[dev.link] cmd/link: store external relocations in Reloc2 format

Store external relocations in (almost) the same format as the Go
objects, so we can handle them more uniformly.

There is a small speedup:

(linking cmd/compile)
Deadcode        67.8ms ± 3%    61.1ms ± 3%   -9.94%  (p=0.008 n=5+5)
Dostkcheck      41.2ms ± 2%    38.8ms ± 3%   -5.99%  (p=0.008 n=5+5)

Change-Id: I8616e10b26235904201d6c9465f5ae32a49c9949
Reviewed-on: https://go-review.googlesource.com/c/go/+/226365
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

6 files changed, 104 insertions, 161 deletions

diff --git a/src/cmd/internal/goobj2/objfile.go b/src/cmd/internal/goobj2/objfile.go
index 2f275f3258..c0d47b4dab 100644
--- a/src/cmd/internal/goobj2/objfile.go
+++ b/src/cmd/internal/goobj2/objfile.go
@@ -321,13 +321,21 @@ func (r *Reloc2) Sym() SymRef {
 	return SymRef{binary.LittleEndian.Uint32(r[14:]), binary.LittleEndian.Uint32(r[18:])}
 }
 
+func (r *Reloc2) SetOff(x int32)  { binary.LittleEndian.PutUint32(r[:], uint32(x)) }
+func (r *Reloc2) SetSiz(x uint8)  { r[4] = x }
+func (r *Reloc2) SetType(x uint8) { r[5] = x }
+func (r *Reloc2) SetAdd(x int64)  { binary.LittleEndian.PutUint64(r[6:], uint64(x)) }
+func (r *Reloc2) SetSym(x SymRef) {
+	binary.LittleEndian.PutUint32(r[14:], x.PkgIdx)
+	binary.LittleEndian.PutUint32(r[18:], x.SymIdx)
+}
+
 func (r *Reloc2) Set(off int32, size uint8, typ uint8, add int64, sym SymRef) {
-	binary.LittleEndian.PutUint32(r[:], uint32(off))
-	r[4] = size
-	r[5] = typ
-	binary.LittleEndian.PutUint64(r[6:], uint64(add))
-	binary.LittleEndian.PutUint32(r[14:], sym.PkgIdx)
-	binary.LittleEndian.PutUint32(r[18:], sym.SymIdx)
+	r.SetOff(off)
+	r.SetSiz(size)
+	r.SetType(typ)
+	r.SetAdd(add)
+	r.SetSym(sym)
 }
 
 // Aux symbol info.
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index f7d8d13863..8ab67effa6 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -602,7 +602,6 @@ func (ctxt *Link) reloc() {
 
 func windynrelocsym(ctxt *Link, rel *loader.SymbolBuilder, s loader.Sym) {
 	var su *loader.SymbolBuilder
-	var rslice []loader.Reloc
 	relocs := ctxt.loader.Relocs(s)
 	for ri := 0; ri < relocs.Count; ri++ {
 		r := relocs.At2(ri)
@@ -627,11 +626,9 @@ func windynrelocsym(ctxt *Link, rel *loader.SymbolBuilder, s loader.Sym) {
 
 			if su == nil {
 				su = ctxt.loader.MakeSymbolUpdater(s)
-				rslice = su.Relocs()
 			}
-			r := &rslice[ri]
-			r.Sym = rel.Sym()
-			r.Add = int64(tplt)
+			r.SetSym(rel.Sym())
+			r.SetAdd(int64(tplt))
 
 			// jmp *addr
 			switch ctxt.Arch.Family {
@@ -654,11 +651,9 @@ func windynrelocsym(ctxt *Link, rel *loader.SymbolBuilder, s loader.Sym) {
 		} else if tplt >= 0 {
 			if su == nil {
 				su = ctxt.loader.MakeSymbolUpdater(s)
-				rslice = su.Relocs()
 			}
-			r := &rslice[ri]
-			r.Sym = rel.Sym()
-			r.Add = int64(tplt)
+			r.SetSym(rel.Sym())
+			r.SetAdd(int64(tplt))
 		}
 	}
 }
diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index 9f67a15c72..41dfa4f660 100644
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -132,16 +132,9 @@ func (c dwctxt2) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int6
 	switch size {
 	default:
 		c.linkctxt.Errorf(ds, "invalid size %d in adddwarfref\n", size)
-		fallthrough
-	case c.arch.PtrSize:
-		dsu.AddAddrPlus(c.arch, tds, 0)
-	case 4:
-		dsu.AddAddrPlus4(c.arch, tds, 0)
+	case c.arch.PtrSize, 4:
 	}
-	rsl := dsu.Relocs()
-	r := &rsl[len(rsl)-1]
-	r.Type = objabi.R_ADDROFF
-	r.Add = ofs
+	dsu.AddSymRef(c.arch, tds, ofs, objabi.R_ADDROFF, size)
 }
 
 func (c dwctxt2) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64) {
@@ -149,14 +142,15 @@ func (c dwctxt2) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64
 	if isDwarf64(c.linkctxt) {
 		size = 8
 	}
-
-	c.AddSectionOffset(s, size, t, ofs)
-
 	ds := loader.Sym(s.(dwSym))
 	dsu := c.ldr.MakeSymbolUpdater(ds)
-	rsl := dsu.Relocs()
-	r := &rsl[len(rsl)-1]
-	r.Type = objabi.R_DWARFSECREF
+	tds := loader.Sym(t.(dwSym))
+	switch size {
+	default:
+		c.linkctxt.Errorf(ds, "invalid size %d in adddwarfref\n", size)
+	case c.arch.PtrSize, 4:
+	}
+	dsu.AddSymRef(c.arch, tds, ofs, objabi.R_DWARFSECREF, size)
 }
 
 func (c dwctxt2) Logf(format string, args ...interface{}) {
@@ -345,15 +339,9 @@ func (d *dwctxt2) adddwarfref(sb *loader.SymbolBuilder, t loader.Sym, size int)
 	switch size {
 	default:
 		d.linkctxt.Errorf(sb.Sym(), "invalid size %d in adddwarfref\n", size)
-		fallthrough
-	case d.arch.PtrSize:
-		result = sb.AddAddrPlus(d.arch, t, 0)
-	case 4:
-		result = sb.AddAddrPlus4(d.arch, t, 0)
-	}
-	rsl := sb.Relocs()
-	r := &rsl[len(rsl)-1]
-	r.Type = objabi.R_DWARFSECREF
+	case d.arch.PtrSize, 4:
+	}
+	result = sb.AddSymRef(d.arch, t, 0, objabi.R_DWARFSECREF, size)
 	return result
 }
 
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index f01264839b..9b71db6d7a 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -68,6 +68,14 @@ type Reloc2 struct {
 
 func (rel Reloc2) Type() objabi.RelocType { return objabi.RelocType(rel.Reloc2.Type()) + rel.typ }
 func (rel Reloc2) Sym() Sym               { return rel.l.resolve(rel.r, rel.Reloc2.Sym()) }
+func (rel Reloc2) SetSym(s Sym)           { rel.Reloc2.SetSym(goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(s)}) }
+
+func (rel Reloc2) SetType(t objabi.RelocType) {
+	if t != objabi.RelocType(uint8(t)) {
+		panic("SetType: type doesn't fit into Reloc2")
+	}
+	rel.Reloc2.SetType(uint8(t))
+}
 
 // Aux2 holds a "handle" to access an aux symbol record from an
 // object file.
@@ -269,14 +277,15 @@ type elfsetstringFunc func(s *sym.Symbol, str string, off int)
 // extSymPayload holds the payload (data + relocations) for linker-synthesized
 // external symbols (note that symbol value is stored in a separate slice).
 type extSymPayload struct {
-	name   string // TODO: would this be better as offset into str table?
-	size   int64
-	ver    int
-	kind   sym.SymKind
-	objidx uint32 // index of original object if sym made by cloneToExternal
-	gotype Sym    // Gotype (0 if not present)
-	relocs []Reloc
-	data   []byte
+	name     string // TODO: would this be better as offset into str table?
+	size     int64
+	ver      int
+	kind     sym.SymKind
+	objidx   uint32 // index of original object if sym made by cloneToExternal
+	gotype   Sym    // Gotype (0 if not present)
+	relocs   []goobj2.Reloc2
+	reltypes []objabi.RelocType // relocation types
+	data     []byte
 }
 
 const (
@@ -1468,91 +1477,15 @@ func (l *Loader) growExtAttrBitmaps() {
 	}
 }
 
-// At method returns the j-th reloc for a global symbol.
-func (relocs *Relocs) At(j int) Reloc {
-	if relocs.l.isExtReader(relocs.r) {
-		pp := relocs.l.payloads[relocs.li]
-		return pp.relocs[j]
-	}
-	rel := goobj2.Reloc{}
-	rel.Read(relocs.r.Reader, relocs.r.RelocOff(relocs.li, j))
-	target := relocs.l.resolve(relocs.r, rel.Sym)
-	return Reloc{
-		Off:  rel.Off,
-		Size: rel.Siz,
-		Type: objabi.RelocType(rel.Type),
-		Add:  rel.Add,
-		Sym:  target,
-	}
-}
-
+// At2 returns the j-th reloc for a global symbol.
 func (relocs *Relocs) At2(j int) Reloc2 {
 	if relocs.l.isExtReader(relocs.r) {
 		pp := relocs.l.payloads[relocs.li]
-		r := pp.relocs[j]
-		// XXX populate a goobj2.Reloc from external reloc record.
-		// Ugly. Maybe we just want to use this format to store the
-		// reloc record in the first place?
-		// Also there is more speedup if we could remove the
-		// conditional here.
-		var b goobj2.Reloc2
-		b.Set(r.Off, r.Size, 0, r.Add, goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(r.Sym)})
-		return Reloc2{&b, relocs.r, relocs.l, r.Type}
+		return Reloc2{&relocs.rs[j], relocs.r, relocs.l, pp.reltypes[j]}
 	}
 	return Reloc2{&relocs.rs[j], relocs.r, relocs.l, 0}
 }
 
-// ReadAll method reads all relocations for a symbol into the
-// specified slice. If the slice capacity is not large enough, a new
-// larger slice will be allocated. Final slice is returned.
-func (relocs *Relocs) ReadAll(dst []Reloc) []Reloc {
-	return relocs.readAll(dst, false)
-}
-
-// ReadSyms method reads all relocation target symbols and reloc types
-// for a symbol into the specified slice. It is like ReadAll but only
-// fill in the Sym and Type fields.
-func (relocs *Relocs) ReadSyms(dst []Reloc) []Reloc {
-	return relocs.readAll(dst, true)
-}
-
-func (relocs *Relocs) readAll(dst []Reloc, onlySymType bool) []Reloc {
-	if relocs.Count == 0 {
-		return dst[:0]
-	}
-
-	if cap(dst) < relocs.Count {
-		dst = make([]Reloc, relocs.Count)
-	}
-	dst = dst[:0]
-
-	if relocs.l.isExtReader(relocs.r) {
-		pp := relocs.l.payloads[relocs.li]
-		dst = append(dst, pp.relocs...)
-		return dst
-	}
-
-	off := relocs.r.RelocOff(relocs.li, 0)
-	rel := goobj2.Reloc{}
-	for i := 0; i < relocs.Count; i++ {
-		if onlySymType {
-			rel.ReadSymType(relocs.r.Reader, off)
-		} else {
-			rel.Read(relocs.r.Reader, off)
-		}
-		off += uint32(rel.Size())
-		target := relocs.l.resolve(relocs.r, rel.Sym)
-		dst = append(dst, Reloc{
-			Off:  rel.Off,
-			Size: rel.Siz,
-			Type: objabi.RelocType(rel.Type),
-			Add:  rel.Add,
-			Sym:  target,
-		})
-	}
-	return dst
-}
-
 // Relocs returns a Relocs object for the given global sym.
 func (l *Loader) Relocs(i Sym) Relocs {
 	r, li := l.toLocal(i)
@@ -1569,6 +1502,7 @@ func (l *Loader) relocs(r *oReader, li int) Relocs {
 	if l.isExtReader(r) {
 		pp := l.payloads[li]
 		n = len(pp.relocs)
+		rs = pp.relocs
 	} else {
 		rs = r.Relocs2(li)
 		n = len(rs)
@@ -2237,7 +2171,15 @@ func (l *Loader) cloneToExternal(symIdx Sym) {
 
 		// Copy relocations
 		relocs := l.Relocs(symIdx)
-		pp.relocs = relocs.ReadAll(nil)
+		pp.relocs = make([]goobj2.Reloc2, relocs.Count)
+		pp.reltypes = make([]objabi.RelocType, relocs.Count)
+		for i := range pp.relocs {
+			// Copy the relocs slice.
+			// Convert local reference to global reference.
+			rel := relocs.At2(i)
+			pp.relocs[i].Set(rel.Off(), rel.Siz(), 0, rel.Add(), goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(rel.Sym())})
+			pp.reltypes[i] = rel.Type()
+		}
 
 		// Copy data
 		pp.data = r.Data(li)
@@ -2634,7 +2576,7 @@ func (l *Loader) convertRelocations(src *Relocs, dst *sym.Symbol, strict bool) {
 		}
 		if rs != 0 && l.Syms[rs] != nil && l.Syms[rs].Type == sym.SABIALIAS {
 			rsrelocs := l.Relocs(rs)
-			rs = rsrelocs.At(0).Sym
+			rs = rsrelocs.At2(0).Sym()
 		}
 		if strict && rs != 0 && l.Syms[rs] == nil && rt != objabi.R_USETYPE {
 			panic("nil reloc target in convertRelocations")
@@ -2659,14 +2601,13 @@ func (l *Loader) convertRelocations(src *Relocs, dst *sym.Symbol, strict bool) {
 // results returned; if "limit" is -1, then all undefs are returned.
 func (l *Loader) UndefinedRelocTargets(limit int) []Sym {
 	result := []Sym{}
-	rslice := []Reloc{}
 	for si := Sym(1); si < Sym(len(l.objSyms)); si++ {
 		relocs := l.Relocs(si)
-		rslice = relocs.ReadSyms(rslice)
 		for ri := 0; ri < relocs.Count; ri++ {
-			r := &rslice[ri]
-			if r.Sym != 0 && l.SymType(r.Sym) == sym.SXREF && l.RawSymName(r.Sym) != ".got" {
-				result = append(result, r.Sym)
+			r := relocs.At2(ri)
+			rs := r.Sym()
+			if rs != 0 && l.SymType(rs) == sym.SXREF && l.RawSymName(rs) != ".got" {
+				result = append(result, rs)
 				if limit != -1 && len(result) >= limit {
 					break
 				}
diff --git a/src/cmd/link/internal/loader/loader_test.go b/src/cmd/link/internal/loader/loader_test.go
index b384c752f4..8c9f7cfffb 100644
--- a/src/cmd/link/internal/loader/loader_test.go
+++ b/src/cmd/link/internal/loader/loader_test.go
@@ -173,14 +173,9 @@ func TestAddMaterializedSymbol(t *testing.T) {
 	for k, sb := range []*SymbolBuilder{sb1, sb2} {
 		rsl := sb.Relocs()
 		exp := expRel[k]
-		if !sameRelocSlice(rsl, exp) {
+		if !sameRelocSlice(&rsl, exp) {
 			t.Errorf("expected relocs %v, got %v", exp, rsl)
 		}
-		relocs := ldr.Relocs(sb.Sym())
-		r0 := relocs.At(0)
-		if r0 != exp[0] {
-			t.Errorf("expected reloc %v, got %v", exp[0], r0)
-		}
 	}
 
 	// ... then data.
@@ -213,12 +208,18 @@ func TestAddMaterializedSymbol(t *testing.T) {
 	}
 }
 
-func sameRelocSlice(s1 []Reloc, s2 []Reloc) bool {
-	if len(s1) != len(s2) {
+func sameRelocSlice(s1 *Relocs, s2 []Reloc) bool {
+	if s1.Count != len(s2) {
 		return false
 	}
-	for i := 0; i < len(s1); i++ {
-		if s1[i] != s2[i] {
+	for i := 0; i < s1.Count; i++ {
+		r1 := s1.At2(i)
+		r2 := &s2[i]
+		if r1.Sym() != r2.Sym ||
+			r1.Type() != r2.Type ||
+			r1.Off() != r2.Off ||
+			r1.Add() != r2.Add ||
+			r1.Siz() != r2.Size {
 			return false
 		}
 	}
@@ -342,10 +343,9 @@ func TestAddDataMethods(t *testing.T) {
 			t.Fatalf("testing Loader.%s: sym updated should be reachable", tp.which)
 		}
 		relocs := ldr.Relocs(mi)
-		rsl := relocs.ReadAll(nil)
-		if !sameRelocSlice(rsl, tp.expRel) {
+		if !sameRelocSlice(&relocs, tp.expRel) {
 			t.Fatalf("testing Loader.%s: got relocslice %+v wanted %+v",
-				tp.which, rsl, tp.expRel)
+				tp.which, relocs, tp.expRel)
 		}
 		pmi = mi
 	}
diff --git a/src/cmd/link/internal/loader/symbolbuilder.go b/src/cmd/link/internal/loader/symbolbuilder.go
index c26646cbdb..0ce5c6bde8 100644
--- a/src/cmd/link/internal/loader/symbolbuilder.go
+++ b/src/cmd/link/internal/loader/symbolbuilder.go
@@ -5,6 +5,7 @@
 package loader
 
 import (
+	"cmd/internal/goobj2"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"cmd/link/internal/sym"
@@ -121,23 +122,37 @@ func (sb *SymbolBuilder) AddBytes(data []byte) {
 	sb.size = int64(len(sb.data))
 }
 
-func (sb *SymbolBuilder) Relocs() []Reloc {
-	return sb.relocs
+func (sb *SymbolBuilder) Relocs() Relocs {
+	return sb.l.Relocs(sb.symIdx)
 }
 
 func (sb *SymbolBuilder) SetRelocs(rslice []Reloc) {
-	sb.relocs = rslice
-}
-
-func (sb *SymbolBuilder) WriteRelocs(rslice []Reloc) {
-	if len(sb.relocs) != len(rslice) {
-		panic("src/dest length mismatch")
+	n := len(rslice)
+	if cap(sb.relocs) < n {
+		sb.relocs = make([]goobj2.Reloc2, n)
+		sb.reltypes = make([]objabi.RelocType, n)
+	} else {
+		sb.relocs = sb.relocs[:n]
+		sb.reltypes = sb.reltypes[:n]
+	}
+	for i := range rslice {
+		sb.SetReloc(i, rslice[i])
 	}
-	copy(sb.relocs, rslice)
 }
 
 func (sb *SymbolBuilder) AddReloc(r Reloc) {
-	sb.relocs = append(sb.relocs, r)
+	// Populate a goobj2.Reloc from external reloc record.
+	var b goobj2.Reloc2
+	b.Set(r.Off, r.Size, 0, r.Add, goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(r.Sym)})
+	sb.relocs = append(sb.relocs, b)
+	sb.reltypes = append(sb.reltypes, r.Type)
+}
+
+// Update the j-th relocation in place.
+func (sb *SymbolBuilder) SetReloc(j int, r Reloc) {
+	// Populate a goobj2.Reloc from external reloc record.
+	sb.relocs[j].Set(r.Off, r.Size, 0, r.Add, goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(r.Sym)})
+	sb.reltypes[j] = r.Type
 }
 
 func (sb *SymbolBuilder) Reachable() bool {
@@ -277,11 +292,6 @@ func (sb *SymbolBuilder) Addstring(str string) int64 {
 	return r
 }
 
-func (sb *SymbolBuilder) addRel() *Reloc {
-	sb.relocs = append(sb.relocs, Reloc{})
-	return &sb.relocs[len(sb.relocs)-1]
-}
-
 func (sb *SymbolBuilder) addSymRef(tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
 	if sb.kind == 0 {
 		sb.kind = sym.SDATA
@@ -291,12 +301,13 @@ func (sb *SymbolBuilder) addSymRef(tgt Sym, add int64, typ objabi.RelocType, rsi
 	sb.size += int64(rsize)
 	sb.Grow(sb.size)
 
-	r := sb.addRel()
+	var r Reloc
 	r.Sym = tgt
 	r.Off = int32(i)
 	r.Size = uint8(rsize)
 	r.Type = typ
 	r.Add = add
+	sb.AddReloc(r)
 
 	return i + int64(r.Size)
 }