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/internal/obj/objfile.go

@@ -15,6 +15,7 @@ import (
 	"log"
 	"path/filepath"
 	"sort"
+	"sync"
 )
 
 // objWriter writes Go object files.
@@ -473,8 +474,33 @@ func (c dwCtxt) AddFileRef(s dwarf.Sym, f interface{}) {
 	r.Type = objabi.R_DWARFFILEREF
 }
 
-// dwarfSym returns the DWARF symbols for TEXT symbol.
-func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym *LSym) {
+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 (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym *LSym) {
 	if s.Type != objabi.STEXT {
 		ctxt.Diag("dwarfSym of non-TEXT %v", s)
 	}
@@ -484,8 +510,12 @@ func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym *
 			s.Func.dwarfLocSym = ctxt.LookupDerived(s, dwarf.LocPrefix+s.Name)
 		}
 		s.Func.dwarfRangesSym = ctxt.LookupDerived(s, dwarf.RangePrefix+s.Name)
+		if s.WasInlined() {
+			s.Func.dwarfAbsFnSym = ctxt.DwFixups.AbsFuncDwarfSym(s)
+		}
+
 	}
-	return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym
+	return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym, s.Func.dwarfAbsFnSym
 }
 
 func (s *LSym) Len() int64 {
@@ -505,20 +535,45 @@ func (ctxt *Link) fileSymbol(fn *LSym) *LSym {
 	return nil
 }
 
-// populateDWARF fills in the DWARF Debugging Information Entries for TEXT symbol s.
-// The DWARFs symbol must already have been initialized in InitTextSym.
-func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym) {
-	info, loc, ranges := ctxt.dwarfSym(s)
+// 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 := 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 = ctxt.DebugInfo(s, curfn)
+		scopes, inlcalls = ctxt.DebugInfo(s, 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,
+	}
+	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)
 	}
-
-	fs := ctxt.fileSymbol(s)
-	err := dwarf.PutFunc(dwCtxt{ctxt}, info, loc, ranges, fs, s.Name, !s.Static(), s, s.Size, scopes)
 	if err != nil {
 		ctxt.Diag("emitting DWARF for %s failed: %v", s.Name, err)
 	}
@@ -536,3 +591,285 @@ func (ctxt *Link) DwarfIntConst(myimportpath, name, typename string, val int64)
 	})
 	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.Func = new(FuncInfo)
+	}
+	scopes, _ := ctxt.DebugInfo(s, 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,
+	}
+	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 betweeen
+// 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.SDWARFINFO
+	ft.ctxt.Data = append(ft.ctxt.Data, 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 := 0; i < len(coffsets); i++ {
+		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 i := 0; i < len(sf.doffsets); i++ {
+			if sf.doffsets[i].dclIdx == f.dclidx {
+				f.refsym.R[f.relidx].Add += int64(sf.doffsets[i].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 i := 0; i < len(fns); i++ {
+		s := fns[i]
+		absfn := ft.AbsFuncDwarfSym(s)
+		slot, found := ft.symtab[absfn]
+		if !found || !ft.svec[slot].defseen {
+			ft.ctxt.GenAbstractFunc(s)
+		}
+	}
+
+	// Apply fixups.
+	for i := 0; i < len(fns); i++ {
+		s := fns[i]
+		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] }