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-rw-r--r--src/cmd/link/internal/wasm/asm.go604
1 files changed, 604 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..99018c8
--- /dev/null
+++ b/src/cmd/link/internal/wasm/asm.go
@@ -0,0 +1,604 @@
+// 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"
+ "internal/buildcfg"
+ "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.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 := 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)
+}
+
+// writeCodeSec 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, buildcfg.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, buildcfg.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)
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-27 20:22:42 +0000