runtime: framepointers are no longer an experiment - hard code them

I think they are no longer experimental status. Might as well promote
them to permanent.

Change-Id: Id1259601b3dd2061dd60df86ee48080bfb575d2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/249857
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -507,7 +507,7 @@ func createSimpleVar(fnsym *obj.LSym, n *Node) *dwarf.Var {
 		if Ctxt.FixedFrameSize() == 0 {
 			offs -= int64(Widthptr)
 		}
-		if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) || objabi.GOARCH == "arm64" {
+		if objabi.Framepointer_enabled || objabi.GOARCH == "arm64" {
 			// There is a word space for FP on ARM64 even if the frame pointer is disabled
 			offs -= int64(Widthptr)
 		}
@@ -703,7 +703,7 @@ func stackOffset(slot ssa.LocalSlot) int32 {
 		if Ctxt.FixedFrameSize() == 0 {
 			base -= int64(Widthptr)
 		}
-		if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) || objabi.GOARCH == "arm64" {
+		if objabi.Framepointer_enabled || objabi.GOARCH == "arm64" {
 			// There is a word space for FP on ARM64 even if the frame pointer is disabled
 			base -= int64(Widthptr)
 		}

src/cmd/compile/internal/ssa/regalloc.go

@@ -588,7 +588,7 @@ func (s *regAllocState) init(f *Func) {
 	if s.f.Config.hasGReg {
 		s.allocatable &^= 1 << s.GReg
 	}
-	if s.f.Config.ctxt.Framepointer_enabled && s.f.Config.FPReg >= 0 {
+	if objabi.Framepointer_enabled && s.f.Config.FPReg >= 0 {
 		s.allocatable &^= 1 << uint(s.f.Config.FPReg)
 	}
 	if s.f.Config.LinkReg != -1 {

src/cmd/internal/obj/arm64/obj7.go

@@ -621,7 +621,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 			prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd)
 
-			if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
+			if objabi.Framepointer_enabled {
 				q1 = obj.Appendp(q1, c.newprog)
 				q1.Pos = p.Pos
 				q1.As = AMOVD
@@ -764,7 +764,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					p.To.Reg = REGSP
 					p.Spadj = -c.autosize
 
-					if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
+					if objabi.Framepointer_enabled {
 						p = obj.Appendp(p, c.newprog)
 						p.As = ASUB
 						p.From.Type = obj.TYPE_CONST
@@ -777,7 +777,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			} else {
 				/* want write-back pre-indexed SP+autosize -> SP, loading REGLINK*/
 
-				if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
+				if objabi.Framepointer_enabled {
 					p.As = AMOVD
 					p.From.Type = obj.TYPE_MEM
 					p.From.Reg = REGSP
@@ -865,7 +865,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			}
 
 		case obj.ADUFFCOPY:
-			if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
+			if objabi.Framepointer_enabled {
 				//  ADR	ret_addr, R27
 				//  STP	(FP, R27), -24(SP)
 				//  SUB	24, SP, FP
@@ -918,7 +918,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			}
 
 		case obj.ADUFFZERO:
-			if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
+			if objabi.Framepointer_enabled {
 				//  ADR	ret_addr, R27
 				//  STP	(FP, R27), -24(SP)
 				//  SUB	24, SP, FP

src/cmd/internal/obj/link.go

@@ -682,10 +682,9 @@ type Link struct {
 	GenAbstractFunc    func(fn *LSym)
 	Errors             int
 
-	InParallel           bool // parallel backend phase in effect
+	InParallel    bool // parallel backend phase in effect
-	Framepointer_enabled bool
+	UseBASEntries bool // use Base Address Selection Entries in location lists and PC ranges
-	UseBASEntries        bool // use Base Address Selection Entries in location lists and PC ranges
+	IsAsm         bool // is the source assembly language, which may contain surprising idioms (e.g., call tables)
-	IsAsm                bool // is the source assembly language, which may contain surprising idioms (e.g., call tables)
 
 	// state for writing objects
 	Text []*LSym

src/cmd/internal/obj/sym.go

@@ -53,7 +53,6 @@ func Linknew(arch *LinkArch) *Link {
 	}
 
 	ctxt.Flag_optimize = true
-	ctxt.Framepointer_enabled = objabi.Framepointer_enabled(objabi.GOOS, arch.Name)
 	return ctxt
 }
 

src/cmd/internal/obj/x86/asm6.go

@@ -4833,12 +4833,12 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 					ctxt.Diag("directly calling duff when dynamically linking Go")
 				}
 
-				if ctxt.Framepointer_enabled && yt.zcase == Zcallduff && ctxt.Arch.Family == sys.AMD64 {
+				if yt.zcase == Zcallduff && ctxt.Arch.Family == sys.AMD64 {
 					// Maintain BP around call, since duffcopy/duffzero can't do it
 					// (the call jumps into the middle of the function).
 					// This makes it possible to see call sites for duffcopy/duffzero in
 					// BP-based profiling tools like Linux perf (which is the
-					// whole point of obj.Framepointer_enabled).
+					// whole point of maintaining frame pointers in Go).
 					// MOVQ BP, -16(SP)
 					// LEAQ -16(SP), BP
 					ab.Put(bpduff1)
@@ -4852,7 +4852,7 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 				r.Siz = 4
 				ab.PutInt32(0)
 
-				if ctxt.Framepointer_enabled && yt.zcase == Zcallduff && ctxt.Arch.Family == sys.AMD64 {
+				if yt.zcase == Zcallduff && ctxt.Arch.Family == sys.AMD64 {
 					// Pop BP pushed above.
 					// MOVQ 0(BP), BP
 					ab.Put(bpduff2)

src/cmd/internal/obj/x86/obj6.go

@@ -582,7 +582,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 	}
 
 	var bpsize int
-	if ctxt.Arch.Family == sys.AMD64 && ctxt.Framepointer_enabled &&
+	if ctxt.Arch.Family == sys.AMD64 &&
 		!p.From.Sym.NoFrame() && // (1) below
 		!(autoffset == 0 && p.From.Sym.NoSplit()) && // (2) below
 		!(autoffset == 0 && !hasCall) { // (3) below

src/cmd/internal/objabi/util.go

@@ -133,9 +133,8 @@ func init() {
 	}
 }
 
-func Framepointer_enabled(goos, goarch string) bool {
+// Note: must agree with runtime.framepointer_enabled.
-	return framepointer_enabled != 0 && (goarch == "amd64" || goarch == "arm64" && (goos == "linux" || goos == "darwin"))
+var Framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" && (GOOS == "linux" || GOOS == "darwin")
-}
 
 func addexp(s string) {
 	// Could do general integer parsing here, but the runtime copy doesn't yet.
@@ -159,7 +158,6 @@ func addexp(s string) {
 }
 
 var (
-	framepointer_enabled      int = 1
 	Fieldtrack_enabled        int
 	Preemptibleloops_enabled  int
 	Staticlockranking_enabled int
@@ -174,7 +172,6 @@ var exper = []struct {
 	val  *int
 }{
 	{"fieldtrack", &Fieldtrack_enabled},
-	{"framepointer", &framepointer_enabled},
 	{"preemptibleloops", &Preemptibleloops_enabled},
 	{"staticlockranking", &Staticlockranking_enabled},
 }

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

@@ -775,14 +775,6 @@ func (ctxt *Link) linksetup() {
 			sb.SetSize(0)
 			sb.AddUint8(uint8(objabi.GOARM))
 		}
-
-		if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
-			fpe := ctxt.loader.LookupOrCreateSym("runtime.framepointer_enabled", 0)
-			sb := ctxt.loader.MakeSymbolUpdater(fpe)
-			sb.SetType(sym.SNOPTRDATA)
-			sb.SetSize(0)
-			sb.AddUint8(1)
-		}
 	} else {
 		// If OTOH the module does not contain the runtime package,
 		// create a local symbol for the moduledata.

src/runtime/cgocall.go

@@ -286,13 +286,8 @@ func cgocallbackg1(ctxt uintptr) {
 		// Additional two words (16-byte alignment) are for saving FP.
 		cb = (*args)(unsafe.Pointer(sp + 7*sys.PtrSize))
 	case "amd64":
-		// On amd64, stack frame is two words, plus caller PC.
+		// On amd64, stack frame is two words, plus caller PC and BP.
-		if framepointer_enabled {
+		cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize))
-			// In this case, there's also saved BP.
-			cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize))
-			break
-		}
-		cb = (*args)(unsafe.Pointer(sp + 3*sys.PtrSize))
 	case "386":
 		// On 386, stack frame is three words, plus caller PC.
 		cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize))

src/runtime/proc.go

@@ -5459,9 +5459,6 @@ func setMaxThreads(in int) (out int) {
 }
 
 func haveexperiment(name string) bool {
-	if name == "framepointer" {
-		return framepointer_enabled // set by linker
-	}
 	x := sys.Goexperiment
 	for x != "" {
 		xname := ""

src/runtime/runtime2.go

@@ -329,7 +329,7 @@ type gobuf struct {
 	ctxt unsafe.Pointer
 	ret  sys.Uintreg
 	lr   uintptr
-	bp   uintptr // for GOEXPERIMENT=framepointer
+	bp   uintptr // for framepointer-enabled architectures
 }
 
 // sudog represents a g in a wait list, such as for sending/receiving
@@ -1046,8 +1046,7 @@ var (
 	isIntel              bool
 	lfenceBeforeRdtsc    bool
 
-	goarm                uint8 // set by cmd/link on arm systems
+	goarm uint8 // set by cmd/link on arm systems
-	framepointer_enabled bool  // set by cmd/link
 )
 
 // Set by the linker so the runtime can determine the buildmode.
@@ -1055,3 +1054,6 @@ var (
 	islibrary bool // -buildmode=c-shared
 	isarchive bool // -buildmode=c-archive
 )
+
+// Must agree with cmd/internal/objabi.Framepointer_enabled.
+const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" && (GOOS == "linux" || GOOS == "darwin")

src/runtime/stack.go

@@ -648,12 +648,8 @@ func adjustframe(frame *stkframe, arg unsafe.Pointer) bool {
 	}
 
 	// Adjust saved base pointer if there is one.
+	// TODO what about arm64 frame pointer adjustment?
 	if sys.ArchFamily == sys.AMD64 && frame.argp-frame.varp == 2*sys.RegSize {
-		if !framepointer_enabled {
-			print("runtime: found space for saved base pointer, but no framepointer experiment\n")
-			print("argp=", hex(frame.argp), " varp=", hex(frame.varp), "\n")
-			throw("bad frame layout")
-		}
 		if stackDebug >= 3 {
 			print("      saved bp\n")
 		}

src/runtime/traceback.go

@@ -269,9 +269,9 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 			frame.varp -= sys.RegSize
 		}
 
-		// If framepointer_enabled and there's a frame, then
+		// For architectures with frame pointers, if there's
-		// there's a saved bp here.
+		// a frame, then there's a saved frame pointer here.
-		if frame.varp > frame.sp && (framepointer_enabled && GOARCH == "amd64" || GOARCH == "arm64") {
+		if frame.varp > frame.sp && (GOARCH == "amd64" || GOARCH == "arm64") {
 			frame.varp -= sys.RegSize
 		}