Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 692 insertions, 0 deletions

diff --git a/src/cmd/internal/obj/dwarf.go b/src/cmd/internal/obj/dwarf.go
new file mode 100644
index 0000000..87c62e2
--- /dev/null
+++ b/src/cmd/internal/obj/dwarf.go
@@ -0,0 +1,692 @@
+// Copyright 2019 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.
+
+// Writes dwarf information to object files.
+
+package obj
+
+import (
+	"cmd/internal/dwarf"
+	"cmd/internal/objabi"
+	"cmd/internal/src"
+	"fmt"
+	"sort"
+	"sync"
+)
+
+// Generate a sequence of opcodes that is as short as possible.
+// See section 6.2.5
+const (
+	LINE_BASE   = -4
+	LINE_RANGE  = 10
+	PC_RANGE    = (255 - OPCODE_BASE) / LINE_RANGE
+	OPCODE_BASE = 11
+)
+
+// generateDebugLinesSymbol fills the debug lines symbol of a given function.
+//
+// It's worth noting that this function doesn't generate the full debug_lines
+// DWARF section, saving that for the linker. This function just generates the
+// state machine part of debug_lines. The full table is generated by the
+// linker.  Also, we use the file numbers from the full package (not just the
+// function in question) when generating the state machine. We do this so we
+// don't have to do a fixup on the indices when writing the full section.
+func (ctxt *Link) generateDebugLinesSymbol(s, lines *LSym) {
+	dctxt := dwCtxt{ctxt}
+
+	// Emit a LNE_set_address extended opcode, so as to establish the
+	// starting text address of this function.
+	dctxt.AddUint8(lines, 0)
+	dwarf.Uleb128put(dctxt, lines, 1+int64(ctxt.Arch.PtrSize))
+	dctxt.AddUint8(lines, dwarf.DW_LNE_set_address)
+	dctxt.AddAddress(lines, s, 0)
+
+	// Set up the debug_lines state machine to the default values
+	// we expect at the start of a new sequence.
+	stmt := true
+	line := int64(1)
+	pc := s.Func().Text.Pc
+	var lastpc int64 // last PC written to line table, not last PC in func
+	name := ""
+	prologue, wrotePrologue := false, false
+	// Walk the progs, generating the DWARF table.
+	for p := s.Func().Text; p != nil; p = p.Link {
+		prologue = prologue || (p.Pos.Xlogue() == src.PosPrologueEnd)
+		// If we're not at a real instruction, keep looping!
+		if p.Pos.Line() == 0 || (p.Link != nil && p.Link.Pc == p.Pc) {
+			continue
+		}
+		newStmt := p.Pos.IsStmt() != src.PosNotStmt
+		newName, newLine := linkgetlineFromPos(ctxt, p.Pos)
+
+		// Output debug info.
+		wrote := false
+		if name != newName {
+			newFile := ctxt.PosTable.FileIndex(newName) + 1 // 1 indexing for the table.
+			dctxt.AddUint8(lines, dwarf.DW_LNS_set_file)
+			dwarf.Uleb128put(dctxt, lines, int64(newFile))
+			name = newName
+			wrote = true
+		}
+		if prologue && !wrotePrologue {
+			dctxt.AddUint8(lines, uint8(dwarf.DW_LNS_set_prologue_end))
+			wrotePrologue = true
+			wrote = true
+		}
+		if stmt != newStmt {
+			dctxt.AddUint8(lines, uint8(dwarf.DW_LNS_negate_stmt))
+			stmt = newStmt
+			wrote = true
+		}
+
+		if line != int64(newLine) || wrote {
+			pcdelta := p.Pc - pc
+			lastpc = p.Pc
+			putpclcdelta(ctxt, dctxt, lines, uint64(pcdelta), int64(newLine)-line)
+			line, pc = int64(newLine), p.Pc
+		}
+	}
+
+	// Because these symbols will be concatenated together by the
+	// linker, we need to reset the state machine that controls the
+	// debug symbols. Do this using an end-of-sequence operator.
+	//
+	// Note: at one point in time, Delve did not support multiple end
+	// sequence ops within a compilation unit (bug for this:
+	// https://github.com/go-delve/delve/issues/1694), however the bug
+	// has since been fixed (Oct 2019).
+	//
+	// Issue 38192: the DWARF standard specifies that when you issue
+	// an end-sequence op, the PC value should be one past the last
+	// text address in the translation unit, so apply a delta to the
+	// text address before the end sequence op. If this isn't done,
+	// GDB will assign a line number of zero the last row in the line
+	// table, which we don't want.
+	lastlen := uint64(s.Size - (lastpc - s.Func().Text.Pc))
+	dctxt.AddUint8(lines, dwarf.DW_LNS_advance_pc)
+	dwarf.Uleb128put(dctxt, lines, int64(lastlen))
+	dctxt.AddUint8(lines, 0) // start extended opcode
+	dwarf.Uleb128put(dctxt, lines, 1)
+	dctxt.AddUint8(lines, dwarf.DW_LNE_end_sequence)
+}
+
+func putpclcdelta(linkctxt *Link, dctxt dwCtxt, s *LSym, deltaPC uint64, deltaLC int64) {
+	// Choose a special opcode that minimizes the number of bytes needed to
+	// encode the remaining PC delta and LC delta.
+	var opcode int64
+	if deltaLC < LINE_BASE {
+		if deltaPC >= PC_RANGE {
+			opcode = OPCODE_BASE + (LINE_RANGE * PC_RANGE)
+		} else {
+			opcode = OPCODE_BASE + (LINE_RANGE * int64(deltaPC))
+		}
+	} else if deltaLC < LINE_BASE+LINE_RANGE {
+		if deltaPC >= PC_RANGE {
+			opcode = OPCODE_BASE + (deltaLC - LINE_BASE) + (LINE_RANGE * PC_RANGE)
+			if opcode > 255 {
+				opcode -= LINE_RANGE
+			}
+		} else {
+			opcode = OPCODE_BASE + (deltaLC - LINE_BASE) + (LINE_RANGE * int64(deltaPC))
+		}
+	} else {
+		if deltaPC <= PC_RANGE {
+			opcode = OPCODE_BASE + (LINE_RANGE - 1) + (LINE_RANGE * int64(deltaPC))
+			if opcode > 255 {
+				opcode = 255
+			}
+		} else {
+			// Use opcode 249 (pc+=23, lc+=5) or 255 (pc+=24, lc+=1).
+			//
+			// Let x=deltaPC-PC_RANGE.  If we use opcode 255, x will be the remaining
+			// deltaPC that we need to encode separately before emitting 255.  If we
+			// use opcode 249, we will need to encode x+1.  If x+1 takes one more
+			// byte to encode than x, then we use opcode 255.
+			//
+			// In all other cases x and x+1 take the same number of bytes to encode,
+			// so we use opcode 249, which may save us a byte in encoding deltaLC,
+			// for similar reasons.
+			switch deltaPC - PC_RANGE {
+			// PC_RANGE is the largest deltaPC we can encode in one byte, using
+			// DW_LNS_const_add_pc.
+			//
+			// (1<<16)-1 is the largest deltaPC we can encode in three bytes, using
+			// DW_LNS_fixed_advance_pc.
+			//
+			// (1<<(7n))-1 is the largest deltaPC we can encode in n+1 bytes for
+			// n=1,3,4,5,..., using DW_LNS_advance_pc.
+			case PC_RANGE, (1 << 7) - 1, (1 << 16) - 1, (1 << 21) - 1, (1 << 28) - 1,
+				(1 << 35) - 1, (1 << 42) - 1, (1 << 49) - 1, (1 << 56) - 1, (1 << 63) - 1:
+				opcode = 255
+			default:
+				opcode = OPCODE_BASE + LINE_RANGE*PC_RANGE - 1 // 249
+			}
+		}
+	}
+	if opcode < OPCODE_BASE || opcode > 255 {
+		panic(fmt.Sprintf("produced invalid special opcode %d", opcode))
+	}
+
+	// Subtract from deltaPC and deltaLC the amounts that the opcode will add.
+	deltaPC -= uint64((opcode - OPCODE_BASE) / LINE_RANGE)
+	deltaLC -= (opcode-OPCODE_BASE)%LINE_RANGE + LINE_BASE
+
+	// Encode deltaPC.
+	if deltaPC != 0 {
+		if deltaPC <= PC_RANGE {
+			// Adjust the opcode so that we can use the 1-byte DW_LNS_const_add_pc
+			// instruction.
+			opcode -= LINE_RANGE * int64(PC_RANGE-deltaPC)
+			if opcode < OPCODE_BASE {
+				panic(fmt.Sprintf("produced invalid special opcode %d", opcode))
+			}
+			dctxt.AddUint8(s, dwarf.DW_LNS_const_add_pc)
+		} else if (1<<14) <= deltaPC && deltaPC < (1<<16) {
+			dctxt.AddUint8(s, dwarf.DW_LNS_fixed_advance_pc)
+			dctxt.AddUint16(s, uint16(deltaPC))
+		} else {
+			dctxt.AddUint8(s, dwarf.DW_LNS_advance_pc)
+			dwarf.Uleb128put(dctxt, s, int64(deltaPC))
+		}
+	}
+
+	// Encode deltaLC.
+	if deltaLC != 0 {
+		dctxt.AddUint8(s, dwarf.DW_LNS_advance_line)
+		dwarf.Sleb128put(dctxt, s, deltaLC)
+	}
+
+	// Output the special opcode.
+	dctxt.AddUint8(s, uint8(opcode))
+}
+
+// implement dwarf.Context
+type dwCtxt struct{ *Link }
+
+func (c dwCtxt) PtrSize() int {
+	return c.Arch.PtrSize
+}
+func (c dwCtxt) AddInt(s dwarf.Sym, size int, i int64) {
+	ls := s.(*LSym)
+	ls.WriteInt(c.Link, ls.Size, size, i)
+}
+func (c dwCtxt) AddUint16(s dwarf.Sym, i uint16) {
+	c.AddInt(s, 2, int64(i))
+}
+func (c dwCtxt) AddUint8(s dwarf.Sym, i uint8) {
+	b := []byte{byte(i)}
+	c.AddBytes(s, b)
+}
+func (c dwCtxt) AddBytes(s dwarf.Sym, b []byte) {
+	ls := s.(*LSym)
+	ls.WriteBytes(c.Link, ls.Size, b)
+}
+func (c dwCtxt) AddString(s dwarf.Sym, v string) {
+	ls := s.(*LSym)
+	ls.WriteString(c.Link, ls.Size, len(v), v)
+	ls.WriteInt(c.Link, ls.Size, 1, 0)
+}
+func (c dwCtxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
+	ls := s.(*LSym)
+	size := c.PtrSize()
+	if data != nil {
+		rsym := data.(*LSym)
+		ls.WriteAddr(c.Link, ls.Size, size, rsym, value)
+	} else {
+		ls.WriteInt(c.Link, ls.Size, size, value)
+	}
+}
+func (c dwCtxt) AddCURelativeAddress(s dwarf.Sym, data interface{}, value int64) {
+	ls := s.(*LSym)
+	rsym := data.(*LSym)
+	ls.WriteCURelativeAddr(c.Link, ls.Size, rsym, value)
+}
+func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
+	panic("should be used only in the linker")
+}
+func (c dwCtxt) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64) {
+	size := 4
+	if isDwarf64(c.Link) {
+		size = 8
+	}
+
+	ls := s.(*LSym)
+	rsym := t.(*LSym)
+	ls.WriteAddr(c.Link, ls.Size, size, rsym, ofs)
+	r := &ls.R[len(ls.R)-1]
+	r.Type = objabi.R_DWARFSECREF
+}
+
+func (c dwCtxt) AddFileRef(s dwarf.Sym, f interface{}) {
+	ls := s.(*LSym)
+	rsym := f.(*LSym)
+	fidx := c.Link.PosTable.FileIndex(rsym.Name)
+	// Note the +1 here -- the value we're writing is going to be an
+	// index into the DWARF line table file section, whose entries
+	// are numbered starting at 1, not 0.
+	ls.WriteInt(c.Link, ls.Size, 4, int64(fidx+1))
+}
+
+func (c dwCtxt) CurrentOffset(s dwarf.Sym) int64 {
+	ls := s.(*LSym)
+	return ls.Size
+}
+
+// Here "from" is a symbol corresponding to an inlined or concrete
+// function, "to" is the symbol for the corresponding abstract
+// function, and "dclIdx" is the index of the symbol of interest with
+// respect to the Dcl slice of the original pre-optimization version
+// of the inlined function.
+func (c dwCtxt) RecordDclReference(from dwarf.Sym, to dwarf.Sym, dclIdx int, inlIndex int) {
+	ls := from.(*LSym)
+	tls := to.(*LSym)
+	ridx := len(ls.R) - 1
+	c.Link.DwFixups.ReferenceChildDIE(ls, ridx, tls, dclIdx, inlIndex)
+}
+
+func (c dwCtxt) RecordChildDieOffsets(s dwarf.Sym, vars []*dwarf.Var, offsets []int32) {
+	ls := s.(*LSym)
+	c.Link.DwFixups.RegisterChildDIEOffsets(ls, vars, offsets)
+}
+
+func (c dwCtxt) Logf(format string, args ...interface{}) {
+	c.Link.Logf(format, args...)
+}
+
+func isDwarf64(ctxt *Link) bool {
+	return ctxt.Headtype == objabi.Haix
+}
+
+func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym, dwarfDebugLines *LSym) {
+	if s.Type != objabi.STEXT {
+		ctxt.Diag("dwarfSym of non-TEXT %v", s)
+	}
+	fn := s.Func()
+	if fn.dwarfInfoSym == nil {
+		fn.dwarfInfoSym = &LSym{
+			Type: objabi.SDWARFFCN,
+		}
+		if ctxt.Flag_locationlists {
+			fn.dwarfLocSym = &LSym{
+				Type: objabi.SDWARFLOC,
+			}
+		}
+		fn.dwarfRangesSym = &LSym{
+			Type: objabi.SDWARFRANGE,
+		}
+		fn.dwarfDebugLinesSym = &LSym{
+			Type: objabi.SDWARFLINES,
+		}
+		if s.WasInlined() {
+			fn.dwarfAbsFnSym = ctxt.DwFixups.AbsFuncDwarfSym(s)
+		}
+	}
+	return fn.dwarfInfoSym, fn.dwarfLocSym, fn.dwarfRangesSym, fn.dwarfAbsFnSym, fn.dwarfDebugLinesSym
+}
+
+func (s *LSym) Length(dwarfContext interface{}) int64 {
+	return s.Size
+}
+
+// fileSymbol returns a symbol corresponding to the source file of the
+// first instruction (prog) of the specified function. This will
+// presumably be the file in which the function is defined.
+func (ctxt *Link) fileSymbol(fn *LSym) *LSym {
+	p := fn.Func().Text
+	if p != nil {
+		f, _ := linkgetlineFromPos(ctxt, p.Pos)
+		fsym := ctxt.Lookup(f)
+		return fsym
+	}
+	return nil
+}
+
+// populateDWARF fills in the DWARF Debugging Information Entries for
+// TEXT symbol 's'. The various DWARF symbols must already have been
+// initialized in InitTextSym.
+func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym, myimportpath string) {
+	info, loc, ranges, absfunc, lines := ctxt.dwarfSym(s)
+	if info.Size != 0 {
+		ctxt.Diag("makeFuncDebugEntry double process %v", s)
+	}
+	var scopes []dwarf.Scope
+	var inlcalls dwarf.InlCalls
+	if ctxt.DebugInfo != nil {
+		scopes, inlcalls = ctxt.DebugInfo(s, info, curfn)
+	}
+	var err error
+	dwctxt := dwCtxt{ctxt}
+	filesym := ctxt.fileSymbol(s)
+	fnstate := &dwarf.FnState{
+		Name:          s.Name,
+		Importpath:    myimportpath,
+		Info:          info,
+		Filesym:       filesym,
+		Loc:           loc,
+		Ranges:        ranges,
+		Absfn:         absfunc,
+		StartPC:       s,
+		Size:          s.Size,
+		External:      !s.Static(),
+		Scopes:        scopes,
+		InlCalls:      inlcalls,
+		UseBASEntries: ctxt.UseBASEntries,
+	}
+	if absfunc != nil {
+		err = dwarf.PutAbstractFunc(dwctxt, fnstate)
+		if err != nil {
+			ctxt.Diag("emitting DWARF for %s failed: %v", s.Name, err)
+		}
+		err = dwarf.PutConcreteFunc(dwctxt, fnstate)
+	} else {
+		err = dwarf.PutDefaultFunc(dwctxt, fnstate)
+	}
+	if err != nil {
+		ctxt.Diag("emitting DWARF for %s failed: %v", s.Name, err)
+	}
+	// Fill in the debug lines symbol.
+	ctxt.generateDebugLinesSymbol(s, lines)
+}
+
+// DwarfIntConst creates a link symbol for an integer constant with the
+// given name, type and value.
+func (ctxt *Link) DwarfIntConst(myimportpath, name, typename string, val int64) {
+	if myimportpath == "" {
+		return
+	}
+	s := ctxt.LookupInit(dwarf.ConstInfoPrefix+myimportpath, func(s *LSym) {
+		s.Type = objabi.SDWARFCONST
+		ctxt.Data = append(ctxt.Data, s)
+	})
+	dwarf.PutIntConst(dwCtxt{ctxt}, s, ctxt.Lookup(dwarf.InfoPrefix+typename), myimportpath+"."+name, val)
+}
+
+func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym, myimportpath string) {
+	absfn := ctxt.DwFixups.AbsFuncDwarfSym(s)
+	if absfn.Size != 0 {
+		ctxt.Diag("internal error: DwarfAbstractFunc double process %v", s)
+	}
+	if s.Func() == nil {
+		s.NewFuncInfo()
+	}
+	scopes, _ := ctxt.DebugInfo(s, absfn, curfn)
+	dwctxt := dwCtxt{ctxt}
+	filesym := ctxt.fileSymbol(s)
+	fnstate := dwarf.FnState{
+		Name:          s.Name,
+		Importpath:    myimportpath,
+		Info:          absfn,
+		Filesym:       filesym,
+		Absfn:         absfn,
+		External:      !s.Static(),
+		Scopes:        scopes,
+		UseBASEntries: ctxt.UseBASEntries,
+	}
+	if err := dwarf.PutAbstractFunc(dwctxt, &fnstate); err != nil {
+		ctxt.Diag("emitting DWARF for %s failed: %v", s.Name, err)
+	}
+}
+
+// This table is designed to aid in the creation of references between
+// DWARF subprogram DIEs.
+//
+// In most cases when one DWARF DIE has to refer to another DWARF DIE,
+// the target of the reference has an LSym, which makes it easy to use
+// the existing relocation mechanism. For DWARF inlined routine DIEs,
+// however, the subprogram DIE has to refer to a child
+// parameter/variable DIE of the abstract subprogram. This child DIE
+// doesn't have an LSym, and also of interest is the fact that when
+// DWARF generation is happening for inlined function F within caller
+// G, it's possible that DWARF generation hasn't happened yet for F,
+// so there is no way to know the offset of a child DIE within F's
+// abstract function. Making matters more complex, each inlined
+// instance of F may refer to a subset of the original F's variables
+// (depending on what happens with optimization, some vars may be
+// eliminated).
+//
+// The fixup table below helps overcome this hurdle. At the point
+// where a parameter/variable reference is made (via a call to
+// "ReferenceChildDIE"), a fixup record is generate that records
+// the relocation that is targeting that child variable. At a later
+// point when the abstract function DIE is emitted, there will be
+// a call to "RegisterChildDIEOffsets", at which point the offsets
+// needed to apply fixups are captured. Finally, once the parallel
+// portion of the compilation is done, fixups can actually be applied
+// during the "Finalize" method (this can't be done during the
+// parallel portion of the compile due to the possibility of data
+// races).
+//
+// This table is also used to record the "precursor" function node for
+// each function that is the target of an inline -- child DIE references
+// have to be made with respect to the original pre-optimization
+// version of the function (to allow for the fact that each inlined
+// body may be optimized differently).
+type DwarfFixupTable struct {
+	ctxt      *Link
+	mu        sync.Mutex
+	symtab    map[*LSym]int // maps abstract fn LSYM to index in svec
+	svec      []symFixups
+	precursor map[*LSym]fnState // maps fn Lsym to precursor Node, absfn sym
+}
+
+type symFixups struct {
+	fixups   []relFixup
+	doffsets []declOffset
+	inlIndex int32
+	defseen  bool
+}
+
+type declOffset struct {
+	// Index of variable within DCL list of pre-optimization function
+	dclIdx int32
+	// Offset of var's child DIE with respect to containing subprogram DIE
+	offset int32
+}
+
+type relFixup struct {
+	refsym *LSym
+	relidx int32
+	dclidx int32
+}
+
+type fnState struct {
+	// precursor function (really *gc.Node)
+	precursor interface{}
+	// abstract function symbol
+	absfn *LSym
+}
+
+func NewDwarfFixupTable(ctxt *Link) *DwarfFixupTable {
+	return &DwarfFixupTable{
+		ctxt:      ctxt,
+		symtab:    make(map[*LSym]int),
+		precursor: make(map[*LSym]fnState),
+	}
+}
+
+func (ft *DwarfFixupTable) GetPrecursorFunc(s *LSym) interface{} {
+	if fnstate, found := ft.precursor[s]; found {
+		return fnstate.precursor
+	}
+	return nil
+}
+
+func (ft *DwarfFixupTable) SetPrecursorFunc(s *LSym, fn interface{}) {
+	if _, found := ft.precursor[s]; found {
+		ft.ctxt.Diag("internal error: DwarfFixupTable.SetPrecursorFunc double call on %v", s)
+	}
+
+	// initialize abstract function symbol now. This is done here so
+	// as to avoid data races later on during the parallel portion of
+	// the back end.
+	absfn := ft.ctxt.LookupDerived(s, dwarf.InfoPrefix+s.Name+dwarf.AbstractFuncSuffix)
+	absfn.Set(AttrDuplicateOK, true)
+	absfn.Type = objabi.SDWARFABSFCN
+	ft.ctxt.Data = append(ft.ctxt.Data, absfn)
+
+	// In the case of "late" inlining (inlines that happen during
+	// wrapper generation as opposed to the main inlining phase) it's
+	// possible that we didn't cache the abstract function sym for the
+	// text symbol -- do so now if needed. See issue 38068.
+	if fn := s.Func(); fn != nil && fn.dwarfAbsFnSym == nil {
+		fn.dwarfAbsFnSym = absfn
+	}
+
+	ft.precursor[s] = fnState{precursor: fn, absfn: absfn}
+}
+
+// Make a note of a child DIE reference: relocation 'ridx' within symbol 's'
+// is targeting child 'c' of DIE with symbol 'tgt'.
+func (ft *DwarfFixupTable) ReferenceChildDIE(s *LSym, ridx int, tgt *LSym, dclidx int, inlIndex int) {
+	// Protect against concurrent access if multiple backend workers
+	ft.mu.Lock()
+	defer ft.mu.Unlock()
+
+	// Create entry for symbol if not already present.
+	idx, found := ft.symtab[tgt]
+	if !found {
+		ft.svec = append(ft.svec, symFixups{inlIndex: int32(inlIndex)})
+		idx = len(ft.svec) - 1
+		ft.symtab[tgt] = idx
+	}
+
+	// Do we have child DIE offsets available? If so, then apply them,
+	// otherwise create a fixup record.
+	sf := &ft.svec[idx]
+	if len(sf.doffsets) > 0 {
+		found := false
+		for _, do := range sf.doffsets {
+			if do.dclIdx == int32(dclidx) {
+				off := do.offset
+				s.R[ridx].Add += int64(off)
+				found = true
+				break
+			}
+		}
+		if !found {
+			ft.ctxt.Diag("internal error: DwarfFixupTable.ReferenceChildDIE unable to locate child DIE offset for dclIdx=%d src=%v tgt=%v", dclidx, s, tgt)
+		}
+	} else {
+		sf.fixups = append(sf.fixups, relFixup{s, int32(ridx), int32(dclidx)})
+	}
+}
+
+// Called once DWARF generation is complete for a given abstract function,
+// whose children might have been referenced via a call above. Stores
+// the offsets for any child DIEs (vars, params) so that they can be
+// consumed later in on DwarfFixupTable.Finalize, which applies any
+// outstanding fixups.
+func (ft *DwarfFixupTable) RegisterChildDIEOffsets(s *LSym, vars []*dwarf.Var, coffsets []int32) {
+	// Length of these two slices should agree
+	if len(vars) != len(coffsets) {
+		ft.ctxt.Diag("internal error: RegisterChildDIEOffsets vars/offsets length mismatch")
+		return
+	}
+
+	// Generate the slice of declOffset's based in vars/coffsets
+	doffsets := make([]declOffset, len(coffsets))
+	for i := range coffsets {
+		doffsets[i].dclIdx = vars[i].ChildIndex
+		doffsets[i].offset = coffsets[i]
+	}
+
+	ft.mu.Lock()
+	defer ft.mu.Unlock()
+
+	// Store offsets for this symbol.
+	idx, found := ft.symtab[s]
+	if !found {
+		sf := symFixups{inlIndex: -1, defseen: true, doffsets: doffsets}
+		ft.svec = append(ft.svec, sf)
+		ft.symtab[s] = len(ft.svec) - 1
+	} else {
+		sf := &ft.svec[idx]
+		sf.doffsets = doffsets
+		sf.defseen = true
+	}
+}
+
+func (ft *DwarfFixupTable) processFixups(slot int, s *LSym) {
+	sf := &ft.svec[slot]
+	for _, f := range sf.fixups {
+		dfound := false
+		for _, doffset := range sf.doffsets {
+			if doffset.dclIdx == f.dclidx {
+				f.refsym.R[f.relidx].Add += int64(doffset.offset)
+				dfound = true
+				break
+			}
+		}
+		if !dfound {
+			ft.ctxt.Diag("internal error: DwarfFixupTable has orphaned fixup on %v targeting %v relidx=%d dclidx=%d", f.refsym, s, f.relidx, f.dclidx)
+		}
+	}
+}
+
+// return the LSym corresponding to the 'abstract subprogram' DWARF
+// info entry for a function.
+func (ft *DwarfFixupTable) AbsFuncDwarfSym(fnsym *LSym) *LSym {
+	// Protect against concurrent access if multiple backend workers
+	ft.mu.Lock()
+	defer ft.mu.Unlock()
+
+	if fnstate, found := ft.precursor[fnsym]; found {
+		return fnstate.absfn
+	}
+	ft.ctxt.Diag("internal error: AbsFuncDwarfSym requested for %v, not seen during inlining", fnsym)
+	return nil
+}
+
+// Called after all functions have been compiled; the main job of this
+// function is to identify cases where there are outstanding fixups.
+// This scenario crops up when we have references to variables of an
+// inlined routine, but that routine is defined in some other package.
+// This helper walks through and locate these fixups, then invokes a
+// helper to create an abstract subprogram DIE for each one.
+func (ft *DwarfFixupTable) Finalize(myimportpath string, trace bool) {
+	if trace {
+		ft.ctxt.Logf("DwarfFixupTable.Finalize invoked for %s\n", myimportpath)
+	}
+
+	// Collect up the keys from the precursor map, then sort the
+	// resulting list (don't want to rely on map ordering here).
+	fns := make([]*LSym, len(ft.precursor))
+	idx := 0
+	for fn := range ft.precursor {
+		fns[idx] = fn
+		idx++
+	}
+	sort.Sort(BySymName(fns))
+
+	// Should not be called during parallel portion of compilation.
+	if ft.ctxt.InParallel {
+		ft.ctxt.Diag("internal error: DwarfFixupTable.Finalize call during parallel backend")
+	}
+
+	// Generate any missing abstract functions.
+	for _, s := range fns {
+		absfn := ft.AbsFuncDwarfSym(s)
+		slot, found := ft.symtab[absfn]
+		if !found || !ft.svec[slot].defseen {
+			ft.ctxt.GenAbstractFunc(s)
+		}
+	}
+
+	// Apply fixups.
+	for _, s := range fns {
+		absfn := ft.AbsFuncDwarfSym(s)
+		slot, found := ft.symtab[absfn]
+		if !found {
+			ft.ctxt.Diag("internal error: DwarfFixupTable.Finalize orphan abstract function for %v", s)
+		} else {
+			ft.processFixups(slot, s)
+		}
+	}
+}
+
+type BySymName []*LSym
+
+func (s BySymName) Len() int           { return len(s) }
+func (s BySymName) Less(i, j int) bool { return s[i].Name < s[j].Name }
+func (s BySymName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }