cmd/compile: move runtime.itab to internal/abi.ITab

Change-Id: I44293452764dc4bc4de8d386153c6402a9cbe409
Reviewed-on: https://go-review.googlesource.com/c/go/+/549435
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

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

@@ -201,7 +201,7 @@ func (d *deadcodePass) flood() {
 				rs := r.Sym()
 				if d.ldr.IsItab(rs) {
 					// This relocation can also point at an itab, in which case it
-					// means "the _type field of that itab".
+					// means "the Type field of that itab".
 					rs = decodeItabType(d.ldr, d.ctxt.Arch, rs)
 				}
 				if !d.ldr.IsGoType(rs) && !d.ctxt.linkShared {

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

@@ -301,7 +301,7 @@ func decodetypeGcprogShlib(ctxt *Link, data []byte) uint64 {
 	return decodeInuxi(ctxt.Arch, data[2*int32(ctxt.Arch.PtrSize)+8+1*int32(ctxt.Arch.PtrSize):], ctxt.Arch.PtrSize)
 }
 
-// decodeItabType returns the itab._type field from an itab.
+// decodeItabType returns the itab.Type field from an itab.
 func decodeItabType(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
 	relocs := ldr.Relocs(symIdx)
 	return decodeRelocSym(ldr, symIdx, &relocs, int32(arch.PtrSize))

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

@@ -1786,7 +1786,7 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
 		"type:internal/abi.SliceType",
 		"type:internal/abi.StructType",
 		"type:internal/abi.InterfaceType",
-		"type:runtime.itab",
+		"type:internal/abi.ITab",
 		"type:internal/abi.Imethod"} {
 		d.defgotype(d.lookupOrDiag(typ))
 	}

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

@@ -65,7 +65,7 @@ func TestRuntimeTypesPresent(t *testing.T) {
 		"internal/abi.SliceType":     true,
 		"internal/abi.StructType":    true,
 		"internal/abi.InterfaceType": true,
-		"runtime.itab":               true,
+		"internal/abi.ITab":          true,
 	}
 
 	found := findTypes(t, dwarf, want)

src/internal/abi/iface.go

@@ -0,0 +1,21 @@
+// Copyright 2023 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 abi
+
+// The first word of every non-empty interface type contains an *ITab.
+// It records the underlying concrete type (Type), the interface type it
+// is implementing (Inter), and some ancillary information.
+//
+// layout of ITab known to compilers
+// allocated in non-garbage-collected memory
+// Needs to be in sync with
+// cmd/compile/internal/reflectdata/reflect.go:/^func.WritePluginTable.
+type ITab struct {
+	Inter *InterfaceType
+	Type  *Type
+	Hash  uint32 // copy of Type.Hash. Used for type switches.
+	_     [4]byte
+	Fun   [1]uintptr // variable sized. fun[0]==0 means Type does not implement Inter.
+}

src/runtime/alg.go

@@ -100,7 +100,7 @@ func interhash(p unsafe.Pointer, h uintptr) uintptr {
 	if tab == nil {
 		return h
 	}
-	t := tab._type
+	t := tab.Type
 	if t.Equal == nil {
 		// Check hashability here. We could do this check inside
 		// typehash, but we want to report the topmost type in
@@ -223,7 +223,7 @@ func mapKeyError2(t *_type, p unsafe.Pointer) error {
 			if a.tab == nil {
 				return nil
 			}
-			t = a.tab._type
+			t = a.tab.Type
 			pdata = &a.data
 		}
 
@@ -329,7 +329,7 @@ func ifaceeq(tab *itab, x, y unsafe.Pointer) bool {
 	if tab == nil {
 		return true
 	}
-	t := tab._type
+	t := tab.Type
 	eq := t.Equal
 	if eq == nil {
 		panic(errorString("comparing uncomparable type " + toRType(t).string()))

src/runtime/heapdump.go

@@ -540,7 +540,7 @@ func dumpparams() {
 }
 
 func itab_callback(tab *itab) {
-	t := tab._type
+	t := tab.Type
 	dumptype(t)
 	dumpint(tagItab)
 	dumpint(uint64(uintptr(unsafe.Pointer(tab))))

src/runtime/iface.go

@@ -66,19 +66,19 @@ func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
 
 	// Entry doesn't exist yet. Make a new entry & add it.
 	m = (*itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(inter.Methods)-1)*goarch.PtrSize, 0, &memstats.other_sys))
-	m.inter = inter
+	m.Inter = inter
-	m._type = typ
+	m.Type = typ
 	// The hash is used in type switches. However, compiler statically generates itab's
 	// for all interface/type pairs used in switches (which are added to itabTable
 	// in itabsinit). The dynamically-generated itab's never participate in type switches,
 	// and thus the hash is irrelevant.
-	// Note: m.hash is _not_ the hash used for the runtime itabTable hash table.
+	// Note: m.Hash is _not_ the hash used for the runtime itabTable hash table.
-	m.hash = 0
+	m.Hash = 0
-	m.init()
+	itabInit(m)
 	itabAdd(m)
 	unlock(&itabLock)
 finish:
-	if m.fun[0] != 0 {
+	if m.Fun[0] != 0 {
 		return m
 	}
 	if canfail {
@@ -90,7 +90,7 @@ finish:
 	// The cached result doesn't record which
 	// interface function was missing, so initialize
 	// the itab again to get the missing function name.
-	panic(&TypeAssertionError{concrete: typ, asserted: &inter.Type, missingMethod: m.init()})
+	panic(&TypeAssertionError{concrete: typ, asserted: &inter.Type, missingMethod: itabInit(m)})
 }
 
 // find finds the given interface/type pair in t.
@@ -110,7 +110,7 @@ func (t *itabTableType) find(inter *interfacetype, typ *_type) *itab {
 		if m == nil {
 			return nil
 		}
-		if m.inter == inter && m._type == typ {
+		if m.Inter == inter && m.Type == typ {
 			return m
 		}
 		h += i
@@ -161,7 +161,7 @@ func (t *itabTableType) add(m *itab) {
 	// See comment in find about the probe sequence.
 	// Insert new itab in the first empty spot in the probe sequence.
 	mask := t.size - 1
-	h := itabHashFunc(m.inter, m._type) & mask
+	h := itabHashFunc(m.Inter, m.Type) & mask
 	for i := uintptr(1); ; i++ {
 		p := (**itab)(add(unsafe.Pointer(&t.entries), h*goarch.PtrSize))
 		m2 := *p
@@ -186,13 +186,13 @@ func (t *itabTableType) add(m *itab) {
 	}
 }
 
-// init fills in the m.fun array with all the code pointers for
+// init fills in the m.Fun array with all the code pointers for
-// the m.inter/m._type pair. If the type does not implement the interface,
+// the m.Inter/m.Type pair. If the type does not implement the interface,
-// it sets m.fun[0] to 0 and returns the name of an interface function that is missing.
+// it sets m.Fun[0] to 0 and returns the name of an interface function that is missing.
 // It is ok to call this multiple times on the same m, even concurrently.
-func (m *itab) init() string {
+func itabInit(m *itab) string {
-	inter := m.inter
+	inter := m.Inter
-	typ := m._type
+	typ := m.Type
 	x := typ.Uncommon()
 
 	// both inter and typ have method sorted by name,
@@ -203,7 +203,7 @@ func (m *itab) init() string {
 	nt := int(x.Mcount)
 	xmhdr := (*[1 << 16]abi.Method)(add(unsafe.Pointer(x), uintptr(x.Moff)))[:nt:nt]
 	j := 0
-	methods := (*[1 << 16]unsafe.Pointer)(unsafe.Pointer(&m.fun[0]))[:ni:ni]
+	methods := (*[1 << 16]unsafe.Pointer)(unsafe.Pointer(&m.Fun[0]))[:ni:ni]
 	var fun0 unsafe.Pointer
 imethods:
 	for k := 0; k < ni; k++ {
@@ -227,7 +227,7 @@ imethods:
 				if tname.IsExported() || pkgPath == ipkg {
 					ifn := rtyp.textOff(t.Ifn)
 					if k == 0 {
-						fun0 = ifn // we'll set m.fun[0] at the end
+						fun0 = ifn // we'll set m.Fun[0] at the end
 					} else {
 						methods[k] = ifn
 					}
@@ -236,10 +236,10 @@ imethods:
 			}
 		}
 		// didn't find method
-		m.fun[0] = 0
+		m.Fun[0] = 0
 		return iname
 	}
-	m.fun[0] = uintptr(fun0)
+	m.Fun[0] = uintptr(fun0)
 	return ""
 }
 
@@ -267,7 +267,7 @@ func panicdottypeE(have, want, iface *_type) {
 func panicdottypeI(have *itab, want, iface *_type) {
 	var t *_type
 	if have != nil {
-		t = have._type
+		t = have.Type
 	}
 	panicdottypeE(t, want, iface)
 }

src/runtime/runtime2.go

@@ -990,17 +990,7 @@ type funcinl struct {
 	startLine int32
 }
 
-// layout of Itab known to compilers
+type itab = abi.ITab
-// allocated in non-garbage-collected memory
-// Needs to be in sync with
-// ../cmd/compile/internal/reflectdata/reflect.go:/^func.WritePluginTable.
-type itab struct {
-	inter *interfacetype
-	_type *_type
-	hash  uint32 // copy of _type.hash. Used for type switches.
-	_     [4]byte
-	fun   [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
-}
 
 // Lock-free stack node.
 // Also known to export_test.go.