symtab.go

     1  // Inferno utils/6l/span.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/span.c
     3  //
     4  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     7  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8  //	Portions Copyright © 2004,2006 Bruce Ellis
     9  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12  //
    13  // Permission is hereby granted, free of charge, to any person obtaining a copy
    14  // of this software and associated documentation files (the "Software"), to deal
    15  // in the Software without restriction, including without limitation the rights
    16  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17  // copies of the Software, and to permit persons to whom the Software is
    18  // furnished to do so, subject to the following conditions:
    19  //
    20  // The above copyright notice and this permission notice shall be included in
    21  // all copies or substantial portions of the Software.
    22  //
    23  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29  // THE SOFTWARE.
    30  
    31  package ld
    32  
    33  import (
    34  	"cmd/internal/obj"
    35  	"cmd/internal/objabi"
    36  	"cmd/link/internal/loader"
    37  	"cmd/link/internal/sym"
    38  	"debug/elf"
    39  	"fmt"
    40  	"internal/buildcfg"
    41  	"path/filepath"
    42  	"strings"
    43  )
    44  
    45  // Symbol table.
    46  
    47  func putelfstr(s string) int {
    48  	if len(elfstrdat) == 0 {
    49  		// first entry must be empty string
    50  		elfstrdat = append(elfstrdat, 0)
    51  		elfstroff = map[string]int{"": 0}
    52  	}
    53  	if off, ok := elfstroff[s]; ok {
    54  		return off
    55  	}
    56  
    57  	off := len(elfstrdat)
    58  	elfstrdat = append(elfstrdat, s...)
    59  	elfstrdat = append(elfstrdat, 0)
    60  	elfstroff[s] = off
    61  	return off
    62  }
    63  
    64  func putelfsyment(out *OutBuf, off int, addr int64, size int64, info uint8, shndx elf.SectionIndex, other int) {
    65  	if elf64 {
    66  		out.Write32(uint32(off))
    67  		out.Write8(info)
    68  		out.Write8(uint8(other))
    69  		out.Write16(uint16(shndx))
    70  		out.Write64(uint64(addr))
    71  		out.Write64(uint64(size))
    72  		symSize += ELF64SYMSIZE
    73  	} else {
    74  		out.Write32(uint32(off))
    75  		out.Write32(uint32(addr))
    76  		out.Write32(uint32(size))
    77  		out.Write8(info)
    78  		out.Write8(uint8(other))
    79  		out.Write16(uint16(shndx))
    80  		symSize += ELF32SYMSIZE
    81  	}
    82  }
    83  
    84  func putelfsym(ctxt *Link, x loader.Sym, typ elf.SymType, curbind elf.SymBind) {
    85  	ldr := ctxt.loader
    86  	addr := ldr.SymValue(x)
    87  	size := ldr.SymSize(x)
    88  
    89  	xo := x
    90  	if ldr.OuterSym(x) != 0 {
    91  		xo = ldr.OuterSym(x)
    92  	}
    93  	xot := ldr.SymType(xo)
    94  	xosect := ldr.SymSect(xo)
    95  
    96  	var elfshnum elf.SectionIndex
    97  	if xot == sym.SDYNIMPORT || xot == sym.SHOSTOBJ || xot == sym.SUNDEFEXT {
    98  		elfshnum = elf.SHN_UNDEF
    99  		size = 0
   100  	} else {
   101  		if xosect == nil {
   102  			ldr.Errorf(x, "missing section in putelfsym")
   103  			return
   104  		}
   105  		if xosect.Elfsect == nil {
   106  			ldr.Errorf(x, "missing ELF section in putelfsym")
   107  			return
   108  		}
   109  		elfshnum = elfShdrShnum(xosect.Elfsect.(*ElfShdr))
   110  	}
   111  
   112  	sname := ldr.SymExtname(x)
   113  	sname = mangleABIName(ctxt, ldr, x, sname)
   114  
   115  	// One pass for each binding: elf.STB_LOCAL, elf.STB_GLOBAL,
   116  	// maybe one day elf.STB_WEAK.
   117  	bind := elf.STB_GLOBAL
   118  	if ldr.IsFileLocal(x) && !isStaticTmp(sname) || ldr.AttrVisibilityHidden(x) || ldr.AttrLocal(x) ||
   119  		(ldr.IsContentHashed(x) && ldr.SymType(x).IsText()) {
   120  		// Static tmp is package local, but a package can be shared among multiple DSOs.
   121  		// They need to have a single view of the static tmp that are writable.
   122  		// Content-hashed text symbols may have the same name. Mark them local to avoid
   123  		// collision.
   124  		bind = elf.STB_LOCAL
   125  	}
   126  
   127  	// In external linking mode, we have to invoke gcc with -rdynamic
   128  	// to get the exported symbols put into the dynamic symbol table.
   129  	// To avoid filling the dynamic table with lots of unnecessary symbols,
   130  	// mark all Go symbols local (not global) in the final executable.
   131  	// But when we're dynamically linking, we need all those global symbols.
   132  	if !ctxt.DynlinkingGo() && ctxt.IsExternal() && !ldr.AttrCgoExportStatic(x) && elfshnum != elf.SHN_UNDEF {
   133  		bind = elf.STB_LOCAL
   134  	}
   135  
   136  	if ctxt.LinkMode == LinkExternal && elfshnum != elf.SHN_UNDEF {
   137  		addr -= int64(xosect.Vaddr)
   138  	}
   139  	other := int(elf.STV_DEFAULT)
   140  	if ldr.AttrVisibilityHidden(x) {
   141  		// TODO(mwhudson): We only set AttrVisibilityHidden in ldelf, i.e. when
   142  		// internally linking. But STV_HIDDEN visibility only matters in object
   143  		// files and shared libraries, and as we are a long way from implementing
   144  		// internal linking for shared libraries and only create object files when
   145  		// externally linking, I don't think this makes a lot of sense.
   146  		other = int(elf.STV_HIDDEN)
   147  	}
   148  	if ctxt.IsPPC64() && typ == elf.STT_FUNC && ldr.AttrShared(x) {
   149  		// On ppc64 the top three bits of the st_other field indicate how many
   150  		// bytes separate the global and local entry points. For non-PCrel shared
   151  		// symbols this is always 8 bytes except for some special functions.
   152  		hasPCrel := buildcfg.GOPPC64 >= 10 && buildcfg.GOOS == "linux"
   153  
   154  		// This should match the preprocessing behavior in cmd/internal/obj/ppc64/obj9.go
   155  		// where the distinct global entry is inserted.
   156  		if !hasPCrel && ldr.SymName(x) != "runtime.duffzero" && ldr.SymName(x) != "runtime.duffcopy" {
   157  			other |= 3 << 5
   158  		}
   159  	}
   160  
   161  	// When dynamically linking, we create Symbols by reading the names from
   162  	// the symbol tables of the shared libraries and so the names need to
   163  	// match exactly. Tools like DTrace will have to wait for now.
   164  	if !ctxt.DynlinkingGo() {
   165  		// Rewrite · to . for ASCII-only tools like DTrace (sigh)
   166  		sname = strings.ReplaceAll(sname, "·", ".")
   167  	}
   168  
   169  	if ctxt.DynlinkingGo() && bind == elf.STB_GLOBAL && curbind == elf.STB_LOCAL && ldr.SymType(x).IsText() {
   170  		// When dynamically linking, we want references to functions defined
   171  		// in this module to always be to the function object, not to the
   172  		// PLT. We force this by writing an additional local symbol for every
   173  		// global function symbol and making all relocations against the
   174  		// global symbol refer to this local symbol instead (see
   175  		// (*sym.Symbol).ElfsymForReloc). This is approximately equivalent to the
   176  		// ELF linker -Bsymbolic-functions option, but that is buggy on
   177  		// several platforms.
   178  		putelfsyment(ctxt.Out, putelfstr("local."+sname), addr, size, elf.ST_INFO(elf.STB_LOCAL, typ), elfshnum, other)
   179  		ldr.SetSymLocalElfSym(x, int32(ctxt.numelfsym))
   180  		ctxt.numelfsym++
   181  		return
   182  	} else if bind != curbind {
   183  		return
   184  	}
   185  
   186  	putelfsyment(ctxt.Out, putelfstr(sname), addr, size, elf.ST_INFO(bind, typ), elfshnum, other)
   187  	ldr.SetSymElfSym(x, int32(ctxt.numelfsym))
   188  	ctxt.numelfsym++
   189  }
   190  
   191  func putelfsectionsym(ctxt *Link, out *OutBuf, s loader.Sym, shndx elf.SectionIndex) {
   192  	putelfsyment(out, 0, 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_SECTION), shndx, 0)
   193  	ctxt.loader.SetSymElfSym(s, int32(ctxt.numelfsym))
   194  	ctxt.numelfsym++
   195  }
   196  
   197  func genelfsym(ctxt *Link, elfbind elf.SymBind) {
   198  	ldr := ctxt.loader
   199  
   200  	// runtime.text marker symbol(s).
   201  	s := ldr.Lookup("runtime.text", 0)
   202  	putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   203  	for k, sect := range Segtext.Sections[1:] {
   204  		n := k + 1
   205  		if sect.Name != ".text" || (ctxt.IsAIX() && ctxt.IsExternal()) {
   206  			// On AIX, runtime.text.X are symbols already in the symtab.
   207  			break
   208  		}
   209  		s = ldr.Lookup(fmt.Sprintf("runtime.text.%d", n), 0)
   210  		if s == 0 {
   211  			break
   212  		}
   213  		if !ldr.SymType(s).IsText() {
   214  			panic("unexpected type for runtime.text symbol")
   215  		}
   216  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   217  	}
   218  
   219  	// Text symbols.
   220  	for _, s := range ctxt.Textp {
   221  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   222  	}
   223  
   224  	// runtime.etext marker symbol.
   225  	s = ldr.Lookup("runtime.etext", 0)
   226  	if ldr.SymType(s).IsText() {
   227  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   228  	}
   229  
   230  	shouldBeInSymbolTable := func(s loader.Sym) bool {
   231  		if ldr.AttrNotInSymbolTable(s) {
   232  			return false
   233  		}
   234  		// FIXME: avoid having to do name inspections here.
   235  		// NB: the restrictions below on file local symbols are a bit
   236  		// arbitrary -- if it turns out we need nameless static
   237  		// symbols they could be relaxed/removed.
   238  		sn := ldr.SymName(s)
   239  		if (sn == "" || sn[0] == '.') && ldr.IsFileLocal(s) {
   240  			panic(fmt.Sprintf("unexpected file local symbol %d %s<%d>\n",
   241  				s, sn, ldr.SymVersion(s)))
   242  		}
   243  		if (sn == "" || sn[0] == '.') && !ldr.IsFileLocal(s) {
   244  			return false
   245  		}
   246  		return true
   247  	}
   248  
   249  	// Data symbols.
   250  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
   251  		if !ldr.AttrReachable(s) {
   252  			continue
   253  		}
   254  		st := ldr.SymType(s)
   255  		if st >= sym.SELFRXSECT && st < sym.SFirstUnallocated {
   256  			typ := elf.STT_OBJECT
   257  			if st == sym.STLSBSS {
   258  				if ctxt.IsInternal() {
   259  					continue
   260  				}
   261  				typ = elf.STT_TLS
   262  			}
   263  			if !shouldBeInSymbolTable(s) {
   264  				continue
   265  			}
   266  			putelfsym(ctxt, s, typ, elfbind)
   267  			continue
   268  		}
   269  		if st == sym.SHOSTOBJ || st == sym.SDYNIMPORT || st == sym.SUNDEFEXT {
   270  			putelfsym(ctxt, s, ldr.SymElfType(s), elfbind)
   271  		}
   272  	}
   273  }
   274  
   275  func asmElfSym(ctxt *Link) {
   276  
   277  	// the first symbol entry is reserved
   278  	putelfsyment(ctxt.Out, 0, 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_NOTYPE), 0, 0)
   279  
   280  	dwarfaddelfsectionsyms(ctxt)
   281  
   282  	// Some linkers will add a FILE sym if one is not present.
   283  	// Avoid having the working directory inserted into the symbol table.
   284  	// It is added with a name to avoid problems with external linking
   285  	// encountered on some versions of Solaris. See issue #14957.
   286  	putelfsyment(ctxt.Out, putelfstr("go.go"), 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_FILE), elf.SHN_ABS, 0)
   287  	ctxt.numelfsym++
   288  
   289  	bindings := []elf.SymBind{elf.STB_LOCAL, elf.STB_GLOBAL}
   290  	for _, elfbind := range bindings {
   291  		if elfbind == elf.STB_GLOBAL {
   292  			elfglobalsymndx = ctxt.numelfsym
   293  		}
   294  		genelfsym(ctxt, elfbind)
   295  	}
   296  }
   297  
   298  func putplan9sym(ctxt *Link, ldr *loader.Loader, s loader.Sym, char SymbolType) {
   299  	t := int(char)
   300  	if ldr.IsFileLocal(s) {
   301  		t += 'a' - 'A'
   302  	}
   303  	l := 4
   304  	addr := ldr.SymValue(s)
   305  	if ctxt.IsAMD64() && !flag8 {
   306  		ctxt.Out.Write32b(uint32(addr >> 32))
   307  		l = 8
   308  	}
   309  
   310  	ctxt.Out.Write32b(uint32(addr))
   311  	ctxt.Out.Write8(uint8(t + 0x80)) /* 0x80 is variable length */
   312  
   313  	name := ldr.SymName(s)
   314  	name = mangleABIName(ctxt, ldr, s, name)
   315  	ctxt.Out.WriteString(name)
   316  	ctxt.Out.Write8(0)
   317  
   318  	symSize += int32(l) + 1 + int32(len(name)) + 1
   319  }
   320  
   321  func asmbPlan9Sym(ctxt *Link) {
   322  	ldr := ctxt.loader
   323  
   324  	// Add special runtime.text and runtime.etext symbols.
   325  	s := ldr.Lookup("runtime.text", 0)
   326  	if ldr.SymType(s).IsText() {
   327  		putplan9sym(ctxt, ldr, s, TextSym)
   328  	}
   329  	s = ldr.Lookup("runtime.etext", 0)
   330  	if ldr.SymType(s).IsText() {
   331  		putplan9sym(ctxt, ldr, s, TextSym)
   332  	}
   333  
   334  	// Add text symbols.
   335  	for _, s := range ctxt.Textp {
   336  		putplan9sym(ctxt, ldr, s, TextSym)
   337  	}
   338  
   339  	shouldBeInSymbolTable := func(s loader.Sym) bool {
   340  		if ldr.AttrNotInSymbolTable(s) {
   341  			return false
   342  		}
   343  		name := ldr.SymName(s) // TODO: try not to read the name
   344  		if name == "" || name[0] == '.' {
   345  			return false
   346  		}
   347  		return true
   348  	}
   349  
   350  	// Add data symbols and external references.
   351  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
   352  		if !ldr.AttrReachable(s) {
   353  			continue
   354  		}
   355  		t := ldr.SymType(s)
   356  		if t >= sym.SELFRXSECT && t < sym.SFirstUnallocated { // data sections handled in dodata
   357  			if t == sym.STLSBSS {
   358  				continue
   359  			}
   360  			if !shouldBeInSymbolTable(s) {
   361  				continue
   362  			}
   363  			char := DataSym
   364  			if t == sym.SBSS || t == sym.SNOPTRBSS {
   365  				char = BSSSym
   366  			}
   367  			putplan9sym(ctxt, ldr, s, char)
   368  		}
   369  	}
   370  }
   371  
   372  // Create a table with information on the text sections.
   373  // Return the symbol of the table, and number of sections.
   374  func textsectionmap(ctxt *Link) (loader.Sym, uint32) {
   375  	ldr := ctxt.loader
   376  	t := ldr.CreateSymForUpdate("runtime.textsectionmap", 0)
   377  	t.SetType(sym.SRODATA)
   378  	nsections := int64(0)
   379  
   380  	for _, sect := range Segtext.Sections {
   381  		if sect.Name == ".text" {
   382  			nsections++
   383  		} else {
   384  			break
   385  		}
   386  	}
   387  	t.Grow(3 * nsections * int64(ctxt.Arch.PtrSize))
   388  
   389  	off := int64(0)
   390  	n := 0
   391  
   392  	// The vaddr for each text section is the difference between the section's
   393  	// Vaddr and the Vaddr for the first text section as determined at compile
   394  	// time.
   395  
   396  	// The symbol for the first text section is named runtime.text as before.
   397  	// Additional text sections are named runtime.text.n where n is the
   398  	// order of creation starting with 1. These symbols provide the section's
   399  	// address after relocation by the linker.
   400  
   401  	textbase := Segtext.Sections[0].Vaddr
   402  	for _, sect := range Segtext.Sections {
   403  		if sect.Name != ".text" {
   404  			break
   405  		}
   406  		// The fields written should match runtime/symtab.go:textsect.
   407  		// They are designed to minimize runtime calculations.
   408  		vaddr := sect.Vaddr - textbase
   409  		off = t.SetUint(ctxt.Arch, off, vaddr) // field vaddr
   410  		end := vaddr + sect.Length
   411  		off = t.SetUint(ctxt.Arch, off, end) // field end
   412  		name := "runtime.text"
   413  		if n != 0 {
   414  			name = fmt.Sprintf("runtime.text.%d", n)
   415  		}
   416  		s := ldr.Lookup(name, 0)
   417  		if s == 0 {
   418  			ctxt.Errorf(s, "Unable to find symbol %s\n", name)
   419  		}
   420  		off = t.SetAddr(ctxt.Arch, off, s) // field baseaddr
   421  		n++
   422  	}
   423  	return t.Sym(), uint32(n)
   424  }
   425  
   426  func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
   427  	ldr := ctxt.loader
   428  
   429  	if !ctxt.IsAIX() && !ctxt.IsWasm() {
   430  		switch ctxt.BuildMode {
   431  		case BuildModeCArchive, BuildModeCShared:
   432  			s := ldr.Lookup(*flagEntrySymbol, sym.SymVerABI0)
   433  			if s != 0 {
   434  				addinitarrdata(ctxt, ldr, s)
   435  			}
   436  		}
   437  	}
   438  
   439  	// Define these so that they'll get put into the symbol table.
   440  	// data.c:/^address will provide the actual values.
   441  	ctxt.xdefine("runtime.rodata", sym.SRODATA, 0)
   442  	ctxt.xdefine("runtime.erodata", sym.SRODATAEND, 0)
   443  	ctxt.xdefine("runtime.types", sym.SRODATA, 0)
   444  	ctxt.xdefine("runtime.etypes", sym.SRODATA, 0)
   445  	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, 0)
   446  	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATAEND, 0)
   447  	ctxt.xdefine("runtime.data", sym.SDATA, 0)
   448  	ctxt.xdefine("runtime.edata", sym.SDATAEND, 0)
   449  	ctxt.xdefine("runtime.bss", sym.SBSS, 0)
   450  	ctxt.xdefine("runtime.ebss", sym.SBSS, 0)
   451  	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, 0)
   452  	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, 0)
   453  	ctxt.xdefine("runtime.gcmask.*", sym.SNOPTRBSS, 0)
   454  	ctxt.xdefine("runtime.covctrs", sym.SNOPTRBSS, 0)
   455  	ctxt.xdefine("runtime.ecovctrs", sym.SNOPTRBSS, 0)
   456  	ctxt.xdefine("runtime.end", sym.SBSS, 0)
   457  	ctxt.xdefine("runtime.epclntab", sym.SRODATA, 0)
   458  
   459  	// garbage collection symbols
   460  	s := ldr.CreateSymForUpdate("runtime.gcdata", 0)
   461  	s.SetType(sym.SRODATA)
   462  	s.SetSize(0)
   463  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, 0)
   464  
   465  	s = ldr.CreateSymForUpdate("runtime.gcbss", 0)
   466  	s.SetType(sym.SRODATA)
   467  	s.SetSize(0)
   468  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, 0)
   469  
   470  	// pseudo-symbols to mark locations of type, string, and go string data.
   471  	s = ldr.CreateSymForUpdate("type:*", 0)
   472  	s.SetType(sym.STYPE)
   473  	s.SetSize(0)
   474  	s.SetAlign(int32(ctxt.Arch.PtrSize))
   475  	symtype := s.Sym()
   476  	setCarrierSym(sym.STYPE, symtype)
   477  
   478  	groupSym := func(name string, t sym.SymKind) loader.Sym {
   479  		s := ldr.CreateSymForUpdate(name, 0)
   480  		s.SetType(t)
   481  		s.SetSize(0)
   482  		s.SetAlign(int32(ctxt.Arch.PtrSize))
   483  		s.SetLocal(true)
   484  		setCarrierSym(t, s.Sym())
   485  		return s.Sym()
   486  	}
   487  	var (
   488  		symgostring = groupSym("go:string.*", sym.SGOSTRING)
   489  		symgofunc   = groupSym("go:funcdesc", sym.SGOFUNC)
   490  		symgcbits   = groupSym("runtime.gcbits.*", sym.SGCBITS)
   491  		symgcmask   = groupSym("runtime.gcmask.*", sym.SGCMASK)
   492  	)
   493  
   494  	// assign specific types so that they sort together.
   495  	// within a type they sort by size, so the .* symbols
   496  	// just defined above will be first.
   497  	// hide the specific symbols.
   498  	// Some of these symbol section conditions are duplicated
   499  	// in cmd/internal/obj.contentHashSection.
   500  	nsym := loader.Sym(ldr.NSym())
   501  	symGroupType := make([]sym.SymKind, nsym)
   502  	for s := loader.Sym(1); s < nsym; s++ {
   503  		if (!ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) && ldr.SymPkg(s) != "") || (ctxt.LinkMode == LinkInternal && ldr.SymType(s) == sym.SCOVERAGE_COUNTER) {
   504  			ldr.SetAttrNotInSymbolTable(s, true)
   505  		}
   506  
   507  		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) {
   508  			continue
   509  		}
   510  
   511  		if ldr.SymType(s) == sym.SNOPTRBSS && strings.HasPrefix(ldr.SymName(s), "type:.gcmask.") {
   512  			symGroupType[s] = sym.SGCMASK
   513  			ldr.SetAttrNotInSymbolTable(s, true)
   514  			ldr.SetCarrierSym(s, symgcmask)
   515  			continue
   516  		}
   517  
   518  		if ldr.SymType(s) != sym.SRODATA && ldr.SymType(s) != sym.SGOFUNC {
   519  			continue
   520  		}
   521  
   522  		name := ldr.SymName(s)
   523  		switch {
   524  		case strings.HasPrefix(name, "go:string."):
   525  			symGroupType[s] = sym.SGOSTRING
   526  			ldr.SetAttrNotInSymbolTable(s, true)
   527  			ldr.SetCarrierSym(s, symgostring)
   528  
   529  		case strings.HasPrefix(name, "runtime.gcbits."):
   530  			symGroupType[s] = sym.SGCBITS
   531  			ldr.SetAttrNotInSymbolTable(s, true)
   532  			ldr.SetCarrierSym(s, symgcbits)
   533  
   534  		case strings.HasSuffix(name, "·f"):
   535  			if !ctxt.DynlinkingGo() {
   536  				ldr.SetAttrNotInSymbolTable(s, true)
   537  				ldr.SetCarrierSym(s, symgofunc)
   538  			}
   539  			symGroupType[s] = sym.SGOFUNC
   540  
   541  		case strings.HasPrefix(name, "type:"):
   542  			if !ctxt.DynlinkingGo() {
   543  				ldr.SetAttrNotInSymbolTable(s, true)
   544  				ldr.SetCarrierSym(s, symtype)
   545  			}
   546  			symGroupType[s] = sym.STYPE
   547  
   548  		case ldr.IsItab(s):
   549  			if !ctxt.DynlinkingGo() {
   550  				ldr.SetAttrNotInSymbolTable(s, true)
   551  				ldr.SetCarrierSym(s, symtype)
   552  			}
   553  			symGroupType[s] = sym.STYPE
   554  		}
   555  	}
   556  
   557  	if ctxt.BuildMode == BuildModeShared {
   558  		abihashgostr := ldr.CreateSymForUpdate("go:link.abihash."+filepath.Base(*flagOutfile), 0)
   559  		abihashgostr.SetType(sym.SRODATA)
   560  		hashsym := ldr.LookupOrCreateSym("go:link.abihashbytes", 0)
   561  		abihashgostr.AddAddr(ctxt.Arch, hashsym)
   562  		abihashgostr.AddUint(ctxt.Arch, uint64(ldr.SymSize(hashsym)))
   563  	}
   564  	if ctxt.BuildMode == BuildModePlugin || ctxt.CanUsePlugins() {
   565  		for _, l := range ctxt.Library {
   566  			s := ldr.CreateSymForUpdate("go:link.pkghashbytes."+l.Pkg, 0)
   567  			s.SetType(sym.SRODATA)
   568  			s.SetSize(int64(len(l.Fingerprint)))
   569  			s.SetData(l.Fingerprint[:])
   570  			str := ldr.CreateSymForUpdate("go:link.pkghash."+l.Pkg, 0)
   571  			str.SetType(sym.SRODATA)
   572  			str.AddAddr(ctxt.Arch, s.Sym())
   573  			str.AddUint(ctxt.Arch, uint64(len(l.Fingerprint)))
   574  		}
   575  	}
   576  
   577  	textsectionmapSym, nsections := textsectionmap(ctxt)
   578  
   579  	// Information about the layout of the executable image for the
   580  	// runtime to use. Any changes here must be matched by changes to
   581  	// the definition of moduledata in runtime/symtab.go.
   582  	// This code uses several global variables that are set by pcln.go:pclntab.
   583  	moduledata := ldr.MakeSymbolUpdater(ctxt.Moduledata)
   584  
   585  	slice := func(sym loader.Sym, len uint64) {
   586  		moduledata.AddAddr(ctxt.Arch, sym)
   587  		moduledata.AddUint(ctxt.Arch, len)
   588  		moduledata.AddUint(ctxt.Arch, len)
   589  	}
   590  
   591  	sliceSym := func(sym loader.Sym) {
   592  		slice(sym, uint64(ldr.SymSize(sym)))
   593  	}
   594  
   595  	nilSlice := func() {
   596  		moduledata.AddUint(ctxt.Arch, 0)
   597  		moduledata.AddUint(ctxt.Arch, 0)
   598  		moduledata.AddUint(ctxt.Arch, 0)
   599  	}
   600  
   601  	// The pcHeader
   602  	moduledata.AddAddr(ctxt.Arch, pcln.pcheader)
   603  
   604  	// The function name slice
   605  	sliceSym(pcln.funcnametab)
   606  
   607  	// The cutab slice
   608  	slice(pcln.cutab, uint64(ldr.SymSize(pcln.cutab))/4)
   609  
   610  	// The filetab slice
   611  	sliceSym(pcln.filetab)
   612  
   613  	// The pctab slice
   614  	sliceSym(pcln.pctab)
   615  
   616  	// The pclntab slice
   617  	sliceSym(pcln.pclntab)
   618  
   619  	// The ftab slice
   620  	slice(pcln.pclntab, uint64(pcln.nfunc+1))
   621  
   622  	// findfunctab
   623  	moduledata.AddAddr(ctxt.Arch, pcln.findfunctab)
   624  	// minpc, maxpc
   625  	moduledata.AddAddr(ctxt.Arch, pcln.firstFunc)
   626  	moduledata.AddAddrPlus(ctxt.Arch, pcln.lastFunc, ldr.SymSize(pcln.lastFunc))
   627  	// pointers to specific parts of the module
   628  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.text", 0))
   629  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etext", 0))
   630  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrdata", 0))
   631  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrdata", 0))
   632  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.data", 0))
   633  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.edata", 0))
   634  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.bss", 0))
   635  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ebss", 0))
   636  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrbss", 0))
   637  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrbss", 0))
   638  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.covctrs", 0))
   639  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ecovctrs", 0))
   640  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.end", 0))
   641  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcdata", 0))
   642  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcbss", 0))
   643  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.types", 0))
   644  	ctxt.moduledataTypeDescOffset = moduledata.Size()
   645  	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
   646  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypes", 0))
   647  	ctxt.moduledataItabOffset = moduledata.Size()
   648  	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
   649  	ctxt.moduledataItabSizeOffset = moduledata.Size()
   650  	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
   651  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.rodata", 0))
   652  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("go:func.*", 0))
   653  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.epclntab", 0))
   654  
   655  	if ctxt.IsAIX() && ctxt.IsExternal() {
   656  		// Add R_XCOFFREF relocation to prevent ld's garbage collection of
   657  		// the following symbols. They might not be referenced in the program.
   658  		addRef := func(name string) {
   659  			s := ldr.Lookup(name, 0)
   660  			if s == 0 {
   661  				return
   662  			}
   663  			r, _ := moduledata.AddRel(objabi.R_XCOFFREF)
   664  			r.SetSym(s)
   665  			r.SetSiz(uint8(ctxt.Arch.PtrSize))
   666  		}
   667  		addRef("runtime.rodata")
   668  		addRef("runtime.erodata")
   669  		addRef("runtime.epclntab")
   670  		addRef("go:func.*")
   671  		// As we use relative addressing for text symbols in functab, it is
   672  		// important that the offsets we computed stay unchanged by the external
   673  		// linker, i.e. all symbols in Textp should not be removed.
   674  		// Most of them are actually referenced (our deadcode pass ensures that),
   675  		// except go:buildid which is generated late and not used by the program.
   676  		addRef("go:buildid")
   677  	}
   678  	if ctxt.IsAIX() {
   679  		// On AIX, an R_ADDR relocation from an RODATA symbol to a DATA symbol
   680  		// does not work. See data.go:relocsym, case R_ADDR.
   681  		// Here we record the unrelocated address in aixStaticDataBase (it is
   682  		// unrelocated as it is in RODATA) so we can compute the delta at
   683  		// run time.
   684  		sb := ldr.CreateSymForUpdate("runtime.aixStaticDataBase", 0)
   685  		sb.SetSize(0)
   686  		sb.AddAddr(ctxt.Arch, ldr.Lookup("runtime.data", 0))
   687  		sb.SetType(sym.SRODATA)
   688  	}
   689  
   690  	// text section information
   691  	slice(textsectionmapSym, uint64(nsections))
   692  
   693  	// The ptab slice
   694  	if ptab := ldr.Lookup("go:plugin.tabs", 0); ptab != 0 && ldr.AttrReachable(ptab) {
   695  		ldr.SetAttrLocal(ptab, true)
   696  		if ldr.SymType(ptab) != sym.SRODATA {
   697  			panic(fmt.Sprintf("go:plugin.tabs is %v, not SRODATA", ldr.SymType(ptab)))
   698  		}
   699  		nentries := uint64(len(ldr.Data(ptab)) / 8) // sizeof(nameOff) + sizeof(typeOff)
   700  		slice(ptab, nentries)
   701  	} else {
   702  		nilSlice()
   703  	}
   704  
   705  	if ctxt.BuildMode == BuildModePlugin {
   706  		addgostring(ctxt, ldr, moduledata, "go:link.thispluginpath", objabi.PathToPrefix(*flagPluginPath))
   707  
   708  		pkghashes := ldr.CreateSymForUpdate("go:link.pkghashes", 0)
   709  		pkghashes.SetLocal(true)
   710  		pkghashes.SetType(sym.SRODATA)
   711  
   712  		for i, l := range ctxt.Library {
   713  			// pkghashes[i].name
   714  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkgname.%d", i), l.Pkg)
   715  			// pkghashes[i].linktimehash
   716  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkglinkhash.%d", i), string(l.Fingerprint[:]))
   717  			// pkghashes[i].runtimehash
   718  			hash := ldr.Lookup("go:link.pkghash."+l.Pkg, 0)
   719  			pkghashes.AddAddr(ctxt.Arch, hash)
   720  		}
   721  		slice(pkghashes.Sym(), uint64(len(ctxt.Library)))
   722  	} else {
   723  		moduledata.AddUint(ctxt.Arch, 0) // pluginpath
   724  		moduledata.AddUint(ctxt.Arch, 0)
   725  		nilSlice() // pkghashes slice
   726  	}
   727  	// Add inittasks slice
   728  	t := ctxt.mainInittasks
   729  	if t != 0 {
   730  		moduledata.AddAddr(ctxt.Arch, t)
   731  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   732  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   733  	} else {
   734  		// Some build modes have no inittasks, like a shared library.
   735  		// Its inittask list will be constructed by a higher-level
   736  		// linking step.
   737  		// This branch can also happen if there are no init tasks at all.
   738  		moduledata.AddUint(ctxt.Arch, 0)
   739  		moduledata.AddUint(ctxt.Arch, 0)
   740  		moduledata.AddUint(ctxt.Arch, 0)
   741  	}
   742  
   743  	if len(ctxt.Shlibs) > 0 {
   744  		thismodulename := filepath.Base(*flagOutfile)
   745  		switch ctxt.BuildMode {
   746  		case BuildModeExe, BuildModePIE:
   747  			// When linking an executable, outfile is just "a.out". Make
   748  			// it something slightly more comprehensible.
   749  			thismodulename = "the executable"
   750  		}
   751  		addgostring(ctxt, ldr, moduledata, "go:link.thismodulename", thismodulename)
   752  
   753  		modulehashes := ldr.CreateSymForUpdate("go:link.abihashes", 0)
   754  		modulehashes.SetLocal(true)
   755  		modulehashes.SetType(sym.SRODATA)
   756  
   757  		for i, shlib := range ctxt.Shlibs {
   758  			// modulehashes[i].modulename
   759  			modulename := filepath.Base(shlib.Path)
   760  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.libname.%d", i), modulename)
   761  
   762  			// modulehashes[i].linktimehash
   763  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.linkhash.%d", i), string(shlib.Hash))
   764  
   765  			// modulehashes[i].runtimehash
   766  			abihash := ldr.LookupOrCreateSym("go:link.abihash."+modulename, 0)
   767  			ldr.SetAttrReachable(abihash, true)
   768  			modulehashes.AddAddr(ctxt.Arch, abihash)
   769  		}
   770  
   771  		slice(modulehashes.Sym(), uint64(len(ctxt.Shlibs)))
   772  	} else {
   773  		moduledata.AddUint(ctxt.Arch, 0) // modulename
   774  		moduledata.AddUint(ctxt.Arch, 0)
   775  		nilSlice() // moduleshashes slice
   776  	}
   777  
   778  	hasmain := ctxt.BuildMode == BuildModeExe || ctxt.BuildMode == BuildModePIE
   779  	if hasmain {
   780  		moduledata.AddUint8(1)
   781  	} else {
   782  		moduledata.AddUint8(0)
   783  	}
   784  
   785  	// The rest of moduledata is zero initialized.
   786  	// When linking an object that does not contain the runtime we are
   787  	// creating the moduledata from scratch and it does not have a
   788  	// compiler-provided size, so read it from the type data.
   789  	moduledatatype := ldr.Lookup("type:runtime.moduledata", 0)
   790  	moduledata.SetSize(decodetypeSize(ctxt.Arch, ldr.Data(moduledatatype)))
   791  	moduledata.Grow(moduledata.Size())
   792  
   793  	lastmoduledatap := ldr.CreateSymForUpdate("runtime.lastmoduledatap", 0)
   794  	if lastmoduledatap.Type() != sym.SDYNIMPORT {
   795  		lastmoduledatap.SetType(sym.SNOPTRDATA)
   796  		lastmoduledatap.SetSize(0) // overwrite existing value
   797  		lastmoduledatap.SetData(nil)
   798  		lastmoduledatap.AddAddr(ctxt.Arch, moduledata.Sym())
   799  	}
   800  	return symGroupType
   801  }
   802  
   803  // CarrierSymByType tracks carrier symbols and their sizes.
   804  var CarrierSymByType [sym.SFirstUnallocated]struct {
   805  	Sym  loader.Sym
   806  	Size int64
   807  }
   808  
   809  func setCarrierSym(typ sym.SymKind, s loader.Sym) {
   810  	if CarrierSymByType[typ].Sym != 0 {
   811  		panic(fmt.Sprintf("carrier symbol for type %v already set", typ))
   812  	}
   813  	CarrierSymByType[typ].Sym = s
   814  }
   815  
   816  func setCarrierSize(typ sym.SymKind, sz int64) {
   817  	if typ == sym.Sxxx {
   818  		panic("setCarrierSize(Sxxx)")
   819  	}
   820  	if CarrierSymByType[typ].Size != 0 {
   821  		panic(fmt.Sprintf("carrier symbol size for type %v already set", typ))
   822  	}
   823  	CarrierSymByType[typ].Size = sz
   824  }
   825  
   826  func isStaticTmp(name string) bool {
   827  	return strings.Contains(name, "."+obj.StaticNamePrefix)
   828  }
   829  
   830  // Mangle function name with ABI information.
   831  func mangleABIName(ctxt *Link, ldr *loader.Loader, x loader.Sym, name string) string {
   832  	// For functions with ABI wrappers, we have to make sure that we
   833  	// don't wind up with two symbol table entries with the same
   834  	// name (since this will generated an error from the external
   835  	// linker). If we have wrappers, keep the ABIInternal name
   836  	// unmangled since we want cross-load-module calls to target
   837  	// ABIInternal, and rename other symbols.
   838  	//
   839  	// TODO: avoid the ldr.Lookup calls below by instead using an aux
   840  	// sym or marker relocation to associate the wrapper with the
   841  	// wrapped function.
   842  	if !buildcfg.Experiment.RegabiWrappers {
   843  		return name
   844  	}
   845  
   846  	if ldr.SymType(x).IsText() && ldr.SymVersion(x) != sym.SymVerABIInternal && ldr.SymVersion(x) < sym.SymVerStatic {
   847  		if s2 := ldr.Lookup(name, sym.SymVerABIInternal); s2 != 0 && ldr.SymType(s2).IsText() {
   848  			name = fmt.Sprintf("%s.abi%d", name, ldr.SymVersion(x))
   849  		}
   850  	}
   851  
   852  	// When loading a shared library, if a symbol has only one ABI,
   853  	// and the name is not mangled, we don't know what ABI it is.
   854  	// So we always mangle ABIInternal function name in shared linkage,
   855  	// except symbols that are exported to C. Type symbols are always
   856  	// ABIInternal so they are not mangled.
   857  	if ctxt.IsShared() {
   858  		if ldr.SymType(x).IsText() && ldr.SymVersion(x) == sym.SymVerABIInternal && !ldr.AttrCgoExport(x) && !strings.HasPrefix(name, "type:") {
   859  			name = fmt.Sprintf("%s.abiinternal", name)
   860  		}
   861  	}
   862  
   863  	return name
   864  }
   865
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