cmd/compile, cmd/link: avoid ABI aliases

In the past we introduced ABI aliases, in preparation for ABI
wrappers. Now that we have ABI wrappers implemented, we don't
need ABI aliases. If ABI wrappers are not enabled, ABI0 and
ABIInternal are actually identical, so we can resolve symbol
references without distinguish them. This CL does so by
normalizing ABIInternal to ABI0 at link time. This way, we no
longer need to generate ABI aliases.

This CL doesn't clean up everything related to ABI aliases, which
will be done in followup CLs.

Change-Id: I5b5db43370d29b8ad153078c70a853e3263ae6f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/351271
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/compile/internal/ssagen/abi.go

@@ -257,10 +257,6 @@ func InitLSym(f *ir.Func, hasBody bool) {
 			// when we see that.
 			staticdata.NeedFuncSym(f)
 		}
-		if !buildcfg.Experiment.RegabiWrappers {
-			// Create ABI aliases instead of wrappers.
-			forEachWrapperABI(f, makeABIAlias)
-		}
 	}
 	if hasBody {
 		setupTextLSym(f, 0)
@@ -281,22 +277,6 @@ func forEachWrapperABI(fn *ir.Func, cb func(fn *ir.Func, wrapperABI obj.ABI)) {
 	}
 }
 
-// makeABIAlias creates a new ABI alias so calls to f via wrapperABI
-// will be resolved directly to f's ABI by the linker.
-func makeABIAlias(f *ir.Func, wrapperABI obj.ABI) {
-	// These LSyms have the same name as the native function, so
-	// we create them directly rather than looking them up.
-	// The uniqueness of f.lsym ensures uniqueness of asym.
-	asym := &obj.LSym{
-		Name: f.LSym.Name,
-		Type: objabi.SABIALIAS,
-		R:    []obj.Reloc{{Sym: f.LSym}}, // 0 size, so "informational"
-	}
-	asym.SetABI(wrapperABI)
-	asym.Set(obj.AttrDuplicateOK, true)
-	base.Ctxt.ABIAliases = append(base.Ctxt.ABIAliases, asym)
-}
-
 // makeABIWrapper creates a new function that will be called with
 // wrapperABI and calls "f" using f.ABI.
 func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {

src/cmd/internal/goobj/builtin.go

@@ -4,6 +4,8 @@
 
 package goobj
 
+import "internal/buildcfg"
+
 // Builtin (compiler-generated) function references appear
 // frequently. We assign special indices for them, so they
 // don't need to be referenced by name.
@@ -27,7 +29,7 @@ func BuiltinIdx(name string, abi int) int {
 	if !ok {
 		return -1
 	}
-	if builtins[i].abi != abi {
+	if buildcfg.Experiment.RegabiWrappers && builtins[i].abi != abi {
 		return -1
 	}
 	return i

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

@@ -96,8 +96,10 @@ func (d *deadcodePass) init() {
 	for _, name := range names {
 		// Mark symbol as a data/ABI0 symbol.
 		d.mark(d.ldr.Lookup(name, 0), 0)
-		// Also mark any Go functions (internal ABI).
+		if abiInternalVer != 0 {
-		d.mark(d.ldr.Lookup(name, sym.SymVerABIInternal), 0)
+			// Also mark any Go functions (internal ABI).
+			d.mark(d.ldr.Lookup(name, abiInternalVer), 0)
+		}
 	}
 
 	// All dynamic exports are roots.
@@ -327,8 +329,8 @@ func deadcode(ctxt *Link) {
 	d.init()
 	d.flood()
 
-	methSym := ldr.Lookup("reflect.Value.Method", sym.SymVerABIInternal)
+	methSym := ldr.Lookup("reflect.Value.Method", abiInternalVer)
-	methByNameSym := ldr.Lookup("reflect.Value.MethodByName", sym.SymVerABIInternal)
+	methByNameSym := ldr.Lookup("reflect.Value.MethodByName", abiInternalVer)
 
 	if ctxt.DynlinkingGo() {
 		// Exported methods may satisfy interfaces we don't know

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

@@ -144,7 +144,7 @@ func (ctxt *Link) setArchSyms() {
 	ctxt.mkArchSym(".dynamic", 0, &ctxt.Dynamic)
 	ctxt.mkArchSym(".dynsym", 0, &ctxt.DynSym)
 	ctxt.mkArchSym(".dynstr", 0, &ctxt.DynStr)
-	ctxt.mkArchSym("runtime.unreachableMethod", sym.SymVerABIInternal, &ctxt.unreachableMethod)
+	ctxt.mkArchSym("runtime.unreachableMethod", abiInternalVer, &ctxt.unreachableMethod)
 
 	if ctxt.IsPPC64() {
 		ctxt.mkArchSym("TOC", 0, &ctxt.TOC)
@@ -281,6 +281,10 @@ const (
 	MINFUNC = 16 // minimum size for a function
 )
 
+// Symbol version of ABIInternal symbols. It is sym.SymVerABIInternal if ABI wrappers
+// are used, 0 otherwise.
+var abiInternalVer = sym.SymVerABIInternal
+
 // DynlinkingGo reports whether we are producing Go code that can live
 // in separate shared libraries linked together at runtime.
 func (ctxt *Link) DynlinkingGo() bool {
@@ -500,10 +504,6 @@ func (ctxt *Link) loadlib() {
 	default:
 		log.Fatalf("invalid -strictdups flag value %d", *FlagStrictDups)
 	}
-	if !buildcfg.Experiment.RegabiWrappers {
-		// Use ABI aliases if ABI wrappers are not used.
-		flags |= loader.FlagUseABIAlias
-	}
 	elfsetstring1 := func(str string, off int) { elfsetstring(ctxt, 0, str, off) }
 	ctxt.loader = loader.NewLoader(flags, elfsetstring1, &ctxt.ErrorReporter.ErrorReporter)
 	ctxt.ErrorReporter.SymName = func(s loader.Sym) string {
@@ -769,7 +769,7 @@ func (ctxt *Link) linksetup() {
 		// Set runtime.disableMemoryProfiling bool if
 		// runtime.MemProfile is not retained in the binary after
 		// deadcode (and we're not dynamically linking).
-		memProfile := ctxt.loader.Lookup("runtime.MemProfile", sym.SymVerABIInternal)
+		memProfile := ctxt.loader.Lookup("runtime.MemProfile", abiInternalVer)
 		if memProfile != 0 && !ctxt.loader.AttrReachable(memProfile) && !ctxt.DynlinkingGo() {
 			memProfSym := ctxt.loader.LookupOrCreateSym("runtime.disableMemoryProfiling", 0)
 			sb := ctxt.loader.MakeSymbolUpdater(memProfSym)
@@ -2115,7 +2115,7 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		ver := 0
 		symname := elfsym.Name // (unmangled) symbol name
 		if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && strings.HasPrefix(elfsym.Name, "type.") {
-			ver = sym.SymVerABIInternal
+			ver = abiInternalVer
 		} else if buildcfg.Experiment.RegabiWrappers && elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC {
 			// Demangle the ABI name. Keep in sync with symtab.go:mangleABIName.
 			if strings.HasSuffix(elfsym.Name, ".abiinternal") {
@@ -2156,19 +2156,6 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		if symname != elfsym.Name {
 			l.SetSymExtname(s, elfsym.Name)
 		}
-
-		// For function symbols, if ABI wrappers are not used, we don't
-		// know what ABI is available, so alias it under both ABIs.
-		if !buildcfg.Experiment.RegabiWrappers && elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && ver == 0 {
-			alias := ctxt.loader.LookupOrCreateSym(symname, sym.SymVerABIInternal)
-			if l.SymType(alias) != 0 {
-				continue
-			}
-			su := l.MakeSymbolUpdater(alias)
-			su.SetType(sym.SABIALIAS)
-			r, _ := su.AddRel(0) // type doesn't matter
-			r.SetSym(s)
-		}
 	}
 	ctxt.Shlibs = append(ctxt.Shlibs, Shlib{Path: libpath, Hash: hash, Deps: deps, File: f})
 }

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

@@ -7,7 +7,6 @@ package ld
 import (
 	"bytes"
 	"cmd/internal/codesign"
-	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"cmd/link/internal/loader"
@@ -561,7 +560,7 @@ func (ctxt *Link) domacho() {
 			ver := 0
 			// _cgo_panic is a Go function, so it uses ABIInternal.
 			if name == "_cgo_panic" {
-				ver = sym.ABIToVersion(obj.ABIInternal)
+				ver = abiInternalVer
 			}
 			s := ctxt.loader.Lookup(name, ver)
 			if s != 0 {

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

@@ -173,6 +173,10 @@ func Main(arch *sys.Arch, theArch Arch) {
 
 	checkStrictDups = *FlagStrictDups
 
+	if !buildcfg.Experiment.RegabiWrappers {
+		abiInternalVer = 0
+	}
+
 	startProfile()
 	if ctxt.BuildMode == BuildModeUnset {
 		ctxt.BuildMode.Set("exe")

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

@@ -739,7 +739,7 @@ func (state *pclntab) writeFuncData(ctxt *Link, sb *loader.SymbolBuilder, funcs
 // writeFuncs writes the func structures and pcdata to runtime.functab.
 func writeFuncs(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, startLocations, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
 	ldr := ctxt.loader
-	deferReturnSym := ldr.Lookup("runtime.deferreturn", sym.SymVerABIInternal)
+	deferReturnSym := ldr.Lookup("runtime.deferreturn", abiInternalVer)
 	funcdata, funcdataoff := []loader.Sym{}, []int64{}
 
 	// Write the individual func objects.

src/cmd/link/internal/loader/loader.go

@@ -2192,7 +2192,7 @@ func (st *loadState) preloadSyms(r *oReader, kind int) {
 		}
 		if strings.HasPrefix(name, "runtime.") ||
 			(loadingRuntimePkg && strings.HasPrefix(name, "type.")) {
-			if bi := goobj.BuiltinIdx(name, v); bi != -1 {
+			if bi := goobj.BuiltinIdx(name, int(osym.ABI())); bi != -1 {
 				// This is a definition of a builtin symbol. Record where it is.
 				l.builtinSyms[bi] = gi
 			}

src/cmd/link/internal/sym/symbol.go

@@ -6,6 +6,7 @@ package sym
 
 import (
 	"cmd/internal/obj"
+	"internal/buildcfg"
 )
 
 const (
@@ -20,6 +21,11 @@ func ABIToVersion(abi obj.ABI) int {
 	case obj.ABI0:
 		return SymVerABI0
 	case obj.ABIInternal:
+		if !buildcfg.Experiment.RegabiWrappers {
+			// If wrappers are not enabled, ABI0 and ABIInternal are actually same
+			// so we normalize everything to ABI0.
+			return SymVerABI0
+		}
 		return SymVerABIInternal
 	}
 	return -1