cmd/compile, etc: use nameOff in uncommonType

linux/amd64 PIE:
	cmd/go:  -62KB (0.5%)
	jujud:  -550KB (0.7%)

For #6853.

Change-Id: Ieb67982abce5832e24b997506f0ae7108f747108
Reviewed-on: https://go-review.googlesource.com/22371
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -75,7 +75,7 @@ func uncommonSize(t *Type) int { // Sizeof(runtime.uncommontype{})
 	if t.Sym == nil && len(methods(t)) == 0 {
 		return 0
 	}
-	return 2 * Widthptr
+	return 4 + 2 + 2
 }
 
 func makefield(name string, t *Type) *Field {
@@ -463,6 +463,9 @@ func dgopkgpathLSym(s *obj.LSym, ot int, pkg *Pkg) int {
 
 // dgopkgpathOffLSym writes an offset relocation in s at offset ot to the pkg path symbol.
 func dgopkgpathOffLSym(s *obj.LSym, ot int, pkg *Pkg) int {
+	if pkg == nil {
+		return duintxxLSym(s, ot, 0, 4)
+	}
 	if pkg == localpkg && myimportpath == "" {
 		// If we don't know the full import path of the package being compiled
 		// (i.e. -p was not passed on the compiler command line), emit a reference to
@@ -597,12 +600,9 @@ func dextratype(s *Sym, ot int, t *Type, dataAdd int) int {
 		dtypesym(a.type_)
 	}
 
-	ot = dgopkgpath(s, ot, typePkg(t))
+	ot = dgopkgpathOffLSym(Linksym(s), ot, typePkg(t))
 
-	dataAdd += Widthptr + 2 + 2
-	if Widthptr == 8 {
-		dataAdd += 4
-	}
+	dataAdd += 4 + 2 + 2
 	mcount := len(m)
 	if mcount != int(uint16(mcount)) {
 		Fatalf("too many methods on %s: %d", t, mcount)
@@ -613,9 +613,6 @@ func dextratype(s *Sym, ot int, t *Type, dataAdd int) int {
 
 	ot = duint16(s, ot, uint16(mcount))
 	ot = duint16(s, ot, uint16(dataAdd))
-	if Widthptr == 8 {
-		ot = duint32(s, ot, 0) // align for following pointers
-	}
 	return ot
 }
 

src/cmd/link/internal/ld/decodesym.go

@@ -61,7 +61,7 @@ func decode_inuxi(p []byte, sz int) uint64 {
 
 func commonsize() int      { return 4*SysArch.PtrSize + 8 + 8 } // runtime._type
 func structfieldSize() int { return 3 * SysArch.PtrSize }       // runtime.structfield
-func uncommonSize() int    { return 2 * SysArch.PtrSize }       // runtime.uncommontype
+func uncommonSize() int    { return 4 + 2 + 2 }                 // runtime.uncommontype
 
 // Type.commonType.kind
 func decodetype_kind(s *LSym) uint8 {
@@ -361,8 +361,8 @@ func decodetype_methods(s *LSym) []methodsig {
 		// just Sizeof(rtype)
 	}
 
-	mcount := int(decode_inuxi(s.P[off+SysArch.PtrSize:], 2))
-	moff := int(decode_inuxi(s.P[off+SysArch.PtrSize+2:], 2))
+	mcount := int(decode_inuxi(s.P[off+4:], 2))
+	moff := int(decode_inuxi(s.P[off+4+2:], 2))
 	off += moff                // offset to array of reflect.method values
 	const sizeofMethod = 4 * 4 // sizeof reflect.method in program
 	return decode_methodsig(s, off, sizeofMethod, mcount)

src/cmd/link/internal/ld/symtab.go

@@ -435,6 +435,11 @@ func symtab() {
 				s.Outer = symtype
 			}
 
+		case strings.HasPrefix(s.Name, "go.importpath.") && UseRelro():
+			// Keep go.importpath symbols in the same section as types and
+			// names, as they can be referred to by a section offset.
+			s.Type = obj.STYPERELRO
+
 		case strings.HasPrefix(s.Name, "go.typelink."):
 			ntypelinks++
 			s.Type = obj.STYPELINK

src/reflect/type.go

@@ -311,7 +311,7 @@ type method struct {
 // Using a pointer to this struct reduces the overall size required
 // to describe an unnamed type with no methods.
 type uncommonType struct {
-	pkgPath name   // import path; empty for built-in types like int, string
+	pkgPath nameOff // import path; empty for built-in types like int, string
 	mcount  uint16  // number of methods
 	moff    uint16  // offset from this uncommontype to [mcount]method
 }
@@ -613,13 +613,6 @@ func (t *uncommonType) methods() []method {
 	return (*[1 << 16]method)(add(unsafe.Pointer(t), uintptr(t.moff)))[:t.mcount:t.mcount]
 }
 
-func (t *uncommonType) PkgPath() string {
-	if t == nil {
-		return ""
-	}
-	return t.pkgPath.name()
-}
-
 // resolveNameOff resolves a name offset from a base pointer.
 // The (*rtype).nameOff method is a convenience wrapper for this function.
 // Implemented in the runtime package.
@@ -799,7 +792,7 @@ func (t *rtype) Method(i int) (m Method) {
 	if !pname.isExported() {
 		m.PkgPath = pname.pkgPath()
 		if m.PkgPath == "" {
-			m.PkgPath = ut.pkgPath.name()
+			m.PkgPath = t.nameOff(ut.pkgPath).name()
 		}
 		fl |= flagStickyRO
 	}
@@ -846,7 +839,11 @@ func (t *rtype) MethodByName(name string) (m Method, ok bool) {
 }
 
 func (t *rtype) PkgPath() string {
-	return t.uncommon().PkgPath()
+	ut := t.uncommon()
+	if ut == nil {
+		return ""
+	}
+	return t.nameOff(ut.pkgPath).name()
 }
 
 func hasPrefix(s, prefix string) bool {

src/runtime/heapdump.go

@@ -183,10 +183,10 @@ func dumptype(t *_type) {
 	dumpint(tagType)
 	dumpint(uint64(uintptr(unsafe.Pointer(t))))
 	dumpint(uint64(t.size))
-	if x := t.uncommon(); x == nil || x.pkgpath.name() == "" {
+	if x := t.uncommon(); x == nil || t.nameOff(x.pkgpath).name() == "" {
 		dumpstr(t.string())
 	} else {
-		pkgpathstr := x.pkgpath.name()
+		pkgpathstr := t.nameOff(x.pkgpath).name()
 		pkgpath := stringStructOf(&pkgpathstr)
 		namestr := t.name()
 		name := stringStructOf(&namestr)

src/runtime/iface.go

@@ -112,7 +112,7 @@ func additab(m *itab, locked, canfail bool) {
 			if typ.typeOff(t.mtyp) == itype && tname.name() == iname {
 				pkgPath := tname.pkgPath()
 				if pkgPath == "" {
-					pkgPath = x.pkgpath.name()
+					pkgPath = typ.nameOff(x.pkgpath).name()
 				}
 				if tname.isExported() || pkgPath == ipkg {
 					if m != nil {

src/runtime/type.go

@@ -304,7 +304,7 @@ type method struct {
 }
 
 type uncommontype struct {
-	pkgpath name
+	pkgpath nameOff
 	mcount  uint16 // number of methods
 	moff    uint16 // offset from this uncommontype to [mcount]method
 }
@@ -524,7 +524,9 @@ func typesEqual(t, v *_type) bool {
 		if ut == nil || uv == nil {
 			return false
 		}
-		if ut.pkgpath.name() != uv.pkgpath.name() {
+		pkgpatht := t.nameOff(ut.pkgpath).name()
+		pkgpathv := v.nameOff(uv.pkgpath).name()
+		if pkgpatht != pkgpathv {
 			return false
 		}
 	}