all: implement wasmimport directive

Go programs can now use the //go:wasmimport module_name function_name
directive to import functions from the WebAssembly runtime.

For now, the directive is restricted to the runtime and syscall/js
packages.

* Derived from CL 350737
* Original work modified to work with changes to the IR conversion code.
* Modification of CL 350737 changes to fully exist in Unified IR path (emp)
* Original work modified to work with changes to the ABI configuration code.
* Fixes golang#38248

Co-authored-by: Vedant Roy <vroy101@gmail.com>
Co-authored-by: Richard Musiol <mail@richard-musiol.de>
Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Change-Id: I740719735d91c306ac718a435a78e1ee9686bc16

misc/wasm/wasm_exec.js

@@ -113,6 +113,10 @@
 				this.mem.setUint32(addr + 4, Math.floor(v / 4294967296), true);
 			}
 
+			const setInt32 = (addr, v) => {
+				this.mem.setUint32(addr + 0, v, true);
+			}
+
 			const getInt64 = (addr) => {
 				const low = this.mem.getUint32(addr + 0, true);
 				const high = this.mem.getInt32(addr + 4, true);
@@ -206,7 +210,10 @@
 
 			const timeOrigin = Date.now() - performance.now();
 			this.importObject = {
-				go: {
+				_gotest: {
+					add: (a, b) => a + b,
+				},
+				gojs: {
 					// Go's SP does not change as long as no Go code is running. Some operations (e.g. calls, getters and setters)
 					// may synchronously trigger a Go event handler. This makes Go code get executed in the middle of the imported
 					// function. A goroutine can switch to a new stack if the current stack is too small (see morestack function).

src/cmd/compile/internal/gc/compile.go

@@ -42,6 +42,10 @@ func enqueueFunc(fn *ir.Func) {
 		return // we'll get this as part of its enclosing function
 	}
 
+	if ssagen.CreateWasmImportWrapper(fn) {
+		return
+	}
+
 	if len(fn.Body) == 0 {
 		// Initialize ABI wrappers if necessary.
 		ir.InitLSym(fn, false)

src/cmd/compile/internal/ir/func.go

@@ -133,6 +133,10 @@ type Func struct {
 	// For wrapper functions, WrappedFunc point to the original Func.
 	// Currently only used for go/defer wrappers.
 	WrappedFunc *Func
+
+	// WasmImport is used by the //go:wasmimport directive to store info about
+	// a WebAssembly function import.
+	WasmImport *WasmImport
 }
 
 func NewFunc(pos src.XPos) *Func {

src/cmd/compile/internal/ir/node.go

@@ -463,6 +463,12 @@ const (
 
 )
 
+// WasmImport stores metadata associated with the //go:wasmimport pragma
+type WasmImport struct {
+	Module string
+	Name   string
+}
+
 func AsNode(n types.Object) Node {
 	if n == nil {
 		return nil

src/cmd/compile/internal/ir/sizeof_test.go

@@ -20,8 +20,8 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Func{}, 184, 320},
-		{Name{}, 100, 176},
+		{Func{}, 196, 328},
+		{Name{}, 112, 176},
 	}
 
 	for _, tt := range tests {

src/cmd/compile/internal/noder/linker.go

@@ -269,6 +269,9 @@ func (l *linker) relocFuncExt(w *pkgbits.Encoder, name *ir.Name) {
 	l.pragmaFlag(w, name.Func.Pragma)
 	l.linkname(w, name)
 
+	w.String("")
+	w.String("")
+
 	// Relocated extension data.
 	w.Bool(true)
 

src/cmd/compile/internal/noder/noder.go

@@ -7,6 +7,7 @@ package noder
 import (
 	"errors"
 	"fmt"
+	"internal/buildcfg"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -166,9 +167,17 @@ var allowedStdPragmas = map[string]bool{
 
 // *pragmas is the value stored in a syntax.pragmas during parsing.
 type pragmas struct {
-	Flag   ir.PragmaFlag // collected bits
-	Pos    []pragmaPos   // position of each individual flag
-	Embeds []pragmaEmbed
+	Flag       ir.PragmaFlag // collected bits
+	Pos        []pragmaPos   // position of each individual flag
+	Embeds     []pragmaEmbed
+	WasmImport *WasmImport
+}
+
+// WasmImport stores metadata associated with the //go:wasmimport pragma
+type WasmImport struct {
+	Pos    syntax.Pos
+	Module string
+	Name   string
 }
 
 type pragmaPos struct {
@@ -192,6 +201,9 @@ func (p *noder) checkUnusedDuringParse(pragma *pragmas) {
 			p.error(syntax.Error{Pos: e.Pos, Msg: "misplaced go:embed directive"})
 		}
 	}
+	if pragma.WasmImport != nil {
+		p.error(syntax.Error{Pos: pragma.WasmImport.Pos, Msg: "misplaced go:wasmimport directive"})
+	}
 }
 
 // pragma is called concurrently if files are parsed concurrently.
@@ -219,6 +231,21 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 	}
 
 	switch {
+	case strings.HasPrefix(text, "go:wasmimport "):
+		if buildcfg.GOARCH == "wasm" {
+			f := strings.Fields(text)
+			if len(f) != 3 {
+				p.error(syntax.Error{Pos: pos, Msg: "usage: //go:wasmimport module_name import_name"})
+			}
+			if !base.Flag.CompilingRuntime && base.Ctxt.Pkgpath != "syscall/js" && base.Ctxt.Pkgpath != "syscall/js_test" {
+				p.error(syntax.Error{Pos: pos, Msg: "//go:wasmimport directive cannot be used outside of runtime or syscall/js"})
+			}
+			pragma.WasmImport = &WasmImport{
+				Pos:    pos,
+				Module: f[1],
+				Name:   f[2],
+			}
+		}
 	case strings.HasPrefix(text, "go:linkname "):
 		f := strings.Fields(text)
 		if !(2 <= len(f) && len(f) <= 3) {

src/cmd/compile/internal/noder/reader.go

@@ -1071,6 +1071,16 @@ func (r *reader) funcExt(name *ir.Name, method *types.Sym) {
 	fn.Pragma = r.pragmaFlag()
 	r.linkname(name)
 
+	xmod := r.String()
+	xname := r.String()
+
+	if xmod != "" && xname != "" {
+		fn.WasmImport = &ir.WasmImport{
+			Module: xmod,
+			Name:   xname,
+		}
+	}
+
 	typecheck.Func(fn)
 
 	if r.Bool() {

src/cmd/compile/internal/noder/writer.go

@@ -1003,11 +1003,15 @@ func (w *writer) funcExt(obj *types2.Func) {
 	if pragma&ir.Systemstack != 0 && pragma&ir.Nosplit != 0 {
 		w.p.errorf(decl, "go:nosplit and go:systemstack cannot be combined")
 	}
+	wi := asWasmImport(decl.Pragma)
 
 	if decl.Body != nil {
 		if pragma&ir.Noescape != 0 {
 			w.p.errorf(decl, "can only use //go:noescape with external func implementations")
 		}
+		if wi != nil {
+			w.p.errorf(decl, "can only use //go:wasmimport with external func implementations")
+		}
 		if (pragma&ir.UintptrKeepAlive != 0 && pragma&ir.UintptrEscapes == 0) && pragma&ir.Nosplit == 0 {
 			// Stack growth can't handle uintptr arguments that may
 			// be pointers (as we don't know which are pointers
@@ -1028,7 +1032,8 @@ func (w *writer) funcExt(obj *types2.Func) {
 		if base.Flag.Complete || decl.Name.Value == "init" {
 			// Linknamed functions are allowed to have no body. Hopefully
 			// the linkname target has a body. See issue 23311.
-			if _, ok := w.p.linknames[obj]; !ok {
+			// Wasmimport functions are also allowed to have no body.
+			if _, ok := w.p.linknames[obj]; !ok && wi == nil {
 				w.p.errorf(decl, "missing function body")
 			}
 		}
@@ -1041,6 +1046,14 @@ func (w *writer) funcExt(obj *types2.Func) {
 	w.Sync(pkgbits.SyncFuncExt)
 	w.pragmaFlag(pragma)
 	w.linkname(obj)
+	if wi != nil {
+		w.String(wi.Module)
+		w.String(wi.Name)
+	} else {
+		w.String("")
+		w.String("")
+	}
+
 	w.Bool(false) // stub extension
 	w.Reloc(pkgbits.RelocBody, body)
 	w.Sync(pkgbits.SyncEOF)
@@ -2728,6 +2741,13 @@ func asPragmaFlag(p syntax.Pragma) ir.PragmaFlag {
 	return p.(*pragmas).Flag
 }
 
+func asWasmImport(p syntax.Pragma) *WasmImport {
+	if p == nil {
+		return nil
+	}
+	return p.(*pragmas).WasmImport
+}
+
 // isPtrTo reports whether from is the type *to.
 func isPtrTo(from, to types2.Type) bool {
 	ptr, ok := from.(*types2.Pointer)

src/cmd/compile/internal/ssagen/abi.go

@@ -11,8 +11,10 @@ import (
 	"os"
 	"strings"
 
+	"cmd/compile/internal/abi"
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
+	"cmd/compile/internal/objw"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
@@ -336,3 +338,88 @@ func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {
 	typecheck.DeclContext = savedclcontext
 	ir.CurFunc = savedcurfn
 }
+
+// CreateWasmImportWrapper creates a wrapper for imported WASM functions to
+// adapt them to the Go calling convention. The body for this function is
+// generated in cmd/internal/obj/wasm/wasmobj.go
+func CreateWasmImportWrapper(fn *ir.Func) bool {
+	if fn.WasmImport == nil {
+		return false
+	}
+	if buildcfg.GOARCH != "wasm" {
+		base.FatalfAt(fn.Pos(), "CreateWasmImportWrapper call not supported on %s: func was %v", buildcfg.GOARCH, fn)
+	}
+
+	ir.InitLSym(fn, true)
+
+	setupWasmABI(fn)
+
+	pp := objw.NewProgs(fn, 0)
+	defer pp.Free()
+	pp.Text.To.Type = obj.TYPE_TEXTSIZE
+	pp.Text.To.Val = int32(types.RoundUp(fn.Type().ArgWidth(), int64(types.RegSize)))
+	// Wrapper functions never need their own stack frame
+	pp.Text.To.Offset = 0
+	pp.Flush()
+
+	return true
+}
+
+func toWasmFields(result *abi.ABIParamResultInfo, abiParams []abi.ABIParamAssignment) []obj.WasmField {
+	wfs := make([]obj.WasmField, len(abiParams))
+	for i, p := range abiParams {
+		t := p.Type
+		switch {
+		case t.IsInteger() && t.Size() == 4:
+			wfs[i].Type = obj.WasmI32
+		case t.IsInteger() && t.Size() == 8:
+			wfs[i].Type = obj.WasmI64
+		case t.IsFloat() && t.Size() == 4:
+			wfs[i].Type = obj.WasmF32
+		case t.IsFloat() && t.Size() == 8:
+			wfs[i].Type = obj.WasmF64
+		case t.IsPtr():
+			wfs[i].Type = obj.WasmPtr
+		default:
+			base.Fatalf("wasm import has bad function signature")
+		}
+		wfs[i].Offset = p.FrameOffset(result)
+	}
+	return wfs
+}
+
+// setupTextLSym initializes the LSym for a with-body text symbol.
+func setupWasmABI(f *ir.Func) {
+	wi := obj.WasmImport{
+		Module: f.WasmImport.Module,
+		Name:   f.WasmImport.Name,
+	}
+	if wi.Module == "gojs" {
+		// Functions that are imported from the "go" module use a special
+		// ABI that just accepts the stack pointer.
+		// Example:
+		//
+		// 	//go:wasmimport gojs add
+		// 	func importedAdd(a, b uint) uint
+		//
+		// will roughly become
+		//
+		// 	(import "go" "add" (func (param i32)))
+		wi.Params = []obj.WasmField{{Type: obj.WasmI32}}
+	} else {
+		// All other imported functions use the normal WASM ABI.
+		// Example:
+		//
+		// 	//go:wasmimport a_module add
+		// 	func importedAdd(a, b uint) uint
+		//
+		// will roughly become
+		//
+		// 	(import "a_module" "add" (func (param i32 i32) (result i32)))
+		abiConfig := AbiForBodylessFuncStackMap(f)
+		abiInfo := abiConfig.ABIAnalyzeFuncType(f.Type().FuncType())
+		wi.Params = toWasmFields(abiInfo, abiInfo.InParams())
+		wi.Results = toWasmFields(abiInfo, abiInfo.OutParams())
+	}
+	f.LSym.Func().WasmImport = &wi
+}

src/cmd/internal/goobj/objfile.go

@@ -440,6 +440,7 @@ const (
 	AuxPcline
 	AuxPcinline
 	AuxPcdata
+	AuxWasmImport
 )
 
 func (a *Aux) Type() uint8 { return a[0] }