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