Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 640 insertions, 0 deletions

diff --git a/src/cmd/link/internal/wasm/asm.go b/src/cmd/link/internal/wasm/asm.go
new file mode 100644
index 0000000..31851fb
--- /dev/null
+++ b/src/cmd/link/internal/wasm/asm.go
@@ -0,0 +1,605 @@
+// 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 (
+	"bytes"
+	"cmd/internal/objabi"
+	"cmd/link/internal/ld"
+	"cmd/link/internal/loader"
+	"cmd/link/internal/sym"
+	"io"
+	"regexp"
+)
+
+const (
+	I32 = 0x7F
+	I64 = 0x7E
+	F32 = 0x7D
+	F64 = 0x7C
+)
+
+const (
+	sectionCustom   = 0
+	sectionType     = 1
+	sectionImport   = 2
+	sectionFunction = 3
+	sectionTable    = 4
+	sectionMemory   = 5
+	sectionGlobal   = 6
+	sectionExport   = 7
+	sectionStart    = 8
+	sectionElement  = 9
+	sectionCode     = 10
+	sectionData     = 11
+)
+
+// funcValueOffset is the offset between the PC_F value of a function and the index of the function in WebAssembly
+const funcValueOffset = 0x1000 // TODO(neelance): make function addresses play nice with heap addresses
+
+func gentext(ctxt *ld.Link, ldr *loader.Loader) {
+}
+
+type wasmFunc struct {
+	Name string
+	Type uint32
+	Code []byte
+}
+
+type wasmFuncType struct {
+	Params  []byte
+	Results []byte
+}
+
+var wasmFuncTypes = map[string]*wasmFuncType{
+	"_rt0_wasm_js":           {Params: []byte{}},                                         //
+	"wasm_export_run":        {Params: []byte{I32, I32}},                                 // argc, argv
+	"wasm_export_resume":     {Params: []byte{}},                                         //
+	"wasm_export_getsp":      {Results: []byte{I32}},                                     // sp
+	"wasm_pc_f_loop":         {Params: []byte{}},                                         //
+	"runtime.wasmMove":       {Params: []byte{I32, I32, I32}},                            // dst, src, len
+	"runtime.wasmZero":       {Params: []byte{I32, I32}},                                 // ptr, len
+	"runtime.wasmDiv":        {Params: []byte{I64, I64}, Results: []byte{I64}},           // x, y -> x/y
+	"runtime.wasmTruncS":     {Params: []byte{F64}, Results: []byte{I64}},                // x -> int(x)
+	"runtime.wasmTruncU":     {Params: []byte{F64}, Results: []byte{I64}},                // x -> uint(x)
+	"runtime.gcWriteBarrier": {Params: []byte{I64, I64}},                                 // ptr, val
+	"cmpbody":                {Params: []byte{I64, I64, I64, I64}, Results: []byte{I64}}, // a, alen, b, blen -> -1/0/1
+	"memeqbody":              {Params: []byte{I64, I64, I64}, Results: []byte{I64}},      // a, b, len -> 0/1
+	"memcmp":                 {Params: []byte{I32, I32, I32}, Results: []byte{I32}},      // a, b, len -> <0/0/>0
+	"memchr":                 {Params: []byte{I32, I32, I32}, Results: []byte{I32}},      // s, c, len -> index
+}
+
+func assignAddress(ldr *loader.Loader, sect *sym.Section, n int, s loader.Sym, va uint64, isTramp bool) (*sym.Section, int, uint64) {
+	// WebAssembly functions do not live in the same address space as the linear memory.
+	// Instead, WebAssembly automatically assigns indices. Imported functions (section "import")
+	// have indices 0 to n. They are followed by native functions (sections "function" and "code")
+	// with indices n+1 and following.
+	//
+	// The following rules describe how wasm handles function indices and addresses:
+	//   PC_F = funcValueOffset + WebAssembly function index (not including the imports)
+	//   s.Value = PC = PC_F<<16 + PC_B
+	//
+	// The funcValueOffset is necessary to avoid conflicts with expectations
+	// that the Go runtime has about function addresses.
+	// The field "s.Value" corresponds to the concept of PC at runtime.
+	// However, there is no PC register, only PC_F and PC_B. PC_F denotes the function,
+	// PC_B the resume point inside of that function. The entry of the function has PC_B = 0.
+	ldr.SetSymSect(s, sect)
+	ldr.SetSymValue(s, int64(funcValueOffset+va/ld.MINFUNC)<<16) // va starts at zero
+	va += uint64(ld.MINFUNC)
+	return sect, n, va
+}
+
+type wasmDataSect struct {
+	sect *sym.Section
+	data []byte
+}
+
+var dataSects []wasmDataSect
+
+func asmb(ctxt *ld.Link, ldr *loader.Loader) {
+	sections := []*sym.Section{
+		ldr.SymSect(ldr.Lookup("runtime.rodata", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.typelink", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.itablink", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.symtab", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.pclntab", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.noptrdata", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.data", 0)),
+	}
+
+	dataSects = make([]wasmDataSect, len(sections))
+	for i, sect := range sections {
+		data := ld.DatblkBytes(ctxt, int64(sect.Vaddr), int64(sect.Length))
+		dataSects[i] = wasmDataSect{sect, data}
+	}
+}
+
+// asmb writes the final WebAssembly module binary.
+// Spec: https://webassembly.github.io/spec/core/binary/modules.html
+func asmb2(ctxt *ld.Link, ldr *loader.Loader) {
+	types := []*wasmFuncType{
+		// For normal Go functions, the single parameter is PC_B,
+		// the return value is
+		// 0 if the function returned normally or
+		// 1 if the stack needs to be unwound.
+		{Params: []byte{I32}, Results: []byte{I32}},
+	}
+
+	// collect host imports (functions that get imported from the WebAssembly host, usually JavaScript)
+	hostImports := []*wasmFunc{
+		{
+			Name: "debug",
+			Type: lookupType(&wasmFuncType{Params: []byte{I32}}, &types),
+		},
+	}
+	hostImportMap := make(map[loader.Sym]int64)
+	for _, fn := range ctxt.Textp {
+		relocs := ldr.Relocs(fn)
+		for ri := 0; ri < relocs.Count(); ri++ {
+			r := relocs.At(ri)
+			if r.Type() == objabi.R_WASMIMPORT {
+				hostImportMap[r.Sym()] = int64(len(hostImports))
+				hostImports = append(hostImports, &wasmFunc{
+					Name: ldr.SymName(r.Sym()),
+					Type: lookupType(&wasmFuncType{Params: []byte{I32}}, &types),
+				})
+			}
+		}
+	}
+
+	// collect functions with WebAssembly body
+	var buildid []byte
+	fns := make([]*wasmFunc, len(ctxt.Textp))
+	for i, fn := range ctxt.Textp {
+		wfn := new(bytes.Buffer)
+		if ldr.SymName(fn) == "go.buildid" {
+			writeUleb128(wfn, 0) // number of sets of locals
+			writeI32Const(wfn, 0)
+			wfn.WriteByte(0x0b) // end
+			buildid = ldr.Data(fn)
+		} else {
+			// Relocations have variable length, handle them here.
+			relocs := ldr.Relocs(fn)
+			P := ldr.Data(fn)
+			off := int32(0)
+			for ri := 0; ri < relocs.Count(); ri++ {
+				r := relocs.At(ri)
+				if r.Siz() == 0 {
+					continue // skip marker relocations
+				}
+				wfn.Write(P[off:r.Off()])
+				off = r.Off()
+				rs := ldr.ResolveABIAlias(r.Sym())
+				switch r.Type() {
+				case objabi.R_ADDR:
+					writeSleb128(wfn, ldr.SymValue(rs)+r.Add())
+				case objabi.R_CALL:
+					writeSleb128(wfn, int64(len(hostImports))+ldr.SymValue(rs)>>16-funcValueOffset)
+				case objabi.R_WASMIMPORT:
+					writeSleb128(wfn, hostImportMap[rs])
+				default:
+					ldr.Errorf(fn, "bad reloc type %d (%s)", r.Type(), sym.RelocName(ctxt.Arch, r.Type()))
+					continue
+				}
+			}
+			wfn.Write(P[off:])
+		}
+
+		typ := uint32(0)
+		if sig, ok := wasmFuncTypes[ldr.SymName(fn)]; ok {
+			typ = lookupType(sig, &types)
+		}
+
+		name := nameRegexp.ReplaceAllString(ldr.SymName(fn), "_")
+		fns[i] = &wasmFunc{Name: name, Type: typ, Code: wfn.Bytes()}
+	}
+
+	ctxt.Out.Write([]byte{0x00, 0x61, 0x73, 0x6d}) // magic
+	ctxt.Out.Write([]byte{0x01, 0x00, 0x00, 0x00}) // version
+
+	// Add any buildid early in the binary:
+	if len(buildid) != 0 {
+		writeBuildID(ctxt, buildid)
+	}
+
+	writeTypeSec(ctxt, types)
+	writeImportSec(ctxt, hostImports)
+	writeFunctionSec(ctxt, fns)
+	writeTableSec(ctxt, fns)
+	writeMemorySec(ctxt, ldr)
+	writeGlobalSec(ctxt)
+	writeExportSec(ctxt, ldr, len(hostImports))
+	writeElementSec(ctxt, uint64(len(hostImports)), uint64(len(fns)))
+	writeCodeSec(ctxt, fns)
+	writeDataSec(ctxt)
+	writeProducerSec(ctxt)
+	if !*ld.FlagS {
+		writeNameSec(ctxt, len(hostImports), fns)
+	}
+}
+
+func lookupType(sig *wasmFuncType, types *[]*wasmFuncType) uint32 {
+	for i, t := range *types {
+		if bytes.Equal(sig.Params, t.Params) && bytes.Equal(sig.Results, t.Results) {
+			return uint32(i)
+		}
+	}
+	*types = append(*types, sig)
+	return uint32(len(*types) - 1)
+}
+
+func writeSecHeader(ctxt *ld.Link, id uint8) int64 {
+	ctxt.Out.WriteByte(id)
+	sizeOffset := ctxt.Out.Offset()
+	ctxt.Out.Write(make([]byte, 5)) // placeholder for length
+	return sizeOffset
+}
+
+func writeSecSize(ctxt *ld.Link, sizeOffset int64) {
+	endOffset := ctxt.Out.Offset()
+	ctxt.Out.SeekSet(sizeOffset)
+	writeUleb128FixedLength(ctxt.Out, uint64(endOffset-sizeOffset-5), 5)
+	ctxt.Out.SeekSet(endOffset)
+}
+
+func writeBuildID(ctxt *ld.Link, buildid []byte) {
+	sizeOffset := writeSecHeader(ctxt, sectionCustom)
+	writeName(ctxt.Out, "go.buildid")
+	ctxt.Out.Write(buildid)
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeTypeSec writes the section that declares all function types
+// so they can be referenced by index.
+func writeTypeSec(ctxt *ld.Link, types []*wasmFuncType) {
+	sizeOffset := writeSecHeader(ctxt, sectionType)
+
+	writeUleb128(ctxt.Out, uint64(len(types)))
+
+	for _, t := range types {
+		ctxt.Out.WriteByte(0x60) // functype
+		writeUleb128(ctxt.Out, uint64(len(t.Params)))
+		for _, v := range t.Params {
+			ctxt.Out.WriteByte(byte(v))
+		}
+		writeUleb128(ctxt.Out, uint64(len(t.Results)))
+		for _, v := range t.Results {
+			ctxt.Out.WriteByte(byte(v))
+		}
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeImportSec writes the section that lists the functions that get
+// imported from the WebAssembly host, usually JavaScript.
+func writeImportSec(ctxt *ld.Link, hostImports []*wasmFunc) {
+	sizeOffset := writeSecHeader(ctxt, sectionImport)
+
+	writeUleb128(ctxt.Out, uint64(len(hostImports))) // number of imports
+	for _, fn := range hostImports {
+		writeName(ctxt.Out, "go") // provided by the import object in wasm_exec.js
+		writeName(ctxt.Out, fn.Name)
+		ctxt.Out.WriteByte(0x00) // func import
+		writeUleb128(ctxt.Out, uint64(fn.Type))
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeFunctionSec writes the section that declares the types of functions.
+// The bodies of these functions will later be provided in the "code" section.
+func writeFunctionSec(ctxt *ld.Link, fns []*wasmFunc) {
+	sizeOffset := writeSecHeader(ctxt, sectionFunction)
+
+	writeUleb128(ctxt.Out, uint64(len(fns)))
+	for _, fn := range fns {
+		writeUleb128(ctxt.Out, uint64(fn.Type))
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeTableSec writes the section that declares tables. Currently there is only a single table
+// that is used by the CallIndirect operation to dynamically call any function.
+// The contents of the table get initialized by the "element" section.
+func writeTableSec(ctxt *ld.Link, fns []*wasmFunc) {
+	sizeOffset := writeSecHeader(ctxt, sectionTable)
+
+	numElements := uint64(funcValueOffset + len(fns))
+	writeUleb128(ctxt.Out, 1)           // number of tables
+	ctxt.Out.WriteByte(0x70)            // type: anyfunc
+	ctxt.Out.WriteByte(0x00)            // no max
+	writeUleb128(ctxt.Out, numElements) // min
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeMemorySec writes the section that declares linear memories. Currently one linear memory is being used.
+// Linear memory always starts at address zero. More memory can be requested with the GrowMemory instruction.
+func writeMemorySec(ctxt *ld.Link, ldr *loader.Loader) {
+	sizeOffset := writeSecHeader(ctxt, sectionMemory)
+
+	dataSection := ldr.SymSect(ldr.Lookup("runtime.data", 0))
+	dataEnd := dataSection.Vaddr + dataSection.Length
+	var initialSize = dataEnd + 16<<20 // 16MB, enough for runtime init without growing
+
+	const wasmPageSize = 64 << 10 // 64KB
+
+	writeUleb128(ctxt.Out, 1)                        // number of memories
+	ctxt.Out.WriteByte(0x00)                         // no maximum memory size
+	writeUleb128(ctxt.Out, initialSize/wasmPageSize) // minimum (initial) memory size
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeGlobalSec writes the section that declares global variables.
+func writeGlobalSec(ctxt *ld.Link) {
+	sizeOffset := writeSecHeader(ctxt, sectionGlobal)
+
+	globalRegs := []byte{
+		I32, // 0: SP
+		I64, // 1: CTXT
+		I64, // 2: g
+		I64, // 3: RET0
+		I64, // 4: RET1
+		I64, // 5: RET2
+		I64, // 6: RET3
+		I32, // 7: PAUSE
+	}
+
+	writeUleb128(ctxt.Out, uint64(len(globalRegs))) // number of globals
+
+	for _, typ := range globalRegs {
+		ctxt.Out.WriteByte(typ)
+		ctxt.Out.WriteByte(0x01) // var
+		switch typ {
+		case I32:
+			writeI32Const(ctxt.Out, 0)
+		case I64:
+			writeI64Const(ctxt.Out, 0)
+		}
+		ctxt.Out.WriteByte(0x0b) // end
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeExportSec writes the section that declares exports.
+// Exports can be accessed by the WebAssembly host, usually JavaScript.
+// The wasm_export_* functions and the linear memory get exported.
+func writeExportSec(ctxt *ld.Link, ldr *loader.Loader, lenHostImports int) {
+	sizeOffset := writeSecHeader(ctxt, sectionExport)
+
+	writeUleb128(ctxt.Out, 4) // number of exports
+
+	for _, name := range []string{"run", "resume", "getsp"} {
+		s := ldr.Lookup("wasm_export_"+name, 0)
+		idx := uint32(lenHostImports) + uint32(ldr.SymValue(s)>>16) - funcValueOffset
+		writeName(ctxt.Out, name)           // inst.exports.run/resume/getsp in wasm_exec.js
+		ctxt.Out.WriteByte(0x00)            // func export
+		writeUleb128(ctxt.Out, uint64(idx)) // funcidx
+	}
+
+	writeName(ctxt.Out, "mem") // inst.exports.mem in wasm_exec.js
+	ctxt.Out.WriteByte(0x02)   // mem export
+	writeUleb128(ctxt.Out, 0)  // memidx
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeElementSec writes the section that initializes the tables declared by the "table" section.
+// The table for CallIndirect gets initialized in a very simple way so that each table index (PC_F value)
+// maps linearly to the function index (numImports + PC_F).
+func writeElementSec(ctxt *ld.Link, numImports, numFns uint64) {
+	sizeOffset := writeSecHeader(ctxt, sectionElement)
+
+	writeUleb128(ctxt.Out, 1) // number of element segments
+
+	writeUleb128(ctxt.Out, 0) // tableidx
+	writeI32Const(ctxt.Out, funcValueOffset)
+	ctxt.Out.WriteByte(0x0b) // end
+
+	writeUleb128(ctxt.Out, numFns) // number of entries
+	for i := uint64(0); i < numFns; i++ {
+		writeUleb128(ctxt.Out, numImports+i)
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeElementSec writes the section that provides the function bodies for the functions
+// declared by the "func" section.
+func writeCodeSec(ctxt *ld.Link, fns []*wasmFunc) {
+	sizeOffset := writeSecHeader(ctxt, sectionCode)
+
+	writeUleb128(ctxt.Out, uint64(len(fns))) // number of code entries
+	for _, fn := range fns {
+		writeUleb128(ctxt.Out, uint64(len(fn.Code)))
+		ctxt.Out.Write(fn.Code)
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeDataSec writes the section that provides data that will be used to initialize the linear memory.
+func writeDataSec(ctxt *ld.Link) {
+	sizeOffset := writeSecHeader(ctxt, sectionData)
+
+	type dataSegment struct {
+		offset int32
+		data   []byte
+	}
+
+	// Omit blocks of zeroes and instead emit data segments with offsets skipping the zeroes.
+	// This reduces the size of the WebAssembly binary. We use 8 bytes as an estimate for the
+	// overhead of adding a new segment (same as wasm-opt's memory-packing optimization uses).
+	const segmentOverhead = 8
+
+	// Generate at most this many segments. A higher number of segments gets rejected by some WebAssembly runtimes.
+	const maxNumSegments = 100000
+
+	var segments []*dataSegment
+	for secIndex, ds := range dataSects {
+		data := ds.data
+		offset := int32(ds.sect.Vaddr)
+
+		// skip leading zeroes
+		for len(data) > 0 && data[0] == 0 {
+			data = data[1:]
+			offset++
+		}
+
+		for len(data) > 0 {
+			dataLen := int32(len(data))
+			var segmentEnd, zeroEnd int32
+			if len(segments)+(len(dataSects)-secIndex) == maxNumSegments {
+				segmentEnd = dataLen
+				zeroEnd = dataLen
+			} else {
+				for {
+					// look for beginning of zeroes
+					for segmentEnd < dataLen && data[segmentEnd] != 0 {
+						segmentEnd++
+					}
+					// look for end of zeroes
+					zeroEnd = segmentEnd
+					for zeroEnd < dataLen && data[zeroEnd] == 0 {
+						zeroEnd++
+					}
+					// emit segment if omitting zeroes reduces the output size
+					if zeroEnd-segmentEnd >= segmentOverhead || zeroEnd == dataLen {
+						break
+					}
+					segmentEnd = zeroEnd
+				}
+			}
+
+			segments = append(segments, &dataSegment{
+				offset: offset,
+				data:   data[:segmentEnd],
+			})
+			data = data[zeroEnd:]
+			offset += zeroEnd
+		}
+	}
+
+	writeUleb128(ctxt.Out, uint64(len(segments))) // number of data entries
+	for _, seg := range segments {
+		writeUleb128(ctxt.Out, 0) // memidx
+		writeI32Const(ctxt.Out, seg.offset)
+		ctxt.Out.WriteByte(0x0b) // end
+		writeUleb128(ctxt.Out, uint64(len(seg.data)))
+		ctxt.Out.Write(seg.data)
+	}
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+// writeProducerSec writes an optional section that reports the source language and compiler version.
+func writeProducerSec(ctxt *ld.Link) {
+	sizeOffset := writeSecHeader(ctxt, sectionCustom)
+	writeName(ctxt.Out, "producers")
+
+	writeUleb128(ctxt.Out, 2) // number of fields
+
+	writeName(ctxt.Out, "language")     // field name
+	writeUleb128(ctxt.Out, 1)           // number of values
+	writeName(ctxt.Out, "Go")           // value: name
+	writeName(ctxt.Out, objabi.Version) // value: version
+
+	writeName(ctxt.Out, "processed-by")   // field name
+	writeUleb128(ctxt.Out, 1)             // number of values
+	writeName(ctxt.Out, "Go cmd/compile") // value: name
+	writeName(ctxt.Out, objabi.Version)   // value: version
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+var nameRegexp = regexp.MustCompile(`[^\w\.]`)
+
+// writeNameSec writes an optional section that assigns names to the functions declared by the "func" section.
+// The names are only used by WebAssembly stack traces, debuggers and decompilers.
+// TODO(neelance): add symbol table of DATA symbols
+func writeNameSec(ctxt *ld.Link, firstFnIndex int, fns []*wasmFunc) {
+	sizeOffset := writeSecHeader(ctxt, sectionCustom)
+	writeName(ctxt.Out, "name")
+
+	sizeOffset2 := writeSecHeader(ctxt, 0x01) // function names
+	writeUleb128(ctxt.Out, uint64(len(fns)))
+	for i, fn := range fns {
+		writeUleb128(ctxt.Out, uint64(firstFnIndex+i))
+		writeName(ctxt.Out, fn.Name)
+	}
+	writeSecSize(ctxt, sizeOffset2)
+
+	writeSecSize(ctxt, sizeOffset)
+}
+
+type nameWriter interface {
+	io.ByteWriter
+	io.Writer
+}
+
+func writeI32Const(w io.ByteWriter, v int32) {
+	w.WriteByte(0x41) // i32.const
+	writeSleb128(w, int64(v))
+}
+
+func writeI64Const(w io.ByteWriter, v int64) {
+	w.WriteByte(0x42) // i64.const
+	writeSleb128(w, v)
+}
+
+func writeName(w nameWriter, name string) {
+	writeUleb128(w, uint64(len(name)))
+	w.Write([]byte(name))
+}
+
+func writeUleb128(w io.ByteWriter, v uint64) {
+	if v < 128 {
+		w.WriteByte(uint8(v))
+		return
+	}
+	more := true
+	for more {
+		c := uint8(v & 0x7f)
+		v >>= 7
+		more = v != 0
+		if more {
+			c |= 0x80
+		}
+		w.WriteByte(c)
+	}
+}
+
+func writeUleb128FixedLength(w io.ByteWriter, v uint64, length int) {
+	for i := 0; i < length; i++ {
+		c := uint8(v & 0x7f)
+		v >>= 7
+		if i < length-1 {
+			c |= 0x80
+		}
+		w.WriteByte(c)
+	}
+	if v != 0 {
+		panic("writeUleb128FixedLength: length too small")
+	}
+}
+
+func writeSleb128(w io.ByteWriter, v int64) {
+	more := true
+	for more {
+		c := uint8(v & 0x7f)
+		s := uint8(v & 0x40)
+		v >>= 7
+		more = !((v == 0 && s == 0) || (v == -1 && s != 0))
+		if more {
+			c |= 0x80
+		}
+		w.WriteByte(c)
+	}
+}
diff --git a/src/cmd/link/internal/wasm/obj.go b/src/cmd/link/internal/wasm/obj.go
new file mode 100644
index 0000000..f8090a3
--- /dev/null
+++ b/src/cmd/link/internal/wasm/obj.go
@@ -0,0 +1,35 @@
+// 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,
+		Asmb2:         asmb2,
+		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
+	}
+}