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 #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
Reviewed-on: https://go-review.googlesource.com/c/go/+/463018
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index da5c1e910d..5dd8d1de2d 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -6,6 +6,7 @@ package noder
 
 import (
 	"fmt"
+	"internal/buildcfg"
 	"internal/pkgbits"
 
 	"cmd/compile/internal/base"
@@ -1003,11 +1004,15 @@ 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 +1033,8 @@ 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 +1047,17 @@ func (w *writer) funcExt(obj *types2.Func) {
 	w.Sync(pkgbits.SyncFuncExt)
 	w.pragmaFlag(pragma)
 	w.linkname(obj)
+
+	if buildcfg.GOARCH == "wasm" {
+		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 +2745,13 @@ 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)