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// Copyright 2021 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 noder
import (
// This file implements the unified IR linker, which combines the
// local package's stub data with imported package data to produce a
// complete export data file. It also rewrites the compiler's
// extension data sections based on the results of compilation (e.g.,
// the function inlining cost and linker symbol index assignments).
// TODO(mdempsky): Using the name "linker" here is confusing, because
// readers are likely to mistake references to it for cmd/link. But
// there's a shortage of good names for "something that combines
// multiple parts into a cohesive whole"... e.g., "assembler" and
// "compiler" are also already taken.
// TODO(mdempsky): Should linker go into pkgbits? Probably the
// low-level linking details can be moved there, but the logic for
// handling extension data needs to stay in the compiler.
// A linker combines a package's stub export data with any referenced
// elements from imported packages into a single, self-contained
// export data file.
type linker struct {
pw pkgbits.PkgEncoder
pkgs map[string]pkgbits.Index
decls map[*types.Sym]pkgbits.Index
bodies map[*types.Sym]pkgbits.Index
// relocAll ensures that all elements specified by pr and relocs are
// copied into the output export data file, and returns the
// corresponding indices in the output.
func (l *linker) relocAll(pr *pkgReader, relocs []pkgbits.RelocEnt) []pkgbits.RelocEnt {
res := make([]pkgbits.RelocEnt, len(relocs))
for i, rent := range relocs {
rent.Idx = l.relocIdx(pr, rent.Kind, rent.Idx)
res[i] = rent
return res
// relocIdx ensures a single element is copied into the output export
// data file, and returns the corresponding index in the output.
func (l *linker) relocIdx(pr *pkgReader, k pkgbits.RelocKind, idx pkgbits.Index) pkgbits.Index {
assert(pr != nil)
absIdx := pr.AbsIdx(k, idx)
if newidx := pr.newindex[absIdx]; newidx != 0 {
return ^newidx
var newidx pkgbits.Index
switch k {
case pkgbits.RelocString:
newidx = l.relocString(pr, idx)
case pkgbits.RelocPkg:
newidx = l.relocPkg(pr, idx)
case pkgbits.RelocObj:
newidx = l.relocObj(pr, idx)
// Generic relocations.
// TODO(mdempsky): Deduplicate more sections? In fact, I think
// every section could be deduplicated. This would also be easier
// if we do external relocations.
w :=
l.relocCommon(pr, &w, k, idx)
newidx = w.Idx
pr.newindex[absIdx] = ^newidx
return newidx
// relocString copies the specified string from pr into the output
// export data file, deduplicating it against other strings.
func (l *linker) relocString(pr *pkgReader, idx pkgbits.Index) pkgbits.Index {
// relocPkg copies the specified package from pr into the output
// export data file, rewriting its import path to match how it was
// imported.
// TODO(mdempsky): Since CL 391014, we already have the compilation
// unit's import path, so there should be no need to rewrite packages
// anymore.
func (l *linker) relocPkg(pr *pkgReader, idx pkgbits.Index) pkgbits.Index {
path := pr.PeekPkgPath(idx)
if newidx, ok := l.pkgs[path]; ok {
return newidx
r := pr.NewDecoder(pkgbits.RelocPkg, idx, pkgbits.SyncPkgDef)
w :=, pkgbits.SyncPkgDef)
l.pkgs[path] = w.Idx
// TODO(mdempsky): We end up leaving an empty string reference here
// from when the package was originally written as "". Probably not
// a big deal, but a little annoying. Maybe relocating
// cross-references in place is the way to go after all.
w.Relocs = l.relocAll(pr, r.Relocs)
_ = r.String() // original path
io.Copy(&w.Data, &r.Data)
return w.Flush()
// relocObj copies the specified object from pr into the output export
// data file, rewriting its compiler-private extension data (e.g.,
// adding inlining cost and escape analysis results for functions).
func (l *linker) relocObj(pr *pkgReader, idx pkgbits.Index) pkgbits.Index {
path, name, tag := pr.PeekObj(idx)
sym := types.NewPkg(path, "").Lookup(name)
if newidx, ok := l.decls[sym]; ok {
return newidx
if tag == pkgbits.ObjStub && path != "builtin" && path != "unsafe" {
pri, ok := objReader[sym]
if !ok {
base.Fatalf("missing reader for %q.%v", path, name)
pr =
idx = pri.idx
path2, name2, tag2 := pr.PeekObj(idx)
sym2 := types.NewPkg(path2, "").Lookup(name2)
assert(sym == sym2)
assert(tag2 != pkgbits.ObjStub)
w :=
wext :=
wname :=
wdict :=
l.decls[sym] = w.Idx
assert(wext.Idx == w.Idx)
assert(wname.Idx == w.Idx)
assert(wdict.Idx == w.Idx)
l.relocCommon(pr, &w, pkgbits.RelocObj, idx)
l.relocCommon(pr, &wname, pkgbits.RelocName, idx)
l.relocCommon(pr, &wdict, pkgbits.RelocObjDict, idx)
// Generic types and functions won't have definitions, and imported
// objects may not either.
obj, _ := sym.Def.(*ir.Name)
local := sym.Pkg == types.LocalPkg
if local && obj != nil {
switch tag {
case pkgbits.ObjFunc:
l.relocFuncExt(&wext, obj)
case pkgbits.ObjType:
l.relocTypeExt(&wext, obj)
case pkgbits.ObjVar:
l.relocVarExt(&wext, obj)
} else {
l.relocCommon(pr, &wext, pkgbits.RelocObjExt, idx)
// Check if we need to export the inline bodies for functions and
// methods.
if obj != nil {
if obj.Op() == ir.ONAME && obj.Class == ir.PFUNC {
l.exportBody(obj, local)
if obj.Op() == ir.OTYPE {
if typ := obj.Type(); !typ.IsInterface() {
for _, method := range typ.Methods().Slice() {
l.exportBody(method.Nname.(*ir.Name), local)
return w.Idx
// exportBody exports the given function or method's body, if
// appropriate. local indicates whether it's a local function or
// method available on a locally declared type. (Due to cross-package
// type aliases, a method may be imported, but still available on a
// locally declared type.)
func (l *linker) exportBody(obj *ir.Name, local bool) {
assert(obj.Op() == ir.ONAME && obj.Class == ir.PFUNC)
fn := obj.Func
if fn.Inl == nil {
return // not inlinable anyway
// As a simple heuristic, if the function was declared in this
// package or we inlined it somewhere in this package, then we'll
// (re)export the function body. This isn't perfect, but seems
// reasonable in practice. In particular, it has the nice property
// that in the worst case, adding a blank import ensures the
// function body is available for inlining.
// TODO(mdempsky): Reimplement the reachable method crawling logic
// from typecheck/crawler.go.
exportBody := local || fn.Inl.Body != nil
if !exportBody {
sym := obj.Sym()
if _, ok := l.bodies[sym]; ok {
// Due to type aliases, we might visit methods multiple times.
base.AssertfAt(obj.Type().Recv() != nil, obj.Pos(), "expected method: %v", obj)
pri, ok := bodyReaderFor(fn)
l.bodies[sym] = l.relocIdx(, pkgbits.RelocBody, pri.idx)
// relocCommon copies the specified element from pr into w,
// recursively relocating any referenced elements as well.
func (l *linker) relocCommon(pr *pkgReader, w *pkgbits.Encoder, k pkgbits.RelocKind, idx pkgbits.Index) {
r := pr.NewDecoderRaw(k, idx)
w.Relocs = l.relocAll(pr, r.Relocs)
io.Copy(&w.Data, &r.Data)
func (l *linker) pragmaFlag(w *pkgbits.Encoder, pragma ir.PragmaFlag) {
func (l *linker) relocFuncExt(w *pkgbits.Encoder, name *ir.Name) {
l.pragmaFlag(w, name.Func.Pragma)
l.linkname(w, name)
// Relocated extension data.
// Record definition ABI so cross-ABI calls can be direct.
// This is important for the performance of calling some
// common functions implemented in assembly (e.g., bytealg).
// Escape analysis.
for _, fs := range &types.RecvsParams {
for _, f := range fs(name.Type()).FieldSlice() {
if inl := name.Func.Inl; w.Bool(inl != nil) {
func (l *linker) relocTypeExt(w *pkgbits.Encoder, name *ir.Name) {
typ := name.Type()
l.pragmaFlag(w, name.Pragma())
// For type T, export the index of type descriptor symbols of T and *T.
l.lsymIdx(w, "", reflectdata.TypeLinksym(typ))
l.lsymIdx(w, "", reflectdata.TypeLinksym(typ.PtrTo()))
if typ.Kind() != types.TINTER {
for _, method := range typ.Methods().Slice() {
l.relocFuncExt(w, method.Nname.(*ir.Name))
func (l *linker) relocVarExt(w *pkgbits.Encoder, name *ir.Name) {
l.linkname(w, name)
func (l *linker) linkname(w *pkgbits.Encoder, name *ir.Name) {
linkname := name.Sym().Linkname
if !l.lsymIdx(w, linkname, name.Linksym()) {
func (l *linker) lsymIdx(w *pkgbits.Encoder, linkname string, lsym *obj.LSym) bool {
if lsym.PkgIdx > goobj.PkgIdxSelf || (lsym.PkgIdx == goobj.PkgIdxInvalid && !lsym.Indexed()) || linkname != "" {
return false
// For a defined symbol, export its index.
// For re-exporting an imported symbol, pass its index through.
return true