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

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // TODO/NICETOHAVE:
     6  //   - eliminate DW_CLS_ if not used
     7  //   - package info in compilation units
     8  //   - assign types to their packages
     9  //   - gdb uses c syntax, meaning clumsy quoting is needed for go identifiers. eg
    10  //     ptype struct '[]uint8' and qualifiers need to be quoted away
    11  //   - file:line info for variables
    12  //   - make strings a typedef so prettyprinters can see the underlying string type
    13  
    14  package ld
    15  
    16  import (
    17  	"cmd/internal/dwarf"
    18  	"cmd/internal/obj"
    19  	"cmd/internal/objabi"
    20  	"cmd/internal/src"
    21  	"cmd/internal/sys"
    22  	"cmd/link/internal/loader"
    23  	"cmd/link/internal/sym"
    24  	"fmt"
    25  	"internal/buildcfg"
    26  	"log"
    27  	"path"
    28  	"runtime"
    29  	"sort"
    30  	"strings"
    31  	"sync"
    32  )
    33  
    34  // dwctxt is a wrapper intended to satisfy the method set of
    35  // dwarf.Context, so that functions like dwarf.PutAttrs will work with
    36  // DIEs that use loader.Sym as opposed to *sym.Symbol. It is also
    37  // being used as a place to store tables/maps that are useful as part
    38  // of type conversion (this is just a convenience; it would be easy to
    39  // split these things out into another type if need be).
    40  type dwctxt struct {
    41  	linkctxt *Link
    42  	ldr      *loader.Loader
    43  	arch     *sys.Arch
    44  
    45  	// This maps type name string (e.g. "uintptr") to loader symbol for
    46  	// the DWARF DIE for that type (e.g. "go.info.type.uintptr")
    47  	tmap map[string]loader.Sym
    48  
    49  	// This maps loader symbol for the DWARF DIE symbol generated for
    50  	// a type (e.g. "go.info.uintptr") to the type symbol itself
    51  	// ("type.uintptr").
    52  	// FIXME: try converting this map (and the next one) to a single
    53  	// array indexed by loader.Sym -- this may perform better.
    54  	rtmap map[loader.Sym]loader.Sym
    55  
    56  	// This maps Go type symbol (e.g. "type.XXX") to loader symbol for
    57  	// the typedef DIE for that type (e.g. "go.info.XXX..def")
    58  	tdmap map[loader.Sym]loader.Sym
    59  
    60  	// Cache these type symbols, so as to avoid repeatedly looking them up
    61  	typeRuntimeEface loader.Sym
    62  	typeRuntimeIface loader.Sym
    63  	uintptrInfoSym   loader.Sym
    64  
    65  	// Used at various points in that parallel portion of DWARF gen to
    66  	// protect against conflicting updates to globals (such as "gdbscript")
    67  	dwmu *sync.Mutex
    68  }
    69  
    70  func newdwctxt(linkctxt *Link, forTypeGen bool) dwctxt {
    71  	d := dwctxt{
    72  		linkctxt: linkctxt,
    73  		ldr:      linkctxt.loader,
    74  		arch:     linkctxt.Arch,
    75  		tmap:     make(map[string]loader.Sym),
    76  		tdmap:    make(map[loader.Sym]loader.Sym),
    77  		rtmap:    make(map[loader.Sym]loader.Sym),
    78  	}
    79  	d.typeRuntimeEface = d.lookupOrDiag("type.runtime.eface")
    80  	d.typeRuntimeIface = d.lookupOrDiag("type.runtime.iface")
    81  	return d
    82  }
    83  
    84  // dwSym wraps a loader.Sym; this type is meant to obey the interface
    85  // rules for dwarf.Sym from the cmd/internal/dwarf package. DwDie and
    86  // DwAttr objects contain references to symbols via this type.
    87  type dwSym loader.Sym
    88  
    89  func (s dwSym) Length(dwarfContext interface{}) int64 {
    90  	l := dwarfContext.(dwctxt).ldr
    91  	return int64(len(l.Data(loader.Sym(s))))
    92  }
    93  
    94  func (c dwctxt) PtrSize() int {
    95  	return c.arch.PtrSize
    96  }
    97  
    98  func (c dwctxt) AddInt(s dwarf.Sym, size int, i int64) {
    99  	ds := loader.Sym(s.(dwSym))
   100  	dsu := c.ldr.MakeSymbolUpdater(ds)
   101  	dsu.AddUintXX(c.arch, uint64(i), size)
   102  }
   103  
   104  func (c dwctxt) AddBytes(s dwarf.Sym, b []byte) {
   105  	ds := loader.Sym(s.(dwSym))
   106  	dsu := c.ldr.MakeSymbolUpdater(ds)
   107  	dsu.AddBytes(b)
   108  }
   109  
   110  func (c dwctxt) AddString(s dwarf.Sym, v string) {
   111  	ds := loader.Sym(s.(dwSym))
   112  	dsu := c.ldr.MakeSymbolUpdater(ds)
   113  	dsu.Addstring(v)
   114  }
   115  
   116  func (c dwctxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
   117  	ds := loader.Sym(s.(dwSym))
   118  	dsu := c.ldr.MakeSymbolUpdater(ds)
   119  	if value != 0 {
   120  		value -= dsu.Value()
   121  	}
   122  	tgtds := loader.Sym(data.(dwSym))
   123  	dsu.AddAddrPlus(c.arch, tgtds, value)
   124  }
   125  
   126  func (c dwctxt) AddCURelativeAddress(s dwarf.Sym, data interface{}, value int64) {
   127  	ds := loader.Sym(s.(dwSym))
   128  	dsu := c.ldr.MakeSymbolUpdater(ds)
   129  	if value != 0 {
   130  		value -= dsu.Value()
   131  	}
   132  	tgtds := loader.Sym(data.(dwSym))
   133  	dsu.AddCURelativeAddrPlus(c.arch, tgtds, value)
   134  }
   135  
   136  func (c dwctxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
   137  	ds := loader.Sym(s.(dwSym))
   138  	dsu := c.ldr.MakeSymbolUpdater(ds)
   139  	tds := loader.Sym(t.(dwSym))
   140  	switch size {
   141  	default:
   142  		c.linkctxt.Errorf(ds, "invalid size %d in adddwarfref\n", size)
   143  	case c.arch.PtrSize, 4:
   144  	}
   145  	dsu.AddSymRef(c.arch, tds, ofs, objabi.R_ADDROFF, size)
   146  }
   147  
   148  func (c dwctxt) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64) {
   149  	size := 4
   150  	if isDwarf64(c.linkctxt) {
   151  		size = 8
   152  	}
   153  	ds := loader.Sym(s.(dwSym))
   154  	dsu := c.ldr.MakeSymbolUpdater(ds)
   155  	tds := loader.Sym(t.(dwSym))
   156  	switch size {
   157  	default:
   158  		c.linkctxt.Errorf(ds, "invalid size %d in adddwarfref\n", size)
   159  	case c.arch.PtrSize, 4:
   160  	}
   161  	dsu.AddSymRef(c.arch, tds, ofs, objabi.R_DWARFSECREF, size)
   162  }
   163  
   164  func (c dwctxt) Logf(format string, args ...interface{}) {
   165  	c.linkctxt.Logf(format, args...)
   166  }
   167  
   168  // At the moment these interfaces are only used in the compiler.
   169  
   170  func (c dwctxt) AddFileRef(s dwarf.Sym, f interface{}) {
   171  	panic("should be used only in the compiler")
   172  }
   173  
   174  func (c dwctxt) CurrentOffset(s dwarf.Sym) int64 {
   175  	panic("should be used only in the compiler")
   176  }
   177  
   178  func (c dwctxt) RecordDclReference(s dwarf.Sym, t dwarf.Sym, dclIdx int, inlIndex int) {
   179  	panic("should be used only in the compiler")
   180  }
   181  
   182  func (c dwctxt) RecordChildDieOffsets(s dwarf.Sym, vars []*dwarf.Var, offsets []int32) {
   183  	panic("should be used only in the compiler")
   184  }
   185  
   186  func isDwarf64(ctxt *Link) bool {
   187  	return ctxt.HeadType == objabi.Haix
   188  }
   189  
   190  var gdbscript string
   191  
   192  // dwarfSecInfo holds information about a DWARF output section,
   193  // specifically a section symbol and a list of symbols contained in
   194  // that section. On the syms list, the first symbol will always be the
   195  // section symbol, then any remaining symbols (if any) will be
   196  // sub-symbols in that section. Note that for some sections (eg:
   197  // .debug_abbrev), the section symbol is all there is (all content is
   198  // contained in it). For other sections (eg: .debug_info), the section
   199  // symbol is empty and all the content is in the sub-symbols. Finally
   200  // there are some sections (eg: .debug_ranges) where it is a mix (both
   201  // the section symbol and the sub-symbols have content)
   202  type dwarfSecInfo struct {
   203  	syms []loader.Sym
   204  }
   205  
   206  // secSym returns the section symbol for the section.
   207  func (dsi *dwarfSecInfo) secSym() loader.Sym {
   208  	if len(dsi.syms) == 0 {
   209  		return 0
   210  	}
   211  	return dsi.syms[0]
   212  }
   213  
   214  // subSyms returns a list of sub-symbols for the section.
   215  func (dsi *dwarfSecInfo) subSyms() []loader.Sym {
   216  	if len(dsi.syms) == 0 {
   217  		return []loader.Sym{}
   218  	}
   219  	return dsi.syms[1:]
   220  }
   221  
   222  // dwarfp stores the collected DWARF symbols created during
   223  // dwarf generation.
   224  var dwarfp []dwarfSecInfo
   225  
   226  func (d *dwctxt) writeabbrev() dwarfSecInfo {
   227  	abrvs := d.ldr.CreateSymForUpdate(".debug_abbrev", 0)
   228  	abrvs.SetType(sym.SDWARFSECT)
   229  	abrvs.AddBytes(dwarf.GetAbbrev())
   230  	return dwarfSecInfo{syms: []loader.Sym{abrvs.Sym()}}
   231  }
   232  
   233  var dwtypes dwarf.DWDie
   234  
   235  // newattr attaches a new attribute to the specified DIE.
   236  //
   237  // FIXME: at the moment attributes are stored in a linked list in a
   238  // fairly space-inefficient way -- it might be better to instead look
   239  // up all attrs in a single large table, then store indices into the
   240  // table in the DIE. This would allow us to common up storage for
   241  // attributes that are shared by many DIEs (ex: byte size of N).
   242  func newattr(die *dwarf.DWDie, attr uint16, cls int, value int64, data interface{}) *dwarf.DWAttr {
   243  	a := new(dwarf.DWAttr)
   244  	a.Link = die.Attr
   245  	die.Attr = a
   246  	a.Atr = attr
   247  	a.Cls = uint8(cls)
   248  	a.Value = value
   249  	a.Data = data
   250  	return a
   251  }
   252  
   253  // Each DIE (except the root ones) has at least 1 attribute: its
   254  // name. getattr moves the desired one to the front so
   255  // frequently searched ones are found faster.
   256  func getattr(die *dwarf.DWDie, attr uint16) *dwarf.DWAttr {
   257  	if die.Attr.Atr == attr {
   258  		return die.Attr
   259  	}
   260  
   261  	a := die.Attr
   262  	b := a.Link
   263  	for b != nil {
   264  		if b.Atr == attr {
   265  			a.Link = b.Link
   266  			b.Link = die.Attr
   267  			die.Attr = b
   268  			return b
   269  		}
   270  
   271  		a = b
   272  		b = b.Link
   273  	}
   274  
   275  	return nil
   276  }
   277  
   278  // Every DIE manufactured by the linker has at least an AT_name
   279  // attribute (but it will only be written out if it is listed in the abbrev).
   280  // The compiler does create nameless DWARF DIEs (ex: concrete subprogram
   281  // instance).
   282  // FIXME: it would be more efficient to bulk-allocate DIEs.
   283  func (d *dwctxt) newdie(parent *dwarf.DWDie, abbrev int, name string, version int) *dwarf.DWDie {
   284  	die := new(dwarf.DWDie)
   285  	die.Abbrev = abbrev
   286  	die.Link = parent.Child
   287  	parent.Child = die
   288  
   289  	newattr(die, dwarf.DW_AT_name, dwarf.DW_CLS_STRING, int64(len(name)), name)
   290  
   291  	// Sanity check: all DIEs created in the linker should have a non-empty
   292  	// name and be version zero.
   293  	if name == "" || version != 0 {
   294  		panic("nameless or version non-zero DWARF DIE")
   295  	}
   296  
   297  	var st sym.SymKind
   298  	switch abbrev {
   299  	case dwarf.DW_ABRV_FUNCTYPEPARAM, dwarf.DW_ABRV_DOTDOTDOT, dwarf.DW_ABRV_STRUCTFIELD, dwarf.DW_ABRV_ARRAYRANGE:
   300  		// There are no relocations against these dies, and their names
   301  		// are not unique, so don't create a symbol.
   302  		return die
   303  	case dwarf.DW_ABRV_COMPUNIT, dwarf.DW_ABRV_COMPUNIT_TEXTLESS:
   304  		// Avoid collisions with "real" symbol names.
   305  		name = fmt.Sprintf(".pkg.%s.%d", name, len(d.linkctxt.compUnits))
   306  		st = sym.SDWARFCUINFO
   307  	case dwarf.DW_ABRV_VARIABLE:
   308  		st = sym.SDWARFVAR
   309  	default:
   310  		// Everything else is assigned a type of SDWARFTYPE. that
   311  		// this also includes loose ends such as STRUCT_FIELD.
   312  		st = sym.SDWARFTYPE
   313  	}
   314  	ds := d.ldr.LookupOrCreateSym(dwarf.InfoPrefix+name, version)
   315  	dsu := d.ldr.MakeSymbolUpdater(ds)
   316  	dsu.SetType(st)
   317  	d.ldr.SetAttrNotInSymbolTable(ds, true)
   318  	d.ldr.SetAttrReachable(ds, true)
   319  	die.Sym = dwSym(ds)
   320  	if abbrev >= dwarf.DW_ABRV_NULLTYPE && abbrev <= dwarf.DW_ABRV_TYPEDECL {
   321  		d.tmap[name] = ds
   322  	}
   323  
   324  	return die
   325  }
   326  
   327  func walktypedef(die *dwarf.DWDie) *dwarf.DWDie {
   328  	if die == nil {
   329  		return nil
   330  	}
   331  	// Resolve typedef if present.
   332  	if die.Abbrev == dwarf.DW_ABRV_TYPEDECL {
   333  		for attr := die.Attr; attr != nil; attr = attr.Link {
   334  			if attr.Atr == dwarf.DW_AT_type && attr.Cls == dwarf.DW_CLS_REFERENCE && attr.Data != nil {
   335  				return attr.Data.(*dwarf.DWDie)
   336  			}
   337  		}
   338  	}
   339  
   340  	return die
   341  }
   342  
   343  func (d *dwctxt) walksymtypedef(symIdx loader.Sym) loader.Sym {
   344  
   345  	// We're being given the loader symbol for the type DIE, e.g.
   346  	// "go.info.type.uintptr". Map that first to the type symbol (e.g.
   347  	// "type.uintptr") and then to the typedef DIE for the type.
   348  	// FIXME: this seems clunky, maybe there is a better way to do this.
   349  
   350  	if ts, ok := d.rtmap[symIdx]; ok {
   351  		if def, ok := d.tdmap[ts]; ok {
   352  			return def
   353  		}
   354  		d.linkctxt.Errorf(ts, "internal error: no entry for sym %d in tdmap\n", ts)
   355  		return 0
   356  	}
   357  	d.linkctxt.Errorf(symIdx, "internal error: no entry for sym %d in rtmap\n", symIdx)
   358  	return 0
   359  }
   360  
   361  // Find child by AT_name using hashtable if available or linear scan
   362  // if not.
   363  func findchild(die *dwarf.DWDie, name string) *dwarf.DWDie {
   364  	var prev *dwarf.DWDie
   365  	for ; die != prev; prev, die = die, walktypedef(die) {
   366  		for a := die.Child; a != nil; a = a.Link {
   367  			if name == getattr(a, dwarf.DW_AT_name).Data {
   368  				return a
   369  			}
   370  		}
   371  		continue
   372  	}
   373  	return nil
   374  }
   375  
   376  // find looks up the loader symbol for the DWARF DIE generated for the
   377  // type with the specified name.
   378  func (d *dwctxt) find(name string) loader.Sym {
   379  	return d.tmap[name]
   380  }
   381  
   382  func (d *dwctxt) mustFind(name string) loader.Sym {
   383  	r := d.find(name)
   384  	if r == 0 {
   385  		Exitf("dwarf find: cannot find %s", name)
   386  	}
   387  	return r
   388  }
   389  
   390  func (d *dwctxt) adddwarfref(sb *loader.SymbolBuilder, t loader.Sym, size int) int64 {
   391  	var result int64
   392  	switch size {
   393  	default:
   394  		d.linkctxt.Errorf(sb.Sym(), "invalid size %d in adddwarfref\n", size)
   395  	case d.arch.PtrSize, 4:
   396  	}
   397  	result = sb.AddSymRef(d.arch, t, 0, objabi.R_DWARFSECREF, size)
   398  	return result
   399  }
   400  
   401  func (d *dwctxt) newrefattr(die *dwarf.DWDie, attr uint16, ref loader.Sym) *dwarf.DWAttr {
   402  	if ref == 0 {
   403  		return nil
   404  	}
   405  	return newattr(die, attr, dwarf.DW_CLS_REFERENCE, 0, dwSym(ref))
   406  }
   407  
   408  func (d *dwctxt) dtolsym(s dwarf.Sym) loader.Sym {
   409  	if s == nil {
   410  		return 0
   411  	}
   412  	dws := loader.Sym(s.(dwSym))
   413  	return dws
   414  }
   415  
   416  func (d *dwctxt) putdie(syms []loader.Sym, die *dwarf.DWDie) []loader.Sym {
   417  	s := d.dtolsym(die.Sym)
   418  	if s == 0 {
   419  		s = syms[len(syms)-1]
   420  	} else {
   421  		syms = append(syms, s)
   422  	}
   423  	sDwsym := dwSym(s)
   424  	dwarf.Uleb128put(d, sDwsym, int64(die.Abbrev))
   425  	dwarf.PutAttrs(d, sDwsym, die.Abbrev, die.Attr)
   426  	if dwarf.HasChildren(die) {
   427  		for die := die.Child; die != nil; die = die.Link {
   428  			syms = d.putdie(syms, die)
   429  		}
   430  		dsu := d.ldr.MakeSymbolUpdater(syms[len(syms)-1])
   431  		dsu.AddUint8(0)
   432  	}
   433  	return syms
   434  }
   435  
   436  func reverselist(list **dwarf.DWDie) {
   437  	curr := *list
   438  	var prev *dwarf.DWDie
   439  	for curr != nil {
   440  		next := curr.Link
   441  		curr.Link = prev
   442  		prev = curr
   443  		curr = next
   444  	}
   445  
   446  	*list = prev
   447  }
   448  
   449  func reversetree(list **dwarf.DWDie) {
   450  	reverselist(list)
   451  	for die := *list; die != nil; die = die.Link {
   452  		if dwarf.HasChildren(die) {
   453  			reversetree(&die.Child)
   454  		}
   455  	}
   456  }
   457  
   458  func newmemberoffsetattr(die *dwarf.DWDie, offs int32) {
   459  	newattr(die, dwarf.DW_AT_data_member_location, dwarf.DW_CLS_CONSTANT, int64(offs), nil)
   460  }
   461  
   462  func (d *dwctxt) lookupOrDiag(n string) loader.Sym {
   463  	symIdx := d.ldr.Lookup(n, 0)
   464  	if symIdx == 0 {
   465  		Exitf("dwarf: missing type: %s", n)
   466  	}
   467  	if len(d.ldr.Data(symIdx)) == 0 {
   468  		Exitf("dwarf: missing type (no data): %s", n)
   469  	}
   470  
   471  	return symIdx
   472  }
   473  
   474  func (d *dwctxt) dotypedef(parent *dwarf.DWDie, gotype loader.Sym, name string, def *dwarf.DWDie) *dwarf.DWDie {
   475  	// Only emit typedefs for real names.
   476  	if strings.HasPrefix(name, "map[") {
   477  		return nil
   478  	}
   479  	if strings.HasPrefix(name, "struct {") {
   480  		return nil
   481  	}
   482  	if strings.HasPrefix(name, "chan ") {
   483  		return nil
   484  	}
   485  	if name[0] == '[' || name[0] == '*' {
   486  		return nil
   487  	}
   488  	if def == nil {
   489  		Errorf(nil, "dwarf: bad def in dotypedef")
   490  	}
   491  
   492  	// Create a new loader symbol for the typedef. We no longer
   493  	// do lookups of typedef symbols by name, so this is going
   494  	// to be an anonymous symbol (we want this for perf reasons).
   495  	tds := d.ldr.CreateExtSym("", 0)
   496  	tdsu := d.ldr.MakeSymbolUpdater(tds)
   497  	tdsu.SetType(sym.SDWARFTYPE)
   498  	def.Sym = dwSym(tds)
   499  	d.ldr.SetAttrNotInSymbolTable(tds, true)
   500  	d.ldr.SetAttrReachable(tds, true)
   501  
   502  	// The typedef entry must be created after the def,
   503  	// so that future lookups will find the typedef instead
   504  	// of the real definition. This hooks the typedef into any
   505  	// circular definition loops, so that gdb can understand them.
   506  	die := d.newdie(parent, dwarf.DW_ABRV_TYPEDECL, name, 0)
   507  
   508  	d.newrefattr(die, dwarf.DW_AT_type, tds)
   509  
   510  	return die
   511  }
   512  
   513  // Define gotype, for composite ones recurse into constituents.
   514  func (d *dwctxt) defgotype(gotype loader.Sym) loader.Sym {
   515  	if gotype == 0 {
   516  		return d.mustFind("<unspecified>")
   517  	}
   518  
   519  	// If we already have a tdmap entry for the gotype, return it.
   520  	if ds, ok := d.tdmap[gotype]; ok {
   521  		return ds
   522  	}
   523  
   524  	sn := d.ldr.SymName(gotype)
   525  	if !strings.HasPrefix(sn, "type.") {
   526  		d.linkctxt.Errorf(gotype, "dwarf: type name doesn't start with \"type.\"")
   527  		return d.mustFind("<unspecified>")
   528  	}
   529  	name := sn[5:] // could also decode from Type.string
   530  
   531  	sdie := d.find(name)
   532  	if sdie != 0 {
   533  		return sdie
   534  	}
   535  
   536  	gtdwSym := d.newtype(gotype)
   537  	d.tdmap[gotype] = loader.Sym(gtdwSym.Sym.(dwSym))
   538  	return loader.Sym(gtdwSym.Sym.(dwSym))
   539  }
   540  
   541  func (d *dwctxt) newtype(gotype loader.Sym) *dwarf.DWDie {
   542  	sn := d.ldr.SymName(gotype)
   543  	name := sn[5:] // could also decode from Type.string
   544  	tdata := d.ldr.Data(gotype)
   545  	kind := decodetypeKind(d.arch, tdata)
   546  	bytesize := decodetypeSize(d.arch, tdata)
   547  
   548  	var die, typedefdie *dwarf.DWDie
   549  	switch kind {
   550  	case objabi.KindBool:
   551  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
   552  		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_boolean, 0)
   553  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   554  
   555  	case objabi.KindInt,
   556  		objabi.KindInt8,
   557  		objabi.KindInt16,
   558  		objabi.KindInt32,
   559  		objabi.KindInt64:
   560  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
   561  		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_signed, 0)
   562  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   563  
   564  	case objabi.KindUint,
   565  		objabi.KindUint8,
   566  		objabi.KindUint16,
   567  		objabi.KindUint32,
   568  		objabi.KindUint64,
   569  		objabi.KindUintptr:
   570  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
   571  		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_unsigned, 0)
   572  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   573  
   574  	case objabi.KindFloat32,
   575  		objabi.KindFloat64:
   576  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
   577  		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_float, 0)
   578  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   579  
   580  	case objabi.KindComplex64,
   581  		objabi.KindComplex128:
   582  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
   583  		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_complex_float, 0)
   584  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   585  
   586  	case objabi.KindArray:
   587  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_ARRAYTYPE, name, 0)
   588  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   589  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   590  		s := decodetypeArrayElem(d.ldr, d.arch, gotype)
   591  		d.newrefattr(die, dwarf.DW_AT_type, d.defgotype(s))
   592  		fld := d.newdie(die, dwarf.DW_ABRV_ARRAYRANGE, "range", 0)
   593  
   594  		// use actual length not upper bound; correct for 0-length arrays.
   595  		newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, decodetypeArrayLen(d.ldr, d.arch, gotype), 0)
   596  
   597  		d.newrefattr(fld, dwarf.DW_AT_type, d.uintptrInfoSym)
   598  
   599  	case objabi.KindChan:
   600  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_CHANTYPE, name, 0)
   601  		s := decodetypeChanElem(d.ldr, d.arch, gotype)
   602  		d.newrefattr(die, dwarf.DW_AT_go_elem, d.defgotype(s))
   603  		// Save elem type for synthesizechantypes. We could synthesize here
   604  		// but that would change the order of DIEs we output.
   605  		d.newrefattr(die, dwarf.DW_AT_type, s)
   606  
   607  	case objabi.KindFunc:
   608  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_FUNCTYPE, name, 0)
   609  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   610  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   611  		data := d.ldr.Data(gotype)
   612  		// FIXME: add caching or reuse reloc slice.
   613  		relocs := d.ldr.Relocs(gotype)
   614  		nfields := decodetypeFuncInCount(d.arch, data)
   615  		for i := 0; i < nfields; i++ {
   616  			s := decodetypeFuncInType(d.ldr, d.arch, gotype, &relocs, i)
   617  			sn := d.ldr.SymName(s)
   618  			fld := d.newdie(die, dwarf.DW_ABRV_FUNCTYPEPARAM, sn[5:], 0)
   619  			d.newrefattr(fld, dwarf.DW_AT_type, d.defgotype(s))
   620  		}
   621  
   622  		if decodetypeFuncDotdotdot(d.arch, data) {
   623  			d.newdie(die, dwarf.DW_ABRV_DOTDOTDOT, "...", 0)
   624  		}
   625  		nfields = decodetypeFuncOutCount(d.arch, data)
   626  		for i := 0; i < nfields; i++ {
   627  			s := decodetypeFuncOutType(d.ldr, d.arch, gotype, &relocs, i)
   628  			sn := d.ldr.SymName(s)
   629  			fld := d.newdie(die, dwarf.DW_ABRV_FUNCTYPEPARAM, sn[5:], 0)
   630  			d.newrefattr(fld, dwarf.DW_AT_type, d.defptrto(d.defgotype(s)))
   631  		}
   632  
   633  	case objabi.KindInterface:
   634  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_IFACETYPE, name, 0)
   635  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   636  		data := d.ldr.Data(gotype)
   637  		nfields := int(decodetypeIfaceMethodCount(d.arch, data))
   638  		var s loader.Sym
   639  		if nfields == 0 {
   640  			s = d.typeRuntimeEface
   641  		} else {
   642  			s = d.typeRuntimeIface
   643  		}
   644  		d.newrefattr(die, dwarf.DW_AT_type, d.defgotype(s))
   645  
   646  	case objabi.KindMap:
   647  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_MAPTYPE, name, 0)
   648  		s := decodetypeMapKey(d.ldr, d.arch, gotype)
   649  		d.newrefattr(die, dwarf.DW_AT_go_key, d.defgotype(s))
   650  		s = decodetypeMapValue(d.ldr, d.arch, gotype)
   651  		d.newrefattr(die, dwarf.DW_AT_go_elem, d.defgotype(s))
   652  		// Save gotype for use in synthesizemaptypes. We could synthesize here,
   653  		// but that would change the order of the DIEs.
   654  		d.newrefattr(die, dwarf.DW_AT_type, gotype)
   655  
   656  	case objabi.KindPtr:
   657  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_PTRTYPE, name, 0)
   658  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   659  		s := decodetypePtrElem(d.ldr, d.arch, gotype)
   660  		d.newrefattr(die, dwarf.DW_AT_type, d.defgotype(s))
   661  
   662  	case objabi.KindSlice:
   663  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_SLICETYPE, name, 0)
   664  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   665  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   666  		s := decodetypeArrayElem(d.ldr, d.arch, gotype)
   667  		elem := d.defgotype(s)
   668  		d.newrefattr(die, dwarf.DW_AT_go_elem, elem)
   669  
   670  	case objabi.KindString:
   671  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_STRINGTYPE, name, 0)
   672  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   673  
   674  	case objabi.KindStruct:
   675  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_STRUCTTYPE, name, 0)
   676  		typedefdie = d.dotypedef(&dwtypes, gotype, name, die)
   677  		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
   678  		nfields := decodetypeStructFieldCount(d.ldr, d.arch, gotype)
   679  		for i := 0; i < nfields; i++ {
   680  			f := decodetypeStructFieldName(d.ldr, d.arch, gotype, i)
   681  			s := decodetypeStructFieldType(d.ldr, d.arch, gotype, i)
   682  			if f == "" {
   683  				sn := d.ldr.SymName(s)
   684  				f = sn[5:] // skip "type."
   685  			}
   686  			fld := d.newdie(die, dwarf.DW_ABRV_STRUCTFIELD, f, 0)
   687  			d.newrefattr(fld, dwarf.DW_AT_type, d.defgotype(s))
   688  			offsetAnon := decodetypeStructFieldOffsAnon(d.ldr, d.arch, gotype, i)
   689  			newmemberoffsetattr(fld, int32(offsetAnon>>1))
   690  			if offsetAnon&1 != 0 { // is embedded field
   691  				newattr(fld, dwarf.DW_AT_go_embedded_field, dwarf.DW_CLS_FLAG, 1, 0)
   692  			}
   693  		}
   694  
   695  	case objabi.KindUnsafePointer:
   696  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_BARE_PTRTYPE, name, 0)
   697  
   698  	default:
   699  		d.linkctxt.Errorf(gotype, "dwarf: definition of unknown kind %d", kind)
   700  		die = d.newdie(&dwtypes, dwarf.DW_ABRV_TYPEDECL, name, 0)
   701  		d.newrefattr(die, dwarf.DW_AT_type, d.mustFind("<unspecified>"))
   702  	}
   703  
   704  	newattr(die, dwarf.DW_AT_go_kind, dwarf.DW_CLS_CONSTANT, int64(kind), 0)
   705  
   706  	if d.ldr.AttrReachable(gotype) {
   707  		newattr(die, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_GO_TYPEREF, 0, dwSym(gotype))
   708  	}
   709  
   710  	// Sanity check.
   711  	if _, ok := d.rtmap[gotype]; ok {
   712  		log.Fatalf("internal error: rtmap entry already installed\n")
   713  	}
   714  
   715  	ds := loader.Sym(die.Sym.(dwSym))
   716  	if typedefdie != nil {
   717  		ds = loader.Sym(typedefdie.Sym.(dwSym))
   718  	}
   719  	d.rtmap[ds] = gotype
   720  
   721  	if _, ok := prototypedies[sn]; ok {
   722  		prototypedies[sn] = die
   723  	}
   724  
   725  	if typedefdie != nil {
   726  		return typedefdie
   727  	}
   728  	return die
   729  }
   730  
   731  func (d *dwctxt) nameFromDIESym(dwtypeDIESym loader.Sym) string {
   732  	sn := d.ldr.SymName(dwtypeDIESym)
   733  	return sn[len(dwarf.InfoPrefix):]
   734  }
   735  
   736  func (d *dwctxt) defptrto(dwtype loader.Sym) loader.Sym {
   737  
   738  	// FIXME: it would be nice if the compiler attached an aux symbol
   739  	// ref from the element type to the pointer type -- it would be
   740  	// more efficient to do it this way as opposed to via name lookups.
   741  
   742  	ptrname := "*" + d.nameFromDIESym(dwtype)
   743  	if die := d.find(ptrname); die != 0 {
   744  		return die
   745  	}
   746  
   747  	pdie := d.newdie(&dwtypes, dwarf.DW_ABRV_PTRTYPE, ptrname, 0)
   748  	d.newrefattr(pdie, dwarf.DW_AT_type, dwtype)
   749  
   750  	// The DWARF info synthesizes pointer types that don't exist at the
   751  	// language level, like *hash<...> and *bucket<...>, and the data
   752  	// pointers of slices. Link to the ones we can find.
   753  	gts := d.ldr.Lookup("type."+ptrname, 0)
   754  	if gts != 0 && d.ldr.AttrReachable(gts) {
   755  		newattr(pdie, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_GO_TYPEREF, 0, dwSym(gts))
   756  	}
   757  
   758  	if gts != 0 {
   759  		ds := loader.Sym(pdie.Sym.(dwSym))
   760  		d.rtmap[ds] = gts
   761  		d.tdmap[gts] = ds
   762  	}
   763  
   764  	return d.dtolsym(pdie.Sym)
   765  }
   766  
   767  // Copies src's children into dst. Copies attributes by value.
   768  // DWAttr.data is copied as pointer only. If except is one of
   769  // the top-level children, it will not be copied.
   770  func (d *dwctxt) copychildrenexcept(ctxt *Link, dst *dwarf.DWDie, src *dwarf.DWDie, except *dwarf.DWDie) {
   771  	for src = src.Child; src != nil; src = src.Link {
   772  		if src == except {
   773  			continue
   774  		}
   775  		c := d.newdie(dst, src.Abbrev, getattr(src, dwarf.DW_AT_name).Data.(string), 0)
   776  		for a := src.Attr; a != nil; a = a.Link {
   777  			newattr(c, a.Atr, int(a.Cls), a.Value, a.Data)
   778  		}
   779  		d.copychildrenexcept(ctxt, c, src, nil)
   780  	}
   781  
   782  	reverselist(&dst.Child)
   783  }
   784  
   785  func (d *dwctxt) copychildren(ctxt *Link, dst *dwarf.DWDie, src *dwarf.DWDie) {
   786  	d.copychildrenexcept(ctxt, dst, src, nil)
   787  }
   788  
   789  // Search children (assumed to have TAG_member) for the one named
   790  // field and set its AT_type to dwtype
   791  func (d *dwctxt) substitutetype(structdie *dwarf.DWDie, field string, dwtype loader.Sym) {
   792  	child := findchild(structdie, field)
   793  	if child == nil {
   794  		Exitf("dwarf substitutetype: %s does not have member %s",
   795  			getattr(structdie, dwarf.DW_AT_name).Data, field)
   796  		return
   797  	}
   798  
   799  	a := getattr(child, dwarf.DW_AT_type)
   800  	if a != nil {
   801  		a.Data = dwSym(dwtype)
   802  	} else {
   803  		d.newrefattr(child, dwarf.DW_AT_type, dwtype)
   804  	}
   805  }
   806  
   807  func (d *dwctxt) findprotodie(ctxt *Link, name string) *dwarf.DWDie {
   808  	die, ok := prototypedies[name]
   809  	if ok && die == nil {
   810  		d.defgotype(d.lookupOrDiag(name))
   811  		die = prototypedies[name]
   812  	}
   813  	if die == nil {
   814  		log.Fatalf("internal error: DIE generation failed for %s\n", name)
   815  	}
   816  	return die
   817  }
   818  
   819  func (d *dwctxt) synthesizestringtypes(ctxt *Link, die *dwarf.DWDie) {
   820  	prototype := walktypedef(d.findprotodie(ctxt, "type.runtime.stringStructDWARF"))
   821  	if prototype == nil {
   822  		return
   823  	}
   824  
   825  	for ; die != nil; die = die.Link {
   826  		if die.Abbrev != dwarf.DW_ABRV_STRINGTYPE {
   827  			continue
   828  		}
   829  		d.copychildren(ctxt, die, prototype)
   830  	}
   831  }
   832  
   833  func (d *dwctxt) synthesizeslicetypes(ctxt *Link, die *dwarf.DWDie) {
   834  	prototype := walktypedef(d.findprotodie(ctxt, "type.runtime.slice"))
   835  	if prototype == nil {
   836  		return
   837  	}
   838  
   839  	for ; die != nil; die = die.Link {
   840  		if die.Abbrev != dwarf.DW_ABRV_SLICETYPE {
   841  			continue
   842  		}
   843  		d.copychildren(ctxt, die, prototype)
   844  		elem := loader.Sym(getattr(die, dwarf.DW_AT_go_elem).Data.(dwSym))
   845  		d.substitutetype(die, "array", d.defptrto(elem))
   846  	}
   847  }
   848  
   849  func mkinternaltypename(base string, arg1 string, arg2 string) string {
   850  	if arg2 == "" {
   851  		return fmt.Sprintf("%s<%s>", base, arg1)
   852  	}
   853  	return fmt.Sprintf("%s<%s,%s>", base, arg1, arg2)
   854  }
   855  
   856  // synthesizemaptypes is way too closely married to runtime/hashmap.c
   857  const (
   858  	MaxKeySize = 128
   859  	MaxValSize = 128
   860  	BucketSize = 8
   861  )
   862  
   863  func (d *dwctxt) mkinternaltype(ctxt *Link, abbrev int, typename, keyname, valname string, f func(*dwarf.DWDie)) loader.Sym {
   864  	name := mkinternaltypename(typename, keyname, valname)
   865  	symname := dwarf.InfoPrefix + name
   866  	s := d.ldr.Lookup(symname, 0)
   867  	if s != 0 && d.ldr.SymType(s) == sym.SDWARFTYPE {
   868  		return s
   869  	}
   870  	die := d.newdie(&dwtypes, abbrev, name, 0)
   871  	f(die)
   872  	return d.dtolsym(die.Sym)
   873  }
   874  
   875  func (d *dwctxt) synthesizemaptypes(ctxt *Link, die *dwarf.DWDie) {
   876  	hash := walktypedef(d.findprotodie(ctxt, "type.runtime.hmap"))
   877  	bucket := walktypedef(d.findprotodie(ctxt, "type.runtime.bmap"))
   878  
   879  	if hash == nil {
   880  		return
   881  	}
   882  
   883  	for ; die != nil; die = die.Link {
   884  		if die.Abbrev != dwarf.DW_ABRV_MAPTYPE {
   885  			continue
   886  		}
   887  		gotype := loader.Sym(getattr(die, dwarf.DW_AT_type).Data.(dwSym))
   888  		keytype := decodetypeMapKey(d.ldr, d.arch, gotype)
   889  		valtype := decodetypeMapValue(d.ldr, d.arch, gotype)
   890  		keydata := d.ldr.Data(keytype)
   891  		valdata := d.ldr.Data(valtype)
   892  		keysize, valsize := decodetypeSize(d.arch, keydata), decodetypeSize(d.arch, valdata)
   893  		keytype, valtype = d.walksymtypedef(d.defgotype(keytype)), d.walksymtypedef(d.defgotype(valtype))
   894  
   895  		// compute size info like hashmap.c does.
   896  		indirectKey, indirectVal := false, false
   897  		if keysize > MaxKeySize {
   898  			keysize = int64(d.arch.PtrSize)
   899  			indirectKey = true
   900  		}
   901  		if valsize > MaxValSize {
   902  			valsize = int64(d.arch.PtrSize)
   903  			indirectVal = true
   904  		}
   905  
   906  		// Construct type to represent an array of BucketSize keys
   907  		keyname := d.nameFromDIESym(keytype)
   908  		dwhks := d.mkinternaltype(ctxt, dwarf.DW_ABRV_ARRAYTYPE, "[]key", keyname, "", func(dwhk *dwarf.DWDie) {
   909  			newattr(dwhk, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize*keysize, 0)
   910  			t := keytype
   911  			if indirectKey {
   912  				t = d.defptrto(keytype)
   913  			}
   914  			d.newrefattr(dwhk, dwarf.DW_AT_type, t)
   915  			fld := d.newdie(dwhk, dwarf.DW_ABRV_ARRAYRANGE, "size", 0)
   916  			newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, BucketSize, 0)
   917  			d.newrefattr(fld, dwarf.DW_AT_type, d.uintptrInfoSym)
   918  		})
   919  
   920  		// Construct type to represent an array of BucketSize values
   921  		valname := d.nameFromDIESym(valtype)
   922  		dwhvs := d.mkinternaltype(ctxt, dwarf.DW_ABRV_ARRAYTYPE, "[]val", valname, "", func(dwhv *dwarf.DWDie) {
   923  			newattr(dwhv, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize*valsize, 0)
   924  			t := valtype
   925  			if indirectVal {
   926  				t = d.defptrto(valtype)
   927  			}
   928  			d.newrefattr(dwhv, dwarf.DW_AT_type, t)
   929  			fld := d.newdie(dwhv, dwarf.DW_ABRV_ARRAYRANGE, "size", 0)
   930  			newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, BucketSize, 0)
   931  			d.newrefattr(fld, dwarf.DW_AT_type, d.uintptrInfoSym)
   932  		})
   933  
   934  		// Construct bucket<K,V>
   935  		dwhbs := d.mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "bucket", keyname, valname, func(dwhb *dwarf.DWDie) {
   936  			// Copy over all fields except the field "data" from the generic
   937  			// bucket. "data" will be replaced with keys/values below.
   938  			d.copychildrenexcept(ctxt, dwhb, bucket, findchild(bucket, "data"))
   939  
   940  			fld := d.newdie(dwhb, dwarf.DW_ABRV_STRUCTFIELD, "keys", 0)
   941  			d.newrefattr(fld, dwarf.DW_AT_type, dwhks)
   942  			newmemberoffsetattr(fld, BucketSize)
   943  			fld = d.newdie(dwhb, dwarf.DW_ABRV_STRUCTFIELD, "values", 0)
   944  			d.newrefattr(fld, dwarf.DW_AT_type, dwhvs)
   945  			newmemberoffsetattr(fld, BucketSize+BucketSize*int32(keysize))
   946  			fld = d.newdie(dwhb, dwarf.DW_ABRV_STRUCTFIELD, "overflow", 0)
   947  			d.newrefattr(fld, dwarf.DW_AT_type, d.defptrto(d.dtolsym(dwhb.Sym)))
   948  			newmemberoffsetattr(fld, BucketSize+BucketSize*(int32(keysize)+int32(valsize)))
   949  			if d.arch.RegSize > d.arch.PtrSize {
   950  				fld = d.newdie(dwhb, dwarf.DW_ABRV_STRUCTFIELD, "pad", 0)
   951  				d.newrefattr(fld, dwarf.DW_AT_type, d.uintptrInfoSym)
   952  				newmemberoffsetattr(fld, BucketSize+BucketSize*(int32(keysize)+int32(valsize))+int32(d.arch.PtrSize))
   953  			}
   954  
   955  			newattr(dwhb, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize+BucketSize*keysize+BucketSize*valsize+int64(d.arch.RegSize), 0)
   956  		})
   957  
   958  		// Construct hash<K,V>
   959  		dwhs := d.mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "hash", keyname, valname, func(dwh *dwarf.DWDie) {
   960  			d.copychildren(ctxt, dwh, hash)
   961  			d.substitutetype(dwh, "buckets", d.defptrto(dwhbs))
   962  			d.substitutetype(dwh, "oldbuckets", d.defptrto(dwhbs))
   963  			newattr(dwh, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(hash, dwarf.DW_AT_byte_size).Value, nil)
   964  		})
   965  
   966  		// make map type a pointer to hash<K,V>
   967  		d.newrefattr(die, dwarf.DW_AT_type, d.defptrto(dwhs))
   968  	}
   969  }
   970  
   971  func (d *dwctxt) synthesizechantypes(ctxt *Link, die *dwarf.DWDie) {
   972  	sudog := walktypedef(d.findprotodie(ctxt, "type.runtime.sudog"))
   973  	waitq := walktypedef(d.findprotodie(ctxt, "type.runtime.waitq"))
   974  	hchan := walktypedef(d.findprotodie(ctxt, "type.runtime.hchan"))
   975  	if sudog == nil || waitq == nil || hchan == nil {
   976  		return
   977  	}
   978  
   979  	sudogsize := int(getattr(sudog, dwarf.DW_AT_byte_size).Value)
   980  
   981  	for ; die != nil; die = die.Link {
   982  		if die.Abbrev != dwarf.DW_ABRV_CHANTYPE {
   983  			continue
   984  		}
   985  		elemgotype := loader.Sym(getattr(die, dwarf.DW_AT_type).Data.(dwSym))
   986  		tname := d.ldr.SymName(elemgotype)
   987  		elemname := tname[5:]
   988  		elemtype := d.walksymtypedef(d.defgotype(d.lookupOrDiag(tname)))
   989  
   990  		// sudog<T>
   991  		dwss := d.mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "sudog", elemname, "", func(dws *dwarf.DWDie) {
   992  			d.copychildren(ctxt, dws, sudog)
   993  			d.substitutetype(dws, "elem", d.defptrto(elemtype))
   994  			newattr(dws, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, int64(sudogsize), nil)
   995  		})
   996  
   997  		// waitq<T>
   998  		dwws := d.mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "waitq", elemname, "", func(dww *dwarf.DWDie) {
   999  
  1000  			d.copychildren(ctxt, dww, waitq)
  1001  			d.substitutetype(dww, "first", d.defptrto(dwss))
  1002  			d.substitutetype(dww, "last", d.defptrto(dwss))
  1003  			newattr(dww, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(waitq, dwarf.DW_AT_byte_size).Value, nil)
  1004  		})
  1005  
  1006  		// hchan<T>
  1007  		dwhs := d.mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "hchan", elemname, "", func(dwh *dwarf.DWDie) {
  1008  			d.copychildren(ctxt, dwh, hchan)
  1009  			d.substitutetype(dwh, "recvq", dwws)
  1010  			d.substitutetype(dwh, "sendq", dwws)
  1011  			newattr(dwh, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(hchan, dwarf.DW_AT_byte_size).Value, nil)
  1012  		})
  1013  
  1014  		d.newrefattr(die, dwarf.DW_AT_type, d.defptrto(dwhs))
  1015  	}
  1016  }
  1017  
  1018  // createUnitLength creates the initial length field with value v and update
  1019  // offset of unit_length if needed.
  1020  func (d *dwctxt) createUnitLength(su *loader.SymbolBuilder, v uint64) {
  1021  	if isDwarf64(d.linkctxt) {
  1022  		su.AddUint32(d.arch, 0xFFFFFFFF)
  1023  	}
  1024  	d.addDwarfAddrField(su, v)
  1025  }
  1026  
  1027  // addDwarfAddrField adds a DWARF field in DWARF 64bits or 32bits.
  1028  func (d *dwctxt) addDwarfAddrField(sb *loader.SymbolBuilder, v uint64) {
  1029  	if isDwarf64(d.linkctxt) {
  1030  		sb.AddUint(d.arch, v)
  1031  	} else {
  1032  		sb.AddUint32(d.arch, uint32(v))
  1033  	}
  1034  }
  1035  
  1036  // addDwarfAddrRef adds a DWARF pointer in DWARF 64bits or 32bits.
  1037  func (d *dwctxt) addDwarfAddrRef(sb *loader.SymbolBuilder, t loader.Sym) {
  1038  	if isDwarf64(d.linkctxt) {
  1039  		d.adddwarfref(sb, t, 8)
  1040  	} else {
  1041  		d.adddwarfref(sb, t, 4)
  1042  	}
  1043  }
  1044  
  1045  // calcCompUnitRanges calculates the PC ranges of the compilation units.
  1046  func (d *dwctxt) calcCompUnitRanges() {
  1047  	var prevUnit *sym.CompilationUnit
  1048  	for _, s := range d.linkctxt.Textp {
  1049  		sym := loader.Sym(s)
  1050  
  1051  		fi := d.ldr.FuncInfo(sym)
  1052  		if !fi.Valid() {
  1053  			continue
  1054  		}
  1055  
  1056  		// Skip linker-created functions (ex: runtime.addmoduledata), since they
  1057  		// don't have DWARF to begin with.
  1058  		unit := d.ldr.SymUnit(sym)
  1059  		if unit == nil {
  1060  			continue
  1061  		}
  1062  
  1063  		// Update PC ranges.
  1064  		//
  1065  		// We don't simply compare the end of the previous
  1066  		// symbol with the start of the next because there's
  1067  		// often a little padding between them. Instead, we
  1068  		// only create boundaries between symbols from
  1069  		// different units.
  1070  		sval := d.ldr.SymValue(sym)
  1071  		u0val := d.ldr.SymValue(loader.Sym(unit.Textp[0]))
  1072  		if prevUnit != unit {
  1073  			unit.PCs = append(unit.PCs, dwarf.Range{Start: sval - u0val})
  1074  			prevUnit = unit
  1075  		}
  1076  		unit.PCs[len(unit.PCs)-1].End = sval - u0val + int64(len(d.ldr.Data(sym)))
  1077  	}
  1078  }
  1079  
  1080  func movetomodule(ctxt *Link, parent *dwarf.DWDie) {
  1081  	die := ctxt.runtimeCU.DWInfo.Child
  1082  	if die == nil {
  1083  		ctxt.runtimeCU.DWInfo.Child = parent.Child
  1084  		return
  1085  	}
  1086  	for die.Link != nil {
  1087  		die = die.Link
  1088  	}
  1089  	die.Link = parent.Child
  1090  }
  1091  
  1092  /*
  1093   * Generate a sequence of opcodes that is as short as possible.
  1094   * See section 6.2.5
  1095   */
  1096  const (
  1097  	LINE_BASE   = -4
  1098  	LINE_RANGE  = 10
  1099  	PC_RANGE    = (255 - OPCODE_BASE) / LINE_RANGE
  1100  	OPCODE_BASE = 11
  1101  )
  1102  
  1103  /*
  1104   * Walk prog table, emit line program and build DIE tree.
  1105   */
  1106  
  1107  func getCompilationDir() string {
  1108  	// OSX requires this be set to something, but it's not easy to choose
  1109  	// a value. Linking takes place in a temporary directory, so there's
  1110  	// no point including it here. Paths in the file table are usually
  1111  	// absolute, in which case debuggers will ignore this value. -trimpath
  1112  	// produces relative paths, but we don't know where they start, so
  1113  	// all we can do here is try not to make things worse.
  1114  	return "."
  1115  }
  1116  
  1117  func (d *dwctxt) importInfoSymbol(dsym loader.Sym) {
  1118  	d.ldr.SetAttrReachable(dsym, true)
  1119  	d.ldr.SetAttrNotInSymbolTable(dsym, true)
  1120  	dst := d.ldr.SymType(dsym)
  1121  	if dst != sym.SDWARFCONST && dst != sym.SDWARFABSFCN {
  1122  		log.Fatalf("error: DWARF info sym %d/%s with incorrect type %s", dsym, d.ldr.SymName(dsym), d.ldr.SymType(dsym).String())
  1123  	}
  1124  	relocs := d.ldr.Relocs(dsym)
  1125  	for i := 0; i < relocs.Count(); i++ {
  1126  		r := relocs.At(i)
  1127  		if r.Type() != objabi.R_DWARFSECREF {
  1128  			continue
  1129  		}
  1130  		rsym := r.Sym()
  1131  		// If there is an entry for the symbol in our rtmap, then it
  1132  		// means we've processed the type already, and can skip this one.
  1133  		if _, ok := d.rtmap[rsym]; ok {
  1134  			// type already generated
  1135  			continue
  1136  		}
  1137  		// FIXME: is there a way we could avoid materializing the
  1138  		// symbol name here?
  1139  		sn := d.ldr.SymName(rsym)
  1140  		tn := sn[len(dwarf.InfoPrefix):]
  1141  		ts := d.ldr.Lookup("type."+tn, 0)
  1142  		d.defgotype(ts)
  1143  	}
  1144  }
  1145  
  1146  func expandFile(fname string) string {
  1147  	if strings.HasPrefix(fname, src.FileSymPrefix) {
  1148  		fname = fname[len(src.FileSymPrefix):]
  1149  	}
  1150  	return expandGoroot(fname)
  1151  }
  1152  
  1153  // writeDirFileTables emits the portion of the DWARF line table
  1154  // prologue containing the include directories and file names,
  1155  // described in section 6.2.4 of the DWARF 4 standard. It walks the
  1156  // filepaths for the unit to discover any common directories, which
  1157  // are emitted to the directory table first, then the file table is
  1158  // emitted after that.
  1159  func (d *dwctxt) writeDirFileTables(unit *sym.CompilationUnit, lsu *loader.SymbolBuilder) {
  1160  	type fileDir struct {
  1161  		base string
  1162  		dir  int
  1163  	}
  1164  	dirNums := make(map[string]int)
  1165  	dirs := []string{""}
  1166  	files := []fileDir{}
  1167  
  1168  	// Preprocess files to collect directories. This assumes that the
  1169  	// file table is already de-duped.
  1170  	for i, name := range unit.FileTable {
  1171  		name := expandFile(name)
  1172  		if len(name) == 0 {
  1173  			// Can't have empty filenames, and having a unique
  1174  			// filename is quite useful for debugging.
  1175  			name = fmt.Sprintf("<missing>_%d", i)
  1176  		}
  1177  		// Note the use of "path" here and not "filepath". The compiler
  1178  		// hard-codes to use "/" in DWARF paths (even for Windows), so we
  1179  		// want to maintain that here.
  1180  		file := path.Base(name)
  1181  		dir := path.Dir(name)
  1182  		dirIdx, ok := dirNums[dir]
  1183  		if !ok && dir != "." {
  1184  			dirIdx = len(dirNums) + 1
  1185  			dirNums[dir] = dirIdx
  1186  			dirs = append(dirs, dir)
  1187  		}
  1188  		files = append(files, fileDir{base: file, dir: dirIdx})
  1189  
  1190  		// We can't use something that may be dead-code
  1191  		// eliminated from a binary here. proc.go contains
  1192  		// main and the scheduler, so it's not going anywhere.
  1193  		if i := strings.Index(name, "runtime/proc.go"); i >= 0 {
  1194  			d.dwmu.Lock()
  1195  			if gdbscript == "" {
  1196  				k := strings.Index(name, "runtime/proc.go")
  1197  				gdbscript = name[:k] + "runtime/runtime-gdb.py"
  1198  			}
  1199  			d.dwmu.Unlock()
  1200  		}
  1201  	}
  1202  
  1203  	// Emit directory section. This is a series of nul terminated
  1204  	// strings, followed by a single zero byte.
  1205  	lsDwsym := dwSym(lsu.Sym())
  1206  	for k := 1; k < len(dirs); k++ {
  1207  		d.AddString(lsDwsym, dirs[k])
  1208  	}
  1209  	lsu.AddUint8(0) // terminator
  1210  
  1211  	// Emit file section.
  1212  	for k := 0; k < len(files); k++ {
  1213  		d.AddString(lsDwsym, files[k].base)
  1214  		dwarf.Uleb128put(d, lsDwsym, int64(files[k].dir))
  1215  		lsu.AddUint8(0) // mtime
  1216  		lsu.AddUint8(0) // length
  1217  	}
  1218  	lsu.AddUint8(0) // terminator
  1219  }
  1220  
  1221  // writelines collects up and chains together the symbols needed to
  1222  // form the DWARF line table for the specified compilation unit,
  1223  // returning a list of symbols. The returned list will include an
  1224  // initial symbol containing the line table header and prologue (with
  1225  // file table), then a series of compiler-emitted line table symbols
  1226  // (one per live function), and finally an epilog symbol containing an
  1227  // end-of-sequence operator. The prologue and epilog symbols are passed
  1228  // in (having been created earlier); here we add content to them.
  1229  func (d *dwctxt) writelines(unit *sym.CompilationUnit, lineProlog loader.Sym) []loader.Sym {
  1230  	is_stmt := uint8(1) // initially = recommended default_is_stmt = 1, tracks is_stmt toggles.
  1231  
  1232  	unitstart := int64(-1)
  1233  	headerstart := int64(-1)
  1234  	headerend := int64(-1)
  1235  
  1236  	syms := make([]loader.Sym, 0, len(unit.Textp)+2)
  1237  	syms = append(syms, lineProlog)
  1238  	lsu := d.ldr.MakeSymbolUpdater(lineProlog)
  1239  	lsDwsym := dwSym(lineProlog)
  1240  	newattr(unit.DWInfo, dwarf.DW_AT_stmt_list, dwarf.DW_CLS_PTR, 0, lsDwsym)
  1241  
  1242  	// Write .debug_line Line Number Program Header (sec 6.2.4)
  1243  	// Fields marked with (*) must be changed for 64-bit dwarf
  1244  	unitLengthOffset := lsu.Size()
  1245  	d.createUnitLength(lsu, 0) // unit_length (*), filled in at end
  1246  	unitstart = lsu.Size()
  1247  	lsu.AddUint16(d.arch, 2) // dwarf version (appendix F) -- version 3 is incompatible w/ XCode 9.0's dsymutil, latest supported on OSX 10.12 as of 2018-05
  1248  	headerLengthOffset := lsu.Size()
  1249  	d.addDwarfAddrField(lsu, 0) // header_length (*), filled in at end
  1250  	headerstart = lsu.Size()
  1251  
  1252  	// cpos == unitstart + 4 + 2 + 4
  1253  	lsu.AddUint8(1)                // minimum_instruction_length
  1254  	lsu.AddUint8(is_stmt)          // default_is_stmt
  1255  	lsu.AddUint8(LINE_BASE & 0xFF) // line_base
  1256  	lsu.AddUint8(LINE_RANGE)       // line_range
  1257  	lsu.AddUint8(OPCODE_BASE)      // opcode_base
  1258  	lsu.AddUint8(0)                // standard_opcode_lengths[1]
  1259  	lsu.AddUint8(1)                // standard_opcode_lengths[2]
  1260  	lsu.AddUint8(1)                // standard_opcode_lengths[3]
  1261  	lsu.AddUint8(1)                // standard_opcode_lengths[4]
  1262  	lsu.AddUint8(1)                // standard_opcode_lengths[5]
  1263  	lsu.AddUint8(0)                // standard_opcode_lengths[6]
  1264  	lsu.AddUint8(0)                // standard_opcode_lengths[7]
  1265  	lsu.AddUint8(0)                // standard_opcode_lengths[8]
  1266  	lsu.AddUint8(1)                // standard_opcode_lengths[9]
  1267  	lsu.AddUint8(0)                // standard_opcode_lengths[10]
  1268  
  1269  	// Call helper to emit dir and file sections.
  1270  	d.writeDirFileTables(unit, lsu)
  1271  
  1272  	// capture length at end of file names.
  1273  	headerend = lsu.Size()
  1274  	unitlen := lsu.Size() - unitstart
  1275  
  1276  	// Output the state machine for each function remaining.
  1277  	for _, s := range unit.Textp {
  1278  		fnSym := loader.Sym(s)
  1279  		_, _, _, lines := d.ldr.GetFuncDwarfAuxSyms(fnSym)
  1280  
  1281  		// Chain the line symbol onto the list.
  1282  		if lines != 0 {
  1283  			syms = append(syms, lines)
  1284  			unitlen += int64(len(d.ldr.Data(lines)))
  1285  		}
  1286  	}
  1287  
  1288  	if d.linkctxt.HeadType == objabi.Haix {
  1289  		addDwsectCUSize(".debug_line", unit.Lib.Pkg, uint64(unitlen))
  1290  	}
  1291  
  1292  	if isDwarf64(d.linkctxt) {
  1293  		lsu.SetUint(d.arch, unitLengthOffset+4, uint64(unitlen)) // +4 because of 0xFFFFFFFF
  1294  		lsu.SetUint(d.arch, headerLengthOffset, uint64(headerend-headerstart))
  1295  	} else {
  1296  		lsu.SetUint32(d.arch, unitLengthOffset, uint32(unitlen))
  1297  		lsu.SetUint32(d.arch, headerLengthOffset, uint32(headerend-headerstart))
  1298  	}
  1299  
  1300  	return syms
  1301  }
  1302  
  1303  // writepcranges generates the DW_AT_ranges table for compilation unit
  1304  // "unit", and returns a collection of ranges symbols (one for the
  1305  // compilation unit DIE itself and the remainder from functions in the unit).
  1306  func (d *dwctxt) writepcranges(unit *sym.CompilationUnit, base loader.Sym, pcs []dwarf.Range, rangeProlog loader.Sym) []loader.Sym {
  1307  
  1308  	syms := make([]loader.Sym, 0, len(unit.RangeSyms)+1)
  1309  	syms = append(syms, rangeProlog)
  1310  	rsu := d.ldr.MakeSymbolUpdater(rangeProlog)
  1311  	rDwSym := dwSym(rangeProlog)
  1312  
  1313  	// Create PC ranges for the compilation unit DIE.
  1314  	newattr(unit.DWInfo, dwarf.DW_AT_ranges, dwarf.DW_CLS_PTR, rsu.Size(), rDwSym)
  1315  	newattr(unit.DWInfo, dwarf.DW_AT_low_pc, dwarf.DW_CLS_ADDRESS, 0, dwSym(base))
  1316  	dwarf.PutBasedRanges(d, rDwSym, pcs)
  1317  
  1318  	// Collect up the ranges for functions in the unit.
  1319  	rsize := uint64(rsu.Size())
  1320  	for _, ls := range unit.RangeSyms {
  1321  		s := loader.Sym(ls)
  1322  		syms = append(syms, s)
  1323  		rsize += uint64(d.ldr.SymSize(s))
  1324  	}
  1325  
  1326  	if d.linkctxt.HeadType == objabi.Haix {
  1327  		addDwsectCUSize(".debug_ranges", unit.Lib.Pkg, rsize)
  1328  	}
  1329  
  1330  	return syms
  1331  }
  1332  
  1333  /*
  1334   *  Emit .debug_frame
  1335   */
  1336  const (
  1337  	dataAlignmentFactor = -4
  1338  )
  1339  
  1340  // appendPCDeltaCFA appends per-PC CFA deltas to b and returns the final slice.
  1341  func appendPCDeltaCFA(arch *sys.Arch, b []byte, deltapc, cfa int64) []byte {
  1342  	b = append(b, dwarf.DW_CFA_def_cfa_offset_sf)
  1343  	b = dwarf.AppendSleb128(b, cfa/dataAlignmentFactor)
  1344  
  1345  	switch {
  1346  	case deltapc < 0x40:
  1347  		b = append(b, uint8(dwarf.DW_CFA_advance_loc+deltapc))
  1348  	case deltapc < 0x100:
  1349  		b = append(b, dwarf.DW_CFA_advance_loc1)
  1350  		b = append(b, uint8(deltapc))
  1351  	case deltapc < 0x10000:
  1352  		b = append(b, dwarf.DW_CFA_advance_loc2, 0, 0)
  1353  		arch.ByteOrder.PutUint16(b[len(b)-2:], uint16(deltapc))
  1354  	default:
  1355  		b = append(b, dwarf.DW_CFA_advance_loc4, 0, 0, 0, 0)
  1356  		arch.ByteOrder.PutUint32(b[len(b)-4:], uint32(deltapc))
  1357  	}
  1358  	return b
  1359  }
  1360  
  1361  func (d *dwctxt) writeframes(fs loader.Sym) dwarfSecInfo {
  1362  	fsd := dwSym(fs)
  1363  	fsu := d.ldr.MakeSymbolUpdater(fs)
  1364  	fsu.SetType(sym.SDWARFSECT)
  1365  	isdw64 := isDwarf64(d.linkctxt)
  1366  	haslr := haslinkregister(d.linkctxt)
  1367  
  1368  	// Length field is 4 bytes on Dwarf32 and 12 bytes on Dwarf64
  1369  	lengthFieldSize := int64(4)
  1370  	if isdw64 {
  1371  		lengthFieldSize += 8
  1372  	}
  1373  
  1374  	// Emit the CIE, Section 6.4.1
  1375  	cieReserve := uint32(16)
  1376  	if haslr {
  1377  		cieReserve = 32
  1378  	}
  1379  	if isdw64 {
  1380  		cieReserve += 4 // 4 bytes added for cid
  1381  	}
  1382  	d.createUnitLength(fsu, uint64(cieReserve))         // initial length, must be multiple of thearch.ptrsize
  1383  	d.addDwarfAddrField(fsu, ^uint64(0))                // cid
  1384  	fsu.AddUint8(3)                                     // dwarf version (appendix F)
  1385  	fsu.AddUint8(0)                                     // augmentation ""
  1386  	dwarf.Uleb128put(d, fsd, 1)                         // code_alignment_factor
  1387  	dwarf.Sleb128put(d, fsd, dataAlignmentFactor)       // all CFI offset calculations include multiplication with this factor
  1388  	dwarf.Uleb128put(d, fsd, int64(thearch.Dwarfreglr)) // return_address_register
  1389  
  1390  	fsu.AddUint8(dwarf.DW_CFA_def_cfa)                  // Set the current frame address..
  1391  	dwarf.Uleb128put(d, fsd, int64(thearch.Dwarfregsp)) // ...to use the value in the platform's SP register (defined in l.go)...
  1392  	if haslr {
  1393  		dwarf.Uleb128put(d, fsd, int64(0)) // ...plus a 0 offset.
  1394  
  1395  		fsu.AddUint8(dwarf.DW_CFA_same_value) // The platform's link register is unchanged during the prologue.
  1396  		dwarf.Uleb128put(d, fsd, int64(thearch.Dwarfreglr))
  1397  
  1398  		fsu.AddUint8(dwarf.DW_CFA_val_offset)               // The previous value...
  1399  		dwarf.Uleb128put(d, fsd, int64(thearch.Dwarfregsp)) // ...of the platform's SP register...
  1400  		dwarf.Uleb128put(d, fsd, int64(0))                  // ...is CFA+0.
  1401  	} else {
  1402  		dwarf.Uleb128put(d, fsd, int64(d.arch.PtrSize)) // ...plus the word size (because the call instruction implicitly adds one word to the frame).
  1403  
  1404  		fsu.AddUint8(dwarf.DW_CFA_offset_extended)                           // The previous value...
  1405  		dwarf.Uleb128put(d, fsd, int64(thearch.Dwarfreglr))                  // ...of the return address...
  1406  		dwarf.Uleb128put(d, fsd, int64(-d.arch.PtrSize)/dataAlignmentFactor) // ...is saved at [CFA - (PtrSize/4)].
  1407  	}
  1408  
  1409  	pad := int64(cieReserve) + lengthFieldSize - int64(len(d.ldr.Data(fs)))
  1410  
  1411  	if pad < 0 {
  1412  		Exitf("dwarf: cieReserve too small by %d bytes.", -pad)
  1413  	}
  1414  
  1415  	internalExec := d.linkctxt.BuildMode == BuildModeExe && d.linkctxt.IsInternal()
  1416  	addAddrPlus := loader.GenAddAddrPlusFunc(internalExec)
  1417  
  1418  	fsu.AddBytes(zeros[:pad])
  1419  
  1420  	var deltaBuf []byte
  1421  	pcsp := obj.NewPCIter(uint32(d.arch.MinLC))
  1422  	for _, s := range d.linkctxt.Textp {
  1423  		fn := loader.Sym(s)
  1424  		fi := d.ldr.FuncInfo(fn)
  1425  		if !fi.Valid() {
  1426  			continue
  1427  		}
  1428  		fpcsp := fi.Pcsp()
  1429  
  1430  		// Emit a FDE, Section 6.4.1.
  1431  		// First build the section contents into a byte buffer.
  1432  		deltaBuf = deltaBuf[:0]
  1433  		if haslr && fi.TopFrame() {
  1434  			// Mark the link register as having an undefined value.
  1435  			// This stops call stack unwinders progressing any further.
  1436  			// TODO: similar mark on non-LR architectures.
  1437  			deltaBuf = append(deltaBuf, dwarf.DW_CFA_undefined)
  1438  			deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(thearch.Dwarfreglr))
  1439  		}
  1440  
  1441  		for pcsp.Init(d.linkctxt.loader.Data(fpcsp)); !pcsp.Done; pcsp.Next() {
  1442  			nextpc := pcsp.NextPC
  1443  
  1444  			// pciterinit goes up to the end of the function,
  1445  			// but DWARF expects us to stop just before the end.
  1446  			if int64(nextpc) == int64(len(d.ldr.Data(fn))) {
  1447  				nextpc--
  1448  				if nextpc < pcsp.PC {
  1449  					continue
  1450  				}
  1451  			}
  1452  
  1453  			spdelta := int64(pcsp.Value)
  1454  			if !haslr {
  1455  				// Return address has been pushed onto stack.
  1456  				spdelta += int64(d.arch.PtrSize)
  1457  			}
  1458  
  1459  			if haslr && !fi.TopFrame() {
  1460  				// TODO(bryanpkc): This is imprecise. In general, the instruction
  1461  				// that stores the return address to the stack frame is not the
  1462  				// same one that allocates the frame.
  1463  				if pcsp.Value > 0 {
  1464  					// The return address is preserved at (CFA-frame_size)
  1465  					// after a stack frame has been allocated.
  1466  					deltaBuf = append(deltaBuf, dwarf.DW_CFA_offset_extended_sf)
  1467  					deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(thearch.Dwarfreglr))
  1468  					deltaBuf = dwarf.AppendSleb128(deltaBuf, -spdelta/dataAlignmentFactor)
  1469  				} else {
  1470  					// The return address is restored into the link register
  1471  					// when a stack frame has been de-allocated.
  1472  					deltaBuf = append(deltaBuf, dwarf.DW_CFA_same_value)
  1473  					deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(thearch.Dwarfreglr))
  1474  				}
  1475  			}
  1476  
  1477  			deltaBuf = appendPCDeltaCFA(d.arch, deltaBuf, int64(nextpc)-int64(pcsp.PC), spdelta)
  1478  		}
  1479  		pad := int(Rnd(int64(len(deltaBuf)), int64(d.arch.PtrSize))) - len(deltaBuf)
  1480  		deltaBuf = append(deltaBuf, zeros[:pad]...)
  1481  
  1482  		// Emit the FDE header, Section 6.4.1.
  1483  		//	4 bytes: length, must be multiple of thearch.ptrsize
  1484  		//	4/8 bytes: Pointer to the CIE above, at offset 0
  1485  		//	ptrsize: initial location
  1486  		//	ptrsize: address range
  1487  
  1488  		fdeLength := uint64(4 + 2*d.arch.PtrSize + len(deltaBuf))
  1489  		if isdw64 {
  1490  			fdeLength += 4 // 4 bytes added for CIE pointer
  1491  		}
  1492  		d.createUnitLength(fsu, fdeLength)
  1493  
  1494  		if d.linkctxt.LinkMode == LinkExternal {
  1495  			d.addDwarfAddrRef(fsu, fs)
  1496  		} else {
  1497  			d.addDwarfAddrField(fsu, 0) // CIE offset
  1498  		}
  1499  		addAddrPlus(fsu, d.arch, s, 0)
  1500  		fsu.AddUintXX(d.arch, uint64(len(d.ldr.Data(fn))), d.arch.PtrSize) // address range
  1501  		fsu.AddBytes(deltaBuf)
  1502  
  1503  		if d.linkctxt.HeadType == objabi.Haix {
  1504  			addDwsectCUSize(".debug_frame", d.ldr.SymPkg(fn), fdeLength+uint64(lengthFieldSize))
  1505  		}
  1506  	}
  1507  
  1508  	return dwarfSecInfo{syms: []loader.Sym{fs}}
  1509  }
  1510  
  1511  /*
  1512   *  Walk DWarfDebugInfoEntries, and emit .debug_info
  1513   */
  1514  
  1515  const (
  1516  	COMPUNITHEADERSIZE = 4 + 2 + 4 + 1
  1517  )
  1518  
  1519  // appendSyms appends the syms from 'src' into 'syms' and returns the
  1520  // result. This can go away once we do away with sym.LoaderSym
  1521  // entirely.
  1522  func appendSyms(syms []loader.Sym, src []sym.LoaderSym) []loader.Sym {
  1523  	for _, s := range src {
  1524  		syms = append(syms, loader.Sym(s))
  1525  	}
  1526  	return syms
  1527  }
  1528  
  1529  func (d *dwctxt) writeUnitInfo(u *sym.CompilationUnit, abbrevsym loader.Sym, infoEpilog loader.Sym) []loader.Sym {
  1530  	syms := []loader.Sym{}
  1531  	if len(u.Textp) == 0 && u.DWInfo.Child == nil && len(u.VarDIEs) == 0 {
  1532  		return syms
  1533  	}
  1534  
  1535  	compunit := u.DWInfo
  1536  	s := d.dtolsym(compunit.Sym)
  1537  	su := d.ldr.MakeSymbolUpdater(s)
  1538  
  1539  	// Write .debug_info Compilation Unit Header (sec 7.5.1)
  1540  	// Fields marked with (*) must be changed for 64-bit dwarf
  1541  	// This must match COMPUNITHEADERSIZE above.
  1542  	d.createUnitLength(su, 0) // unit_length (*), will be filled in later.
  1543  	su.AddUint16(d.arch, 4)   // dwarf version (appendix F)
  1544  
  1545  	// debug_abbrev_offset (*)
  1546  	d.addDwarfAddrRef(su, abbrevsym)
  1547  
  1548  	su.AddUint8(uint8(d.arch.PtrSize)) // address_size
  1549  
  1550  	ds := dwSym(s)
  1551  	dwarf.Uleb128put(d, ds, int64(compunit.Abbrev))
  1552  	dwarf.PutAttrs(d, ds, compunit.Abbrev, compunit.Attr)
  1553  
  1554  	// This is an under-estimate; more will be needed for type DIEs.
  1555  	cu := make([]loader.Sym, 0, len(u.AbsFnDIEs)+len(u.FuncDIEs))
  1556  	cu = append(cu, s)
  1557  	cu = appendSyms(cu, u.AbsFnDIEs)
  1558  	cu = appendSyms(cu, u.FuncDIEs)
  1559  	if u.Consts != 0 {
  1560  		cu = append(cu, loader.Sym(u.Consts))
  1561  	}
  1562  	cu = appendSyms(cu, u.VarDIEs)
  1563  	var cusize int64
  1564  	for _, child := range cu {
  1565  		cusize += int64(len(d.ldr.Data(child)))
  1566  	}
  1567  
  1568  	for die := compunit.Child; die != nil; die = die.Link {
  1569  		l := len(cu)
  1570  		lastSymSz := int64(len(d.ldr.Data(cu[l-1])))
  1571  		cu = d.putdie(cu, die)
  1572  		if lastSymSz != int64(len(d.ldr.Data(cu[l-1]))) {
  1573  			// putdie will sometimes append directly to the last symbol of the list
  1574  			cusize = cusize - lastSymSz + int64(len(d.ldr.Data(cu[l-1])))
  1575  		}
  1576  		for _, child := range cu[l:] {
  1577  			cusize += int64(len(d.ldr.Data(child)))
  1578  		}
  1579  	}
  1580  
  1581  	culu := d.ldr.MakeSymbolUpdater(infoEpilog)
  1582  	culu.AddUint8(0) // closes compilation unit DIE
  1583  	cu = append(cu, infoEpilog)
  1584  	cusize++
  1585  
  1586  	// Save size for AIX symbol table.
  1587  	if d.linkctxt.HeadType == objabi.Haix {
  1588  		addDwsectCUSize(".debug_info", d.getPkgFromCUSym(s), uint64(cusize))
  1589  	}
  1590  	if isDwarf64(d.linkctxt) {
  1591  		cusize -= 12                          // exclude the length field.
  1592  		su.SetUint(d.arch, 4, uint64(cusize)) // 4 because of 0XFFFFFFFF
  1593  	} else {
  1594  		cusize -= 4 // exclude the length field.
  1595  		su.SetUint32(d.arch, 0, uint32(cusize))
  1596  	}
  1597  	return append(syms, cu...)
  1598  }
  1599  
  1600  func (d *dwctxt) writegdbscript() dwarfSecInfo {
  1601  	// TODO (aix): make it available
  1602  	if d.linkctxt.HeadType == objabi.Haix {
  1603  		return dwarfSecInfo{}
  1604  	}
  1605  	if d.linkctxt.LinkMode == LinkExternal && d.linkctxt.HeadType == objabi.Hwindows && d.linkctxt.BuildMode == BuildModeCArchive {
  1606  		// gcc on Windows places .debug_gdb_scripts in the wrong location, which
  1607  		// causes the program not to run. See https://golang.org/issue/20183
  1608  		// Non c-archives can avoid this issue via a linker script
  1609  		// (see fix near writeGDBLinkerScript).
  1610  		// c-archive users would need to specify the linker script manually.
  1611  		// For UX it's better not to deal with this.
  1612  		return dwarfSecInfo{}
  1613  	}
  1614  	if gdbscript == "" {
  1615  		return dwarfSecInfo{}
  1616  	}
  1617  
  1618  	gs := d.ldr.CreateSymForUpdate(".debug_gdb_scripts", 0)
  1619  	gs.SetType(sym.SDWARFSECT)
  1620  
  1621  	gs.AddUint8(1) // magic 1 byte?
  1622  	gs.Addstring(gdbscript)
  1623  	return dwarfSecInfo{syms: []loader.Sym{gs.Sym()}}
  1624  }
  1625  
  1626  // FIXME: might be worth looking replacing this map with a function
  1627  // that switches based on symbol instead.
  1628  
  1629  var prototypedies map[string]*dwarf.DWDie
  1630  
  1631  func dwarfEnabled(ctxt *Link) bool {
  1632  	if *FlagW { // disable dwarf
  1633  		return false
  1634  	}
  1635  	if *FlagS && ctxt.HeadType != objabi.Hdarwin {
  1636  		return false
  1637  	}
  1638  	if ctxt.HeadType == objabi.Hplan9 || ctxt.HeadType == objabi.Hjs {
  1639  		return false
  1640  	}
  1641  
  1642  	if ctxt.LinkMode == LinkExternal {
  1643  		switch {
  1644  		case ctxt.IsELF:
  1645  		case ctxt.HeadType == objabi.Hdarwin:
  1646  		case ctxt.HeadType == objabi.Hwindows:
  1647  		case ctxt.HeadType == objabi.Haix:
  1648  			res, err := dwarf.IsDWARFEnabledOnAIXLd(ctxt.extld())
  1649  			if err != nil {
  1650  				Exitf("%v", err)
  1651  			}
  1652  			return res
  1653  		default:
  1654  			return false
  1655  		}
  1656  	}
  1657  
  1658  	return true
  1659  }
  1660  
  1661  // mkBuiltinType populates the dwctxt2 sym lookup maps for the
  1662  // newly created builtin type DIE 'typeDie'.
  1663  func (d *dwctxt) mkBuiltinType(ctxt *Link, abrv int, tname string) *dwarf.DWDie {
  1664  	// create type DIE
  1665  	die := d.newdie(&dwtypes, abrv, tname, 0)
  1666  
  1667  	// Look up type symbol.
  1668  	gotype := d.lookupOrDiag("type." + tname)
  1669  
  1670  	// Map from die sym to type sym
  1671  	ds := loader.Sym(die.Sym.(dwSym))
  1672  	d.rtmap[ds] = gotype
  1673  
  1674  	// Map from type to def sym
  1675  	d.tdmap[gotype] = ds
  1676  
  1677  	return die
  1678  }
  1679  
  1680  // dwarfVisitFunction takes a function (text) symbol and processes the
  1681  // subprogram DIE for the function and picks up any other DIEs
  1682  // (absfns, types) that it references.
  1683  func (d *dwctxt) dwarfVisitFunction(fnSym loader.Sym, unit *sym.CompilationUnit) {
  1684  	// The DWARF subprogram DIE symbol is listed as an aux sym
  1685  	// of the text (fcn) symbol, so ask the loader to retrieve it,
  1686  	// as well as the associated range symbol.
  1687  	infosym, _, rangesym, _ := d.ldr.GetFuncDwarfAuxSyms(fnSym)
  1688  	if infosym == 0 {
  1689  		return
  1690  	}
  1691  	d.ldr.SetAttrNotInSymbolTable(infosym, true)
  1692  	d.ldr.SetAttrReachable(infosym, true)
  1693  	unit.FuncDIEs = append(unit.FuncDIEs, sym.LoaderSym(infosym))
  1694  	if rangesym != 0 {
  1695  		d.ldr.SetAttrNotInSymbolTable(rangesym, true)
  1696  		d.ldr.SetAttrReachable(rangesym, true)
  1697  		unit.RangeSyms = append(unit.RangeSyms, sym.LoaderSym(rangesym))
  1698  	}
  1699  
  1700  	// Walk the relocations of the subprogram DIE symbol to discover
  1701  	// references to abstract function DIEs, Go type DIES, and
  1702  	// (via R_USETYPE relocs) types that were originally assigned to
  1703  	// locals/params but were optimized away.
  1704  	drelocs := d.ldr.Relocs(infosym)
  1705  	for ri := 0; ri < drelocs.Count(); ri++ {
  1706  		r := drelocs.At(ri)
  1707  		// Look for "use type" relocs.
  1708  		if r.Type() == objabi.R_USETYPE {
  1709  			d.defgotype(r.Sym())
  1710  			continue
  1711  		}
  1712  		if r.Type() != objabi.R_DWARFSECREF {
  1713  			continue
  1714  		}
  1715  
  1716  		rsym := r.Sym()
  1717  		rst := d.ldr.SymType(rsym)
  1718  
  1719  		// Look for abstract function references.
  1720  		if rst == sym.SDWARFABSFCN {
  1721  			if !d.ldr.AttrOnList(rsym) {
  1722  				// abstract function
  1723  				d.ldr.SetAttrOnList(rsym, true)
  1724  				unit.AbsFnDIEs = append(unit.AbsFnDIEs, sym.LoaderSym(rsym))
  1725  				d.importInfoSymbol(rsym)
  1726  			}
  1727  			continue
  1728  		}
  1729  
  1730  		// Look for type references.
  1731  		if rst != sym.SDWARFTYPE && rst != sym.Sxxx {
  1732  			continue
  1733  		}
  1734  		if _, ok := d.rtmap[rsym]; ok {
  1735  			// type already generated
  1736  			continue
  1737  		}
  1738  
  1739  		rsn := d.ldr.SymName(rsym)
  1740  		tn := rsn[len(dwarf.InfoPrefix):]
  1741  		ts := d.ldr.Lookup("type."+tn, 0)
  1742  		d.defgotype(ts)
  1743  	}
  1744  }
  1745  
  1746  // dwarfGenerateDebugInfo generated debug info entries for all types,
  1747  // variables and functions in the program.
  1748  // Along with dwarfGenerateDebugSyms they are the two main entry points into
  1749  // dwarf generation: dwarfGenerateDebugInfo does all the work that should be
  1750  // done before symbol names are mangled while dwarfGenerateDebugSyms does
  1751  // all the work that can only be done after addresses have been assigned to
  1752  // text symbols.
  1753  func dwarfGenerateDebugInfo(ctxt *Link) {
  1754  	if !dwarfEnabled(ctxt) {
  1755  		return
  1756  	}
  1757  
  1758  	d := newdwctxt(ctxt, true)
  1759  
  1760  	if ctxt.HeadType == objabi.Haix {
  1761  		// Initial map used to store package size for each DWARF section.
  1762  		dwsectCUSize = make(map[string]uint64)
  1763  	}
  1764  
  1765  	// For ctxt.Diagnostic messages.
  1766  	newattr(&dwtypes, dwarf.DW_AT_name, dwarf.DW_CLS_STRING, int64(len("dwtypes")), "dwtypes")
  1767  
  1768  	// Unspecified type. There are no references to this in the symbol table.
  1769  	d.newdie(&dwtypes, dwarf.DW_ABRV_NULLTYPE, "<unspecified>", 0)
  1770  
  1771  	// Some types that must exist to define other ones (uintptr in particular
  1772  	// is needed for array size)
  1773  	d.mkBuiltinType(ctxt, dwarf.DW_ABRV_BARE_PTRTYPE, "unsafe.Pointer")
  1774  	die := d.mkBuiltinType(ctxt, dwarf.DW_ABRV_BASETYPE, "uintptr")
  1775  	newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_unsigned, 0)
  1776  	newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, int64(d.arch.PtrSize), 0)
  1777  	newattr(die, dwarf.DW_AT_go_kind, dwarf.DW_CLS_CONSTANT, objabi.KindUintptr, 0)
  1778  	newattr(die, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_ADDRESS, 0, dwSym(d.lookupOrDiag("type.uintptr")))
  1779  
  1780  	d.uintptrInfoSym = d.mustFind("uintptr")
  1781  
  1782  	// Prototypes needed for type synthesis.
  1783  	prototypedies = map[string]*dwarf.DWDie{
  1784  		"type.runtime.stringStructDWARF": nil,
  1785  		"type.runtime.slice":             nil,
  1786  		"type.runtime.hmap":              nil,
  1787  		"type.runtime.bmap":              nil,
  1788  		"type.runtime.sudog":             nil,
  1789  		"type.runtime.waitq":             nil,
  1790  		"type.runtime.hchan":             nil,
  1791  	}
  1792  
  1793  	// Needed by the prettyprinter code for interface inspection.
  1794  	for _, typ := range []string{
  1795  		"type.runtime._type",
  1796  		"type.runtime.arraytype",
  1797  		"type.runtime.chantype",
  1798  		"type.runtime.functype",
  1799  		"type.runtime.maptype",
  1800  		"type.runtime.ptrtype",
  1801  		"type.runtime.slicetype",
  1802  		"type.runtime.structtype",
  1803  		"type.runtime.interfacetype",
  1804  		"type.runtime.itab",
  1805  		"type.runtime.imethod"} {
  1806  		d.defgotype(d.lookupOrDiag(typ))
  1807  	}
  1808  
  1809  	// fake root DIE for compile unit DIEs
  1810  	var dwroot dwarf.DWDie
  1811  	flagVariants := make(map[string]bool)
  1812  
  1813  	for _, lib := range ctxt.Library {
  1814  
  1815  		consts := d.ldr.Lookup(dwarf.ConstInfoPrefix+lib.Pkg, 0)
  1816  		for _, unit := range lib.Units {
  1817  			// We drop the constants into the first CU.
  1818  			if consts != 0 {
  1819  				unit.Consts = sym.LoaderSym(consts)
  1820  				d.importInfoSymbol(consts)
  1821  				consts = 0
  1822  			}
  1823  			ctxt.compUnits = append(ctxt.compUnits, unit)
  1824  
  1825  			// We need at least one runtime unit.
  1826  			if unit.Lib.Pkg == "runtime" {
  1827  				ctxt.runtimeCU = unit
  1828  			}
  1829  
  1830  			cuabrv := dwarf.DW_ABRV_COMPUNIT
  1831  			if len(unit.Textp) == 0 {
  1832  				cuabrv = dwarf.DW_ABRV_COMPUNIT_TEXTLESS
  1833  			}
  1834  			unit.DWInfo = d.newdie(&dwroot, cuabrv, unit.Lib.Pkg, 0)
  1835  			newattr(unit.DWInfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(dwarf.DW_LANG_Go), 0)
  1836  			// OS X linker requires compilation dir or absolute path in comp unit name to output debug info.
  1837  			compDir := getCompilationDir()
  1838  			// TODO: Make this be the actual compilation directory, not
  1839  			// the linker directory. If we move CU construction into the
  1840  			// compiler, this should happen naturally.
  1841  			newattr(unit.DWInfo, dwarf.DW_AT_comp_dir, dwarf.DW_CLS_STRING, int64(len(compDir)), compDir)
  1842  
  1843  			var peData []byte
  1844  			if producerExtra := d.ldr.Lookup(dwarf.CUInfoPrefix+"producer."+unit.Lib.Pkg, 0); producerExtra != 0 {
  1845  				peData = d.ldr.Data(producerExtra)
  1846  			}
  1847  			producer := "Go cmd/compile " + buildcfg.Version
  1848  			if len(peData) > 0 {
  1849  				// We put a semicolon before the flags to clearly
  1850  				// separate them from the version, which can be long
  1851  				// and have lots of weird things in it in development
  1852  				// versions. We promise not to put a semicolon in the
  1853  				// version, so it should be safe for readers to scan
  1854  				// forward to the semicolon.
  1855  				producer += "; " + string(peData)
  1856  				flagVariants[string(peData)] = true
  1857  			} else {
  1858  				flagVariants[""] = true
  1859  			}
  1860  
  1861  			newattr(unit.DWInfo, dwarf.DW_AT_producer, dwarf.DW_CLS_STRING, int64(len(producer)), producer)
  1862  
  1863  			var pkgname string
  1864  			if pnSymIdx := d.ldr.Lookup(dwarf.CUInfoPrefix+"packagename."+unit.Lib.Pkg, 0); pnSymIdx != 0 {
  1865  				pnsData := d.ldr.Data(pnSymIdx)
  1866  				pkgname = string(pnsData)
  1867  			}
  1868  			newattr(unit.DWInfo, dwarf.DW_AT_go_package_name, dwarf.DW_CLS_STRING, int64(len(pkgname)), pkgname)
  1869  
  1870  			// Scan all functions in this compilation unit, create
  1871  			// DIEs for all referenced types, find all referenced
  1872  			// abstract functions, visit range symbols. Note that
  1873  			// Textp has been dead-code-eliminated already.
  1874  			for _, s := range unit.Textp {
  1875  				d.dwarfVisitFunction(loader.Sym(s), unit)
  1876  			}
  1877  		}
  1878  	}
  1879  
  1880  	// Fix for 31034: if the objects feeding into this link were compiled
  1881  	// with different sets of flags, then don't issue an error if
  1882  	// the -strictdups checks fail.
  1883  	if checkStrictDups > 1 && len(flagVariants) > 1 {
  1884  		checkStrictDups = 1
  1885  	}
  1886  
  1887  	// Make a pass through all data symbols, looking for those
  1888  	// corresponding to reachable, Go-generated, user-visible
  1889  	// global variables. For each global of this sort, locate
  1890  	// the corresponding compiler-generated DIE symbol and tack
  1891  	// it onto the list associated with the unit.
  1892  	for idx := loader.Sym(1); idx < loader.Sym(d.ldr.NDef()); idx++ {
  1893  		if !d.ldr.AttrReachable(idx) ||
  1894  			d.ldr.AttrNotInSymbolTable(idx) ||
  1895  			d.ldr.SymVersion(idx) >= sym.SymVerStatic {
  1896  			continue
  1897  		}
  1898  		t := d.ldr.SymType(idx)
  1899  		switch t {
  1900  		case sym.SRODATA, sym.SDATA, sym.SNOPTRDATA, sym.STYPE, sym.SBSS, sym.SNOPTRBSS, sym.STLSBSS:
  1901  			// ok
  1902  		default:
  1903  			continue
  1904  		}
  1905  		// Skip things with no type
  1906  		gt := d.ldr.SymGoType(idx)
  1907  		if gt == 0 {
  1908  			continue
  1909  		}
  1910  		// Skip file local symbols (this includes static tmps, stack
  1911  		// object symbols, and local symbols in assembler src files).
  1912  		if d.ldr.IsFileLocal(idx) {
  1913  			continue
  1914  		}
  1915  		sn := d.ldr.SymName(idx)
  1916  		if sn == "" {
  1917  			// skip aux symbols
  1918  			continue
  1919  		}
  1920  
  1921  		// Find compiler-generated DWARF info sym for global in question,
  1922  		// and tack it onto the appropriate unit.  Note that there are
  1923  		// circumstances under which we can't find the compiler-generated
  1924  		// symbol-- this typically happens as a result of compiler options
  1925  		// (e.g. compile package X with "-dwarf=0").
  1926  
  1927  		// FIXME: use an aux sym or a relocation here instead of a
  1928  		// name lookup.
  1929  		varDIE := d.ldr.Lookup(dwarf.InfoPrefix+sn, 0)
  1930  		if varDIE != 0 {
  1931  			unit := d.ldr.SymUnit(idx)
  1932  			d.defgotype(gt)
  1933  			unit.VarDIEs = append(unit.VarDIEs, sym.LoaderSym(varDIE))
  1934  		}
  1935  	}
  1936  
  1937  	d.synthesizestringtypes(ctxt, dwtypes.Child)
  1938  	d.synthesizeslicetypes(ctxt, dwtypes.Child)
  1939  	d.synthesizemaptypes(ctxt, dwtypes.Child)
  1940  	d.synthesizechantypes(ctxt, dwtypes.Child)
  1941  }
  1942  
  1943  // dwarfGenerateDebugSyms constructs debug_line, debug_frame, and
  1944  // debug_loc. It also writes out the debug_info section using symbols
  1945  // generated in dwarfGenerateDebugInfo2.
  1946  func dwarfGenerateDebugSyms(ctxt *Link) {
  1947  	if !dwarfEnabled(ctxt) {
  1948  		return
  1949  	}
  1950  	d := &dwctxt{
  1951  		linkctxt: ctxt,
  1952  		ldr:      ctxt.loader,
  1953  		arch:     ctxt.Arch,
  1954  		dwmu:     new(sync.Mutex),
  1955  	}
  1956  	d.dwarfGenerateDebugSyms()
  1957  }
  1958  
  1959  // dwUnitSyms stores input and output symbols for DWARF generation
  1960  // for a given compilation unit.
  1961  type dwUnitSyms struct {
  1962  	// Inputs for a given unit.
  1963  	lineProlog  loader.Sym
  1964  	rangeProlog loader.Sym
  1965  	infoEpilog  loader.Sym
  1966  
  1967  	// Outputs for a given unit.
  1968  	linesyms   []loader.Sym
  1969  	infosyms   []loader.Sym
  1970  	locsyms    []loader.Sym
  1971  	rangessyms []loader.Sym
  1972  }
  1973  
  1974  // dwUnitPortion assembles the DWARF content for a given compilation
  1975  // unit: debug_info, debug_lines, debug_ranges, debug_loc (debug_frame
  1976  // is handled elsewere). Order is important; the calls to writelines
  1977  // and writepcranges below make updates to the compilation unit DIE,
  1978  // hence they have to happen before the call to writeUnitInfo.
  1979  func (d *dwctxt) dwUnitPortion(u *sym.CompilationUnit, abbrevsym loader.Sym, us *dwUnitSyms) {
  1980  	if u.DWInfo.Abbrev != dwarf.DW_ABRV_COMPUNIT_TEXTLESS {
  1981  		us.linesyms = d.writelines(u, us.lineProlog)
  1982  		base := loader.Sym(u.Textp[0])
  1983  		us.rangessyms = d.writepcranges(u, base, u.PCs, us.rangeProlog)
  1984  		us.locsyms = d.collectUnitLocs(u)
  1985  	}
  1986  	us.infosyms = d.writeUnitInfo(u, abbrevsym, us.infoEpilog)
  1987  }
  1988  
  1989  func (d *dwctxt) dwarfGenerateDebugSyms() {
  1990  	abbrevSec := d.writeabbrev()
  1991  	dwarfp = append(dwarfp, abbrevSec)
  1992  	d.calcCompUnitRanges()
  1993  	sort.Sort(compilationUnitByStartPC(d.linkctxt.compUnits))
  1994  
  1995  	// newdie adds DIEs to the *beginning* of the parent's DIE list.
  1996  	// Now that we're done creating DIEs, reverse the trees so DIEs
  1997  	// appear in the order they were created.
  1998  	for _, u := range d.linkctxt.compUnits {
  1999  		reversetree(&u.DWInfo.Child)
  2000  	}
  2001  	reversetree(&dwtypes.Child)
  2002  	movetomodule(d.linkctxt, &dwtypes)
  2003  
  2004  	mkSecSym := func(name string) loader.Sym {
  2005  		s := d.ldr.CreateSymForUpdate(name, 0)
  2006  		s.SetType(sym.SDWARFSECT)
  2007  		s.SetReachable(true)
  2008  		return s.Sym()
  2009  	}
  2010  	mkAnonSym := func(kind sym.SymKind) loader.Sym {
  2011  		s := d.ldr.MakeSymbolUpdater(d.ldr.CreateExtSym("", 0))
  2012  		s.SetType(kind)
  2013  		s.SetReachable(true)
  2014  		return s.Sym()
  2015  	}
  2016  
  2017  	// Create the section symbols.
  2018  	frameSym := mkSecSym(".debug_frame")
  2019  	locSym := mkSecSym(".debug_loc")
  2020  	lineSym := mkSecSym(".debug_line")
  2021  	rangesSym := mkSecSym(".debug_ranges")
  2022  	infoSym := mkSecSym(".debug_info")
  2023  
  2024  	// Create the section objects
  2025  	lineSec := dwarfSecInfo{syms: []loader.Sym{lineSym}}
  2026  	locSec := dwarfSecInfo{syms: []loader.Sym{locSym}}
  2027  	rangesSec := dwarfSecInfo{syms: []loader.Sym{rangesSym}}
  2028  	frameSec := dwarfSecInfo{syms: []loader.Sym{frameSym}}
  2029  	infoSec := dwarfSecInfo{syms: []loader.Sym{infoSym}}
  2030  
  2031  	// Create any new symbols that will be needed during the
  2032  	// parallel portion below.
  2033  	ncu := len(d.linkctxt.compUnits)
  2034  	unitSyms := make([]dwUnitSyms, ncu)
  2035  	for i := 0; i < ncu; i++ {
  2036  		us := &unitSyms[i]
  2037  		us.lineProlog = mkAnonSym(sym.SDWARFLINES)
  2038  		us.rangeProlog = mkAnonSym(sym.SDWARFRANGE)
  2039  		us.infoEpilog = mkAnonSym(sym.SDWARFFCN)
  2040  	}
  2041  
  2042  	var wg sync.WaitGroup
  2043  	sema := make(chan struct{}, runtime.GOMAXPROCS(0))
  2044  
  2045  	// Kick off generation of .debug_frame, since it doesn't have
  2046  	// any entanglements and can be started right away.
  2047  	wg.Add(1)
  2048  	go func() {
  2049  		sema <- struct{}{}
  2050  		defer func() {
  2051  			<-sema
  2052  			wg.Done()
  2053  		}()
  2054  		frameSec = d.writeframes(frameSym)
  2055  	}()
  2056  
  2057  	// Create a goroutine per comp unit to handle the generation that
  2058  	// unit's portion of .debug_line, .debug_loc, .debug_ranges, and
  2059  	// .debug_info.
  2060  	wg.Add(len(d.linkctxt.compUnits))
  2061  	for i := 0; i < ncu; i++ {
  2062  		go func(u *sym.CompilationUnit, us *dwUnitSyms) {
  2063  			sema <- struct{}{}
  2064  			defer func() {
  2065  				<-sema
  2066  				wg.Done()
  2067  			}()
  2068  			d.dwUnitPortion(u, abbrevSec.secSym(), us)
  2069  		}(d.linkctxt.compUnits[i], &unitSyms[i])
  2070  	}
  2071  	wg.Wait()
  2072  
  2073  	markReachable := func(syms []loader.Sym) []loader.Sym {
  2074  		for _, s := range syms {
  2075  			d.ldr.SetAttrNotInSymbolTable(s, true)
  2076  			d.ldr.SetAttrReachable(s, true)
  2077  		}
  2078  		return syms
  2079  	}
  2080  
  2081  	// Stitch together the results.
  2082  	for i := 0; i < ncu; i++ {
  2083  		r := &unitSyms[i]
  2084  		lineSec.syms = append(lineSec.syms, markReachable(r.linesyms)...)
  2085  		infoSec.syms = append(infoSec.syms, markReachable(r.infosyms)...)
  2086  		locSec.syms = append(locSec.syms, markReachable(r.locsyms)...)
  2087  		rangesSec.syms = append(rangesSec.syms, markReachable(r.rangessyms)...)
  2088  	}
  2089  	dwarfp = append(dwarfp, lineSec)
  2090  	dwarfp = append(dwarfp, frameSec)
  2091  	gdbScriptSec := d.writegdbscript()
  2092  	if gdbScriptSec.secSym() != 0 {
  2093  		dwarfp = append(dwarfp, gdbScriptSec)
  2094  	}
  2095  	dwarfp = append(dwarfp, infoSec)
  2096  	if len(locSec.syms) > 1 {
  2097  		dwarfp = append(dwarfp, locSec)
  2098  	}
  2099  	dwarfp = append(dwarfp, rangesSec)
  2100  
  2101  	// Check to make sure we haven't listed any symbols more than once
  2102  	// in the info section. This used to be done by setting and
  2103  	// checking the OnList attribute in "putdie", but that strategy
  2104  	// was not friendly for concurrency.
  2105  	seen := loader.MakeBitmap(d.ldr.NSym())
  2106  	for _, s := range infoSec.syms {
  2107  		if seen.Has(s) {
  2108  			log.Fatalf("symbol %s listed multiple times", d.ldr.SymName(s))
  2109  		}
  2110  		seen.Set(s)
  2111  	}
  2112  }
  2113  
  2114  func (d *dwctxt) collectUnitLocs(u *sym.CompilationUnit) []loader.Sym {
  2115  	syms := []loader.Sym{}
  2116  	for _, fn := range u.FuncDIEs {
  2117  		relocs := d.ldr.Relocs(loader.Sym(fn))
  2118  		for i := 0; i < relocs.Count(); i++ {
  2119  			reloc := relocs.At(i)
  2120  			if reloc.Type() != objabi.R_DWARFSECREF {
  2121  				continue
  2122  			}
  2123  			rsym := reloc.Sym()
  2124  			if d.ldr.SymType(rsym) == sym.SDWARFLOC {
  2125  				syms = append(syms, rsym)
  2126  				// One location list entry per function, but many relocations to it. Don't duplicate.
  2127  				break
  2128  			}
  2129  		}
  2130  	}
  2131  	return syms
  2132  }
  2133  
  2134  /*
  2135   *  Elf.
  2136   */
  2137  func dwarfaddshstrings(ctxt *Link, shstrtab *loader.SymbolBuilder) {
  2138  	if *FlagW { // disable dwarf
  2139  		return
  2140  	}
  2141  
  2142  	secs := []string{"abbrev", "frame", "info", "loc", "line", "gdb_scripts", "ranges"}
  2143  	for _, sec := range secs {
  2144  		shstrtab.Addstring(".debug_" + sec)
  2145  		if ctxt.IsExternal() {
  2146  			shstrtab.Addstring(elfRelType + ".debug_" + sec)
  2147  		} else {
  2148  			shstrtab.Addstring(".zdebug_" + sec)
  2149  		}
  2150  	}
  2151  }
  2152  
  2153  func dwarfaddelfsectionsyms(ctxt *Link) {
  2154  	if *FlagW { // disable dwarf
  2155  		return
  2156  	}
  2157  	if ctxt.LinkMode != LinkExternal {
  2158  		return
  2159  	}
  2160  
  2161  	ldr := ctxt.loader
  2162  	for _, si := range dwarfp {
  2163  		s := si.secSym()
  2164  		sect := ldr.SymSect(si.secSym())
  2165  		putelfsectionsym(ctxt, ctxt.Out, s, sect.Elfsect.(*ElfShdr).shnum)
  2166  	}
  2167  }
  2168  
  2169  // dwarfcompress compresses the DWARF sections. Relocations are applied
  2170  // on the fly. After this, dwarfp will contain a different (new) set of
  2171  // symbols, and sections may have been replaced.
  2172  func dwarfcompress(ctxt *Link) {
  2173  	// compressedSect is a helper type for parallelizing compression.
  2174  	type compressedSect struct {
  2175  		index      int
  2176  		compressed []byte
  2177  		syms       []loader.Sym
  2178  	}
  2179  
  2180  	supported := ctxt.IsELF || ctxt.IsWindows() || ctxt.IsDarwin()
  2181  	if !ctxt.compressDWARF || !supported || ctxt.IsExternal() {
  2182  		return
  2183  	}
  2184  
  2185  	var compressedCount int
  2186  	resChannel := make(chan compressedSect)
  2187  	for i := range dwarfp {
  2188  		go func(resIndex int, syms []loader.Sym) {
  2189  			resChannel <- compressedSect{resIndex, compressSyms(ctxt, syms), syms}
  2190  		}(compressedCount, dwarfp[i].syms)
  2191  		compressedCount++
  2192  	}
  2193  	res := make([]compressedSect, compressedCount)
  2194  	for ; compressedCount > 0; compressedCount-- {
  2195  		r := <-resChannel
  2196  		res[r.index] = r
  2197  	}
  2198  
  2199  	ldr := ctxt.loader
  2200  	var newDwarfp []dwarfSecInfo
  2201  	Segdwarf.Sections = Segdwarf.Sections[:0]
  2202  	for _, z := range res {
  2203  		s := z.syms[0]
  2204  		if z.compressed == nil {
  2205  			// Compression didn't help.
  2206  			ds := dwarfSecInfo{syms: z.syms}
  2207  			newDwarfp = append(newDwarfp, ds)
  2208  			Segdwarf.Sections = append(Segdwarf.Sections, ldr.SymSect(s))
  2209  		} else {
  2210  			compressedSegName := ".zdebug_" + ldr.SymSect(s).Name[len(".debug_"):]
  2211  			sect := addsection(ctxt.loader, ctxt.Arch, &Segdwarf, compressedSegName, 04)
  2212  			sect.Align = 1
  2213  			sect.Length = uint64(len(z.compressed))
  2214  			newSym := ldr.CreateSymForUpdate(compressedSegName, 0)
  2215  			newSym.SetData(z.compressed)
  2216  			newSym.SetSize(int64(len(z.compressed)))
  2217  			ldr.SetSymSect(newSym.Sym(), sect)
  2218  			ds := dwarfSecInfo{syms: []loader.Sym{newSym.Sym()}}
  2219  			newDwarfp = append(newDwarfp, ds)
  2220  
  2221  			// compressed symbols are no longer needed.
  2222  			for _, s := range z.syms {
  2223  				ldr.SetAttrReachable(s, false)
  2224  				ldr.FreeSym(s)
  2225  			}
  2226  		}
  2227  	}
  2228  	dwarfp = newDwarfp
  2229  
  2230  	// Re-compute the locations of the compressed DWARF symbols
  2231  	// and sections, since the layout of these within the file is
  2232  	// based on Section.Vaddr and Symbol.Value.
  2233  	pos := Segdwarf.Vaddr
  2234  	var prevSect *sym.Section
  2235  	for _, si := range dwarfp {
  2236  		for _, s := range si.syms {
  2237  			ldr.SetSymValue(s, int64(pos))
  2238  			sect := ldr.SymSect(s)
  2239  			if sect != prevSect {
  2240  				sect.Vaddr = uint64(pos)
  2241  				prevSect = sect
  2242  			}
  2243  			if ldr.SubSym(s) != 0 {
  2244  				log.Fatalf("%s: unexpected sub-symbols", ldr.SymName(s))
  2245  			}
  2246  			pos += uint64(ldr.SymSize(s))
  2247  			if ctxt.IsWindows() {
  2248  				pos = uint64(Rnd(int64(pos), PEFILEALIGN))
  2249  			}
  2250  		}
  2251  	}
  2252  	Segdwarf.Length = pos - Segdwarf.Vaddr
  2253  }
  2254  
  2255  type compilationUnitByStartPC []*sym.CompilationUnit
  2256  
  2257  func (v compilationUnitByStartPC) Len() int      { return len(v) }
  2258  func (v compilationUnitByStartPC) Swap(i, j int) { v[i], v[j] = v[j], v[i] }
  2259  
  2260  func (v compilationUnitByStartPC) Less(i, j int) bool {
  2261  	switch {
  2262  	case len(v[i].Textp) == 0 && len(v[j].Textp) == 0:
  2263  		return v[i].Lib.Pkg < v[j].Lib.Pkg
  2264  	case len(v[i].Textp) != 0 && len(v[j].Textp) == 0:
  2265  		return true
  2266  	case len(v[i].Textp) == 0 && len(v[j].Textp) != 0:
  2267  		return false
  2268  	default:
  2269  		return v[i].PCs[0].Start < v[j].PCs[0].Start
  2270  	}
  2271  }
  2272  
  2273  // getPkgFromCUSym returns the package name for the compilation unit
  2274  // represented by s.
  2275  // The prefix dwarf.InfoPrefix+".pkg." needs to be removed in order to get
  2276  // the package name.
  2277  func (d *dwctxt) getPkgFromCUSym(s loader.Sym) string {
  2278  	return strings.TrimPrefix(d.ldr.SymName(s), dwarf.InfoPrefix+".pkg.")
  2279  }
  2280  
  2281  // On AIX, the symbol table needs to know where are the compilation units parts
  2282  // for a specific package in each .dw section.
  2283  // dwsectCUSize map will save the size of a compilation unit for
  2284  // the corresponding .dw section.
  2285  // This size can later be retrieved with the index "sectionName.pkgName".
  2286  var dwsectCUSizeMu sync.Mutex
  2287  var dwsectCUSize map[string]uint64
  2288  
  2289  // getDwsectCUSize retrieves the corresponding package size inside the current section.
  2290  func getDwsectCUSize(sname string, pkgname string) uint64 {
  2291  	return dwsectCUSize[sname+"."+pkgname]
  2292  }
  2293  
  2294  func addDwsectCUSize(sname string, pkgname string, size uint64) {
  2295  	dwsectCUSizeMu.Lock()
  2296  	defer dwsectCUSizeMu.Unlock()
  2297  	dwsectCUSize[sname+"."+pkgname] += size
  2298  }
  2299  

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