compiler,linker: support for DWARF inlined instances

Compiler and linker changes to support DWARF inlined instances,
see https://go.googlesource.com/proposal/+/HEAD/design/22080-dwarf-inlining.md
for design details.

This functionality is gated via the cmd/compile option -gendwarfinl=N,
where N={0,1,2}, where a value of 0 disables dwarf inline generation,
a value of 1 turns on dwarf generation without tracking of formal/local
vars from inlined routines, and a value of 2 enables inlines with
variable tracking.

Updates #22080

Change-Id: I69309b3b815d9fed04aebddc0b8d33d0dbbfad6e
Reviewed-on: https://go-review.googlesource.com/75550
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/asm/internal/asm/endtoend_test.go

@@ -186,7 +186,7 @@ Diff:
 		t.Errorf(format, args...)
 		ok = false
 	}
-	obj.Flushplist(ctxt, pList, nil)
+	obj.Flushplist(ctxt, pList, nil, "")
 
 	for p := top; p != nil; p = p.Link {
 		if p.As == obj.ATEXT {
@@ -290,7 +290,7 @@ func testErrors(t *testing.T, goarch, file string) {
 		errBuf.WriteString(s)
 	}
 	pList.Firstpc, ok = parser.Parse()
-	obj.Flushplist(ctxt, pList, nil)
+	obj.Flushplist(ctxt, pList, nil, "")
 	if ok && !failed {
 		t.Errorf("asm: %s had no errors", goarch)
 	}

src/cmd/asm/main.go

@@ -72,7 +72,7 @@ func main() {
 			break
 		}
 		// reports errors to parser.Errorf
-		obj.Flushplist(ctxt, pList, nil)
+		obj.Flushplist(ctxt, pList, nil, "")
 	}
 	if ok {
 		obj.WriteObjFile(ctxt, buf)

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

+// Copyright 2017 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 gc
+
+import (
+	"cmd/internal/dwarf"
+	"cmd/internal/obj"
+	"cmd/internal/src"
+	"sort"
+	"strings"
+)
+
+// To identify variables by original source position.
+type varPos struct {
+	DeclFile string
+	DeclLine uint
+	DeclCol  uint
+}
+
+// This is the main entry point for collection of raw material to
+// drive generation of DWARF "inlined subroutine" DIEs. See proposal
+// 22080 for more details and background info.
+func assembleInlines(fnsym *obj.LSym, fn *Node, dwVars []*dwarf.Var) dwarf.InlCalls {
+	var inlcalls dwarf.InlCalls
+
+	if Debug_gendwarfinl != 0 {
+		Ctxt.Logf("assembling DWARF inlined routine info for %v\n", fnsym.Name)
+	}
+
+	// This maps inline index (from Ctxt.InlTree) to index in inlcalls.Calls
+	imap := make(map[int]int)
+
+	// Walk progs to build up the InlCalls data structure
+	var prevpos src.XPos
+	for p := fnsym.Func.Text; p != nil; p = p.Link {
+		if p.Pos == prevpos {
+			continue
+		}
+		ii := posInlIndex(p.Pos)
+		if ii >= 0 {
+			insertInlCall(&inlcalls, ii, imap)
+		}
+		prevpos = p.Pos
+	}
+
+	// This is used to partition DWARF vars by inline index. Vars not
+	// produced by the inliner will wind up in the vmap[0] entry.
+	vmap := make(map[int32][]*dwarf.Var)
+
+	// Now walk the dwarf vars and partition them based on whether they
+	// were produced by the inliner (dwv.InlIndex > 0) or were original
+	// vars/params from the function (dwv.InlIndex == 0).
+	for _, dwv := range dwVars {
+
+		vmap[dwv.InlIndex] = append(vmap[dwv.InlIndex], dwv)
+
+		// Zero index => var was not produced by an inline
+		if dwv.InlIndex == 0 {
+			continue
+		}
+
+		// Look up index in our map, then tack the var in question
+		// onto the vars list for the correct inlined call.
+		ii := int(dwv.InlIndex) - 1
+		idx, ok := imap[ii]
+		if !ok {
+			// We can occasionally encounter a var produced by the
+			// inliner for which there is no remaining prog; add a new
+			// entry to the call list in this scenario.
+			idx = insertInlCall(&inlcalls, ii, imap)
+		}
+		inlcalls.Calls[idx].InlVars =
+			append(inlcalls.Calls[idx].InlVars, dwv)
+	}
+
+	// Post process the map above to assign child indices to vars. For
+	// variables that weren't produced by an inline, sort them
+	// according to class and name and assign indices that way. For
+	// vars produced by an inline, assign child index by looking up
+	// the var name in the origin pre-optimization dcl list for the
+	// inlined function.
+	for ii, sl := range vmap {
+		if ii == 0 {
+			sort.Sort(byClassThenName(sl))
+			for j := 0; j < len(sl); j++ {
+				sl[j].ChildIndex = int32(j)
+			}
+		} else {
+			// Assign child index based on pre-inlined decls
+			ifnlsym := Ctxt.InlTree.InlinedFunction(int(ii - 1))
+			dcl, _ := preInliningDcls(ifnlsym)
+			m := make(map[varPos]int)
+			for i := 0; i < len(dcl); i++ {
+				n := dcl[i]
+				pos := Ctxt.InnermostPos(n.Pos)
+				vp := varPos{
+					DeclFile: pos.Base().SymFilename(),
+					DeclLine: pos.Line(),
+					DeclCol:  pos.Col(),
+				}
+				m[vp] = i
+			}
+			for j := 0; j < len(sl); j++ {
+				vp := varPos{
+					DeclFile: sl[j].DeclFile,
+					DeclLine: sl[j].DeclLine,
+					DeclCol:  sl[j].DeclCol,
+				}
+				if idx, found := m[vp]; found {
+					sl[j].ChildIndex = int32(idx)
+				} else {
+					Fatalf("unexpected: can't find var %s in preInliningDcls for %v\n", sl[j].Name, Ctxt.InlTree.InlinedFunction(int(ii-1)))
+				}
+			}
+		}
+	}
+
+	// Make a second pass through the progs to compute PC ranges
+	// for the various inlined calls.
+	curii := -1
+	var crange *dwarf.Range
+	var prevp *obj.Prog
+	for p := fnsym.Func.Text; p != nil; prevp, p = p, p.Link {
+		if prevp != nil && p.Pos == prevp.Pos {
+			continue
+		}
+		ii := posInlIndex(p.Pos)
+		if ii == curii {
+			continue
+		} else {
+			// Close out the current range
+			endRange(crange, prevp)
+
+			// Begin new range
+			crange = beginRange(inlcalls.Calls, p, ii, imap)
+			curii = ii
+		}
+	}
+	if prevp != nil {
+		endRange(crange, prevp)
+	}
+
+	// Debugging
+	if Debug_gendwarfinl != 0 {
+		dumpInlCalls(inlcalls)
+		dumpInlVars(dwVars)
+	}
+
+	return inlcalls
+}
+
+// Secondary hook for DWARF inlined subroutine generation. This is called
+// late in the compilation when it is determined that we need an
+// abstract function DIE for an inlined routine imported from a
+// previously compiled package.
+func genAbstractFunc(fn *obj.LSym) {
+	ifn := Ctxt.DwFixups.GetPrecursorFunc(fn)
+	if ifn == nil {
+		Ctxt.Diag("failed to locate precursor fn for %v", fn)
+		return
+	}
+	if Debug_gendwarfinl != 0 {
+		Ctxt.Logf("DwarfAbstractFunc(%v)\n", fn.Name)
+	}
+	Ctxt.DwarfAbstractFunc(ifn, fn, myimportpath)
+}
+
+func insertInlCall(dwcalls *dwarf.InlCalls, inlIdx int, imap map[int]int) int {
+	callIdx, found := imap[inlIdx]
+	if found {
+		return callIdx
+	}
+
+	// Haven't seen this inline yet. Visit parent of inline if there
+	// is one. We do this first so that parents appear before their
+	// children in the resulting table.
+	parCallIdx := -1
+	parInlIdx := Ctxt.InlTree.Parent(inlIdx)
+	if parInlIdx >= 0 {
+		parCallIdx = insertInlCall(dwcalls, parInlIdx, imap)
+	}
+
+	// Create new entry for this inline
+	inlinedFn := Ctxt.InlTree.InlinedFunction(int(inlIdx))
+	callXPos := Ctxt.InlTree.CallPos(int(inlIdx))
+	absFnSym := Ctxt.DwFixups.AbsFuncDwarfSym(inlinedFn)
+	pb := Ctxt.PosTable.Pos(callXPos).Base()
+	callFileSym := Ctxt.Lookup(pb.SymFilename())
+	ic := dwarf.InlCall{
+		InlIndex:  inlIdx,
+		CallFile:  callFileSym,
+		CallLine:  uint32(callXPos.Line()),
+		AbsFunSym: absFnSym,
+		Root:      parCallIdx == -1,
+	}
+	dwcalls.Calls = append(dwcalls.Calls, ic)
+	callIdx = len(dwcalls.Calls) - 1
+	imap[inlIdx] = callIdx
+
+	if parCallIdx != -1 {
+		// Add this inline to parent's child list
+		dwcalls.Calls[parCallIdx].Children = append(dwcalls.Calls[parCallIdx].Children, callIdx)
+	}
+
+	return callIdx
+}
+
+// Given a src.XPos, return its associated inlining index if it
+// corresponds to something created as a result of an inline, or -1 if
+// there is no inline info. Note that the index returned will refer to
+// the deepest call in the inlined stack, e.g. if you have "A calls B
+// calls C calls D" and all three callees are inlined (B, C, and D),
+// the index for a node from the inlined body of D will refer to the
+// call to D from C. Whew.
+func posInlIndex(xpos src.XPos) int {
+	pos := Ctxt.PosTable.Pos(xpos)
+	if b := pos.Base(); b != nil {
+		ii := b.InliningIndex()
+		if ii >= 0 {
+			return ii
+		}
+	}
+	return -1
+}
+
+func endRange(crange *dwarf.Range, p *obj.Prog) {
+	if crange == nil {
+		return
+	}
+	crange.End = p.Pc
+}
+
+func beginRange(calls []dwarf.InlCall, p *obj.Prog, ii int, imap map[int]int) *dwarf.Range {
+	if ii == -1 {
+		return nil
+	}
+	callIdx, found := imap[ii]
+	if !found {
+		Fatalf("internal error: can't find inlIndex %d in imap for prog at %d\n", ii, p.Pc)
+	}
+	call := &calls[callIdx]
+
+	// Set up range and append to correct inlined call
+	call.Ranges = append(call.Ranges, dwarf.Range{Start: p.Pc, End: -1})
+	return &call.Ranges[len(call.Ranges)-1]
+}
+
+func cmpDwarfVar(a, b *dwarf.Var) bool {
+	// named before artificial
+	aart := 0
+	if strings.HasPrefix(a.Name, "~r") {
+		aart = 1
+	}
+	bart := 0
+	if strings.HasPrefix(b.Name, "~r") {
+		bart = 1
+	}
+	if aart != bart {
+		return aart < bart
+	}
+
+	// otherwise sort by name
+	return a.Name < b.Name
+}
+
+// byClassThenName implements sort.Interface for []*dwarf.Var using cmpDwarfVar.
+type byClassThenName []*dwarf.Var
+
+func (s byClassThenName) Len() int           { return len(s) }
+func (s byClassThenName) Less(i, j int) bool { return cmpDwarfVar(s[i], s[j]) }
+func (s byClassThenName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+func dumpInlCall(inlcalls dwarf.InlCalls, idx, ilevel int) {
+	for i := 0; i < ilevel; i += 1 {
+		Ctxt.Logf("  ")
+	}
+	ic := inlcalls.Calls[idx]
+	callee := Ctxt.InlTree.InlinedFunction(ic.InlIndex)
+	Ctxt.Logf("  %d: II:%d (%s) V: (", idx, ic.InlIndex, callee.Name)
+	for _, f := range ic.InlVars {
+		Ctxt.Logf(" %v", f.Name)
+	}
+	Ctxt.Logf(" ) C: (")
+	for _, k := range ic.Children {
+		Ctxt.Logf(" %v", k)
+	}
+	Ctxt.Logf(" ) R:")
+	for _, r := range ic.Ranges {
+		Ctxt.Logf(" [%d,%d)", r.Start, r.End)
+	}
+	Ctxt.Logf("\n")
+	for _, k := range ic.Children {
+		dumpInlCall(inlcalls, k, ilevel+1)
+	}
+
+}
+
+func dumpInlCalls(inlcalls dwarf.InlCalls) {
+	n := len(inlcalls.Calls)
+	for k := 0; k < n; k += 1 {
+		if inlcalls.Calls[k].Root {
+			dumpInlCall(inlcalls, k, 0)
+		}
+	}
+}
+
+func dumpInlVars(dwvars []*dwarf.Var) {
+	for i, dwv := range dwvars {
+		typ := "local"
+		if dwv.Abbrev == dwarf.DW_ABRV_PARAM_LOCLIST || dwv.Abbrev == dwarf.DW_ABRV_PARAM {
+			typ = "param"
+		}
+		Ctxt.Logf("V%d: %s CI:%d II:%d %s\n", i, dwv.Name, dwv.ChildIndex, dwv.InlIndex-1, typ)
+	}
+}

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

@@ -219,6 +219,11 @@ var instrumenting bool
 // Whether we are tracking lexical scopes for DWARF.
 var trackScopes bool
 
+// Controls generation of DWARF inlined instance records. Zero
+// disables, 1 emits inlined routines but suppresses var info,
+// and 2 emits inlined routines with tracking of formals/locals.
+var genDwarfInline int
+
 var debuglive int
 
 var Ctxt *obj.Link

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

@@ -84,7 +84,7 @@ func (pp *Progs) NewProg() *obj.Prog {
 // Flush converts from pp to machine code.
 func (pp *Progs) Flush() {
 	plist := &obj.Plist{Firstpc: pp.Text, Curfn: pp.curfn}
-	obj.Flushplist(Ctxt, plist, pp.NewProg)
+	obj.Flushplist(Ctxt, plist, pp.NewProg, myimportpath)
 }
 
 // Free clears pp and any associated resources.

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

@@ -31,8 +31,11 @@ package gc
 
 import (
 	"cmd/compile/internal/types"
+	"cmd/internal/obj"
 	"cmd/internal/src"
 	"fmt"
+	"sort"
+	"strings"
 )
 
 // Get the function's package. For ordinary functions it's on the ->sym, but for imported methods
@@ -809,6 +812,9 @@ func mkinlcall1(n, fn *Node, isddd bool) *Node {
 	// Make temp names to use instead of the originals.
 	inlvars := make(map[*Node]*Node)
 
+	// record formals/locals for later post-processing
+	var inlfvars []*Node
+
 	// Find declarations corresponding to inlineable body.
 	var dcl []*Node
 	if fn.Name.Defn != nil {
@@ -867,13 +873,25 @@ func mkinlcall1(n, fn *Node, isddd bool) *Node {
 		if ln.Class() == PPARAM || ln.Name.Param.Stackcopy != nil && ln.Name.Param.Stackcopy.Class() == PPARAM {
 			ninit.Append(nod(ODCL, inlvars[ln], nil))
 		}
+		if genDwarfInline > 0 {
+			inlf := inlvars[ln]
+			if ln.Class() == PPARAM {
+				inlf.SetInlFormal(true)
+			} else {
+				inlf.SetInlLocal(true)
+			}
+			inlf.Pos = ln.Pos
+			inlfvars = append(inlfvars, inlf)
+		}
 	}
 
 	// temporaries for return values.
 	var retvars []*Node
 	for i, t := range fn.Type.Results().Fields().Slice() {
 		var m *Node
+		var mpos src.XPos
 		if t != nil && asNode(t.Nname) != nil && !isblank(asNode(t.Nname)) {
+			mpos = asNode(t.Nname).Pos
 			m = inlvar(asNode(t.Nname))
 			m = typecheck(m, Erv)
 			inlvars[asNode(t.Nname)] = m
@@ -882,6 +900,17 @@ func mkinlcall1(n, fn *Node, isddd bool) *Node {
 			m = retvar(t, i)
 		}
 
+		if genDwarfInline > 0 {
+			// Don't update the src.Pos on a return variable if it
+			// was manufactured by the inliner (e.g. "~r2"); such vars
+			// were not part of the original callee.
+			if !strings.HasPrefix(m.Sym.Name, "~r") {
+				m.SetInlFormal(true)
+				m.Pos = mpos
+				inlfvars = append(inlfvars, m)
+			}
+		}
+
 		ninit.Append(nod(ODCL, m, nil))
 		retvars = append(retvars, m)
 	}
@@ -976,8 +1005,16 @@ func mkinlcall1(n, fn *Node, isddd bool) *Node {
 	if b := Ctxt.PosTable.Pos(n.Pos).Base(); b != nil {
 		parent = b.InliningIndex()
 	}
+	sort.Sort(byNodeName(dcl))
 	newIndex := Ctxt.InlTree.Add(parent, n.Pos, fn.Sym.Linksym())
 
+	if genDwarfInline > 0 {
+		if !fn.Sym.Linksym().WasInlined() {
+			Ctxt.DwFixups.SetPrecursorFunc(fn.Sym.Linksym(), fn)
+			fn.Sym.Linksym().Set(obj.AttrWasInlined, true)
+		}
+	}
+
 	subst := inlsubst{
 		retlabel:    retlabel,
 		retvars:     retvars,
@@ -993,6 +1030,12 @@ func mkinlcall1(n, fn *Node, isddd bool) *Node {
 
 	typecheckslice(body, Etop)
 
+	if genDwarfInline > 0 {
+		for _, v := range inlfvars {
+			v.Pos = subst.updatedPos(v.Pos)
+		}
+	}
+
 	//dumplist("ninit post", ninit);
 
 	call := nod(OINLCALL, nil, nil)
@@ -1192,3 +1235,28 @@ func (subst *inlsubst) updatedPos(xpos src.XPos) src.XPos {
 	pos.SetBase(newbase)
 	return Ctxt.PosTable.XPos(pos)
 }
+
+func cmpNodeName(a, b *Node) bool {
+	// named before artificial
+	aart := 0
+	if strings.HasPrefix(a.Sym.Name, "~r") {
+		aart = 1
+	}
+	bart := 0
+	if strings.HasPrefix(b.Sym.Name, "~r") {
+		bart = 1
+	}
+	if aart != bart {
+		return aart < bart
+	}
+
+	// otherwise sort by name
+	return a.Sym.Name < b.Sym.Name
+}
+
+// byNodeName implements sort.Interface for []*Node using cmpNodeName.
+type byNodeName []*Node
+
+func (s byNodeName) Len() int           { return len(s) }
+func (s byNodeName) Less(i, j int) bool { return cmpNodeName(s[i], s[j]) }
+func (s byNodeName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

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

@@ -48,6 +48,7 @@ var (
 	Debug_pctab        string
 	Debug_locationlist int
 	Debug_typecheckinl int
+	Debug_gendwarfinl  int
 )
 
 // Debug arguments.
@@ -76,6 +77,7 @@ var debugtab = []struct {
 	{"pctab", "print named pc-value table", &Debug_pctab},
 	{"locationlists", "print information about DWARF location list creation", &Debug_locationlist},
 	{"typecheckinl", "eager typechecking of inline function bodies", &Debug_typecheckinl},
+	{"dwarfinl", "print information about DWARF inlined function creation", &Debug_gendwarfinl},
 }
 
 const debugHelpHeader = `usage: -d arg[,arg]* and arg is <key>[=<value>]
@@ -191,6 +193,7 @@ func Main(archInit func(*Arch)) {
 	flag.StringVar(&debugstr, "d", "", "print debug information about items in `list`; try -d help")
 	flag.BoolVar(&flagDWARF, "dwarf", true, "generate DWARF symbols")
 	flag.BoolVar(&Ctxt.Flag_locationlists, "dwarflocationlists", false, "add location lists to DWARF in optimized mode")
+	flag.IntVar(&genDwarfInline, "gendwarfinl", 2, "generate DWARF inline info records")
 	objabi.Flagcount("e", "no limit on number of errors reported", &Debug['e'])
 	objabi.Flagcount("f", "debug stack frames", &Debug['f'])
 	objabi.Flagcount("h", "halt on error", &Debug['h'])
@@ -247,6 +250,11 @@ func Main(archInit func(*Arch)) {
 	Ctxt.Debugvlog = Debug_vlog
 	if flagDWARF {
 		Ctxt.DebugInfo = debuginfo
+		Ctxt.GenAbstractFunc = genAbstractFunc
+		Ctxt.DwFixups = obj.NewDwarfFixupTable(Ctxt)
+	} else {
+		// turn off inline generation if no dwarf at all
+		genDwarfInline = 0
 	}
 
 	if flag.NArg() < 1 && debugstr != "help" && debugstr != "ssa/help" {
@@ -381,6 +389,9 @@ func Main(archInit func(*Arch)) {
 
 	// set via a -d flag
 	Ctxt.Debugpcln = Debug_pctab
+	if flagDWARF {
+		dwarf.EnableLogging(Debug_gendwarfinl != 0)
+	}
 
 	// enable inlining.  for now:
 	//	default: inlining on.  (debug['l'] == 1)
@@ -631,6 +642,15 @@ func Main(archInit func(*Arch)) {
 			nowritebarrierrecCheck = nil
 		}
 
+		// Finalize DWARF inline routine DIEs, then explicitly turn off
+		// DWARF inlining gen so as to avoid problems with generated
+		// method wrappers.
+		if Ctxt.DwFixups != nil {
+			Ctxt.DwFixups.Finalize(myimportpath, Debug_gendwarfinl != 0)
+			Ctxt.DwFixups = nil
+			genDwarfInline = 0
+		}
+
 		// Check whether any of the functions we have compiled have gigantic stack frames.
 		obj.SortSlice(largeStackFrames, func(i, j int) bool {
 			return largeStackFrames[i].Before(largeStackFrames[j])

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

@@ -16,6 +16,7 @@ import (
 	"math"
 	"math/rand"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 )
@@ -279,6 +280,7 @@ func compileFunctions() {
 			})
 		}
 		var wg sync.WaitGroup
+		Ctxt.InParallel = true
 		c := make(chan *Node, nBackendWorkers)
 		for i := 0; i < nBackendWorkers; i++ {
 			wg.Add(1)
@@ -295,16 +297,19 @@ func compileFunctions() {
 		close(c)
 		compilequeue = nil
 		wg.Wait()
+		Ctxt.InParallel = false
 		sizeCalculationDisabled = false
 	}
 }
 
-func debuginfo(fnsym *obj.LSym, curfn interface{}) []dwarf.Scope {
+func debuginfo(fnsym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) {
 	fn := curfn.(*Node)
 	debugInfo := fn.Func.DebugInfo
 	fn.Func.DebugInfo = nil
-	if expect := fn.Func.Nname.Sym.Linksym(); fnsym != expect {
-		Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
+	if fn.Func.Nname != nil {
+		if expect := fn.Func.Nname.Sym.Linksym(); fnsym != expect {
+			Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
+		}
 	}
 
 	var automDecls []*Node
@@ -335,13 +340,7 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) []dwarf.Scope {
 		})
 	}
 
-	var dwarfVars []*dwarf.Var
-	var decls []*Node
-	if Ctxt.Flag_locationlists && Ctxt.Flag_optimize {
-		decls, dwarfVars = createComplexVars(fnsym, debugInfo, automDecls)
-	} else {
-		decls, dwarfVars = createSimpleVars(automDecls)
-	}
+	decls, dwarfVars := createDwarfVars(fnsym, debugInfo, automDecls)
 
 	var varScopes []ScopeID
 	for _, decl := range decls {
@@ -365,14 +364,21 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) []dwarf.Scope {
 		}
 		varScopes = append(varScopes, findScope(fn.Func.Marks, pos))
 	}
-	return assembleScopes(fnsym, fn, dwarfVars, varScopes)
+
+	scopes := assembleScopes(fnsym, fn, dwarfVars, varScopes)
+	var inlcalls dwarf.InlCalls
+	if genDwarfInline > 0 {
+		inlcalls = assembleInlines(fnsym, fn, dwarfVars)
+	}
+	return scopes, inlcalls
 }
 
 // createSimpleVars creates a DWARF entry for every variable declared in the
 // function, claiming that they are permanently on the stack.
-func createSimpleVars(automDecls []*Node) ([]*Node, []*dwarf.Var) {
+func createSimpleVars(automDecls []*Node) ([]*Node, []*dwarf.Var, map[*Node]bool) {
 	var vars []*dwarf.Var
 	var decls []*Node
+	selected := make(map[*Node]bool)
 	for _, n := range automDecls {
 		if n.IsAutoTmp() {
 			continue
@@ -397,18 +403,31 @@ func createSimpleVars(automDecls []*Node) ([]*Node, []*dwarf.Var) {
 			Fatalf("createSimpleVars unexpected type %v for node %v", n.Class(), n)
 		}
 
+		selected[n] = true
 		typename := dwarf.InfoPrefix + typesymname(n.Type)
 		decls = append(decls, n)
+		inlIndex := 0
+		if genDwarfInline > 1 {
+			if n.InlFormal() || n.InlLocal() {
+				inlIndex = posInlIndex(n.Pos) + 1
+			}
+		}
+		declpos := Ctxt.InnermostPos(n.Pos)
 		vars = append(vars, &dwarf.Var{
 			Name:          n.Sym.Name,
 			IsReturnValue: n.Class() == PPARAMOUT,
+			IsInlFormal:   n.InlFormal(),
 			Abbrev:        abbrev,
 			StackOffset:   int32(offs),
 			Type:          Ctxt.Lookup(typename),
-			DeclLine:      n.Pos.Line(),
+			DeclFile:      declpos.Base().SymFilename(),
+			DeclLine:      declpos.Line(),
+			DeclCol:       declpos.Col(),
+			InlIndex:      int32(inlIndex),
+			ChildIndex:    -1,
 		})
 	}
-	return decls, vars
+	return decls, vars, selected
 }
 
 type varPart struct {
@@ -416,7 +435,7 @@ type varPart struct {
 	slot      ssa.SlotID
 }
 
-func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*Node) ([]*Node, []*dwarf.Var) {
+func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*Node) ([]*Node, []*dwarf.Var, map[*Node]bool) {
 	for _, blockDebug := range debugInfo.Blocks {
 		for _, locList := range blockDebug.Variables {
 			for _, loc := range locList.Locations {
@@ -475,20 +494,43 @@ func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*
 		}
 	}
 
-	// The machinery above will create a dwarf.Var for only those
-	// variables that are decomposed into SSA names. Fill in the list
-	// with entries for the remaining variables (including things too
-	// big to decompose). Since optimization is enabled, the recipe
-	// below creates a conservative location. The idea here is that we
-	// want to communicate to the user that "yes, there is a variable
-	// named X in this function, but no, I don't have enough
-	// information to reliably report its contents."
-	for _, n := range automDecls {
-		if _, found := ssaVars[n]; found {
+	return decls, vars, ssaVars
+}
+
+func createDwarfVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*Node) ([]*Node, []*dwarf.Var) {
+	// Collect a raw list of DWARF vars.
+	var vars []*dwarf.Var
+	var decls []*Node
+	var selected map[*Node]bool
+	if Ctxt.Flag_locationlists && Ctxt.Flag_optimize && debugInfo != nil {
+		decls, vars, selected = createComplexVars(fnsym, debugInfo, automDecls)
+	} else {
+		decls, vars, selected = createSimpleVars(automDecls)
+	}
+
+	var dcl []*Node
+	var chopVersion bool
+	if fnsym.WasInlined() {
+		dcl, chopVersion = preInliningDcls(fnsym)
+	} else {
+		dcl = automDecls
+	}
+
+	// If optimization is enabled, the list above will typically be
+	// missing some of the original pre-optimization variables in the
+	// function (they may have been promoted to registers, folded into
+	// constants, dead-coded away, etc). Here we add back in entries
+	// for selected missing vars. Note that the recipe below creates a
+	// conservative location. The idea here is that we want to
+	// communicate to the user that "yes, there is a variable named X
+	// in this function, but no, I don't have enough information to
+	// reliably report its contents."
+	for _, n := range dcl {
+		if _, found := selected[n]; found {
 			continue
 		}
 		c := n.Sym.Name[0]
-		if c == '~' || c == '.' {
+		if c == '~' || c == '.' || n.Type.IsUntyped() {
 			continue
 		}
 		typename := dwarf.InfoPrefix + typesymname(n.Type)
@@ -497,19 +539,70 @@ func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*
 		if n.Class() == PPARAM || n.Class() == PPARAMOUT {
 			abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
 		}
+		inlIndex := 0
+		if genDwarfInline > 1 {
+			if n.InlFormal() || n.InlLocal() {
+				inlIndex = posInlIndex(n.Pos) + 1
+			}
+		}
+		declpos := Ctxt.InnermostPos(n.Pos)
 		vars = append(vars, &dwarf.Var{
 			Name:          n.Sym.Name,
 			IsReturnValue: n.Class() == PPARAMOUT,
 			Abbrev:        abbrev,
 			StackOffset:   int32(n.Xoffset),
 			Type:          Ctxt.Lookup(typename),
-			DeclLine:      n.Pos.Line(),
+			DeclFile:      declpos.Base().SymFilename(),
+			DeclLine:      declpos.Line(),
+			DeclCol:       declpos.Col(),
+			InlIndex:      int32(inlIndex),
+			ChildIndex:    -1,
 		})
 	}
 
+	// Parameter and local variable names are given middle dot
+	// version numbers as part of the writing them out to export
+	// data (see issue 4326).  If DWARF inlined routine generation
+	// is turned on, undo this versioning, since DWARF variables
+	// in question will be parented by the inlined routine and
+	// not the top-level caller.
+	if genDwarfInline > 1 && chopVersion {
+		for _, v := range vars {
+			if v.InlIndex != -1 {
+				if i := strings.Index(v.Name, "·"); i > 0 {
+					v.Name = v.Name[:i] // cut off Vargen
+				}
+			}
+		}
+	}
+
 	return decls, vars
 }
 
+// Given a function that was inlined at some point during the compilation,
+// return a list of nodes corresponding to the autos/locals in that
+// function prior to inlining. Untyped and compiler-synthesized vars are
+// stripped out along the way.
+func preInliningDcls(fnsym *obj.LSym) ([]*Node, bool) {
+	fn := Ctxt.DwFixups.GetPrecursorFunc(fnsym).(*Node)
+	imported := false
+	var dcl, rdcl []*Node
+	if fn.Name.Defn != nil {
+		dcl = fn.Func.Inldcl.Slice() // local function
+	} else {
+		dcl = fn.Func.Dcl // imported function
+		imported = true
+	}
+	for _, n := range dcl {
+		c := n.Sym.Name[0]
+		if c == '~' || c == '.' || n.Type.IsUntyped() {
+			continue
+		}
+		rdcl = append(rdcl, n)
+	}
+	return rdcl, imported
+}
+
 // varOffset returns the offset of slot within the user variable it was
 // decomposed from. This has nothing to do with its stack offset.
 func varOffset(slot *ssa.LocalSlot) int64 {
@@ -570,16 +663,29 @@ func createComplexVar(debugInfo *ssa.FuncDebug, n *Node, parts []varPart) *dwarf
 
 	gotype := ngotype(n).Linksym()
 	typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
+	inlIndex := 0
+	if genDwarfInline > 1 {
+		if n.InlFormal() || n.InlLocal() {
+			inlIndex = posInlIndex(n.Pos) + 1
+		}
+	}
+	declpos := Ctxt.InnermostPos(n.Pos)
 	dvar := &dwarf.Var{
-		Name:   n.Sym.Name,
-		Abbrev: abbrev,
-		Type:   Ctxt.Lookup(typename),
+		Name:          n.Sym.Name,
+		IsReturnValue: n.Class() == PPARAMOUT,
+		IsInlFormal:   n.InlFormal(),
+		Abbrev:        abbrev,
+		Type:          Ctxt.Lookup(typename),
 		// The stack offset is used as a sorting key, so for decomposed
 		// variables just give it the lowest one. It's not used otherwise.
 		// This won't work well if the first slot hasn't been assigned a stack
 		// location, but it's not obvious how to do better.
 		StackOffset: int32(stackOffset(slots[parts[0].slot])),
-		DeclLine:    n.Pos.Line(),
+		DeclFile:    declpos.Base().SymFilename(),
+		DeclLine:    declpos.Line(),
+		DeclCol:     declpos.Col(),
+		InlIndex:    int32(inlIndex),
+		ChildIndex:  -1,
 	}
 
 	if Debug_locationlist != 0 {

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

@@ -85,18 +85,20 @@ const (
 	_, nodeAssigned  // is the variable ever assigned to
 	_, nodeAddrtaken // address taken, even if not moved to heap
 	_, nodeImplicit
-	_, nodeIsddd    // is the argument variadic
-	_, nodeDiag     // already printed error about this
-	_, nodeColas    // OAS resulting from :=
-	_, nodeNonNil   // guaranteed to be non-nil
-	_, nodeNoescape // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
-	_, nodeBounded  // bounds check unnecessary
-	_, nodeAddable  // addressable
-	_, nodeHasCall  // expression contains a function call
-	_, nodeLikely   // if statement condition likely
-	_, nodeHasVal   // node.E contains a Val
-	_, nodeHasOpt   // node.E contains an Opt
-	_, nodeEmbedded // ODCLFIELD embedded type
+	_, nodeIsddd     // is the argument variadic
+	_, nodeDiag      // already printed error about this
+	_, nodeColas     // OAS resulting from :=
+	_, nodeNonNil    // guaranteed to be non-nil
+	_, nodeNoescape  // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
+	_, nodeBounded   // bounds check unnecessary
+	_, nodeAddable   // addressable
+	_, nodeHasCall   // expression contains a function call
+	_, nodeLikely    // if statement condition likely
+	_, nodeHasVal    // node.E contains a Val
+	_, nodeHasOpt    // node.E contains an Opt
+	_, nodeEmbedded  // ODCLFIELD embedded type
+	_, nodeInlFormal // OPAUTO created by inliner, derived from callee formal
+	_, nodeInlLocal  // OPAUTO created by inliner, derived from callee local
 )
 
 func (n *Node) Class() Class     { return Class(n.flags.get3(nodeClass)) }
@@ -123,6 +125,8 @@ func (n *Node) Likely() bool                { return n.flags&nodeLikely != 0 }
 func (n *Node) HasVal() bool                { return n.flags&nodeHasVal != 0 }
 func (n *Node) HasOpt() bool                { return n.flags&nodeHasOpt != 0 }
 func (n *Node) Embedded() bool              { return n.flags&nodeEmbedded != 0 }
+func (n *Node) InlFormal() bool             { return n.flags&nodeInlFormal != 0 }
+func (n *Node) InlLocal() bool              { return n.flags&nodeInlLocal != 0 }
 
 func (n *Node) SetClass(b Class)     { n.flags.set3(nodeClass, uint8(b)) }
 func (n *Node) SetWalkdef(b uint8)   { n.flags.set2(nodeWalkdef, b) }
@@ -148,6 +152,8 @@ func (n *Node) SetLikely(b bool)                { n.flags.set(nodeLikely, b) }
 func (n *Node) SetHasVal(b bool)                { n.flags.set(nodeHasVal, b) }
 func (n *Node) SetHasOpt(b bool)                { n.flags.set(nodeHasOpt, b) }
 func (n *Node) SetEmbedded(b bool)              { n.flags.set(nodeEmbedded, b) }
+func (n *Node) SetInlFormal(b bool)             { n.flags.set(nodeInlFormal, b) }
+func (n *Node) SetInlLocal(b bool)              { n.flags.set(nodeInlLocal, b) }
 
 // Val returns the Val for the node.
 func (n *Node) Val() Val {

src/cmd/internal/obj/inl.go

@@ -6,7 +6,7 @@ package obj
 
 import "cmd/internal/src"
 
-// InlTree s a collection of inlined calls. The Parent field of an
+// InlTree is a collection of inlined calls. The Parent field of an
 // InlinedCall is the index of another InlinedCall in InlTree.
 //
 // The compiler maintains a global inlining tree and adds a node to it
@@ -64,6 +64,18 @@ func (tree *InlTree) Add(parent int, pos src.XPos, func_ *LSym) int {
 	return r
 }
 
+func (tree *InlTree) Parent(inlIndex int) int {
+	return tree.nodes[inlIndex].Parent
+}
+
+func (tree *InlTree) InlinedFunction(inlIndex int) *LSym {
+	return tree.nodes[inlIndex].Func
+}
+
+func (tree *InlTree) CallPos(inlIndex int) src.XPos {
+	return tree.nodes[inlIndex].Pos
+}
+
 // 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

src/cmd/internal/obj/link.go

@@ -389,6 +389,7 @@ type FuncInfo struct {
 	dwarfInfoSym   *LSym
 	dwarfLocSym    *LSym
 	dwarfRangesSym *LSym
+	dwarfAbsFnSym  *LSym
 
 	GCArgs   LSym
 	GCLocals LSym
@@ -427,6 +428,10 @@ const (
 	// definition. (When not compiling to support Go shared libraries, all symbols are
 	// local in this sense unless there is a cgo_export_* directive).
 	AttrLocal
+
+	// For function symbols; indicates that the specified function was the
+	// target of an inline during compilation
+	AttrWasInlined
 )
 
 func (a Attribute) DuplicateOK() bool   { return a&AttrDuplicateOK != 0 }
@@ -442,6 +447,7 @@ func (a Attribute) Wrapper() bool       { return a&AttrWrapper != 0 }
 func (a Attribute) NeedCtxt() bool      { return a&AttrNeedCtxt != 0 }
 func (a Attribute) NoFrame() bool       { return a&AttrNoFrame != 0 }
 func (a Attribute) Static() bool        { return a&AttrStatic != 0 }
+func (a Attribute) WasInlined() bool    { return a&AttrWasInlined != 0 }
 
 func (a *Attribute) Set(flag Attribute, value bool) {
 	if value {
@@ -468,6 +474,7 @@ var textAttrStrings = [...]struct {
 	{bit: AttrNeedCtxt, s: "NEEDCTXT"},
 	{bit: AttrNoFrame, s: "NOFRAME"},
 	{bit: AttrStatic, s: "STATIC"},
+	{bit: AttrWasInlined, s: ""},
 }
 
 // TextAttrString formats a for printing in as part of a TEXT prog.
@@ -549,12 +556,15 @@ type Link struct {
 	statichash         map[string]*LSym // name -> sym mapping for static syms
 	PosTable           src.PosTable
 	InlTree            InlTree // global inlining tree used by gc/inl.go
+	DwFixups           *DwarfFixupTable
 	Imports            []string
 	DiagFunc           func(string, ...interface{})
 	DiagFlush          func()
-	DebugInfo          func(fn *LSym, curfn interface{}) []dwarf.Scope // if non-nil, curfn is a *gc.Node
+	DebugInfo          func(fn *LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) // if non-nil, curfn is a *gc.Node
+	GenAbstractFunc    func(fn *LSym)
 	Errors             int
 
+	InParallel           bool // parallel backend phase in effect
 	Framepointer_enabled bool
 
 	// state for writing objects

src/cmd/internal/obj/plist.go

@@ -19,7 +19,7 @@ type Plist struct {
 // It is used to provide access to cached/bulk-allocated Progs to the assemblers.
 type ProgAlloc func() *Prog
 
-func Flushplist(ctxt *Link, plist *Plist, newprog ProgAlloc) {
+func Flushplist(ctxt *Link, plist *Plist, newprog ProgAlloc, myimportpath string) {
 	// Build list of symbols, and assign instructions to lists.
 	var curtext *LSym
 	var etext *Prog
@@ -106,7 +106,7 @@ func Flushplist(ctxt *Link, plist *Plist, newprog ProgAlloc) {
 		ctxt.Arch.Preprocess(ctxt, s, newprog)
 		ctxt.Arch.Assemble(ctxt, s, newprog)
 		linkpcln(ctxt, s)
-		ctxt.populateDWARF(plist.Curfn, s)
+		ctxt.populateDWARF(plist.Curfn, s, myimportpath)
 	}
 }
 
@@ -136,7 +136,7 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int) {
 	ctxt.Text = append(ctxt.Text, s)
 
 	// Set up DWARF entries for s.
-	info, loc, ranges := ctxt.dwarfSym(s)
+	info, loc, ranges, _ := ctxt.dwarfSym(s)
 	info.Type = objabi.SDWARFINFO
 	info.Set(AttrDuplicateOK, s.DuplicateOK())
 	if loc != nil {

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

@@ -72,10 +72,28 @@ func (c dwctxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64
 	r.Add = ofs
 }
 
+func (c dwctxt) Logf(format string, args ...interface{}) {
+	c.linkctxt.Logf(format, args...)
+}
+
+// At the moment these interfaces are only used in the compiler.
+
 func (c dwctxt) AddFileRef(s dwarf.Sym, f interface{}) {
 	panic("should be used only in the compiler")
 }
 
+func (c dwctxt) CurrentOffset(s dwarf.Sym) int64 {
+	panic("should be used only in the compiler")
+}
+
+func (c dwctxt) RecordDclReference(s dwarf.Sym, t dwarf.Sym, dclIdx int, inlIndex int) {
+	panic("should be used only in the compiler")
+}
+
+func (c dwctxt) RecordChildDieOffsets(s dwarf.Sym, vars []*dwarf.Var, offsets []int32) {
+	panic("should be used only in the compiler")
+}
+
 var gdbscript string
 
 var dwarfp []*sym.Symbol
@@ -132,8 +150,10 @@ func getattr(die *dwarf.DWDie, attr uint16) *dwarf.DWAttr {
 	return nil
 }
 
-// Every DIE has at least an AT_name attribute (but it will only be
-// written out if it is listed in the abbrev).
+// Every DIE manufactured by the linker has at least an AT_name
+// attribute (but it will only be written out if it is listed in the abbrev).
+// The compiler does create nameless DWARF DIEs (ex: concrete subprogram
+// instance).
 func newdie(ctxt *Link, parent *dwarf.DWDie, abbrev int, name string, version int) *dwarf.DWDie {
 	die := new(dwarf.DWDie)
 	die.Abbrev = abbrev
@@ -849,11 +869,12 @@ func defdwsymb(ctxt *Link, s *sym.Symbol, str string, t SymbolType, v int64, got
 // compilationUnit is per-compilation unit (equivalently, per-package)
 // debug-related data.
 type compilationUnit struct {
-	lib      *sym.Library
-	consts   *sym.Symbol   // Package constants DIEs
-	pcs      []dwarf.Range // PC ranges, relative to textp[0]
-	dwinfo   *dwarf.DWDie  // CU root DIE
-	funcDIEs []*sym.Symbol // Function DIE subtrees
+	lib       *sym.Library
+	consts    *sym.Symbol   // Package constants DIEs
+	pcs       []dwarf.Range // PC ranges, relative to textp[0]
+	dwinfo    *dwarf.DWDie  // CU root DIE
+	funcDIEs  []*sym.Symbol // Function DIE subtrees
+	absFnDIEs []*sym.Symbol // Abstract function DIE subtrees
 }
 
 // getCompilationUnits divides the symbols in ctxt.Textp by package.
@@ -1052,7 +1073,52 @@ func importInfoSymbol(ctxt *Link, dsym *sym.Symbol) {
 	}
 }
 
-func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbol) (dwinfo *dwarf.DWDie, funcs []*sym.Symbol) {
+// For the specified function, collect symbols corresponding to any
+// "abstract" subprogram DIEs referenced. The first case of interest
+// is a concrete subprogram DIE, which will refer to its corresponding
+// abstract subprogram DIE, and then there can be references from a
+// non-abstract subprogram DIE to the abstract subprogram DIEs for any
+// functions inlined into this one.
+//
+// A given abstract subprogram DIE can be referenced in numerous
+// places (even within the same DIE), so it is important to make sure
+// it gets imported and added to the absfuncs lists only once.
+
+func collectAbstractFunctions(ctxt *Link, fn *sym.Symbol, dsym *sym.Symbol, absfuncs []*sym.Symbol) []*sym.Symbol {
+
+	var newabsfns []*sym.Symbol
+
+	// Walk the relocations on the primary subprogram DIE and look for
+	// references to abstract funcs.
+	for _, reloc := range dsym.R {
+		candsym := reloc.Sym
+		if reloc.Type != objabi.R_DWARFSECREF {
+			continue
+		}
+		if !strings.HasPrefix(candsym.Name, dwarf.InfoPrefix) {
+			continue
+		}
+		if !strings.HasSuffix(candsym.Name, dwarf.AbstractFuncSuffix) {
+			continue
+		}
+		if candsym.Attr.OnList() {
+			continue
+		}
+		candsym.Attr |= sym.AttrOnList
+		newabsfns = append(newabsfns, candsym)
+	}
+
+	// Import any new symbols that have turned up.
+	for _, absdsym := range newabsfns {
+		importInfoSymbol(ctxt, absdsym)
+		absfuncs = append(absfuncs, absdsym)
+	}
+
+	return absfuncs
+}
+
+func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbol) (dwinfo *dwarf.DWDie, funcs []*sym.Symbol, absfuncs []*sym.Symbol) {
+
 	var dwarfctxt dwarf.Context = dwctxt{ctxt}
 
 	unitstart := int64(-1)
@@ -1125,6 +1191,27 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
 			ls.AddUint8(0)
 			ls.AddUint8(0)
 		}
+
+		// Look up the .debug_info sym for the function. We do this
+		// now so that we can walk the sym's relocations to discover
+		// files that aren't mentioned in S.FuncInfo.File (for
+		// example, files mentioned only in an inlined subroutine).
+		dsym := ctxt.Syms.Lookup(dwarf.InfoPrefix+s.Name, int(s.Version))
+		importInfoSymbol(ctxt, dsym)
+		for ri := 0; ri < len(dsym.R); ri++ {
+			r := &dsym.R[ri]
+			if r.Type != objabi.R_DWARFFILEREF {
+				continue
+			}
+			_, ok := fileNums[int(r.Sym.Value)]
+			if !ok {
+				fileNums[int(r.Sym.Value)] = len(fileNums) + 1
+				Addstring(ls, r.Sym.Name)
+				ls.AddUint8(0)
+				ls.AddUint8(0)
+				ls.AddUint8(0)
+			}
+		}
 	}
 
 	// 4 zeros: the string termination + 3 fields.
@@ -1146,8 +1233,8 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
 	var pcline Pciter
 	for _, s := range textp {
 		dsym := ctxt.Syms.Lookup(dwarf.InfoPrefix+s.Name, int(s.Version))
-		importInfoSymbol(ctxt, dsym)
 		funcs = append(funcs, dsym)
+		absfuncs = collectAbstractFunctions(ctxt, s, dsym, absfuncs)
 
 		finddebugruntimepath(s)
 
@@ -1201,6 +1288,7 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
 	// changed to generate DW_AT_decl_file attributes for other
 	// DIE flavors (ex: variables) then those DIEs would need to
 	// be included below.
+	missing := make(map[int]interface{})
 	for fidx := 0; fidx < len(funcs); fidx++ {
 		f := funcs[fidx]
 		for ri := 0; ri < len(f.R); ri++ {
@@ -1224,12 +1312,16 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
 				}
 				ctxt.Arch.ByteOrder.PutUint32(f.P[r.Off:r.Off+4], uint32(idx))
 			} else {
-				Errorf(f, "R_DWARFFILEREF relocation file missing: %v", r.Sym)
+				_, found := missing[int(r.Sym.Value)]
+				if !found {
+					Errorf(f, "R_DWARFFILEREF relocation file missing: %v idx %d", r.Sym, r.Sym.Value)
+					missing[int(r.Sym.Value)] = nil
+				}
 			}
 		}
 	}
 
-	return dwinfo, funcs
+	return dwinfo, funcs, absfuncs
 }
 
 // writepcranges generates the DW_AT_ranges table for compilation unit cu.
@@ -1434,6 +1526,7 @@ func writeinfo(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit, abbrevs
 		dwarf.PutAttrs(dwarfctxt, s, compunit.Abbrev, compunit.Attr)
 
 		cu := []*sym.Symbol{s}
+		cu = append(cu, u.absFnDIEs...)
 		cu = append(cu, u.funcDIEs...)
 		if u.consts != nil {
 			cu = append(cu, u.consts)
@@ -1621,7 +1714,7 @@ func dwarfgeneratedebugsyms(ctxt *Link) {
 	debugRanges.Attr |= sym.AttrReachable
 	syms = append(syms, debugLine)
 	for _, u := range units {
-		u.dwinfo, u.funcDIEs = writelines(ctxt, u.lib, u.lib.Textp, debugLine)
+		u.dwinfo, u.funcDIEs, u.absFnDIEs = writelines(ctxt, u.lib, u.lib.Textp, debugLine)
 		writepcranges(ctxt, u.dwinfo, u.lib.Textp[0], u.pcs, debugRanges)
 	}
 

src/runtime/runtime-gdb_test.go

@@ -218,7 +218,7 @@ func testGdbPython(t *testing.T, cgo bool) {
 	// a collection of scalar vars holding the fields. In such cases
 	// the DWARF variable location expression should be of the
 	// form "var.field" and not just "field".
-	infoLocalsRe := regexp.MustCompile(`^slicevar.len = `)
+	infoLocalsRe := regexp.MustCompile(`.*\sslicevar.cap = `)
 	if bl := blocks["info locals"]; !infoLocalsRe.MatchString(bl) {
 		t.Fatalf("info locals failed: %s", bl)
 	}