cmd/internal/goobj: store relocation type as uint16

Currently, relocation type is stored as uint8 in object files, as
Go relocations do not exceed 255. In the linker, however, it is
used as a 16-bit type, because external relocations can exceed
255. The linker has to store the extra byte in a side table. This
complicates many things.

Just store it as uint16 in object files. This simplifies things,
with a small cost of increasing the object file sizes.

               before      after
hello.o         1672        1678
runtime.a    7927784     8056194

Change-Id: I313cf44ad0b8b3b76e35055ae55d911ff35e3158
Reviewed-on: https://go-review.googlesource.com/c/go/+/268477
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

6 files changed, 40 insertions, 64 deletions

diff --git a/src/cmd/internal/goobj/objfile.go b/src/cmd/internal/goobj/objfile.go
index 247cc695f0..e2858bd57d 100644
--- a/src/cmd/internal/goobj/objfile.go
+++ b/src/cmd/internal/goobj/objfile.go
@@ -33,7 +33,7 @@ import (
 // New object file format.
 //
 //    Header struct {
-//       Magic       [...]byte   // "\x00go116ld"
+//       Magic       [...]byte   // "\x00go117ld"
 //       Fingerprint [8]byte
 //       Flags       uint32
 //       Offsets     [...]uint32 // byte offset of each block below
@@ -89,7 +89,7 @@ import (
 //    Relocs [...]struct {
 //       Off  int32
 //       Size uint8
-//       Type uint8
+//       Type uint16
 //       Add  int64
 //       Sym  symRef
 //    }
@@ -219,7 +219,7 @@ type Header struct {
 	Offsets     [NBlk]uint32
 }
 
-const Magic = "\x00go116ld"
+const Magic = "\x00go117ld"
 
 func (h *Header) Write(w *Writer) {
 	w.RawString(h.Magic)
@@ -373,32 +373,32 @@ const HashSize = sha1.Size
 // Reloc struct {
 //    Off  int32
 //    Siz  uint8
-//    Type uint8
+//    Type uint16
 //    Add  int64
 //    Sym  SymRef
 // }
 type Reloc [RelocSize]byte
 
-const RelocSize = 4 + 1 + 1 + 8 + 8
+const RelocSize = 4 + 1 + 2 + 8 + 8
 
-func (r *Reloc) Off() int32  { return int32(binary.LittleEndian.Uint32(r[:])) }
-func (r *Reloc) Siz() uint8  { return r[4] }
-func (r *Reloc) Type() uint8 { return r[5] }
-func (r *Reloc) Add() int64  { return int64(binary.LittleEndian.Uint64(r[6:])) }
+func (r *Reloc) Off() int32   { return int32(binary.LittleEndian.Uint32(r[:])) }
+func (r *Reloc) Siz() uint8   { return r[4] }
+func (r *Reloc) Type() uint16 { return binary.LittleEndian.Uint16(r[5:]) }
+func (r *Reloc) Add() int64   { return int64(binary.LittleEndian.Uint64(r[7:])) }
 func (r *Reloc) Sym() SymRef {
-	return SymRef{binary.LittleEndian.Uint32(r[14:]), binary.LittleEndian.Uint32(r[18:])}
+	return SymRef{binary.LittleEndian.Uint32(r[15:]), binary.LittleEndian.Uint32(r[19:])}
 }
 
-func (r *Reloc) SetOff(x int32)  { binary.LittleEndian.PutUint32(r[:], uint32(x)) }
-func (r *Reloc) SetSiz(x uint8)  { r[4] = x }
-func (r *Reloc) SetType(x uint8) { r[5] = x }
-func (r *Reloc) SetAdd(x int64)  { binary.LittleEndian.PutUint64(r[6:], uint64(x)) }
+func (r *Reloc) SetOff(x int32)   { binary.LittleEndian.PutUint32(r[:], uint32(x)) }
+func (r *Reloc) SetSiz(x uint8)   { r[4] = x }
+func (r *Reloc) SetType(x uint16) { binary.LittleEndian.PutUint16(r[5:], x) }
+func (r *Reloc) SetAdd(x int64)   { binary.LittleEndian.PutUint64(r[7:], uint64(x)) }
 func (r *Reloc) SetSym(x SymRef) {
-	binary.LittleEndian.PutUint32(r[14:], x.PkgIdx)
-	binary.LittleEndian.PutUint32(r[18:], x.SymIdx)
+	binary.LittleEndian.PutUint32(r[15:], x.PkgIdx)
+	binary.LittleEndian.PutUint32(r[19:], x.SymIdx)
 }
 
-func (r *Reloc) Set(off int32, size uint8, typ uint8, add int64, sym SymRef) {
+func (r *Reloc) Set(off int32, size uint8, typ uint16, add int64, sym SymRef) {
 	r.SetOff(off)
 	r.SetSiz(size)
 	r.SetType(typ)
diff --git a/src/cmd/internal/goobj/objfile_test.go b/src/cmd/internal/goobj/objfile_test.go
index 99d02a1bf1..ad80ede0f3 100644
--- a/src/cmd/internal/goobj/objfile_test.go
+++ b/src/cmd/internal/goobj/objfile_test.go
@@ -40,7 +40,7 @@ func TestReadWrite(t *testing.T) {
 	var r Reloc
 	r.SetOff(12)
 	r.SetSiz(4)
-	r.SetType(uint8(objabi.R_ADDR))
+	r.SetType(uint16(objabi.R_ADDR))
 	r.SetAdd(54321)
 	r.SetSym(SymRef{11, 22})
 	r.Write(w)
@@ -63,7 +63,7 @@ func TestReadWrite(t *testing.T) {
 	b = b[SymSize:]
 	var r2 Reloc
 	r2.fromBytes(b)
-	if r2.Off() != 12 || r2.Siz() != 4 || r2.Type() != uint8(objabi.R_ADDR) || r2.Add() != 54321 || r2.Sym() != (SymRef{11, 22}) {
+	if r2.Off() != 12 || r2.Siz() != 4 || r2.Type() != uint16(objabi.R_ADDR) || r2.Add() != 54321 || r2.Sym() != (SymRef{11, 22}) {
 		t.Errorf("read Reloc2 mismatch: got %v %v %v %v %v", r2.Off(), r2.Siz(), r2.Type(), r2.Add(), r2.Sym())
 	}
 
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index b031afbc36..24fb5a19de 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -498,7 +498,7 @@ func (w *writer) Reloc(r *Reloc) {
 	var o goobj.Reloc
 	o.SetOff(r.Off)
 	o.SetSiz(r.Siz)
-	o.SetType(uint8(r.Type))
+	o.SetType(uint16(r.Type))
 	o.SetAdd(r.Add)
 	o.SetSym(makeSymRef(r.Sym))
 	o.Write(w.Writer)
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index c05309a141..6d2e7dcabc 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -51,30 +51,13 @@ type Reloc struct {
 	*goobj.Reloc
 	r *oReader
 	l *Loader
-
-	// External reloc types may not fit into a uint8 which the Go object file uses.
-	// Store it here, instead of in the byte of goobj.Reloc.
-	// For Go symbols this will always be zero.
-	// goobj.Reloc.Type() + typ is always the right type, for both Go and external
-	// symbols.
-	typ objabi.RelocType
 }
 
-func (rel Reloc) Type() objabi.RelocType { return objabi.RelocType(rel.Reloc.Type()) + rel.typ }
-func (rel Reloc) Sym() Sym               { return rel.l.resolve(rel.r, rel.Reloc.Sym()) }
-func (rel Reloc) SetSym(s Sym)           { rel.Reloc.SetSym(goobj.SymRef{PkgIdx: 0, SymIdx: uint32(s)}) }
-func (rel Reloc) IsMarker() bool         { return rel.Siz() == 0 }
-
-func (rel Reloc) SetType(t objabi.RelocType) {
-	if t != objabi.RelocType(uint8(t)) {
-		panic("SetType: type doesn't fit into Reloc")
-	}
-	rel.Reloc.SetType(uint8(t))
-	if rel.typ != 0 {
-		// should use SymbolBuilder.SetRelocType
-		panic("wrong method to set reloc type")
-	}
-}
+func (rel Reloc) Type() objabi.RelocType     { return objabi.RelocType(rel.Reloc.Type()) }
+func (rel Reloc) SetType(t objabi.RelocType) { rel.Reloc.SetType(uint16(t)) }
+func (rel Reloc) Sym() Sym                   { return rel.l.resolve(rel.r, rel.Reloc.Sym()) }
+func (rel Reloc) SetSym(s Sym)               { rel.Reloc.SetSym(goobj.SymRef{PkgIdx: 0, SymIdx: uint32(s)}) }
+func (rel Reloc) IsMarker() bool             { return rel.Siz() == 0 }
 
 // Aux holds a "handle" to access an aux symbol record from an
 // object file.
@@ -307,15 +290,14 @@ type elfsetstringFunc func(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
-	relocs   []goobj.Reloc
-	reltypes []objabi.RelocType // relocation types
-	data     []byte
-	auxs     []goobj.Aux
+	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
+	relocs []goobj.Reloc
+	data   []byte
+	auxs   []goobj.Aux
 }
 
 const (
@@ -1833,10 +1815,9 @@ func (relocs *Relocs) Count() int { return len(relocs.rs) }
 // At 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 Reloc{&relocs.rs[j], relocs.r, relocs.l, pp.reltypes[j]}
+		return Reloc{&relocs.rs[j], relocs.r, relocs.l}
 	}
-	return Reloc{&relocs.rs[j], relocs.r, relocs.l, 0}
+	return Reloc{&relocs.rs[j], relocs.r, relocs.l}
 }
 
 // Relocs returns a Relocs object for the given global sym.
@@ -2337,13 +2318,11 @@ func (l *Loader) cloneToExternal(symIdx Sym) {
 		// Copy relocations
 		relocs := l.Relocs(symIdx)
 		pp.relocs = make([]goobj.Reloc, 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.At(i)
-			pp.relocs[i].Set(rel.Off(), rel.Siz(), 0, rel.Add(), goobj.SymRef{PkgIdx: 0, SymIdx: uint32(rel.Sym())})
-			pp.reltypes[i] = rel.Type()
+			pp.relocs[i].Set(rel.Off(), rel.Siz(), uint16(rel.Type()), rel.Add(), goobj.SymRef{PkgIdx: 0, SymIdx: uint32(rel.Sym())})
 		}
 
 		// Copy data
diff --git a/src/cmd/link/internal/loader/loader_test.go b/src/cmd/link/internal/loader/loader_test.go
index 1371c2a541..15ae830dc9 100644
--- a/src/cmd/link/internal/loader/loader_test.go
+++ b/src/cmd/link/internal/loader/loader_test.go
@@ -237,7 +237,8 @@ func sameRelocSlice(s1 *Relocs, s2 []Reloc) bool {
 type addFunc func(l *Loader, s Sym, s2 Sym) Sym
 
 func mkReloc(l *Loader, typ objabi.RelocType, off int32, siz uint8, add int64, sym Sym) Reloc {
-	r := Reloc{&goobj.Reloc{}, l.extReader, l, typ}
+	r := Reloc{&goobj.Reloc{}, l.extReader, l}
+	r.SetType(typ)
 	r.SetOff(off)
 	r.SetSiz(siz)
 	r.SetAdd(add)
diff --git a/src/cmd/link/internal/loader/symbolbuilder.go b/src/cmd/link/internal/loader/symbolbuilder.go
index 5d37da8ac6..204d04412d 100644
--- a/src/cmd/link/internal/loader/symbolbuilder.go
+++ b/src/cmd/link/internal/loader/symbolbuilder.go
@@ -121,13 +121,11 @@ func (sb *SymbolBuilder) Relocs() Relocs {
 // ResetRelocs removes all relocations on this symbol.
 func (sb *SymbolBuilder) ResetRelocs() {
 	sb.relocs = sb.relocs[:0]
-	sb.reltypes = sb.reltypes[:0]
 }
 
 // SetRelocType sets the type of the 'i'-th relocation on this sym to 't'
 func (sb *SymbolBuilder) SetRelocType(i int, t objabi.RelocType) {
-	sb.relocs[i].SetType(0)
-	sb.reltypes[i] = t
+	sb.relocs[i].SetType(uint16(t))
 }
 
 // SetRelocSym sets the target sym of the 'i'-th relocation on this sym to 's'
@@ -143,7 +141,6 @@ func (sb *SymbolBuilder) SetRelocAdd(i int, a int64) {
 // Add n relocations, return a handle to the relocations.
 func (sb *SymbolBuilder) AddRelocs(n int) Relocs {
 	sb.relocs = append(sb.relocs, make([]goobj.Reloc, n)...)
-	sb.reltypes = append(sb.reltypes, make([]objabi.RelocType, n)...)
 	return sb.l.Relocs(sb.symIdx)
 }
 
@@ -152,7 +149,7 @@ func (sb *SymbolBuilder) AddRelocs(n int) Relocs {
 func (sb *SymbolBuilder) AddRel(typ objabi.RelocType) (Reloc, int) {
 	j := len(sb.relocs)
 	sb.relocs = append(sb.relocs, goobj.Reloc{})
-	sb.reltypes = append(sb.reltypes, typ)
+	sb.relocs[j].SetType(uint16(typ))
 	relocs := sb.Relocs()
 	return relocs.At(j), j
 }
@@ -169,7 +166,6 @@ func (p *relocsByOff) Len() int           { return len(p.relocs) }
 func (p *relocsByOff) Less(i, j int) bool { return p.relocs[i].Off() < p.relocs[j].Off() }
 func (p *relocsByOff) Swap(i, j int) {
 	p.relocs[i], p.relocs[j] = p.relocs[j], p.relocs[i]
-	p.reltypes[i], p.reltypes[j] = p.reltypes[j], p.reltypes[i]
 }
 
 func (sb *SymbolBuilder) Reachable() bool {