cmd/link: add wasm architecture

This commit adds the wasm architecture to the link command.

Design doc: https://docs.google.com/document/d/131vjr4DH6JFnb-blm_uRdaC0_Nv3OUwjEY5qVCxCup4

Updates #18892

Change-Id: I5aef29954984537f2979679b5d393209e462f564
Reviewed-on: https://go-review.googlesource.com/103795
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

misc/wasm/wasm_exec.js

@@ -145,7 +145,7 @@ async function compile(source) {
 
 async function run() {
 	let importObject = {
-		js: {
+		go: {
 			// func wasmexit(code int32)
 			"runtime.wasmexit": function (sp) {
 				process.exit(mem().getInt32(sp + 8, true));

src/cmd/dist/build.go

@@ -68,12 +68,14 @@ var okgoarch = []string{
 	"ppc64",
 	"ppc64le",
 	"s390x",
+	"wasm",
 }
 
 // The known operating systems.
 var okgoos = []string{
 	"darwin",
 	"dragonfly",
+	"js",
 	"linux",
 	"android",
 	"solaris",

src/cmd/dist/buildtool.go

@@ -80,6 +80,7 @@ var bootstrapDirs = []string{
 	"cmd/link/internal/s390x",
 	"cmd/link/internal/sym",
 	"cmd/link/internal/x86",
+	"cmd/link/internal/wasm",
 	"container/heap",
 	"debug/dwarf",
 	"debug/elf",

src/cmd/link/internal/ld/data.go

@@ -1852,6 +1852,10 @@ func (ctxt *Link) textaddress() {
 // Note: once we have trampoline insertion support for external linking, this function
 // will not need to create new text sections, and so no need to return sect and n.
 func assignAddress(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint64, isTramp bool) (*sym.Section, int, uint64) {
+	if thearch.AssignAddress != nil {
+		return thearch.AssignAddress(ctxt, sect, n, s, va, isTramp)
+	}
+
 	s.Sect = sect
 	if s.Attr.SubSymbol() {
 		return sect, n, va

src/cmd/link/internal/ld/dwarf.go

@@ -1675,7 +1675,7 @@ func dwarfgeneratedebugsyms(ctxt *Link) {
 	if *FlagS && ctxt.HeadType != objabi.Hdarwin {
 		return
 	}
-	if ctxt.HeadType == objabi.Hplan9 {
+	if ctxt.HeadType == objabi.Hplan9 || ctxt.HeadType == objabi.Hjs {
 		return
 	}
 

src/cmd/link/internal/ld/lib.go

@@ -121,6 +121,9 @@ type Arch struct {
 	// symbol in an executable, which is typical when internally
 	// linking PIE binaries.
 	TLSIEtoLE func(s *sym.Symbol, off, size int)
+
+	// optional override for assignAddress
+	AssignAddress func(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint64, isTramp bool) (*sym.Section, int, uint64)
 }
 
 var (

src/cmd/link/internal/ld/outbuf.go

@@ -60,6 +60,12 @@ func (out *OutBuf) Write8(v uint8) {
 	}
 }
 
+// WriteByte is an alias for Write8 to fulfill the io.ByteWriter interface.
+func (out *OutBuf) WriteByte(v byte) error {
+	out.Write8(v)
+	return nil
+}
+
 func (out *OutBuf) Write16(v uint16) {
 	out.arch.ByteOrder.PutUint16(out.encbuf[:], v)
 	out.Write(out.encbuf[:2])

src/cmd/link/internal/ld/sym.go

@@ -66,7 +66,7 @@ func (ctxt *Link) computeTLSOffset() {
 	default:
 		log.Fatalf("unknown thread-local storage offset for %v", ctxt.HeadType)
 
-	case objabi.Hplan9, objabi.Hwindows:
+	case objabi.Hplan9, objabi.Hwindows, objabi.Hjs:
 		break
 
 		/*

src/cmd/link/internal/wasm/obj.go

+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package wasm
+
+import (
+	"cmd/internal/sys"
+	"cmd/link/internal/ld"
+)
+
+func Init() (*sys.Arch, ld.Arch) {
+	theArch := ld.Arch{
+		Funcalign: 16,
+		Maxalign:  32,
+		Minalign:  1,
+
+		Archinit:      archinit,
+		AssignAddress: assignAddress,
+		Asmb:          asmb,
+		Gentext:       gentext,
+	}
+
+	return sys.ArchWasm, theArch
+}
+
+func archinit(ctxt *ld.Link) {
+	if *ld.FlagRound == -1 {
+		*ld.FlagRound = 4096
+	}
+	if *ld.FlagTextAddr == -1 {
+		*ld.FlagTextAddr = 0
+	}
+}

src/cmd/link/main.go

@@ -15,6 +15,7 @@ import (
 	"cmd/link/internal/mips64"
 	"cmd/link/internal/ppc64"
 	"cmd/link/internal/s390x"
+	"cmd/link/internal/wasm"
 	"cmd/link/internal/x86"
 	"fmt"
 	"os"
@@ -58,6 +59,8 @@ func main() {
 		arch, theArch = ppc64.Init()
 	case "s390x":
 		arch, theArch = s390x.Init()
+	case "wasm":
+		arch, theArch = wasm.Init()
 	}
 	ld.Main(arch, theArch)
 }

src/runtime/asm.s

@@ -25,6 +25,9 @@ GLOBL runtime·memstats(SB), NOPTR, $0
 #ifdef GOARCH_amd64p32
 #define SKIP4 BYTE $0x90; BYTE $0x90; BYTE $0x90; BYTE $0x90
 #endif
+#ifdef GOARCH_wasm
+#define SKIP4 UNDEF; UNDEF; UNDEF; UNDEF
+#endif
 #ifndef SKIP4
 #define SKIP4 WORD $0
 #endif