1 // Inferno utils/8l/asm.c
2 // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/8l/asm.c
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.
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:
20 // The above copyright notice and this permission notice shall be included in
21 // all copies or substantial portions of the Software.
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
52 "cmd/internal/notsha256"
55 "cmd/link/internal/loadelf"
56 "cmd/link/internal/loader"
57 "cmd/link/internal/loadmacho"
58 "cmd/link/internal/loadpe"
59 "cmd/link/internal/loadxcoff"
60 "cmd/link/internal/sym"
63 // Data layout and relocation.
65 // Derived from Inferno utils/6l/l.h
66 // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/l.h
68 // Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
69 // Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
70 // Portions Copyright © 1997-1999 Vita Nuova Limited
71 // Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
72 // Portions Copyright © 2004,2006 Bruce Ellis
73 // Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
74 // Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
75 // Portions Copyright © 2009 The Go Authors. All rights reserved.
77 // Permission is hereby granted, free of charge, to any person obtaining a copy
78 // of this software and associated documentation files (the "Software"), to deal
79 // in the Software without restriction, including without limitation the rights
80 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
81 // copies of the Software, and to permit persons to whom the Software is
82 // furnished to do so, subject to the following conditions:
84 // The above copyright notice and this permission notice shall be included in
85 // all copies or substantial portions of the Software.
87 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
88 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
89 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
90 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
91 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
92 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
95 // ArchSyms holds a number of architecture specific symbols used during
96 // relocation. Rather than allowing them universal access to all symbols,
97 // we keep a subset for relocation application.
98 type ArchSyms struct {
104 LinkEditGOT loader.Sym
105 LinkEditPLT loader.Sym
108 DotTOC []loader.Sym // for each version
121 unreachableMethod loader.Sym
124 // mkArchSym is a helper for setArchSyms, to set up a special symbol.
125 func (ctxt *Link) mkArchSym(name string, ver int, ls *loader.Sym) {
126 *ls = ctxt.loader.LookupOrCreateSym(name, ver)
127 ctxt.loader.SetAttrReachable(*ls, true)
130 // mkArchSymVec is similar to setArchSyms, but operates on elements within
131 // a slice, where each element corresponds to some symbol version.
132 func (ctxt *Link) mkArchSymVec(name string, ver int, ls []loader.Sym) {
133 ls[ver] = ctxt.loader.LookupOrCreateSym(name, ver)
134 ctxt.loader.SetAttrReachable(ls[ver], true)
137 // setArchSyms sets up the ArchSyms structure, and must be called before
138 // relocations are applied.
139 func (ctxt *Link) setArchSyms() {
140 ctxt.mkArchSym(".got", 0, &ctxt.GOT)
141 ctxt.mkArchSym(".plt", 0, &ctxt.PLT)
142 ctxt.mkArchSym(".got.plt", 0, &ctxt.GOTPLT)
143 ctxt.mkArchSym(".dynamic", 0, &ctxt.Dynamic)
144 ctxt.mkArchSym(".dynsym", 0, &ctxt.DynSym)
145 ctxt.mkArchSym(".dynstr", 0, &ctxt.DynStr)
146 ctxt.mkArchSym("runtime.unreachableMethod", abiInternalVer, &ctxt.unreachableMethod)
149 ctxt.mkArchSym("TOC", 0, &ctxt.TOC)
151 ctxt.DotTOC = make([]loader.Sym, ctxt.MaxVersion()+1)
152 for i := 0; i <= ctxt.MaxVersion(); i++ {
153 if i >= sym.SymVerABICount && i < sym.SymVerStatic { // these versions are not used currently
156 ctxt.mkArchSymVec(".TOC.", i, ctxt.DotTOC)
160 ctxt.mkArchSym(".rel", 0, &ctxt.Rel)
161 ctxt.mkArchSym(".rela", 0, &ctxt.Rela)
162 ctxt.mkArchSym(".rel.plt", 0, &ctxt.RelPLT)
163 ctxt.mkArchSym(".rela.plt", 0, &ctxt.RelaPLT)
166 ctxt.mkArchSym(".linkedit.got", 0, &ctxt.LinkEditGOT)
167 ctxt.mkArchSym(".linkedit.plt", 0, &ctxt.LinkEditPLT)
178 // Threshold of total text size, used for trampoline insertion. If the total
179 // text size is smaller than TrampLimit, we won't need to insert trampolines.
180 // It is pretty close to the offset range of a direct CALL machine instruction.
181 // We leave some room for extra stuff like PLT stubs.
184 // Empty spaces between codeblocks will be padded with this value.
185 // For example an architecture might want to pad with a trap instruction to
186 // catch wayward programs. Architectures that do not define a padding value
187 // are padded with zeros.
194 Adddynrel func(*Target, *loader.Loader, *ArchSyms, loader.Sym, loader.Reloc, int) bool
196 // Archreloc is an arch-specific hook that assists in relocation processing
197 // (invoked by 'relocsym'); it handles target-specific relocation tasks.
198 // Here "rel" is the current relocation being examined, "sym" is the symbol
199 // containing the chunk of data to which the relocation applies, and "off"
200 // is the contents of the to-be-relocated data item (from sym.P). Return
201 // value is the appropriately relocated value (to be written back to the
202 // same spot in sym.P), number of external _host_ relocations needed (i.e.
203 // ELF/Mach-O/etc. relocations, not Go relocations, this must match ELF.Reloc1,
204 // etc.), and a boolean indicating success/failure (a failing value indicates
206 Archreloc func(*Target, *loader.Loader, *ArchSyms, loader.Reloc, loader.Sym,
207 int64) (relocatedOffset int64, nExtReloc int, ok bool)
208 // Archrelocvariant is a second arch-specific hook used for
209 // relocation processing; it handles relocations where r.Type is
210 // insufficient to describe the relocation (r.Variant !=
211 // sym.RV_NONE). Here "rel" is the relocation being applied, "sym"
212 // is the symbol containing the chunk of data to which the
213 // relocation applies, and "off" is the contents of the
214 // to-be-relocated data item (from sym.P). Return is an updated
216 Archrelocvariant func(target *Target, ldr *loader.Loader, rel loader.Reloc,
217 rv sym.RelocVariant, sym loader.Sym, offset int64, data []byte) (relocatedOffset int64)
219 // Generate a trampoline for a call from s to rs if necessary. ri is
220 // index of the relocation.
221 Trampoline func(ctxt *Link, ldr *loader.Loader, ri int, rs, s loader.Sym)
223 // Assembling the binary breaks into two phases, writing the code/data/
224 // dwarf information (which is rather generic), and some more architecture
225 // specific work like setting up the elf headers/dynamic relocations, etc.
226 // The phases are called "Asmb" and "Asmb2". Asmb2 needs to be defined for
227 // every architecture, but only if architecture has an Asmb function will
228 // it be used for assembly. Otherwise a generic assembly Asmb function is
230 Asmb func(*Link, *loader.Loader)
231 Asmb2 func(*Link, *loader.Loader)
233 // Extreloc is an arch-specific hook that converts a Go relocation to an
234 // external relocation. Return the external relocation and whether it is
236 Extreloc func(*Target, *loader.Loader, loader.Reloc, loader.Sym) (loader.ExtReloc, bool)
238 Gentext func(*Link, *loader.Loader) // Generate text before addressing has been performed.
239 Machoreloc1 func(*sys.Arch, *OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool
240 MachorelocSize uint32 // size of an Mach-O relocation record, must match Machoreloc1.
241 PEreloc1 func(*sys.Arch, *OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool
242 Xcoffreloc1 func(*sys.Arch, *OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool
244 // Generate additional symbols for the native symbol table just prior to
246 GenSymsLate func(*Link, *loader.Loader)
248 // TLSIEtoLE converts a TLS Initial Executable relocation to
249 // a TLS Local Executable relocation.
251 // This is possible when a TLS IE relocation refers to a local
252 // symbol in an executable, which is typical when internally
253 // linking PIE binaries.
254 TLSIEtoLE func(P []byte, off, size int)
256 // optional override for assignAddress
257 AssignAddress func(ldr *loader.Loader, sect *sym.Section, n int, s loader.Sym, va uint64, isTramp bool) (*sym.Section, int, uint64)
259 // ELF specific information.
272 MINFUNC = 16 // minimum size for a function
275 // Symbol version of ABIInternal symbols. It is sym.SymVerABIInternal if ABI wrappers
276 // are used, 0 otherwise.
277 var abiInternalVer = sym.SymVerABIInternal
279 // DynlinkingGo reports whether we are producing Go code that can live
280 // in separate shared libraries linked together at runtime.
281 func (ctxt *Link) DynlinkingGo() bool {
283 panic("DynlinkingGo called before all symbols loaded")
285 return ctxt.BuildMode == BuildModeShared || ctxt.linkShared || ctxt.BuildMode == BuildModePlugin || ctxt.canUsePlugins
288 // CanUsePlugins reports whether a plugins can be used
289 func (ctxt *Link) CanUsePlugins() bool {
291 panic("CanUsePlugins called before all symbols loaded")
293 return ctxt.canUsePlugins
296 // NeedCodeSign reports whether we need to code-sign the output binary.
297 func (ctxt *Link) NeedCodeSign() bool {
298 return ctxt.IsDarwin() && ctxt.IsARM64()
310 debug_s bool // backup old value of debug['s']
314 liveness int64 // size of liveness data (funcdata), printed if -v
316 // See -strictdups command line flag.
317 checkStrictDups int // 0=off 1=warning 2=error
318 strictDupMsgCount int
323 Segrodata sym.Segment
324 Segrelrodata sym.Segment
328 Segments = []*sym.Segment{&Segtext, &Segrodata, &Segrelrodata, &Segdata, &Segdwarf}
331 const pkgdef = "__.PKGDEF"
334 // externalobj is set to true if we see an object compiled by
335 // the host compiler that is not from a package that is known
336 // to support internal linking mode.
339 // dynimportfail is a list of packages for which generating
340 // the dynimport file, _cgo_import.go, failed. If there are
341 // any of these objects, we must link externally. Issue 52863.
342 dynimportfail []string
344 // unknownObjFormat is set to true if we see an object whose
345 // format we don't recognize.
346 unknownObjFormat = false
351 func Lflag(ctxt *Link, arg string) {
352 ctxt.Libdir = append(ctxt.Libdir, arg)
356 * Unix doesn't like it when we write to a running (or, sometimes,
357 * recently run) binary, so remove the output file before writing it.
358 * On Windows 7, remove() can force a subsequent create() to fail.
359 * S_ISREG() does not exist on Plan 9.
361 func mayberemoveoutfile() {
362 if fi, err := os.Lstat(*flagOutfile); err == nil && !fi.Mode().IsRegular() {
365 os.Remove(*flagOutfile)
368 func libinit(ctxt *Link) {
369 Funcalign = thearch.Funcalign
371 // add goroot to the end of the libdir list.
375 if *flagInstallSuffix != "" {
377 suffix = *flagInstallSuffix
378 } else if *flagRace {
381 } else if *flagMsan {
384 } else if *flagAsan {
389 if buildcfg.GOROOT != "" {
390 Lflag(ctxt, filepath.Join(buildcfg.GOROOT, "pkg", fmt.Sprintf("%s_%s%s%s", buildcfg.GOOS, buildcfg.GOARCH, suffixsep, suffix)))
395 if err := ctxt.Out.Open(*flagOutfile); err != nil {
396 Exitf("cannot create %s: %v", *flagOutfile, err)
399 if *flagEntrySymbol == "" {
400 switch ctxt.BuildMode {
401 case BuildModeCShared, BuildModeCArchive:
402 *flagEntrySymbol = fmt.Sprintf("_rt0_%s_%s_lib", buildcfg.GOARCH, buildcfg.GOOS)
403 case BuildModeExe, BuildModePIE:
404 *flagEntrySymbol = fmt.Sprintf("_rt0_%s_%s", buildcfg.GOARCH, buildcfg.GOOS)
405 case BuildModeShared, BuildModePlugin:
406 // No *flagEntrySymbol for -buildmode=shared and plugin
408 Errorf(nil, "unknown *flagEntrySymbol for buildmode %v", ctxt.BuildMode)
413 func exitIfErrors() {
414 if nerrors != 0 || checkStrictDups > 1 && strictDupMsgCount > 0 {
426 func loadinternal(ctxt *Link, name string) *sym.Library {
427 zerofp := goobj.FingerprintType{}
428 if ctxt.linkShared && ctxt.PackageShlib != nil {
429 if shlib := ctxt.PackageShlib[name]; shlib != "" {
430 return addlibpath(ctxt, "internal", "internal", "", name, shlib, zerofp)
433 if ctxt.PackageFile != nil {
434 if pname := ctxt.PackageFile[name]; pname != "" {
435 return addlibpath(ctxt, "internal", "internal", pname, name, "", zerofp)
437 ctxt.Logf("loadinternal: cannot find %s\n", name)
441 for _, libdir := range ctxt.Libdir {
443 shlibname := filepath.Join(libdir, name+".shlibname")
444 if ctxt.Debugvlog != 0 {
445 ctxt.Logf("searching for %s.a in %s\n", name, shlibname)
447 if _, err := os.Stat(shlibname); err == nil {
448 return addlibpath(ctxt, "internal", "internal", "", name, shlibname, zerofp)
451 pname := filepath.Join(libdir, name+".a")
452 if ctxt.Debugvlog != 0 {
453 ctxt.Logf("searching for %s.a in %s\n", name, pname)
455 if _, err := os.Stat(pname); err == nil {
456 return addlibpath(ctxt, "internal", "internal", pname, name, "", zerofp)
460 if name == "runtime" {
461 Exitf("error: unable to find runtime.a")
463 ctxt.Logf("warning: unable to find %s.a\n", name)
467 // extld returns the current external linker.
468 func (ctxt *Link) extld() []string {
469 if len(flagExtld) == 0 {
470 // Return the default external linker for the platform.
471 // This only matters when link tool is called directly without explicit -extld,
472 // go tool already passes the correct linker in other cases.
473 switch buildcfg.GOOS {
474 case "darwin", "freebsd", "openbsd":
475 flagExtld = []string{"clang"}
477 flagExtld = []string{"gcc"}
483 // findLibPathCmd uses cmd command to find gcc library libname.
484 // It returns library full path if found, or "none" if not found.
485 func (ctxt *Link) findLibPathCmd(cmd, libname string) string {
486 extld := ctxt.extld()
487 name, args := extld[0], extld[1:]
488 args = append(args, hostlinkArchArgs(ctxt.Arch)...)
489 args = append(args, cmd)
490 if ctxt.Debugvlog != 0 {
491 ctxt.Logf("%s %v\n", extld, args)
493 out, err := exec.Command(name, args...).Output()
495 if ctxt.Debugvlog != 0 {
496 ctxt.Logf("not using a %s file because compiler failed\n%v\n%s\n", libname, err, out)
500 return strings.TrimSpace(string(out))
503 // findLibPath searches for library libname.
504 // It returns library full path if found, or "none" if not found.
505 func (ctxt *Link) findLibPath(libname string) string {
506 return ctxt.findLibPathCmd("--print-file-name="+libname, libname)
509 func (ctxt *Link) loadlib() {
511 switch *FlagStrictDups {
515 flags |= loader.FlagStrictDups
517 log.Fatalf("invalid -strictdups flag value %d", *FlagStrictDups)
519 elfsetstring1 := func(str string, off int) { elfsetstring(ctxt, 0, str, off) }
520 ctxt.loader = loader.NewLoader(flags, elfsetstring1, &ctxt.ErrorReporter.ErrorReporter)
521 ctxt.ErrorReporter.SymName = func(s loader.Sym) string {
522 return ctxt.loader.SymName(s)
525 // ctxt.Library grows during the loop, so not a range loop.
527 for ; i < len(ctxt.Library); i++ {
528 lib := ctxt.Library[i]
530 if ctxt.Debugvlog > 1 {
531 ctxt.Logf("autolib: %s (from %s)\n", lib.File, lib.Objref)
533 loadobjfile(ctxt, lib)
537 // load internal packages, if not already
539 loadinternal(ctxt, "runtime/race")
542 loadinternal(ctxt, "runtime/msan")
545 loadinternal(ctxt, "runtime/asan")
547 loadinternal(ctxt, "runtime")
548 for ; i < len(ctxt.Library); i++ {
549 lib := ctxt.Library[i]
551 loadobjfile(ctxt, lib)
554 // At this point, the Go objects are "preloaded". Not all the symbols are
555 // added to the symbol table (only defined package symbols are). Looking
556 // up symbol by name may not get expected result.
558 iscgo = ctxt.LibraryByPkg["runtime/cgo"] != nil
560 // Plugins a require cgo support to function. Similarly, plugins may require additional
561 // internal linker support on some platforms which may not be implemented.
562 ctxt.canUsePlugins = ctxt.LibraryByPkg["plugin"] != nil && iscgo
564 // We now have enough information to determine the link mode.
565 determineLinkMode(ctxt)
567 if ctxt.LinkMode == LinkExternal && !iscgo && !(buildcfg.GOOS == "darwin" && ctxt.BuildMode != BuildModePlugin && ctxt.Arch.Family == sys.AMD64) {
568 // This indicates a user requested -linkmode=external.
569 // The startup code uses an import of runtime/cgo to decide
570 // whether to initialize the TLS. So give it one. This could
571 // be handled differently but it's an unusual case.
572 if lib := loadinternal(ctxt, "runtime/cgo"); lib != nil && lib.Shlib == "" {
573 if ctxt.BuildMode == BuildModeShared || ctxt.linkShared {
574 Exitf("cannot implicitly include runtime/cgo in a shared library")
576 for ; i < len(ctxt.Library); i++ {
577 lib := ctxt.Library[i]
579 loadobjfile(ctxt, lib)
585 // Add non-package symbols and references of externally defined symbols.
586 ctxt.loader.LoadSyms(ctxt.Arch)
588 // Load symbols from shared libraries, after all Go object symbols are loaded.
589 for _, lib := range ctxt.Library {
591 if ctxt.Debugvlog > 1 {
592 ctxt.Logf("autolib: %s (from %s)\n", lib.Shlib, lib.Objref)
594 ldshlibsyms(ctxt, lib.Shlib)
598 // Process cgo directives (has to be done before host object loading).
599 ctxt.loadcgodirectives()
601 // Conditionally load host objects, or setup for external linking.
605 if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
606 // If we have any undefined symbols in external
607 // objects, try to read them from the libgcc file.
609 undefs, froms := ctxt.loader.UndefinedRelocTargets(1)
612 if ctxt.Debugvlog > 1 {
613 ctxt.Logf("loadlib: first unresolved is %s [%d] from %s [%d]\n",
614 ctxt.loader.SymName(undefs[0]), undefs[0],
615 ctxt.loader.SymName(froms[0]), froms[0])
619 if *flagLibGCC == "" {
620 *flagLibGCC = ctxt.findLibPathCmd("--print-libgcc-file-name", "libgcc")
622 if runtime.GOOS == "openbsd" && *flagLibGCC == "libgcc.a" {
623 // On OpenBSD `clang --print-libgcc-file-name` returns "libgcc.a".
624 // In this case we fail to load libgcc.a and can encounter link
625 // errors - see if we can find libcompiler_rt.a instead.
626 *flagLibGCC = ctxt.findLibPathCmd("--print-file-name=libcompiler_rt.a", "libcompiler_rt")
628 if ctxt.HeadType == objabi.Hwindows {
629 loadWindowsHostArchives(ctxt)
631 if *flagLibGCC != "none" {
632 hostArchive(ctxt, *flagLibGCC)
634 // For glibc systems, the linker setup used by GCC
637 // GROUP ( /lib/x86_64-linux-gnu/libc.so.6
638 // /usr/lib/x86_64-linux-gnu/libc_nonshared.a
639 // AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )
641 // where libc_nonshared.a contains a small set of
642 // symbols including "__stack_chk_fail_local" and a
643 // few others. Thus if we are doing internal linking
644 // and "__stack_chk_fail_local" is unresolved (most
645 // likely due to the use of -fstack-protector), try
646 // loading libc_nonshared.a to resolve it.
648 // On Alpine Linux (musl-based), the library providing
649 // this symbol is called libssp_nonshared.a.
650 isunresolved := symbolsAreUnresolved(ctxt, []string{"__stack_chk_fail_local"})
652 if p := ctxt.findLibPath("libc_nonshared.a"); p != "none" {
655 if p := ctxt.findLibPath("libssp_nonshared.a"); p != "none" {
662 // We've loaded all the code now.
665 strictDupMsgCount = ctxt.loader.NStrictDupMsgs()
668 // loadWindowsHostArchives loads in host archives and objects when
669 // doing internal linking on windows. Older toolchains seem to require
670 // just a single pass through the various archives, but some modern
671 // toolchains when linking a C program with mingw pass library paths
672 // multiple times to the linker, e.g. "... -lmingwex -lmingw32 ...
673 // -lmingwex -lmingw32 ...". To accommodate this behavior, we make two
674 // passes over the host archives below.
675 func loadWindowsHostArchives(ctxt *Link) {
677 for i := 0; any && i < 2; i++ {
678 // Link crt2.o (if present) to resolve "atexit" when
679 // using LLVM-based compilers.
680 isunresolved := symbolsAreUnresolved(ctxt, []string{"atexit"})
682 if p := ctxt.findLibPath("crt2.o"); p != "none" {
683 hostObject(ctxt, "crt2", p)
687 if p := ctxt.findLibPath("libsynchronization.a"); p != "none" {
691 if p := ctxt.findLibPath("libmingwex.a"); p != "none" {
694 if p := ctxt.findLibPath("libmingw32.a"); p != "none" {
697 // Link libmsvcrt.a to resolve '__acrt_iob_func' symbol
698 // (see https://golang.org/issue/23649 for details).
699 if p := ctxt.findLibPath("libmsvcrt.a"); p != "none" {
703 undefs, froms := ctxt.loader.UndefinedRelocTargets(1)
706 if ctxt.Debugvlog > 1 {
707 ctxt.Logf("loadWindowsHostArchives: remaining unresolved is %s [%d] from %s [%d]\n",
708 ctxt.loader.SymName(undefs[0]), undefs[0],
709 ctxt.loader.SymName(froms[0]), froms[0])
713 // If needed, create the __CTOR_LIST__ and __DTOR_LIST__
714 // symbols (referenced by some of the mingw support library
715 // routines). Creation of these symbols is normally done by the
716 // linker if not already present.
717 want := []string{"__CTOR_LIST__", "__DTOR_LIST__"}
718 isunresolved := symbolsAreUnresolved(ctxt, want)
719 for k, w := range want {
721 sb := ctxt.loader.CreateSymForUpdate(w, 0)
722 sb.SetType(sym.SDATA)
723 sb.AddUint64(ctxt.Arch, 0)
724 sb.SetReachable(true)
725 ctxt.loader.SetAttrSpecial(sb.Sym(), true)
729 // Fix up references to DLL import symbols now that we're done
730 // pulling in new objects.
731 if err := loadpe.PostProcessImports(); err != nil {
732 Errorf(nil, "%v", err)
735 // TODO: maybe do something similar to peimporteddlls to collect
736 // all lib names and try link them all to final exe just like
737 // libmingwex.a and libmingw32.a:
740 #cgo windows LDFLAGS: -lmsvcrt -lm
746 // loadcgodirectives reads the previously discovered cgo directives, creating
747 // symbols in preparation for host object loading or use later in the link.
748 func (ctxt *Link) loadcgodirectives() {
750 hostObjSyms := make(map[loader.Sym]struct{})
751 for _, d := range ctxt.cgodata {
752 setCgoAttr(ctxt, d.file, d.pkg, d.directives, hostObjSyms)
756 if ctxt.LinkMode == LinkInternal {
757 // Drop all the cgo_import_static declarations.
758 // Turns out we won't be needing them.
759 for symIdx := range hostObjSyms {
760 if l.SymType(symIdx) == sym.SHOSTOBJ {
761 // If a symbol was marked both
762 // cgo_import_static and cgo_import_dynamic,
763 // then we want to make it cgo_import_dynamic
765 su := l.MakeSymbolUpdater(symIdx)
766 if l.SymExtname(symIdx) != "" && l.SymDynimplib(symIdx) != "" && !(l.AttrCgoExportStatic(symIdx) || l.AttrCgoExportDynamic(symIdx)) {
767 su.SetType(sym.SDYNIMPORT)
776 // Set up flags and special symbols depending on the platform build mode.
777 // This version works with loader.Loader.
778 func (ctxt *Link) linksetup() {
779 switch ctxt.BuildMode {
780 case BuildModeCShared, BuildModePlugin:
781 symIdx := ctxt.loader.LookupOrCreateSym("runtime.islibrary", 0)
782 sb := ctxt.loader.MakeSymbolUpdater(symIdx)
783 sb.SetType(sym.SNOPTRDATA)
785 case BuildModeCArchive:
786 symIdx := ctxt.loader.LookupOrCreateSym("runtime.isarchive", 0)
787 sb := ctxt.loader.MakeSymbolUpdater(symIdx)
788 sb.SetType(sym.SNOPTRDATA)
792 // Recalculate pe parameters now that we have ctxt.LinkMode set.
793 if ctxt.HeadType == objabi.Hwindows {
797 if ctxt.LinkMode == LinkExternal {
798 // When external linking, we are creating an object file. The
799 // absolute address is irrelevant.
803 // If there are no dynamic libraries needed, gcc disables dynamic linking.
804 // Because of this, glibc's dynamic ELF loader occasionally (like in version 2.13)
805 // assumes that a dynamic binary always refers to at least one dynamic library.
806 // Rather than be a source of test cases for glibc, disable dynamic linking
807 // the same way that gcc would.
809 // Exception: on OS X, programs such as Shark only work with dynamic
810 // binaries, so leave it enabled on OS X (Mach-O) binaries.
811 // Also leave it enabled on Solaris which doesn't support
812 // statically linked binaries.
813 if ctxt.BuildMode == BuildModeExe {
814 if havedynamic == 0 && ctxt.HeadType != objabi.Hdarwin && ctxt.HeadType != objabi.Hsolaris {
819 if ctxt.LinkMode == LinkExternal && ctxt.Arch.Family == sys.PPC64 && buildcfg.GOOS != "aix" {
820 toc := ctxt.loader.LookupOrCreateSym(".TOC.", 0)
821 sb := ctxt.loader.MakeSymbolUpdater(toc)
822 sb.SetType(sym.SDYNIMPORT)
825 // The Android Q linker started to complain about underalignment of the our TLS
826 // section. We don't actually use the section on android, so don't
828 if buildcfg.GOOS != "android" {
829 tlsg := ctxt.loader.LookupOrCreateSym("runtime.tlsg", 0)
830 sb := ctxt.loader.MakeSymbolUpdater(tlsg)
832 // runtime.tlsg is used for external linking on platforms that do not define
833 // a variable to hold g in assembly (currently only intel).
835 sb.SetType(sym.STLSBSS)
836 sb.SetSize(int64(ctxt.Arch.PtrSize))
837 } else if sb.Type() != sym.SDYNIMPORT {
838 Errorf(nil, "runtime declared tlsg variable %v", sb.Type())
840 ctxt.loader.SetAttrReachable(tlsg, true)
844 var moduledata loader.Sym
845 var mdsb *loader.SymbolBuilder
846 if ctxt.BuildMode == BuildModePlugin {
847 moduledata = ctxt.loader.LookupOrCreateSym("local.pluginmoduledata", 0)
848 mdsb = ctxt.loader.MakeSymbolUpdater(moduledata)
849 ctxt.loader.SetAttrLocal(moduledata, true)
851 moduledata = ctxt.loader.LookupOrCreateSym("runtime.firstmoduledata", 0)
852 mdsb = ctxt.loader.MakeSymbolUpdater(moduledata)
854 if mdsb.Type() != 0 && mdsb.Type() != sym.SDYNIMPORT {
855 // If the module (toolchain-speak for "executable or shared
856 // library") we are linking contains the runtime package, it
857 // will define the runtime.firstmoduledata symbol and we
858 // truncate it back to 0 bytes so we can define its entire
859 // contents in symtab.go:symtab().
862 // In addition, on ARM, the runtime depends on the linker
863 // recording the value of GOARM.
864 if ctxt.Arch.Family == sys.ARM {
865 goarm := ctxt.loader.LookupOrCreateSym("runtime.goarm", 0)
866 sb := ctxt.loader.MakeSymbolUpdater(goarm)
867 sb.SetType(sym.SDATA)
869 sb.AddUint8(uint8(buildcfg.GOARM))
872 // Set runtime.disableMemoryProfiling bool if
873 // runtime.MemProfile is not retained in the binary after
874 // deadcode (and we're not dynamically linking).
875 memProfile := ctxt.loader.Lookup("runtime.MemProfile", abiInternalVer)
876 if memProfile != 0 && !ctxt.loader.AttrReachable(memProfile) && !ctxt.DynlinkingGo() {
877 memProfSym := ctxt.loader.LookupOrCreateSym("runtime.disableMemoryProfiling", 0)
878 sb := ctxt.loader.MakeSymbolUpdater(memProfSym)
879 sb.SetType(sym.SDATA)
881 sb.AddUint8(1) // true bool
884 // If OTOH the module does not contain the runtime package,
885 // create a local symbol for the moduledata.
886 moduledata = ctxt.loader.LookupOrCreateSym("local.moduledata", 0)
887 mdsb = ctxt.loader.MakeSymbolUpdater(moduledata)
888 ctxt.loader.SetAttrLocal(moduledata, true)
890 // In all cases way we mark the moduledata as noptrdata to hide it from
892 mdsb.SetType(sym.SNOPTRDATA)
893 ctxt.loader.SetAttrReachable(moduledata, true)
894 ctxt.Moduledata = moduledata
896 if ctxt.Arch == sys.Arch386 && ctxt.HeadType != objabi.Hwindows {
897 if (ctxt.BuildMode == BuildModeCArchive && ctxt.IsELF) || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE || ctxt.DynlinkingGo() {
898 got := ctxt.loader.LookupOrCreateSym("_GLOBAL_OFFSET_TABLE_", 0)
899 sb := ctxt.loader.MakeSymbolUpdater(got)
900 sb.SetType(sym.SDYNIMPORT)
901 ctxt.loader.SetAttrReachable(got, true)
905 // DWARF-gen and other phases require that the unit Textp slices
906 // be populated, so that it can walk the functions in each unit.
907 // Call into the loader to do this (requires that we collect the
908 // set of internal libraries first). NB: might be simpler if we
909 // moved isRuntimeDepPkg to cmd/internal and then did the test in
910 // loader.AssignTextSymbolOrder.
911 ctxt.Library = postorder(ctxt.Library)
913 for _, lib := range ctxt.Library {
914 intlibs = append(intlibs, isRuntimeDepPkg(lib.Pkg))
916 ctxt.Textp = ctxt.loader.AssignTextSymbolOrder(ctxt.Library, intlibs, ctxt.Textp)
919 // mangleTypeSym shortens the names of symbols that represent Go types
920 // if they are visible in the symbol table.
922 // As the names of these symbols are derived from the string of
923 // the type, they can run to many kilobytes long. So we shorten
924 // them using a SHA-1 when the name appears in the final binary.
925 // This also removes characters that upset external linkers.
927 // These are the symbols that begin with the prefix 'type.' and
928 // contain run-time type information used by the runtime and reflect
929 // packages. All Go binaries contain these symbols, but only
930 // those programs loaded dynamically in multiple parts need these
931 // symbols to have entries in the symbol table.
932 func (ctxt *Link) mangleTypeSym() {
933 if ctxt.BuildMode != BuildModeShared && !ctxt.linkShared && ctxt.BuildMode != BuildModePlugin && !ctxt.CanUsePlugins() {
938 for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
939 if !ldr.AttrReachable(s) && !ctxt.linkShared {
940 // If -linkshared, the GCProg generation code may need to reach
941 // out to the shared library for the type descriptor's data, even
942 // the type descriptor itself is not actually needed at run time
943 // (therefore not reachable). We still need to mangle its name,
944 // so it is consistent with the one stored in the shared library.
947 name := ldr.SymName(s)
948 newName := typeSymbolMangle(name)
950 ldr.SetSymExtname(s, newName)
952 // When linking against a shared library, the Go object file may
953 // have reference to the original symbol name whereas the shared
954 // library provides a symbol with the mangled name. We need to
955 // copy the payload of mangled to original.
956 // XXX maybe there is a better way to do this.
957 dup := ldr.Lookup(newName, ldr.SymVersion(s))
960 dt := ldr.SymType(dup)
961 if st == sym.Sxxx && dt != sym.Sxxx {
969 // typeSymbolMangle mangles the given symbol name into something shorter.
971 // Keep the type:. prefix, which parts of the linker (like the
972 // DWARF generator) know means the symbol is not decodable.
973 // Leave type:runtime. symbols alone, because other parts of
974 // the linker manipulates them.
975 func typeSymbolMangle(name string) string {
976 if !strings.HasPrefix(name, "type:") {
979 if strings.HasPrefix(name, "type:runtime.") {
982 if len(name) <= 14 && !strings.Contains(name, "@") { // Issue 19529
985 hash := notsha256.Sum256([]byte(name))
990 return prefix + base64.StdEncoding.EncodeToString(hash[:6])
994 * look for the next file in an archive.
995 * adapted from libmach.
997 func nextar(bp *bio.Reader, off int64, a *ArHdr) int64 {
1002 var buf [SAR_HDR]byte
1003 if n, err := io.ReadFull(bp, buf[:]); err != nil {
1004 if n == 0 && err != io.EOF {
1010 a.name = artrim(buf[0:16])
1011 a.date = artrim(buf[16:28])
1012 a.uid = artrim(buf[28:34])
1013 a.gid = artrim(buf[34:40])
1014 a.mode = artrim(buf[40:48])
1015 a.size = artrim(buf[48:58])
1016 a.fmag = artrim(buf[58:60])
1018 arsize := atolwhex(a.size)
1022 return arsize + SAR_HDR
1025 func loadobjfile(ctxt *Link, lib *sym.Library) {
1026 pkg := objabi.PathToPrefix(lib.Pkg)
1028 if ctxt.Debugvlog > 1 {
1029 ctxt.Logf("ldobj: %s (%s)\n", lib.File, pkg)
1031 f, err := bio.Open(lib.File)
1033 Exitf("cannot open file %s: %v", lib.File, err)
1037 if pkg == "main" && !lib.Main {
1038 Exitf("%s: not package main", lib.File)
1042 for i := 0; i < len(ARMAG); i++ {
1043 if c, err := f.ReadByte(); err == nil && c == ARMAG[i] {
1047 /* load it as a regular file */
1048 l := f.MustSeek(0, 2)
1050 ldobj(ctxt, f, lib, l, lib.File, lib.File)
1055 * load all the object files from the archive now.
1056 * this gives us sequential file access and keeps us
1057 * from needing to come back later to pick up more
1058 * objects. it breaks the usual C archive model, but
1059 * this is Go, not C. the common case in Go is that
1060 * we need to load all the objects, and then we throw away
1061 * the individual symbols that are unused.
1063 * loading every object will also make it possible to
1064 * load foreign objects not referenced by __.PKGDEF.
1069 l := nextar(f, off, &arhdr)
1074 Exitf("%s: malformed archive", lib.File)
1078 // __.PKGDEF isn't a real Go object file, and it's
1079 // absent in -linkobj builds anyway. Skipping it
1080 // ensures consistency between -linkobj and normal
1082 if arhdr.name == pkgdef {
1086 if arhdr.name == "dynimportfail" {
1087 dynimportfail = append(dynimportfail, lib.Pkg)
1090 // Skip other special (non-object-file) sections that
1091 // build tools may have added. Such sections must have
1092 // short names so that the suffix is not truncated.
1093 if len(arhdr.name) < 16 {
1094 if ext := filepath.Ext(arhdr.name); ext != ".o" && ext != ".syso" {
1099 pname := fmt.Sprintf("%s(%s)", lib.File, arhdr.name)
1100 l = atolwhex(arhdr.size)
1101 ldobj(ctxt, f, lib, l, pname, lib.File)
1105 type Hostobj struct {
1106 ld func(*Link, *bio.Reader, string, int64, string)
1114 var hostobj []Hostobj
1116 // These packages can use internal linking mode.
1117 // Others trigger external mode.
1118 var internalpkg = []string{
1119 "crypto/internal/boring",
1120 "crypto/internal/boring/syso",
1126 "runtime/race/internal/amd64v1",
1127 "runtime/race/internal/amd64v3",
1132 func ldhostobj(ld func(*Link, *bio.Reader, string, int64, string), headType objabi.HeadType, f *bio.Reader, pkg string, length int64, pn string, file string) *Hostobj {
1134 for _, intpkg := range internalpkg {
1141 // DragonFly declares errno with __thread, which results in a symbol
1142 // type of R_386_TLS_GD or R_X86_64_TLSGD. The Go linker does not
1143 // currently know how to handle TLS relocations, hence we have to
1144 // force external linking for any libraries that link in code that
1145 // uses errno. This can be removed if the Go linker ever supports
1146 // these relocation types.
1147 if headType == objabi.Hdragonfly {
1148 if pkg == "net" || pkg == "os/user" {
1157 hostobj = append(hostobj, Hostobj{})
1158 h := &hostobj[len(hostobj)-1]
1168 func hostobjs(ctxt *Link) {
1169 if ctxt.LinkMode != LinkInternal {
1174 for i := 0; i < len(hostobj); i++ {
1176 f, err := bio.Open(h.file)
1178 Exitf("cannot reopen %s: %v", h.pn, err)
1180 f.MustSeek(h.off, 0)
1182 Errorf(nil, "%s: unrecognized object file format", h.pn)
1185 h.ld(ctxt, f, h.pkg, h.length, h.pn)
1186 if *flagCaptureHostObjs != "" {
1193 func hostlinksetup(ctxt *Link) {
1194 if ctxt.LinkMode != LinkExternal {
1198 // For external link, record that we need to tell the external linker -s,
1199 // and turn off -s internally: the external linker needs the symbol
1200 // information for its final link.
1204 // create temporary directory and arrange cleanup
1205 if *flagTmpdir == "" {
1206 dir, err := os.MkdirTemp("", "go-link-")
1213 os.RemoveAll(*flagTmpdir)
1217 // change our output to temporary object file
1218 if err := ctxt.Out.Close(); err != nil {
1219 Exitf("error closing output file")
1221 mayberemoveoutfile()
1223 p := filepath.Join(*flagTmpdir, "go.o")
1224 if err := ctxt.Out.Open(p); err != nil {
1225 Exitf("cannot create %s: %v", p, err)
1229 // hostobjCopy creates a copy of the object files in hostobj in a
1230 // temporary directory.
1231 func (ctxt *Link) hostobjCopy() (paths []string) {
1232 var wg sync.WaitGroup
1233 sema := make(chan struct{}, runtime.NumCPU()) // limit open file descriptors
1234 for i, h := range hostobj {
1236 dst := filepath.Join(*flagTmpdir, fmt.Sprintf("%06d.o", i))
1237 paths = append(paths, dst)
1238 if ctxt.Debugvlog != 0 {
1239 ctxt.Logf("host obj copy: %s from pkg %s -> %s\n", h.pn, h.pkg, dst)
1249 f, err := os.Open(h.file)
1251 Exitf("cannot reopen %s: %v", h.pn, err)
1254 if _, err := f.Seek(h.off, 0); err != nil {
1255 Exitf("cannot seek %s: %v", h.pn, err)
1258 w, err := os.Create(dst)
1260 Exitf("cannot create %s: %v", dst, err)
1262 if _, err := io.CopyN(w, f, h.length); err != nil {
1263 Exitf("cannot write %s: %v", dst, err)
1265 if err := w.Close(); err != nil {
1266 Exitf("cannot close %s: %v", dst, err)
1274 // writeGDBLinkerScript creates gcc linker script file in temp
1275 // directory. writeGDBLinkerScript returns created file path.
1276 // The script is used to work around gcc bug
1277 // (see https://golang.org/issue/20183 for details).
1278 func writeGDBLinkerScript() string {
1279 name := "fix_debug_gdb_scripts.ld"
1280 path := filepath.Join(*flagTmpdir, name)
1283 .debug_gdb_scripts BLOCK(__section_alignment__) (NOLOAD) :
1285 *(.debug_gdb_scripts)
1288 INSERT AFTER .debug_types;
1290 err := os.WriteFile(path, []byte(src), 0666)
1292 Errorf(nil, "WriteFile %s failed: %v", name, err)
1297 // archive builds a .a archive from the hostobj object files.
1298 func (ctxt *Link) archive() {
1299 if ctxt.BuildMode != BuildModeCArchive {
1305 if *flagExtar == "" {
1309 mayberemoveoutfile()
1311 // Force the buffer to flush here so that external
1312 // tools will see a complete file.
1313 if err := ctxt.Out.Close(); err != nil {
1314 Exitf("error closing %v", *flagOutfile)
1317 argv := []string{*flagExtar, "-q", "-c", "-s"}
1318 if ctxt.HeadType == objabi.Haix {
1319 argv = append(argv, "-X64")
1321 argv = append(argv, *flagOutfile)
1322 argv = append(argv, filepath.Join(*flagTmpdir, "go.o"))
1323 argv = append(argv, ctxt.hostobjCopy()...)
1325 if ctxt.Debugvlog != 0 {
1326 ctxt.Logf("archive: %s\n", strings.Join(argv, " "))
1329 // If supported, use syscall.Exec() to invoke the archive command,
1330 // which should be the final remaining step needed for the link.
1331 // This will reduce peak RSS for the link (and speed up linking of
1332 // large applications), since when the archive command runs we
1333 // won't be holding onto all of the linker's live memory.
1334 if syscallExecSupported && !ownTmpDir {
1336 ctxt.execArchive(argv)
1337 panic("should not get here")
1340 // Otherwise invoke 'ar' in the usual way (fork + exec).
1341 if out, err := exec.Command(argv[0], argv[1:]...).CombinedOutput(); err != nil {
1342 Exitf("running %s failed: %v\n%s", argv[0], err, out)
1346 func (ctxt *Link) hostlink() {
1347 if ctxt.LinkMode != LinkExternal || nerrors > 0 {
1350 if ctxt.BuildMode == BuildModeCArchive {
1355 argv = append(argv, ctxt.extld()...)
1356 argv = append(argv, hostlinkArchArgs(ctxt.Arch)...)
1358 if *FlagS || debug_s {
1359 if ctxt.HeadType == objabi.Hdarwin {
1360 // Recent versions of macOS print
1361 // ld: warning: option -s is obsolete and being ignored
1362 // so do not pass any arguments.
1364 argv = append(argv, "-s")
1368 // On darwin, whether to combine DWARF into executable.
1369 // Only macOS supports unmapped segments such as our __DWARF segment.
1370 combineDwarf := ctxt.IsDarwin() && !*FlagS && !*FlagW && !debug_s && machoPlatform == PLATFORM_MACOS
1372 switch ctxt.HeadType {
1373 case objabi.Hdarwin:
1375 // Leave room for DWARF combining.
1376 // -headerpad is incompatible with -fembed-bitcode.
1377 argv = append(argv, "-Wl,-headerpad,1144")
1379 if ctxt.DynlinkingGo() && buildcfg.GOOS != "ios" {
1380 // -flat_namespace is deprecated on iOS.
1381 // It is useful for supporting plugins. We don't support plugins on iOS.
1382 // -flat_namespace may cause the dynamic linker to hang at forkExec when
1383 // resolving a lazy binding. See issue 38824.
1384 // Force eager resolution to work around.
1385 argv = append(argv, "-Wl,-flat_namespace", "-Wl,-bind_at_load")
1388 argv = append(argv, "-Wl,-S") // suppress STAB (symbolic debugging) symbols
1390 case objabi.Hopenbsd:
1391 argv = append(argv, "-Wl,-nopie")
1392 argv = append(argv, "-pthread")
1393 case objabi.Hwindows:
1395 argv = append(argv, "-mwindows")
1397 argv = append(argv, "-mconsole")
1399 // Mark as having awareness of terminal services, to avoid
1400 // ancient compatibility hacks.
1401 argv = append(argv, "-Wl,--tsaware")
1404 argv = append(argv, "-Wl,--nxcompat")
1406 argv = append(argv, fmt.Sprintf("-Wl,--major-os-version=%d", PeMinimumTargetMajorVersion))
1407 argv = append(argv, fmt.Sprintf("-Wl,--minor-os-version=%d", PeMinimumTargetMinorVersion))
1408 argv = append(argv, fmt.Sprintf("-Wl,--major-subsystem-version=%d", PeMinimumTargetMajorVersion))
1409 argv = append(argv, fmt.Sprintf("-Wl,--minor-subsystem-version=%d", PeMinimumTargetMinorVersion))
1411 argv = append(argv, "-pthread")
1412 // prevent ld to reorder .text functions to keep the same
1413 // first/last functions for moduledata.
1414 argv = append(argv, "-Wl,-bnoobjreorder")
1415 // mcmodel=large is needed for every gcc generated files, but
1416 // ld still need -bbigtoc in order to allow larger TOC.
1417 argv = append(argv, "-mcmodel=large")
1418 argv = append(argv, "-Wl,-bbigtoc")
1421 // On PPC64, verify the external toolchain supports Power10. This is needed when
1422 // PC relative relocations might be generated by Go. Only targets compiling ELF
1423 // binaries might generate these relocations.
1424 if ctxt.IsPPC64() && ctxt.IsElf() && buildcfg.GOPPC64 >= 10 {
1425 if !linkerFlagSupported(ctxt.Arch, argv[0], "", "-mcpu=power10") {
1426 Exitf("The external toolchain does not support -mcpu=power10. " +
1427 " This is required to externally link GOPPC64 >= power10")
1431 // Enable/disable ASLR on Windows.
1432 addASLRargs := func(argv []string, val bool) []string {
1433 // Old/ancient versions of GCC support "--dynamicbase" and
1434 // "--high-entropy-va" but don't enable it by default. In
1435 // addition, they don't accept "--disable-dynamicbase" or
1436 // "--no-dynamicbase", so the only way to disable ASLR is to
1437 // not pass any flags at all.
1439 // More modern versions of GCC (and also clang) enable ASLR
1440 // by default. With these compilers, however you can turn it
1441 // off if you want using "--disable-dynamicbase" or
1442 // "--no-dynamicbase".
1444 // The strategy below is to try using "--disable-dynamicbase";
1445 // if this succeeds, then assume we're working with more
1446 // modern compilers and act accordingly. If it fails, assume
1447 // an ancient compiler with ancient defaults.
1450 dbon := "--dynamicbase"
1451 heon := "--high-entropy-va"
1452 dboff := "--disable-dynamicbase"
1453 heoff := "--disable-high-entropy-va"
1458 // Test to see whether "--disable-dynamicbase" works.
1459 newer := linkerFlagSupported(ctxt.Arch, argv[0], "", "-Wl,"+dboff)
1461 // Newer compiler, which supports both on/off options.
1465 // older toolchain: we have to say nothing in order to
1466 // get a no-ASLR binary.
1472 argv = append(argv, "-Wl,"+dbopt)
1474 // enable high-entropy ASLR on 64-bit.
1475 if ctxt.Arch.PtrSize >= 8 && heopt != "" {
1476 argv = append(argv, "-Wl,"+heopt)
1481 switch ctxt.BuildMode {
1483 if ctxt.HeadType == objabi.Hdarwin {
1484 if machoPlatform == PLATFORM_MACOS && ctxt.IsAMD64() {
1485 argv = append(argv, "-Wl,-no_pie")
1488 if *flagRace && ctxt.HeadType == objabi.Hwindows {
1489 // Current windows/amd64 race detector tsan support
1490 // library can't handle PIE mode (see #53539 for more details).
1491 // For now, explicitly disable PIE (since some compilers
1492 // default to it) if -race is in effect.
1493 argv = addASLRargs(argv, false)
1496 switch ctxt.HeadType {
1497 case objabi.Hdarwin, objabi.Haix:
1498 case objabi.Hwindows:
1499 if *flagAslr && *flagRace {
1500 // Current windows/amd64 race detector tsan support
1501 // library can't handle PIE mode (see #53539 for more details).
1502 // Disable alsr if -race in effect.
1505 argv = addASLRargs(argv, *flagAslr)
1508 if ctxt.UseRelro() {
1509 argv = append(argv, "-Wl,-z,relro")
1511 argv = append(argv, "-pie")
1513 case BuildModeCShared:
1514 if ctxt.HeadType == objabi.Hdarwin {
1515 argv = append(argv, "-dynamiclib")
1517 if ctxt.UseRelro() {
1518 argv = append(argv, "-Wl,-z,relro")
1520 argv = append(argv, "-shared")
1521 if ctxt.HeadType == objabi.Hwindows {
1522 argv = addASLRargs(argv, *flagAslr)
1524 // Pass -z nodelete to mark the shared library as
1525 // non-closeable: a dlclose will do nothing.
1526 argv = append(argv, "-Wl,-z,nodelete")
1527 // Only pass Bsymbolic on non-Windows.
1528 argv = append(argv, "-Wl,-Bsymbolic")
1531 case BuildModeShared:
1532 if ctxt.UseRelro() {
1533 argv = append(argv, "-Wl,-z,relro")
1535 argv = append(argv, "-shared")
1536 case BuildModePlugin:
1537 if ctxt.HeadType == objabi.Hdarwin {
1538 argv = append(argv, "-dynamiclib")
1540 if ctxt.UseRelro() {
1541 argv = append(argv, "-Wl,-z,relro")
1543 argv = append(argv, "-shared")
1547 var altLinker string
1548 if ctxt.IsELF && ctxt.DynlinkingGo() {
1549 // We force all symbol resolution to be done at program startup
1550 // because lazy PLT resolution can use large amounts of stack at
1551 // times we cannot allow it to do so.
1552 argv = append(argv, "-Wl,-z,now")
1554 // Do not let the host linker generate COPY relocations. These
1555 // can move symbols out of sections that rely on stable offsets
1556 // from the beginning of the section (like sym.STYPE).
1557 argv = append(argv, "-Wl,-z,nocopyreloc")
1559 if buildcfg.GOOS == "android" {
1560 // Use lld to avoid errors from default linker (issue #38838)
1564 if ctxt.Arch.InFamily(sys.ARM64) && buildcfg.GOOS == "linux" {
1565 // On ARM64, the GNU linker will fail with
1566 // -znocopyreloc if it thinks a COPY relocation is
1567 // required. Switch to gold.
1568 // https://sourceware.org/bugzilla/show_bug.cgi?id=19962
1569 // https://go.dev/issue/22040
1572 // If gold is not installed, gcc will silently switch
1573 // back to ld.bfd. So we parse the version information
1574 // and provide a useful error if gold is missing.
1575 name, args := flagExtld[0], flagExtld[1:]
1576 args = append(args, "-fuse-ld=gold", "-Wl,--version")
1577 cmd := exec.Command(name, args...)
1578 if out, err := cmd.CombinedOutput(); err == nil {
1579 if !bytes.Contains(out, []byte("GNU gold")) {
1580 log.Fatalf("ARM64 external linker must be gold (issue #15696, 22040), but is not: %s", out)
1585 if ctxt.Arch.Family == sys.ARM64 && buildcfg.GOOS == "freebsd" {
1586 // Switch to ld.bfd on freebsd/arm64.
1589 // Provide a useful error if ld.bfd is missing.
1590 name, args := flagExtld[0], flagExtld[1:]
1591 args = append(args, "-fuse-ld=bfd", "-Wl,--version")
1592 cmd := exec.Command(name, args...)
1593 if out, err := cmd.CombinedOutput(); err == nil {
1594 if !bytes.Contains(out, []byte("GNU ld")) {
1595 log.Fatalf("ARM64 external linker must be ld.bfd (issue #35197), please install devel/binutils")
1599 if altLinker != "" {
1600 argv = append(argv, "-fuse-ld="+altLinker)
1603 if ctxt.IsELF && len(buildinfo) > 0 {
1604 argv = append(argv, fmt.Sprintf("-Wl,--build-id=0x%x", buildinfo))
1607 // On Windows, given -o foo, GCC will append ".exe" to produce
1608 // "foo.exe". We have decided that we want to honor the -o
1609 // option. To make this work, we append a '.' so that GCC
1610 // will decide that the file already has an extension. We
1611 // only want to do this when producing a Windows output file
1612 // on a Windows host.
1613 outopt := *flagOutfile
1614 if buildcfg.GOOS == "windows" && runtime.GOOS == "windows" && filepath.Ext(outopt) == "" {
1617 argv = append(argv, "-o")
1618 argv = append(argv, outopt)
1620 if rpath.val != "" {
1621 argv = append(argv, fmt.Sprintf("-Wl,-rpath,%s", rpath.val))
1624 if *flagInterpreter != "" {
1625 // Many linkers support both -I and the --dynamic-linker flags
1626 // to set the ELF interpreter, but lld only supports
1627 // --dynamic-linker so prefer that (ld on very old Solaris only
1628 // supports -I but that seems less important).
1629 argv = append(argv, fmt.Sprintf("-Wl,--dynamic-linker,%s", *flagInterpreter))
1632 // Force global symbols to be exported for dlopen, etc.
1634 if ctxt.DynlinkingGo() || ctxt.BuildMode == BuildModeCShared || !linkerFlagSupported(ctxt.Arch, argv[0], altLinker, "-Wl,--export-dynamic-symbol=main") {
1635 argv = append(argv, "-rdynamic")
1637 ctxt.loader.ForAllCgoExportDynamic(func(s loader.Sym) {
1638 argv = append(argv, "-Wl,--export-dynamic-symbol="+ctxt.loader.SymExtname(s))
1642 if ctxt.HeadType == objabi.Haix {
1643 fileName := xcoffCreateExportFile(ctxt)
1644 argv = append(argv, "-Wl,-bE:"+fileName)
1647 const unusedArguments = "-Qunused-arguments"
1648 if linkerFlagSupported(ctxt.Arch, argv[0], altLinker, unusedArguments) {
1649 argv = append(argv, unusedArguments)
1652 if ctxt.IsWindows() {
1653 // Suppress generation of the PE file header timestamp,
1654 // so as to avoid spurious build ID differences between
1655 // linked binaries that are otherwise identical other than
1656 // the date/time they were linked.
1657 const noTimeStamp = "-Wl,--no-insert-timestamp"
1658 if linkerFlagSupported(ctxt.Arch, argv[0], altLinker, noTimeStamp) {
1659 argv = append(argv, noTimeStamp)
1663 const compressDWARF = "-Wl,--compress-debug-sections=zlib"
1664 if ctxt.compressDWARF && linkerFlagSupported(ctxt.Arch, argv[0], altLinker, compressDWARF) {
1665 argv = append(argv, compressDWARF)
1668 argv = append(argv, filepath.Join(*flagTmpdir, "go.o"))
1669 argv = append(argv, ctxt.hostobjCopy()...)
1670 if ctxt.HeadType == objabi.Haix {
1671 // We want to have C files after Go files to remove
1672 // trampolines csects made by ld.
1673 argv = append(argv, "-nostartfiles")
1674 argv = append(argv, "/lib/crt0_64.o")
1676 extld := ctxt.extld()
1677 name, args := extld[0], extld[1:]
1678 // Get starting files.
1679 getPathFile := func(file string) string {
1680 args := append(args, "-maix64", "--print-file-name="+file)
1681 out, err := exec.Command(name, args...).CombinedOutput()
1683 log.Fatalf("running %s failed: %v\n%s", extld, err, out)
1685 return strings.Trim(string(out), "\n")
1687 // Since GCC version 11, the 64-bit version of GCC starting files
1688 // are now suffixed by "_64". Even under "-maix64" multilib directory
1689 // "crtcxa.o" is 32-bit.
1690 crtcxa := getPathFile("crtcxa_64.o")
1691 if !filepath.IsAbs(crtcxa) {
1692 crtcxa = getPathFile("crtcxa.o")
1694 crtdbase := getPathFile("crtdbase_64.o")
1695 if !filepath.IsAbs(crtdbase) {
1696 crtdbase = getPathFile("crtdbase.o")
1698 argv = append(argv, crtcxa)
1699 argv = append(argv, crtdbase)
1702 if ctxt.linkShared {
1703 seenDirs := make(map[string]bool)
1704 seenLibs := make(map[string]bool)
1705 addshlib := func(path string) {
1706 dir, base := filepath.Split(path)
1708 argv = append(argv, "-L"+dir)
1710 argv = append(argv, "-Wl,-rpath="+dir)
1712 seenDirs[dir] = true
1714 base = strings.TrimSuffix(base, ".so")
1715 base = strings.TrimPrefix(base, "lib")
1716 if !seenLibs[base] {
1717 argv = append(argv, "-l"+base)
1718 seenLibs[base] = true
1721 for _, shlib := range ctxt.Shlibs {
1722 addshlib(shlib.Path)
1723 for _, dep := range shlib.Deps {
1727 libpath := findshlib(ctxt, dep)
1735 // clang, unlike GCC, passes -rdynamic to the linker
1736 // even when linking with -static, causing a linker
1737 // error when using GNU ld. So take out -rdynamic if
1738 // we added it. We do it in this order, rather than
1739 // only adding -rdynamic later, so that -extldflags
1740 // can override -rdynamic without using -static.
1741 // Similarly for -Wl,--dynamic-linker.
1742 checkStatic := func(arg string) {
1743 if ctxt.IsELF && arg == "-static" {
1744 for i := range argv {
1745 if argv[i] == "-rdynamic" || strings.HasPrefix(argv[i], "-Wl,--dynamic-linker,") {
1752 for _, p := range ldflag {
1753 argv = append(argv, p)
1757 // When building a program with the default -buildmode=exe the
1758 // gc compiler generates code requires DT_TEXTREL in a
1759 // position independent executable (PIE). On systems where the
1760 // toolchain creates PIEs by default, and where DT_TEXTREL
1761 // does not work, the resulting programs will not run. See
1762 // issue #17847. To avoid this problem pass -no-pie to the
1763 // toolchain if it is supported.
1764 if ctxt.BuildMode == BuildModeExe && !ctxt.linkShared && !(ctxt.IsDarwin() && ctxt.IsARM64()) {
1765 // GCC uses -no-pie, clang uses -nopie.
1766 for _, nopie := range []string{"-no-pie", "-nopie"} {
1767 if linkerFlagSupported(ctxt.Arch, argv[0], altLinker, nopie) {
1768 argv = append(argv, nopie)
1774 for _, p := range flagExtldflags {
1775 argv = append(argv, p)
1778 if ctxt.HeadType == objabi.Hwindows {
1779 // Determine which linker we're using. Add in the extldflags in
1780 // case used has specified "-fuse-ld=...".
1781 extld := ctxt.extld()
1782 name, args := extld[0], extld[1:]
1783 args = append(args, trimLinkerArgv(flagExtldflags)...)
1784 args = append(args, "-Wl,--version")
1785 cmd := exec.Command(name, args...)
1787 if out, err := cmd.CombinedOutput(); err == nil {
1788 if bytes.Contains(out, []byte("LLD ")) {
1793 // use gcc linker script to work around gcc bug
1794 // (see https://golang.org/issue/20183 for details).
1796 p := writeGDBLinkerScript()
1797 argv = append(argv, "-Wl,-T,"+p)
1800 if p := ctxt.findLibPath("libsynchronization.a"); p != "libsynchronization.a" {
1801 argv = append(argv, "-lsynchronization")
1804 // libmingw32 and libmingwex have some inter-dependencies,
1805 // so must use linker groups.
1806 argv = append(argv, "-Wl,--start-group", "-lmingwex", "-lmingw32", "-Wl,--end-group")
1807 argv = append(argv, peimporteddlls()...)
1810 argv = ctxt.passLongArgsInResponseFile(argv, altLinker)
1812 if ctxt.Debugvlog != 0 {
1813 ctxt.Logf("host link:")
1814 for _, v := range argv {
1820 out, err := exec.Command(argv[0], argv[1:]...).CombinedOutput()
1822 Exitf("running %s failed: %v\n%s", argv[0], err, out)
1825 // Filter out useless linker warnings caused by bugs outside Go.
1826 // See also cmd/go/internal/work/exec.go's gccld method.
1829 for _, line := range bytes.SplitAfter(out, []byte("\n")) {
1830 // golang.org/issue/26073 - Apple Xcode bug
1831 if bytes.Contains(line, []byte("ld: warning: text-based stub file")) {
1840 // Remove TOC overflow warning on AIX.
1841 if bytes.Contains(line, []byte("ld: 0711-783")) {
1846 save = append(save, line)
1848 out = bytes.Join(save, nil)
1851 // always print external output even if the command is successful, so that we don't
1852 // swallow linker warnings (see https://golang.org/issue/17935).
1853 if ctxt.IsDarwin() && ctxt.IsAMD64() {
1854 const noPieWarning = "ld: warning: -no_pie is deprecated when targeting new OS versions\n"
1855 if i := bytes.Index(out, []byte(noPieWarning)); i >= 0 {
1856 // swallow -no_pie deprecation warning, issue 54482
1857 out = append(out[:i], out[i+len(noPieWarning):]...)
1860 ctxt.Logf("%s", out)
1864 // Find "dsymutils" and "strip" tools using CC --print-prog-name.
1866 cc = append(cc, ctxt.extld()...)
1867 cc = append(cc, hostlinkArchArgs(ctxt.Arch)...)
1868 cc = append(cc, "--print-prog-name", "dsymutil")
1869 out, err := exec.Command(cc[0], cc[1:]...).CombinedOutput()
1871 Exitf("%s: finding dsymutil failed: %v\n%s", os.Args[0], err, out)
1873 dsymutilCmd := strings.TrimSuffix(string(out), "\n")
1875 cc[len(cc)-1] = "strip"
1876 out, err = exec.Command(cc[0], cc[1:]...).CombinedOutput()
1878 Exitf("%s: finding strip failed: %v\n%s", os.Args[0], err, out)
1880 stripCmd := strings.TrimSuffix(string(out), "\n")
1882 dsym := filepath.Join(*flagTmpdir, "go.dwarf")
1883 if out, err := exec.Command(dsymutilCmd, "-f", *flagOutfile, "-o", dsym).CombinedOutput(); err != nil {
1884 Exitf("%s: running dsymutil failed: %v\n%s", os.Args[0], err, out)
1886 // Remove STAB (symbolic debugging) symbols after we are done with them (by dsymutil).
1887 // They contain temporary file paths and make the build not reproducible.
1888 if out, err := exec.Command(stripCmd, "-S", *flagOutfile).CombinedOutput(); err != nil {
1889 Exitf("%s: running strip failed: %v\n%s", os.Args[0], err, out)
1891 // Skip combining if `dsymutil` didn't generate a file. See #11994.
1892 if _, err := os.Stat(dsym); os.IsNotExist(err) {
1895 // For os.Rename to work reliably, must be in same directory as outfile.
1896 combinedOutput := *flagOutfile + "~"
1897 exef, err := os.Open(*flagOutfile)
1899 Exitf("%s: combining dwarf failed: %v", os.Args[0], err)
1902 exem, err := macho.NewFile(exef)
1904 Exitf("%s: parsing Mach-O header failed: %v", os.Args[0], err)
1906 if err := machoCombineDwarf(ctxt, exef, exem, dsym, combinedOutput); err != nil {
1907 Exitf("%s: combining dwarf failed: %v", os.Args[0], err)
1909 os.Remove(*flagOutfile)
1910 if err := os.Rename(combinedOutput, *flagOutfile); err != nil {
1911 Exitf("%s: %v", os.Args[0], err)
1914 if ctxt.NeedCodeSign() {
1915 err := machoCodeSign(ctxt, *flagOutfile)
1917 Exitf("%s: code signing failed: %v", os.Args[0], err)
1922 // passLongArgsInResponseFile writes the arguments into a file if they
1924 func (ctxt *Link) passLongArgsInResponseFile(argv []string, altLinker string) []string {
1926 for _, arg := range argv {
1930 if c < sys.ExecArgLengthLimit {
1934 // Only use response files if they are supported.
1935 response := filepath.Join(*flagTmpdir, "response")
1936 if err := os.WriteFile(response, nil, 0644); err != nil {
1937 log.Fatalf("failed while testing response file: %v", err)
1939 if !linkerFlagSupported(ctxt.Arch, argv[0], altLinker, "@"+response) {
1940 if ctxt.Debugvlog != 0 {
1941 ctxt.Logf("not using response file because linker does not support one")
1946 var buf bytes.Buffer
1947 for _, arg := range argv[1:] {
1948 // The external linker response file supports quoted strings.
1949 fmt.Fprintf(&buf, "%q\n", arg)
1951 if err := os.WriteFile(response, buf.Bytes(), 0644); err != nil {
1952 log.Fatalf("failed while writing response file: %v", err)
1954 if ctxt.Debugvlog != 0 {
1955 ctxt.Logf("response file %s contents:\n%s", response, buf.Bytes())
1963 var createTrivialCOnce sync.Once
1965 func linkerFlagSupported(arch *sys.Arch, linker, altLinker, flag string) bool {
1966 createTrivialCOnce.Do(func() {
1967 src := filepath.Join(*flagTmpdir, "trivial.c")
1968 if err := os.WriteFile(src, []byte("int main() { return 0; }"), 0666); err != nil {
1969 Errorf(nil, "WriteFile trivial.c failed: %v", err)
1973 flags := hostlinkArchArgs(arch)
1975 moreFlags := trimLinkerArgv(append(flagExtldflags, ldflag...))
1976 flags = append(flags, moreFlags...)
1978 if altLinker != "" {
1979 flags = append(flags, "-fuse-ld="+altLinker)
1981 flags = append(flags, flag, "trivial.c")
1983 cmd := exec.Command(linker, flags...)
1984 cmd.Dir = *flagTmpdir
1985 cmd.Env = append([]string{"LC_ALL=C"}, os.Environ()...)
1986 out, err := cmd.CombinedOutput()
1987 // GCC says "unrecognized command line option ‘-no-pie’"
1988 // clang says "unknown argument: '-no-pie'"
1989 return err == nil && !bytes.Contains(out, []byte("unrecognized")) && !bytes.Contains(out, []byte("unknown"))
1992 // trimLinkerArgv returns a new copy of argv that does not include flags
1993 // that are not relevant for testing whether some linker option works.
1994 func trimLinkerArgv(argv []string) []string {
1995 flagsWithNextArgSkip := []string{
2004 flagsWithNextArgKeep := []string{
2010 prefixesToKeep := []string{
2024 for _, f := range argv {
2026 flags = append(flags, f)
2030 } else if f == "" || f[0] != '-' {
2031 } else if contains(flagsWithNextArgSkip, f) {
2033 } else if contains(flagsWithNextArgKeep, f) {
2034 flags = append(flags, f)
2037 for _, p := range prefixesToKeep {
2038 if strings.HasPrefix(f, p) {
2039 flags = append(flags, f)
2048 // hostlinkArchArgs returns arguments to pass to the external linker
2049 // based on the architecture.
2050 func hostlinkArchArgs(arch *sys.Arch) []string {
2051 switch arch.Family {
2053 return []string{"-m32"}
2055 if buildcfg.GOOS == "darwin" {
2056 return []string{"-arch", "x86_64", "-m64"}
2058 return []string{"-m64"}
2060 return []string{"-m64"}
2062 return []string{"-marm"}
2064 if buildcfg.GOOS == "darwin" {
2065 return []string{"-arch", "arm64"}
2068 return []string{"-mabi=lp64d"}
2070 return []string{"-mabi=64"}
2072 return []string{"-mabi=32"}
2074 if buildcfg.GOOS == "aix" {
2075 return []string{"-maix64"}
2077 return []string{"-m64"}
2084 var wantHdr = objabi.HeaderString()
2086 // ldobj loads an input object. If it is a host object (an object
2087 // compiled by a non-Go compiler) it returns the Hostobj pointer. If
2088 // it is a Go object, it returns nil.
2089 func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string, file string) *Hostobj {
2090 pkg := objabi.PathToPrefix(lib.Pkg)
2092 eof := f.Offset() + length
2098 f.MustSeek(start, 0)
2100 unit := &sym.CompilationUnit{Lib: lib}
2101 lib.Units = append(lib.Units, unit)
2103 magic := uint32(c1)<<24 | uint32(c2)<<16 | uint32(c3)<<8 | uint32(c4)
2104 if magic == 0x7f454c46 { // \x7F E L F
2105 ldelf := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
2106 textp, flags, err := loadelf.Load(ctxt.loader, ctxt.Arch, ctxt.IncVersion(), f, pkg, length, pn, ehdr.Flags)
2108 Errorf(nil, "%v", err)
2112 ctxt.Textp = append(ctxt.Textp, textp...)
2114 return ldhostobj(ldelf, ctxt.HeadType, f, pkg, length, pn, file)
2117 if magic&^1 == 0xfeedface || magic&^0x01000000 == 0xcefaedfe {
2118 ldmacho := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
2119 textp, err := loadmacho.Load(ctxt.loader, ctxt.Arch, ctxt.IncVersion(), f, pkg, length, pn)
2121 Errorf(nil, "%v", err)
2124 ctxt.Textp = append(ctxt.Textp, textp...)
2126 return ldhostobj(ldmacho, ctxt.HeadType, f, pkg, length, pn, file)
2134 ldpe := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
2135 textp, rsrc, err := loadpe.Load(ctxt.loader, ctxt.Arch, ctxt.IncVersion(), f, pkg, length, pn)
2137 Errorf(nil, "%v", err)
2141 setpersrc(ctxt, rsrc)
2143 ctxt.Textp = append(ctxt.Textp, textp...)
2145 return ldhostobj(ldpe, ctxt.HeadType, f, pkg, length, pn, file)
2148 if c1 == 0x01 && (c2 == 0xD7 || c2 == 0xF7) {
2149 ldxcoff := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
2150 textp, err := loadxcoff.Load(ctxt.loader, ctxt.Arch, ctxt.IncVersion(), f, pkg, length, pn)
2152 Errorf(nil, "%v", err)
2155 ctxt.Textp = append(ctxt.Textp, textp...)
2157 return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
2160 if c1 != 'g' || c2 != 'o' || c3 != ' ' || c4 != 'o' {
2161 // An unrecognized object is just passed to the external linker.
2162 // If we try to read symbols from this object, we will
2163 // report an error at that time.
2164 unknownObjFormat = true
2165 return ldhostobj(nil, ctxt.HeadType, f, pkg, length, pn, file)
2168 /* check the header */
2169 line, err := f.ReadString('\n')
2171 Errorf(nil, "truncated object file: %s: %v", pn, err)
2175 if !strings.HasPrefix(line, "go object ") {
2176 if strings.HasSuffix(pn, ".go") {
2177 Exitf("%s: uncompiled .go source file", pn)
2181 if line == ctxt.Arch.Name {
2182 // old header format: just $GOOS
2183 Errorf(nil, "%s: stale object file", pn)
2187 Errorf(nil, "%s: not an object file: @%d %q", pn, start, line)
2191 // First, check that the basic GOOS, GOARCH, and Version match.
2192 if line != wantHdr {
2193 Errorf(nil, "%s: linked object header mismatch:\nhave %q\nwant %q\n", pn, line, wantHdr)
2196 // Skip over exports and other info -- ends with \n!\n.
2198 // Note: It's possible for "\n!\n" to appear within the binary
2199 // package export data format. To avoid truncating the package
2200 // definition prematurely (issue 21703), we keep track of
2201 // how many "$$" delimiters we've seen.
2203 import0 := f.Offset()
2205 c1 = '\n' // the last line ended in \n
2211 if markers%2 == 0 && c2 == '!' && c3 == '\n' {
2214 if c2 == '$' && c3 == '$' {
2223 Errorf(nil, "truncated object file: %s", pn)
2228 import1 := f.Offset()
2230 f.MustSeek(import0, 0)
2231 ldpkg(ctxt, f, lib, import1-import0-2, pn) // -2 for !\n
2232 f.MustSeek(import1, 0)
2234 fingerprint := ctxt.loader.Preload(ctxt.IncVersion(), f, lib, unit, eof-f.Offset())
2235 if !fingerprint.IsZero() { // Assembly objects don't have fingerprints. Ignore them.
2236 // Check fingerprint, to ensure the importing and imported packages
2237 // have consistent view of symbol indices.
2238 // Normally the go command should ensure this. But in case something
2239 // goes wrong, it could lead to obscure bugs like run-time crash.
2240 // Check it here to be sure.
2241 if lib.Fingerprint.IsZero() { // Not yet imported. Update its fingerprint.
2242 lib.Fingerprint = fingerprint
2244 checkFingerprint(lib, fingerprint, lib.Srcref, lib.Fingerprint)
2247 addImports(ctxt, lib, pn)
2251 // symbolsAreUnresolved scans through the loader's list of unresolved
2252 // symbols and checks to see whether any of them match the names of the
2253 // symbols in 'want'. Return value is a list of bools, with list[K] set
2254 // to true if there is an unresolved reference to the symbol in want[K].
2255 func symbolsAreUnresolved(ctxt *Link, want []string) []bool {
2256 returnAllUndefs := -1
2257 undefs, _ := ctxt.loader.UndefinedRelocTargets(returnAllUndefs)
2258 seen := make(map[loader.Sym]struct{})
2259 rval := make([]bool, len(want))
2260 wantm := make(map[string]int)
2261 for k, w := range want {
2265 for _, s := range undefs {
2266 if _, ok := seen[s]; ok {
2269 seen[s] = struct{}{}
2270 if k, ok := wantm[ctxt.loader.SymName(s)]; ok {
2273 if count == len(want) {
2281 // hostObject reads a single host object file (compare to "hostArchive").
2282 // This is used as part of internal linking when we need to pull in
2283 // files such as "crt?.o".
2284 func hostObject(ctxt *Link, objname string, path string) {
2285 if ctxt.Debugvlog > 1 {
2286 ctxt.Logf("hostObject(%s)\n", path)
2288 objlib := sym.Library{
2291 f, err := bio.Open(path)
2293 Exitf("cannot open host object %q file %s: %v", objname, path, err)
2296 h := ldobj(ctxt, f, &objlib, 0, path, path)
2298 Exitf("unrecognized object file format in %s", path)
2301 h.length = f.MustSeek(0, 2)
2302 f.MustSeek(h.off, 0)
2303 h.ld(ctxt, f, h.pkg, h.length, h.pn)
2304 if *flagCaptureHostObjs != "" {
2309 func checkFingerprint(lib *sym.Library, libfp goobj.FingerprintType, src string, srcfp goobj.FingerprintType) {
2311 Exitf("fingerprint mismatch: %s has %x, import from %s expecting %x", lib, libfp, src, srcfp)
2315 func readelfsymboldata(ctxt *Link, f *elf.File, sym *elf.Symbol) []byte {
2316 data := make([]byte, sym.Size)
2317 sect := f.Sections[sym.Section]
2318 if sect.Type != elf.SHT_PROGBITS && sect.Type != elf.SHT_NOTE {
2319 Errorf(nil, "reading %s from non-data section", sym.Name)
2321 n, err := sect.ReadAt(data, int64(sym.Value-sect.Addr))
2322 if uint64(n) != sym.Size {
2323 Errorf(nil, "reading contents of %s: %v", sym.Name, err)
2328 func readwithpad(r io.Reader, sz int32) ([]byte, error) {
2329 data := make([]byte, Rnd(int64(sz), 4))
2330 _, err := io.ReadFull(r, data)
2338 func readnote(f *elf.File, name []byte, typ int32) ([]byte, error) {
2339 for _, sect := range f.Sections {
2340 if sect.Type != elf.SHT_NOTE {
2345 var namesize, descsize, noteType int32
2346 err := binary.Read(r, f.ByteOrder, &namesize)
2351 return nil, fmt.Errorf("read namesize failed: %v", err)
2353 err = binary.Read(r, f.ByteOrder, &descsize)
2355 return nil, fmt.Errorf("read descsize failed: %v", err)
2357 err = binary.Read(r, f.ByteOrder, ¬eType)
2359 return nil, fmt.Errorf("read type failed: %v", err)
2361 noteName, err := readwithpad(r, namesize)
2363 return nil, fmt.Errorf("read name failed: %v", err)
2365 desc, err := readwithpad(r, descsize)
2367 return nil, fmt.Errorf("read desc failed: %v", err)
2369 if string(name) == string(noteName) && typ == noteType {
2377 func findshlib(ctxt *Link, shlib string) string {
2378 if filepath.IsAbs(shlib) {
2381 for _, libdir := range ctxt.Libdir {
2382 libpath := filepath.Join(libdir, shlib)
2383 if _, err := os.Stat(libpath); err == nil {
2387 Errorf(nil, "cannot find shared library: %s", shlib)
2391 func ldshlibsyms(ctxt *Link, shlib string) {
2393 if filepath.IsAbs(shlib) {
2395 shlib = filepath.Base(shlib)
2397 libpath = findshlib(ctxt, shlib)
2402 for _, processedlib := range ctxt.Shlibs {
2403 if processedlib.Path == libpath {
2407 if ctxt.Debugvlog > 1 {
2408 ctxt.Logf("ldshlibsyms: found library with name %s at %s\n", shlib, libpath)
2411 f, err := elf.Open(libpath)
2413 Errorf(nil, "cannot open shared library: %s", libpath)
2416 // Keep the file open as decodetypeGcprog needs to read from it.
2417 // TODO: fix. Maybe mmap the file.
2420 hash, err := readnote(f, ELF_NOTE_GO_NAME, ELF_NOTE_GOABIHASH_TAG)
2422 Errorf(nil, "cannot read ABI hash from shared library %s: %v", libpath, err)
2426 depsbytes, err := readnote(f, ELF_NOTE_GO_NAME, ELF_NOTE_GODEPS_TAG)
2428 Errorf(nil, "cannot read dep list from shared library %s: %v", libpath, err)
2432 for _, dep := range strings.Split(string(depsbytes), "\n") {
2436 if !filepath.IsAbs(dep) {
2437 // If the dep can be interpreted as a path relative to the shlib
2438 // in which it was found, do that. Otherwise, we will leave it
2439 // to be resolved by libdir lookup.
2440 abs := filepath.Join(filepath.Dir(libpath), dep)
2441 if _, err := os.Stat(abs); err == nil {
2445 deps = append(deps, dep)
2448 syms, err := f.DynamicSymbols()
2450 Errorf(nil, "cannot read symbols from shared library: %s", libpath)
2454 for _, elfsym := range syms {
2455 if elf.ST_TYPE(elfsym.Info) == elf.STT_NOTYPE || elf.ST_TYPE(elfsym.Info) == elf.STT_SECTION {
2459 // Symbols whose names start with "type:" are compiler generated,
2460 // so make functions with that prefix internal.
2462 symname := elfsym.Name // (unmangled) symbol name
2463 if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && strings.HasPrefix(elfsym.Name, "type:") {
2464 ver = abiInternalVer
2465 } else if buildcfg.Experiment.RegabiWrappers && elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC {
2466 // Demangle the ABI name. Keep in sync with symtab.go:mangleABIName.
2467 if strings.HasSuffix(elfsym.Name, ".abiinternal") {
2468 ver = sym.SymVerABIInternal
2469 symname = strings.TrimSuffix(elfsym.Name, ".abiinternal")
2470 } else if strings.HasSuffix(elfsym.Name, ".abi0") {
2472 symname = strings.TrimSuffix(elfsym.Name, ".abi0")
2477 s := l.LookupOrCreateSym(symname, ver)
2479 // Because loadlib above loads all .a files before loading
2480 // any shared libraries, any non-dynimport symbols we find
2481 // that duplicate symbols already loaded should be ignored
2482 // (the symbols from the .a files "win").
2483 if l.SymType(s) != 0 && l.SymType(s) != sym.SDYNIMPORT {
2486 su := l.MakeSymbolUpdater(s)
2487 su.SetType(sym.SDYNIMPORT)
2488 l.SetSymElfType(s, elf.ST_TYPE(elfsym.Info))
2489 su.SetSize(int64(elfsym.Size))
2490 if elfsym.Section != elf.SHN_UNDEF {
2491 // Set .File for the library that actually defines the symbol.
2492 l.SetSymPkg(s, libpath)
2494 // The decodetype_* functions in decodetype.go need access to
2496 sname := l.SymName(s)
2497 if strings.HasPrefix(sname, "type:") && !strings.HasPrefix(sname, "type:.") {
2498 su.SetData(readelfsymboldata(ctxt, f, &elfsym))
2502 if symname != elfsym.Name {
2503 l.SetSymExtname(s, elfsym.Name)
2506 ctxt.Shlibs = append(ctxt.Shlibs, Shlib{Path: libpath, Hash: hash, Deps: deps, File: f})
2509 func addsection(ldr *loader.Loader, arch *sys.Arch, seg *sym.Segment, name string, rwx int) *sym.Section {
2510 sect := ldr.NewSection()
2511 sect.Rwx = uint8(rwx)
2514 sect.Align = int32(arch.PtrSize) // everything is at least pointer-aligned
2515 seg.Sections = append(seg.Sections, sect)
2520 fmt.Fprintf(os.Stderr, "usage: link [options] main.o\n")
2521 objabi.Flagprint(os.Stderr)
2525 type SymbolType int8 // TODO: after genasmsym is gone, maybe rename to plan9typeChar or something
2528 // see also https://9p.io/magic/man2html/1/nm
2529 TextSym SymbolType = 'T'
2530 DataSym SymbolType = 'D'
2531 BSSSym SymbolType = 'B'
2532 UndefinedSym SymbolType = 'U'
2533 TLSSym SymbolType = 't'
2534 FrameSym SymbolType = 'm'
2535 ParamSym SymbolType = 'p'
2536 AutoSym SymbolType = 'a'
2538 // Deleted auto (not a real sym, just placeholder for type)
2539 DeletedAutoSym = 'x'
2542 // defineInternal defines a symbol used internally by the go runtime.
2543 func (ctxt *Link) defineInternal(p string, t sym.SymKind) loader.Sym {
2544 s := ctxt.loader.CreateSymForUpdate(p, 0)
2551 func (ctxt *Link) xdefine(p string, t sym.SymKind, v int64) loader.Sym {
2552 s := ctxt.defineInternal(p, t)
2553 ctxt.loader.SetSymValue(s, v)
2557 func datoff(ldr *loader.Loader, s loader.Sym, addr int64) int64 {
2558 if uint64(addr) >= Segdata.Vaddr {
2559 return int64(uint64(addr) - Segdata.Vaddr + Segdata.Fileoff)
2561 if uint64(addr) >= Segtext.Vaddr {
2562 return int64(uint64(addr) - Segtext.Vaddr + Segtext.Fileoff)
2564 ldr.Errorf(s, "invalid datoff %#x", addr)
2568 func Entryvalue(ctxt *Link) int64 {
2569 a := *flagEntrySymbol
2570 if a[0] >= '0' && a[0] <= '9' {
2574 s := ldr.Lookup(a, 0)
2576 Errorf(nil, "missing entry symbol %q", a)
2579 st := ldr.SymType(s)
2581 return *FlagTextAddr
2583 if !ctxt.IsAIX() && st != sym.STEXT {
2584 ldr.Errorf(s, "entry not text")
2586 return ldr.SymValue(s)
2589 func (ctxt *Link) callgraph() {
2595 for _, s := range ctxt.Textp {
2596 relocs := ldr.Relocs(s)
2597 for i := 0; i < relocs.Count(); i++ {
2603 if r.Type().IsDirectCall() && ldr.SymType(rs) == sym.STEXT {
2604 ctxt.Logf("%s calls %s\n", ldr.SymName(s), ldr.SymName(rs))
2610 func Rnd(v int64, r int64) int64 {
2623 func bgetc(r *bio.Reader) int {
2624 c, err := r.ReadByte()
2627 log.Fatalf("reading input: %v", err)
2634 type markKind uint8 // for postorder traversal
2641 func postorder(libs []*sym.Library) []*sym.Library {
2642 order := make([]*sym.Library, 0, len(libs)) // hold the result
2643 mark := make(map[*sym.Library]markKind, len(libs))
2644 for _, lib := range libs {
2645 dfs(lib, mark, &order)
2650 func dfs(lib *sym.Library, mark map[*sym.Library]markKind, order *[]*sym.Library) {
2651 if mark[lib] == visited {
2654 if mark[lib] == visiting {
2655 panic("found import cycle while visiting " + lib.Pkg)
2657 mark[lib] = visiting
2658 for _, i := range lib.Imports {
2662 *order = append(*order, lib)
2665 func ElfSymForReloc(ctxt *Link, s loader.Sym) int32 {
2666 // If putelfsym created a local version of this symbol, use that in all
2668 les := ctxt.loader.SymLocalElfSym(s)
2672 return ctxt.loader.SymElfSym(s)
2676 func AddGotSym(target *Target, ldr *loader.Loader, syms *ArchSyms, s loader.Sym, elfRelocTyp uint32) {
2677 if ldr.SymGot(s) >= 0 {
2681 Adddynsym(ldr, target, syms, s)
2682 got := ldr.MakeSymbolUpdater(syms.GOT)
2683 ldr.SetGot(s, int32(got.Size()))
2684 got.AddUint(target.Arch, 0)
2687 if target.Arch.PtrSize == 8 {
2688 rela := ldr.MakeSymbolUpdater(syms.Rela)
2689 rela.AddAddrPlus(target.Arch, got.Sym(), int64(ldr.SymGot(s)))
2690 rela.AddUint64(target.Arch, elf.R_INFO(uint32(ldr.SymDynid(s)), elfRelocTyp))
2691 rela.AddUint64(target.Arch, 0)
2693 rel := ldr.MakeSymbolUpdater(syms.Rel)
2694 rel.AddAddrPlus(target.Arch, got.Sym(), int64(ldr.SymGot(s)))
2695 rel.AddUint32(target.Arch, elf.R_INFO32(uint32(ldr.SymDynid(s)), elfRelocTyp))
2697 } else if target.IsDarwin() {
2698 leg := ldr.MakeSymbolUpdater(syms.LinkEditGOT)
2699 leg.AddUint32(target.Arch, uint32(ldr.SymDynid(s)))
2700 if target.IsPIE() && target.IsInternal() {
2701 // Mach-O relocations are a royal pain to lay out.
2702 // They use a compact stateful bytecode representation.
2703 // Here we record what are needed and encode them later.
2704 MachoAddBind(int64(ldr.SymGot(s)), s)
2707 ldr.Errorf(s, "addgotsym: unsupported binary format")
2711 var hostobjcounter int
2713 // captureHostObj writes out the content of a host object (pulled from
2714 // an archive or loaded from a *.o file directly) to a directory
2715 // specified via the linker's "-capturehostobjs" debugging flag. This
2716 // is intended to make it easier for a developer to inspect the actual
2717 // object feeding into "CGO internal" link step.
2718 func captureHostObj(h *Hostobj) {
2719 // Form paths for info file and obj file.
2720 ofile := fmt.Sprintf("captured-obj-%d.o", hostobjcounter)
2721 ifile := fmt.Sprintf("captured-obj-%d.txt", hostobjcounter)
2723 opath := filepath.Join(*flagCaptureHostObjs, ofile)
2724 ipath := filepath.Join(*flagCaptureHostObjs, ifile)
2726 // Write the info file.
2727 info := fmt.Sprintf("pkg: %s\npn: %s\nfile: %s\noff: %d\nlen: %d\n",
2728 h.pkg, h.pn, h.file, h.off, h.length)
2729 if err := os.WriteFile(ipath, []byte(info), 0666); err != nil {
2730 log.Fatalf("error writing captured host obj info %s: %v", ipath, err)
2733 readObjData := func() []byte {
2734 inf, err := os.Open(h.file)
2736 log.Fatalf("capturing host obj: open failed on %s: %v", h.pn, err)
2738 res := make([]byte, h.length)
2739 if n, err := inf.ReadAt(res, h.off); err != nil || n != int(h.length) {
2740 log.Fatalf("capturing host obj: readat failed on %s: %v", h.pn, err)
2745 // Write the object file.
2746 if err := os.WriteFile(opath, readObjData(), 0666); err != nil {
2747 log.Fatalf("error writing captured host object %s: %v", opath, err)
2750 fmt.Fprintf(os.Stderr, "link: info: captured host object %s to %s\n",