parts)-1))
+					continue
+				}
+				name := parts[1]
+				if name == "_start" || name == "_initialize" {
+					c.addError(f.Pos(), fmt.Sprintf("//go:wasmexport does not allow %#v", name))
+					continue
+				}
+				if c.BuildMode != "c-shared" && f.RelString(nil) == "main.main" {
+					c.addError(f.Pos(), fmt.Sprintf("//go:wasmexport does not allow main.main to be exported with -buildmode=%s", c.BuildMode))
+					continue
+				}
+				if c.archFamily() != "wasm32" {
+					c.addError(f.Pos(), "//go:wasmexport is only supported on wasm")
+				}
+				c.checkWasmImportExport(f, comment.Text)
+				info.wasmExport = name
+				info.wasmExportPos = comment.Slash
 			case "//go:inline":
 				info.inline = inlineHint
 			case "//go:noinline":
@@ -346,22 +391,17 @@ func (c *compilerContext) parsePragmas(info *functionInfo, f *ssa.Function) {
 	}
 }
 
-// Check whether this function cannot be used in //go:wasmimport. It will add an
-// error if this is the case.
+// Check whether this function can be used in //go:wasmimport or
+// //go:wasmexport. It will add an error if this is not the case.
 //
 // The list of allowed types is based on this proposal:
 // https://github.com/golang/go/issues/59149
-func (c *compilerContext) checkWasmImport(f *ssa.Function, pragma string) {
+func (c *compilerContext) checkWasmImportExport(f *ssa.Function, pragma string) {
 	if c.pkg.Path() == "runtime" || c.pkg.Path() == "syscall/js" || c.pkg.Path() == "syscall" {
 		// The runtime is a special case. Allow all kinds of parameters
 		// (importantly, including pointers).
 		return
 	}
-	if f.Blocks != nil {
-		// Defined functions cannot be exported.
-		c.addError(f.Pos(), "can only use //go:wasmimport on declarations")
-		return
-	}
 	if f.Signature.Results().Len() > 1 {
 		c.addError(f.Signature.Results().At(1).Pos(), fmt.Sprintf("%s: too many return values", pragma))
 	} else if f.Signature.Results().Len() == 1 {
diff --git a/go.mod b/go.mod
index bf85ef3ad..a4de14136 100644
--- a/go.mod
+++ b/go.mod
@@ -14,6 +14,7 @@ require (
 	github.com/mattn/go-colorable v0.1.13
 	github.com/mattn/go-tty v0.0.4
 	github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3
+	github.com/tetratelabs/wazero v1.6.0
 	go.bug.st/serial v1.6.0
 	golang.org/x/net v0.26.0
 	golang.org/x/sys v0.21.0
diff --git a/go.sum b/go.sum
index 7a6d1f4a9..d3c1bd310 100644
--- a/go.sum
+++ b/go.sum
@@ -12,7 +12,6 @@ github.com/chromedp/sysutil v1.0.0/go.mod h1:kgWmDdq8fTzXYcKIBqIYvRRTnYb9aNS9moA
 github.com/creack/goselect v0.1.2 h1:2DNy14+JPjRBgPzAd1thbQp4BSIihxcBf0IXhQXDRa0=
 github.com/creack/goselect v0.1.2/go.mod h1:a/NhLweNvqIYMuxcMOuWY516Cimucms3DglDzQP3hKY=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
-github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/gobwas/httphead v0.1.0 h1:exrUm0f4YX0L7EBwZHuCF4GDp8aJfVeBrlLQrs6NqWU=
 github.com/gobwas/httphead v0.1.0/go.mod h1:O/RXo79gxV8G+RqlR/otEwx4Q36zl9rqC5u12GKvMCM=
 github.com/gobwas/pool v0.2.1 h1:xfeeEhW7pwmX8nuLVlqbzVc7udMDrwetjEv+TZIz1og=
@@ -45,19 +44,18 @@ github.com/mattn/go-tty v0.0.4/go.mod h1:u5GGXBtZU6RQoKV8gY5W6UhMudbR5vXnUe7j3px
 github.com/orisano/pixelmatch v0.0.0-20210112091706-4fa4c7ba91d5 h1:1SoBaSPudixRecmlHXb/GxmaD3fLMtHIDN13QujwQuc=
 github.com/orisano/pixelmatch v0.0.0-20210112091706-4fa4c7ba91d5/go.mod h1:nZgzbfBr3hhjoZnS66nKrHmduYNpc34ny7RK4z5/HM0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
-github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3 h1:aQKxg3+2p+IFXXg97McgDGT5zcMrQoi0EICZs8Pgchs=
 github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3/go.mod h1:9/etS5gpQq9BJsJMWg1wpLbfuSnkm8dPF6FdW2JXVhA=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
 github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+github.com/tetratelabs/wazero v1.6.0 h1:z0H1iikCdP8t+q341xqepY4EWvHEw8Es7tlqiVzlP3g=
+github.com/tetratelabs/wazero v1.6.0/go.mod h1:0U0G41+ochRKoPKCJlh0jMg1CHkyfK8kDqiirMmKY8A=
 go.bug.st/serial v1.6.0 h1:mAbRGN4cKE2J5gMwsMHC2KQisdLRQssO9WSM+rbZJ8A=
 go.bug.st/serial v1.6.0/go.mod h1:UABfsluHAiaNI+La2iESysd9Vetq7VRdpxvjx7CmmOE=
 golang.org/x/mod v0.18.0 h1:5+9lSbEzPSdWkH32vYPBwEpX8KwDbM52Ud9xBUvNlb0=
-golang.org/x/mod v0.18.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/net v0.26.0 h1:soB7SVo0PWrY4vPW/+ay0jKDNScG2X9wFeYlXIvJsOQ=
 golang.org/x/net v0.26.0/go.mod h1:5YKkiSynbBIh3p6iOc/vibscux0x38BZDkn8sCUPxHE=
 golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
-golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20191008105621-543471e840be/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -76,6 +74,5 @@ gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
 gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
-gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 tinygo.org/x/go-llvm v0.0.0-20240627184919-3b50c76783a8 h1:bLsZXRUBavt++CJlMN7sppNziqu3LyamESLhFJcpqFQ=
 tinygo.org/x/go-llvm v0.0.0-20240627184919-3b50c76783a8/go.mod h1:GFbusT2VTA4I+l4j80b17KFK+6whv69Wtny5U+T8RR0=
diff --git a/main.go b/main.go
index 6f257d1b2..fe8a3fb15 100644
--- a/main.go
+++ b/main.go
@@ -1500,6 +1500,7 @@ func main() {
 	var tags buildutil.TagsFlag
 	flag.Var(&tags, "tags", "a space-separated list of extra build tags")
 	target := flag.String("target", "", "chip/board name or JSON target specification file")
+	buildMode := flag.String("buildmode", "", "build mode to use (default, c-shared)")
 	var stackSize uint64
 	flag.Func("stack-size", "goroutine stack size (if unknown at compile time)", func(s string) error {
 		size, err := bytesize.Parse(s)
@@ -1608,6 +1609,7 @@ func main() {
 		GOARM:           goenv.Get("GOARM"),
 		GOMIPS:          goenv.Get("GOMIPS"),
 		Target:          *target,
+		BuildMode:       *buildMode,
 		StackSize:       stackSize,
 		Opt:             *opt,
 		GC:              *gc,
diff --git a/main_test.go b/main_test.go
index c131070c8..3bbb31da3 100644
--- a/main_test.go
+++ b/main_test.go
@@ -6,6 +6,7 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"errors"
 	"flag"
 	"io"
@@ -21,6 +22,9 @@ import (
 	"time"
 
 	"github.com/aykevl/go-wasm"
+	"github.com/tetratelabs/wazero"
+	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
 	"github.com/tinygo-org/tinygo/builder"
 	"github.com/tinygo-org/tinygo/compileopts"
 	"github.com/tinygo-org/tinygo/diagnostics"
@@ -524,6 +528,189 @@ func TestWebAssembly(t *testing.T) {
 	}
 }
 
+func TestWasmExport(t *testing.T) {
+	t.Parallel()
+
+	type testCase struct {
+		name      string
+		target    string
+		buildMode string
+		scheduler string
+		file      string
+		noOutput  bool
+		command   bool // call _start (command mode) instead of _initialize
+	}
+
+	tests := []testCase{
+		// "command mode" WASI
+		{
+			name:    "WASIp1-command",
+			target:  "wasip1",
+			command: true,
+		},
+		// "reactor mode" WASI (with -buildmode=c-shared)
+		{
+			name:      "WASIp1-reactor",
+			target:    "wasip1",
+			buildMode: "c-shared",
+		},
+		// Make sure reactor mode also works without a scheduler.
+		{
+			name:      "WASIp1-reactor-noscheduler",
+			target:    "wasip1",
+			buildMode: "c-shared",
+			scheduler: "none",
+			file:      "wasmexport-noscheduler.go",
+		},
+		// Test -target=wasm-unknown with the default build mode (which is
+		// c-shared).
+		{
+			name:     "wasm-unknown-reactor",
+			target:   "wasm-unknown",
+			file:     "wasmexport-noscheduler.go",
+			noOutput: true, // wasm-unknown cannot produce output
+		},
+		// Test -target=wasm-unknown with -buildmode=default, which makes it run
+		// in command mode.
+		{
+			name:      "wasm-unknown-command",
+			target:    "wasm-unknown",
+			buildMode: "default",
+			file:      "wasmexport-noscheduler.go",
+			noOutput:  true, // wasm-unknown cannot produce output
+			command:   true,
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			// Build the wasm binary.
+			tmpdir := t.TempDir()
+			options := optionsFromTarget(tc.target, sema)
+			options.BuildMode = tc.buildMode
+			options.Scheduler = tc.scheduler
+			buildConfig, err := builder.NewConfig(&options)
+			if err != nil {
+				t.Fatal(err)
+			}
+			filename := "wasmexport.go"
+			if tc.file != "" {
+				filename = tc.file
+			}
+			result, err := builder.Build("testdata/"+filename, ".wasm", tmpdir, buildConfig)
+			if err != nil {
+				t.Fatal("failed to build binary:", err)
+			}
+
+			// Read the wasm binary back into memory.
+			data, err := os.ReadFile(result.Binary)
+			if err != nil {
+				t.Fatal("could not read wasm binary: ", err)
+			}
+
+			// Set up the wazero runtime.
+			output := &bytes.Buffer{}
+			ctx := context.Background()
+			r := wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfigInterpreter())
+			defer r.Close(ctx)
+			config := wazero.NewModuleConfig().
+				WithStdout(output).WithStderr(output).
+				WithStartFunctions()
+
+			// Prepare for testing.
+			var mod api.Module
+			mustCall := func(results []uint64, err error) []uint64 {
+				if err != nil {
+					t.Error("failed to run function:", err)
+				}
+				return results
+			}
+			checkResult := func(name string, results []uint64, expected []uint64) {
+				if len(results) != len(expected) {
+					t.Errorf("%s: expected %v but got %v", name, expected, results)
+				}
+				for i, result := range results {
+					if result != expected[i] {
+						t.Errorf("%s: expected %v but got %v", name, expected, results)
+						break
+					}
+				}
+			}
+			runTests := func() {
+				// Test an exported function without params or return value.
+				checkResult("hello()", mustCall(mod.ExportedFunction("hello").Call(ctx)), nil)
+
+				// Test that we can call an exported function more than once.
+				checkResult("add(3, 5)", mustCall(mod.ExportedFunction("add").Call(ctx, 3, 5)), []uint64{8})
+				checkResult("add(7, 9)", mustCall(mod.ExportedFunction("add").Call(ctx, 7, 9)), []uint64{16})
+				checkResult("add(6, 1)", mustCall(mod.ExportedFunction("add").Call(ctx, 6, 1)), []uint64{7})
+
+				// Test that imported functions can call exported functions
+				// again.
+				checkResult("reentrantCall(2, 3)", mustCall(mod.ExportedFunction("reentrantCall").Call(ctx, 2, 3)), []uint64{5})
+				checkResult("reentrantCall(1, 8)", mustCall(mod.ExportedFunction("reentrantCall").Call(ctx, 1, 8)), []uint64{9})
+			}
+
+			// Add wasip1 module.
+			wasi_snapshot_preview1.MustInstantiate(ctx, r)
+
+			// Add custom "tester" module.
+			callOutside := func(a, b int32) int32 {
+				results, err := mod.ExportedFunction("add").Call(ctx, uint64(a), uint64(b))
+				if err != nil {
+					t.Error("could not call exported add function:", err)
+				}
+				return int32(results[0])
+			}
+			callTestMain := func() {
+				runTests()
+			}
+			builder := r.NewHostModuleBuilder("tester")
+			builder.NewFunctionBuilder().WithFunc(callOutside).Export("callOutside")
+			builder.NewFunctionBuilder().WithFunc(callTestMain).Export("callTestMain")
+			_, err = builder.Instantiate(ctx)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// Parse and instantiate the wasm.
+			mod, err = r.InstantiateWithConfig(ctx, data, config)
+			if err != nil {
+				t.Fatal("could not instantiate wasm module:", err)
+			}
+
+			// Initialize the module and run the tests.
+			if tc.command {
+				// Call _start (the entry point), which calls
+				// tester.callTestMain, which then runs all the tests.
+				mustCall(mod.ExportedFunction("_start").Call(ctx))
+			} else {
+				// Run the _initialize call, because this is reactor mode wasm.
+				mustCall(mod.ExportedFunction("_initialize").Call(ctx))
+				runTests()
+			}
+
+			// Check that the output matches the expected output.
+			// (Skip this for wasm-unknown because it can't produce output).
+			if !tc.noOutput {
+				expectedOutput, err := os.ReadFile("testdata/wasmexport.txt")
+				if err != nil {
+					t.Fatal("could not read output file:", err)
+				}
+				actual := output.Bytes()
+				expectedOutput = bytes.ReplaceAll(expectedOutput, []byte("\r\n"), []byte("\n"))
+				actual = bytes.ReplaceAll(actual, []byte("\r\n"), []byte("\n"))
+				if !bytes.Equal(actual, expectedOutput) {
+					t.Error(string(Diff("expected", expectedOutput, "actual", actual)))
+				}
+			}
+		})
+	}
+}
+
 func TestTest(t *testing.T) {
 	t.Parallel()
 
diff --git a/src/runtime/runtime_tinygowasm.go b/src/runtime/runtime_tinygowasm.go
index 744e138af..f791ffacd 100644
--- a/src/runtime/runtime_tinygowasm.go
+++ b/src/runtime/runtime_tinygowasm.go
@@ -1,5 +1,8 @@
 //go:build tinygo.wasm && !wasm_unknown && !wasip2
 
+// This file is for wasm/wasip1 and for wasm/js, which both use much of the
+// WASIp1 API.
+
 package runtime
 
 import (
diff --git a/src/runtime/runtime_wasip1.go b/src/runtime/runtime_wasip1.go
index 4a1afb2ab..ad66b0d86 100644
--- a/src/runtime/runtime_wasip1.go
+++ b/src/runtime/runtime_wasip1.go
@@ -13,15 +13,6 @@ type timeUnit int64
 //export __wasm_call_ctors
 func __wasm_call_ctors()
 
-//export _start
-func _start() {
-	// These need to be initialized early so that the heap can be initialized.
-	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
-	run()
-	__stdio_exit()
-}
-
 // Read the command line arguments from WASI.
 // For example, they can be passed to a program with wasmtime like this:
 //
@@ -100,6 +91,10 @@ func ticks() timeUnit {
 	return timeUnit(nano)
 }
 
+func beforeExit() {
+	__stdio_exit()
+}
+
 // Implementations of WASI APIs
 
 //go:wasmimport wasi_snapshot_preview1 args_get
diff --git a/src/runtime/runtime_wasm_js_scheduler.go b/src/runtime/runtime_wasm_js_scheduler.go
index 0edde29eb..94018336e 100644
--- a/src/runtime/runtime_wasm_js_scheduler.go
+++ b/src/runtime/runtime_wasm_js_scheduler.go
@@ -14,7 +14,7 @@ func resume() {
 	}
 
 	wasmNested = true
-	scheduler()
+	scheduler(false)
 	wasmNested = false
 }
 
@@ -26,6 +26,6 @@ func go_scheduler() {
 	}
 
 	wasmNested = true
-	scheduler()
+	scheduler(false)
 	wasmNested = false
 }
diff --git a/src/runtime/runtime_wasm_unknown.go b/src/runtime/runtime_wasm_unknown.go
index d307a4f87..846b95d2a 100644
--- a/src/runtime/runtime_wasm_unknown.go
+++ b/src/runtime/runtime_wasm_unknown.go
@@ -2,7 +2,8 @@
 
 package runtime
 
-import "unsafe"
+// TODO: this is essentially reactor mode wasm. So we might want to support
+// -buildmode=c-shared (and default to it).
 
 type timeUnit int64
 
@@ -11,14 +12,6 @@ type timeUnit int64
 //export __wasm_call_ctors
 func __wasm_call_ctors()
 
-//export _initialize
-func _initialize() {
-	// These need to be initialized early so that the heap can be initialized.
-	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
-	initAll()
-}
-
 func init() {
 	__wasm_call_ctors()
 }
@@ -40,3 +33,6 @@ func sleepTicks(d timeUnit) {
 func ticks() timeUnit {
 	return timeUnit(0)
 }
+
+func beforeExit() {
+}
diff --git a/src/runtime/runtime_wasmentry.go b/src/runtime/runtime_wasmentry.go
new file mode 100644
index 000000000..5a135f428
--- /dev/null
+++ b/src/runtime/runtime_wasmentry.go
@@ -0,0 +1,100 @@
+//go:build tinygo.wasm && !wasip2 && !js
+
+package runtime
+
+// Entry points for WebAssembly modules, and runtime support for
+// //go:wasmexport: runtime.wasmExport* function calls are inserted by the
+// compiler for //go:wasmexport support.
+
+import (
+	"internal/task"
+	"unsafe"
+)
+
+// This is the _start entry point, when using -buildmode=default.
+func wasmEntryCommand() {
+	// These need to be initialized early so that the heap can be initialized.
+	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
+	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
+	wasmExportState = wasmExportStateInMain
+	run()
+	wasmExportState = wasmExportStateExited
+	beforeExit()
+}
+
+// This is the _initialize entry point, when using -buildmode=c-shared.
+func wasmEntryReactor() {
+	// This function is called before any //go:wasmexport functions are called
+	// to initialize everything. It must not block.
+
+	// Initialize the heap.
+	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
+	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
+	initHeap()
+
+	if hasScheduler {
+		// A package initializer might do funky stuff like start a goroutine and
+		// wait until it completes, so we have to run package initializers in a
+		// goroutine.
+		go func() {
+			initAll()
+			wasmExportState = wasmExportStateReactor
+		}()
+		scheduler(true)
+		if wasmExportState != wasmExportStateReactor {
+			// Unlikely, but if package initializers do something blocking (like
+			// time.Sleep()), that's a bug.
+			runtimePanic("package initializer blocks")
+		}
+	} else {
+		// There are no goroutines (except for the main one, if you can call it
+		// that), so we can just run all the package initializers.
+		initAll()
+		wasmExportState = wasmExportStateReactor
+	}
+}
+
+// Track which state we're in: before (or during) init, running inside
+// main.main, after main.main returned, or reactor mode (after init).
+var wasmExportState uint8
+
+const (
+	wasmExportStateInit = iota
+	wasmExportStateInMain
+	wasmExportStateExited
+	wasmExportStateReactor
+)
+
+func wasmExportCheckRun() {
+	switch wasmExportState {
+	case wasmExportStateInit:
+		runtimePanic("//go:wasmexport function called before runtime initialization")
+	case wasmExportStateExited:
+		runtimePanic("//go:wasmexport function called after main.main returned")
+	}
+}
+
+// Called from within a //go:wasmexport wrapper (the one that's exported from
+// the wasm module) after the goroutine has been queued. Just run the scheduler,
+// and check that the goroutine finished when the scheduler is idle (as required
+// by the //go:wasmexport proposal).
+//
+// This function is not called when the scheduler is disabled.
+func wasmExportRun(done *bool) {
+	scheduler(true)
+	if !*done {
+		runtimePanic("//go:wasmexport function did not finish")
+	}
+}
+
+// Called from the goroutine wrapper for the //go:wasmexport function. It just
+// signals to the runtime that the //go:wasmexport call has finished, and can
+// switch back to the wasmExportRun function.
+//
+// This function is not called when the scheduler is disabled.
+func wasmExportExit() {
+	task.Pause()
+
+	// TODO: we could cache the allocated stack so we don't have to keep
+	// allocating a new stack on every //go:wasmexport call.
+}
diff --git a/src/runtime/scheduler.go b/src/runtime/scheduler.go
index 30b2da8a6..2f2287652 100644
--- a/src/runtime/scheduler.go
+++ b/src/runtime/scheduler.go
@@ -157,7 +157,13 @@ func removeTimer(tim *timer) bool {
 }
 
 // Run the scheduler until all tasks have finished.
-func scheduler() {
+// There are a few special cases:
+//   - When returnAtDeadlock is true, it also returns when there are no more
+//     runnable goroutines.
+//   - When using the asyncify scheduler, it returns when it has to wait
+//     (JavaScript uses setTimeout so the scheduler must return to the JS
+//     environment).
+func scheduler(returnAtDeadlock bool) {
 	// Main scheduler loop.
 	var now timeUnit
 	for !schedulerDone {
@@ -193,6 +199,9 @@ func scheduler() {
 		t := runqueue.Pop()
 		if t == nil {
 			if sleepQueue == nil && timerQueue == nil {
+				if returnAtDeadlock {
+					return
+				}
 				if asyncScheduler {
 					// JavaScript is treated specially, see below.
 					return
diff --git a/src/runtime/scheduler_any.go b/src/runtime/scheduler_any.go
index 0911a2dc7..5e969f84f 100644
--- a/src/runtime/scheduler_any.go
+++ b/src/runtime/scheduler_any.go
@@ -25,7 +25,7 @@ func run() {
 		callMain()
 		schedulerDone = true
 	}()
-	scheduler()
+	scheduler(false)
 }
 
 const hasScheduler = true
diff --git a/targets/wasm-unknown.json b/targets/wasm-unknown.json
index 93a4d391e..92c166ee5 100644
--- a/targets/wasm-unknown.json
+++ b/targets/wasm-unknown.json
@@ -3,6 +3,7 @@
 	"cpu":           "generic",
 	"features":      "+mutable-globals,+nontrapping-fptoint,+sign-ext,-bulk-memory",
 	"build-tags":    ["tinygo.wasm", "wasm_unknown"],
+	"buildmode":    "c-shared",
 	"goos":          "linux",
 	"goarch":        "arm",
 	"linker":        "wasm-ld",
diff --git a/testdata/wasmexport-noscheduler.go b/testdata/wasmexport-noscheduler.go
new file mode 100644
index 000000000..844c8d158
--- /dev/null
+++ b/testdata/wasmexport-noscheduler.go
@@ -0,0 +1,35 @@
+package main
+
+func init() {
+	println("called init")
+}
+
+//go:wasmimport tester callTestMain
+func callTestMain()
+
+func main() {
+	// main.main is not used when using -buildmode=c-shared.
+	callTestMain()
+}
+
+//go:wasmexport hello
+func hello() {
+	println("hello!")
+}
+
+//go:wasmexport add
+func add(a, b int) int {
+	println("called add:", a, b)
+	return a + b
+}
+
+//go:wasmimport tester callOutside
+func callOutside(a, b int) int
+
+//go:wasmexport reentrantCall
+func reentrantCall(a, b int) int {
+	println("reentrantCall:", a, b)
+	result := callOutside(a, b)
+	println("reentrantCall result:", result)
+	return result
+}
diff --git a/testdata/wasmexport.go b/testdata/wasmexport.go
new file mode 100644
index 000000000..9065d6e92
--- /dev/null
+++ b/testdata/wasmexport.go
@@ -0,0 +1,52 @@
+package main
+
+import "time"
+
+func init() {
+	println("called init")
+	go adder()
+}
+
+//go:wasmimport tester callTestMain
+func callTestMain()
+
+func main() {
+	// main.main is not used when using -buildmode=c-shared.
+	callTestMain()
+}
+
+//go:wasmexport hello
+func hello() {
+	println("hello!")
+}
+
+//go:wasmexport add
+func add(a, b int) int {
+	println("called add:", a, b)
+	addInputs <- a
+	addInputs <- b
+	return <-addOutput
+}
+
+var addInputs = make(chan int)
+var addOutput = make(chan int)
+
+func adder() {
+	for {
+		a := <-addInputs
+		b := <-addInputs
+		time.Sleep(time.Millisecond)
+		addOutput <- a + b
+	}
+}
+
+//go:wasmimport tester callOutside
+func callOutside(a, b int) int
+
+//go:wasmexport reentrantCall
+func reentrantCall(a, b int) int {
+	println("reentrantCall:", a, b)
+	result := callOutside(a, b)
+	println("reentrantCall result:", result)
+	return result
+}
diff --git a/testdata/wasmexport.txt b/testdata/wasmexport.txt
new file mode 100644
index 000000000..484a0ce8d
--- /dev/null
+++ b/testdata/wasmexport.txt
@@ -0,0 +1,11 @@
+called init
+hello!
+called add: 3 5
+called add: 7 9
+called add: 6 1
+reentrantCall: 2 3
+called add: 2 3
+reentrantCall result: 5
+reentrantCall: 1 8
+called add: 1 8
+reentrantCall result: 9