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 && s != "" {
    49  		// first entry must be empty string
    50  		putelfstr("")
    51  	}
    52  
    53  	off := len(elfstrdat)
    54  	elfstrdat = append(elfstrdat, s...)
    55  	elfstrdat = append(elfstrdat, 0)
    56  	return off
    57  }
    58  
    59  func putelfsyment(out *OutBuf, off int, addr int64, size int64, info uint8, shndx elf.SectionIndex, other int) {
    60  	if elf64 {
    61  		out.Write32(uint32(off))
    62  		out.Write8(info)
    63  		out.Write8(uint8(other))
    64  		out.Write16(uint16(shndx))
    65  		out.Write64(uint64(addr))
    66  		out.Write64(uint64(size))
    67  		symSize += ELF64SYMSIZE
    68  	} else {
    69  		out.Write32(uint32(off))
    70  		out.Write32(uint32(addr))
    71  		out.Write32(uint32(size))
    72  		out.Write8(info)
    73  		out.Write8(uint8(other))
    74  		out.Write16(uint16(shndx))
    75  		symSize += ELF32SYMSIZE
    76  	}
    77  }
    78  
    79  func putelfsym(ctxt *Link, x loader.Sym, typ elf.SymType, curbind elf.SymBind) {
    80  	ldr := ctxt.loader
    81  	addr := ldr.SymValue(x)
    82  	size := ldr.SymSize(x)
    83  
    84  	xo := x
    85  	if ldr.OuterSym(x) != 0 {
    86  		xo = ldr.OuterSym(x)
    87  	}
    88  	xot := ldr.SymType(xo)
    89  	xosect := ldr.SymSect(xo)
    90  
    91  	var elfshnum elf.SectionIndex
    92  	if xot == sym.SDYNIMPORT || xot == sym.SHOSTOBJ || xot == sym.SUNDEFEXT {
    93  		elfshnum = elf.SHN_UNDEF
    94  		size = 0
    95  	} else {
    96  		if xosect == nil {
    97  			ldr.Errorf(x, "missing section in putelfsym")
    98  			return
    99  		}
   100  		if xosect.Elfsect == nil {
   101  			ldr.Errorf(x, "missing ELF section in putelfsym")
   102  			return
   103  		}
   104  		elfshnum = xosect.Elfsect.(*ElfShdr).shnum
   105  	}
   106  
   107  	sname := ldr.SymExtname(x)
   108  	sname = mangleABIName(ctxt, ldr, x, sname)
   109  
   110  	// One pass for each binding: elf.STB_LOCAL, elf.STB_GLOBAL,
   111  	// maybe one day elf.STB_WEAK.
   112  	bind := elf.STB_GLOBAL
   113  	if ldr.IsFileLocal(x) && !isStaticTmp(sname) || ldr.AttrVisibilityHidden(x) || ldr.AttrLocal(x) {
   114  		// Static tmp is package local, but a package can be shared among multiple DSOs.
   115  		// They need to have a single view of the static tmp that are writable.
   116  		bind = elf.STB_LOCAL
   117  	}
   118  
   119  	// In external linking mode, we have to invoke gcc with -rdynamic
   120  	// to get the exported symbols put into the dynamic symbol table.
   121  	// To avoid filling the dynamic table with lots of unnecessary symbols,
   122  	// mark all Go symbols local (not global) in the final executable.
   123  	// But when we're dynamically linking, we need all those global symbols.
   124  	if !ctxt.DynlinkingGo() && ctxt.IsExternal() && !ldr.AttrCgoExportStatic(x) && elfshnum != elf.SHN_UNDEF {
   125  		bind = elf.STB_LOCAL
   126  	}
   127  
   128  	if ctxt.LinkMode == LinkExternal && elfshnum != elf.SHN_UNDEF {
   129  		addr -= int64(xosect.Vaddr)
   130  	}
   131  	other := int(elf.STV_DEFAULT)
   132  	if ldr.AttrVisibilityHidden(x) {
   133  		// TODO(mwhudson): We only set AttrVisibilityHidden in ldelf, i.e. when
   134  		// internally linking. But STV_HIDDEN visibility only matters in object
   135  		// files and shared libraries, and as we are a long way from implementing
   136  		// internal linking for shared libraries and only create object files when
   137  		// externally linking, I don't think this makes a lot of sense.
   138  		other = int(elf.STV_HIDDEN)
   139  	}
   140  	if ctxt.IsPPC64() && typ == elf.STT_FUNC && ldr.AttrShared(x) {
   141  		// On ppc64 the top three bits of the st_other field indicate how many
   142  		// bytes separate the global and local entry points. For non-PCrel shared
   143  		// symbols this is always 8 bytes except for some special functions.
   144  		hasPCrel := buildcfg.GOPPC64 >= 10 && buildcfg.GOOS == "linux"
   145  
   146  		// This should match the preprocessing behavior in cmd/internal/obj/ppc64/obj9.go
   147  		// where the distinct global entry is inserted.
   148  		if !hasPCrel && ldr.SymName(x) != "runtime.duffzero" && ldr.SymName(x) != "runtime.duffcopy" {
   149  			other |= 3 << 5
   150  		}
   151  	}
   152  
   153  	// When dynamically linking, we create Symbols by reading the names from
   154  	// the symbol tables of the shared libraries and so the names need to
   155  	// match exactly. Tools like DTrace will have to wait for now.
   156  	if !ctxt.DynlinkingGo() {
   157  		// Rewrite · to . for ASCII-only tools like DTrace (sigh)
   158  		sname = strings.Replace(sname, "·", ".", -1)
   159  	}
   160  
   161  	if ctxt.DynlinkingGo() && bind == elf.STB_GLOBAL && curbind == elf.STB_LOCAL && ldr.SymType(x).IsText() {
   162  		// When dynamically linking, we want references to functions defined
   163  		// in this module to always be to the function object, not to the
   164  		// PLT. We force this by writing an additional local symbol for every
   165  		// global function symbol and making all relocations against the
   166  		// global symbol refer to this local symbol instead (see
   167  		// (*sym.Symbol).ElfsymForReloc). This is approximately equivalent to the
   168  		// ELF linker -Bsymbolic-functions option, but that is buggy on
   169  		// several platforms.
   170  		putelfsyment(ctxt.Out, putelfstr("local."+sname), addr, size, elf.ST_INFO(elf.STB_LOCAL, typ), elfshnum, other)
   171  		ldr.SetSymLocalElfSym(x, int32(ctxt.numelfsym))
   172  		ctxt.numelfsym++
   173  		return
   174  	} else if bind != curbind {
   175  		return
   176  	}
   177  
   178  	putelfsyment(ctxt.Out, putelfstr(sname), addr, size, elf.ST_INFO(bind, typ), elfshnum, other)
   179  	ldr.SetSymElfSym(x, int32(ctxt.numelfsym))
   180  	ctxt.numelfsym++
   181  }
   182  
   183  func putelfsectionsym(ctxt *Link, out *OutBuf, s loader.Sym, shndx elf.SectionIndex) {
   184  	putelfsyment(out, 0, 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_SECTION), shndx, 0)
   185  	ctxt.loader.SetSymElfSym(s, int32(ctxt.numelfsym))
   186  	ctxt.numelfsym++
   187  }
   188  
   189  func genelfsym(ctxt *Link, elfbind elf.SymBind) {
   190  	ldr := ctxt.loader
   191  
   192  	// runtime.text marker symbol(s).
   193  	s := ldr.Lookup("runtime.text", 0)
   194  	putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   195  	for k, sect := range Segtext.Sections[1:] {
   196  		n := k + 1
   197  		if sect.Name != ".text" || (ctxt.IsAIX() && ctxt.IsExternal()) {
   198  			// On AIX, runtime.text.X are symbols already in the symtab.
   199  			break
   200  		}
   201  		s = ldr.Lookup(fmt.Sprintf("runtime.text.%d", n), 0)
   202  		if s == 0 {
   203  			break
   204  		}
   205  		if !ldr.SymType(s).IsText() {
   206  			panic("unexpected type for runtime.text symbol")
   207  		}
   208  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   209  	}
   210  
   211  	// Text symbols.
   212  	for _, s := range ctxt.Textp {
   213  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   214  	}
   215  
   216  	// runtime.etext marker symbol.
   217  	s = ldr.Lookup("runtime.etext", 0)
   218  	if ldr.SymType(s).IsText() {
   219  		putelfsym(ctxt, s, elf.STT_FUNC, elfbind)
   220  	}
   221  
   222  	shouldBeInSymbolTable := func(s loader.Sym) bool {
   223  		if ldr.AttrNotInSymbolTable(s) {
   224  			return false
   225  		}
   226  		// FIXME: avoid having to do name inspections here.
   227  		// NB: the restrictions below on file local symbols are a bit
   228  		// arbitrary -- if it turns out we need nameless static
   229  		// symbols they could be relaxed/removed.
   230  		sn := ldr.SymName(s)
   231  		if (sn == "" || sn[0] == '.') && ldr.IsFileLocal(s) {
   232  			panic(fmt.Sprintf("unexpected file local symbol %d %s<%d>\n",
   233  				s, sn, ldr.SymVersion(s)))
   234  		}
   235  		if (sn == "" || sn[0] == '.') && !ldr.IsFileLocal(s) {
   236  			return false
   237  		}
   238  		return true
   239  	}
   240  
   241  	// Data symbols.
   242  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
   243  		if !ldr.AttrReachable(s) {
   244  			continue
   245  		}
   246  		st := ldr.SymType(s)
   247  		if st >= sym.SELFRXSECT && st < sym.SXREF {
   248  			typ := elf.STT_OBJECT
   249  			if st == sym.STLSBSS {
   250  				if ctxt.IsInternal() {
   251  					continue
   252  				}
   253  				typ = elf.STT_TLS
   254  			}
   255  			if !shouldBeInSymbolTable(s) {
   256  				continue
   257  			}
   258  			putelfsym(ctxt, s, typ, elfbind)
   259  			continue
   260  		}
   261  		if st == sym.SHOSTOBJ || st == sym.SDYNIMPORT || st == sym.SUNDEFEXT {
   262  			putelfsym(ctxt, s, ldr.SymElfType(s), elfbind)
   263  		}
   264  	}
   265  }
   266  
   267  func asmElfSym(ctxt *Link) {
   268  
   269  	// the first symbol entry is reserved
   270  	putelfsyment(ctxt.Out, 0, 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_NOTYPE), 0, 0)
   271  
   272  	dwarfaddelfsectionsyms(ctxt)
   273  
   274  	// Some linkers will add a FILE sym if one is not present.
   275  	// Avoid having the working directory inserted into the symbol table.
   276  	// It is added with a name to avoid problems with external linking
   277  	// encountered on some versions of Solaris. See issue #14957.
   278  	putelfsyment(ctxt.Out, putelfstr("go.go"), 0, 0, elf.ST_INFO(elf.STB_LOCAL, elf.STT_FILE), elf.SHN_ABS, 0)
   279  	ctxt.numelfsym++
   280  
   281  	bindings := []elf.SymBind{elf.STB_LOCAL, elf.STB_GLOBAL}
   282  	for _, elfbind := range bindings {
   283  		if elfbind == elf.STB_GLOBAL {
   284  			elfglobalsymndx = ctxt.numelfsym
   285  		}
   286  		genelfsym(ctxt, elfbind)
   287  	}
   288  }
   289  
   290  func putplan9sym(ctxt *Link, ldr *loader.Loader, s loader.Sym, char SymbolType) {
   291  	t := int(char)
   292  	if ldr.IsFileLocal(s) {
   293  		t += 'a' - 'A'
   294  	}
   295  	l := 4
   296  	addr := ldr.SymValue(s)
   297  	if ctxt.IsAMD64() && !flag8 {
   298  		ctxt.Out.Write32b(uint32(addr >> 32))
   299  		l = 8
   300  	}
   301  
   302  	ctxt.Out.Write32b(uint32(addr))
   303  	ctxt.Out.Write8(uint8(t + 0x80)) /* 0x80 is variable length */
   304  
   305  	name := ldr.SymName(s)
   306  	name = mangleABIName(ctxt, ldr, s, name)
   307  	ctxt.Out.WriteString(name)
   308  	ctxt.Out.Write8(0)
   309  
   310  	symSize += int32(l) + 1 + int32(len(name)) + 1
   311  }
   312  
   313  func asmbPlan9Sym(ctxt *Link) {
   314  	ldr := ctxt.loader
   315  
   316  	// Add special runtime.text and runtime.etext symbols.
   317  	s := ldr.Lookup("runtime.text", 0)
   318  	if ldr.SymType(s).IsText() {
   319  		putplan9sym(ctxt, ldr, s, TextSym)
   320  	}
   321  	s = ldr.Lookup("runtime.etext", 0)
   322  	if ldr.SymType(s).IsText() {
   323  		putplan9sym(ctxt, ldr, s, TextSym)
   324  	}
   325  
   326  	// Add text symbols.
   327  	for _, s := range ctxt.Textp {
   328  		putplan9sym(ctxt, ldr, s, TextSym)
   329  	}
   330  
   331  	shouldBeInSymbolTable := func(s loader.Sym) bool {
   332  		if ldr.AttrNotInSymbolTable(s) {
   333  			return false
   334  		}
   335  		name := ldr.SymName(s) // TODO: try not to read the name
   336  		if name == "" || name[0] == '.' {
   337  			return false
   338  		}
   339  		return true
   340  	}
   341  
   342  	// Add data symbols and external references.
   343  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
   344  		if !ldr.AttrReachable(s) {
   345  			continue
   346  		}
   347  		t := ldr.SymType(s)
   348  		if t >= sym.SELFRXSECT && t < sym.SXREF { // data sections handled in dodata
   349  			if t == sym.STLSBSS {
   350  				continue
   351  			}
   352  			if !shouldBeInSymbolTable(s) {
   353  				continue
   354  			}
   355  			char := DataSym
   356  			if t == sym.SBSS || t == sym.SNOPTRBSS {
   357  				char = BSSSym
   358  			}
   359  			putplan9sym(ctxt, ldr, s, char)
   360  		}
   361  	}
   362  }
   363  
   364  // Create a table with information on the text sections.
   365  // Return the symbol of the table, and number of sections.
   366  func textsectionmap(ctxt *Link) (loader.Sym, uint32) {
   367  	ldr := ctxt.loader
   368  	t := ldr.CreateSymForUpdate("runtime.textsectionmap", 0)
   369  	t.SetType(sym.SRODATA)
   370  	nsections := int64(0)
   371  
   372  	for _, sect := range Segtext.Sections {
   373  		if sect.Name == ".text" {
   374  			nsections++
   375  		} else {
   376  			break
   377  		}
   378  	}
   379  	t.Grow(3 * nsections * int64(ctxt.Arch.PtrSize))
   380  
   381  	off := int64(0)
   382  	n := 0
   383  
   384  	// The vaddr for each text section is the difference between the section's
   385  	// Vaddr and the Vaddr for the first text section as determined at compile
   386  	// time.
   387  
   388  	// The symbol for the first text section is named runtime.text as before.
   389  	// Additional text sections are named runtime.text.n where n is the
   390  	// order of creation starting with 1. These symbols provide the section's
   391  	// address after relocation by the linker.
   392  
   393  	textbase := Segtext.Sections[0].Vaddr
   394  	for _, sect := range Segtext.Sections {
   395  		if sect.Name != ".text" {
   396  			break
   397  		}
   398  		// The fields written should match runtime/symtab.go:textsect.
   399  		// They are designed to minimize runtime calculations.
   400  		vaddr := sect.Vaddr - textbase
   401  		off = t.SetUint(ctxt.Arch, off, vaddr) // field vaddr
   402  		end := vaddr + sect.Length
   403  		off = t.SetUint(ctxt.Arch, off, end) // field end
   404  		name := "runtime.text"
   405  		if n != 0 {
   406  			name = fmt.Sprintf("runtime.text.%d", n)
   407  		}
   408  		s := ldr.Lookup(name, 0)
   409  		if s == 0 {
   410  			ctxt.Errorf(s, "Unable to find symbol %s\n", name)
   411  		}
   412  		off = t.SetAddr(ctxt.Arch, off, s) // field baseaddr
   413  		n++
   414  	}
   415  	return t.Sym(), uint32(n)
   416  }
   417  
   418  func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
   419  	ldr := ctxt.loader
   420  
   421  	if !ctxt.IsAIX() && !ctxt.IsWasm() {
   422  		switch ctxt.BuildMode {
   423  		case BuildModeCArchive, BuildModeCShared:
   424  			s := ldr.Lookup(*flagEntrySymbol, sym.SymVerABI0)
   425  			if s != 0 {
   426  				addinitarrdata(ctxt, ldr, s)
   427  			}
   428  		}
   429  	}
   430  
   431  	// Define these so that they'll get put into the symbol table.
   432  	// data.c:/^address will provide the actual values.
   433  	ctxt.xdefine("runtime.rodata", sym.SRODATA, 0)
   434  	ctxt.xdefine("runtime.erodata", sym.SRODATAEND, 0)
   435  	ctxt.xdefine("runtime.types", sym.SRODATA, 0)
   436  	ctxt.xdefine("runtime.etypes", sym.SRODATA, 0)
   437  	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, 0)
   438  	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATAEND, 0)
   439  	ctxt.xdefine("runtime.data", sym.SDATA, 0)
   440  	ctxt.xdefine("runtime.edata", sym.SDATAEND, 0)
   441  	ctxt.xdefine("runtime.bss", sym.SBSS, 0)
   442  	ctxt.xdefine("runtime.ebss", sym.SBSS, 0)
   443  	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, 0)
   444  	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, 0)
   445  	ctxt.xdefine("runtime.covctrs", sym.SNOPTRBSS, 0)
   446  	ctxt.xdefine("runtime.ecovctrs", sym.SNOPTRBSS, 0)
   447  	ctxt.xdefine("runtime.end", sym.SBSS, 0)
   448  	ctxt.xdefine("runtime.epclntab", sym.SRODATA, 0)
   449  	ctxt.xdefine("runtime.esymtab", sym.SRODATA, 0)
   450  
   451  	// garbage collection symbols
   452  	s := ldr.CreateSymForUpdate("runtime.gcdata", 0)
   453  	s.SetType(sym.SRODATA)
   454  	s.SetSize(0)
   455  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, 0)
   456  
   457  	s = ldr.CreateSymForUpdate("runtime.gcbss", 0)
   458  	s.SetType(sym.SRODATA)
   459  	s.SetSize(0)
   460  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, 0)
   461  
   462  	// pseudo-symbols to mark locations of type, string, and go string data.
   463  	var symtype, symtyperel loader.Sym
   464  	if !ctxt.DynlinkingGo() {
   465  		if ctxt.UseRelro() && (ctxt.BuildMode == BuildModeCArchive || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE) {
   466  			s = ldr.CreateSymForUpdate("type:*", 0)
   467  			s.SetType(sym.STYPE)
   468  			s.SetSize(0)
   469  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   470  			symtype = s.Sym()
   471  
   472  			s = ldr.CreateSymForUpdate("typerel.*", 0)
   473  			s.SetType(sym.STYPERELRO)
   474  			s.SetSize(0)
   475  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   476  			symtyperel = s.Sym()
   477  		} else {
   478  			s = ldr.CreateSymForUpdate("type:*", 0)
   479  			s.SetType(sym.STYPE)
   480  			s.SetSize(0)
   481  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   482  			symtype = s.Sym()
   483  			symtyperel = s.Sym()
   484  		}
   485  		setCarrierSym(sym.STYPE, symtype)
   486  		setCarrierSym(sym.STYPERELRO, symtyperel)
   487  	}
   488  
   489  	groupSym := func(name string, t sym.SymKind) loader.Sym {
   490  		s := ldr.CreateSymForUpdate(name, 0)
   491  		s.SetType(t)
   492  		s.SetSize(0)
   493  		s.SetAlign(int32(ctxt.Arch.PtrSize))
   494  		s.SetLocal(true)
   495  		setCarrierSym(t, s.Sym())
   496  		return s.Sym()
   497  	}
   498  	var (
   499  		symgostring = groupSym("go:string.*", sym.SGOSTRING)
   500  		symgofunc   = groupSym("go:func.*", sym.SGOFUNC)
   501  		symgcbits   = groupSym("runtime.gcbits.*", sym.SGCBITS)
   502  	)
   503  
   504  	symgofuncrel := symgofunc
   505  	if ctxt.UseRelro() {
   506  		symgofuncrel = groupSym("go:funcrel.*", sym.SGOFUNCRELRO)
   507  	}
   508  
   509  	symt := ldr.CreateSymForUpdate("runtime.symtab", 0)
   510  	symt.SetType(sym.SSYMTAB)
   511  	symt.SetSize(0)
   512  	symt.SetLocal(true)
   513  
   514  	// assign specific types so that they sort together.
   515  	// within a type they sort by size, so the .* symbols
   516  	// just defined above will be first.
   517  	// hide the specific symbols.
   518  	// Some of these symbol section conditions are duplicated
   519  	// in cmd/internal/obj.contentHashSection.
   520  	nsym := loader.Sym(ldr.NSym())
   521  	symGroupType := make([]sym.SymKind, nsym)
   522  	for s := loader.Sym(1); s < nsym; s++ {
   523  		if (!ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) && ldr.SymPkg(s) != "") || (ctxt.LinkMode == LinkInternal && ldr.SymType(s) == sym.SCOVERAGE_COUNTER) {
   524  			ldr.SetAttrNotInSymbolTable(s, true)
   525  		}
   526  		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) || (ldr.SymType(s) != sym.SRODATA && ldr.SymType(s) != sym.SGOFUNC) {
   527  			continue
   528  		}
   529  
   530  		name := ldr.SymName(s)
   531  		switch {
   532  		case strings.HasPrefix(name, "go:string."):
   533  			symGroupType[s] = sym.SGOSTRING
   534  			ldr.SetAttrNotInSymbolTable(s, true)
   535  			ldr.SetCarrierSym(s, symgostring)
   536  
   537  		case strings.HasPrefix(name, "runtime.gcbits."),
   538  			strings.HasPrefix(name, "type:.gcprog."):
   539  			symGroupType[s] = sym.SGCBITS
   540  			ldr.SetAttrNotInSymbolTable(s, true)
   541  			ldr.SetCarrierSym(s, symgcbits)
   542  
   543  		case strings.HasSuffix(name, "·f"):
   544  			if !ctxt.DynlinkingGo() {
   545  				ldr.SetAttrNotInSymbolTable(s, true)
   546  			}
   547  			if ctxt.UseRelro() {
   548  				symGroupType[s] = sym.SGOFUNCRELRO
   549  				if !ctxt.DynlinkingGo() {
   550  					ldr.SetCarrierSym(s, symgofuncrel)
   551  				}
   552  			} else {
   553  				symGroupType[s] = sym.SGOFUNC
   554  				ldr.SetCarrierSym(s, symgofunc)
   555  			}
   556  
   557  		case strings.HasPrefix(name, "gcargs."),
   558  			strings.HasPrefix(name, "gclocals."),
   559  			strings.HasPrefix(name, "gclocals·"),
   560  			ldr.SymType(s) == sym.SGOFUNC && s != symgofunc, // inltree, see pcln.go
   561  			strings.HasSuffix(name, ".opendefer"),
   562  			strings.HasSuffix(name, ".arginfo0"),
   563  			strings.HasSuffix(name, ".arginfo1"),
   564  			strings.HasSuffix(name, ".argliveinfo"),
   565  			strings.HasSuffix(name, ".wrapinfo"),
   566  			strings.HasSuffix(name, ".args_stackmap"),
   567  			strings.HasSuffix(name, ".stkobj"):
   568  			ldr.SetAttrNotInSymbolTable(s, true)
   569  			symGroupType[s] = sym.SGOFUNC
   570  			ldr.SetCarrierSym(s, symgofunc)
   571  			if ctxt.Debugvlog != 0 {
   572  				align := ldr.SymAlign(s)
   573  				liveness += (ldr.SymSize(s) + int64(align) - 1) &^ (int64(align) - 1)
   574  			}
   575  
   576  		// Note: Check for "type:" prefix after checking for .arginfo1 suffix.
   577  		// That way symbols like "type:.eq.[2]interface {}.arginfo1" that belong
   578  		// in go:func.* end up there.
   579  		case strings.HasPrefix(name, "type:"):
   580  			if !ctxt.DynlinkingGo() {
   581  				ldr.SetAttrNotInSymbolTable(s, true)
   582  			}
   583  			if ctxt.UseRelro() {
   584  				symGroupType[s] = sym.STYPERELRO
   585  				if symtyperel != 0 {
   586  					ldr.SetCarrierSym(s, symtyperel)
   587  				}
   588  			} else {
   589  				symGroupType[s] = sym.STYPE
   590  				if symtyperel != 0 {
   591  					ldr.SetCarrierSym(s, symtype)
   592  				}
   593  			}
   594  		}
   595  	}
   596  
   597  	if ctxt.BuildMode == BuildModeShared {
   598  		abihashgostr := ldr.CreateSymForUpdate("go:link.abihash."+filepath.Base(*flagOutfile), 0)
   599  		abihashgostr.SetType(sym.SRODATA)
   600  		hashsym := ldr.LookupOrCreateSym("go:link.abihashbytes", 0)
   601  		abihashgostr.AddAddr(ctxt.Arch, hashsym)
   602  		abihashgostr.AddUint(ctxt.Arch, uint64(ldr.SymSize(hashsym)))
   603  	}
   604  	if ctxt.BuildMode == BuildModePlugin || ctxt.CanUsePlugins() {
   605  		for _, l := range ctxt.Library {
   606  			s := ldr.CreateSymForUpdate("go:link.pkghashbytes."+l.Pkg, 0)
   607  			s.SetType(sym.SRODATA)
   608  			s.SetSize(int64(len(l.Fingerprint)))
   609  			s.SetData(l.Fingerprint[:])
   610  			str := ldr.CreateSymForUpdate("go:link.pkghash."+l.Pkg, 0)
   611  			str.SetType(sym.SRODATA)
   612  			str.AddAddr(ctxt.Arch, s.Sym())
   613  			str.AddUint(ctxt.Arch, uint64(len(l.Fingerprint)))
   614  		}
   615  	}
   616  
   617  	textsectionmapSym, nsections := textsectionmap(ctxt)
   618  
   619  	// Information about the layout of the executable image for the
   620  	// runtime to use. Any changes here must be matched by changes to
   621  	// the definition of moduledata in runtime/symtab.go.
   622  	// This code uses several global variables that are set by pcln.go:pclntab.
   623  	moduledata := ldr.MakeSymbolUpdater(ctxt.Moduledata)
   624  
   625  	slice := func(sym loader.Sym, len uint64) {
   626  		moduledata.AddAddr(ctxt.Arch, sym)
   627  		moduledata.AddUint(ctxt.Arch, len)
   628  		moduledata.AddUint(ctxt.Arch, len)
   629  	}
   630  
   631  	sliceSym := func(sym loader.Sym) {
   632  		slice(sym, uint64(ldr.SymSize(sym)))
   633  	}
   634  
   635  	nilSlice := func() {
   636  		moduledata.AddUint(ctxt.Arch, 0)
   637  		moduledata.AddUint(ctxt.Arch, 0)
   638  		moduledata.AddUint(ctxt.Arch, 0)
   639  	}
   640  
   641  	// The pcHeader
   642  	moduledata.AddAddr(ctxt.Arch, pcln.pcheader)
   643  
   644  	// The function name slice
   645  	sliceSym(pcln.funcnametab)
   646  
   647  	// The cutab slice
   648  	sliceSym(pcln.cutab)
   649  
   650  	// The filetab slice
   651  	sliceSym(pcln.filetab)
   652  
   653  	// The pctab slice
   654  	sliceSym(pcln.pctab)
   655  
   656  	// The pclntab slice
   657  	slice(pcln.pclntab, uint64(ldr.SymSize(pcln.pclntab)))
   658  
   659  	// The ftab slice
   660  	slice(pcln.pclntab, uint64(pcln.nfunc+1))
   661  
   662  	// findfunctab
   663  	moduledata.AddAddr(ctxt.Arch, pcln.findfunctab)
   664  	// minpc, maxpc
   665  	moduledata.AddAddr(ctxt.Arch, pcln.firstFunc)
   666  	moduledata.AddAddrPlus(ctxt.Arch, pcln.lastFunc, ldr.SymSize(pcln.lastFunc))
   667  	// pointers to specific parts of the module
   668  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.text", 0))
   669  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etext", 0))
   670  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrdata", 0))
   671  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrdata", 0))
   672  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.data", 0))
   673  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.edata", 0))
   674  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.bss", 0))
   675  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ebss", 0))
   676  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrbss", 0))
   677  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrbss", 0))
   678  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.covctrs", 0))
   679  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ecovctrs", 0))
   680  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.end", 0))
   681  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcdata", 0))
   682  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcbss", 0))
   683  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.types", 0))
   684  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypes", 0))
   685  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.rodata", 0))
   686  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("go:func.*", 0))
   687  
   688  	if ctxt.IsAIX() && ctxt.IsExternal() {
   689  		// Add R_XCOFFREF relocation to prevent ld's garbage collection of
   690  		// the following symbols. They might not be referenced in the program.
   691  		addRef := func(name string) {
   692  			s := ldr.Lookup(name, 0)
   693  			if s == 0 {
   694  				return
   695  			}
   696  			r, _ := moduledata.AddRel(objabi.R_XCOFFREF)
   697  			r.SetSym(s)
   698  			r.SetSiz(uint8(ctxt.Arch.PtrSize))
   699  		}
   700  		addRef("runtime.rodata")
   701  		addRef("runtime.erodata")
   702  		addRef("runtime.epclntab")
   703  		// As we use relative addressing for text symbols in functab, it is
   704  		// important that the offsets we computed stay unchanged by the external
   705  		// linker, i.e. all symbols in Textp should not be removed.
   706  		// Most of them are actually referenced (our deadcode pass ensures that),
   707  		// except go:buildid which is generated late and not used by the program.
   708  		addRef("go:buildid")
   709  	}
   710  
   711  	// text section information
   712  	slice(textsectionmapSym, uint64(nsections))
   713  
   714  	// The typelinks slice
   715  	typelinkSym := ldr.Lookup("runtime.typelink", 0)
   716  	ntypelinks := uint64(ldr.SymSize(typelinkSym)) / 4
   717  	slice(typelinkSym, ntypelinks)
   718  
   719  	// The itablinks slice
   720  	itablinkSym := ldr.Lookup("runtime.itablink", 0)
   721  	nitablinks := uint64(ldr.SymSize(itablinkSym)) / uint64(ctxt.Arch.PtrSize)
   722  	slice(itablinkSym, nitablinks)
   723  
   724  	// The ptab slice
   725  	if ptab := ldr.Lookup("go:plugin.tabs", 0); ptab != 0 && ldr.AttrReachable(ptab) {
   726  		ldr.SetAttrLocal(ptab, true)
   727  		if ldr.SymType(ptab) != sym.SRODATA {
   728  			panic(fmt.Sprintf("go:plugin.tabs is %v, not SRODATA", ldr.SymType(ptab)))
   729  		}
   730  		nentries := uint64(len(ldr.Data(ptab)) / 8) // sizeof(nameOff) + sizeof(typeOff)
   731  		slice(ptab, nentries)
   732  	} else {
   733  		nilSlice()
   734  	}
   735  
   736  	if ctxt.BuildMode == BuildModePlugin {
   737  		addgostring(ctxt, ldr, moduledata, "go:link.thispluginpath", objabi.PathToPrefix(*flagPluginPath))
   738  
   739  		pkghashes := ldr.CreateSymForUpdate("go:link.pkghashes", 0)
   740  		pkghashes.SetLocal(true)
   741  		pkghashes.SetType(sym.SRODATA)
   742  
   743  		for i, l := range ctxt.Library {
   744  			// pkghashes[i].name
   745  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkgname.%d", i), l.Pkg)
   746  			// pkghashes[i].linktimehash
   747  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkglinkhash.%d", i), string(l.Fingerprint[:]))
   748  			// pkghashes[i].runtimehash
   749  			hash := ldr.Lookup("go:link.pkghash."+l.Pkg, 0)
   750  			pkghashes.AddAddr(ctxt.Arch, hash)
   751  		}
   752  		slice(pkghashes.Sym(), uint64(len(ctxt.Library)))
   753  	} else {
   754  		moduledata.AddUint(ctxt.Arch, 0) // pluginpath
   755  		moduledata.AddUint(ctxt.Arch, 0)
   756  		nilSlice() // pkghashes slice
   757  	}
   758  	// Add inittasks slice
   759  	t := ctxt.mainInittasks
   760  	if t != 0 {
   761  		moduledata.AddAddr(ctxt.Arch, t)
   762  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   763  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   764  	} else {
   765  		// Some build modes have no inittasks, like a shared library.
   766  		// Its inittask list will be constructed by a higher-level
   767  		// linking step.
   768  		// This branch can also happen if there are no init tasks at all.
   769  		moduledata.AddUint(ctxt.Arch, 0)
   770  		moduledata.AddUint(ctxt.Arch, 0)
   771  		moduledata.AddUint(ctxt.Arch, 0)
   772  	}
   773  
   774  	if len(ctxt.Shlibs) > 0 {
   775  		thismodulename := filepath.Base(*flagOutfile)
   776  		switch ctxt.BuildMode {
   777  		case BuildModeExe, BuildModePIE:
   778  			// When linking an executable, outfile is just "a.out". Make
   779  			// it something slightly more comprehensible.
   780  			thismodulename = "the executable"
   781  		}
   782  		addgostring(ctxt, ldr, moduledata, "go:link.thismodulename", thismodulename)
   783  
   784  		modulehashes := ldr.CreateSymForUpdate("go:link.abihashes", 0)
   785  		modulehashes.SetLocal(true)
   786  		modulehashes.SetType(sym.SRODATA)
   787  
   788  		for i, shlib := range ctxt.Shlibs {
   789  			// modulehashes[i].modulename
   790  			modulename := filepath.Base(shlib.Path)
   791  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.libname.%d", i), modulename)
   792  
   793  			// modulehashes[i].linktimehash
   794  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.linkhash.%d", i), string(shlib.Hash))
   795  
   796  			// modulehashes[i].runtimehash
   797  			abihash := ldr.LookupOrCreateSym("go:link.abihash."+modulename, 0)
   798  			ldr.SetAttrReachable(abihash, true)
   799  			modulehashes.AddAddr(ctxt.Arch, abihash)
   800  		}
   801  
   802  		slice(modulehashes.Sym(), uint64(len(ctxt.Shlibs)))
   803  	} else {
   804  		moduledata.AddUint(ctxt.Arch, 0) // modulename
   805  		moduledata.AddUint(ctxt.Arch, 0)
   806  		nilSlice() // moduleshashes slice
   807  	}
   808  
   809  	hasmain := ctxt.BuildMode == BuildModeExe || ctxt.BuildMode == BuildModePIE
   810  	if hasmain {
   811  		moduledata.AddUint8(1)
   812  	} else {
   813  		moduledata.AddUint8(0)
   814  	}
   815  
   816  	// The rest of moduledata is zero initialized.
   817  	// When linking an object that does not contain the runtime we are
   818  	// creating the moduledata from scratch and it does not have a
   819  	// compiler-provided size, so read it from the type data.
   820  	moduledatatype := ldr.Lookup("type:runtime.moduledata", 0)
   821  	moduledata.SetSize(decodetypeSize(ctxt.Arch, ldr.Data(moduledatatype)))
   822  	moduledata.Grow(moduledata.Size())
   823  
   824  	lastmoduledatap := ldr.CreateSymForUpdate("runtime.lastmoduledatap", 0)
   825  	if lastmoduledatap.Type() != sym.SDYNIMPORT {
   826  		lastmoduledatap.SetType(sym.SNOPTRDATA)
   827  		lastmoduledatap.SetSize(0) // overwrite existing value
   828  		lastmoduledatap.SetData(nil)
   829  		lastmoduledatap.AddAddr(ctxt.Arch, moduledata.Sym())
   830  	}
   831  	return symGroupType
   832  }
   833  
   834  // CarrierSymByType tracks carrier symbols and their sizes.
   835  var CarrierSymByType [sym.SXREF]struct {
   836  	Sym  loader.Sym
   837  	Size int64
   838  }
   839  
   840  func setCarrierSym(typ sym.SymKind, s loader.Sym) {
   841  	if CarrierSymByType[typ].Sym != 0 {
   842  		panic(fmt.Sprintf("carrier symbol for type %v already set", typ))
   843  	}
   844  	CarrierSymByType[typ].Sym = s
   845  }
   846  
   847  func setCarrierSize(typ sym.SymKind, sz int64) {
   848  	if typ == sym.Sxxx {
   849  		panic("setCarrierSize(Sxxx)")
   850  	}
   851  	if CarrierSymByType[typ].Size != 0 {
   852  		panic(fmt.Sprintf("carrier symbol size for type %v already set", typ))
   853  	}
   854  	CarrierSymByType[typ].Size = sz
   855  }
   856  
   857  func isStaticTmp(name string) bool {
   858  	return strings.Contains(name, "."+obj.StaticNamePrefix)
   859  }
   860  
   861  // Mangle function name with ABI information.
   862  func mangleABIName(ctxt *Link, ldr *loader.Loader, x loader.Sym, name string) string {
   863  	// For functions with ABI wrappers, we have to make sure that we
   864  	// don't wind up with two symbol table entries with the same
   865  	// name (since this will generated an error from the external
   866  	// linker). If we have wrappers, keep the ABIInternal name
   867  	// unmangled since we want cross-load-module calls to target
   868  	// ABIInternal, and rename other symbols.
   869  	//
   870  	// TODO: avoid the ldr.Lookup calls below by instead using an aux
   871  	// sym or marker relocation to associate the wrapper with the
   872  	// wrapped function.
   873  	if !buildcfg.Experiment.RegabiWrappers {
   874  		return name
   875  	}
   876  
   877  	if ldr.SymType(x).IsText() && ldr.SymVersion(x) != sym.SymVerABIInternal && ldr.SymVersion(x) < sym.SymVerStatic {
   878  		if s2 := ldr.Lookup(name, sym.SymVerABIInternal); s2 != 0 && ldr.SymType(s2).IsText() {
   879  			name = fmt.Sprintf("%s.abi%d", name, ldr.SymVersion(x))
   880  		}
   881  	}
   882  
   883  	// When loading a shared library, if a symbol has only one ABI,
   884  	// and the name is not mangled, we don't know what ABI it is.
   885  	// So we always mangle ABIInternal function name in shared linkage,
   886  	// except symbols that are exported to C. Type symbols are always
   887  	// ABIInternal so they are not mangled.
   888  	if ctxt.IsShared() {
   889  		if ldr.SymType(x).IsText() && ldr.SymVersion(x) == sym.SymVerABIInternal && !ldr.AttrCgoExport(x) && !strings.HasPrefix(name, "type:") {
   890  			name = fmt.Sprintf("%s.abiinternal", name)
   891  		}
   892  	}
   893  
   894  	return name
   895  }
   896
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