[dev.link] cmd/{compile,link}: split SDWARFINFO symtype into sub-types

This change splits the SDWARFINFO symbol type (a generic container of
DWARF content) into separate sub-classes. The new symbol types are

 SDWARFCUINFO    comp unit DIE, also CU info and CU packagename syms
 SDWARFCONST     constant DIE
 SDWARFFCN       subprogram DIE (default and concrete)
 SDWARFABSFCN    abstract function DIE
 SDWARFTYPE      type DIE
 SDWARFVAR       global variable DIE

Advantage of doing this: in the linker there are several places where
we have to iterate over a symbol's relocations to pick out references
to specific classes of DWARF sub-symbols (for example, looking for all
abstract function DIEs referenced by a subprogram DIE, or looking at
all the type DIEs used in a subprogram DIE). By splitting SDWARFINFO
into parts clients can now look only at the relocation target's sym
type as opposed to having to materialize the target sym name, or do a
lookup.

Change-Id: I4e0ee3216d3c8f1a78bec3d296c01e95b3d025b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/234684
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

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

@@ -1488,7 +1488,7 @@ func recordFlags(flags ...string) {
 		return
 	}
 	s := Ctxt.Lookup(dwarf.CUInfoPrefix + "producer." + myimportpath)
-	s.Type = objabi.SDWARFINFO
+	s.Type = objabi.SDWARFCUINFO
 	// Sometimes (for example when building tests) we can link
 	// together two package main archives. So allow dups.
 	s.Set(obj.AttrDuplicateOK, true)
@@ -1500,7 +1500,7 @@ func recordFlags(flags ...string) {
 // compiled, so that the linker can save it in the compile unit's DIE.
 func recordPackageName() {
 	s := Ctxt.Lookup(dwarf.CUInfoPrefix + "packagename." + myimportpath)
-	s.Type = objabi.SDWARFINFO
+	s.Type = objabi.SDWARFCUINFO
 	// Sometimes (for example when building tests) we can link
 	// together two package main archives. So allow dups.
 	s.Set(obj.AttrDuplicateOK, true)

src/cmd/internal/obj/objfile.go

@@ -205,7 +205,7 @@ func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym,
 	}
 	if s.Func.dwarfInfoSym == nil {
 		s.Func.dwarfInfoSym = &LSym{
-			Type: objabi.SDWARFINFO,
+			Type: objabi.SDWARFFCN,
 		}
 		if ctxt.Flag_locationlists {
 			s.Func.dwarfLocSym = &LSym{
@@ -296,7 +296,7 @@ func (ctxt *Link) DwarfIntConst(myimportpath, name, typename string, val int64)
 		return
 	}
 	s := ctxt.LookupInit(dwarf.ConstInfoPrefix+myimportpath, func(s *LSym) {
-		s.Type = objabi.SDWARFINFO
+		s.Type = objabi.SDWARFCONST
 		ctxt.Data = append(ctxt.Data, s)
 	})
 	dwarf.PutIntConst(dwCtxt{ctxt}, s, ctxt.Lookup(dwarf.InfoPrefix+typename), myimportpath+"."+name, val)
@@ -422,7 +422,7 @@ func (ft *DwarfFixupTable) SetPrecursorFunc(s *LSym, fn interface{}) {
 	// the back end.
 	absfn := ft.ctxt.LookupDerived(s, dwarf.InfoPrefix+s.Name+dwarf.AbstractFuncSuffix)
 	absfn.Set(AttrDuplicateOK, true)
-	absfn.Type = objabi.SDWARFINFO
+	absfn.Type = objabi.SDWARFABSFCN
 	ft.ctxt.Data = append(ft.ctxt.Data, absfn)
 
 	// In the case of "late" inlining (inlines that happen during

src/cmd/internal/obj/objfile2.go

@@ -428,7 +428,8 @@ func writeAuxSymDebug(ctxt *Link, par *LSym, aux *LSym) {
 	// Most aux symbols (ex: funcdata) are not interesting--
 	// pick out just the DWARF ones for now.
 	if aux.Type != objabi.SDWARFLOC &&
-		aux.Type != objabi.SDWARFINFO &&
+		aux.Type != objabi.SDWARFFCN &&
+		aux.Type != objabi.SDWARFABSFCN &&
 		aux.Type != objabi.SDWARFLINES &&
 		aux.Type != objabi.SDWARFRANGE {
 		return

src/cmd/internal/objabi/symkind.go

@@ -56,7 +56,12 @@ const (
 	// Thread-local data that is initially all 0s
 	STLSBSS
 	// Debugging data
-	SDWARFINFO
+	SDWARFCUINFO
+	SDWARFCONST
+	SDWARFFCN
+	SDWARFABSFCN
+	SDWARFTYPE
+	SDWARFVAR
 	SDWARFRANGE
 	SDWARFLOC
 	SDWARFLINES

src/cmd/internal/objabi/symkind_string.go

@@ -16,17 +16,22 @@ func _() {
 	_ = x[SBSS-5]
 	_ = x[SNOPTRBSS-6]
 	_ = x[STLSBSS-7]
-	_ = x[SDWARFINFO-8]
+	_ = x[SDWARFCUINFO-8]
-	_ = x[SDWARFRANGE-9]
+	_ = x[SDWARFCONST-9]
-	_ = x[SDWARFLOC-10]
+	_ = x[SDWARFFCN-10]
-	_ = x[SDWARFLINES-11]
+	_ = x[SDWARFABSFCN-11]
-	_ = x[SABIALIAS-12]
+	_ = x[SDWARFTYPE-12]
-	_ = x[SLIBFUZZER_EXTRA_COUNTER-13]
+	_ = x[SDWARFVAR-13]
+	_ = x[SDWARFRANGE-14]
+	_ = x[SDWARFLOC-15]
+	_ = x[SDWARFLINES-16]
+	_ = x[SABIALIAS-17]
+	_ = x[SLIBFUZZER_EXTRA_COUNTER-18]
 }
 
-const _SymKind_name = "SxxxSTEXTSRODATASNOPTRDATASDATASBSSSNOPTRBSSSTLSBSSSDWARFINFOSDWARFRANGESDWARFLOCSDWARFLINESSABIALIASSLIBFUZZER_EXTRA_COUNTER"
+const _SymKind_name = "SxxxSTEXTSRODATASNOPTRDATASDATASBSSSNOPTRBSSSTLSBSSSDWARFCUINFOSDWARFCONSTSDWARFFCNSDWARFABSFCNSDWARFTYPESDWARFVARSDWARFRANGESDWARFLOCSDWARFLINESSABIALIASSLIBFUZZER_EXTRA_COUNTER"
 
-var _SymKind_index = [...]uint8{0, 4, 9, 16, 26, 31, 35, 44, 51, 61, 72, 81, 92, 101, 125}
+var _SymKind_index = [...]uint8{0, 4, 9, 16, 26, 31, 35, 44, 51, 63, 74, 83, 95, 105, 114, 125, 134, 145, 154, 178}
 
 func (i SymKind) String() string {
 	if i >= SymKind(len(_SymKind_index)-1) {

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

@@ -277,24 +277,37 @@ func (d *dwctxt) newdie(parent *dwarf.DWDie, abbrev int, name string, version in
 
 	newattr(die, dwarf.DW_AT_name, dwarf.DW_CLS_STRING, int64(len(name)), name)
 
-	if name != "" && (abbrev <= dwarf.DW_ABRV_VARIABLE || abbrev >= dwarf.DW_ABRV_NULLTYPE) {
+	// Sanity check: all DIEs created in the linker should have a non-empty
-		// Q: do we need version here? My understanding is that all these
+	// name and be version zero.
-		// symbols should be version 0.
+	if name == "" || version != 0 {
-		if abbrev != dwarf.DW_ABRV_VARIABLE || version == 0 {
+		panic("nameless or version non-zero DWARF DIE")
-			if abbrev == dwarf.DW_ABRV_COMPUNIT {
+	}
-				// Avoid collisions with "real" symbol names.
+
-				name = fmt.Sprintf(".pkg.%s.%d", name, len(d.linkctxt.compUnits))
+	var st sym.SymKind
-			}
+	switch abbrev {
-			ds := d.ldr.LookupOrCreateSym(dwarf.InfoPrefix+name, version)
+	case dwarf.DW_ABRV_FUNCTYPEPARAM, dwarf.DW_ABRV_DOTDOTDOT, dwarf.DW_ABRV_STRUCTFIELD, dwarf.DW_ABRV_ARRAYRANGE:
-			dsu := d.ldr.MakeSymbolUpdater(ds)
+		// There are no relocations against these dies, and their names
-			dsu.SetType(sym.SDWARFINFO)
+		// are not unique, so don't create a symbol.
-			d.ldr.SetAttrNotInSymbolTable(ds, true)
+		return die
-			d.ldr.SetAttrReachable(ds, true)
+	case dwarf.DW_ABRV_COMPUNIT, dwarf.DW_ABRV_COMPUNIT_TEXTLESS:
-			die.Sym = dwSym(ds)
+		// Avoid collisions with "real" symbol names.
-			if abbrev >= dwarf.DW_ABRV_NULLTYPE && abbrev <= dwarf.DW_ABRV_TYPEDECL {
+		name = fmt.Sprintf(".pkg.%s.%d", name, len(d.linkctxt.compUnits))
-				d.tmap[name] = ds
+		st = sym.SDWARFCUINFO
-			}
+	case dwarf.DW_ABRV_VARIABLE:
-		}
+		st = sym.SDWARFVAR
+	default:
+		// Everything else is assigned a type of SDWARFTYPE. that
+		// this also includes loose ends such as STRUCT_FIELD.
+		st = sym.SDWARFTYPE
+	}
+	ds := d.ldr.LookupOrCreateSym(dwarf.InfoPrefix+name, version)
+	dsu := d.ldr.MakeSymbolUpdater(ds)
+	dsu.SetType(st)
+	d.ldr.SetAttrNotInSymbolTable(ds, true)
+	d.ldr.SetAttrReachable(ds, true)
+	die.Sym = dwSym(ds)
+	if abbrev >= dwarf.DW_ABRV_NULLTYPE && abbrev <= dwarf.DW_ABRV_TYPEDECL {
+		d.tmap[name] = ds
 	}
 
 	return die
@@ -480,7 +493,7 @@ func (d *dwctxt) dotypedef(parent *dwarf.DWDie, gotype loader.Sym, name string,
 	// to be an anonymous symbol (we want this for perf reasons).
 	tds := d.ldr.CreateExtSym("", 0)
 	tdsu := d.ldr.MakeSymbolUpdater(tds)
-	tdsu.SetType(sym.SDWARFINFO)
+	tdsu.SetType(sym.SDWARFTYPE)
 	def.Sym = dwSym(tds)
 	d.ldr.SetAttrNotInSymbolTable(tds, true)
 	d.ldr.SetAttrReachable(tds, true)
@@ -850,7 +863,7 @@ func (d *dwctxt) mkinternaltype(ctxt *Link, abbrev int, typename, keyname, valna
 	name := mkinternaltypename(typename, keyname, valname)
 	symname := dwarf.InfoPrefix + name
 	s := d.ldr.Lookup(symname, 0)
-	if s != 0 && d.ldr.SymType(s) == sym.SDWARFINFO {
+	if s != 0 && d.ldr.SymType(s) == sym.SDWARFTYPE {
 		return s
 	}
 	die := d.newdie(&dwtypes, abbrev, name, 0)
@@ -1122,7 +1135,8 @@ func getCompilationDir() string {
 func (d *dwctxt) importInfoSymbol(ctxt *Link, dsym loader.Sym) {
 	d.ldr.SetAttrReachable(dsym, true)
 	d.ldr.SetAttrNotInSymbolTable(dsym, true)
-	if d.ldr.SymType(dsym) != sym.SDWARFINFO {
+	dst := d.ldr.SymType(dsym)
+	if dst != sym.SDWARFCONST && dst != sym.SDWARFABSFCN {
 		log.Fatalf("error: DWARF info sym %d/%s with incorrect type %s", dsym, d.ldr.SymName(dsym), d.ldr.SymType(dsym).String())
 	}
 	relocs := d.ldr.Relocs(dsym)
@@ -1492,7 +1506,7 @@ func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym, p
 
 	infosec := d.ldr.LookupOrCreateSym(".debug_info", 0)
 	disu := d.ldr.MakeSymbolUpdater(infosec)
-	disu.SetType(sym.SDWARFINFO)
+	disu.SetType(sym.SDWARFCUINFO)
 	d.ldr.SetAttrReachable(infosec, true)
 	syms := []loader.Sym{infosec}
 
@@ -1814,7 +1828,11 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
 				ctxt.runtimeCU = unit
 			}
 
-			unit.DWInfo = d.newdie(&dwroot, dwarf.DW_ABRV_COMPUNIT, unit.Lib.Pkg, 0)
+			cuabrv := dwarf.DW_ABRV_COMPUNIT
+			if len(unit.Textp) == 0 {
+				cuabrv = dwarf.DW_ABRV_COMPUNIT_TEXTLESS
+			}
+			unit.DWInfo = d.newdie(&dwroot, cuabrv, unit.Lib.Pkg, 0)
 			newattr(unit.DWInfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(dwarf.DW_LANG_Go), 0)
 			// OS X linker requires compilation dir or absolute path in comp unit name to output debug info.
 			compDir := getCompilationDir()
@@ -1850,10 +1868,6 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
 			}
 			newattr(unit.DWInfo, dwarf.DW_AT_go_package_name, dwarf.DW_CLS_STRING, int64(len(pkgname)), pkgname)
 
-			if len(unit.Textp) == 0 {
-				unit.DWInfo.Abbrev = dwarf.DW_ABRV_COMPUNIT_TEXTLESS
-			}
-
 			// Scan all functions in this compilation unit, create DIEs for all
 			// referenced types, create the file table for debug_line, find all
 			// referenced abstract functions.

src/cmd/link/internal/loader/loader.go

@@ -1539,7 +1539,7 @@ func (l *Loader) GetFuncDwarfAuxSyms(fnSymIdx Sym) (auxDwarfInfo, auxDwarfLoc, a
 		switch a.Type() {
 		case goobj2.AuxDwarfInfo:
 			auxDwarfInfo = l.resolve(r, a.Sym())
-			if l.SymType(auxDwarfInfo) != sym.SDWARFINFO {
+			if l.SymType(auxDwarfInfo) != sym.SDWARFFCN {
 				panic("aux dwarf info sym with wrong type")
 			}
 		case goobj2.AuxDwarfLoc:
@@ -2105,7 +2105,7 @@ func topLevelSym(sname string, skind sym.SymKind) bool {
 		return true
 	}
 	switch skind {
-	case sym.SDWARFINFO, sym.SDWARFRANGE, sym.SDWARFLOC, sym.SDWARFLINES, sym.SGOFUNC:
+	case sym.SDWARFFCN, sym.SDWARFABSFCN, sym.SDWARFTYPE, sym.SDWARFCONST, sym.SDWARFCUINFO, sym.SDWARFRANGE, sym.SDWARFLOC, sym.SDWARFLINES, sym.SGOFUNC:
 		return true
 	default:
 		return false

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

@@ -108,7 +108,13 @@ const (
 
 	// Sections for debugging information
 	SDWARFSECT
-	SDWARFINFO
+	// DWARF symbol types
+	SDWARFCUINFO
+	SDWARFCONST
+	SDWARFFCN
+	SDWARFABSFCN
+	SDWARFTYPE
+	SDWARFVAR
 	SDWARFRANGE
 	SDWARFLOC
 	SDWARFLINES
@@ -128,7 +134,12 @@ var AbiSymKindToSymKind = [...]SymKind{
 	SBSS,
 	SNOPTRBSS,
 	STLSBSS,
-	SDWARFINFO,
+	SDWARFCUINFO,
+	SDWARFCONST,
+	SDWARFFCN,
+	SDWARFABSFCN,
+	SDWARFTYPE,
+	SDWARFVAR,
 	SDWARFRANGE,
 	SDWARFLOC,
 	SDWARFLINES,

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

@@ -1,4 +1,4 @@
-// Code generated by "stringer -type=SymKind"; DO NOT EDIT.
+// Code generated by "stringer -type=SymKindstringer -type=SymKind"; DO NOT EDIT.
 
 package sym
 
@@ -56,16 +56,21 @@ func _() {
 	_ = x[SHOSTOBJ-45]
 	_ = x[SUNDEFEXT-46]
 	_ = x[SDWARFSECT-47]
-	_ = x[SDWARFINFO-48]
+	_ = x[SDWARFCUINFO-48]
-	_ = x[SDWARFRANGE-49]
+	_ = x[SDWARFCONST-49]
-	_ = x[SDWARFLOC-50]
+	_ = x[SDWARFFCN-50]
-	_ = x[SDWARFLINES-51]
+	_ = x[SDWARFABSFCN-51]
-	_ = x[SABIALIAS-52]
+	_ = x[SDWARFTYPE-52]
+	_ = x[SDWARFVAR-53]
+	_ = x[SDWARFRANGE-54]
+	_ = x[SDWARFLOC-55]
+	_ = x[SDWARFLINES-56]
+	_ = x[SABIALIAS-57]
 }
 
-const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSFirstWritableSBUILDINFOSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASXCOFFTOCSBSSSNOPTRBSSSLIBFUZZER_EXTRA_COUNTERSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSDYNIMPORTSHOSTOBJSUNDEFEXTSDWARFSECTSDWARFINFOSDWARFRANGESDWARFLOCSDWARFLINESSABIALIAS"
+const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSFirstWritableSBUILDINFOSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASXCOFFTOCSBSSSNOPTRBSSSLIBFUZZER_EXTRA_COUNTERSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSDYNIMPORTSHOSTOBJSUNDEFEXTSDWARFSECTSDWARFCUINFOSDWARFCONSTSDWARFFCNSDWARFABSFCNSDWARFTYPESDWARFVARSDWARFRANGESDWARFLOCSDWARFLINESSABIALIAS"
 
-var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 220, 230, 238, 244, 253, 261, 268, 278, 286, 291, 300, 304, 313, 337, 344, 349, 361, 373, 390, 407, 416, 426, 434, 443, 453, 463, 474, 483, 494, 503}
+var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 220, 230, 238, 244, 253, 261, 268, 278, 286, 291, 300, 304, 313, 337, 344, 349, 361, 373, 390, 407, 416, 426, 434, 443, 453, 465, 476, 485, 497, 507, 516, 527, 536, 547, 556}
 
 func (i SymKind) String() string {
 	if i >= SymKind(len(_SymKind_index)-1) {