1 //===- SyntheticSections.cpp ----------------------------------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This file contains linker-synthesized sections. Currently,
10 // synthetic sections are created either output sections or input sections,
11 // but we are rewriting code so that all synthetic sections are created as
14 //===----------------------------------------------------------------------===//
16 #include "SyntheticSections.h"
18 #include "InputFiles.h"
19 #include "LinkerScript.h"
20 #include "OutputSections.h"
21 #include "SymbolTable.h"
25 #include "lld/Common/DWARF.h"
26 #include "lld/Common/ErrorHandler.h"
27 #include "lld/Common/Memory.h"
28 #include "lld/Common/Strings.h"
29 #include "lld/Common/Version.h"
30 #include "llvm/ADT/SetOperations.h"
31 #include "llvm/ADT/StringExtras.h"
32 #include "llvm/BinaryFormat/Dwarf.h"
33 #include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
34 #include "llvm/Object/ELFObjectFile.h"
35 #include "llvm/Support/Compression.h"
36 #include "llvm/Support/Endian.h"
37 #include "llvm/Support/LEB128.h"
38 #include "llvm/Support/MD5.h"
39 #include "llvm/Support/Parallel.h"
40 #include "llvm/Support/TimeProfiler.h"
45 using namespace llvm::dwarf;
46 using namespace llvm::ELF;
47 using namespace llvm::object;
48 using namespace llvm::support;
50 using namespace lld::elf;
52 using llvm::support::endian::read32le;
53 using llvm::support::endian::write32le;
54 using llvm::support::endian::write64le;
56 constexpr size_t MergeNoTailSection::numShards;
58 static uint64_t readUint(uint8_t *buf) {
59 return config->is64 ? read64(buf) : read32(buf);
62 static void writeUint(uint8_t *buf, uint64_t val) {
69 // Returns an LLD version string.
70 static ArrayRef<uint8_t> getVersion() {
71 // Check LLD_VERSION first for ease of testing.
72 // You can get consistent output by using the environment variable.
73 // This is only for testing.
74 StringRef s = getenv("LLD_VERSION");
76 s = saver.save(Twine("Linker: ") + getLLDVersion());
78 // +1 to include the terminating '\0'.
79 return {(const uint8_t *)s.data(), s.size() + 1};
82 // Creates a .comment section containing LLD version info.
83 // With this feature, you can identify LLD-generated binaries easily
84 // by "readelf --string-dump .comment <file>".
85 // The returned object is a mergeable string section.
86 MergeInputSection *elf::createCommentSection() {
87 return make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1,
88 getVersion(), ".comment");
91 // .MIPS.abiflags section.
93 MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags flags)
94 : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
96 this->entsize = sizeof(Elf_Mips_ABIFlags);
99 template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *buf) {
100 memcpy(buf, &flags, sizeof(flags));
103 template <class ELFT>
104 MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
105 Elf_Mips_ABIFlags flags = {};
108 for (InputSectionBase *sec : inputSections) {
109 if (sec->type != SHT_MIPS_ABIFLAGS)
114 std::string filename = toString(sec->file);
115 const size_t size = sec->data().size();
116 // Older version of BFD (such as the default FreeBSD linker) concatenate
117 // .MIPS.abiflags instead of merging. To allow for this case (or potential
118 // zero padding) we ignore everything after the first Elf_Mips_ABIFlags
119 if (size < sizeof(Elf_Mips_ABIFlags)) {
120 error(filename + ": invalid size of .MIPS.abiflags section: got " +
121 Twine(size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
124 auto *s = reinterpret_cast<const Elf_Mips_ABIFlags *>(sec->data().data());
125 if (s->version != 0) {
126 error(filename + ": unexpected .MIPS.abiflags version " +
131 // LLD checks ISA compatibility in calcMipsEFlags(). Here we just
132 // select the highest number of ISA/Rev/Ext.
133 flags.isa_level = std::max(flags.isa_level, s->isa_level);
134 flags.isa_rev = std::max(flags.isa_rev, s->isa_rev);
135 flags.isa_ext = std::max(flags.isa_ext, s->isa_ext);
136 flags.gpr_size = std::max(flags.gpr_size, s->gpr_size);
137 flags.cpr1_size = std::max(flags.cpr1_size, s->cpr1_size);
138 flags.cpr2_size = std::max(flags.cpr2_size, s->cpr2_size);
139 flags.ases |= s->ases;
140 flags.flags1 |= s->flags1;
141 flags.flags2 |= s->flags2;
142 flags.fp_abi = elf::getMipsFpAbiFlag(flags.fp_abi, s->fp_abi, filename);
146 return make<MipsAbiFlagsSection<ELFT>>(flags);
150 // .MIPS.options section.
151 template <class ELFT>
152 MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo reginfo)
153 : SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
155 this->entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
158 template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *buf) {
159 auto *options = reinterpret_cast<Elf_Mips_Options *>(buf);
160 options->kind = ODK_REGINFO;
161 options->size = getSize();
163 if (!config->relocatable)
164 reginfo.ri_gp_value = in.mipsGot->getGp();
165 memcpy(buf + sizeof(Elf_Mips_Options), ®info, sizeof(reginfo));
168 template <class ELFT>
169 MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
174 std::vector<InputSectionBase *> sections;
175 for (InputSectionBase *sec : inputSections)
176 if (sec->type == SHT_MIPS_OPTIONS)
177 sections.push_back(sec);
179 if (sections.empty())
182 Elf_Mips_RegInfo reginfo = {};
183 for (InputSectionBase *sec : sections) {
186 std::string filename = toString(sec->file);
187 ArrayRef<uint8_t> d = sec->data();
190 if (d.size() < sizeof(Elf_Mips_Options)) {
191 error(filename + ": invalid size of .MIPS.options section");
195 auto *opt = reinterpret_cast<const Elf_Mips_Options *>(d.data());
196 if (opt->kind == ODK_REGINFO) {
197 reginfo.ri_gprmask |= opt->getRegInfo().ri_gprmask;
198 sec->getFile<ELFT>()->mipsGp0 = opt->getRegInfo().ri_gp_value;
203 fatal(filename + ": zero option descriptor size");
204 d = d.slice(opt->size);
208 return make<MipsOptionsSection<ELFT>>(reginfo);
211 // MIPS .reginfo section.
212 template <class ELFT>
213 MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo reginfo)
214 : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
216 this->entsize = sizeof(Elf_Mips_RegInfo);
219 template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *buf) {
220 if (!config->relocatable)
221 reginfo.ri_gp_value = in.mipsGot->getGp();
222 memcpy(buf, ®info, sizeof(reginfo));
225 template <class ELFT>
226 MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
227 // Section should be alive for O32 and N32 ABIs only.
231 std::vector<InputSectionBase *> sections;
232 for (InputSectionBase *sec : inputSections)
233 if (sec->type == SHT_MIPS_REGINFO)
234 sections.push_back(sec);
236 if (sections.empty())
239 Elf_Mips_RegInfo reginfo = {};
240 for (InputSectionBase *sec : sections) {
243 if (sec->data().size() != sizeof(Elf_Mips_RegInfo)) {
244 error(toString(sec->file) + ": invalid size of .reginfo section");
248 auto *r = reinterpret_cast<const Elf_Mips_RegInfo *>(sec->data().data());
249 reginfo.ri_gprmask |= r->ri_gprmask;
250 sec->getFile<ELFT>()->mipsGp0 = r->ri_gp_value;
253 return make<MipsReginfoSection<ELFT>>(reginfo);
256 InputSection *elf::createInterpSection() {
257 // StringSaver guarantees that the returned string ends with '\0'.
258 StringRef s = saver.save(config->dynamicLinker);
259 ArrayRef<uint8_t> contents = {(const uint8_t *)s.data(), s.size() + 1};
261 return make<InputSection>(nullptr, SHF_ALLOC, SHT_PROGBITS, 1, contents,
265 Defined *elf::addSyntheticLocal(StringRef name, uint8_t type, uint64_t value,
266 uint64_t size, InputSectionBase §ion) {
267 auto *s = make<Defined>(section.file, name, STB_LOCAL, STV_DEFAULT, type,
268 value, size, §ion);
270 in.symTab->addSymbol(s);
274 static size_t getHashSize() {
275 switch (config->buildId) {
276 case BuildIdKind::Fast:
278 case BuildIdKind::Md5:
279 case BuildIdKind::Uuid:
281 case BuildIdKind::Sha1:
283 case BuildIdKind::Hexstring:
284 return config->buildIdVector.size();
286 llvm_unreachable("unknown BuildIdKind");
290 // This class represents a linker-synthesized .note.gnu.property section.
292 // In x86 and AArch64, object files may contain feature flags indicating the
293 // features that they have used. The flags are stored in a .note.gnu.property
296 // lld reads the sections from input files and merges them by computing AND of
297 // the flags. The result is written as a new .note.gnu.property section.
299 // If the flag is zero (which indicates that the intersection of the feature
300 // sets is empty, or some input files didn't have .note.gnu.property sections),
301 // we don't create this section.
302 GnuPropertySection::GnuPropertySection()
303 : SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE,
304 config->wordsize, ".note.gnu.property") {}
306 void GnuPropertySection::writeTo(uint8_t *buf) {
307 uint32_t featureAndType = config->emachine == EM_AARCH64
308 ? GNU_PROPERTY_AARCH64_FEATURE_1_AND
309 : GNU_PROPERTY_X86_FEATURE_1_AND;
311 write32(buf, 4); // Name size
312 write32(buf + 4, config->is64 ? 16 : 12); // Content size
313 write32(buf + 8, NT_GNU_PROPERTY_TYPE_0); // Type
314 memcpy(buf + 12, "GNU", 4); // Name string
315 write32(buf + 16, featureAndType); // Feature type
316 write32(buf + 20, 4); // Feature size
317 write32(buf + 24, config->andFeatures); // Feature flags
319 write32(buf + 28, 0); // Padding
322 size_t GnuPropertySection::getSize() const { return config->is64 ? 32 : 28; }
324 BuildIdSection::BuildIdSection()
325 : SyntheticSection(SHF_ALLOC, SHT_NOTE, 4, ".note.gnu.build-id"),
326 hashSize(getHashSize()) {}
328 void BuildIdSection::writeTo(uint8_t *buf) {
329 write32(buf, 4); // Name size
330 write32(buf + 4, hashSize); // Content size
331 write32(buf + 8, NT_GNU_BUILD_ID); // Type
332 memcpy(buf + 12, "GNU", 4); // Name string
336 void BuildIdSection::writeBuildId(ArrayRef<uint8_t> buf) {
337 assert(buf.size() == hashSize);
338 memcpy(hashBuf, buf.data(), hashSize);
341 BssSection::BssSection(StringRef name, uint64_t size, uint32_t alignment)
342 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, alignment, name) {
347 EhFrameSection::EhFrameSection()
348 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}
350 // Search for an existing CIE record or create a new one.
351 // CIE records from input object files are uniquified by their contents
352 // and where their relocations point to.
353 template <class ELFT, class RelTy>
354 CieRecord *EhFrameSection::addCie(EhSectionPiece &cie, ArrayRef<RelTy> rels) {
355 Symbol *personality = nullptr;
356 unsigned firstRelI = cie.firstRelocation;
357 if (firstRelI != (unsigned)-1)
359 &cie.sec->template getFile<ELFT>()->getRelocTargetSym(rels[firstRelI]);
361 // Search for an existing CIE by CIE contents/relocation target pair.
362 CieRecord *&rec = cieMap[{cie.data(), personality}];
364 // If not found, create a new one.
366 rec = make<CieRecord>();
368 cieRecords.push_back(rec);
373 // There is one FDE per function. Returns true if a given FDE
374 // points to a live function.
375 template <class ELFT, class RelTy>
376 bool EhFrameSection::isFdeLive(EhSectionPiece &fde, ArrayRef<RelTy> rels) {
377 auto *sec = cast<EhInputSection>(fde.sec);
378 unsigned firstRelI = fde.firstRelocation;
380 // An FDE should point to some function because FDEs are to describe
381 // functions. That's however not always the case due to an issue of
382 // ld.gold with -r. ld.gold may discard only functions and leave their
383 // corresponding FDEs, which results in creating bad .eh_frame sections.
384 // To deal with that, we ignore such FDEs.
385 if (firstRelI == (unsigned)-1)
388 const RelTy &rel = rels[firstRelI];
389 Symbol &b = sec->template getFile<ELFT>()->getRelocTargetSym(rel);
391 // FDEs for garbage-collected or merged-by-ICF sections, or sections in
392 // another partition, are dead.
393 if (auto *d = dyn_cast<Defined>(&b))
394 if (SectionBase *sec = d->section)
395 return sec->partition == partition;
399 // .eh_frame is a sequence of CIE or FDE records. In general, there
400 // is one CIE record per input object file which is followed by
401 // a list of FDEs. This function searches an existing CIE or create a new
402 // one and associates FDEs to the CIE.
403 template <class ELFT, class RelTy>
404 void EhFrameSection::addRecords(EhInputSection *sec, ArrayRef<RelTy> rels) {
406 for (EhSectionPiece &piece : sec->pieces) {
407 // The empty record is the end marker.
411 size_t offset = piece.inputOff;
412 uint32_t id = read32(piece.data().data() + 4);
414 offsetToCie[offset] = addCie<ELFT>(piece, rels);
418 uint32_t cieOffset = offset + 4 - id;
419 CieRecord *rec = offsetToCie[cieOffset];
421 fatal(toString(sec) + ": invalid CIE reference");
423 if (!isFdeLive<ELFT>(piece, rels))
425 rec->fdes.push_back(&piece);
430 template <class ELFT>
431 void EhFrameSection::addSectionAux(EhInputSection *sec) {
434 if (sec->areRelocsRela)
435 addRecords<ELFT>(sec, sec->template relas<ELFT>());
437 addRecords<ELFT>(sec, sec->template rels<ELFT>());
440 void EhFrameSection::addSection(EhInputSection *sec) {
443 alignment = std::max(alignment, sec->alignment);
444 sections.push_back(sec);
446 for (auto *ds : sec->dependentSections)
447 dependentSections.push_back(ds);
450 static void writeCieFde(uint8_t *buf, ArrayRef<uint8_t> d) {
451 memcpy(buf, d.data(), d.size());
453 size_t aligned = alignTo(d.size(), config->wordsize);
455 // Zero-clear trailing padding if it exists.
456 memset(buf + d.size(), 0, aligned - d.size());
458 // Fix the size field. -4 since size does not include the size field itself.
459 write32(buf, aligned - 4);
462 void EhFrameSection::finalizeContents() {
463 assert(!this->size); // Not finalized.
465 switch (config->ekind) {
467 llvm_unreachable("invalid ekind");
469 for (EhInputSection *sec : sections)
470 addSectionAux<ELF32LE>(sec);
473 for (EhInputSection *sec : sections)
474 addSectionAux<ELF32BE>(sec);
477 for (EhInputSection *sec : sections)
478 addSectionAux<ELF64LE>(sec);
481 for (EhInputSection *sec : sections)
482 addSectionAux<ELF64BE>(sec);
487 for (CieRecord *rec : cieRecords) {
488 rec->cie->outputOff = off;
489 off += alignTo(rec->cie->size, config->wordsize);
491 for (EhSectionPiece *fde : rec->fdes) {
492 fde->outputOff = off;
493 off += alignTo(fde->size, config->wordsize);
497 // The LSB standard does not allow a .eh_frame section with zero
498 // Call Frame Information records. glibc unwind-dw2-fde.c
499 // classify_object_over_fdes expects there is a CIE record length 0 as a
500 // terminator. Thus we add one unconditionally.
506 // Returns data for .eh_frame_hdr. .eh_frame_hdr is a binary search table
507 // to get an FDE from an address to which FDE is applied. This function
508 // returns a list of such pairs.
509 std::vector<EhFrameSection::FdeData> EhFrameSection::getFdeData() const {
510 uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff;
511 std::vector<FdeData> ret;
513 uint64_t va = getPartition().ehFrameHdr->getVA();
514 for (CieRecord *rec : cieRecords) {
515 uint8_t enc = getFdeEncoding(rec->cie);
516 for (EhSectionPiece *fde : rec->fdes) {
517 uint64_t pc = getFdePc(buf, fde->outputOff, enc);
518 uint64_t fdeVA = getParent()->addr + fde->outputOff;
519 if (!isInt<32>(pc - va))
520 fatal(toString(fde->sec) + ": PC offset is too large: 0x" +
521 Twine::utohexstr(pc - va));
522 ret.push_back({uint32_t(pc - va), uint32_t(fdeVA - va)});
526 // Sort the FDE list by their PC and uniqueify. Usually there is only
527 // one FDE for a PC (i.e. function), but if ICF merges two functions
528 // into one, there can be more than one FDEs pointing to the address.
529 auto less = [](const FdeData &a, const FdeData &b) {
530 return a.pcRel < b.pcRel;
532 llvm::stable_sort(ret, less);
533 auto eq = [](const FdeData &a, const FdeData &b) {
534 return a.pcRel == b.pcRel;
536 ret.erase(std::unique(ret.begin(), ret.end(), eq), ret.end());
541 static uint64_t readFdeAddr(uint8_t *buf, int size) {
543 case DW_EH_PE_udata2:
545 case DW_EH_PE_sdata2:
546 return (int16_t)read16(buf);
547 case DW_EH_PE_udata4:
549 case DW_EH_PE_sdata4:
550 return (int32_t)read32(buf);
551 case DW_EH_PE_udata8:
552 case DW_EH_PE_sdata8:
554 case DW_EH_PE_absptr:
555 return readUint(buf);
557 fatal("unknown FDE size encoding");
560 // Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
561 // We need it to create .eh_frame_hdr section.
562 uint64_t EhFrameSection::getFdePc(uint8_t *buf, size_t fdeOff,
564 // The starting address to which this FDE applies is
565 // stored at FDE + 8 byte.
566 size_t off = fdeOff + 8;
567 uint64_t addr = readFdeAddr(buf + off, enc & 0xf);
568 if ((enc & 0x70) == DW_EH_PE_absptr)
570 if ((enc & 0x70) == DW_EH_PE_pcrel)
571 return addr + getParent()->addr + off;
572 fatal("unknown FDE size relative encoding");
575 void EhFrameSection::writeTo(uint8_t *buf) {
576 // Write CIE and FDE records.
577 for (CieRecord *rec : cieRecords) {
578 size_t cieOffset = rec->cie->outputOff;
579 writeCieFde(buf + cieOffset, rec->cie->data());
581 for (EhSectionPiece *fde : rec->fdes) {
582 size_t off = fde->outputOff;
583 writeCieFde(buf + off, fde->data());
585 // FDE's second word should have the offset to an associated CIE.
587 write32(buf + off + 4, off + 4 - cieOffset);
591 // Apply relocations. .eh_frame section contents are not contiguous
592 // in the output buffer, but relocateAlloc() still works because
593 // getOffset() takes care of discontiguous section pieces.
594 for (EhInputSection *s : sections)
595 s->relocateAlloc(buf, nullptr);
597 if (getPartition().ehFrameHdr && getPartition().ehFrameHdr->getParent())
598 getPartition().ehFrameHdr->write();
601 GotSection::GotSection()
602 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
604 // If ElfSym::globalOffsetTable is relative to .got and is referenced,
605 // increase numEntries by the number of entries used to emit
606 // ElfSym::globalOffsetTable.
607 if (ElfSym::globalOffsetTable && !target->gotBaseSymInGotPlt)
608 numEntries += target->gotHeaderEntriesNum;
611 void GotSection::addEntry(Symbol &sym) {
612 sym.gotIndex = numEntries;
616 bool GotSection::addDynTlsEntry(Symbol &sym) {
617 if (sym.globalDynIndex != -1U)
619 sym.globalDynIndex = numEntries;
620 // Global Dynamic TLS entries take two GOT slots.
625 // Reserves TLS entries for a TLS module ID and a TLS block offset.
626 // In total it takes two GOT slots.
627 bool GotSection::addTlsIndex() {
628 if (tlsIndexOff != uint32_t(-1))
630 tlsIndexOff = numEntries * config->wordsize;
635 uint64_t GotSection::getGlobalDynAddr(const Symbol &b) const {
636 return this->getVA() + b.globalDynIndex * config->wordsize;
639 uint64_t GotSection::getGlobalDynOffset(const Symbol &b) const {
640 return b.globalDynIndex * config->wordsize;
643 void GotSection::finalizeContents() {
644 size = numEntries * config->wordsize;
647 bool GotSection::isNeeded() const {
648 // We need to emit a GOT even if it's empty if there's a relocation that is
649 // relative to GOT(such as GOTOFFREL).
650 return numEntries || hasGotOffRel;
653 void GotSection::writeTo(uint8_t *buf) {
654 // Buf points to the start of this section's buffer,
655 // whereas InputSectionBase::relocateAlloc() expects its argument
656 // to point to the start of the output section.
657 target->writeGotHeader(buf);
658 relocateAlloc(buf - outSecOff, buf - outSecOff + size);
661 static uint64_t getMipsPageAddr(uint64_t addr) {
662 return (addr + 0x8000) & ~0xffff;
665 static uint64_t getMipsPageCount(uint64_t size) {
666 return (size + 0xfffe) / 0xffff + 1;
669 MipsGotSection::MipsGotSection()
670 : SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
673 void MipsGotSection::addEntry(InputFile &file, Symbol &sym, int64_t addend,
675 FileGot &g = getGot(file);
676 if (expr == R_MIPS_GOT_LOCAL_PAGE) {
677 if (const OutputSection *os = sym.getOutputSection())
678 g.pagesMap.insert({os, {}});
680 g.local16.insert({{nullptr, getMipsPageAddr(sym.getVA(addend))}, 0});
681 } else if (sym.isTls())
682 g.tls.insert({&sym, 0});
683 else if (sym.isPreemptible && expr == R_ABS)
684 g.relocs.insert({&sym, 0});
685 else if (sym.isPreemptible)
686 g.global.insert({&sym, 0});
687 else if (expr == R_MIPS_GOT_OFF32)
688 g.local32.insert({{&sym, addend}, 0});
690 g.local16.insert({{&sym, addend}, 0});
693 void MipsGotSection::addDynTlsEntry(InputFile &file, Symbol &sym) {
694 getGot(file).dynTlsSymbols.insert({&sym, 0});
697 void MipsGotSection::addTlsIndex(InputFile &file) {
698 getGot(file).dynTlsSymbols.insert({nullptr, 0});
701 size_t MipsGotSection::FileGot::getEntriesNum() const {
702 return getPageEntriesNum() + local16.size() + global.size() + relocs.size() +
703 tls.size() + dynTlsSymbols.size() * 2;
706 size_t MipsGotSection::FileGot::getPageEntriesNum() const {
708 for (const std::pair<const OutputSection *, FileGot::PageBlock> &p : pagesMap)
709 num += p.second.count;
713 size_t MipsGotSection::FileGot::getIndexedEntriesNum() const {
714 size_t count = getPageEntriesNum() + local16.size() + global.size();
715 // If there are relocation-only entries in the GOT, TLS entries
716 // are allocated after them. TLS entries should be addressable
717 // by 16-bit index so count both reloc-only and TLS entries.
718 if (!tls.empty() || !dynTlsSymbols.empty())
719 count += relocs.size() + tls.size() + dynTlsSymbols.size() * 2;
723 MipsGotSection::FileGot &MipsGotSection::getGot(InputFile &f) {
724 if (!f.mipsGotIndex.hasValue()) {
726 gots.back().file = &f;
727 f.mipsGotIndex = gots.size() - 1;
729 return gots[*f.mipsGotIndex];
732 uint64_t MipsGotSection::getPageEntryOffset(const InputFile *f,
734 int64_t addend) const {
735 const FileGot &g = gots[*f->mipsGotIndex];
737 if (const OutputSection *outSec = sym.getOutputSection()) {
738 uint64_t secAddr = getMipsPageAddr(outSec->addr);
739 uint64_t symAddr = getMipsPageAddr(sym.getVA(addend));
740 index = g.pagesMap.lookup(outSec).firstIndex + (symAddr - secAddr) / 0xffff;
742 index = g.local16.lookup({nullptr, getMipsPageAddr(sym.getVA(addend))});
744 return index * config->wordsize;
747 uint64_t MipsGotSection::getSymEntryOffset(const InputFile *f, const Symbol &s,
748 int64_t addend) const {
749 const FileGot &g = gots[*f->mipsGotIndex];
750 Symbol *sym = const_cast<Symbol *>(&s);
752 return g.tls.lookup(sym) * config->wordsize;
753 if (sym->isPreemptible)
754 return g.global.lookup(sym) * config->wordsize;
755 return g.local16.lookup({sym, addend}) * config->wordsize;
758 uint64_t MipsGotSection::getTlsIndexOffset(const InputFile *f) const {
759 const FileGot &g = gots[*f->mipsGotIndex];
760 return g.dynTlsSymbols.lookup(nullptr) * config->wordsize;
763 uint64_t MipsGotSection::getGlobalDynOffset(const InputFile *f,
764 const Symbol &s) const {
765 const FileGot &g = gots[*f->mipsGotIndex];
766 Symbol *sym = const_cast<Symbol *>(&s);
767 return g.dynTlsSymbols.lookup(sym) * config->wordsize;
770 const Symbol *MipsGotSection::getFirstGlobalEntry() const {
773 const FileGot &primGot = gots.front();
774 if (!primGot.global.empty())
775 return primGot.global.front().first;
776 if (!primGot.relocs.empty())
777 return primGot.relocs.front().first;
781 unsigned MipsGotSection::getLocalEntriesNum() const {
783 return headerEntriesNum;
784 return headerEntriesNum + gots.front().getPageEntriesNum() +
785 gots.front().local16.size();
788 bool MipsGotSection::tryMergeGots(FileGot &dst, FileGot &src, bool isPrimary) {
790 set_union(tmp.pagesMap, src.pagesMap);
791 set_union(tmp.local16, src.local16);
792 set_union(tmp.global, src.global);
793 set_union(tmp.relocs, src.relocs);
794 set_union(tmp.tls, src.tls);
795 set_union(tmp.dynTlsSymbols, src.dynTlsSymbols);
797 size_t count = isPrimary ? headerEntriesNum : 0;
798 count += tmp.getIndexedEntriesNum();
800 if (count * config->wordsize > config->mipsGotSize)
807 void MipsGotSection::finalizeContents() { updateAllocSize(); }
809 bool MipsGotSection::updateAllocSize() {
810 size = headerEntriesNum * config->wordsize;
811 for (const FileGot &g : gots)
812 size += g.getEntriesNum() * config->wordsize;
816 void MipsGotSection::build() {
820 std::vector<FileGot> mergedGots(1);
822 // For each GOT move non-preemptible symbols from the `Global`
823 // to `Local16` list. Preemptible symbol might become non-preemptible
824 // one if, for example, it gets a related copy relocation.
825 for (FileGot &got : gots) {
826 for (auto &p: got.global)
827 if (!p.first->isPreemptible)
828 got.local16.insert({{p.first, 0}, 0});
829 got.global.remove_if([&](const std::pair<Symbol *, size_t> &p) {
830 return !p.first->isPreemptible;
834 // For each GOT remove "reloc-only" entry if there is "global"
835 // entry for the same symbol. And add local entries which indexed
836 // using 32-bit value at the end of 16-bit entries.
837 for (FileGot &got : gots) {
838 got.relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
839 return got.global.count(p.first);
841 set_union(got.local16, got.local32);
845 // Evaluate number of "reloc-only" entries in the resulting GOT.
846 // To do that put all unique "reloc-only" and "global" entries
847 // from all GOTs to the future primary GOT.
848 FileGot *primGot = &mergedGots.front();
849 for (FileGot &got : gots) {
850 set_union(primGot->relocs, got.global);
851 set_union(primGot->relocs, got.relocs);
855 // Evaluate number of "page" entries in each GOT.
856 for (FileGot &got : gots) {
857 for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
859 const OutputSection *os = p.first;
860 uint64_t secSize = 0;
861 for (BaseCommand *cmd : os->sectionCommands) {
862 if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
863 for (InputSection *isec : isd->sections) {
864 uint64_t off = alignTo(secSize, isec->alignment);
865 secSize = off + isec->getSize();
868 p.second.count = getMipsPageCount(secSize);
872 // Merge GOTs. Try to join as much as possible GOTs but do not exceed
873 // maximum GOT size. At first, try to fill the primary GOT because
874 // the primary GOT can be accessed in the most effective way. If it
875 // is not possible, try to fill the last GOT in the list, and finally
876 // create a new GOT if both attempts failed.
877 for (FileGot &srcGot : gots) {
878 InputFile *file = srcGot.file;
879 if (tryMergeGots(mergedGots.front(), srcGot, true)) {
880 file->mipsGotIndex = 0;
882 // If this is the first time we failed to merge with the primary GOT,
883 // MergedGots.back() will also be the primary GOT. We must make sure not
884 // to try to merge again with isPrimary=false, as otherwise, if the
885 // inputs are just right, we could allow the primary GOT to become 1 or 2
886 // words bigger due to ignoring the header size.
887 if (mergedGots.size() == 1 ||
888 !tryMergeGots(mergedGots.back(), srcGot, false)) {
889 mergedGots.emplace_back();
890 std::swap(mergedGots.back(), srcGot);
892 file->mipsGotIndex = mergedGots.size() - 1;
895 std::swap(gots, mergedGots);
897 // Reduce number of "reloc-only" entries in the primary GOT
898 // by subtracting "global" entries in the primary GOT.
899 primGot = &gots.front();
900 primGot->relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
901 return primGot->global.count(p.first);
904 // Calculate indexes for each GOT entry.
905 size_t index = headerEntriesNum;
906 for (FileGot &got : gots) {
907 got.startIndex = &got == primGot ? 0 : index;
908 for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
910 // For each output section referenced by GOT page relocations calculate
911 // and save into pagesMap an upper bound of MIPS GOT entries required
912 // to store page addresses of local symbols. We assume the worst case -
913 // each 64kb page of the output section has at least one GOT relocation
914 // against it. And take in account the case when the section intersects
916 p.second.firstIndex = index;
917 index += p.second.count;
919 for (auto &p: got.local16)
921 for (auto &p: got.global)
923 for (auto &p: got.relocs)
925 for (auto &p: got.tls)
927 for (auto &p: got.dynTlsSymbols) {
933 // Update Symbol::gotIndex field to use this
934 // value later in the `sortMipsSymbols` function.
935 for (auto &p : primGot->global)
936 p.first->gotIndex = p.second;
937 for (auto &p : primGot->relocs)
938 p.first->gotIndex = p.second;
940 // Create dynamic relocations.
941 for (FileGot &got : gots) {
942 // Create dynamic relocations for TLS entries.
943 for (std::pair<Symbol *, size_t> &p : got.tls) {
945 uint64_t offset = p.second * config->wordsize;
946 if (s->isPreemptible)
947 mainPart->relaDyn->addReloc(target->tlsGotRel, this, offset, s);
949 for (std::pair<Symbol *, size_t> &p : got.dynTlsSymbols) {
951 uint64_t offset = p.second * config->wordsize;
955 mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, this, offset, s);
957 // When building a shared library we still need a dynamic relocation
958 // for the module index. Therefore only checking for
959 // S->isPreemptible is not sufficient (this happens e.g. for
960 // thread-locals that have been marked as local through a linker script)
961 if (!s->isPreemptible && !config->isPic)
963 mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, this, offset, s);
964 // However, we can skip writing the TLS offset reloc for non-preemptible
965 // symbols since it is known even in shared libraries
966 if (!s->isPreemptible)
968 offset += config->wordsize;
969 mainPart->relaDyn->addReloc(target->tlsOffsetRel, this, offset, s);
973 // Do not create dynamic relocations for non-TLS
974 // entries in the primary GOT.
978 // Dynamic relocations for "global" entries.
979 for (const std::pair<Symbol *, size_t> &p : got.global) {
980 uint64_t offset = p.second * config->wordsize;
981 mainPart->relaDyn->addReloc(target->relativeRel, this, offset, p.first);
985 // Dynamic relocations for "local" entries in case of PIC.
986 for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
988 size_t pageCount = l.second.count;
989 for (size_t pi = 0; pi < pageCount; ++pi) {
990 uint64_t offset = (l.second.firstIndex + pi) * config->wordsize;
991 mainPart->relaDyn->addReloc({target->relativeRel, this, offset, l.first,
992 int64_t(pi * 0x10000)});
995 for (const std::pair<GotEntry, size_t> &p : got.local16) {
996 uint64_t offset = p.second * config->wordsize;
997 mainPart->relaDyn->addReloc({target->relativeRel, this, offset, true,
998 p.first.first, p.first.second});
1003 bool MipsGotSection::isNeeded() const {
1004 // We add the .got section to the result for dynamic MIPS target because
1005 // its address and properties are mentioned in the .dynamic section.
1006 return !config->relocatable;
1009 uint64_t MipsGotSection::getGp(const InputFile *f) const {
1010 // For files without related GOT or files refer a primary GOT
1011 // returns "common" _gp value. For secondary GOTs calculate
1012 // individual _gp values.
1013 if (!f || !f->mipsGotIndex.hasValue() || *f->mipsGotIndex == 0)
1014 return ElfSym::mipsGp->getVA(0);
1015 return getVA() + gots[*f->mipsGotIndex].startIndex * config->wordsize +
1019 void MipsGotSection::writeTo(uint8_t *buf) {
1020 // Set the MSB of the second GOT slot. This is not required by any
1021 // MIPS ABI documentation, though.
1023 // There is a comment in glibc saying that "The MSB of got[1] of a
1024 // gnu object is set to identify gnu objects," and in GNU gold it
1025 // says "the second entry will be used by some runtime loaders".
1026 // But how this field is being used is unclear.
1028 // We are not really willing to mimic other linkers behaviors
1029 // without understanding why they do that, but because all files
1030 // generated by GNU tools have this special GOT value, and because
1031 // we've been doing this for years, it is probably a safe bet to
1032 // keep doing this for now. We really need to revisit this to see
1033 // if we had to do this.
1034 writeUint(buf + config->wordsize, (uint64_t)1 << (config->wordsize * 8 - 1));
1035 for (const FileGot &g : gots) {
1036 auto write = [&](size_t i, const Symbol *s, int64_t a) {
1040 writeUint(buf + i * config->wordsize, va);
1042 // Write 'page address' entries to the local part of the GOT.
1043 for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
1045 size_t pageCount = l.second.count;
1046 uint64_t firstPageAddr = getMipsPageAddr(l.first->addr);
1047 for (size_t pi = 0; pi < pageCount; ++pi)
1048 write(l.second.firstIndex + pi, nullptr, firstPageAddr + pi * 0x10000);
1050 // Local, global, TLS, reloc-only entries.
1051 // If TLS entry has a corresponding dynamic relocations, leave it
1052 // initialized by zero. Write down adjusted TLS symbol's values otherwise.
1053 // To calculate the adjustments use offsets for thread-local storage.
1054 // https://www.linux-mips.org/wiki/NPTL
1055 for (const std::pair<GotEntry, size_t> &p : g.local16)
1056 write(p.second, p.first.first, p.first.second);
1057 // Write VA to the primary GOT only. For secondary GOTs that
1058 // will be done by REL32 dynamic relocations.
1059 if (&g == &gots.front())
1060 for (const std::pair<Symbol *, size_t> &p : g.global)
1061 write(p.second, p.first, 0);
1062 for (const std::pair<Symbol *, size_t> &p : g.relocs)
1063 write(p.second, p.first, 0);
1064 for (const std::pair<Symbol *, size_t> &p : g.tls)
1065 write(p.second, p.first, p.first->isPreemptible ? 0 : -0x7000);
1066 for (const std::pair<Symbol *, size_t> &p : g.dynTlsSymbols) {
1067 if (p.first == nullptr && !config->isPic)
1068 write(p.second, nullptr, 1);
1069 else if (p.first && !p.first->isPreemptible) {
1070 // If we are emitting PIC code with relocations we mustn't write
1071 // anything to the GOT here. When using Elf_Rel relocations the value
1072 // one will be treated as an addend and will cause crashes at runtime
1074 write(p.second, nullptr, 1);
1075 write(p.second + 1, p.first, -0x8000);
1081 // On PowerPC the .plt section is used to hold the table of function addresses
1082 // instead of the .got.plt, and the type is SHT_NOBITS similar to a .bss
1083 // section. I don't know why we have a BSS style type for the section but it is
1084 // consistent across both 64-bit PowerPC ABIs as well as the 32-bit PowerPC ABI.
1085 GotPltSection::GotPltSection()
1086 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
1088 if (config->emachine == EM_PPC) {
1090 } else if (config->emachine == EM_PPC64) {
1096 void GotPltSection::addEntry(Symbol &sym) {
1097 assert(sym.pltIndex == entries.size());
1098 entries.push_back(&sym);
1101 size_t GotPltSection::getSize() const {
1102 return (target->gotPltHeaderEntriesNum + entries.size()) * config->wordsize;
1105 void GotPltSection::writeTo(uint8_t *buf) {
1106 target->writeGotPltHeader(buf);
1107 buf += target->gotPltHeaderEntriesNum * config->wordsize;
1108 for (const Symbol *b : entries) {
1109 target->writeGotPlt(buf, *b);
1110 buf += config->wordsize;
1114 bool GotPltSection::isNeeded() const {
1115 // We need to emit GOTPLT even if it's empty if there's a relocation relative
1117 return !entries.empty() || hasGotPltOffRel;
1120 static StringRef getIgotPltName() {
1121 // On ARM the IgotPltSection is part of the GotSection.
1122 if (config->emachine == EM_ARM)
1125 // On PowerPC64 the GotPltSection is renamed to '.plt' so the IgotPltSection
1126 // needs to be named the same.
1127 if (config->emachine == EM_PPC64)
1133 // On PowerPC64 the GotPltSection type is SHT_NOBITS so we have to follow suit
1134 // with the IgotPltSection.
1135 IgotPltSection::IgotPltSection()
1136 : SyntheticSection(SHF_ALLOC | SHF_WRITE,
1137 config->emachine == EM_PPC64 ? SHT_NOBITS : SHT_PROGBITS,
1138 config->wordsize, getIgotPltName()) {}
1140 void IgotPltSection::addEntry(Symbol &sym) {
1141 assert(sym.pltIndex == entries.size());
1142 entries.push_back(&sym);
1145 size_t IgotPltSection::getSize() const {
1146 return entries.size() * config->wordsize;
1149 void IgotPltSection::writeTo(uint8_t *buf) {
1150 for (const Symbol *b : entries) {
1151 target->writeIgotPlt(buf, *b);
1152 buf += config->wordsize;
1156 StringTableSection::StringTableSection(StringRef name, bool dynamic)
1157 : SyntheticSection(dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, name),
1159 // ELF string tables start with a NUL byte.
1163 // Adds a string to the string table. If `hashIt` is true we hash and check for
1164 // duplicates. It is optional because the name of global symbols are already
1165 // uniqued and hashing them again has a big cost for a small value: uniquing
1166 // them with some other string that happens to be the same.
1167 unsigned StringTableSection::addString(StringRef s, bool hashIt) {
1169 auto r = stringMap.insert(std::make_pair(s, this->size));
1171 return r.first->second;
1173 unsigned ret = this->size;
1174 this->size = this->size + s.size() + 1;
1175 strings.push_back(s);
1179 void StringTableSection::writeTo(uint8_t *buf) {
1180 for (StringRef s : strings) {
1181 memcpy(buf, s.data(), s.size());
1182 buf[s.size()] = '\0';
1183 buf += s.size() + 1;
1187 // Returns the number of entries in .gnu.version_d: the number of
1188 // non-VER_NDX_LOCAL-non-VER_NDX_GLOBAL definitions, plus 1.
1189 // Note that we don't support vd_cnt > 1 yet.
1190 static unsigned getVerDefNum() {
1191 return namedVersionDefs().size() + 1;
1194 template <class ELFT>
1195 DynamicSection<ELFT>::DynamicSection()
1196 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, config->wordsize,
1198 this->entsize = ELFT::Is64Bits ? 16 : 8;
1200 // .dynamic section is not writable on MIPS and on Fuchsia OS
1201 // which passes -z rodynamic.
1202 // See "Special Section" in Chapter 4 in the following document:
1203 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1204 if (config->emachine == EM_MIPS || config->zRodynamic)
1205 this->flags = SHF_ALLOC;
1208 template <class ELFT>
1209 void DynamicSection<ELFT>::add(int32_t tag, std::function<uint64_t()> fn) {
1210 entries.push_back({tag, fn});
1213 template <class ELFT>
1214 void DynamicSection<ELFT>::addInt(int32_t tag, uint64_t val) {
1215 entries.push_back({tag, [=] { return val; }});
1218 template <class ELFT>
1219 void DynamicSection<ELFT>::addInSec(int32_t tag, InputSection *sec) {
1220 entries.push_back({tag, [=] { return sec->getVA(0); }});
1223 template <class ELFT>
1224 void DynamicSection<ELFT>::addInSecRelative(int32_t tag, InputSection *sec) {
1225 size_t tagOffset = entries.size() * entsize;
1227 {tag, [=] { return sec->getVA(0) - (getVA() + tagOffset); }});
1230 template <class ELFT>
1231 void DynamicSection<ELFT>::addOutSec(int32_t tag, OutputSection *sec) {
1232 entries.push_back({tag, [=] { return sec->addr; }});
1235 template <class ELFT>
1236 void DynamicSection<ELFT>::addSize(int32_t tag, OutputSection *sec) {
1237 entries.push_back({tag, [=] { return sec->size; }});
1240 template <class ELFT>
1241 void DynamicSection<ELFT>::addSym(int32_t tag, Symbol *sym) {
1242 entries.push_back({tag, [=] { return sym->getVA(); }});
1245 // The output section .rela.dyn may include these synthetic sections:
1248 // - in.relaIplt: this is included if in.relaIplt is named .rela.dyn
1249 // - in.relaPlt: this is included if a linker script places .rela.plt inside
1252 // DT_RELASZ is the total size of the included sections.
1253 static std::function<uint64_t()> addRelaSz(RelocationBaseSection *relaDyn) {
1255 size_t size = relaDyn->getSize();
1256 if (in.relaIplt->getParent() == relaDyn->getParent())
1257 size += in.relaIplt->getSize();
1258 if (in.relaPlt->getParent() == relaDyn->getParent())
1259 size += in.relaPlt->getSize();
1264 // A Linker script may assign the RELA relocation sections to the same
1265 // output section. When this occurs we cannot just use the OutputSection
1266 // Size. Moreover the [DT_JMPREL, DT_JMPREL + DT_PLTRELSZ) is permitted to
1267 // overlap with the [DT_RELA, DT_RELA + DT_RELASZ).
1268 static uint64_t addPltRelSz() {
1269 size_t size = in.relaPlt->getSize();
1270 if (in.relaIplt->getParent() == in.relaPlt->getParent() &&
1271 in.relaIplt->name == in.relaPlt->name)
1272 size += in.relaIplt->getSize();
1276 // Add remaining entries to complete .dynamic contents.
1277 template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
1278 elf::Partition &part = getPartition();
1279 bool isMain = part.name.empty();
1281 for (StringRef s : config->filterList)
1282 addInt(DT_FILTER, part.dynStrTab->addString(s));
1283 for (StringRef s : config->auxiliaryList)
1284 addInt(DT_AUXILIARY, part.dynStrTab->addString(s));
1286 if (!config->rpath.empty())
1287 addInt(config->enableNewDtags ? DT_RUNPATH : DT_RPATH,
1288 part.dynStrTab->addString(config->rpath));
1290 for (SharedFile *file : sharedFiles)
1292 addInt(DT_NEEDED, part.dynStrTab->addString(file->soName));
1295 if (!config->soName.empty())
1296 addInt(DT_SONAME, part.dynStrTab->addString(config->soName));
1298 if (!config->soName.empty())
1299 addInt(DT_NEEDED, part.dynStrTab->addString(config->soName));
1300 addInt(DT_SONAME, part.dynStrTab->addString(part.name));
1303 // Set DT_FLAGS and DT_FLAGS_1.
1304 uint32_t dtFlags = 0;
1305 uint32_t dtFlags1 = 0;
1306 if (config->bsymbolic)
1307 dtFlags |= DF_SYMBOLIC;
1308 if (config->zGlobal)
1309 dtFlags1 |= DF_1_GLOBAL;
1310 if (config->zInitfirst)
1311 dtFlags1 |= DF_1_INITFIRST;
1312 if (config->zInterpose)
1313 dtFlags1 |= DF_1_INTERPOSE;
1314 if (config->zNodefaultlib)
1315 dtFlags1 |= DF_1_NODEFLIB;
1316 if (config->zNodelete)
1317 dtFlags1 |= DF_1_NODELETE;
1318 if (config->zNodlopen)
1319 dtFlags1 |= DF_1_NOOPEN;
1321 dtFlags1 |= DF_1_PIE;
1323 dtFlags |= DF_BIND_NOW;
1324 dtFlags1 |= DF_1_NOW;
1326 if (config->zOrigin) {
1327 dtFlags |= DF_ORIGIN;
1328 dtFlags1 |= DF_1_ORIGIN;
1331 dtFlags |= DF_TEXTREL;
1332 if (config->hasStaticTlsModel)
1333 dtFlags |= DF_STATIC_TLS;
1336 addInt(DT_FLAGS, dtFlags);
1338 addInt(DT_FLAGS_1, dtFlags1);
1340 // DT_DEBUG is a pointer to debug information used by debuggers at runtime. We
1341 // need it for each process, so we don't write it for DSOs. The loader writes
1342 // the pointer into this entry.
1344 // DT_DEBUG is the only .dynamic entry that needs to be written to. Some
1345 // systems (currently only Fuchsia OS) provide other means to give the
1346 // debugger this information. Such systems may choose make .dynamic read-only.
1347 // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
1348 if (!config->shared && !config->relocatable && !config->zRodynamic)
1349 addInt(DT_DEBUG, 0);
1351 if (OutputSection *sec = part.dynStrTab->getParent())
1352 this->link = sec->sectionIndex;
1354 if (part.relaDyn->isNeeded() ||
1355 (in.relaIplt->isNeeded() &&
1356 part.relaDyn->getParent() == in.relaIplt->getParent())) {
1357 addInSec(part.relaDyn->dynamicTag, part.relaDyn);
1358 entries.push_back({part.relaDyn->sizeDynamicTag, addRelaSz(part.relaDyn)});
1360 bool isRela = config->isRela;
1361 addInt(isRela ? DT_RELAENT : DT_RELENT,
1362 isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel));
1364 // MIPS dynamic loader does not support RELCOUNT tag.
1365 // The problem is in the tight relation between dynamic
1366 // relocations and GOT. So do not emit this tag on MIPS.
1367 if (config->emachine != EM_MIPS) {
1368 size_t numRelativeRels = part.relaDyn->getRelativeRelocCount();
1369 if (config->zCombreloc && numRelativeRels)
1370 addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels);
1373 if (part.relrDyn && !part.relrDyn->relocs.empty()) {
1374 addInSec(config->useAndroidRelrTags ? DT_ANDROID_RELR : DT_RELR,
1376 addSize(config->useAndroidRelrTags ? DT_ANDROID_RELRSZ : DT_RELRSZ,
1377 part.relrDyn->getParent());
1378 addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRENT : DT_RELRENT,
1381 // .rel[a].plt section usually consists of two parts, containing plt and
1382 // iplt relocations. It is possible to have only iplt relocations in the
1383 // output. In that case relaPlt is empty and have zero offset, the same offset
1384 // as relaIplt has. And we still want to emit proper dynamic tags for that
1385 // case, so here we always use relaPlt as marker for the beginning of
1386 // .rel[a].plt section.
1387 if (isMain && (in.relaPlt->isNeeded() || in.relaIplt->isNeeded())) {
1388 addInSec(DT_JMPREL, in.relaPlt);
1389 entries.push_back({DT_PLTRELSZ, addPltRelSz});
1390 switch (config->emachine) {
1392 addInSec(DT_MIPS_PLTGOT, in.gotPlt);
1395 addInSec(DT_PLTGOT, in.plt);
1398 addInSec(DT_PLTGOT, in.gotPlt);
1401 addInt(DT_PLTREL, config->isRela ? DT_RELA : DT_REL);
1404 if (config->emachine == EM_AARCH64) {
1405 if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
1406 addInt(DT_AARCH64_BTI_PLT, 0);
1407 if (config->zPacPlt)
1408 addInt(DT_AARCH64_PAC_PLT, 0);
1411 addInSec(DT_SYMTAB, part.dynSymTab);
1412 addInt(DT_SYMENT, sizeof(Elf_Sym));
1413 addInSec(DT_STRTAB, part.dynStrTab);
1414 addInt(DT_STRSZ, part.dynStrTab->getSize());
1416 addInt(DT_TEXTREL, 0);
1417 if (part.gnuHashTab)
1418 addInSec(DT_GNU_HASH, part.gnuHashTab);
1420 addInSec(DT_HASH, part.hashTab);
1423 if (Out::preinitArray) {
1424 addOutSec(DT_PREINIT_ARRAY, Out::preinitArray);
1425 addSize(DT_PREINIT_ARRAYSZ, Out::preinitArray);
1427 if (Out::initArray) {
1428 addOutSec(DT_INIT_ARRAY, Out::initArray);
1429 addSize(DT_INIT_ARRAYSZ, Out::initArray);
1431 if (Out::finiArray) {
1432 addOutSec(DT_FINI_ARRAY, Out::finiArray);
1433 addSize(DT_FINI_ARRAYSZ, Out::finiArray);
1436 if (Symbol *b = symtab->find(config->init))
1439 if (Symbol *b = symtab->find(config->fini))
1444 if (part.verSym && part.verSym->isNeeded())
1445 addInSec(DT_VERSYM, part.verSym);
1446 if (part.verDef && part.verDef->isLive()) {
1447 addInSec(DT_VERDEF, part.verDef);
1448 addInt(DT_VERDEFNUM, getVerDefNum());
1450 if (part.verNeed && part.verNeed->isNeeded()) {
1451 addInSec(DT_VERNEED, part.verNeed);
1452 unsigned needNum = 0;
1453 for (SharedFile *f : sharedFiles)
1454 if (!f->vernauxs.empty())
1456 addInt(DT_VERNEEDNUM, needNum);
1459 if (config->emachine == EM_MIPS) {
1460 addInt(DT_MIPS_RLD_VERSION, 1);
1461 addInt(DT_MIPS_FLAGS, RHF_NOTPOT);
1462 addInt(DT_MIPS_BASE_ADDRESS, target->getImageBase());
1463 addInt(DT_MIPS_SYMTABNO, part.dynSymTab->getNumSymbols());
1465 add(DT_MIPS_LOCAL_GOTNO, [] { return in.mipsGot->getLocalEntriesNum(); });
1467 if (const Symbol *b = in.mipsGot->getFirstGlobalEntry())
1468 addInt(DT_MIPS_GOTSYM, b->dynsymIndex);
1470 addInt(DT_MIPS_GOTSYM, part.dynSymTab->getNumSymbols());
1471 addInSec(DT_PLTGOT, in.mipsGot);
1472 if (in.mipsRldMap) {
1474 addInSec(DT_MIPS_RLD_MAP, in.mipsRldMap);
1475 // Store the offset to the .rld_map section
1476 // relative to the address of the tag.
1477 addInSecRelative(DT_MIPS_RLD_MAP_REL, in.mipsRldMap);
1481 // DT_PPC_GOT indicates to glibc Secure PLT is used. If DT_PPC_GOT is absent,
1482 // glibc assumes the old-style BSS PLT layout which we don't support.
1483 if (config->emachine == EM_PPC)
1484 add(DT_PPC_GOT, [] { return in.got->getVA(); });
1486 // Glink dynamic tag is required by the V2 abi if the plt section isn't empty.
1487 if (config->emachine == EM_PPC64 && in.plt->isNeeded()) {
1488 // The Glink tag points to 32 bytes before the first lazy symbol resolution
1489 // stub, which starts directly after the header.
1490 entries.push_back({DT_PPC64_GLINK, [=] {
1491 unsigned offset = target->pltHeaderSize - 32;
1492 return in.plt->getVA(0) + offset;
1498 getParent()->link = this->link;
1499 this->size = entries.size() * this->entsize;
1502 template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *buf) {
1503 auto *p = reinterpret_cast<Elf_Dyn *>(buf);
1505 for (std::pair<int32_t, std::function<uint64_t()>> &kv : entries) {
1506 p->d_tag = kv.first;
1507 p->d_un.d_val = kv.second();
1512 uint64_t DynamicReloc::getOffset() const {
1513 return inputSec->getVA(offsetInSec);
1516 int64_t DynamicReloc::computeAddend() const {
1518 return sym->getVA(addend);
1521 // See the comment in the DynamicReloc ctor.
1522 return getMipsPageAddr(outputSec->addr) + addend;
1525 uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {
1526 if (sym && !useSymVA)
1527 return symTab->getSymbolIndex(sym);
1531 RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type,
1533 int32_t sizeDynamicTag)
1534 : SyntheticSection(SHF_ALLOC, type, config->wordsize, name),
1535 dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag) {}
1537 void RelocationBaseSection::addReloc(RelType dynType, InputSectionBase *isec,
1538 uint64_t offsetInSec, Symbol *sym) {
1539 addReloc({dynType, isec, offsetInSec, false, sym, 0});
1542 void RelocationBaseSection::addReloc(RelType dynType,
1543 InputSectionBase *inputSec,
1544 uint64_t offsetInSec, Symbol *sym,
1545 int64_t addend, RelExpr expr,
1547 // Write the addends to the relocated address if required. We skip
1548 // it if the written value would be zero.
1549 if (config->writeAddends && (expr != R_ADDEND || addend != 0))
1550 inputSec->relocations.push_back({expr, type, offsetInSec, addend, sym});
1551 addReloc({dynType, inputSec, offsetInSec, expr != R_ADDEND, sym, addend});
1554 void RelocationBaseSection::addReloc(const DynamicReloc &reloc) {
1555 if (reloc.type == target->relativeRel)
1556 ++numRelativeRelocs;
1557 relocs.push_back(reloc);
1560 void RelocationBaseSection::finalizeContents() {
1561 SymbolTableBaseSection *symTab = getPartition().dynSymTab;
1563 // When linking glibc statically, .rel{,a}.plt contains R_*_IRELATIVE
1564 // relocations due to IFUNC (e.g. strcpy). sh_link will be set to 0 in that
1566 if (symTab && symTab->getParent())
1567 getParent()->link = symTab->getParent()->sectionIndex;
1569 getParent()->link = 0;
1571 if (in.relaPlt == this)
1572 getParent()->info = in.gotPlt->getParent()->sectionIndex;
1573 if (in.relaIplt == this)
1574 getParent()->info = in.igotPlt->getParent()->sectionIndex;
1577 RelrBaseSection::RelrBaseSection()
1578 : SyntheticSection(SHF_ALLOC,
1579 config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR,
1580 config->wordsize, ".relr.dyn") {}
1582 template <class ELFT>
1583 static void encodeDynamicReloc(SymbolTableBaseSection *symTab,
1584 typename ELFT::Rela *p,
1585 const DynamicReloc &rel) {
1587 p->r_addend = rel.computeAddend();
1588 p->r_offset = rel.getOffset();
1589 p->setSymbolAndType(rel.getSymIndex(symTab), rel.type, config->isMips64EL);
1592 template <class ELFT>
1593 RelocationSection<ELFT>::RelocationSection(StringRef name, bool sort)
1594 : RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL,
1595 config->isRela ? DT_RELA : DT_REL,
1596 config->isRela ? DT_RELASZ : DT_RELSZ),
1598 this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1601 template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
1602 SymbolTableBaseSection *symTab = getPartition().dynSymTab;
1604 // Sort by (!IsRelative,SymIndex,r_offset). DT_REL[A]COUNT requires us to
1605 // place R_*_RELATIVE first. SymIndex is to improve locality, while r_offset
1606 // is to make results easier to read.
1609 relocs, [&](const DynamicReloc &a, const DynamicReloc &b) {
1610 return std::make_tuple(a.type != target->relativeRel,
1611 a.getSymIndex(symTab), a.getOffset()) <
1612 std::make_tuple(b.type != target->relativeRel,
1613 b.getSymIndex(symTab), b.getOffset());
1616 for (const DynamicReloc &rel : relocs) {
1617 encodeDynamicReloc<ELFT>(symTab, reinterpret_cast<Elf_Rela *>(buf), rel);
1618 buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1622 template <class ELFT>
1623 AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection(
1625 : RelocationBaseSection(
1626 name, config->isRela ? SHT_ANDROID_RELA : SHT_ANDROID_REL,
1627 config->isRela ? DT_ANDROID_RELA : DT_ANDROID_REL,
1628 config->isRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ) {
1632 template <class ELFT>
1633 bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
1634 // This function computes the contents of an Android-format packed relocation
1637 // This format compresses relocations by using relocation groups to factor out
1638 // fields that are common between relocations and storing deltas from previous
1639 // relocations in SLEB128 format (which has a short representation for small
1640 // numbers). A good example of a relocation type with common fields is
1641 // R_*_RELATIVE, which is normally used to represent function pointers in
1642 // vtables. In the REL format, each relative relocation has the same r_info
1643 // field, and is only different from other relative relocations in terms of
1644 // the r_offset field. By sorting relocations by offset, grouping them by
1645 // r_info and representing each relocation with only the delta from the
1646 // previous offset, each 8-byte relocation can be compressed to as little as 1
1647 // byte (or less with run-length encoding). This relocation packer was able to
1648 // reduce the size of the relocation section in an Android Chromium DSO from
1649 // 2,911,184 bytes to 174,693 bytes, or 6% of the original size.
1651 // A relocation section consists of a header containing the literal bytes
1652 // 'APS2' followed by a sequence of SLEB128-encoded integers. The first two
1653 // elements are the total number of relocations in the section and an initial
1654 // r_offset value. The remaining elements define a sequence of relocation
1655 // groups. Each relocation group starts with a header consisting of the
1656 // following elements:
1658 // - the number of relocations in the relocation group
1659 // - flags for the relocation group
1660 // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is set) the r_offset delta
1661 // for each relocation in the group.
1662 // - (if RELOCATION_GROUPED_BY_INFO_FLAG is set) the value of the r_info
1663 // field for each relocation in the group.
1664 // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG and
1665 // RELOCATION_GROUPED_BY_ADDEND_FLAG are set) the r_addend delta for
1666 // each relocation in the group.
1668 // Following the relocation group header are descriptions of each of the
1669 // relocations in the group. They consist of the following elements:
1671 // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is not set) the r_offset
1672 // delta for this relocation.
1673 // - (if RELOCATION_GROUPED_BY_INFO_FLAG is not set) the value of the r_info
1674 // field for this relocation.
1675 // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG is set and
1676 // RELOCATION_GROUPED_BY_ADDEND_FLAG is not set) the r_addend delta for
1679 size_t oldSize = relocData.size();
1681 relocData = {'A', 'P', 'S', '2'};
1682 raw_svector_ostream os(relocData);
1683 auto add = [&](int64_t v) { encodeSLEB128(v, os); };
1685 // The format header includes the number of relocations and the initial
1686 // offset (we set this to zero because the first relocation group will
1687 // perform the initial adjustment).
1691 std::vector<Elf_Rela> relatives, nonRelatives;
1693 for (const DynamicReloc &rel : relocs) {
1695 encodeDynamicReloc<ELFT>(getPartition().dynSymTab, &r, rel);
1697 if (r.getType(config->isMips64EL) == target->relativeRel)
1698 relatives.push_back(r);
1700 nonRelatives.push_back(r);
1703 llvm::sort(relatives, [](const Elf_Rel &a, const Elf_Rel &b) {
1704 return a.r_offset < b.r_offset;
1707 // Try to find groups of relative relocations which are spaced one word
1708 // apart from one another. These generally correspond to vtable entries. The
1709 // format allows these groups to be encoded using a sort of run-length
1710 // encoding, but each group will cost 7 bytes in addition to the offset from
1711 // the previous group, so it is only profitable to do this for groups of
1712 // size 8 or larger.
1713 std::vector<Elf_Rela> ungroupedRelatives;
1714 std::vector<std::vector<Elf_Rela>> relativeGroups;
1715 for (auto i = relatives.begin(), e = relatives.end(); i != e;) {
1716 std::vector<Elf_Rela> group;
1718 group.push_back(*i++);
1719 } while (i != e && (i - 1)->r_offset + config->wordsize == i->r_offset);
1721 if (group.size() < 8)
1722 ungroupedRelatives.insert(ungroupedRelatives.end(), group.begin(),
1725 relativeGroups.emplace_back(std::move(group));
1728 // For non-relative relocations, we would like to:
1729 // 1. Have relocations with the same symbol offset to be consecutive, so
1730 // that the runtime linker can speed-up symbol lookup by implementing an
1732 // 2. Group relocations by r_info to reduce the size of the relocation
1734 // Since the symbol offset is the high bits in r_info, sorting by r_info
1735 // allows us to do both.
1737 // For Rela, we also want to sort by r_addend when r_info is the same. This
1738 // enables us to group by r_addend as well.
1739 llvm::stable_sort(nonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
1740 if (a.r_info != b.r_info)
1741 return a.r_info < b.r_info;
1743 return a.r_addend < b.r_addend;
1747 // Group relocations with the same r_info. Note that each group emits a group
1748 // header and that may make the relocation section larger. It is hard to
1749 // estimate the size of a group header as the encoded size of that varies
1750 // based on r_info. However, we can approximate this trade-off by the number
1751 // of values encoded. Each group header contains 3 values, and each relocation
1752 // in a group encodes one less value, as compared to when it is not grouped.
1753 // Therefore, we only group relocations if there are 3 or more of them with
1756 // For Rela, the addend for most non-relative relocations is zero, and thus we
1757 // can usually get a smaller relocation section if we group relocations with 0
1759 std::vector<Elf_Rela> ungroupedNonRelatives;
1760 std::vector<std::vector<Elf_Rela>> nonRelativeGroups;
1761 for (auto i = nonRelatives.begin(), e = nonRelatives.end(); i != e;) {
1763 while (j != e && i->r_info == j->r_info &&
1764 (!config->isRela || i->r_addend == j->r_addend))
1766 if (j - i < 3 || (config->isRela && i->r_addend != 0))
1767 ungroupedNonRelatives.insert(ungroupedNonRelatives.end(), i, j);
1769 nonRelativeGroups.emplace_back(i, j);
1773 // Sort ungrouped relocations by offset to minimize the encoded length.
1774 llvm::sort(ungroupedNonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
1775 return a.r_offset < b.r_offset;
1778 unsigned hasAddendIfRela =
1779 config->isRela ? RELOCATION_GROUP_HAS_ADDEND_FLAG : 0;
1781 uint64_t offset = 0;
1782 uint64_t addend = 0;
1784 // Emit the run-length encoding for the groups of adjacent relative
1785 // relocations. Each group is represented using two groups in the packed
1786 // format. The first is used to set the current offset to the start of the
1787 // group (and also encodes the first relocation), and the second encodes the
1788 // remaining relocations.
1789 for (std::vector<Elf_Rela> &g : relativeGroups) {
1790 // The first relocation in the group.
1792 add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
1793 RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
1794 add(g[0].r_offset - offset);
1795 add(target->relativeRel);
1796 if (config->isRela) {
1797 add(g[0].r_addend - addend);
1798 addend = g[0].r_addend;
1801 // The remaining relocations.
1803 add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
1804 RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
1805 add(config->wordsize);
1806 add(target->relativeRel);
1807 if (config->isRela) {
1808 for (auto i = g.begin() + 1, e = g.end(); i != e; ++i) {
1809 add(i->r_addend - addend);
1810 addend = i->r_addend;
1814 offset = g.back().r_offset;
1817 // Now the ungrouped relatives.
1818 if (!ungroupedRelatives.empty()) {
1819 add(ungroupedRelatives.size());
1820 add(RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
1821 add(target->relativeRel);
1822 for (Elf_Rela &r : ungroupedRelatives) {
1823 add(r.r_offset - offset);
1824 offset = r.r_offset;
1825 if (config->isRela) {
1826 add(r.r_addend - addend);
1827 addend = r.r_addend;
1832 // Grouped non-relatives.
1833 for (ArrayRef<Elf_Rela> g : nonRelativeGroups) {
1835 add(RELOCATION_GROUPED_BY_INFO_FLAG);
1837 for (const Elf_Rela &r : g) {
1838 add(r.r_offset - offset);
1839 offset = r.r_offset;
1844 // Finally the ungrouped non-relative relocations.
1845 if (!ungroupedNonRelatives.empty()) {
1846 add(ungroupedNonRelatives.size());
1847 add(hasAddendIfRela);
1848 for (Elf_Rela &r : ungroupedNonRelatives) {
1849 add(r.r_offset - offset);
1850 offset = r.r_offset;
1852 if (config->isRela) {
1853 add(r.r_addend - addend);
1854 addend = r.r_addend;
1859 // Don't allow the section to shrink; otherwise the size of the section can
1860 // oscillate infinitely.
1861 if (relocData.size() < oldSize)
1862 relocData.append(oldSize - relocData.size(), 0);
1864 // Returns whether the section size changed. We need to keep recomputing both
1865 // section layout and the contents of this section until the size converges
1866 // because changing this section's size can affect section layout, which in
1867 // turn can affect the sizes of the LEB-encoded integers stored in this
1869 return relocData.size() != oldSize;
1872 template <class ELFT> RelrSection<ELFT>::RelrSection() {
1873 this->entsize = config->wordsize;
1876 template <class ELFT> bool RelrSection<ELFT>::updateAllocSize() {
1877 // This function computes the contents of an SHT_RELR packed relocation
1880 // Proposal for adding SHT_RELR sections to generic-abi is here:
1881 // https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
1883 // The encoded sequence of Elf64_Relr entries in a SHT_RELR section looks
1884 // like [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
1886 // i.e. start with an address, followed by any number of bitmaps. The address
1887 // entry encodes 1 relocation. The subsequent bitmap entries encode up to 63
1888 // relocations each, at subsequent offsets following the last address entry.
1890 // The bitmap entries must have 1 in the least significant bit. The assumption
1891 // here is that an address cannot have 1 in lsb. Odd addresses are not
1894 // Excluding the least significant bit in the bitmap, each non-zero bit in
1895 // the bitmap represents a relocation to be applied to a corresponding machine
1896 // word that follows the base address word. The second least significant bit
1897 // represents the machine word immediately following the initial address, and
1898 // each bit that follows represents the next word, in linear order. As such,
1899 // a single bitmap can encode up to 31 relocations in a 32-bit object, and
1900 // 63 relocations in a 64-bit object.
1902 // This encoding has a couple of interesting properties:
1903 // 1. Looking at any entry, it is clear whether it's an address or a bitmap:
1904 // even means address, odd means bitmap.
1905 // 2. Just a simple list of addresses is a valid encoding.
1907 size_t oldSize = relrRelocs.size();
1910 // Same as Config->Wordsize but faster because this is a compile-time
1912 const size_t wordsize = sizeof(typename ELFT::uint);
1914 // Number of bits to use for the relocation offsets bitmap.
1915 // Must be either 63 or 31.
1916 const size_t nBits = wordsize * 8 - 1;
1918 // Get offsets for all relative relocations and sort them.
1919 std::vector<uint64_t> offsets;
1920 for (const RelativeReloc &rel : relocs)
1921 offsets.push_back(rel.getOffset());
1922 llvm::sort(offsets);
1924 // For each leading relocation, find following ones that can be folded
1925 // as a bitmap and fold them.
1926 for (size_t i = 0, e = offsets.size(); i < e;) {
1927 // Add a leading relocation.
1928 relrRelocs.push_back(Elf_Relr(offsets[i]));
1929 uint64_t base = offsets[i] + wordsize;
1932 // Find foldable relocations to construct bitmaps.
1934 uint64_t bitmap = 0;
1937 uint64_t delta = offsets[i] - base;
1939 // If it is too far, it cannot be folded.
1940 if (delta >= nBits * wordsize)
1943 // If it is not a multiple of wordsize away, it cannot be folded.
1944 if (delta % wordsize)
1948 bitmap |= 1ULL << (delta / wordsize);
1955 relrRelocs.push_back(Elf_Relr((bitmap << 1) | 1));
1956 base += nBits * wordsize;
1960 // Don't allow the section to shrink; otherwise the size of the section can
1961 // oscillate infinitely. Trailing 1s do not decode to more relocations.
1962 if (relrRelocs.size() < oldSize) {
1963 log(".relr.dyn needs " + Twine(oldSize - relrRelocs.size()) +
1964 " padding word(s)");
1965 relrRelocs.resize(oldSize, Elf_Relr(1));
1968 return relrRelocs.size() != oldSize;
1971 SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &strTabSec)
1972 : SyntheticSection(strTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
1973 strTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
1975 strTabSec.isDynamic() ? ".dynsym" : ".symtab"),
1976 strTabSec(strTabSec) {}
1978 // Orders symbols according to their positions in the GOT,
1979 // in compliance with MIPS ABI rules.
1980 // See "Global Offset Table" in Chapter 5 in the following document
1981 // for detailed description:
1982 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1983 static bool sortMipsSymbols(const SymbolTableEntry &l,
1984 const SymbolTableEntry &r) {
1985 // Sort entries related to non-local preemptible symbols by GOT indexes.
1986 // All other entries go to the beginning of a dynsym in arbitrary order.
1987 if (l.sym->isInGot() && r.sym->isInGot())
1988 return l.sym->gotIndex < r.sym->gotIndex;
1989 if (!l.sym->isInGot() && !r.sym->isInGot())
1991 return !l.sym->isInGot();
1994 void SymbolTableBaseSection::finalizeContents() {
1995 if (OutputSection *sec = strTabSec.getParent())
1996 getParent()->link = sec->sectionIndex;
1998 if (this->type != SHT_DYNSYM) {
1999 sortSymTabSymbols();
2003 // If it is a .dynsym, there should be no local symbols, but we need
2004 // to do a few things for the dynamic linker.
2006 // Section's Info field has the index of the first non-local symbol.
2007 // Because the first symbol entry is a null entry, 1 is the first.
2008 getParent()->info = 1;
2010 if (getPartition().gnuHashTab) {
2011 // NB: It also sorts Symbols to meet the GNU hash table requirements.
2012 getPartition().gnuHashTab->addSymbols(symbols);
2013 } else if (config->emachine == EM_MIPS) {
2014 llvm::stable_sort(symbols, sortMipsSymbols);
2017 // Only the main partition's dynsym indexes are stored in the symbols
2018 // themselves. All other partitions use a lookup table.
2019 if (this == mainPart->dynSymTab) {
2021 for (const SymbolTableEntry &s : symbols)
2022 s.sym->dynsymIndex = ++i;
2026 // The ELF spec requires that all local symbols precede global symbols, so we
2027 // sort symbol entries in this function. (For .dynsym, we don't do that because
2028 // symbols for dynamic linking are inherently all globals.)
2030 // Aside from above, we put local symbols in groups starting with the STT_FILE
2031 // symbol. That is convenient for purpose of identifying where are local symbols
2033 void SymbolTableBaseSection::sortSymTabSymbols() {
2034 // Move all local symbols before global symbols.
2035 auto e = std::stable_partition(
2036 symbols.begin(), symbols.end(), [](const SymbolTableEntry &s) {
2037 return s.sym->isLocal() || s.sym->computeBinding() == STB_LOCAL;
2039 size_t numLocals = e - symbols.begin();
2040 getParent()->info = numLocals + 1;
2042 // We want to group the local symbols by file. For that we rebuild the local
2043 // part of the symbols vector. We do not need to care about the STT_FILE
2044 // symbols, they are already naturally placed first in each group. That
2045 // happens because STT_FILE is always the first symbol in the object and hence
2046 // precede all other local symbols we add for a file.
2047 MapVector<InputFile *, std::vector<SymbolTableEntry>> arr;
2048 for (const SymbolTableEntry &s : llvm::make_range(symbols.begin(), e))
2049 arr[s.sym->file].push_back(s);
2051 auto i = symbols.begin();
2052 for (std::pair<InputFile *, std::vector<SymbolTableEntry>> &p : arr)
2053 for (SymbolTableEntry &entry : p.second)
2057 void SymbolTableBaseSection::addSymbol(Symbol *b) {
2058 // Adding a local symbol to a .dynsym is a bug.
2059 assert(this->type != SHT_DYNSYM || !b->isLocal());
2061 bool hashIt = b->isLocal();
2062 symbols.push_back({b, strTabSec.addString(b->getName(), hashIt)});
2065 size_t SymbolTableBaseSection::getSymbolIndex(Symbol *sym) {
2066 if (this == mainPart->dynSymTab)
2067 return sym->dynsymIndex;
2069 // Initializes symbol lookup tables lazily. This is used only for -r,
2070 // -emit-relocs and dynsyms in partitions other than the main one.
2071 llvm::call_once(onceFlag, [&] {
2072 symbolIndexMap.reserve(symbols.size());
2074 for (const SymbolTableEntry &e : symbols) {
2075 if (e.sym->type == STT_SECTION)
2076 sectionIndexMap[e.sym->getOutputSection()] = ++i;
2078 symbolIndexMap[e.sym] = ++i;
2082 // Section symbols are mapped based on their output sections
2083 // to maintain their semantics.
2084 if (sym->type == STT_SECTION)
2085 return sectionIndexMap.lookup(sym->getOutputSection());
2086 return symbolIndexMap.lookup(sym);
2089 template <class ELFT>
2090 SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &strTabSec)
2091 : SymbolTableBaseSection(strTabSec) {
2092 this->entsize = sizeof(Elf_Sym);
2095 static BssSection *getCommonSec(Symbol *sym) {
2096 if (!config->defineCommon)
2097 if (auto *d = dyn_cast<Defined>(sym))
2098 return dyn_cast_or_null<BssSection>(d->section);
2102 static uint32_t getSymSectionIndex(Symbol *sym) {
2103 if (getCommonSec(sym))
2105 if (!isa<Defined>(sym) || sym->needsPltAddr)
2107 if (const OutputSection *os = sym->getOutputSection())
2108 return os->sectionIndex >= SHN_LORESERVE ? (uint32_t)SHN_XINDEX
2113 // Write the internal symbol table contents to the output symbol table.
2114 template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *buf) {
2115 // The first entry is a null entry as per the ELF spec.
2116 memset(buf, 0, sizeof(Elf_Sym));
2117 buf += sizeof(Elf_Sym);
2119 auto *eSym = reinterpret_cast<Elf_Sym *>(buf);
2121 for (SymbolTableEntry &ent : symbols) {
2122 Symbol *sym = ent.sym;
2123 bool isDefinedHere = type == SHT_SYMTAB || sym->partition == partition;
2125 // Set st_info and st_other.
2127 if (sym->isLocal()) {
2128 eSym->setBindingAndType(STB_LOCAL, sym->type);
2130 eSym->setBindingAndType(sym->computeBinding(), sym->type);
2131 eSym->setVisibility(sym->visibility);
2134 // The 3 most significant bits of st_other are used by OpenPOWER ABI.
2135 // See getPPC64GlobalEntryToLocalEntryOffset() for more details.
2136 if (config->emachine == EM_PPC64)
2137 eSym->st_other |= sym->stOther & 0xe0;
2139 eSym->st_name = ent.strTabOffset;
2141 eSym->st_shndx = getSymSectionIndex(ent.sym);
2145 // Copy symbol size if it is a defined symbol. st_size is not significant
2146 // for undefined symbols, so whether copying it or not is up to us if that's
2147 // the case. We'll leave it as zero because by not setting a value, we can
2148 // get the exact same outputs for two sets of input files that differ only
2149 // in undefined symbol size in DSOs.
2150 if (eSym->st_shndx == SHN_UNDEF || !isDefinedHere)
2153 eSym->st_size = sym->getSize();
2155 // st_value is usually an address of a symbol, but that has a
2156 // special meaning for uninstantiated common symbols (this can
2157 // occur if -r is given).
2158 if (BssSection *commonSec = getCommonSec(ent.sym))
2159 eSym->st_value = commonSec->alignment;
2160 else if (isDefinedHere)
2161 eSym->st_value = sym->getVA();
2168 // On MIPS we need to mark symbol which has a PLT entry and requires
2169 // pointer equality by STO_MIPS_PLT flag. That is necessary to help
2170 // dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
2171 // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
2172 if (config->emachine == EM_MIPS) {
2173 auto *eSym = reinterpret_cast<Elf_Sym *>(buf);
2175 for (SymbolTableEntry &ent : symbols) {
2176 Symbol *sym = ent.sym;
2177 if (sym->isInPlt() && sym->needsPltAddr)
2178 eSym->st_other |= STO_MIPS_PLT;
2179 if (isMicroMips()) {
2180 // We already set the less-significant bit for symbols
2181 // marked by the `STO_MIPS_MICROMIPS` flag and for microMIPS PLT
2182 // records. That allows us to distinguish such symbols in
2183 // the `MIPS<ELFT>::relocate()` routine. Now we should
2184 // clear that bit for non-dynamic symbol table, so tools
2185 // like `objdump` will be able to deal with a correct
2187 if (sym->isDefined() &&
2188 ((sym->stOther & STO_MIPS_MICROMIPS) || sym->needsPltAddr)) {
2189 if (!strTabSec.isDynamic())
2190 eSym->st_value &= ~1;
2191 eSym->st_other |= STO_MIPS_MICROMIPS;
2194 if (config->relocatable)
2195 if (auto *d = dyn_cast<Defined>(sym))
2196 if (isMipsPIC<ELFT>(d))
2197 eSym->st_other |= STO_MIPS_PIC;
2203 SymtabShndxSection::SymtabShndxSection()
2204 : SyntheticSection(0, SHT_SYMTAB_SHNDX, 4, ".symtab_shndx") {
2208 void SymtabShndxSection::writeTo(uint8_t *buf) {
2209 // We write an array of 32 bit values, where each value has 1:1 association
2210 // with an entry in .symtab. If the corresponding entry contains SHN_XINDEX,
2211 // we need to write actual index, otherwise, we must write SHN_UNDEF(0).
2212 buf += 4; // Ignore .symtab[0] entry.
2213 for (const SymbolTableEntry &entry : in.symTab->getSymbols()) {
2214 if (getSymSectionIndex(entry.sym) == SHN_XINDEX)
2215 write32(buf, entry.sym->getOutputSection()->sectionIndex);
2220 bool SymtabShndxSection::isNeeded() const {
2221 // SHT_SYMTAB can hold symbols with section indices values up to
2222 // SHN_LORESERVE. If we need more, we want to use extension SHT_SYMTAB_SHNDX
2223 // section. Problem is that we reveal the final section indices a bit too
2224 // late, and we do not know them here. For simplicity, we just always create
2225 // a .symtab_shndx section when the amount of output sections is huge.
2227 for (BaseCommand *base : script->sectionCommands)
2228 if (isa<OutputSection>(base))
2230 return size >= SHN_LORESERVE;
2233 void SymtabShndxSection::finalizeContents() {
2234 getParent()->link = in.symTab->getParent()->sectionIndex;
2237 size_t SymtabShndxSection::getSize() const {
2238 return in.symTab->getNumSymbols() * 4;
2241 // .hash and .gnu.hash sections contain on-disk hash tables that map
2242 // symbol names to their dynamic symbol table indices. Their purpose
2243 // is to help the dynamic linker resolve symbols quickly. If ELF files
2244 // don't have them, the dynamic linker has to do linear search on all
2245 // dynamic symbols, which makes programs slower. Therefore, a .hash
2246 // section is added to a DSO by default. A .gnu.hash is added if you
2247 // give the -hash-style=gnu or -hash-style=both option.
2249 // The Unix semantics of resolving dynamic symbols is somewhat expensive.
2250 // Each ELF file has a list of DSOs that the ELF file depends on and a
2251 // list of dynamic symbols that need to be resolved from any of the
2252 // DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
2253 // where m is the number of DSOs and n is the number of dynamic
2254 // symbols. For modern large programs, both m and n are large. So
2255 // making each step faster by using hash tables substantially
2256 // improves time to load programs.
2258 // (Note that this is not the only way to design the shared library.
2259 // For instance, the Windows DLL takes a different approach. On
2260 // Windows, each dynamic symbol has a name of DLL from which the symbol
2261 // has to be resolved. That makes the cost of symbol resolution O(n).
2262 // This disables some hacky techniques you can use on Unix such as
2263 // LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
2265 // Due to historical reasons, we have two different hash tables, .hash
2266 // and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
2267 // and better version of .hash. .hash is just an on-disk hash table, but
2268 // .gnu.hash has a bloom filter in addition to a hash table to skip
2269 // DSOs very quickly. If you are sure that your dynamic linker knows
2270 // about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
2271 // safe bet is to specify -hash-style=both for backward compatibility.
2272 GnuHashTableSection::GnuHashTableSection()
2273 : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, config->wordsize, ".gnu.hash") {
2276 void GnuHashTableSection::finalizeContents() {
2277 if (OutputSection *sec = getPartition().dynSymTab->getParent())
2278 getParent()->link = sec->sectionIndex;
2280 // Computes bloom filter size in word size. We want to allocate 12
2281 // bits for each symbol. It must be a power of two.
2282 if (symbols.empty()) {
2285 uint64_t numBits = symbols.size() * 12;
2286 maskWords = NextPowerOf2(numBits / (config->wordsize * 8));
2289 size = 16; // Header
2290 size += config->wordsize * maskWords; // Bloom filter
2291 size += nBuckets * 4; // Hash buckets
2292 size += symbols.size() * 4; // Hash values
2295 void GnuHashTableSection::writeTo(uint8_t *buf) {
2296 // The output buffer is not guaranteed to be zero-cleared because we pre-
2297 // fill executable sections with trap instructions. This is a precaution
2298 // for that case, which happens only when -no-rosegment is given.
2299 memset(buf, 0, size);
2302 write32(buf, nBuckets);
2303 write32(buf + 4, getPartition().dynSymTab->getNumSymbols() - symbols.size());
2304 write32(buf + 8, maskWords);
2305 write32(buf + 12, Shift2);
2308 // Write a bloom filter and a hash table.
2309 writeBloomFilter(buf);
2310 buf += config->wordsize * maskWords;
2311 writeHashTable(buf);
2314 // This function writes a 2-bit bloom filter. This bloom filter alone
2315 // usually filters out 80% or more of all symbol lookups [1].
2316 // The dynamic linker uses the hash table only when a symbol is not
2317 // filtered out by a bloom filter.
2319 // [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
2320 // p.9, https://www.akkadia.org/drepper/dsohowto.pdf
2321 void GnuHashTableSection::writeBloomFilter(uint8_t *buf) {
2322 unsigned c = config->is64 ? 64 : 32;
2323 for (const Entry &sym : symbols) {
2324 // When C = 64, we choose a word with bits [6:...] and set 1 to two bits in
2325 // the word using bits [0:5] and [26:31].
2326 size_t i = (sym.hash / c) & (maskWords - 1);
2327 uint64_t val = readUint(buf + i * config->wordsize);
2328 val |= uint64_t(1) << (sym.hash % c);
2329 val |= uint64_t(1) << ((sym.hash >> Shift2) % c);
2330 writeUint(buf + i * config->wordsize, val);
2334 void GnuHashTableSection::writeHashTable(uint8_t *buf) {
2335 uint32_t *buckets = reinterpret_cast<uint32_t *>(buf);
2336 uint32_t oldBucket = -1;
2337 uint32_t *values = buckets + nBuckets;
2338 for (auto i = symbols.begin(), e = symbols.end(); i != e; ++i) {
2339 // Write a hash value. It represents a sequence of chains that share the
2340 // same hash modulo value. The last element of each chain is terminated by
2342 uint32_t hash = i->hash;
2343 bool isLastInChain = (i + 1) == e || i->bucketIdx != (i + 1)->bucketIdx;
2344 hash = isLastInChain ? hash | 1 : hash & ~1;
2345 write32(values++, hash);
2347 if (i->bucketIdx == oldBucket)
2349 // Write a hash bucket. Hash buckets contain indices in the following hash
2351 write32(buckets + i->bucketIdx,
2352 getPartition().dynSymTab->getSymbolIndex(i->sym));
2353 oldBucket = i->bucketIdx;
2357 static uint32_t hashGnu(StringRef name) {
2359 for (uint8_t c : name)
2360 h = (h << 5) + h + c;
2364 // Add symbols to this symbol hash table. Note that this function
2365 // destructively sort a given vector -- which is needed because
2366 // GNU-style hash table places some sorting requirements.
2367 void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &v) {
2368 // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
2369 // its type correctly.
2370 std::vector<SymbolTableEntry>::iterator mid =
2371 std::stable_partition(v.begin(), v.end(), [&](const SymbolTableEntry &s) {
2372 return !s.sym->isDefined() || s.sym->partition != partition;
2375 // We chose load factor 4 for the on-disk hash table. For each hash
2376 // collision, the dynamic linker will compare a uint32_t hash value.
2377 // Since the integer comparison is quite fast, we believe we can
2378 // make the load factor even larger. 4 is just a conservative choice.
2380 // Note that we don't want to create a zero-sized hash table because
2381 // Android loader as of 2018 doesn't like a .gnu.hash containing such
2382 // table. If that's the case, we create a hash table with one unused
2384 nBuckets = std::max<size_t>((v.end() - mid) / 4, 1);
2389 for (SymbolTableEntry &ent : llvm::make_range(mid, v.end())) {
2390 Symbol *b = ent.sym;
2391 uint32_t hash = hashGnu(b->getName());
2392 uint32_t bucketIdx = hash % nBuckets;
2393 symbols.push_back({b, ent.strTabOffset, hash, bucketIdx});
2396 llvm::stable_sort(symbols, [](const Entry &l, const Entry &r) {
2397 return l.bucketIdx < r.bucketIdx;
2400 v.erase(mid, v.end());
2401 for (const Entry &ent : symbols)
2402 v.push_back({ent.sym, ent.strTabOffset});
2405 HashTableSection::HashTableSection()
2406 : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
2410 void HashTableSection::finalizeContents() {
2411 SymbolTableBaseSection *symTab = getPartition().dynSymTab;
2413 if (OutputSection *sec = symTab->getParent())
2414 getParent()->link = sec->sectionIndex;
2416 unsigned numEntries = 2; // nbucket and nchain.
2417 numEntries += symTab->getNumSymbols(); // The chain entries.
2419 // Create as many buckets as there are symbols.
2420 numEntries += symTab->getNumSymbols();
2421 this->size = numEntries * 4;
2424 void HashTableSection::writeTo(uint8_t *buf) {
2425 SymbolTableBaseSection *symTab = getPartition().dynSymTab;
2427 // See comment in GnuHashTableSection::writeTo.
2428 memset(buf, 0, size);
2430 unsigned numSymbols = symTab->getNumSymbols();
2432 uint32_t *p = reinterpret_cast<uint32_t *>(buf);
2433 write32(p++, numSymbols); // nbucket
2434 write32(p++, numSymbols); // nchain
2436 uint32_t *buckets = p;
2437 uint32_t *chains = p + numSymbols;
2439 for (const SymbolTableEntry &s : symTab->getSymbols()) {
2440 Symbol *sym = s.sym;
2441 StringRef name = sym->getName();
2442 unsigned i = sym->dynsymIndex;
2443 uint32_t hash = hashSysV(name) % numSymbols;
2444 chains[i] = buckets[hash];
2445 write32(buckets + hash, i);
2449 PltSection::PltSection()
2450 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
2451 headerSize(target->pltHeaderSize) {
2452 // On PowerPC, this section contains lazy symbol resolvers.
2453 if (config->emachine == EM_PPC64) {
2458 // On x86 when IBT is enabled, this section contains the second PLT (lazy
2459 // symbol resolvers).
2460 if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
2461 (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT))
2464 // The PLT needs to be writable on SPARC as the dynamic linker will
2465 // modify the instructions in the PLT entries.
2466 if (config->emachine == EM_SPARCV9)
2467 this->flags |= SHF_WRITE;
2470 void PltSection::writeTo(uint8_t *buf) {
2471 // At beginning of PLT, we have code to call the dynamic
2472 // linker to resolve dynsyms at runtime. Write such code.
2473 target->writePltHeader(buf);
2474 size_t off = headerSize;
2476 for (const Symbol *sym : entries) {
2477 target->writePlt(buf + off, *sym, getVA() + off);
2478 off += target->pltEntrySize;
2482 void PltSection::addEntry(Symbol &sym) {
2483 sym.pltIndex = entries.size();
2484 entries.push_back(&sym);
2487 size_t PltSection::getSize() const {
2488 return headerSize + entries.size() * target->pltEntrySize;
2491 bool PltSection::isNeeded() const {
2492 // For -z retpolineplt, .iplt needs the .plt header.
2493 return !entries.empty() || (config->zRetpolineplt && in.iplt->isNeeded());
2496 // Used by ARM to add mapping symbols in the PLT section, which aid
2498 void PltSection::addSymbols() {
2499 target->addPltHeaderSymbols(*this);
2501 size_t off = headerSize;
2502 for (size_t i = 0; i < entries.size(); ++i) {
2503 target->addPltSymbols(*this, off);
2504 off += target->pltEntrySize;
2508 IpltSection::IpltSection()
2509 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".iplt") {
2510 if (config->emachine == EM_PPC || config->emachine == EM_PPC64) {
2516 void IpltSection::writeTo(uint8_t *buf) {
2518 for (const Symbol *sym : entries) {
2519 target->writeIplt(buf + off, *sym, getVA() + off);
2520 off += target->ipltEntrySize;
2524 size_t IpltSection::getSize() const {
2525 return entries.size() * target->ipltEntrySize;
2528 void IpltSection::addEntry(Symbol &sym) {
2529 sym.pltIndex = entries.size();
2530 entries.push_back(&sym);
2533 // ARM uses mapping symbols to aid disassembly.
2534 void IpltSection::addSymbols() {
2536 for (size_t i = 0, e = entries.size(); i != e; ++i) {
2537 target->addPltSymbols(*this, off);
2538 off += target->pltEntrySize;
2542 PPC32GlinkSection::PPC32GlinkSection() {
2547 void PPC32GlinkSection::writeTo(uint8_t *buf) {
2548 writePPC32GlinkSection(buf, entries.size());
2551 size_t PPC32GlinkSection::getSize() const {
2552 return headerSize + entries.size() * target->pltEntrySize + footerSize;
2555 // This is an x86-only extra PLT section and used only when a security
2556 // enhancement feature called CET is enabled. In this comment, I'll explain what
2557 // the feature is and why we have two PLT sections if CET is enabled.
2559 // So, what does CET do? CET introduces a new restriction to indirect jump
2560 // instructions. CET works this way. Assume that CET is enabled. Then, if you
2561 // execute an indirect jump instruction, the processor verifies that a special
2562 // "landing pad" instruction (which is actually a repurposed NOP instruction and
2563 // now called "endbr32" or "endbr64") is at the jump target. If the jump target
2564 // does not start with that instruction, the processor raises an exception
2565 // instead of continuing executing code.
2567 // If CET is enabled, the compiler emits endbr to all locations where indirect
2568 // jumps may jump to.
2570 // This mechanism makes it extremely hard to transfer the control to a middle of
2571 // a function that is not supporsed to be a indirect jump target, preventing
2572 // certain types of attacks such as ROP or JOP.
2574 // Note that the processors in the market as of 2019 don't actually support the
2575 // feature. Only the spec is available at the moment.
2577 // Now, I'll explain why we have this extra PLT section for CET.
2579 // Since you can indirectly jump to a PLT entry, we have to make PLT entries
2580 // start with endbr. The problem is there's no extra space for endbr (which is 4
2581 // bytes long), as the PLT entry is only 16 bytes long and all bytes are already
2584 // In order to deal with the issue, we split a PLT entry into two PLT entries.
2585 // Remember that each PLT entry contains code to jump to an address read from
2586 // .got.plt AND code to resolve a dynamic symbol lazily. With the 2-PLT scheme,
2587 // the former code is written to .plt.sec, and the latter code is written to
2590 // Lazy symbol resolution in the 2-PLT scheme works in the usual way, except
2591 // that the regular .plt is now called .plt.sec and .plt is repurposed to
2592 // contain only code for lazy symbol resolution.
2594 // In other words, this is how the 2-PLT scheme works. Application code is
2595 // supposed to jump to .plt.sec to call an external function. Each .plt.sec
2596 // entry contains code to read an address from a corresponding .got.plt entry
2597 // and jump to that address. Addresses in .got.plt initially point to .plt, so
2598 // when an application calls an external function for the first time, the
2599 // control is transferred to a function that resolves a symbol name from
2600 // external shared object files. That function then rewrites a .got.plt entry
2601 // with a resolved address, so that the subsequent function calls directly jump
2602 // to a desired location from .plt.sec.
2604 // There is an open question as to whether the 2-PLT scheme was desirable or
2605 // not. We could have simply extended the PLT entry size to 32-bytes to
2606 // accommodate endbr, and that scheme would have been much simpler than the
2607 // 2-PLT scheme. One reason to split PLT was, by doing that, we could keep hot
2608 // code (.plt.sec) from cold code (.plt). But as far as I know no one proved
2609 // that the optimization actually makes a difference.
2611 // That said, the 2-PLT scheme is a part of the ABI, debuggers and other tools
2612 // depend on it, so we implement the ABI.
2613 IBTPltSection::IBTPltSection()
2614 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt") {}
2616 void IBTPltSection::writeTo(uint8_t *buf) {
2617 target->writeIBTPlt(buf, in.plt->getNumEntries());
2620 size_t IBTPltSection::getSize() const {
2621 // 16 is the header size of .plt.
2622 return 16 + in.plt->getNumEntries() * target->pltEntrySize;
2625 // The string hash function for .gdb_index.
2626 static uint32_t computeGdbHash(StringRef s) {
2629 h = h * 67 + toLower(c) - 113;
2633 GdbIndexSection::GdbIndexSection()
2634 : SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index") {}
2636 // Returns the desired size of an on-disk hash table for a .gdb_index section.
2637 // There's a tradeoff between size and collision rate. We aim 75% utilization.
2638 size_t GdbIndexSection::computeSymtabSize() const {
2639 return std::max<size_t>(NextPowerOf2(symbols.size() * 4 / 3), 1024);
2642 // Compute the output section size.
2643 void GdbIndexSection::initOutputSize() {
2644 size = sizeof(GdbIndexHeader) + computeSymtabSize() * 8;
2646 for (GdbChunk &chunk : chunks)
2647 size += chunk.compilationUnits.size() * 16 + chunk.addressAreas.size() * 20;
2649 // Add the constant pool size if exists.
2650 if (!symbols.empty()) {
2651 GdbSymbol &sym = symbols.back();
2652 size += sym.nameOff + sym.name.size() + 1;
2656 static std::vector<InputSection *> getDebugInfoSections() {
2657 std::vector<InputSection *> ret;
2658 for (InputSectionBase *s : inputSections)
2659 if (InputSection *isec = dyn_cast<InputSection>(s))
2660 if (isec->name == ".debug_info")
2661 ret.push_back(isec);
2665 static std::vector<GdbIndexSection::CuEntry> readCuList(DWARFContext &dwarf) {
2666 std::vector<GdbIndexSection::CuEntry> ret;
2667 for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units())
2668 ret.push_back({cu->getOffset(), cu->getLength() + 4});
2672 static std::vector<GdbIndexSection::AddressEntry>
2673 readAddressAreas(DWARFContext &dwarf, InputSection *sec) {
2674 std::vector<GdbIndexSection::AddressEntry> ret;
2677 for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units()) {
2678 if (Error e = cu->tryExtractDIEsIfNeeded(false)) {
2679 warn(toString(sec) + ": " + toString(std::move(e)));
2682 Expected<DWARFAddressRangesVector> ranges = cu->collectAddressRanges();
2684 warn(toString(sec) + ": " + toString(ranges.takeError()));
2688 ArrayRef<InputSectionBase *> sections = sec->file->getSections();
2689 for (DWARFAddressRange &r : *ranges) {
2690 if (r.SectionIndex == -1ULL)
2692 // Range list with zero size has no effect.
2693 InputSectionBase *s = sections[r.SectionIndex];
2694 if (s && s != &InputSection::discarded && s->isLive())
2695 if (r.LowPC != r.HighPC)
2696 ret.push_back({cast<InputSection>(s), r.LowPC, r.HighPC, cuIdx});
2704 template <class ELFT>
2705 static std::vector<GdbIndexSection::NameAttrEntry>
2706 readPubNamesAndTypes(const LLDDwarfObj<ELFT> &obj,
2707 const std::vector<GdbIndexSection::CuEntry> &cus) {
2708 const LLDDWARFSection &pubNames = obj.getGnuPubnamesSection();
2709 const LLDDWARFSection &pubTypes = obj.getGnuPubtypesSection();
2711 std::vector<GdbIndexSection::NameAttrEntry> ret;
2712 for (const LLDDWARFSection *pub : {&pubNames, &pubTypes}) {
2713 DWARFDataExtractor data(obj, *pub, config->isLE, config->wordsize);
2714 DWARFDebugPubTable table;
2715 table.extract(data, /*GnuStyle=*/true, [&](Error e) {
2716 warn(toString(pub->sec) + ": " + toString(std::move(e)));
2718 for (const DWARFDebugPubTable::Set &set : table.getData()) {
2719 // The value written into the constant pool is kind << 24 | cuIndex. As we
2720 // don't know how many compilation units precede this object to compute
2721 // cuIndex, we compute (kind << 24 | cuIndexInThisObject) instead, and add
2722 // the number of preceding compilation units later.
2723 uint32_t i = llvm::partition_point(cus,
2724 [&](GdbIndexSection::CuEntry cu) {
2725 return cu.cuOffset < set.Offset;
2728 for (const DWARFDebugPubTable::Entry &ent : set.Entries)
2729 ret.push_back({{ent.Name, computeGdbHash(ent.Name)},
2730 (ent.Descriptor.toBits() << 24) | i});
2736 // Create a list of symbols from a given list of symbol names and types
2737 // by uniquifying them by name.
2738 static std::vector<GdbIndexSection::GdbSymbol>
2739 createSymbols(ArrayRef<std::vector<GdbIndexSection::NameAttrEntry>> nameAttrs,
2740 const std::vector<GdbIndexSection::GdbChunk> &chunks) {
2741 using GdbSymbol = GdbIndexSection::GdbSymbol;
2742 using NameAttrEntry = GdbIndexSection::NameAttrEntry;
2744 // For each chunk, compute the number of compilation units preceding it.
2746 std::vector<uint32_t> cuIdxs(chunks.size());
2747 for (uint32_t i = 0, e = chunks.size(); i != e; ++i) {
2749 cuIdx += chunks[i].compilationUnits.size();
2752 // The number of symbols we will handle in this function is of the order
2753 // of millions for very large executables, so we use multi-threading to
2755 constexpr size_t numShards = 32;
2756 size_t concurrency = PowerOf2Floor(
2757 std::min<size_t>(hardware_concurrency(parallel::strategy.ThreadsRequested)
2758 .compute_thread_count(),
2761 // A sharded map to uniquify symbols by name.
2762 std::vector<DenseMap<CachedHashStringRef, size_t>> map(numShards);
2763 size_t shift = 32 - countTrailingZeros(numShards);
2765 // Instantiate GdbSymbols while uniqufying them by name.
2766 std::vector<std::vector<GdbSymbol>> symbols(numShards);
2767 parallelForEachN(0, concurrency, [&](size_t threadId) {
2769 for (ArrayRef<NameAttrEntry> entries : nameAttrs) {
2770 for (const NameAttrEntry &ent : entries) {
2771 size_t shardId = ent.name.hash() >> shift;
2772 if ((shardId & (concurrency - 1)) != threadId)
2775 uint32_t v = ent.cuIndexAndAttrs + cuIdxs[i];
2776 size_t &idx = map[shardId][ent.name];
2778 symbols[shardId][idx - 1].cuVector.push_back(v);
2782 idx = symbols[shardId].size() + 1;
2783 symbols[shardId].push_back({ent.name, {v}, 0, 0});
2789 size_t numSymbols = 0;
2790 for (ArrayRef<GdbSymbol> v : symbols)
2791 numSymbols += v.size();
2793 // The return type is a flattened vector, so we'll copy each vector
2795 std::vector<GdbSymbol> ret;
2796 ret.reserve(numSymbols);
2797 for (std::vector<GdbSymbol> &vec : symbols)
2798 for (GdbSymbol &sym : vec)
2799 ret.push_back(std::move(sym));
2801 // CU vectors and symbol names are adjacent in the output file.
2802 // We can compute their offsets in the output file now.
2804 for (GdbSymbol &sym : ret) {
2805 sym.cuVectorOff = off;
2806 off += (sym.cuVector.size() + 1) * 4;
2808 for (GdbSymbol &sym : ret) {
2810 off += sym.name.size() + 1;
2816 // Returns a newly-created .gdb_index section.
2817 template <class ELFT> GdbIndexSection *GdbIndexSection::create() {
2818 std::vector<InputSection *> sections = getDebugInfoSections();
2820 // .debug_gnu_pub{names,types} are useless in executables.
2821 // They are present in input object files solely for creating
2822 // a .gdb_index. So we can remove them from the output.
2823 for (InputSectionBase *s : inputSections)
2824 if (s->name == ".debug_gnu_pubnames" || s->name == ".debug_gnu_pubtypes")
2827 std::vector<GdbChunk> chunks(sections.size());
2828 std::vector<std::vector<NameAttrEntry>> nameAttrs(sections.size());
2830 parallelForEachN(0, sections.size(), [&](size_t i) {
2831 // To keep memory usage low, we don't want to keep cached DWARFContext, so
2832 // avoid getDwarf() here.
2833 ObjFile<ELFT> *file = sections[i]->getFile<ELFT>();
2834 DWARFContext dwarf(std::make_unique<LLDDwarfObj<ELFT>>(file));
2836 chunks[i].sec = sections[i];
2837 chunks[i].compilationUnits = readCuList(dwarf);
2838 chunks[i].addressAreas = readAddressAreas(dwarf, sections[i]);
2839 nameAttrs[i] = readPubNamesAndTypes<ELFT>(
2840 static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj()),
2841 chunks[i].compilationUnits);
2844 auto *ret = make<GdbIndexSection>();
2845 ret->chunks = std::move(chunks);
2846 ret->symbols = createSymbols(nameAttrs, ret->chunks);
2847 ret->initOutputSize();
2851 void GdbIndexSection::writeTo(uint8_t *buf) {
2852 // Write the header.
2853 auto *hdr = reinterpret_cast<GdbIndexHeader *>(buf);
2854 uint8_t *start = buf;
2856 buf += sizeof(*hdr);
2858 // Write the CU list.
2859 hdr->cuListOff = buf - start;
2860 for (GdbChunk &chunk : chunks) {
2861 for (CuEntry &cu : chunk.compilationUnits) {
2862 write64le(buf, chunk.sec->outSecOff + cu.cuOffset);
2863 write64le(buf + 8, cu.cuLength);
2868 // Write the address area.
2869 hdr->cuTypesOff = buf - start;
2870 hdr->addressAreaOff = buf - start;
2872 for (GdbChunk &chunk : chunks) {
2873 for (AddressEntry &e : chunk.addressAreas) {
2874 uint64_t baseAddr = e.section->getVA(0);
2875 write64le(buf, baseAddr + e.lowAddress);
2876 write64le(buf + 8, baseAddr + e.highAddress);
2877 write32le(buf + 16, e.cuIndex + cuOff);
2880 cuOff += chunk.compilationUnits.size();
2883 // Write the on-disk open-addressing hash table containing symbols.
2884 hdr->symtabOff = buf - start;
2885 size_t symtabSize = computeSymtabSize();
2886 uint32_t mask = symtabSize - 1;
2888 for (GdbSymbol &sym : symbols) {
2889 uint32_t h = sym.name.hash();
2890 uint32_t i = h & mask;
2891 uint32_t step = ((h * 17) & mask) | 1;
2893 while (read32le(buf + i * 8))
2894 i = (i + step) & mask;
2896 write32le(buf + i * 8, sym.nameOff);
2897 write32le(buf + i * 8 + 4, sym.cuVectorOff);
2900 buf += symtabSize * 8;
2902 // Write the string pool.
2903 hdr->constantPoolOff = buf - start;
2904 parallelForEach(symbols, [&](GdbSymbol &sym) {
2905 memcpy(buf + sym.nameOff, sym.name.data(), sym.name.size());
2908 // Write the CU vectors.
2909 for (GdbSymbol &sym : symbols) {
2910 write32le(buf, sym.cuVector.size());
2912 for (uint32_t val : sym.cuVector) {
2913 write32le(buf, val);
2919 bool GdbIndexSection::isNeeded() const { return !chunks.empty(); }
2921 EhFrameHeader::EhFrameHeader()
2922 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".eh_frame_hdr") {}
2924 void EhFrameHeader::writeTo(uint8_t *buf) {
2925 // Unlike most sections, the EhFrameHeader section is written while writing
2926 // another section, namely EhFrameSection, which calls the write() function
2927 // below from its writeTo() function. This is necessary because the contents
2928 // of EhFrameHeader depend on the relocated contents of EhFrameSection and we
2929 // don't know which order the sections will be written in.
2932 // .eh_frame_hdr contains a binary search table of pointers to FDEs.
2933 // Each entry of the search table consists of two values,
2934 // the starting PC from where FDEs covers, and the FDE's address.
2935 // It is sorted by PC.
2936 void EhFrameHeader::write() {
2937 uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff;
2938 using FdeData = EhFrameSection::FdeData;
2940 std::vector<FdeData> fdes = getPartition().ehFrame->getFdeData();
2943 buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
2944 buf[2] = DW_EH_PE_udata4;
2945 buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
2947 getPartition().ehFrame->getParent()->addr - this->getVA() - 4);
2948 write32(buf + 8, fdes.size());
2951 for (FdeData &fde : fdes) {
2952 write32(buf, fde.pcRel);
2953 write32(buf + 4, fde.fdeVARel);
2958 size_t EhFrameHeader::getSize() const {
2959 // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
2960 return 12 + getPartition().ehFrame->numFdes * 8;
2963 bool EhFrameHeader::isNeeded() const {
2964 return isLive() && getPartition().ehFrame->isNeeded();
2967 VersionDefinitionSection::VersionDefinitionSection()
2968 : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
2969 ".gnu.version_d") {}
2971 StringRef VersionDefinitionSection::getFileDefName() {
2972 if (!getPartition().name.empty())
2973 return getPartition().name;
2974 if (!config->soName.empty())
2975 return config->soName;
2976 return config->outputFile;
2979 void VersionDefinitionSection::finalizeContents() {
2980 fileDefNameOff = getPartition().dynStrTab->addString(getFileDefName());
2981 for (const VersionDefinition &v : namedVersionDefs())
2982 verDefNameOffs.push_back(getPartition().dynStrTab->addString(v.name));
2984 if (OutputSection *sec = getPartition().dynStrTab->getParent())
2985 getParent()->link = sec->sectionIndex;
2987 // sh_info should be set to the number of definitions. This fact is missed in
2988 // documentation, but confirmed by binutils community:
2989 // https://sourceware.org/ml/binutils/2014-11/msg00355.html
2990 getParent()->info = getVerDefNum();
2993 void VersionDefinitionSection::writeOne(uint8_t *buf, uint32_t index,
2994 StringRef name, size_t nameOff) {
2995 uint16_t flags = index == 1 ? VER_FLG_BASE : 0;
2998 write16(buf, 1); // vd_version
2999 write16(buf + 2, flags); // vd_flags
3000 write16(buf + 4, index); // vd_ndx
3001 write16(buf + 6, 1); // vd_cnt
3002 write32(buf + 8, hashSysV(name)); // vd_hash
3003 write32(buf + 12, 20); // vd_aux
3004 write32(buf + 16, 28); // vd_next
3007 write32(buf + 20, nameOff); // vda_name
3008 write32(buf + 24, 0); // vda_next
3011 void VersionDefinitionSection::writeTo(uint8_t *buf) {
3012 writeOne(buf, 1, getFileDefName(), fileDefNameOff);
3014 auto nameOffIt = verDefNameOffs.begin();
3015 for (const VersionDefinition &v : namedVersionDefs()) {
3017 writeOne(buf, v.id, v.name, *nameOffIt++);
3020 // Need to terminate the last version definition.
3021 write32(buf + 16, 0); // vd_next
3024 size_t VersionDefinitionSection::getSize() const {
3025 return EntrySize * getVerDefNum();
3028 // .gnu.version is a table where each entry is 2 byte long.
3029 VersionTableSection::VersionTableSection()
3030 : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
3035 void VersionTableSection::finalizeContents() {
3036 // At the moment of june 2016 GNU docs does not mention that sh_link field
3037 // should be set, but Sun docs do. Also readelf relies on this field.
3038 getParent()->link = getPartition().dynSymTab->getParent()->sectionIndex;
3041 size_t VersionTableSection::getSize() const {
3042 return (getPartition().dynSymTab->getSymbols().size() + 1) * 2;
3045 void VersionTableSection::writeTo(uint8_t *buf) {
3047 for (const SymbolTableEntry &s : getPartition().dynSymTab->getSymbols()) {
3048 write16(buf, s.sym->versionId);
3053 bool VersionTableSection::isNeeded() const {
3055 (getPartition().verDef || getPartition().verNeed->isNeeded());
3058 void elf::addVerneed(Symbol *ss) {
3059 auto &file = cast<SharedFile>(*ss->file);
3060 if (ss->verdefIndex == VER_NDX_GLOBAL) {
3061 ss->versionId = VER_NDX_GLOBAL;
3065 if (file.vernauxs.empty())
3066 file.vernauxs.resize(file.verdefs.size());
3068 // Select a version identifier for the vernaux data structure, if we haven't
3069 // already allocated one. The verdef identifiers cover the range
3070 // [1..getVerDefNum()]; this causes the vernaux identifiers to start from
3071 // getVerDefNum()+1.
3072 if (file.vernauxs[ss->verdefIndex] == 0)
3073 file.vernauxs[ss->verdefIndex] = ++SharedFile::vernauxNum + getVerDefNum();
3075 ss->versionId = file.vernauxs[ss->verdefIndex];
3078 template <class ELFT>
3079 VersionNeedSection<ELFT>::VersionNeedSection()
3080 : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
3081 ".gnu.version_r") {}
3083 template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
3084 for (SharedFile *f : sharedFiles) {
3085 if (f->vernauxs.empty())
3087 verneeds.emplace_back();
3088 Verneed &vn = verneeds.back();
3089 vn.nameStrTab = getPartition().dynStrTab->addString(f->soName);
3090 for (unsigned i = 0; i != f->vernauxs.size(); ++i) {
3091 if (f->vernauxs[i] == 0)
3094 reinterpret_cast<const typename ELFT::Verdef *>(f->verdefs[i]);
3095 vn.vernauxs.push_back(
3096 {verdef->vd_hash, f->vernauxs[i],
3097 getPartition().dynStrTab->addString(f->getStringTable().data() +
3098 verdef->getAux()->vda_name)});
3102 if (OutputSection *sec = getPartition().dynStrTab->getParent())
3103 getParent()->link = sec->sectionIndex;
3104 getParent()->info = verneeds.size();
3107 template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *buf) {
3108 // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
3109 auto *verneed = reinterpret_cast<Elf_Verneed *>(buf);
3110 auto *vernaux = reinterpret_cast<Elf_Vernaux *>(verneed + verneeds.size());
3112 for (auto &vn : verneeds) {
3113 // Create an Elf_Verneed for this DSO.
3114 verneed->vn_version = 1;
3115 verneed->vn_cnt = vn.vernauxs.size();
3116 verneed->vn_file = vn.nameStrTab;
3118 reinterpret_cast<char *>(vernaux) - reinterpret_cast<char *>(verneed);
3119 verneed->vn_next = sizeof(Elf_Verneed);
3122 // Create the Elf_Vernauxs for this Elf_Verneed.
3123 for (auto &vna : vn.vernauxs) {
3124 vernaux->vna_hash = vna.hash;
3125 vernaux->vna_flags = 0;
3126 vernaux->vna_other = vna.verneedIndex;
3127 vernaux->vna_name = vna.nameStrTab;
3128 vernaux->vna_next = sizeof(Elf_Vernaux);
3132 vernaux[-1].vna_next = 0;
3134 verneed[-1].vn_next = 0;
3137 template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
3138 return verneeds.size() * sizeof(Elf_Verneed) +
3139 SharedFile::vernauxNum * sizeof(Elf_Vernaux);
3142 template <class ELFT> bool VersionNeedSection<ELFT>::isNeeded() const {
3143 return isLive() && SharedFile::vernauxNum != 0;
3146 void MergeSyntheticSection::addSection(MergeInputSection *ms) {
3148 sections.push_back(ms);
3149 assert(alignment == ms->alignment || !(ms->flags & SHF_STRINGS));
3150 alignment = std::max(alignment, ms->alignment);
3153 MergeTailSection::MergeTailSection(StringRef name, uint32_t type,
3154 uint64_t flags, uint32_t alignment)
3155 : MergeSyntheticSection(name, type, flags, alignment),
3156 builder(StringTableBuilder::RAW, alignment) {}
3158 size_t MergeTailSection::getSize() const { return builder.getSize(); }
3160 void MergeTailSection::writeTo(uint8_t *buf) { builder.write(buf); }
3162 void MergeTailSection::finalizeContents() {
3163 // Add all string pieces to the string table builder to create section
3165 for (MergeInputSection *sec : sections)
3166 for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
3167 if (sec->pieces[i].live)
3168 builder.add(sec->getData(i));
3170 // Fix the string table content. After this, the contents will never change.
3173 // finalize() fixed tail-optimized strings, so we can now get
3174 // offsets of strings. Get an offset for each string and save it
3175 // to a corresponding SectionPiece for easy access.
3176 for (MergeInputSection *sec : sections)
3177 for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
3178 if (sec->pieces[i].live)
3179 sec->pieces[i].outputOff = builder.getOffset(sec->getData(i));
3182 void MergeNoTailSection::writeTo(uint8_t *buf) {
3183 for (size_t i = 0; i < numShards; ++i)
3184 shards[i].write(buf + shardOffsets[i]);
3187 // This function is very hot (i.e. it can take several seconds to finish)
3188 // because sometimes the number of inputs is in an order of magnitude of
3189 // millions. So, we use multi-threading.
3191 // For any strings S and T, we know S is not mergeable with T if S's hash
3192 // value is different from T's. If that's the case, we can safely put S and
3193 // T into different string builders without worrying about merge misses.
3194 // We do it in parallel.
3195 void MergeNoTailSection::finalizeContents() {
3196 // Initializes string table builders.
3197 for (size_t i = 0; i < numShards; ++i)
3198 shards.emplace_back(StringTableBuilder::RAW, alignment);
3200 // Concurrency level. Must be a power of 2 to avoid expensive modulo
3201 // operations in the following tight loop.
3202 size_t concurrency = PowerOf2Floor(
3203 std::min<size_t>(hardware_concurrency(parallel::strategy.ThreadsRequested)
3204 .compute_thread_count(),
3207 // Add section pieces to the builders.
3208 parallelForEachN(0, concurrency, [&](size_t threadId) {
3209 for (MergeInputSection *sec : sections) {
3210 for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) {
3211 if (!sec->pieces[i].live)
3213 size_t shardId = getShardId(sec->pieces[i].hash);
3214 if ((shardId & (concurrency - 1)) == threadId)
3215 sec->pieces[i].outputOff = shards[shardId].add(sec->getData(i));
3220 // Compute an in-section offset for each shard.
3222 for (size_t i = 0; i < numShards; ++i) {
3223 shards[i].finalizeInOrder();
3224 if (shards[i].getSize() > 0)
3225 off = alignTo(off, alignment);
3226 shardOffsets[i] = off;
3227 off += shards[i].getSize();
3231 // So far, section pieces have offsets from beginning of shards, but
3232 // we want offsets from beginning of the whole section. Fix them.
3233 parallelForEach(sections, [&](MergeInputSection *sec) {
3234 for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
3235 if (sec->pieces[i].live)
3236 sec->pieces[i].outputOff +=
3237 shardOffsets[getShardId(sec->pieces[i].hash)];
3241 MergeSyntheticSection *elf::createMergeSynthetic(StringRef name, uint32_t type,
3243 uint32_t alignment) {
3244 bool shouldTailMerge = (flags & SHF_STRINGS) && config->optimize >= 2;
3245 if (shouldTailMerge)
3246 return make<MergeTailSection>(name, type, flags, alignment);
3247 return make<MergeNoTailSection>(name, type, flags, alignment);
3250 template <class ELFT> void elf::splitSections() {
3251 llvm::TimeTraceScope timeScope("Split sections");
3252 // splitIntoPieces needs to be called on each MergeInputSection
3253 // before calling finalizeContents().
3254 parallelForEach(inputSections, [](InputSectionBase *sec) {
3255 if (auto *s = dyn_cast<MergeInputSection>(sec))
3256 s->splitIntoPieces();
3257 else if (auto *eh = dyn_cast<EhInputSection>(sec))
3262 MipsRldMapSection::MipsRldMapSection()
3263 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
3266 ARMExidxSyntheticSection::ARMExidxSyntheticSection()
3267 : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
3268 config->wordsize, ".ARM.exidx") {}
3270 static InputSection *findExidxSection(InputSection *isec) {
3271 for (InputSection *d : isec->dependentSections)
3272 if (d->type == SHT_ARM_EXIDX && d->isLive())
3277 static bool isValidExidxSectionDep(InputSection *isec) {
3278 return (isec->flags & SHF_ALLOC) && (isec->flags & SHF_EXECINSTR) &&
3279 isec->getSize() > 0;
3282 bool ARMExidxSyntheticSection::addSection(InputSection *isec) {
3283 if (isec->type == SHT_ARM_EXIDX) {
3284 if (InputSection *dep = isec->getLinkOrderDep())
3285 if (isValidExidxSectionDep(dep)) {
3286 exidxSections.push_back(isec);
3287 // Every exidxSection is 8 bytes, we need an estimate of
3288 // size before assignAddresses can be called. Final size
3289 // will only be known after finalize is called.
3295 if (isValidExidxSectionDep(isec)) {
3296 executableSections.push_back(isec);
3300 // FIXME: we do not output a relocation section when --emit-relocs is used
3301 // as we do not have relocation sections for linker generated table entries
3302 // and we would have to erase at a late stage relocations from merged entries.
3303 // Given that exception tables are already position independent and a binary
3304 // analyzer could derive the relocations we choose to erase the relocations.
3305 if (config->emitRelocs && isec->type == SHT_REL)
3306 if (InputSectionBase *ex = isec->getRelocatedSection())
3307 if (isa<InputSection>(ex) && ex->type == SHT_ARM_EXIDX)
3313 // References to .ARM.Extab Sections have bit 31 clear and are not the
3314 // special EXIDX_CANTUNWIND bit-pattern.
3315 static bool isExtabRef(uint32_t unwind) {
3316 return (unwind & 0x80000000) == 0 && unwind != 0x1;
3319 // Return true if the .ARM.exidx section Cur can be merged into the .ARM.exidx
3320 // section Prev, where Cur follows Prev in the table. This can be done if the
3321 // unwinding instructions in Cur are identical to Prev. Linker generated
3322 // EXIDX_CANTUNWIND entries are represented by nullptr as they do not have an
3324 static bool isDuplicateArmExidxSec(InputSection *prev, InputSection *cur) {
3330 // Get the last table Entry from the previous .ARM.exidx section. If Prev is
3331 // nullptr then it will be a synthesized EXIDX_CANTUNWIND entry.
3332 ExidxEntry prevEntry = {ulittle32_t(0), ulittle32_t(1)};
3334 prevEntry = prev->getDataAs<ExidxEntry>().back();
3335 if (isExtabRef(prevEntry.unwind))
3338 // We consider the unwind instructions of an .ARM.exidx table entry
3339 // a duplicate if the previous unwind instructions if:
3340 // - Both are the special EXIDX_CANTUNWIND.
3341 // - Both are the same inline unwind instructions.
3342 // We do not attempt to follow and check links into .ARM.extab tables as
3343 // consecutive identical entries are rare and the effort to check that they
3344 // are identical is high.
3346 // If Cur is nullptr then this is synthesized EXIDX_CANTUNWIND entry.
3348 return prevEntry.unwind == 1;
3350 for (const ExidxEntry entry : cur->getDataAs<ExidxEntry>())
3351 if (isExtabRef(entry.unwind) || entry.unwind != prevEntry.unwind)
3354 // All table entries in this .ARM.exidx Section can be merged into the
3355 // previous Section.
3359 // The .ARM.exidx table must be sorted in ascending order of the address of the
3360 // functions the table describes. Optionally duplicate adjacent table entries
3361 // can be removed. At the end of the function the executableSections must be
3362 // sorted in ascending order of address, Sentinel is set to the InputSection
3363 // with the highest address and any InputSections that have mergeable
3364 // .ARM.exidx table entries are removed from it.
3365 void ARMExidxSyntheticSection::finalizeContents() {
3366 // The executableSections and exidxSections that we use to derive the final
3367 // contents of this SyntheticSection are populated before
3368 // processSectionCommands() and ICF. A /DISCARD/ entry in SECTIONS command or
3369 // ICF may remove executable InputSections and their dependent .ARM.exidx
3370 // section that we recorded earlier.
3371 auto isDiscarded = [](const InputSection *isec) { return !isec->isLive(); };
3372 llvm::erase_if(exidxSections, isDiscarded);
3373 // We need to remove discarded InputSections and InputSections without
3374 // .ARM.exidx sections that if we generated the .ARM.exidx it would be out
3376 auto isDiscardedOrOutOfRange = [this](InputSection *isec) {
3377 if (!isec->isLive())
3379 if (findExidxSection(isec))
3381 int64_t off = static_cast<int64_t>(isec->getVA() - getVA());
3382 return off != llvm::SignExtend64(off, 31);
3384 llvm::erase_if(executableSections, isDiscardedOrOutOfRange);
3386 // Sort the executable sections that may or may not have associated
3387 // .ARM.exidx sections by order of ascending address. This requires the
3388 // relative positions of InputSections and OutputSections to be known.
3389 auto compareByFilePosition = [](const InputSection *a,
3390 const InputSection *b) {
3391 OutputSection *aOut = a->getParent();
3392 OutputSection *bOut = b->getParent();
3395 return aOut->addr < bOut->addr;
3396 return a->outSecOff < b->outSecOff;
3398 llvm::stable_sort(executableSections, compareByFilePosition);
3399 sentinel = executableSections.back();
3400 // Optionally merge adjacent duplicate entries.
3401 if (config->mergeArmExidx) {
3402 std::vector<InputSection *> selectedSections;
3403 selectedSections.reserve(executableSections.size());
3404 selectedSections.push_back(executableSections[0]);
3406 for (size_t i = 1; i < executableSections.size(); ++i) {
3407 InputSection *ex1 = findExidxSection(executableSections[prev]);
3408 InputSection *ex2 = findExidxSection(executableSections[i]);
3409 if (!isDuplicateArmExidxSec(ex1, ex2)) {
3410 selectedSections.push_back(executableSections[i]);
3414 executableSections = std::move(selectedSections);
3419 for (InputSection *isec : executableSections) {
3420 if (InputSection *d = findExidxSection(isec)) {
3421 d->outSecOff = offset;
3422 d->parent = getParent();
3423 offset += d->getSize();
3428 // Size includes Sentinel.
3432 InputSection *ARMExidxSyntheticSection::getLinkOrderDep() const {
3433 return executableSections.front();
3436 // To write the .ARM.exidx table from the ExecutableSections we have three cases
3437 // 1.) The InputSection has a .ARM.exidx InputSection in its dependent sections.
3438 // We write the .ARM.exidx section contents and apply its relocations.
3439 // 2.) The InputSection does not have a dependent .ARM.exidx InputSection. We
3440 // must write the contents of an EXIDX_CANTUNWIND directly. We use the
3441 // start of the InputSection as the purpose of the linker generated
3442 // section is to terminate the address range of the previous entry.
3443 // 3.) A trailing EXIDX_CANTUNWIND sentinel section is required at the end of
3444 // the table to terminate the address range of the final entry.
3445 void ARMExidxSyntheticSection::writeTo(uint8_t *buf) {
3447 const uint8_t cantUnwindData[8] = {0, 0, 0, 0, // PREL31 to target
3448 1, 0, 0, 0}; // EXIDX_CANTUNWIND
3450 uint64_t offset = 0;
3451 for (InputSection *isec : executableSections) {
3452 assert(isec->getParent() != nullptr);
3453 if (InputSection *d = findExidxSection(isec)) {
3454 memcpy(buf + offset, d->data().data(), d->data().size());
3455 d->relocateAlloc(buf, buf + d->getSize());
3456 offset += d->getSize();
3458 // A Linker generated CANTUNWIND section.
3459 memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData));
3460 uint64_t s = isec->getVA();
3461 uint64_t p = getVA() + offset;
3462 target->relocateNoSym(buf + offset, R_ARM_PREL31, s - p);
3467 memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData));
3468 uint64_t s = sentinel->getVA(sentinel->getSize());
3469 uint64_t p = getVA() + offset;
3470 target->relocateNoSym(buf + offset, R_ARM_PREL31, s - p);
3471 assert(size == offset + 8);
3474 bool ARMExidxSyntheticSection::isNeeded() const {
3475 return llvm::find_if(exidxSections, [](InputSection *isec) {
3476 return isec->isLive();
3477 }) != exidxSections.end();
3480 bool ARMExidxSyntheticSection::classof(const SectionBase *d) {
3481 return d->kind() == InputSectionBase::Synthetic && d->type == SHT_ARM_EXIDX;
3484 ThunkSection::ThunkSection(OutputSection *os, uint64_t off)
3485 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 4,
3488 this->outSecOff = off;
3491 size_t ThunkSection::getSize() const {
3492 if (roundUpSizeForErrata)
3493 return alignTo(size, 4096);
3497 void ThunkSection::addThunk(Thunk *t) {
3498 thunks.push_back(t);
3499 t->addSymbols(*this);
3502 void ThunkSection::writeTo(uint8_t *buf) {
3503 for (Thunk *t : thunks)
3504 t->writeTo(buf + t->offset);
3507 InputSection *ThunkSection::getTargetInputSection() const {
3510 const Thunk *t = thunks.front();
3511 return t->getTargetInputSection();
3514 bool ThunkSection::assignOffsets() {
3516 for (Thunk *t : thunks) {
3517 off = alignTo(off, t->alignment);
3519 uint32_t size = t->size();
3520 t->getThunkTargetSym()->size = size;
3523 bool changed = off != size;
3528 PPC32Got2Section::PPC32Got2Section()
3529 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, 4, ".got2") {}
3531 bool PPC32Got2Section::isNeeded() const {
3532 // See the comment below. This is not needed if there is no other
3534 for (BaseCommand *base : getParent()->sectionCommands)
3535 if (auto *isd = dyn_cast<InputSectionDescription>(base))
3536 for (InputSection *isec : isd->sections)
3542 void PPC32Got2Section::finalizeContents() {
3543 // PPC32 may create multiple GOT sections for -fPIC/-fPIE, one per file in
3544 // .got2 . This function computes outSecOff of each .got2 to be used in
3545 // PPC32PltCallStub::writeTo(). The purpose of this empty synthetic section is
3546 // to collect input sections named ".got2".
3547 uint32_t offset = 0;
3548 for (BaseCommand *base : getParent()->sectionCommands)
3549 if (auto *isd = dyn_cast<InputSectionDescription>(base)) {
3550 for (InputSection *isec : isd->sections) {
3553 isec->file->ppc32Got2OutSecOff = offset;
3554 offset += (uint32_t)isec->getSize();
3559 // If linking position-dependent code then the table will store the addresses
3560 // directly in the binary so the section has type SHT_PROGBITS. If linking
3561 // position-independent code the section has type SHT_NOBITS since it will be
3562 // allocated and filled in by the dynamic linker.
3563 PPC64LongBranchTargetSection::PPC64LongBranchTargetSection()
3564 : SyntheticSection(SHF_ALLOC | SHF_WRITE,
3565 config->isPic ? SHT_NOBITS : SHT_PROGBITS, 8,
3568 uint64_t PPC64LongBranchTargetSection::getEntryVA(const Symbol *sym,
3570 return getVA() + entry_index.find({sym, addend})->second * 8;
3573 Optional<uint32_t> PPC64LongBranchTargetSection::addEntry(const Symbol *sym,
3576 entry_index.try_emplace(std::make_pair(sym, addend), entries.size());
3579 entries.emplace_back(sym, addend);
3580 return res.first->second;
3583 size_t PPC64LongBranchTargetSection::getSize() const {
3584 return entries.size() * 8;
3587 void PPC64LongBranchTargetSection::writeTo(uint8_t *buf) {
3588 // If linking non-pic we have the final addresses of the targets and they get
3589 // written to the table directly. For pic the dynamic linker will allocate
3590 // the section and fill it it.
3594 for (auto entry : entries) {
3595 const Symbol *sym = entry.first;
3596 int64_t addend = entry.second;
3597 assert(sym->getVA());
3598 // Need calls to branch to the local entry-point since a long-branch
3599 // must be a local-call.
3600 write64(buf, sym->getVA(addend) +
3601 getPPC64GlobalEntryToLocalEntryOffset(sym->stOther));
3606 bool PPC64LongBranchTargetSection::isNeeded() const {
3607 // `removeUnusedSyntheticSections()` is called before thunk allocation which
3608 // is too early to determine if this section will be empty or not. We need
3609 // Finalized to keep the section alive until after thunk creation. Finalized
3610 // only gets set to true once `finalizeSections()` is called after thunk
3611 // creation. Because of this, if we don't create any long-branch thunks we end
3612 // up with an empty .branch_lt section in the binary.
3613 return !finalized || !entries.empty();
3616 static uint8_t getAbiVersion() {
3617 // MIPS non-PIC executable gets ABI version 1.
3618 if (config->emachine == EM_MIPS) {
3619 if (!config->isPic && !config->relocatable &&
3620 (config->eflags & (EF_MIPS_PIC | EF_MIPS_CPIC)) == EF_MIPS_CPIC)
3625 if (config->emachine == EM_AMDGPU) {
3626 uint8_t ver = objectFiles[0]->abiVersion;
3627 for (InputFile *file : makeArrayRef(objectFiles).slice(1))
3628 if (file->abiVersion != ver)
3629 error("incompatible ABI version: " + toString(file));
3636 template <typename ELFT> void elf::writeEhdr(uint8_t *buf, Partition &part) {
3637 // For executable segments, the trap instructions are written before writing
3638 // the header. Setting Elf header bytes to zero ensures that any unused bytes
3639 // in header are zero-cleared, instead of having trap instructions.
3640 memset(buf, 0, sizeof(typename ELFT::Ehdr));
3641 memcpy(buf, "\177ELF", 4);
3643 auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
3644 eHdr->e_ident[EI_CLASS] = config->is64 ? ELFCLASS64 : ELFCLASS32;
3645 eHdr->e_ident[EI_DATA] = config->isLE ? ELFDATA2LSB : ELFDATA2MSB;
3646 eHdr->e_ident[EI_VERSION] = EV_CURRENT;
3647 eHdr->e_ident[EI_OSABI] = config->osabi;
3648 eHdr->e_ident[EI_ABIVERSION] = getAbiVersion();
3649 eHdr->e_machine = config->emachine;
3650 eHdr->e_version = EV_CURRENT;
3651 eHdr->e_flags = config->eflags;
3652 eHdr->e_ehsize = sizeof(typename ELFT::Ehdr);
3653 eHdr->e_phnum = part.phdrs.size();
3654 eHdr->e_shentsize = sizeof(typename ELFT::Shdr);
3656 if (!config->relocatable) {
3657 eHdr->e_phoff = sizeof(typename ELFT::Ehdr);
3658 eHdr->e_phentsize = sizeof(typename ELFT::Phdr);
3662 template <typename ELFT> void elf::writePhdrs(uint8_t *buf, Partition &part) {
3663 // Write the program header table.
3664 auto *hBuf = reinterpret_cast<typename ELFT::Phdr *>(buf);
3665 for (PhdrEntry *p : part.phdrs) {
3666 hBuf->p_type = p->p_type;
3667 hBuf->p_flags = p->p_flags;
3668 hBuf->p_offset = p->p_offset;
3669 hBuf->p_vaddr = p->p_vaddr;
3670 hBuf->p_paddr = p->p_paddr;
3671 hBuf->p_filesz = p->p_filesz;
3672 hBuf->p_memsz = p->p_memsz;
3673 hBuf->p_align = p->p_align;
3678 template <typename ELFT>
3679 PartitionElfHeaderSection<ELFT>::PartitionElfHeaderSection()
3680 : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_EHDR, 1, "") {}
3682 template <typename ELFT>
3683 size_t PartitionElfHeaderSection<ELFT>::getSize() const {
3684 return sizeof(typename ELFT::Ehdr);
3687 template <typename ELFT>
3688 void PartitionElfHeaderSection<ELFT>::writeTo(uint8_t *buf) {
3689 writeEhdr<ELFT>(buf, getPartition());
3691 // Loadable partitions are always ET_DYN.
3692 auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
3693 eHdr->e_type = ET_DYN;
3696 template <typename ELFT>
3697 PartitionProgramHeadersSection<ELFT>::PartitionProgramHeadersSection()
3698 : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_PHDR, 1, ".phdrs") {}
3700 template <typename ELFT>
3701 size_t PartitionProgramHeadersSection<ELFT>::getSize() const {
3702 return sizeof(typename ELFT::Phdr) * getPartition().phdrs.size();
3705 template <typename ELFT>
3706 void PartitionProgramHeadersSection<ELFT>::writeTo(uint8_t *buf) {
3707 writePhdrs<ELFT>(buf, getPartition());
3710 PartitionIndexSection::PartitionIndexSection()
3711 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".rodata") {}
3713 size_t PartitionIndexSection::getSize() const {
3714 return 12 * (partitions.size() - 1);
3717 void PartitionIndexSection::finalizeContents() {
3718 for (size_t i = 1; i != partitions.size(); ++i)
3719 partitions[i].nameStrTab = mainPart->dynStrTab->addString(partitions[i].name);
3722 void PartitionIndexSection::writeTo(uint8_t *buf) {
3723 uint64_t va = getVA();
3724 for (size_t i = 1; i != partitions.size(); ++i) {
3725 write32(buf, mainPart->dynStrTab->getVA() + partitions[i].nameStrTab - va);
3726 write32(buf + 4, partitions[i].elfHeader->getVA() - (va + 4));
3728 SyntheticSection *next =
3729 i == partitions.size() - 1 ? in.partEnd : partitions[i + 1].elfHeader;
3730 write32(buf + 8, next->getVA() - partitions[i].elfHeader->getVA());
3739 std::vector<Partition> elf::partitions;
3740 Partition *elf::mainPart;
3742 template GdbIndexSection *GdbIndexSection::create<ELF32LE>();
3743 template GdbIndexSection *GdbIndexSection::create<ELF32BE>();
3744 template GdbIndexSection *GdbIndexSection::create<ELF64LE>();
3745 template GdbIndexSection *GdbIndexSection::create<ELF64BE>();
3747 template void elf::splitSections<ELF32LE>();
3748 template void elf::splitSections<ELF32BE>();
3749 template void elf::splitSections<ELF64LE>();
3750 template void elf::splitSections<ELF64BE>();
3752 template class elf::MipsAbiFlagsSection<ELF32LE>;
3753 template class elf::MipsAbiFlagsSection<ELF32BE>;
3754 template class elf::MipsAbiFlagsSection<ELF64LE>;
3755 template class elf::MipsAbiFlagsSection<ELF64BE>;
3757 template class elf::MipsOptionsSection<ELF32LE>;
3758 template class elf::MipsOptionsSection<ELF32BE>;
3759 template class elf::MipsOptionsSection<ELF64LE>;
3760 template class elf::MipsOptionsSection<ELF64BE>;
3762 template class elf::MipsReginfoSection<ELF32LE>;
3763 template class elf::MipsReginfoSection<ELF32BE>;
3764 template class elf::MipsReginfoSection<ELF64LE>;
3765 template class elf::MipsReginfoSection<ELF64BE>;
3767 template class elf::DynamicSection<ELF32LE>;
3768 template class elf::DynamicSection<ELF32BE>;
3769 template class elf::DynamicSection<ELF64LE>;
3770 template class elf::DynamicSection<ELF64BE>;
3772 template class elf::RelocationSection<ELF32LE>;
3773 template class elf::RelocationSection<ELF32BE>;
3774 template class elf::RelocationSection<ELF64LE>;
3775 template class elf::RelocationSection<ELF64BE>;
3777 template class elf::AndroidPackedRelocationSection<ELF32LE>;
3778 template class elf::AndroidPackedRelocationSection<ELF32BE>;
3779 template class elf::AndroidPackedRelocationSection<ELF64LE>;
3780 template class elf::AndroidPackedRelocationSection<ELF64BE>;
3782 template class elf::RelrSection<ELF32LE>;
3783 template class elf::RelrSection<ELF32BE>;
3784 template class elf::RelrSection<ELF64LE>;
3785 template class elf::RelrSection<ELF64BE>;
3787 template class elf::SymbolTableSection<ELF32LE>;
3788 template class elf::SymbolTableSection<ELF32BE>;
3789 template class elf::SymbolTableSection<ELF64LE>;
3790 template class elf::SymbolTableSection<ELF64BE>;
3792 template class elf::VersionNeedSection<ELF32LE>;
3793 template class elf::VersionNeedSection<ELF32BE>;
3794 template class elf::VersionNeedSection<ELF64LE>;
3795 template class elf::VersionNeedSection<ELF64BE>;
3797 template void elf::writeEhdr<ELF32LE>(uint8_t *Buf, Partition &Part);
3798 template void elf::writeEhdr<ELF32BE>(uint8_t *Buf, Partition &Part);
3799 template void elf::writeEhdr<ELF64LE>(uint8_t *Buf, Partition &Part);
3800 template void elf::writeEhdr<ELF64BE>(uint8_t *Buf, Partition &Part);
3802 template void elf::writePhdrs<ELF32LE>(uint8_t *Buf, Partition &Part);
3803 template void elf::writePhdrs<ELF32BE>(uint8_t *Buf, Partition &Part);
3804 template void elf::writePhdrs<ELF64LE>(uint8_t *Buf, Partition &Part);
3805 template void elf::writePhdrs<ELF64BE>(uint8_t *Buf, Partition &Part);
3807 template class elf::PartitionElfHeaderSection<ELF32LE>;
3808 template class elf::PartitionElfHeaderSection<ELF32BE>;
3809 template class elf::PartitionElfHeaderSection<ELF64LE>;
3810 template class elf::PartitionElfHeaderSection<ELF64BE>;
3812 template class elf::PartitionProgramHeadersSection<ELF32LE>;
3813 template class elf::PartitionProgramHeadersSection<ELF32BE>;
3814 template class elf::PartitionProgramHeadersSection<ELF64LE>;
3815 template class elf::PartitionProgramHeadersSection<ELF64BE>;