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 = elfShdrShnum(xosect.Elfsect.(*ElfShdr))
   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.ReplaceAll(sname, "·", ".")
   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.SFirstUnallocated {
   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.SFirstUnallocated { // 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  
   450  	// garbage collection symbols
   451  	s := ldr.CreateSymForUpdate("runtime.gcdata", 0)
   452  	s.SetType(sym.SRODATA)
   453  	s.SetSize(0)
   454  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, 0)
   455  
   456  	s = ldr.CreateSymForUpdate("runtime.gcbss", 0)
   457  	s.SetType(sym.SRODATA)
   458  	s.SetSize(0)
   459  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, 0)
   460  
   461  	// pseudo-symbols to mark locations of type, string, and go string data.
   462  	var symtype, symtyperel loader.Sym
   463  	if !ctxt.DynlinkingGo() {
   464  		if ctxt.UseRelro() && (ctxt.BuildMode == BuildModeCArchive || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE) {
   465  			s = ldr.CreateSymForUpdate("type:*", 0)
   466  			s.SetType(sym.STYPE)
   467  			s.SetSize(0)
   468  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   469  			symtype = s.Sym()
   470  
   471  			s = ldr.CreateSymForUpdate("typerel.*", 0)
   472  			s.SetType(sym.STYPERELRO)
   473  			s.SetSize(0)
   474  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   475  			symtyperel = s.Sym()
   476  		} else {
   477  			s = ldr.CreateSymForUpdate("type:*", 0)
   478  			s.SetType(sym.STYPE)
   479  			s.SetSize(0)
   480  			s.SetAlign(int32(ctxt.Arch.PtrSize))
   481  			symtype = s.Sym()
   482  			symtyperel = s.Sym()
   483  		}
   484  		setCarrierSym(sym.STYPE, symtype)
   485  		setCarrierSym(sym.STYPERELRO, symtyperel)
   486  	}
   487  
   488  	groupSym := func(name string, t sym.SymKind) loader.Sym {
   489  		s := ldr.CreateSymForUpdate(name, 0)
   490  		s.SetType(t)
   491  		s.SetSize(0)
   492  		s.SetAlign(int32(ctxt.Arch.PtrSize))
   493  		s.SetLocal(true)
   494  		setCarrierSym(t, s.Sym())
   495  		return s.Sym()
   496  	}
   497  	var (
   498  		symgostring = groupSym("go:string.*", sym.SGOSTRING)
   499  		symgofunc   = groupSym("go:funcdesc", sym.SGOFUNC)
   500  		symgcbits   = groupSym("runtime.gcbits.*", sym.SGCBITS)
   501  	)
   502  
   503  	symgofuncrel := symgofunc
   504  	if ctxt.UseRelro() {
   505  		symgofuncrel = groupSym("go:funcdescrel", sym.SGOFUNCRELRO)
   506  	}
   507  
   508  	// assign specific types so that they sort together.
   509  	// within a type they sort by size, so the .* symbols
   510  	// just defined above will be first.
   511  	// hide the specific symbols.
   512  	// Some of these symbol section conditions are duplicated
   513  	// in cmd/internal/obj.contentHashSection.
   514  	nsym := loader.Sym(ldr.NSym())
   515  	symGroupType := make([]sym.SymKind, nsym)
   516  	for s := loader.Sym(1); s < nsym; s++ {
   517  		if (!ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) && ldr.SymPkg(s) != "") || (ctxt.LinkMode == LinkInternal && ldr.SymType(s) == sym.SCOVERAGE_COUNTER) {
   518  			ldr.SetAttrNotInSymbolTable(s, true)
   519  		}
   520  		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) || (ldr.SymType(s) != sym.SRODATA && ldr.SymType(s) != sym.SGOFUNC) {
   521  			continue
   522  		}
   523  
   524  		name := ldr.SymName(s)
   525  		switch {
   526  		case strings.HasPrefix(name, "go:string."):
   527  			symGroupType[s] = sym.SGOSTRING
   528  			ldr.SetAttrNotInSymbolTable(s, true)
   529  			ldr.SetCarrierSym(s, symgostring)
   530  
   531  		case strings.HasPrefix(name, "runtime.gcbits."),
   532  			strings.HasPrefix(name, "type:.gcprog."):
   533  			symGroupType[s] = sym.SGCBITS
   534  			ldr.SetAttrNotInSymbolTable(s, true)
   535  			ldr.SetCarrierSym(s, symgcbits)
   536  
   537  		case strings.HasSuffix(name, "·f"):
   538  			if !ctxt.DynlinkingGo() {
   539  				ldr.SetAttrNotInSymbolTable(s, true)
   540  			}
   541  			if ctxt.UseRelro() {
   542  				symGroupType[s] = sym.SGOFUNCRELRO
   543  				if !ctxt.DynlinkingGo() {
   544  					ldr.SetCarrierSym(s, symgofuncrel)
   545  				}
   546  			} else {
   547  				symGroupType[s] = sym.SGOFUNC
   548  				ldr.SetCarrierSym(s, symgofunc)
   549  			}
   550  
   551  		case strings.HasPrefix(name, "type:"):
   552  			if !ctxt.DynlinkingGo() {
   553  				ldr.SetAttrNotInSymbolTable(s, true)
   554  			}
   555  			if ctxt.UseRelro() {
   556  				symGroupType[s] = sym.STYPERELRO
   557  				if symtyperel != 0 {
   558  					ldr.SetCarrierSym(s, symtyperel)
   559  				}
   560  			} else {
   561  				symGroupType[s] = sym.STYPE
   562  				if symtyperel != 0 {
   563  					ldr.SetCarrierSym(s, symtype)
   564  				}
   565  			}
   566  		}
   567  	}
   568  
   569  	if ctxt.BuildMode == BuildModeShared {
   570  		abihashgostr := ldr.CreateSymForUpdate("go:link.abihash."+filepath.Base(*flagOutfile), 0)
   571  		abihashgostr.SetType(sym.SRODATA)
   572  		hashsym := ldr.LookupOrCreateSym("go:link.abihashbytes", 0)
   573  		abihashgostr.AddAddr(ctxt.Arch, hashsym)
   574  		abihashgostr.AddUint(ctxt.Arch, uint64(ldr.SymSize(hashsym)))
   575  	}
   576  	if ctxt.BuildMode == BuildModePlugin || ctxt.CanUsePlugins() {
   577  		for _, l := range ctxt.Library {
   578  			s := ldr.CreateSymForUpdate("go:link.pkghashbytes."+l.Pkg, 0)
   579  			s.SetType(sym.SRODATA)
   580  			s.SetSize(int64(len(l.Fingerprint)))
   581  			s.SetData(l.Fingerprint[:])
   582  			str := ldr.CreateSymForUpdate("go:link.pkghash."+l.Pkg, 0)
   583  			str.SetType(sym.SRODATA)
   584  			str.AddAddr(ctxt.Arch, s.Sym())
   585  			str.AddUint(ctxt.Arch, uint64(len(l.Fingerprint)))
   586  		}
   587  	}
   588  
   589  	textsectionmapSym, nsections := textsectionmap(ctxt)
   590  
   591  	// Information about the layout of the executable image for the
   592  	// runtime to use. Any changes here must be matched by changes to
   593  	// the definition of moduledata in runtime/symtab.go.
   594  	// This code uses several global variables that are set by pcln.go:pclntab.
   595  	moduledata := ldr.MakeSymbolUpdater(ctxt.Moduledata)
   596  
   597  	slice := func(sym loader.Sym, len uint64) {
   598  		moduledata.AddAddr(ctxt.Arch, sym)
   599  		moduledata.AddUint(ctxt.Arch, len)
   600  		moduledata.AddUint(ctxt.Arch, len)
   601  	}
   602  
   603  	sliceSym := func(sym loader.Sym) {
   604  		slice(sym, uint64(ldr.SymSize(sym)))
   605  	}
   606  
   607  	nilSlice := func() {
   608  		moduledata.AddUint(ctxt.Arch, 0)
   609  		moduledata.AddUint(ctxt.Arch, 0)
   610  		moduledata.AddUint(ctxt.Arch, 0)
   611  	}
   612  
   613  	// The pcHeader
   614  	moduledata.AddAddr(ctxt.Arch, pcln.pcheader)
   615  
   616  	// The function name slice
   617  	sliceSym(pcln.funcnametab)
   618  
   619  	// The cutab slice
   620  	slice(pcln.cutab, uint64(ldr.SymSize(pcln.cutab))/4)
   621  
   622  	// The filetab slice
   623  	sliceSym(pcln.filetab)
   624  
   625  	// The pctab slice
   626  	sliceSym(pcln.pctab)
   627  
   628  	// The pclntab slice
   629  	sliceSym(pcln.pclntab)
   630  
   631  	// The ftab slice
   632  	slice(pcln.pclntab, uint64(pcln.nfunc+1))
   633  
   634  	// findfunctab
   635  	moduledata.AddAddr(ctxt.Arch, pcln.findfunctab)
   636  	// minpc, maxpc
   637  	moduledata.AddAddr(ctxt.Arch, pcln.firstFunc)
   638  	moduledata.AddAddrPlus(ctxt.Arch, pcln.lastFunc, ldr.SymSize(pcln.lastFunc))
   639  	// pointers to specific parts of the module
   640  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.text", 0))
   641  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etext", 0))
   642  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrdata", 0))
   643  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrdata", 0))
   644  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.data", 0))
   645  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.edata", 0))
   646  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.bss", 0))
   647  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ebss", 0))
   648  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrbss", 0))
   649  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrbss", 0))
   650  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.covctrs", 0))
   651  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ecovctrs", 0))
   652  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.end", 0))
   653  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcdata", 0))
   654  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcbss", 0))
   655  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.types", 0))
   656  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypes", 0))
   657  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.rodata", 0))
   658  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("go:func.*", 0))
   659  	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.epclntab", 0))
   660  
   661  	if ctxt.IsAIX() && ctxt.IsExternal() {
   662  		// Add R_XCOFFREF relocation to prevent ld's garbage collection of
   663  		// the following symbols. They might not be referenced in the program.
   664  		addRef := func(name string) {
   665  			s := ldr.Lookup(name, 0)
   666  			if s == 0 {
   667  				return
   668  			}
   669  			r, _ := moduledata.AddRel(objabi.R_XCOFFREF)
   670  			r.SetSym(s)
   671  			r.SetSiz(uint8(ctxt.Arch.PtrSize))
   672  		}
   673  		addRef("runtime.rodata")
   674  		addRef("runtime.erodata")
   675  		addRef("runtime.epclntab")
   676  		addRef("go:func.*")
   677  		// As we use relative addressing for text symbols in functab, it is
   678  		// important that the offsets we computed stay unchanged by the external
   679  		// linker, i.e. all symbols in Textp should not be removed.
   680  		// Most of them are actually referenced (our deadcode pass ensures that),
   681  		// except go:buildid which is generated late and not used by the program.
   682  		addRef("go:buildid")
   683  	}
   684  	if ctxt.IsAIX() {
   685  		// On AIX, an R_ADDR relocation from an RODATA symbol to a DATA symbol
   686  		// does not work. See data.go:relocsym, case R_ADDR.
   687  		// Here we record the unrelocated address in aixStaticDataBase (it is
   688  		// unrelocated as it is in RODATA) so we can compute the delta at
   689  		// run time.
   690  		sb := ldr.CreateSymForUpdate("runtime.aixStaticDataBase", 0)
   691  		sb.SetSize(0)
   692  		sb.AddAddr(ctxt.Arch, ldr.Lookup("runtime.data", 0))
   693  		sb.SetType(sym.SRODATA)
   694  	}
   695  
   696  	// text section information
   697  	slice(textsectionmapSym, uint64(nsections))
   698  
   699  	// The typelinks slice
   700  	typelinkSym := ldr.Lookup("runtime.typelink", 0)
   701  	ntypelinks := uint64(ldr.SymSize(typelinkSym)) / 4
   702  	slice(typelinkSym, ntypelinks)
   703  
   704  	// The itablinks slice
   705  	itablinkSym := ldr.Lookup("runtime.itablink", 0)
   706  	nitablinks := uint64(ldr.SymSize(itablinkSym)) / uint64(ctxt.Arch.PtrSize)
   707  	slice(itablinkSym, nitablinks)
   708  
   709  	// The ptab slice
   710  	if ptab := ldr.Lookup("go:plugin.tabs", 0); ptab != 0 && ldr.AttrReachable(ptab) {
   711  		ldr.SetAttrLocal(ptab, true)
   712  		if ldr.SymType(ptab) != sym.SRODATA {
   713  			panic(fmt.Sprintf("go:plugin.tabs is %v, not SRODATA", ldr.SymType(ptab)))
   714  		}
   715  		nentries := uint64(len(ldr.Data(ptab)) / 8) // sizeof(nameOff) + sizeof(typeOff)
   716  		slice(ptab, nentries)
   717  	} else {
   718  		nilSlice()
   719  	}
   720  
   721  	if ctxt.BuildMode == BuildModePlugin {
   722  		addgostring(ctxt, ldr, moduledata, "go:link.thispluginpath", objabi.PathToPrefix(*flagPluginPath))
   723  
   724  		pkghashes := ldr.CreateSymForUpdate("go:link.pkghashes", 0)
   725  		pkghashes.SetLocal(true)
   726  		pkghashes.SetType(sym.SRODATA)
   727  
   728  		for i, l := range ctxt.Library {
   729  			// pkghashes[i].name
   730  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkgname.%d", i), l.Pkg)
   731  			// pkghashes[i].linktimehash
   732  			addgostring(ctxt, ldr, pkghashes, fmt.Sprintf("go:link.pkglinkhash.%d", i), string(l.Fingerprint[:]))
   733  			// pkghashes[i].runtimehash
   734  			hash := ldr.Lookup("go:link.pkghash."+l.Pkg, 0)
   735  			pkghashes.AddAddr(ctxt.Arch, hash)
   736  		}
   737  		slice(pkghashes.Sym(), uint64(len(ctxt.Library)))
   738  	} else {
   739  		moduledata.AddUint(ctxt.Arch, 0) // pluginpath
   740  		moduledata.AddUint(ctxt.Arch, 0)
   741  		nilSlice() // pkghashes slice
   742  	}
   743  	// Add inittasks slice
   744  	t := ctxt.mainInittasks
   745  	if t != 0 {
   746  		moduledata.AddAddr(ctxt.Arch, t)
   747  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   748  		moduledata.AddUint(ctxt.Arch, uint64(ldr.SymSize(t)/int64(ctxt.Arch.PtrSize)))
   749  	} else {
   750  		// Some build modes have no inittasks, like a shared library.
   751  		// Its inittask list will be constructed by a higher-level
   752  		// linking step.
   753  		// This branch can also happen if there are no init tasks at all.
   754  		moduledata.AddUint(ctxt.Arch, 0)
   755  		moduledata.AddUint(ctxt.Arch, 0)
   756  		moduledata.AddUint(ctxt.Arch, 0)
   757  	}
   758  
   759  	if len(ctxt.Shlibs) > 0 {
   760  		thismodulename := filepath.Base(*flagOutfile)
   761  		switch ctxt.BuildMode {
   762  		case BuildModeExe, BuildModePIE:
   763  			// When linking an executable, outfile is just "a.out". Make
   764  			// it something slightly more comprehensible.
   765  			thismodulename = "the executable"
   766  		}
   767  		addgostring(ctxt, ldr, moduledata, "go:link.thismodulename", thismodulename)
   768  
   769  		modulehashes := ldr.CreateSymForUpdate("go:link.abihashes", 0)
   770  		modulehashes.SetLocal(true)
   771  		modulehashes.SetType(sym.SRODATA)
   772  
   773  		for i, shlib := range ctxt.Shlibs {
   774  			// modulehashes[i].modulename
   775  			modulename := filepath.Base(shlib.Path)
   776  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.libname.%d", i), modulename)
   777  
   778  			// modulehashes[i].linktimehash
   779  			addgostring(ctxt, ldr, modulehashes, fmt.Sprintf("go:link.linkhash.%d", i), string(shlib.Hash))
   780  
   781  			// modulehashes[i].runtimehash
   782  			abihash := ldr.LookupOrCreateSym("go:link.abihash."+modulename, 0)
   783  			ldr.SetAttrReachable(abihash, true)
   784  			modulehashes.AddAddr(ctxt.Arch, abihash)
   785  		}
   786  
   787  		slice(modulehashes.Sym(), uint64(len(ctxt.Shlibs)))
   788  	} else {
   789  		moduledata.AddUint(ctxt.Arch, 0) // modulename
   790  		moduledata.AddUint(ctxt.Arch, 0)
   791  		nilSlice() // moduleshashes slice
   792  	}
   793  
   794  	hasmain := ctxt.BuildMode == BuildModeExe || ctxt.BuildMode == BuildModePIE
   795  	if hasmain {
   796  		moduledata.AddUint8(1)
   797  	} else {
   798  		moduledata.AddUint8(0)
   799  	}
   800  
   801  	// The rest of moduledata is zero initialized.
   802  	// When linking an object that does not contain the runtime we are
   803  	// creating the moduledata from scratch and it does not have a
   804  	// compiler-provided size, so read it from the type data.
   805  	moduledatatype := ldr.Lookup("type:runtime.moduledata", 0)
   806  	moduledata.SetSize(decodetypeSize(ctxt.Arch, ldr.Data(moduledatatype)))
   807  	moduledata.Grow(moduledata.Size())
   808  
   809  	lastmoduledatap := ldr.CreateSymForUpdate("runtime.lastmoduledatap", 0)
   810  	if lastmoduledatap.Type() != sym.SDYNIMPORT {
   811  		lastmoduledatap.SetType(sym.SNOPTRDATA)
   812  		lastmoduledatap.SetSize(0) // overwrite existing value
   813  		lastmoduledatap.SetData(nil)
   814  		lastmoduledatap.AddAddr(ctxt.Arch, moduledata.Sym())
   815  	}
   816  	return symGroupType
   817  }
   818  
   819  // CarrierSymByType tracks carrier symbols and their sizes.
   820  var CarrierSymByType [sym.SFirstUnallocated]struct {
   821  	Sym  loader.Sym
   822  	Size int64
   823  }
   824  
   825  func setCarrierSym(typ sym.SymKind, s loader.Sym) {
   826  	if CarrierSymByType[typ].Sym != 0 {
   827  		panic(fmt.Sprintf("carrier symbol for type %v already set", typ))
   828  	}
   829  	CarrierSymByType[typ].Sym = s
   830  }
   831  
   832  func setCarrierSize(typ sym.SymKind, sz int64) {
   833  	if typ == sym.Sxxx {
   834  		panic("setCarrierSize(Sxxx)")
   835  	}
   836  	if CarrierSymByType[typ].Size != 0 {
   837  		panic(fmt.Sprintf("carrier symbol size for type %v already set", typ))
   838  	}
   839  	CarrierSymByType[typ].Size = sz
   840  }
   841  
   842  func isStaticTmp(name string) bool {
   843  	return strings.Contains(name, "."+obj.StaticNamePrefix)
   844  }
   845  
   846  // Mangle function name with ABI information.
   847  func mangleABIName(ctxt *Link, ldr *loader.Loader, x loader.Sym, name string) string {
   848  	// For functions with ABI wrappers, we have to make sure that we
   849  	// don't wind up with two symbol table entries with the same
   850  	// name (since this will generated an error from the external
   851  	// linker). If we have wrappers, keep the ABIInternal name
   852  	// unmangled since we want cross-load-module calls to target
   853  	// ABIInternal, and rename other symbols.
   854  	//
   855  	// TODO: avoid the ldr.Lookup calls below by instead using an aux
   856  	// sym or marker relocation to associate the wrapper with the
   857  	// wrapped function.
   858  	if !buildcfg.Experiment.RegabiWrappers {
   859  		return name
   860  	}
   861  
   862  	if ldr.SymType(x).IsText() && ldr.SymVersion(x) != sym.SymVerABIInternal && ldr.SymVersion(x) < sym.SymVerStatic {
   863  		if s2 := ldr.Lookup(name, sym.SymVerABIInternal); s2 != 0 && ldr.SymType(s2).IsText() {
   864  			name = fmt.Sprintf("%s.abi%d", name, ldr.SymVersion(x))
   865  		}
   866  	}
   867  
   868  	// When loading a shared library, if a symbol has only one ABI,
   869  	// and the name is not mangled, we don't know what ABI it is.
   870  	// So we always mangle ABIInternal function name in shared linkage,
   871  	// except symbols that are exported to C. Type symbols are always
   872  	// ABIInternal so they are not mangled.
   873  	if ctxt.IsShared() {
   874  		if ldr.SymType(x).IsText() && ldr.SymVersion(x) == sym.SymVerABIInternal && !ldr.AttrCgoExport(x) && !strings.HasPrefix(name, "type:") {
   875  			name = fmt.Sprintf("%s.abiinternal", name)
   876  		}
   877  	}
   878  
   879  	return name
   880  }
   881
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