go/src/cmd/link/internal/objfile/objfile2.go

// Copyright 2019 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 objfile

import (
	"bytes"
	"cmd/internal/bio"
	"cmd/internal/dwarf"
	"cmd/internal/goobj2"
	"cmd/internal/obj"
	"cmd/internal/objabi"
	"cmd/internal/sys"
	"cmd/link/internal/sym"
	"fmt"
	"log"
	"os"
	"sort"
	"strconv"
	"strings"
)

var _ = fmt.Print

// Sym encapsulates a global symbol index, used to identify a specific
// Go symbol. The 0-valued Sym is corresponds to an invalid symbol.
type Sym int

// oReader is a wrapper type of obj.Reader, along with some
// extra information.
// TODO: rename to objReader once the old one is gone?
type oReader struct {
	*goobj2.Reader
	unit      *sym.CompilationUnit
	version   int // version of static symbol
	pkgprefix string
}

type objIdx struct {
	r *oReader
	i Sym // start index
}

type nameVer struct {
	name string
	v    int
}

// A Loader loads new object files and resolves indexed symbol references.
//
// TODO: describe local-global index mapping.
type Loader struct {
	start map[*oReader]Sym // map from object file to its start index
	objs  []objIdx         // sorted by start index (i.e. objIdx.i)
	max   Sym              // current max index

	symsByName map[nameVer]Sym // map symbol name to index

	objByPkg map[string]*oReader // map package path to its Go object reader

	Syms []*sym.Symbol // indexed symbols. XXX we still make sym.Symbol for now.
}

func NewLoader() *Loader {
	return &Loader{
		start:      make(map[*oReader]Sym),
		objs:       []objIdx{{nil, 0}},
		symsByName: make(map[nameVer]Sym),
		objByPkg:   make(map[string]*oReader),
		Syms:       []*sym.Symbol{nil},
	}
}

// Return the start index in the global index space for a given object file.
func (l *Loader) StartIndex(r *oReader) Sym {
	return l.start[r]
}

// Add object file r, return the start index.
func (l *Loader) AddObj(pkg string, r *oReader) Sym {
	if _, ok := l.start[r]; ok {
		panic("already added")
	}
	if _, ok := l.objByPkg[pkg]; !ok {
		l.objByPkg[pkg] = r
	}
	n := r.NSym() + r.NNonpkgdef()
	i := l.max + 1
	l.start[r] = i
	l.objs = append(l.objs, objIdx{r, i})
	l.max += Sym(n)
	return i
}

// Add a symbol with a given index, return if it is added.
func (l *Loader) AddSym(name string, ver int, i Sym, dupok bool) bool {
	nv := nameVer{name, ver}
	if _, ok := l.symsByName[nv]; ok {
		if dupok || true { // TODO: "true" isn't quite right. need to implement "overwrite" logic.
			return false
		}
		panic("duplicated definition of symbol " + name)
	}
	l.symsByName[nv] = i
	return true
}

// Add an external symbol (without index). Return the index of newly added
// symbol, or 0 if not added.
func (l *Loader) AddExtSym(name string, ver int) Sym {
	nv := nameVer{name, ver}
	if _, ok := l.symsByName[nv]; ok {
		return 0
	}
	i := l.max + 1
	l.symsByName[nv] = i
	l.max++
	return i
}

// Convert a local index to a global index.
func (l *Loader) ToGlobal(r *oReader, i int) Sym {
	return l.StartIndex(r) + Sym(i)
}

// Convert a global index to a local index.
func (l *Loader) ToLocal(i Sym) (*oReader, int) {
	k := sort.Search(int(i), func(k int) bool {
		return l.objs[k].i >= i
	})
	if k == len(l.objs) {
		return nil, 0
	}
	return l.objs[k].r, int(i - l.objs[k].i)
}

// Resolve a local symbol reference. Return global index.
func (l *Loader) Resolve(r *oReader, s goobj2.SymRef) Sym {
	var rr *oReader
	switch p := s.PkgIdx; p {
	case goobj2.PkgIdxInvalid:
		if s.SymIdx != 0 {
			panic("bad sym ref")
		}
		return 0
	case goobj2.PkgIdxNone:
		// Resolve by name
		i := int(s.SymIdx) + r.NSym()
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
		v := abiToVer(osym.ABI, r.version)
		nv := nameVer{name, v}
		return l.symsByName[nv]
	case goobj2.PkgIdxBuiltin:
		panic("PkgIdxBuiltin not used")
	case goobj2.PkgIdxSelf:
		rr = r
	default:
		pkg := r.Pkg(int(p))
		rr = l.objByPkg[pkg]
	}
	return l.ToGlobal(rr, int(s.SymIdx))
}

// Look up a symbol by name, return global index, or 0 if not found.
// This is more like Syms.ROLookup than Lookup -- it doesn't create
// new symbol.
func (l *Loader) Lookup(name string, ver int) Sym {
	nv := nameVer{name, ver}
	return l.symsByName[nv]
}

// Preload a package: add autolibs, add symbols to the symbol table.
// Does not read symbol data yet.
func LoadNew(l *Loader, arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *sym.Library, unit *sym.CompilationUnit, length int64, pn string, flags int) {
	roObject, readonly, err := f.Slice(uint64(length))
	if err != nil {
		log.Fatal("cannot read object file:", err)
	}
	r := goobj2.NewReaderFromBytes(roObject, readonly)
	if r == nil {
		panic("cannot read object file")
	}
	localSymVersion := syms.IncVersion()
	pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
	or := &oReader{r, unit, localSymVersion, pkgprefix}

	// Autolib
	npkg := r.NPkg()
	lib.ImportStrings = append(lib.ImportStrings, make([]string, npkg-1)...)[:len(lib.ImportStrings)]
	for i := 1; i < npkg; i++ {
		lib.ImportStrings = append(lib.ImportStrings, r.Pkg(i))
	}

	// DWARF file table
	nfile := r.NDwarfFile()
	unit.DWARFFileTable = make([]string, nfile)
	for i := range unit.DWARFFileTable {
		unit.DWARFFileTable[i] = r.DwarfFile(i)
	}

	istart := l.AddObj(lib.Pkg, or)

	ndef := r.NSym()
	nnonpkgdef := r.NNonpkgdef()

	// XXX add all symbols for now
	l.Syms = append(l.Syms, make([]*sym.Symbol, ndef+nnonpkgdef)...)
	for i, n := 0, ndef+nnonpkgdef; i < n; i++ {
		osym := goobj2.Sym{}
		osym.Read(r, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", pkgprefix, -1)
		if name == "" {
			continue // don't add unnamed aux symbol
		}
		v := abiToVer(osym.ABI, localSymVersion)
		dupok := osym.Flag&goobj2.SymFlagDupok != 0
		if l.AddSym(name, v, istart+Sym(i), dupok) {
			s := syms.Newsym(name, v)
			preprocess(arch, s) // TODO: put this at a better place
			l.Syms[istart+Sym(i)] = s
		}
	}

	// The caller expects us consuming all the data
	f.MustSeek(length, os.SEEK_CUR)
}

// Make sure referenced symbols are added. Most of them should already be added.
// This should only be needed for referenced external symbols.
func LoadRefs(l *Loader, arch *sys.Arch, syms *sym.Symbols) {
	for _, o := range l.objs[1:] {
		loadObjRefs(l, o.r, arch, syms)
	}
}

func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch, syms *sym.Symbols) {
	lib := r.unit.Lib
	pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
	ndef := r.NSym() + r.NNonpkgdef()
	for i, n := 0, r.NNonpkgref(); i < n; i++ {
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(ndef+i))
		name := strings.Replace(osym.Name, "\"\".", pkgprefix, -1)
		v := abiToVer(osym.ABI, r.version)
		if ii := l.AddExtSym(name, v); ii != 0 {
			s := syms.Newsym(name, v)
			preprocess(arch, s) // TODO: put this at a better place
			if ii != Sym(len(l.Syms)) {
				panic("AddExtSym returned bad index")
			}
			l.Syms = append(l.Syms, s)
		}
	}
}

func abiToVer(abi uint16, localSymVersion int) int {
	var v int
	if abi == goobj2.SymABIstatic {
		// Static
		v = localSymVersion
	} else if abiver := sym.ABIToVersion(obj.ABI(abi)); abiver != -1 {
		// Note that data symbols are "ABI0", which maps to version 0.
		v = abiver
	} else {
		log.Fatalf("invalid symbol ABI: %d", abi)
	}
	return v
}

func preprocess(arch *sys.Arch, s *sym.Symbol) {
	if s.Name != "" && s.Name[0] == '$' && len(s.Name) > 5 && s.Type == 0 && len(s.P) == 0 {
		x, err := strconv.ParseUint(s.Name[5:], 16, 64)
		if err != nil {
			log.Panicf("failed to parse $-symbol %s: %v", s.Name, err)
		}
		s.Type = sym.SRODATA
		s.Attr |= sym.AttrLocal
		switch s.Name[:5] {
		case "$f32.":
			if uint64(uint32(x)) != x {
				log.Panicf("$-symbol %s too large: %d", s.Name, x)
			}
			s.AddUint32(arch, uint32(x))
		case "$f64.", "$i64.":
			s.AddUint64(arch, x)
		default:
			log.Panicf("unrecognized $-symbol: %s", s.Name)
		}
		s.Attr.Set(sym.AttrReachable, false)
	}
}

// Load relocations for building the dependency graph in deadcode pass.
// For now, we load symbol types, relocations, gotype, and the contents
// of type symbols, which are needed in deadcode.
func LoadReloc(l *Loader) {
	for _, o := range l.objs[1:] {
		loadObjReloc(l, o.r)
	}
}

func loadObjReloc(l *Loader, r *oReader) {
	lib := r.unit.Lib
	pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
	istart := l.StartIndex(r)

	resolveSymRef := func(s goobj2.SymRef) *sym.Symbol {
		i := l.Resolve(r, s)
		return l.Syms[i]
	}

	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		s := l.Syms[istart+Sym(i)]
		if s == nil || s.Name == "" {
			continue
		}

		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", pkgprefix, -1)
		if s.Name != name { // Sanity check. We can remove it in the final version.
			fmt.Println("name mismatch:", lib, i, s.Name, name)
			panic("name mismatch")
		}

		if s.Type != 0 && s.Type != sym.SXREF {
			fmt.Println("symbol already processed:", lib, i, s)
			panic("symbol already processed")
		}

		t := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)]
		if t == sym.SXREF {
			log.Fatalf("bad sxref")
		}
		if t == 0 {
			log.Fatalf("missing type for %s in %s", s.Name, lib)
		}
		if t == sym.SBSS && (s.Type == sym.SRODATA || s.Type == sym.SNOPTRBSS) {
			t = s.Type
		}
		s.Type = t
		s.Unit = r.unit

		// Reloc
		nreloc := r.NReloc(i)
		s.R = make([]sym.Reloc, nreloc)
		for j := range s.R {
			rel := goobj2.Reloc{}
			rel.Read(r.Reader, r.RelocOff(i, j))
			s.R[j] = sym.Reloc{
				Off:  rel.Off,
				Siz:  rel.Siz,
				Type: objabi.RelocType(rel.Type),
				Add:  rel.Add,
				Sym:  resolveSymRef(rel.Sym),
			}
		}

		// XXX deadcode needs symbol data for type symbols. Read it now.
		if strings.HasPrefix(name, "type.") {
			s.P = r.Data(i)
			s.Attr.Set(sym.AttrReadOnly, r.ReadOnly())
			s.Size = int64(osym.Siz)
		}

		// Aux symbol
		naux := r.NAux(i)
		for j := 0; j < naux; j++ {
			a := goobj2.Aux{}
			a.Read(r.Reader, r.AuxOff(i, j))
			switch a.Type {
			case goobj2.AuxGotype:
				typ := resolveSymRef(a.Sym)
				if typ != nil {
					s.Gotype = typ
				}
			case goobj2.AuxFuncdata:
				pc := s.FuncInfo
				if pc == nil {
					pc = &sym.FuncInfo{Funcdata: make([]*sym.Symbol, 0, 4)}
					s.FuncInfo = pc
				}
				pc.Funcdata = append(pc.Funcdata, resolveSymRef(a.Sym))
			}
		}

		if s.Type == sym.STEXT {
			dupok := osym.Flag&goobj2.SymFlagDupok != 0
			if !dupok {
				if s.Attr.OnList() {
					log.Fatalf("symbol %s listed multiple times", s.Name)
				}
				s.Attr |= sym.AttrOnList
				lib.Textp = append(lib.Textp, s)
			} else {
				// there may ba a dup in another package
				// put into a temp list and add to text later
				lib.DupTextSyms = append(lib.DupTextSyms, s)
			}
		}
	}
}

// Load full contents.
// TODO: For now, some contents are already load in LoadReloc. Maybe
// we should combine LoadReloc back into this, once we rewrite deadcode
// pass to use index directly.
func LoadFull(l *Loader) {
	for _, o := range l.objs[1:] {
		loadObjFull(l, o.r)
	}
}

func loadObjFull(l *Loader, r *oReader) {
	lib := r.unit.Lib
	pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
	istart := l.StartIndex(r)

	resolveSymRef := func(s goobj2.SymRef) *sym.Symbol {
		i := l.Resolve(r, s)
		return l.Syms[i]
	}

	pcdataBase := r.PcdataBase()
	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		s := l.Syms[istart+Sym(i)]
		if s == nil || s.Name == "" {
			continue
		}
		if !s.Attr.Reachable() && (s.Type < sym.SDWARFSECT || s.Type > sym.SDWARFLINES) {
			// No need to load unreachable symbols.
			// XXX DWARF symbols may be used but are not marked reachable.
			continue
		}

		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", pkgprefix, -1)
		if s.Name != name { // Sanity check. We can remove it in the final version.
			fmt.Println("name mismatch:", lib, i, s.Name, name)
			panic("name mismatch")
		}

		dupok := osym.Flag&goobj2.SymFlagDupok != 0
		local := osym.Flag&goobj2.SymFlagLocal != 0
		makeTypelink := osym.Flag&goobj2.SymFlagTypelink != 0
		size := osym.Siz

		// Symbol data
		s.P = r.Data(i)
		s.Attr.Set(sym.AttrReadOnly, r.ReadOnly())

		// Aux symbol info
		isym := -1
		naux := r.NAux(i)
		for j := 0; j < naux; j++ {
			a := goobj2.Aux{}
			a.Read(r.Reader, r.AuxOff(i, j))
			switch a.Type {
			case goobj2.AuxGotype, goobj2.AuxFuncdata:
				// already loaded
			case goobj2.AuxFuncInfo:
				if a.Sym.PkgIdx != goobj2.PkgIdxSelf {
					panic("funcinfo symbol not defined in current package")
				}
				isym = int(a.Sym.SymIdx)
			default:
				panic("unknown aux type")
			}
		}

		s.File = pkgprefix[:len(pkgprefix)-1]
		if dupok {
			s.Attr |= sym.AttrDuplicateOK
		}
		if s.Size < int64(size) {
			s.Size = int64(size)
		}
		s.Attr.Set(sym.AttrLocal, local)
		s.Attr.Set(sym.AttrMakeTypelink, makeTypelink)

		if s.Type == sym.SDWARFINFO {
			// For DWARF symbols, replace `"".` to actual package prefix
			// in the symbol content.
			// TODO: maybe we should do this in the compiler and get rid
			// of this.
			patchDWARFName(s, r)
		}

		if s.Type != sym.STEXT {
			continue
		}

		// FuncInfo
		if isym == -1 {
			continue
		}
		b := r.Data(isym)
		info := goobj2.FuncInfo{}
		info.Read(b)

		if info.NoSplit != 0 {
			s.Attr |= sym.AttrNoSplit
		}
		if info.Flags&goobj2.FuncFlagReflectMethod != 0 {
			s.Attr |= sym.AttrReflectMethod
		}
		if info.Flags&goobj2.FuncFlagShared != 0 {
			s.Attr |= sym.AttrShared
		}
		if info.Flags&goobj2.FuncFlagTopFrame != 0 {
			s.Attr |= sym.AttrTopFrame
		}

		info.Pcdata = append(info.Pcdata, info.PcdataEnd) // for the ease of knowing where it ends
		pc := s.FuncInfo
		if pc == nil {
			pc = &sym.FuncInfo{}
			s.FuncInfo = pc
		}
		pc.Args = int32(info.Args)
		pc.Locals = int32(info.Locals)
		pc.Pcdata = make([]sym.Pcdata, len(info.Pcdata)-1) // -1 as we appended one above
		pc.Funcdataoff = make([]int64, len(info.Funcdataoff))
		pc.File = make([]*sym.Symbol, len(info.File))
		pc.Pcsp.P = r.BytesAt(pcdataBase+info.Pcsp, int(info.Pcfile-info.Pcsp))
		pc.Pcfile.P = r.BytesAt(pcdataBase+info.Pcfile, int(info.Pcline-info.Pcfile))
		pc.Pcline.P = r.BytesAt(pcdataBase+info.Pcline, int(info.Pcinline-info.Pcline))
		pc.Pcinline.P = r.BytesAt(pcdataBase+info.Pcinline, int(info.Pcdata[0]-info.Pcinline))
		for k := range pc.Pcdata {
			pc.Pcdata[k].P = r.BytesAt(pcdataBase+info.Pcdata[k], int(info.Pcdata[k+1]-info.Pcdata[k]))
		}
		for k := range pc.Funcdataoff {
			pc.Funcdataoff[k] = int64(info.Funcdataoff[k])
		}
		for k := range pc.File {
			pc.File[k] = resolveSymRef(info.File[k])
		}
	}
}

func patchDWARFName(s *sym.Symbol, r *oReader) {
	// This is kind of ugly. Really the package name should not
	// even be included here.
	if s.Size < 1 || s.P[0] != dwarf.DW_ABRV_FUNCTION {
		return
	}
	e := bytes.IndexByte(s.P, 0)
	if e == -1 {
		return
	}
	p := bytes.Index(s.P[:e], emptyPkg)
	if p == -1 {
		return
	}
	pkgprefix := []byte(r.pkgprefix)
	patched := bytes.Replace(s.P[:e], emptyPkg, pkgprefix, -1)

	s.P = append(patched, s.P[e:]...)
	s.Attr.Set(sym.AttrReadOnly, false)
	delta := int64(len(s.P)) - s.Size
	s.Size = int64(len(s.P))
	for i := range s.R {
		r := &s.R[i]
		if r.Off > int32(e) {
			r.Off += int32(delta)
		}
	}
}