cmd/compile,runtime: redo mid-stack inlining tracebacks

Work involved in getting a stack trace is divided between
runtime.Callers and runtime.CallersFrames.

Before this CL, runtime.Callers returns a pc per runtime frame.
runtime.CallersFrames is responsible for expanding a runtime frame
into potentially multiple user frames.

After this CL, runtime.Callers returns a pc per user frame.
runtime.CallersFrames just maps those to user frame info.

Entries in the result of runtime.Callers are now pcs
of the calls (or of the inline marks), not of the instruction
just after the call.

Fixes #29007
Fixes #28640
Update #26320

Change-Id: I1c9567596ff73dc73271311005097a9188c3406f
Reviewed-on: https://go-review.googlesource.com/c/152537
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

misc/cgo/test/callback.go

@@ -179,7 +179,6 @@ func testCallbackCallers(t *testing.T) {
 	pc := make([]uintptr, 100)
 	n := 0
 	name := []string{
-		"runtime.call16",
 		"runtime.cgocallbackg1",
 		"runtime.cgocallbackg",
 		"runtime.cgocallback_gofunc",
@@ -193,9 +192,6 @@ func testCallbackCallers(t *testing.T) {
 		"testing.tRunner",
 		"runtime.goexit",
 	}
-	if unsafe.Sizeof((*byte)(nil)) == 8 {
-		name[0] = "runtime.call32"
-	}
 	nestedCall(func() {
 		n = runtime.Callers(4, pc)
 	})

src/cmd/compile/internal/amd64/ggen.go

@@ -141,7 +141,7 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	// This is actually not the x86 NOP anymore,
 	// but at the point where it gets used, AX is dead
 	// so it's okay if we lose the high bits.
@@ -150,4 +150,5 @@ func ginsnop(pp *gc.Progs) {
 	p.From.Reg = x86.REG_AX
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = x86.REG_AX
+	return p
 }

src/cmd/compile/internal/arm/ggen.go

@@ -68,11 +68,12 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(arm.AAND)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = arm.REG_R0
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = arm.REG_R0
 	p.Scond = arm.C_SCOND_EQ
+	return p
 }

src/cmd/compile/internal/arm64/ggen.go

@@ -79,7 +79,8 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(arm64.AHINT)
 	p.From.Type = obj.TYPE_CONST
+	return p
 }

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

@@ -174,6 +174,7 @@ var goopnames = []string{
 	OGT:       ">",
 	OIF:       "if",
 	OIMAG:     "imag",
+	OINLMARK:  "inlmark",
 	ODEREF:    "*",
 	OLEN:      "len",
 	OLE:       "<=",
@@ -942,6 +943,9 @@ func (n *Node) stmtfmt(s fmt.State, mode fmtMode) {
 	case ORETJMP:
 		mode.Fprintf(s, "retjmp %v", n.Sym)
 
+	case OINLMARK:
+		mode.Fprintf(s, "inlmark %d", n.Xoffset)
+
 	case OGO:
 		mode.Fprintf(s, "go %v", n.Left)
 

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

@@ -257,7 +257,7 @@ type Arch struct {
 
 	PadFrame  func(int64) int64
 	ZeroRange func(*Progs, *obj.Prog, int64, int64, *uint32) *obj.Prog
-	Ginsnop   func(*Progs)
+	Ginsnop   func(*Progs) *obj.Prog
 
 	// SSAMarkMoves marks any MOVXconst ops that need to avoid clobbering flags.
 	SSAMarkMoves func(*SSAGenState, *ssa.Block)

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

@@ -1063,6 +1063,15 @@ func mkinlcall(n, fn *Node, maxCost int32) *Node {
 	}
 	newIndex := Ctxt.InlTree.Add(parent, n.Pos, fn.Sym.Linksym())
 
+	// Add a inline mark just before the inlined body.
+	// This mark is inline in the code so that it's a reasonable spot
+	// to put a breakpoint. Not sure if that's really necessary or not
+	// (in which case it could go at the end of the function instead).
+	inlMark := nod(OINLMARK, nil, nil)
+	inlMark.Pos = n.Pos
+	inlMark.Xoffset = int64(newIndex)
+	ninit.Append(inlMark)
+
 	if genDwarfInline > 0 {
 		if !fn.Sym.Linksym().WasInlined() {
 			Ctxt.DwFixups.SetPrecursorFunc(fn.Sym.Linksym(), fn)

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

@@ -553,7 +553,7 @@ func (o *Order) stmt(n *Node) {
 	default:
 		Fatalf("orderstmt %v", n.Op)
 
-	case OVARKILL, OVARLIVE:
+	case OVARKILL, OVARLIVE, OINLMARK:
 		o.out = append(o.out, n)
 
 	case OAS:

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

@@ -1204,6 +1204,9 @@ func (s *state) stmt(n *Node) {
 		p := s.expr(n.Left)
 		s.nilCheck(p)
 
+	case OINLMARK:
+		s.newValue1I(ssa.OpInlMark, types.TypeVoid, n.Xoffset, s.mem())
+
 	default:
 		s.Fatalf("unhandled stmt %v", n.Op)
 	}
@@ -5163,6 +5166,14 @@ func genssa(f *ssa.Func, pp *Progs) {
 				if v.Args[0].Reg() != v.Reg() {
 					v.Fatalf("OpConvert should be a no-op: %s; %s", v.Args[0].LongString(), v.LongString())
 				}
+			case ssa.OpInlMark:
+				p := thearch.Ginsnop(s.pp)
+				if pp.curfn.Func.lsym != nil {
+					// lsym is nil if the function name is "_".
+					pp.curfn.Func.lsym.Func.AddInlMark(p, v.AuxInt32())
+				}
+				// TODO: if matching line number, merge somehow with previous instruction?
+
 			default:
 				// let the backend handle it
 				// Special case for first line in function; move it to the start.
@@ -5543,6 +5554,7 @@ func (s *SSAGenState) Call(v *ssa.Value) *obj.Prog {
 	s.PrepareCall(v)
 
 	p := s.Prog(obj.ACALL)
+	p.Pos = v.Pos
 	if sym, ok := v.Aux.(*obj.LSym); ok {
 		p.To.Type = obj.TYPE_MEM
 		p.To.Name = obj.NAME_EXTERN

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

@@ -46,6 +46,7 @@ type Node struct {
 	// - ODOT, ODOTPTR, and OINDREGSP use it to indicate offset relative to their base address.
 	// - OSTRUCTKEY uses it to store the named field's offset.
 	// - Named OLITERALs use it to store their ambient iota value.
+	// - OINLMARK stores an index into the inlTree data structure.
 	// Possibly still more uses. If you find any, document them.
 	Xoffset int64
 
@@ -750,6 +751,7 @@ const (
 	OVARKILL    // variable is dead
 	OVARLIVE    // variable is alive
 	OINDREGSP   // offset plus indirect of REGSP, such as 8(SP).
+	OINLMARK    // start of an inlined body, with file/line of caller. Xoffset is an index into the inline tree.
 
 	// arch-specific opcodes
 	ORETJMP // return to other function

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

@@ -322,6 +322,9 @@ func walkstmt(n *Node) *Node {
 	case ORETJMP:
 		break
 
+	case OINLMARK:
+		break
+
 	case OSELECT:
 		walkselect(n)
 

src/cmd/compile/internal/mips/ggen.go

@@ -59,10 +59,11 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(mips.ANOR)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = mips.REG_R0
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = mips.REG_R0
+	return p
 }

src/cmd/compile/internal/mips64/ggen.go

@@ -63,10 +63,11 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(mips.ANOR)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = mips.REG_R0
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = mips.REG_R0
+	return p
 }

src/cmd/compile/internal/ppc64/ggen.go

@@ -58,15 +58,16 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(ppc64.AOR)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = ppc64.REG_R0
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = ppc64.REG_R0
+	return p
 }
 
-func ginsnop2(pp *gc.Progs) {
+func ginsnop2(pp *gc.Progs) *obj.Prog {
 	// PPC64 is unusual because TWO nops are required
 	// (see gc/cgen.go, gc/plive.go -- copy of comment below)
 	//
@@ -87,7 +88,7 @@ func ginsnop2(pp *gc.Progs) {
 		p.From.Reg = ppc64.REGSP
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = ppc64.REG_R2
-	} else {
-		ginsnop(pp)
+		return p
 	}
+	return ginsnop(pp)
 }

src/cmd/compile/internal/s390x/ggen.go

@@ -104,10 +104,11 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(s390x.AOR)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = int16(s390x.REG_R0)
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = int16(s390x.REG_R0)
+	return p
 }

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

@@ -85,7 +85,7 @@ func liveValues(f *Func, reachable []bool) (live []bool, liveOrderStmts []*Value
 				}
 			}
 			if v.Type.IsVoid() && !live[v.ID] {
-				// The only Void ops are nil checks.  We must keep these.
+				// The only Void ops are nil checks and inline marks.  We must keep these.
 				live[v.ID] = true
 				q = append(q, v)
 				if v.Pos.IsStmt() != src.PosNotStmt {

src/cmd/compile/internal/ssa/gen/genericOps.go

@@ -480,6 +480,10 @@ var genericOps = []opData{
 	{name: "VarLive", argLength: 1, aux: "Sym", symEffect: "Read", zeroWidth: true}, // aux is a *gc.Node of a variable that must be kept live.  arg0=mem, returns mem
 	{name: "KeepAlive", argLength: 2, typ: "Mem", zeroWidth: true},                  // arg[0] is a value that must be kept alive until this mark.  arg[1]=mem, returns mem
 
+	// InlMark marks the start of an inlined function body. Its AuxInt field
+	// distinguishes which entry in the local inline tree it is marking.
+	{name: "InlMark", argLength: 1, aux: "Int32", typ: "Void"}, // arg[0]=mem, returns void.
+
 	// Ops for breaking 64-bit operations on 32-bit architectures
 	{name: "Int64Make", argLength: 2, typ: "UInt64"}, // arg0=hi, arg1=lo
 	{name: "Int64Hi", argLength: 1, typ: "UInt32"},   // high 32-bit of arg0

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

@@ -21,7 +21,7 @@ func checkLower(f *Func) {
 				continue // lowered
 			}
 			switch v.Op {
-			case OpSP, OpSB, OpInitMem, OpArg, OpPhi, OpVarDef, OpVarKill, OpVarLive, OpKeepAlive, OpSelect0, OpSelect1, OpConvert:
+			case OpSP, OpSB, OpInitMem, OpArg, OpPhi, OpVarDef, OpVarKill, OpVarLive, OpKeepAlive, OpSelect0, OpSelect1, OpConvert, OpInlMark:
 				continue // ok not to lower
 			case OpGetG:
 				if f.Config.hasGReg {

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

@@ -2398,6 +2398,7 @@ const (
 	OpVarKill
 	OpVarLive
 	OpKeepAlive
+	OpInlMark
 	OpInt64Make
 	OpInt64Hi
 	OpInt64Lo
@@ -29796,6 +29797,12 @@ var opcodeTable = [...]opInfo{
 		zeroWidth: true,
 		generic:   true,
 	},
+	{
+		name:    "InlMark",
+		auxType: auxInt32,
+		argLen:  1,
+		generic: true,
+	},
 	{
 		name:    "Int64Make",
 		argLen:  2,

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

@@ -58,8 +58,8 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
-	pp.Prog(wasm.ANop)
+func ginsnop(pp *gc.Progs) *obj.Prog {
+	return pp.Prog(wasm.ANop)
 }
 
 func ssaMarkMoves(s *gc.SSAGenState, b *ssa.Block) {
@@ -134,10 +134,12 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		if sym, ok := v.Aux.(*obj.LSym); ok {
 			p := s.Prog(obj.ACALL)
 			p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: sym}
+			p.Pos = v.Pos
 		} else {
 			getValue64(s, v.Args[0])
 			p := s.Prog(obj.ACALL)
 			p.To = obj.Addr{Type: obj.TYPE_NONE}
+			p.Pos = v.Pos
 		}
 
 	case ssa.OpWasmLoweredMove:

src/cmd/compile/internal/x86/ggen.go

@@ -53,10 +53,11 @@ func zeroAuto(pp *gc.Progs, n *gc.Node) {
 	}
 }
 
-func ginsnop(pp *gc.Progs) {
+func ginsnop(pp *gc.Progs) *obj.Prog {
 	p := pp.Prog(x86.AXCHGL)
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = x86.REG_AX
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = x86.REG_AX
+	return p
 }

src/cmd/internal/goobj/read.go

@@ -119,10 +119,11 @@ type FuncData struct {
 // An InlinedCall is a node in an InlTree.
 // See cmd/internal/obj.InlTree for details.
 type InlinedCall struct {
-	Parent int64
-	File   string
-	Line   int64
-	Func   SymID
+	Parent   int64
+	File     string
+	Line     int64
+	Func     SymID
+	ParentPC int64
 }
 
 // A Package is a parsed Go object file or archive defining a Go package.
@@ -610,6 +611,7 @@ func (r *objReader) parseObject(prefix []byte) error {
 				f.InlTree[i].File = r.readSymID().Name
 				f.InlTree[i].Line = r.readInt()
 				f.InlTree[i].Func = r.readSymID()
+				f.InlTree[i].ParentPC = r.readInt()
 			}
 		}
 	}

src/cmd/internal/obj/inl.go

@@ -47,9 +47,10 @@ type InlTree struct {
 
 // InlinedCall is a node in an InlTree.
 type InlinedCall struct {
-	Parent int      // index of the parent in the InlTree or < 0 if outermost call
-	Pos    src.XPos // position of the inlined call
-	Func   *LSym    // function that was inlined
+	Parent   int      // index of the parent in the InlTree or < 0 if outermost call
+	Pos      src.XPos // position of the inlined call
+	Func     *LSym    // function that was inlined
+	ParentPC int32    // PC of instruction just before inlined body. Only valid in local trees.
 }
 
 // Add adds a new call to the tree, returning its index.
@@ -76,6 +77,10 @@ func (tree *InlTree) CallPos(inlIndex int) src.XPos {
 	return tree.nodes[inlIndex].Pos
 }
 
+func (tree *InlTree) setParentPC(inlIndex int, pc int32) {
+	tree.nodes[inlIndex].ParentPC = pc
+}
+
 // OutermostPos returns the outermost position corresponding to xpos,
 // which is where xpos was ultimately inlined to. In the example for
 // InlTree, main() contains inlined AST nodes from h(), but the
@@ -106,6 +111,6 @@ func (ctxt *Link) InnermostPos(xpos src.XPos) src.Pos {
 func dumpInlTree(ctxt *Link, tree InlTree) {
 	for i, call := range tree.nodes {
 		pos := ctxt.PosTable.Pos(call.Pos)
-		ctxt.Logf("%0d | %0d | %s (%s)\n", i, call.Parent, call.Func, pos)
+		ctxt.Logf("%0d | %0d | %s (%s) pc=%d\n", i, call.Parent, call.Func, pos, call.ParentPC)
 	}
 }

src/cmd/internal/obj/link.go

@@ -393,11 +393,12 @@ type LSym struct {
 
 // A FuncInfo contains extra fields for STEXT symbols.
 type FuncInfo struct {
-	Args   int32
-	Locals int32
-	Text   *Prog
-	Autom  []*Auto
-	Pcln   Pcln
+	Args     int32
+	Locals   int32
+	Text     *Prog
+	Autom    []*Auto
+	Pcln     Pcln
+	InlMarks []InlMark
 
 	dwarfInfoSym   *LSym
 	dwarfLocSym    *LSym
@@ -411,6 +412,23 @@ type FuncInfo struct {
 	StackObjects *LSym
 }
 
+type InlMark struct {
+	// When unwinding from an instruction in an inlined body, mark
+	// where we should unwind to.
+	// id records the global inlining id of the inlined body.
+	// p records the location of an instruction in the parent (inliner) frame.
+	p  *Prog
+	id int32
+}
+
+// Mark p as the instruction to set as the pc when
+// "unwinding" the inlining global frame id. Usually it should be
+// instruction with a file:line at the callsite, and occur
+// just before the body of the inlined function.
+func (fi *FuncInfo) AddInlMark(p *Prog, id int32) {
+	fi.InlMarks = append(fi.InlMarks, InlMark{p: p, id: id})
+}
+
 //go:generate stringer -type ABI
 
 // ABI is the calling convention of a text symbol.

src/cmd/internal/obj/objfile.go

@@ -388,6 +388,7 @@ func (w *objWriter) writeSym(s *LSym) {
 		w.writeRefIndex(fsym)
 		w.writeInt(int64(l))
 		w.writeRefIndex(call.Func)
+		w.writeInt(int64(call.ParentPC))
 	}
 }
 

src/cmd/internal/obj/pcln.go

@@ -193,6 +193,19 @@ func (s *pcinlineState) addBranch(ctxt *Link, globalIndex int) int {
 	return localIndex
 }
 
+func (s *pcinlineState) setParentPC(ctxt *Link, globalIndex int, pc int32) {
+	localIndex, ok := s.globalToLocal[globalIndex]
+	if !ok {
+		// We know where to unwind to when we need to unwind a body identified
+		// by globalIndex. But there may be no instructions generated by that
+		// body (it's empty, or its instructions were CSEd with other things, etc.).
+		// In that case, we don't need an unwind entry.
+		// TODO: is this really right? Seems to happen a whole lot...
+		return
+	}
+	s.localTree.setParentPC(localIndex, pc)
+}
+
 // pctoinline computes the index into the local inlining tree to use at p.
 // If p is not the result of inlining, pctoinline returns -1. Because p.Pos
 // applies to p, phase == 0 (before p) takes care of the update.
@@ -323,6 +336,9 @@ func linkpcln(ctxt *Link, cursym *LSym) {
 
 	pcinlineState := new(pcinlineState)
 	funcpctab(ctxt, &pcln.Pcinline, cursym, "pctoinline", pcinlineState.pctoinline, nil)
+	for _, inlMark := range cursym.Func.InlMarks {
+		pcinlineState.setParentPC(ctxt, int(inlMark.id), int32(inlMark.p.Pc))
+	}
 	pcln.InlTree = pcinlineState.localTree
 	if ctxt.Debugpcln == "pctoinline" && len(pcln.InlTree.nodes) > 0 {
 		ctxt.Logf("-- inlining tree for %s:\n", cursym)

src/cmd/internal/obj/wasm/wasmobj.go

@@ -243,7 +243,6 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 	for p := s.Func.Text; p != nil; p = p.Link {
 		prevBase := base
 		base = ctxt.PosTable.Pos(p.Pos).Base()
-
 		switch p.As {
 		case ABlock, ALoop, AIf:
 			explicitBlockDepth++
@@ -279,7 +278,7 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 		// more often to avoid bloat of the BrTable instruction.
 		// The "base != prevBase" condition detects inlined instructions. They are an
 		// implicit call, so entering and leaving this section affects the stack trace.
-		if p.As == ACALLNORESUME || p.As == obj.ANOP || p.Spadj != 0 || base != prevBase {
+		if p.As == ACALLNORESUME || p.As == obj.ANOP || p.As == ANop || p.Spadj != 0 || base != prevBase {
 			pc++
 		}
 	}

src/cmd/internal/objabi/funcid.go

@@ -4,6 +4,11 @@
 
 package objabi
 
+import (
+	"strconv"
+	"strings"
+)
+
 // A FuncID identifies particular functions that need to be treated
 // specially by the runtime.
 // Note that in some situations involving plugins, there may be multiple
@@ -30,4 +35,62 @@ const (
 	FuncID_gogo
 	FuncID_externalthreadhandler
 	FuncID_debugCallV1
+	FuncID_gopanic
+	FuncID_panicwrap
+	FuncID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
 )
+
+// Get the function ID for the named function in the named file.
+// The function should be package-qualified.
+func GetFuncID(name, file string) FuncID {
+	switch name {
+	case "runtime.main":
+		return FuncID_runtime_main
+	case "runtime.goexit":
+		return FuncID_goexit
+	case "runtime.jmpdefer":
+		return FuncID_jmpdefer
+	case "runtime.mcall":
+		return FuncID_mcall
+	case "runtime.morestack":
+		return FuncID_morestack
+	case "runtime.mstart":
+		return FuncID_mstart
+	case "runtime.rt0_go":
+		return FuncID_rt0_go
+	case "runtime.asmcgocall":
+		return FuncID_asmcgocall
+	case "runtime.sigpanic":
+		return FuncID_sigpanic
+	case "runtime.runfinq":
+		return FuncID_runfinq
+	case "runtime.gcBgMarkWorker":
+		return FuncID_gcBgMarkWorker
+	case "runtime.systemstack_switch":
+		return FuncID_systemstack_switch
+	case "runtime.systemstack":
+		return FuncID_systemstack
+	case "runtime.cgocallback_gofunc":
+		return FuncID_cgocallback_gofunc
+	case "runtime.gogo":
+		return FuncID_gogo
+	case "runtime.externalthreadhandler":
+		return FuncID_externalthreadhandler
+	case "runtime.debugCallV1":
+		return FuncID_debugCallV1
+	case "runtime.gopanic":
+		return FuncID_gopanic
+	case "runtime.panicwrap":
+		return FuncID_panicwrap
+	}
+	if file == "<autogenerated>" && !strings.HasSuffix(name, ".init") {
+		return FuncID_wrapper
+	}
+	if strings.HasPrefix(name, "runtime.call") {
+		if _, err := strconv.Atoi(name[12:]); err == nil {
+			// runtime.callXX reflect call wrappers.
+			return FuncID_wrapper
+		}
+	}
+	return FuncID_normal
+}

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

@@ -368,10 +368,13 @@ func (ctxt *Link) pclntab() {
 				numberfile(ctxt, call.File)
 				nameoff := nameToOffset(call.Func.Name)
 
-				inlTreeSym.SetUint32(ctxt.Arch, int64(i*16+0), uint32(call.Parent))
-				inlTreeSym.SetUint32(ctxt.Arch, int64(i*16+4), uint32(call.File.Value))
-				inlTreeSym.SetUint32(ctxt.Arch, int64(i*16+8), uint32(call.Line))
-				inlTreeSym.SetUint32(ctxt.Arch, int64(i*16+12), uint32(nameoff))
+				inlTreeSym.SetUint16(ctxt.Arch, int64(i*20+0), uint16(call.Parent))
+				inlTreeSym.SetUint8(ctxt.Arch, int64(i*20+2), uint8(objabi.GetFuncID(call.Func.Name, call.Func.File)))
+				// byte 3 is unused
+				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+4), uint32(call.File.Value))
+				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+8), uint32(call.Line))
+				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+12), uint32(nameoff))
+				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+16), uint32(call.ParentPC))
 			}
 
 			pcln.Funcdata[objabi.FUNCDATA_InlTree] = inlTreeSym
@@ -386,43 +389,12 @@ func (ctxt *Link) pclntab() {
 		off = int32(ftab.SetUint32(ctxt.Arch, int64(off), uint32(len(pcln.Pcdata))))
 
 		// funcID uint8
-		funcID := objabi.FuncID_normal
-		switch s.Name {
-		case "runtime.main":
-			funcID = objabi.FuncID_runtime_main
-		case "runtime.goexit":
-			funcID = objabi.FuncID_goexit
-		case "runtime.jmpdefer":
-			funcID = objabi.FuncID_jmpdefer
-		case "runtime.mcall":
-			funcID = objabi.FuncID_mcall
-		case "runtime.morestack":
-			funcID = objabi.FuncID_morestack
-		case "runtime.mstart":
-			funcID = objabi.FuncID_mstart
-		case "runtime.rt0_go":
-			funcID = objabi.FuncID_rt0_go
-		case "runtime.asmcgocall":
-			funcID = objabi.FuncID_asmcgocall
-		case "runtime.sigpanic":
-			funcID = objabi.FuncID_sigpanic
-		case "runtime.runfinq":
-			funcID = objabi.FuncID_runfinq
-		case "runtime.gcBgMarkWorker":
-			funcID = objabi.FuncID_gcBgMarkWorker
-		case "runtime.systemstack_switch":
-			funcID = objabi.FuncID_systemstack_switch
-		case "runtime.systemstack":
-			funcID = objabi.FuncID_systemstack
-		case "runtime.cgocallback_gofunc":
-			funcID = objabi.FuncID_cgocallback_gofunc
-		case "runtime.gogo":
-			funcID = objabi.FuncID_gogo
-		case "runtime.externalthreadhandler":
-			funcID = objabi.FuncID_externalthreadhandler
-		case "runtime.debugCallV1":
-			funcID = objabi.FuncID_debugCallV1
+		var file string
+		if s.FuncInfo != nil && len(s.FuncInfo.File) > 0 {
+			file = s.FuncInfo.File[0].Name
 		}
+		funcID := objabi.GetFuncID(s.Name, file)
+
 		off = int32(ftab.SetUint8(ctxt.Arch, int64(off), uint8(funcID)))
 
 		// unused

src/cmd/link/internal/objfile/objfile.go

@@ -318,6 +318,7 @@ overwrite:
 			pc.InlTree[i].File = r.readSymIndex()
 			pc.InlTree[i].Line = r.readInt32()
 			pc.InlTree[i].Func = r.readSymIndex()
+			pc.InlTree[i].ParentPC = r.readInt32()
 		}
 
 		if !dupok {

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

@@ -28,7 +28,7 @@ type Symbol struct {
 	Sub         *Symbol
 	Outer       *Symbol
 	Gotype      *Symbol
-	File        string
+	File        string // actually package!
 	auxinfo     *AuxSymbol
 	Sect        *Section
 	FuncInfo    *FuncInfo
@@ -150,6 +150,10 @@ func (s *Symbol) SetUint8(arch *sys.Arch, r int64, v uint8) int64 {
 	return s.setUintXX(arch, r, uint64(v), 1)
 }
 
+func (s *Symbol) SetUint16(arch *sys.Arch, r int64, v uint16) int64 {
+	return s.setUintXX(arch, r, uint64(v), 2)
+}
+
 func (s *Symbol) SetUint32(arch *sys.Arch, r int64, v uint32) int64 {
 	return s.setUintXX(arch, r, uint64(v), 4)
 }
@@ -507,10 +511,11 @@ type FuncInfo struct {
 
 // InlinedCall is a node in a local inlining tree (FuncInfo.InlTree).
 type InlinedCall struct {
-	Parent int32   // index of parent in InlTree
-	File   *Symbol // file of the inlined call
-	Line   int32   // line number of the inlined call
-	Func   *Symbol // function that was inlined
+	Parent   int32   // index of parent in InlTree
+	File     *Symbol // file of the inlined call
+	Line     int32   // line number of the inlined call
+	Func     *Symbol // function that was inlined
+	ParentPC int32   // PC of the instruction just before the inlined body (offset from function start)
 }
 
 type Pcdata struct {

src/runtime/extern.go

@@ -166,27 +166,13 @@ import "runtime/internal/sys"
 // program counter, file name, and line number within the file of the corresponding
 // call. The boolean ok is false if it was not possible to recover the information.
 func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
-	// Make room for three PCs: the one we were asked for,
-	// what it called, so that CallersFrames can see if it "called"
-	// sigpanic, and possibly a PC for skipPleaseUseCallersFrames.
-	var rpc [3]uintptr
-	if callers(skip, rpc[:]) < 2 {
+	rpc := make([]uintptr, 1)
+	n := callers(skip+1, rpc[:])
+	if n < 1 {
 		return
 	}
-	var stackExpander stackExpander
-	callers := stackExpander.init(rpc[:])
-	// We asked for one extra, so skip that one. If this is sigpanic,
-	// stepping over this frame will set up state in Frames so the
-	// next frame is correct.
-	callers, _, ok = stackExpander.next(callers, true)
-	if !ok {
-		return
-	}
-	_, frame, _ := stackExpander.next(callers, true)
-	pc = frame.PC
-	file = frame.File
-	line = frame.Line
-	return
+	frame, _ := CallersFrames(rpc).Next()
+	return frame.PC, frame.File, frame.Line, frame.PC != 0
 }
 
 // Callers fills the slice pc with the return program counters of function invocations

src/runtime/pprof/proto.go

@@ -208,7 +208,7 @@ func (b *profileBuilder) pbMapping(tag int, id, base, limit, offset uint64, file
 }
 
 // locForPC returns the location ID for addr.
-// addr must be a return PC. This returns the location of the call.
+// addr must a PC which is part of a call or the PC of an inline marker. This returns the location of the call.
 // It may emit to b.pb, so there must be no message encoding in progress.
 func (b *profileBuilder) locForPC(addr uintptr) uint64 {
 	id := uint64(b.locs[addr])
@@ -236,7 +236,7 @@ func (b *profileBuilder) locForPC(addr uintptr) uint64 {
 	if frame.PC == 0 {
 		// If we failed to resolve the frame, at least make up
 		// a reasonable call PC. This mostly happens in tests.
-		frame.PC = addr - 1
+		frame.PC = addr
 	}
 
 	// We can't write out functions while in the middle of the
@@ -403,16 +403,7 @@ func (b *profileBuilder) build() {
 		}
 
 		locs = locs[:0]
-		for i, addr := range e.stk {
-			// Addresses from stack traces point to the
-			// next instruction after each call, except
-			// for the leaf, which points to where the
-			// signal occurred. locForPC expects return
-			// PCs, so increment the leaf address to look
-			// like a return PC.
-			if i == 0 {
-				addr++
-			}
+		for _, addr := range e.stk {
 			l := b.locForPC(addr)
 			if l == 0 { // runtime.goexit
 				continue

src/runtime/pprof/proto_test.go

@@ -133,11 +133,11 @@ func TestConvertCPUProfile(t *testing.T) {
 	samples := []*profile.Sample{
 		{Value: []int64{20, 20 * 2000 * 1000}, Location: []*profile.Location{
 			{ID: 1, Mapping: map1, Address: addr1},
-			{ID: 2, Mapping: map1, Address: addr1 + 1},
+			{ID: 2, Mapping: map1, Address: addr1 + 2},
 		}},
 		{Value: []int64{40, 40 * 2000 * 1000}, Location: []*profile.Location{
 			{ID: 3, Mapping: map2, Address: addr2},
-			{ID: 4, Mapping: map2, Address: addr2 + 1},
+			{ID: 4, Mapping: map2, Address: addr2 + 2},
 		}},
 	}
 	checkProfile(t, p, period, periodType, sampleType, samples, "")

src/runtime/pprof/protomem_test.go

@@ -14,11 +14,7 @@ import (
 func TestConvertMemProfile(t *testing.T) {
 	addr1, addr2, map1, map2 := testPCs(t)
 
-	// MemProfileRecord stacks are return PCs, so add one to the
-	// addresses recorded in the "profile". The proto profile
-	// locations are call PCs, so conversion will subtract one
-	// from these and get back to addr1 and addr2.
-	a1, a2 := uintptr(addr1)+1, uintptr(addr2)+1
+	a1, a2 := uintptr(addr1), uintptr(addr2)
 	rate := int64(512 * 1024)
 	rec := []runtime.MemProfileRecord{
 		{AllocBytes: 4096, FreeBytes: 1024, AllocObjects: 4, FreeObjects: 1, Stack0: [32]uintptr{a1, a2}},

src/runtime/symtab.go

@@ -13,17 +13,12 @@ import (
 // Frames may be used to get function/file/line information for a
 // slice of PC values returned by Callers.
 type Frames struct {
-	// callers is a slice of PCs that have not yet been expanded.
+	// callers is a slice of PCs that have not yet been expanded to frames.
 	callers []uintptr
 
-	// stackExpander expands callers into a sequence of Frames,
-	// tracking the necessary state across PCs.
-	stackExpander stackExpander
-
-	// elideWrapper indicates that, if the next frame is an
-	// autogenerated wrapper function, it should be elided from
-	// the stack.
-	elideWrapper bool
+	// frames is a slice of Frames that have yet to be returned.
+	frames     []Frame
+	frameStore [2]Frame
 }
 
 // Frame is the information returned by Frames for each call frame.
@@ -59,224 +54,79 @@ type Frame struct {
 	Entry uintptr
 }
 
-// stackExpander expands a call stack of PCs into a sequence of
-// Frames. It tracks state across PCs necessary to perform this
-// expansion.
-//
-// This is the core of the Frames implementation, but is a separate
-// internal API to make it possible to use within the runtime without
-// heap-allocating the PC slice. The only difference with the public
-// Frames API is that the caller is responsible for threading the PC
-// slice between expansion steps in this API. If escape analysis were
-// smarter, we may not need this (though it may have to be a lot
-// smarter).
-type stackExpander struct {
-	// pcExpander expands the current PC into a sequence of Frames.
-	pcExpander pcExpander
-
-	// If previous caller in iteration was a panic, then the next
-	// PC in the call stack is the address of the faulting
-	// instruction instead of the return address of the call.
-	wasPanic bool
-
-	// skip > 0 indicates that skip frames in the expansion of the
-	// first PC should be skipped over and callers[1] should also
-	// be skipped.
-	skip int
-}
-
 // CallersFrames takes a slice of PC values returned by Callers and
 // prepares to return function/file/line information.
 // Do not change the slice until you are done with the Frames.
 func CallersFrames(callers []uintptr) *Frames {
-	ci := &Frames{}
-	ci.callers = ci.stackExpander.init(callers)
-	return ci
-}
-
-func (se *stackExpander) init(callers []uintptr) []uintptr {
-	if len(callers) >= 1 {
-		pc := callers[0]
-		s := pc - skipPC
-		if s >= 0 && s < sizeofSkipFunction {
-			// Ignore skip frame callers[0] since this means the caller trimmed the PC slice.
-			return callers[1:]
-		}
-	}
-	if len(callers) >= 2 {
-		pc := callers[1]
-		s := pc - skipPC
-		if s > 0 && s < sizeofSkipFunction {
-			// Skip the first s inlined frames when we expand the first PC.
-			se.skip = int(s)
-		}
-	}
-	return callers
+	f := &Frames{callers: callers}
+	f.frames = f.frameStore[:0]
+	return f
 }
 
 // Next returns frame information for the next caller.
 // If more is false, there are no more callers (the Frame value is valid).
 func (ci *Frames) Next() (frame Frame, more bool) {
-	ci.callers, frame, more = ci.stackExpander.next(ci.callers, ci.elideWrapper)
-	ci.elideWrapper = elideWrapperCalling(frame.Function)
-	return
-}
-
-func (se *stackExpander) next(callers []uintptr, elideWrapper bool) (ncallers []uintptr, frame Frame, more bool) {
-	ncallers = callers
-again:
-	if !se.pcExpander.more {
-		// Expand the next PC.
-		if len(ncallers) == 0 {
-			se.wasPanic = false
-			return ncallers, Frame{}, false
+	for len(ci.frames) < 2 {
+		// Find the next frame.
+		// We need to look for 2 frames so we know what
+		// to return for the "more" result.
+		if len(ci.callers) == 0 {
+			break
 		}
-		se.pcExpander.init(ncallers[0], se.wasPanic)
-		ncallers = ncallers[1:]
-		se.wasPanic = se.pcExpander.funcInfo.valid() && se.pcExpander.funcInfo.funcID == funcID_sigpanic
-		if se.skip > 0 {
-			for ; se.skip > 0; se.skip-- {
-				se.pcExpander.next()
+		pc := ci.callers[0]
+		ci.callers = ci.callers[1:]
+		funcInfo := findfunc(pc)
+		if !funcInfo.valid() {
+			if cgoSymbolizer != nil {
+				// Pre-expand cgo frames. We could do this
+				// incrementally, too, but there's no way to
+				// avoid allocation in this case anyway.
+				ci.frames = append(ci.frames, expandCgoFrames(pc)...)
 			}
-			se.skip = 0
-			// Drop skipPleaseUseCallersFrames.
-			ncallers = ncallers[1:]
+			continue
 		}
-		if !se.pcExpander.more {
-			// No symbolic information for this PC.
-			// However, we return at least one frame for
-			// every PC, so return an invalid frame.
-			return ncallers, Frame{}, len(ncallers) > 0
+		f := funcInfo._Func()
+		entry := f.Entry()
+		name := funcname(funcInfo)
+		file, line := funcline1(funcInfo, pc, false)
+		if inldata := funcdata(funcInfo, _FUNCDATA_InlTree); inldata != nil {
+			inltree := (*[1 << 20]inlinedCall)(inldata)
+			ix := pcdatavalue(funcInfo, _PCDATA_InlTreeIndex, pc, nil)
+			if ix >= 0 {
+				// Note: entry is not modified. It always refers to a real frame, not an inlined one.
+				f = nil
+				name = funcnameFromNameoff(funcInfo, inltree[ix].func_)
+				// File/line is already correct.
+				// TODO: remove file/line from InlinedCall?
+			}
 		}
+		ci.frames = append(ci.frames, Frame{
+			PC:       pc,
+			Func:     f,
+			Function: name,
+			File:     file,
+			Line:     int(line),
+			Entry:    entry,
+		})
 	}
 
-	frame = se.pcExpander.next()
-	if elideWrapper && frame.File == "<autogenerated>" {
-		// Ignore autogenerated functions such as pointer
-		// method forwarding functions. These are an
-		// implementation detail that doesn't reflect the
-		// source code.
-		goto again
-	}
-	return ncallers, frame, se.pcExpander.more || len(ncallers) > 0
-}
-
-// A pcExpander expands a single PC into a sequence of Frames.
-type pcExpander struct {
-	// more indicates that the next call to next will return a
-	// valid frame.
-	more bool
-
-	// pc is the pc being expanded.
-	pc uintptr
-
-	// frames is a pre-expanded set of Frames to return from the
-	// iterator. If this is set, then this is everything that will
-	// be returned from the iterator.
-	frames []Frame
-
-	// funcInfo is the funcInfo of the function containing pc.
-	funcInfo funcInfo
-
-	// inlTree is the inlining tree of the function containing pc.
-	inlTree *[1 << 20]inlinedCall
-
-	// file and line are the file name and line number of the next
-	// frame.
-	file string
-	line int32
-
-	// inlIndex is the inlining index of the next frame, or -1 if
-	// the next frame is an outermost frame.
-	inlIndex int32
-}
-
-// init initializes this pcExpander to expand pc. It sets ex.more if
-// pc expands to any Frames.
-//
-// A pcExpander can be reused by calling init again.
-//
-// If pc was a "call" to sigpanic, panicCall should be true. In this
-// case, pc is treated as the address of a faulting instruction
-// instead of the return address of a call.
-func (ex *pcExpander) init(pc uintptr, panicCall bool) {
-	ex.more = false
-
-	ex.funcInfo = findfunc(pc)
-	if !ex.funcInfo.valid() {
-		if cgoSymbolizer != nil {
-			// Pre-expand cgo frames. We could do this
-			// incrementally, too, but there's no way to
-			// avoid allocation in this case anyway.
-			ex.frames = expandCgoFrames(pc)
-			ex.more = len(ex.frames) > 0
-		}
-		return
-	}
-
-	ex.more = true
-	entry := ex.funcInfo.entry
-	ex.pc = pc
-	if ex.pc > entry && !panicCall {
-		ex.pc--
-	}
-
-	// file and line are the innermost position at pc.
-	ex.file, ex.line = funcline1(ex.funcInfo, ex.pc, false)
-
-	// Get inlining tree at pc
-	inldata := funcdata(ex.funcInfo, _FUNCDATA_InlTree)
-	if inldata != nil {
-		ex.inlTree = (*[1 << 20]inlinedCall)(inldata)
-		ex.inlIndex = pcdatavalue(ex.funcInfo, _PCDATA_InlTreeIndex, ex.pc, nil)
-	} else {
-		ex.inlTree = nil
-		ex.inlIndex = -1
-	}
-}
-
-// next returns the next Frame in the expansion of pc and sets ex.more
-// if there are more Frames to follow.
-func (ex *pcExpander) next() Frame {
-	if !ex.more {
-		return Frame{}
-	}
-
-	if len(ex.frames) > 0 {
-		// Return pre-expended frame.
-		frame := ex.frames[0]
-		ex.frames = ex.frames[1:]
-		ex.more = len(ex.frames) > 0
-		return frame
-	}
-
-	if ex.inlIndex >= 0 {
-		// Return inner inlined frame.
-		call := ex.inlTree[ex.inlIndex]
-		frame := Frame{
-			PC:       ex.pc,
-			Func:     nil, // nil for inlined functions
-			Function: funcnameFromNameoff(ex.funcInfo, call.func_),
-			File:     ex.file,
-			Line:     int(ex.line),
-			Entry:    ex.funcInfo.entry,
-		}
-		ex.file = funcfile(ex.funcInfo, call.file)
-		ex.line = call.line
-		ex.inlIndex = call.parent
-		return frame
-	}
-
-	// No inlining or pre-expanded frames.
-	ex.more = false
-	return Frame{
-		PC:       ex.pc,
-		Func:     ex.funcInfo._Func(),
-		Function: funcname(ex.funcInfo),
-		File:     ex.file,
-		Line:     int(ex.line),
-		Entry:    ex.funcInfo.entry,
+	// Pop one frame from the frame list. Keep the rest.
+	// Avoid allocation in the common case, which is 1 or 2 frames.
+	switch len(ci.frames) {
+	case 0: // In the rare case when there are no frames at all, we return Frame{}.
+	case 1:
+		frame = ci.frames[0]
+		ci.frames = ci.frameStore[:0]
+	case 2:
+		frame = ci.frames[0]
+		ci.frameStore[0] = ci.frames[1]
+		ci.frames = ci.frameStore[:1]
+	default:
+		frame = ci.frames[0]
+		ci.frames = ci.frames[1:]
 	}
+	more = len(ci.frames) > 0
+	return
 }
 
 // expandCgoFrames expands frame information for pc, known to be
@@ -378,6 +228,9 @@ const (
 	funcID_gogo
 	funcID_externalthreadhandler
 	funcID_debugCallV1
+	funcID_gopanic
+	funcID_panicwrap
+	funcID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
 )
 
 // moduledata records information about the layout of the executable
@@ -943,8 +796,11 @@ func stackmapdata(stkmap *stackmap, n int32) bitvector {
 
 // inlinedCall is the encoding of entries in the FUNCDATA_InlTree table.
 type inlinedCall struct {
-	parent int32 // index of parent in the inltree, or < 0
-	file   int32 // fileno index into filetab
-	line   int32 // line number of the call site
-	func_  int32 // offset into pclntab for name of called function
+	parent   int16  // index of parent in the inltree, or < 0
+	funcID   funcID // type of the called function
+	_        byte
+	file     int32 // fileno index into filetab
+	line     int32 // line number of the call site
+	func_    int32 // offset into pclntab for name of called function
+	parentPc int32 // position of an instruction whose source position is the call site (offset from entry)
 }

src/runtime/traceback.go

@@ -179,6 +179,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 
 	var cache pcvalueCache
 
+	lastFuncID := funcID_normal
 	n := 0
 	for n < max {
 		// Typically:
@@ -344,48 +345,44 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 		}
 
 		if pcbuf != nil {
-			if skip == 0 {
-				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
-			} else {
-				// backup to CALL instruction to read inlining info (same logic as below)
-				tracepc := frame.pc
-				if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
-					tracepc--
-				}
-				inldata := funcdata(f, _FUNCDATA_InlTree)
+			// backup to CALL instruction to read inlining info (same logic as below)
+			tracepc := frame.pc
+			if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
+				tracepc--
+			}
 
-				// no inlining info, skip the physical frame
-				if inldata == nil {
-					skip--
-					goto skipped
-				}
-
-				ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, &cache)
+			// If there is inlining info, record the inner frames.
+			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
 				inltree := (*[1 << 20]inlinedCall)(inldata)
-				// skip the logical (inlined) frames
-				logicalSkipped := 0
-				for ix >= 0 && skip > 0 {
-					skip--
-					logicalSkipped++
-					ix = inltree[ix].parent
-				}
-
-				// skip the physical frame if there's more to skip
-				if skip > 0 {
-					skip--
-					goto skipped
-				}
-
-				// now we have a partially skipped frame
-				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
-
-				// if there's room, pcbuf[1] is a skip PC that encodes the number of skipped frames in pcbuf[0]
-				if n+1 < max {
-					n++
-					pc := skipPC + uintptr(logicalSkipped)
-					(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
+				for {
+					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, &cache)
+					if ix < 0 {
+						break
+					}
+					if inltree[ix].funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
+						// ignore wrappers
+					} else if skip > 0 {
+						skip--
+					} else if n < max {
+						(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = tracepc
+						n++
+					}
+					lastFuncID = inltree[ix].funcID
+					// Back up to an instruction in the "caller".
+					tracepc = frame.fn.entry + uintptr(inltree[ix].parentPc)
 				}
 			}
+			// Record the main frame.
+			if f.funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
+				// Ignore wrapper functions (except when they trigger panics).
+			} else if skip > 0 {
+				skip--
+			} else if n < max {
+				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = tracepc
+				n++
+			}
+			lastFuncID = f.funcID
+			n-- // offset n++ below
 		}
 
 		if printing {
@@ -396,7 +393,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 			// called panic rather than the wrapped
 			// function. Otherwise, leave them out.
 			name := funcname(f)
-			nextElideWrapper := elideWrapperCalling(name)
+			nextElideWrapper := elideWrapperCalling(f.funcID)
 			if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, elideWrapper && nprint != 0) {
 				// Print during crash.
 				//	main(0x1, 0x2, 0x3)
@@ -418,7 +415,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 
 						file = funcfile(f, inltree[ix].file)
 						line = inltree[ix].line
-						ix = inltree[ix].parent
+						ix = int32(inltree[ix].parent)
 					}
 				}
 				if name == "runtime.gopanic" {
@@ -451,7 +448,6 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 		}
 		n++
 
-	skipped:
 		if f.funcID == funcID_cgocallback_gofunc && len(cgoCtxt) > 0 {
 			ctxt := cgoCtxt[len(cgoCtxt)-1]
 			cgoCtxt = cgoCtxt[:len(cgoCtxt)-1]
@@ -798,7 +794,7 @@ func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) bool {
 
 			file = funcfile(f, inltree[ix].file)
 			line = inltree[ix].line
-			ix = inltree[ix].parent
+			ix = int32(inltree[ix].parent)
 		}
 	}
 	name := funcname(f)
@@ -811,7 +807,7 @@ func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) bool {
 		print(" +", hex(pc-f.entry))
 	}
 	print("\n")
-	return elideWrapperCalling(name)
+	return elideWrapperCalling(f.funcID)
 }
 
 func callers(skip int, pcbuf []uintptr) int {
@@ -877,11 +873,11 @@ func isExportedRuntime(name string) bool {
 }
 
 // elideWrapperCalling reports whether a wrapper function that called
-// function "name" should be elided from stack traces.
-func elideWrapperCalling(name string) bool {
+// function id should be elided from stack traces.
+func elideWrapperCalling(id funcID) bool {
 	// If the wrapper called a panic function instead of the
 	// wrapped function, we want to include it in stacks.
-	return !(name == "runtime.gopanic" || name == "runtime.sigpanic" || name == "runtime.panicwrap")
+	return !(id == funcID_gopanic || id == funcID_sigpanic || id == funcID_panicwrap)
 }
 
 var gStatusStrings = [...]string{

test/fixedbugs/issue5856.go

@@ -29,7 +29,7 @@ func f() {
 }
 
 func g() {
-	_, file, line, _ := runtime.Caller(3)
+	_, file, line, _ := runtime.Caller(2)
 	if !strings.HasSuffix(file, "issue5856.go") || line != 28 {
 		fmt.Printf("BUG: defer called from %s:%d, want issue5856.go:28\n", file, line)
 		os.Exit(1)

test/inline_callers.go

@@ -56,11 +56,11 @@ func testCallersFrames(skp int) (frames []string) {
 }
 
 var expectedFrames [][]string = [][]string{
-	0: {"runtime.Callers", "main.testCallers", "main.main"},
-	1: {"main.testCallers", "main.main"},
-	2: {"main.testCallers", "runtime.skipPleaseUseCallersFrames", "main.main"},
-	3: {"main.testCallers", "runtime.skipPleaseUseCallersFrames", "main.main"},
-	4: {"main.testCallers", "runtime.skipPleaseUseCallersFrames", "main.main"},
+	0: {"runtime.Callers", "main.testCallers", "main.testCallers", "main.testCallers", "main.testCallers", "main.main"},
+	1: {"main.testCallers", "main.testCallers", "main.testCallers", "main.testCallers", "main.main"},
+	2: {"main.testCallers", "main.testCallers", "main.testCallers", "main.main"},
+	3: {"main.testCallers", "main.testCallers", "main.main"},
+	4: {"main.testCallers", "main.main"},
 	5: {"main.main"},
 }