1//===- SyntheticSection.h ---------------------------------------*- C++ -*-===//
2//
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
6//
7//===----------------------------------------------------------------------===//
8//
9// Synthetic sections represent chunks of linker-created data. If you
10// need to create a chunk of data that to be included in some section
11// in the result, you probably want to create that as a synthetic section.
12//
13// Synthetic sections are designed as input sections as opposed to
14// output sections because we want to allow them to be manipulated
15// using linker scripts just like other input sections from regular
16// files.
17//
18//===----------------------------------------------------------------------===//
19
20#ifndef LLD_ELF_SYNTHETIC_SECTIONS_H
21#define LLD_ELF_SYNTHETIC_SECTIONS_H
22
23#include "Config.h"
24#include "DWARF.h"
25#include "InputSection.h"
26#include "Symbols.h"
27#include "llvm/ADT/DenseSet.h"
28#include "llvm/ADT/FoldingSet.h"
29#include "llvm/ADT/MapVector.h"
30#include "llvm/ADT/STLFunctionalExtras.h"
31#include "llvm/BinaryFormat/ELF.h"
32#include "llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h"
33#include "llvm/MC/StringTableBuilder.h"
34#include "llvm/Support/Allocator.h"
35#include "llvm/Support/Compiler.h"
36#include "llvm/Support/Endian.h"
37#include "llvm/Support/Parallel.h"
38#include "llvm/Support/Threading.h"
39
40namespace lld::elf {
41class Defined;
42struct PhdrEntry;
43class SymbolTableBaseSection;
44
45struct CieRecord {
46 EhSectionPiece *cie = nullptr;
47 SmallVector<EhSectionPiece *, 0> fdes;
48};
49
50// Section for .eh_frame.
51class EhFrameSection final : public SyntheticSection {
52public:
53 EhFrameSection();
54 void writeTo(uint8_t *buf) override;
55 void finalizeContents() override;
56 bool isNeeded() const override { return !sections.empty(); }
57 size_t getSize() const override { return size; }
58
59 static bool classof(const SectionBase *d) {
60 return SyntheticSection::classof(sec: d) && d->name == ".eh_frame";
61 }
62
63 SmallVector<EhInputSection *, 0> sections;
64 size_t numFdes = 0;
65
66 struct FdeData {
67 uint32_t pcRel;
68 uint32_t fdeVARel;
69 };
70
71 SmallVector<FdeData, 0> getFdeData() const;
72 ArrayRef<CieRecord *> getCieRecords() const { return cieRecords; }
73 template <class ELFT>
74 void iterateFDEWithLSDA(llvm::function_ref<void(InputSection &)> fn);
75
76private:
77 // This is used only when parsing EhInputSection. We keep it here to avoid
78 // allocating one for each EhInputSection.
79 llvm::DenseMap<size_t, CieRecord *> offsetToCie;
80
81 uint64_t size = 0;
82
83 template <class ELFT, class RelTy>
84 void addRecords(EhInputSection *s, llvm::ArrayRef<RelTy> rels);
85 template <class ELFT> void addSectionAux(EhInputSection *s);
86 template <class ELFT, class RelTy>
87 void iterateFDEWithLSDAAux(EhInputSection &sec, ArrayRef<RelTy> rels,
88 llvm::DenseSet<size_t> &ciesWithLSDA,
89 llvm::function_ref<void(InputSection &)> fn);
90
91 template <class ELFT, class RelTy>
92 CieRecord *addCie(EhSectionPiece &piece, ArrayRef<RelTy> rels);
93
94 template <class ELFT, class RelTy>
95 Defined *isFdeLive(EhSectionPiece &piece, ArrayRef<RelTy> rels);
96
97 uint64_t getFdePc(uint8_t *buf, size_t off, uint8_t enc) const;
98
99 SmallVector<CieRecord *, 0> cieRecords;
100
101 // CIE records are uniquified by their contents and personality functions.
102 llvm::DenseMap<std::pair<ArrayRef<uint8_t>, Symbol *>, CieRecord *> cieMap;
103};
104
105class GotSection final : public SyntheticSection {
106public:
107 GotSection();
108 size_t getSize() const override { return size; }
109 void finalizeContents() override;
110 bool isNeeded() const override;
111 void writeTo(uint8_t *buf) override;
112
113 void addConstant(const Relocation &r);
114 void addEntry(const Symbol &sym);
115 bool addTlsDescEntry(const Symbol &sym);
116 bool addDynTlsEntry(const Symbol &sym);
117 bool addTlsIndex();
118 uint32_t getTlsDescOffset(const Symbol &sym) const;
119 uint64_t getTlsDescAddr(const Symbol &sym) const;
120 uint64_t getGlobalDynAddr(const Symbol &b) const;
121 uint64_t getGlobalDynOffset(const Symbol &b) const;
122
123 uint64_t getTlsIndexVA() { return this->getVA() + tlsIndexOff; }
124 uint32_t getTlsIndexOff() const { return tlsIndexOff; }
125
126 // Flag to force GOT to be in output if we have relocations
127 // that relies on its address.
128 std::atomic<bool> hasGotOffRel = false;
129
130protected:
131 size_t numEntries = 0;
132 uint32_t tlsIndexOff = -1;
133 uint64_t size = 0;
134};
135
136// .note.GNU-stack section.
137class GnuStackSection : public SyntheticSection {
138public:
139 GnuStackSection()
140 : SyntheticSection(0, llvm::ELF::SHT_PROGBITS, 1, ".note.GNU-stack") {}
141 void writeTo(uint8_t *buf) override {}
142 size_t getSize() const override { return 0; }
143};
144
145class GnuPropertySection final : public SyntheticSection {
146public:
147 GnuPropertySection();
148 void writeTo(uint8_t *buf) override;
149 size_t getSize() const override;
150};
151
152// .note.gnu.build-id section.
153class BuildIdSection : public SyntheticSection {
154 // First 16 bytes are a header.
155 static const unsigned headerSize = 16;
156
157public:
158 const size_t hashSize;
159 BuildIdSection();
160 void writeTo(uint8_t *buf) override;
161 size_t getSize() const override { return headerSize + hashSize; }
162 void writeBuildId(llvm::ArrayRef<uint8_t> buf);
163
164private:
165 uint8_t *hashBuf;
166};
167
168// BssSection is used to reserve space for copy relocations and common symbols.
169// We create three instances of this class for .bss, .bss.rel.ro and "COMMON",
170// that are used for writable symbols, read-only symbols and common symbols,
171// respectively.
172class BssSection final : public SyntheticSection {
173public:
174 BssSection(StringRef name, uint64_t size, uint32_t addralign);
175 void writeTo(uint8_t *) override {}
176 bool isNeeded() const override { return size != 0; }
177 size_t getSize() const override { return size; }
178
179 static bool classof(const SectionBase *s) { return s->bss; }
180 uint64_t size;
181};
182
183class MipsGotSection final : public SyntheticSection {
184public:
185 MipsGotSection();
186 void writeTo(uint8_t *buf) override;
187 size_t getSize() const override { return size; }
188 bool updateAllocSize() override;
189 void finalizeContents() override;
190 bool isNeeded() const override;
191
192 // Join separate GOTs built for each input file to generate
193 // primary and optional multiple secondary GOTs.
194 void build();
195
196 void addEntry(InputFile &file, Symbol &sym, int64_t addend, RelExpr expr);
197 void addDynTlsEntry(InputFile &file, Symbol &sym);
198 void addTlsIndex(InputFile &file);
199
200 uint64_t getPageEntryOffset(const InputFile *f, const Symbol &s,
201 int64_t addend) const;
202 uint64_t getSymEntryOffset(const InputFile *f, const Symbol &s,
203 int64_t addend) const;
204 uint64_t getGlobalDynOffset(const InputFile *f, const Symbol &s) const;
205 uint64_t getTlsIndexOffset(const InputFile *f) const;
206
207 // Returns the symbol which corresponds to the first entry of the global part
208 // of GOT on MIPS platform. It is required to fill up MIPS-specific dynamic
209 // table properties.
210 // Returns nullptr if the global part is empty.
211 const Symbol *getFirstGlobalEntry() const;
212
213 // Returns the number of entries in the local part of GOT including
214 // the number of reserved entries.
215 unsigned getLocalEntriesNum() const;
216
217 // Return _gp value for primary GOT (nullptr) or particular input file.
218 uint64_t getGp(const InputFile *f = nullptr) const;
219
220private:
221 // MIPS GOT consists of three parts: local, global and tls. Each part
222 // contains different types of entries. Here is a layout of GOT:
223 // - Header entries |
224 // - Page entries | Local part
225 // - Local entries (16-bit access) |
226 // - Local entries (32-bit access) |
227 // - Normal global entries || Global part
228 // - Reloc-only global entries ||
229 // - TLS entries ||| TLS part
230 //
231 // Header:
232 // Two entries hold predefined value 0x0 and 0x80000000.
233 // Page entries:
234 // These entries created by R_MIPS_GOT_PAGE relocation and R_MIPS_GOT16
235 // relocation against local symbols. They are initialized by higher 16-bit
236 // of the corresponding symbol's value. So each 64kb of address space
237 // requires a single GOT entry.
238 // Local entries (16-bit access):
239 // These entries created by GOT relocations against global non-preemptible
240 // symbols so dynamic linker is not necessary to resolve the symbol's
241 // values. "16-bit access" means that corresponding relocations address
242 // GOT using 16-bit index. Each unique Symbol-Addend pair has its own
243 // GOT entry.
244 // Local entries (32-bit access):
245 // These entries are the same as above but created by relocations which
246 // address GOT using 32-bit index (R_MIPS_GOT_HI16/LO16 etc).
247 // Normal global entries:
248 // These entries created by GOT relocations against preemptible global
249 // symbols. They need to be initialized by dynamic linker and they ordered
250 // exactly as the corresponding entries in the dynamic symbols table.
251 // Reloc-only global entries:
252 // These entries created for symbols that are referenced by dynamic
253 // relocations R_MIPS_REL32. These entries are not accessed with gp-relative
254 // addressing, but MIPS ABI requires that these entries be present in GOT.
255 // TLS entries:
256 // Entries created by TLS relocations.
257 //
258 // If the sum of local, global and tls entries is less than 64K only single
259 // got is enough. Otherwise, multi-got is created. Series of primary and
260 // multiple secondary GOTs have the following layout:
261 // - Primary GOT
262 // Header
263 // Local entries
264 // Global entries
265 // Relocation only entries
266 // TLS entries
267 //
268 // - Secondary GOT
269 // Local entries
270 // Global entries
271 // TLS entries
272 // ...
273 //
274 // All GOT entries required by relocations from a single input file entirely
275 // belong to either primary or one of secondary GOTs. To reference GOT entries
276 // each GOT has its own _gp value points to the "middle" of the GOT.
277 // In the code this value loaded to the register which is used for GOT access.
278 //
279 // MIPS 32 function's prologue:
280 // lui v0,0x0
281 // 0: R_MIPS_HI16 _gp_disp
282 // addiu v0,v0,0
283 // 4: R_MIPS_LO16 _gp_disp
284 //
285 // MIPS 64:
286 // lui at,0x0
287 // 14: R_MIPS_GPREL16 main
288 //
289 // Dynamic linker does not know anything about secondary GOTs and cannot
290 // use a regular MIPS mechanism for GOT entries initialization. So we have
291 // to use an approach accepted by other architectures and create dynamic
292 // relocations R_MIPS_REL32 to initialize global entries (and local in case
293 // of PIC code) in secondary GOTs. But ironically MIPS dynamic linker
294 // requires GOT entries and correspondingly ordered dynamic symbol table
295 // entries to deal with dynamic relocations. To handle this problem
296 // relocation-only section in the primary GOT contains entries for all
297 // symbols referenced in global parts of secondary GOTs. Although the sum
298 // of local and normal global entries of the primary got should be less
299 // than 64K, the size of the primary got (including relocation-only entries
300 // can be greater than 64K, because parts of the primary got that overflow
301 // the 64K limit are used only by the dynamic linker at dynamic link-time
302 // and not by 16-bit gp-relative addressing at run-time.
303 //
304 // For complete multi-GOT description see the following link
305 // https://dmz-portal.mips.com/wiki/MIPS_Multi_GOT
306
307 // Number of "Header" entries.
308 static const unsigned headerEntriesNum = 2;
309
310 uint64_t size = 0;
311
312 // Symbol and addend.
313 using GotEntry = std::pair<Symbol *, int64_t>;
314
315 struct FileGot {
316 InputFile *file = nullptr;
317 size_t startIndex = 0;
318
319 struct PageBlock {
320 size_t firstIndex;
321 size_t count;
322 PageBlock() : firstIndex(0), count(0) {}
323 };
324
325 // Map output sections referenced by MIPS GOT relocations
326 // to the description (index/count) "page" entries allocated
327 // for this section.
328 llvm::SmallMapVector<const OutputSection *, PageBlock, 16> pagesMap;
329 // Maps from Symbol+Addend pair or just Symbol to the GOT entry index.
330 llvm::MapVector<GotEntry, size_t> local16;
331 llvm::MapVector<GotEntry, size_t> local32;
332 llvm::MapVector<Symbol *, size_t> global;
333 llvm::MapVector<Symbol *, size_t> relocs;
334 llvm::MapVector<Symbol *, size_t> tls;
335 // Set of symbols referenced by dynamic TLS relocations.
336 llvm::MapVector<Symbol *, size_t> dynTlsSymbols;
337
338 // Total number of all entries.
339 size_t getEntriesNum() const;
340 // Number of "page" entries.
341 size_t getPageEntriesNum() const;
342 // Number of entries require 16-bit index to access.
343 size_t getIndexedEntriesNum() const;
344 };
345
346 // Container of GOT created for each input file.
347 // After building a final series of GOTs this container
348 // holds primary and secondary GOT's.
349 std::vector<FileGot> gots;
350
351 // Return (and create if necessary) `FileGot`.
352 FileGot &getGot(InputFile &f);
353
354 // Try to merge two GOTs. In case of success the `Dst` contains
355 // result of merging and the function returns true. In case of
356 // overflow the `Dst` is unchanged and the function returns false.
357 bool tryMergeGots(FileGot & dst, FileGot & src, bool isPrimary);
358};
359
360class GotPltSection final : public SyntheticSection {
361public:
362 GotPltSection();
363 void addEntry(Symbol &sym);
364 size_t getSize() const override;
365 void writeTo(uint8_t *buf) override;
366 bool isNeeded() const override;
367
368 // Flag to force GotPlt to be in output if we have relocations
369 // that relies on its address.
370 std::atomic<bool> hasGotPltOffRel = false;
371
372private:
373 SmallVector<const Symbol *, 0> entries;
374};
375
376// The IgotPltSection is a Got associated with the PltSection for GNU Ifunc
377// Symbols that will be relocated by Target->IRelativeRel.
378// On most Targets the IgotPltSection will immediately follow the GotPltSection
379// on ARM the IgotPltSection will immediately follow the GotSection.
380class IgotPltSection final : public SyntheticSection {
381public:
382 IgotPltSection();
383 void addEntry(Symbol &sym);
384 size_t getSize() const override;
385 void writeTo(uint8_t *buf) override;
386 bool isNeeded() const override { return !entries.empty(); }
387
388private:
389 SmallVector<const Symbol *, 0> entries;
390};
391
392class StringTableSection final : public SyntheticSection {
393public:
394 StringTableSection(StringRef name, bool dynamic);
395 unsigned addString(StringRef s, bool hashIt = true);
396 void writeTo(uint8_t *buf) override;
397 size_t getSize() const override { return size; }
398 bool isDynamic() const { return dynamic; }
399
400private:
401 const bool dynamic;
402
403 uint64_t size = 0;
404
405 llvm::DenseMap<llvm::CachedHashStringRef, unsigned> stringMap;
406 SmallVector<StringRef, 0> strings;
407};
408
409class DynamicReloc {
410public:
411 enum Kind {
412 /// The resulting dynamic relocation does not reference a symbol (#sym must
413 /// be nullptr) and uses #addend as the result of computeAddend().
414 AddendOnly,
415 /// The resulting dynamic relocation will not reference a symbol: #sym is
416 /// only used to compute the addend with InputSection::getRelocTargetVA().
417 /// Useful for various relative and TLS relocations (e.g. R_X86_64_TPOFF64).
418 AddendOnlyWithTargetVA,
419 /// The resulting dynamic relocation references symbol #sym from the dynamic
420 /// symbol table and uses #addend as the value of computeAddend().
421 AgainstSymbol,
422 /// The resulting dynamic relocation references symbol #sym from the dynamic
423 /// symbol table and uses InputSection::getRelocTargetVA() + #addend for the
424 /// final addend. It can be used for relocations that write the symbol VA as
425 // the addend (e.g. R_MIPS_TLS_TPREL64) but still reference the symbol.
426 AgainstSymbolWithTargetVA,
427 /// This is used by the MIPS multi-GOT implementation. It relocates
428 /// addresses of 64kb pages that lie inside the output section.
429 MipsMultiGotPage,
430 };
431 /// This constructor records a relocation against a symbol.
432 DynamicReloc(RelType type, const InputSectionBase *inputSec,
433 uint64_t offsetInSec, Kind kind, Symbol &sym, int64_t addend,
434 RelExpr expr)
435 : sym(&sym), inputSec(inputSec), offsetInSec(offsetInSec), type(type),
436 addend(addend), kind(kind), expr(expr) {}
437 /// This constructor records a relative relocation with no symbol.
438 DynamicReloc(RelType type, const InputSectionBase *inputSec,
439 uint64_t offsetInSec, int64_t addend = 0)
440 : sym(nullptr), inputSec(inputSec), offsetInSec(offsetInSec), type(type),
441 addend(addend), kind(AddendOnly), expr(R_ADDEND) {}
442 /// This constructor records dynamic relocation settings used by the MIPS
443 /// multi-GOT implementation.
444 DynamicReloc(RelType type, const InputSectionBase *inputSec,
445 uint64_t offsetInSec, const OutputSection *outputSec,
446 int64_t addend)
447 : sym(nullptr), outputSec(outputSec), inputSec(inputSec),
448 offsetInSec(offsetInSec), type(type), addend(addend),
449 kind(MipsMultiGotPage), expr(R_ADDEND) {}
450
451 uint64_t getOffset() const;
452 uint32_t getSymIndex(SymbolTableBaseSection *symTab) const;
453 bool needsDynSymIndex() const {
454 return kind == AgainstSymbol || kind == AgainstSymbolWithTargetVA;
455 }
456
457 /// Computes the addend of the dynamic relocation. Note that this is not the
458 /// same as the #addend member variable as it may also include the symbol
459 /// address/the address of the corresponding GOT entry/etc.
460 int64_t computeAddend() const;
461
462 void computeRaw(SymbolTableBaseSection *symtab);
463
464 Symbol *sym;
465 const OutputSection *outputSec = nullptr;
466 const InputSectionBase *inputSec;
467 uint64_t offsetInSec;
468 uint64_t r_offset;
469 RelType type;
470 uint32_t r_sym;
471 // Initially input addend, then the output addend after
472 // RelocationSection<ELFT>::writeTo.
473 int64_t addend;
474
475private:
476 Kind kind;
477 // The kind of expression used to calculate the added (required e.g. for
478 // relative GOT relocations).
479 RelExpr expr;
480};
481
482template <class ELFT> class DynamicSection final : public SyntheticSection {
483 LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)
484
485public:
486 DynamicSection();
487 void finalizeContents() override;
488 void writeTo(uint8_t *buf) override;
489 size_t getSize() const override { return size; }
490
491private:
492 std::vector<std::pair<int32_t, uint64_t>> computeContents();
493 uint64_t size = 0;
494};
495
496class RelocationBaseSection : public SyntheticSection {
497public:
498 RelocationBaseSection(StringRef name, uint32_t type, int32_t dynamicTag,
499 int32_t sizeDynamicTag, bool combreloc,
500 unsigned concurrency);
501 /// Add a dynamic relocation without writing an addend to the output section.
502 /// This overload can be used if the addends are written directly instead of
503 /// using relocations on the input section (e.g. MipsGotSection::writeTo()).
504 template <bool shard = false> void addReloc(const DynamicReloc &reloc) {
505 relocs.push_back(Elt: reloc);
506 }
507 /// Add a dynamic relocation against \p sym with an optional addend.
508 void addSymbolReloc(RelType dynType, InputSectionBase &isec,
509 uint64_t offsetInSec, Symbol &sym, int64_t addend = 0,
510 std::optional<RelType> addendRelType = {});
511 /// Add a relative dynamic relocation that uses the target address of \p sym
512 /// (i.e. InputSection::getRelocTargetVA()) + \p addend as the addend.
513 /// This function should only be called for non-preemptible symbols or
514 /// RelExpr values that refer to an address inside the output file (e.g. the
515 /// address of the GOT entry for a potentially preemptible symbol).
516 template <bool shard = false>
517 void addRelativeReloc(RelType dynType, InputSectionBase &isec,
518 uint64_t offsetInSec, Symbol &sym, int64_t addend,
519 RelType addendRelType, RelExpr expr) {
520 assert(expr != R_ADDEND && "expected non-addend relocation expression");
521 addReloc<shard>(DynamicReloc::AddendOnlyWithTargetVA, dynType, isec,
522 offsetInSec, sym, addend, expr, addendRelType);
523 }
524 /// Add a dynamic relocation using the target address of \p sym as the addend
525 /// if \p sym is non-preemptible. Otherwise add a relocation against \p sym.
526 void addAddendOnlyRelocIfNonPreemptible(RelType dynType, GotSection &sec,
527 uint64_t offsetInSec, Symbol &sym,
528 RelType addendRelType);
529 template <bool shard = false>
530 void addReloc(DynamicReloc::Kind kind, RelType dynType, InputSectionBase &sec,
531 uint64_t offsetInSec, Symbol &sym, int64_t addend, RelExpr expr,
532 RelType addendRelType) {
533 // Write the addends to the relocated address if required. We skip
534 // it if the written value would be zero.
535 if (config->writeAddends && (expr != R_ADDEND || addend != 0))
536 sec.addReloc(r: {.expr: expr, .type: addendRelType, .offset: offsetInSec, .addend: addend, .sym: &sym});
537 addReloc<shard>({dynType, &sec, offsetInSec, kind, sym, addend, expr});
538 }
539 bool isNeeded() const override {
540 return !relocs.empty() ||
541 llvm::any_of(Range: relocsVec, P: [](auto &v) { return !v.empty(); });
542 }
543 size_t getSize() const override { return relocs.size() * this->entsize; }
544 size_t getRelativeRelocCount() const { return numRelativeRelocs; }
545 void mergeRels();
546 void partitionRels();
547 void finalizeContents() override;
548 static bool classof(const SectionBase *d) {
549 return SyntheticSection::classof(sec: d) &&
550 (d->type == llvm::ELF::SHT_RELA || d->type == llvm::ELF::SHT_REL ||
551 d->type == llvm::ELF::SHT_RELR);
552 }
553 int32_t dynamicTag, sizeDynamicTag;
554 SmallVector<DynamicReloc, 0> relocs;
555
556protected:
557 void computeRels();
558 // Used when parallel relocation scanning adds relocations. The elements
559 // will be moved into relocs by mergeRel().
560 SmallVector<SmallVector<DynamicReloc, 0>, 0> relocsVec;
561 size_t numRelativeRelocs = 0; // used by -z combreloc
562 bool combreloc;
563};
564
565template <>
566inline void RelocationBaseSection::addReloc<true>(const DynamicReloc &reloc) {
567 relocsVec[llvm::parallel::getThreadIndex()].push_back(Elt: reloc);
568}
569
570template <class ELFT>
571class RelocationSection final : public RelocationBaseSection {
572 using Elf_Rel = typename ELFT::Rel;
573 using Elf_Rela = typename ELFT::Rela;
574
575public:
576 RelocationSection(StringRef name, bool combreloc, unsigned concurrency);
577 void writeTo(uint8_t *buf) override;
578};
579
580template <class ELFT>
581class AndroidPackedRelocationSection final : public RelocationBaseSection {
582 using Elf_Rel = typename ELFT::Rel;
583 using Elf_Rela = typename ELFT::Rela;
584
585public:
586 AndroidPackedRelocationSection(StringRef name, unsigned concurrency);
587
588 bool updateAllocSize() override;
589 size_t getSize() const override { return relocData.size(); }
590 void writeTo(uint8_t *buf) override {
591 memcpy(dest: buf, src: relocData.data(), n: relocData.size());
592 }
593
594private:
595 SmallVector<char, 0> relocData;
596};
597
598struct RelativeReloc {
599 uint64_t getOffset() const { return inputSec->getVA(offset: offsetInSec); }
600
601 const InputSectionBase *inputSec;
602 uint64_t offsetInSec;
603};
604
605class RelrBaseSection : public SyntheticSection {
606public:
607 RelrBaseSection(unsigned concurrency);
608 void mergeRels();
609 bool isNeeded() const override {
610 return !relocs.empty() ||
611 llvm::any_of(Range: relocsVec, P: [](auto &v) { return !v.empty(); });
612 }
613 SmallVector<RelativeReloc, 0> relocs;
614 SmallVector<SmallVector<RelativeReloc, 0>, 0> relocsVec;
615};
616
617// RelrSection is used to encode offsets for relative relocations.
618// Proposal for adding SHT_RELR sections to generic-abi is here:
619// https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
620// For more details, see the comment in RelrSection::updateAllocSize().
621template <class ELFT> class RelrSection final : public RelrBaseSection {
622 using Elf_Relr = typename ELFT::Relr;
623
624public:
625 RelrSection(unsigned concurrency);
626
627 bool updateAllocSize() override;
628 size_t getSize() const override { return relrRelocs.size() * this->entsize; }
629 void writeTo(uint8_t *buf) override {
630 memcpy(buf, relrRelocs.data(), getSize());
631 }
632
633private:
634 SmallVector<Elf_Relr, 0> relrRelocs;
635};
636
637struct SymbolTableEntry {
638 Symbol *sym;
639 size_t strTabOffset;
640};
641
642class SymbolTableBaseSection : public SyntheticSection {
643public:
644 SymbolTableBaseSection(StringTableSection &strTabSec);
645 void finalizeContents() override;
646 size_t getSize() const override { return getNumSymbols() * entsize; }
647 void addSymbol(Symbol *sym);
648 unsigned getNumSymbols() const { return symbols.size() + 1; }
649 size_t getSymbolIndex(const Symbol &sym);
650 ArrayRef<SymbolTableEntry> getSymbols() const { return symbols; }
651
652protected:
653 void sortSymTabSymbols();
654
655 // A vector of symbols and their string table offsets.
656 SmallVector<SymbolTableEntry, 0> symbols;
657
658 StringTableSection &strTabSec;
659
660 llvm::once_flag onceFlag;
661 llvm::DenseMap<Symbol *, size_t> symbolIndexMap;
662 llvm::DenseMap<OutputSection *, size_t> sectionIndexMap;
663};
664
665template <class ELFT>
666class SymbolTableSection final : public SymbolTableBaseSection {
667 using Elf_Sym = typename ELFT::Sym;
668
669public:
670 SymbolTableSection(StringTableSection &strTabSec);
671 void writeTo(uint8_t *buf) override;
672};
673
674class SymtabShndxSection final : public SyntheticSection {
675public:
676 SymtabShndxSection();
677
678 void writeTo(uint8_t *buf) override;
679 size_t getSize() const override;
680 bool isNeeded() const override;
681 void finalizeContents() override;
682};
683
684// Outputs GNU Hash section. For detailed explanation see:
685// https://blogs.oracle.com/ali/entry/gnu_hash_elf_sections
686class GnuHashTableSection final : public SyntheticSection {
687public:
688 GnuHashTableSection();
689 void finalizeContents() override;
690 void writeTo(uint8_t *buf) override;
691 size_t getSize() const override { return size; }
692
693 // Adds symbols to the hash table.
694 // Sorts the input to satisfy GNU hash section requirements.
695 void addSymbols(llvm::SmallVectorImpl<SymbolTableEntry> &symbols);
696
697private:
698 // See the comment in writeBloomFilter.
699 enum { Shift2 = 26 };
700
701 struct Entry {
702 Symbol *sym;
703 size_t strTabOffset;
704 uint32_t hash;
705 uint32_t bucketIdx;
706 };
707
708 SmallVector<Entry, 0> symbols;
709 size_t maskWords;
710 size_t nBuckets = 0;
711 size_t size = 0;
712};
713
714class HashTableSection final : public SyntheticSection {
715public:
716 HashTableSection();
717 void finalizeContents() override;
718 void writeTo(uint8_t *buf) override;
719 size_t getSize() const override { return size; }
720
721private:
722 size_t size = 0;
723};
724
725// Used for PLT entries. It usually has a PLT header for lazy binding. Each PLT
726// entry is associated with a JUMP_SLOT relocation, which may be resolved lazily
727// at runtime.
728//
729// On PowerPC, this section contains lazy symbol resolvers. A branch instruction
730// jumps to a PLT call stub, which will then jump to the target (BIND_NOW) or a
731// lazy symbol resolver.
732//
733// On x86 when IBT is enabled, this section (.plt.sec) contains PLT call stubs.
734// A call instruction jumps to a .plt.sec entry, which will then jump to the
735// target (BIND_NOW) or a .plt entry.
736class PltSection : public SyntheticSection {
737public:
738 PltSection();
739 void writeTo(uint8_t *buf) override;
740 size_t getSize() const override;
741 bool isNeeded() const override;
742 void addSymbols();
743 void addEntry(Symbol &sym);
744 size_t getNumEntries() const { return entries.size(); }
745
746 size_t headerSize;
747
748 SmallVector<const Symbol *, 0> entries;
749};
750
751// Used for non-preemptible ifuncs. It does not have a header. Each entry is
752// associated with an IRELATIVE relocation, which will be resolved eagerly at
753// runtime. PltSection can only contain entries associated with JUMP_SLOT
754// relocations, so IPLT entries are in a separate section.
755class IpltSection final : public SyntheticSection {
756 SmallVector<const Symbol *, 0> entries;
757
758public:
759 IpltSection();
760 void writeTo(uint8_t *buf) override;
761 size_t getSize() const override;
762 bool isNeeded() const override { return !entries.empty(); }
763 void addSymbols();
764 void addEntry(Symbol &sym);
765};
766
767class PPC32GlinkSection : public PltSection {
768public:
769 PPC32GlinkSection();
770 void writeTo(uint8_t *buf) override;
771 size_t getSize() const override;
772
773 SmallVector<const Symbol *, 0> canonical_plts;
774 static constexpr size_t footerSize = 64;
775};
776
777// This is x86-only.
778class IBTPltSection : public SyntheticSection {
779public:
780 IBTPltSection();
781 void writeTo(uint8_t *Buf) override;
782 bool isNeeded() const override;
783 size_t getSize() const override;
784};
785
786// Used to align the end of the PT_GNU_RELRO segment and the associated PT_LOAD
787// segment to a common-page-size boundary. This padding section ensures that all
788// pages in the PT_LOAD segment is covered by at least one section.
789class RelroPaddingSection final : public SyntheticSection {
790public:
791 RelroPaddingSection();
792 size_t getSize() const override { return 0; }
793 void writeTo(uint8_t *buf) override {}
794};
795
796// Used by the merged DWARF32 .debug_names (a per-module index). If we
797// move to DWARF64, most of this data will need to be re-sized.
798class DebugNamesBaseSection : public SyntheticSection {
799public:
800 struct Abbrev : llvm::FoldingSetNode {
801 uint32_t code;
802 uint32_t tag;
803 SmallVector<llvm::DWARFDebugNames::AttributeEncoding, 2> attributes;
804
805 void Profile(llvm::FoldingSetNodeID &id) const;
806 };
807
808 struct AttrValue {
809 uint32_t attrValue;
810 uint8_t attrSize;
811 };
812
813 struct IndexEntry {
814 uint32_t abbrevCode;
815 uint32_t poolOffset;
816 union {
817 uint64_t parentOffset = 0;
818 IndexEntry *parentEntry;
819 };
820 SmallVector<AttrValue, 3> attrValues;
821 };
822
823 struct NameEntry {
824 const char *name;
825 uint32_t hashValue;
826 uint32_t stringOffset;
827 uint32_t entryOffset;
828 // Used to relocate `stringOffset` in the merged section.
829 uint32_t chunkIdx;
830 SmallVector<IndexEntry *, 0> indexEntries;
831
832 llvm::iterator_range<
833 llvm::pointee_iterator<typename SmallVector<IndexEntry *, 0>::iterator>>
834 entries() {
835 return llvm::make_pointee_range(Range&: indexEntries);
836 }
837 };
838
839 // The contents of one input .debug_names section. An InputChunk
840 // typically contains one NameData, but might contain more, especially
841 // in LTO builds.
842 struct NameData {
843 llvm::DWARFDebugNames::Header hdr;
844 llvm::DenseMap<uint32_t, uint32_t> abbrevCodeMap;
845 SmallVector<NameEntry, 0> nameEntries;
846 };
847
848 // InputChunk and OutputChunk hold per-file contributions to the merged index.
849 // InputChunk instances will be discarded after `init` completes.
850 struct InputChunk {
851 uint32_t baseCuIdx;
852 LLDDWARFSection section;
853 SmallVector<NameData, 0> nameData;
854 std::optional<llvm::DWARFDebugNames> llvmDebugNames;
855 };
856
857 struct OutputChunk {
858 // Pointer to the .debug_info section that contains compile units, used to
859 // compute the relocated CU offsets.
860 InputSection *infoSec;
861 // This initially holds section offsets. After relocation, the section
862 // offsets are changed to CU offsets relative the the output section.
863 SmallVector<uint32_t, 0> compUnits;
864 };
865
866 DebugNamesBaseSection();
867 size_t getSize() const override { return size; }
868 bool isNeeded() const override { return numChunks > 0; }
869
870protected:
871 void init(llvm::function_ref<void(InputFile *, InputChunk &, OutputChunk &)>);
872 static void
873 parseDebugNames(InputChunk &inputChunk, OutputChunk &chunk,
874 llvm::DWARFDataExtractor &namesExtractor,
875 llvm::DataExtractor &strExtractor,
876 llvm::function_ref<SmallVector<uint32_t, 0>(
877 uint32_t numCUs, const llvm::DWARFDebugNames::Header &hdr,
878 const llvm::DWARFDebugNames::DWARFDebugNamesOffsets &)>
879 readOffsets);
880 void computeHdrAndAbbrevTable(MutableArrayRef<InputChunk> inputChunks);
881 std::pair<uint32_t, uint32_t>
882 computeEntryPool(MutableArrayRef<InputChunk> inputChunks);
883
884 // Input .debug_names sections for relocating string offsets in the name table
885 // in `finalizeContents`.
886 SmallVector<InputSection *, 0> inputSections;
887
888 llvm::DWARFDebugNames::Header hdr;
889 size_t numChunks;
890 std::unique_ptr<OutputChunk[]> chunks;
891 llvm::SpecificBumpPtrAllocator<Abbrev> abbrevAlloc;
892 SmallVector<Abbrev *, 0> abbrevTable;
893 SmallVector<char, 0> abbrevTableBuf;
894
895 ArrayRef<OutputChunk> getChunks() const {
896 return ArrayRef(chunks.get(), numChunks);
897 }
898
899 // Sharded name entries that will be used to compute bucket_count and the
900 // count name table.
901 static constexpr size_t numShards = 32;
902 SmallVector<NameEntry, 0> nameVecs[numShards];
903};
904
905// Complement DebugNamesBaseSection for ELFT-aware code: reading offsets,
906// relocating string offsets, and writeTo.
907template <class ELFT>
908class DebugNamesSection final : public DebugNamesBaseSection {
909public:
910 DebugNamesSection();
911 void finalizeContents() override;
912 void writeTo(uint8_t *buf) override;
913
914 template <class RelTy>
915 void getNameRelocs(InputSection *sec, ArrayRef<RelTy> rels,
916 llvm::DenseMap<uint32_t, uint32_t> &relocs);
917
918private:
919 static void readOffsets(InputChunk &inputChunk, OutputChunk &chunk,
920 llvm::DWARFDataExtractor &namesExtractor,
921 llvm::DataExtractor &strExtractor);
922};
923
924class GdbIndexSection final : public SyntheticSection {
925public:
926 struct AddressEntry {
927 InputSection *section;
928 uint64_t lowAddress;
929 uint64_t highAddress;
930 uint32_t cuIndex;
931 };
932
933 struct CuEntry {
934 uint64_t cuOffset;
935 uint64_t cuLength;
936 };
937
938 struct NameAttrEntry {
939 llvm::CachedHashStringRef name;
940 uint32_t cuIndexAndAttrs;
941 };
942
943 struct GdbChunk {
944 InputSection *sec;
945 SmallVector<AddressEntry, 0> addressAreas;
946 SmallVector<CuEntry, 0> compilationUnits;
947 };
948
949 struct GdbSymbol {
950 llvm::CachedHashStringRef name;
951 SmallVector<uint32_t, 0> cuVector;
952 uint32_t nameOff;
953 uint32_t cuVectorOff;
954 };
955
956 GdbIndexSection();
957 template <typename ELFT> static std::unique_ptr<GdbIndexSection> create();
958 void writeTo(uint8_t *buf) override;
959 size_t getSize() const override { return size; }
960 bool isNeeded() const override;
961
962private:
963 struct GdbIndexHeader {
964 llvm::support::ulittle32_t version;
965 llvm::support::ulittle32_t cuListOff;
966 llvm::support::ulittle32_t cuTypesOff;
967 llvm::support::ulittle32_t addressAreaOff;
968 llvm::support::ulittle32_t symtabOff;
969 llvm::support::ulittle32_t constantPoolOff;
970 };
971
972 size_t computeSymtabSize() const;
973
974 // Each chunk contains information gathered from debug sections of a
975 // single object file.
976 SmallVector<GdbChunk, 0> chunks;
977
978 // A symbol table for this .gdb_index section.
979 SmallVector<GdbSymbol, 0> symbols;
980
981 size_t size;
982};
983
984// --eh-frame-hdr option tells linker to construct a header for all the
985// .eh_frame sections. This header is placed to a section named .eh_frame_hdr
986// and also to a PT_GNU_EH_FRAME segment.
987// At runtime the unwinder then can find all the PT_GNU_EH_FRAME segments by
988// calling dl_iterate_phdr.
989// This section contains a lookup table for quick binary search of FDEs.
990// Detailed info about internals can be found in Ian Lance Taylor's blog:
991// http://www.airs.com/blog/archives/460 (".eh_frame")
992// http://www.airs.com/blog/archives/462 (".eh_frame_hdr")
993class EhFrameHeader final : public SyntheticSection {
994public:
995 EhFrameHeader();
996 void write();
997 void writeTo(uint8_t *buf) override;
998 size_t getSize() const override;
999 bool isNeeded() const override;
1000};
1001
1002// For more information about .gnu.version and .gnu.version_r see:
1003// https://www.akkadia.org/drepper/symbol-versioning
1004
1005// The .gnu.version_d section which has a section type of SHT_GNU_verdef shall
1006// contain symbol version definitions. The number of entries in this section
1007// shall be contained in the DT_VERDEFNUM entry of the .dynamic section.
1008// The section shall contain an array of Elf_Verdef structures, optionally
1009// followed by an array of Elf_Verdaux structures.
1010class VersionDefinitionSection final : public SyntheticSection {
1011public:
1012 VersionDefinitionSection();
1013 void finalizeContents() override;
1014 size_t getSize() const override;
1015 void writeTo(uint8_t *buf) override;
1016
1017private:
1018 enum { EntrySize = 28 };
1019 void writeOne(uint8_t *buf, uint32_t index, StringRef name, size_t nameOff);
1020 StringRef getFileDefName();
1021
1022 unsigned fileDefNameOff;
1023 SmallVector<unsigned, 0> verDefNameOffs;
1024};
1025
1026// The .gnu.version section specifies the required version of each symbol in the
1027// dynamic symbol table. It contains one Elf_Versym for each dynamic symbol
1028// table entry. An Elf_Versym is just a 16-bit integer that refers to a version
1029// identifier defined in the either .gnu.version_r or .gnu.version_d section.
1030// The values 0 and 1 are reserved. All other values are used for versions in
1031// the own object or in any of the dependencies.
1032class VersionTableSection final : public SyntheticSection {
1033public:
1034 VersionTableSection();
1035 void finalizeContents() override;
1036 size_t getSize() const override;
1037 void writeTo(uint8_t *buf) override;
1038 bool isNeeded() const override;
1039};
1040
1041// The .gnu.version_r section defines the version identifiers used by
1042// .gnu.version. It contains a linked list of Elf_Verneed data structures. Each
1043// Elf_Verneed specifies the version requirements for a single DSO, and contains
1044// a reference to a linked list of Elf_Vernaux data structures which define the
1045// mapping from version identifiers to version names.
1046template <class ELFT>
1047class VersionNeedSection final : public SyntheticSection {
1048 using Elf_Verneed = typename ELFT::Verneed;
1049 using Elf_Vernaux = typename ELFT::Vernaux;
1050
1051 struct Vernaux {
1052 uint64_t hash;
1053 uint32_t verneedIndex;
1054 uint64_t nameStrTab;
1055 };
1056
1057 struct Verneed {
1058 uint64_t nameStrTab;
1059 std::vector<Vernaux> vernauxs;
1060 };
1061
1062 SmallVector<Verneed, 0> verneeds;
1063
1064public:
1065 VersionNeedSection();
1066 void finalizeContents() override;
1067 void writeTo(uint8_t *buf) override;
1068 size_t getSize() const override;
1069 bool isNeeded() const override;
1070};
1071
1072// MergeSyntheticSection is a class that allows us to put mergeable sections
1073// with different attributes in a single output sections. To do that
1074// we put them into MergeSyntheticSection synthetic input sections which are
1075// attached to regular output sections.
1076class MergeSyntheticSection : public SyntheticSection {
1077public:
1078 void addSection(MergeInputSection *ms);
1079 SmallVector<MergeInputSection *, 0> sections;
1080
1081protected:
1082 MergeSyntheticSection(StringRef name, uint32_t type, uint64_t flags,
1083 uint32_t addralign)
1084 : SyntheticSection(flags, type, addralign, name) {}
1085};
1086
1087class MergeTailSection final : public MergeSyntheticSection {
1088public:
1089 MergeTailSection(StringRef name, uint32_t type, uint64_t flags,
1090 uint32_t addralign);
1091
1092 size_t getSize() const override;
1093 void writeTo(uint8_t *buf) override;
1094 void finalizeContents() override;
1095
1096private:
1097 llvm::StringTableBuilder builder;
1098};
1099
1100class MergeNoTailSection final : public MergeSyntheticSection {
1101public:
1102 MergeNoTailSection(StringRef name, uint32_t type, uint64_t flags,
1103 uint32_t addralign)
1104 : MergeSyntheticSection(name, type, flags, addralign) {}
1105
1106 size_t getSize() const override { return size; }
1107 void writeTo(uint8_t *buf) override;
1108 void finalizeContents() override;
1109
1110private:
1111 // We use the most significant bits of a hash as a shard ID.
1112 // The reason why we don't want to use the least significant bits is
1113 // because DenseMap also uses lower bits to determine a bucket ID.
1114 // If we use lower bits, it significantly increases the probability of
1115 // hash collisions.
1116 size_t getShardId(uint32_t hash) {
1117 assert((hash >> 31) == 0);
1118 return hash >> (31 - llvm::countr_zero(Val: numShards));
1119 }
1120
1121 // Section size
1122 size_t size;
1123
1124 // String table contents
1125 constexpr static size_t numShards = 32;
1126 SmallVector<llvm::StringTableBuilder, 0> shards;
1127 size_t shardOffsets[numShards];
1128};
1129
1130// .MIPS.abiflags section.
1131template <class ELFT>
1132class MipsAbiFlagsSection final : public SyntheticSection {
1133 using Elf_Mips_ABIFlags = llvm::object::Elf_Mips_ABIFlags<ELFT>;
1134
1135public:
1136 static std::unique_ptr<MipsAbiFlagsSection> create();
1137
1138 MipsAbiFlagsSection(Elf_Mips_ABIFlags flags);
1139 size_t getSize() const override { return sizeof(Elf_Mips_ABIFlags); }
1140 void writeTo(uint8_t *buf) override;
1141
1142private:
1143 Elf_Mips_ABIFlags flags;
1144};
1145
1146// .MIPS.options section.
1147template <class ELFT> class MipsOptionsSection final : public SyntheticSection {
1148 using Elf_Mips_Options = llvm::object::Elf_Mips_Options<ELFT>;
1149 using Elf_Mips_RegInfo = llvm::object::Elf_Mips_RegInfo<ELFT>;
1150
1151public:
1152 static std::unique_ptr<MipsOptionsSection<ELFT>> create();
1153
1154 MipsOptionsSection(Elf_Mips_RegInfo reginfo);
1155 void writeTo(uint8_t *buf) override;
1156
1157 size_t getSize() const override {
1158 return sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
1159 }
1160
1161private:
1162 Elf_Mips_RegInfo reginfo;
1163};
1164
1165// MIPS .reginfo section.
1166template <class ELFT> class MipsReginfoSection final : public SyntheticSection {
1167 using Elf_Mips_RegInfo = llvm::object::Elf_Mips_RegInfo<ELFT>;
1168
1169public:
1170 static std::unique_ptr<MipsReginfoSection> create();
1171
1172 MipsReginfoSection(Elf_Mips_RegInfo reginfo);
1173 size_t getSize() const override { return sizeof(Elf_Mips_RegInfo); }
1174 void writeTo(uint8_t *buf) override;
1175
1176private:
1177 Elf_Mips_RegInfo reginfo;
1178};
1179
1180// This is a MIPS specific section to hold a space within the data segment
1181// of executable file which is pointed to by the DT_MIPS_RLD_MAP entry.
1182// See "Dynamic section" in Chapter 5 in the following document:
1183// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1184class MipsRldMapSection final : public SyntheticSection {
1185public:
1186 MipsRldMapSection();
1187 size_t getSize() const override { return config->wordsize; }
1188 void writeTo(uint8_t *buf) override {}
1189};
1190
1191// Representation of the combined .ARM.Exidx input sections. We process these
1192// as a SyntheticSection like .eh_frame as we need to merge duplicate entries
1193// and add terminating sentinel entries.
1194//
1195// The .ARM.exidx input sections after SHF_LINK_ORDER processing is done form
1196// a table that the unwinder can derive (Addresses are encoded as offsets from
1197// table):
1198// | Address of function | Unwind instructions for function |
1199// where the unwind instructions are either a small number of unwind or the
1200// special EXIDX_CANTUNWIND entry representing no unwinding information.
1201// When an exception is thrown from an address A, the unwinder searches the
1202// table for the closest table entry with Address of function <= A. This means
1203// that for two consecutive table entries:
1204// | A1 | U1 |
1205// | A2 | U2 |
1206// The range of addresses described by U1 is [A1, A2)
1207//
1208// There are two cases where we need a linker generated table entry to fixup
1209// the address ranges in the table
1210// Case 1:
1211// - A sentinel entry added with an address higher than all
1212// executable sections. This was needed to work around libunwind bug pr31091.
1213// - After address assignment we need to find the highest addressed executable
1214// section and use the limit of that section so that the unwinder never
1215// matches it.
1216// Case 2:
1217// - InputSections without a .ARM.exidx section (usually from Assembly)
1218// need a table entry so that they terminate the range of the previously
1219// function. This is pr40277.
1220//
1221// Instead of storing pointers to the .ARM.exidx InputSections from
1222// InputObjects, we store pointers to the executable sections that need
1223// .ARM.exidx sections. We can then use the dependentSections of these to
1224// either find the .ARM.exidx section or know that we need to generate one.
1225class ARMExidxSyntheticSection : public SyntheticSection {
1226public:
1227 ARMExidxSyntheticSection();
1228
1229 // Add an input section to the ARMExidxSyntheticSection. Returns whether the
1230 // section needs to be removed from the main input section list.
1231 bool addSection(InputSection *isec);
1232
1233 size_t getSize() const override { return size; }
1234 void writeTo(uint8_t *buf) override;
1235 bool isNeeded() const override;
1236 // Sort and remove duplicate entries.
1237 void finalizeContents() override;
1238 InputSection *getLinkOrderDep() const;
1239
1240 static bool classof(const SectionBase *sec) {
1241 return sec->kind() == InputSectionBase::Synthetic &&
1242 sec->type == llvm::ELF::SHT_ARM_EXIDX;
1243 }
1244
1245 // Links to the ARMExidxSections so we can transfer the relocations once the
1246 // layout is known.
1247 SmallVector<InputSection *, 0> exidxSections;
1248
1249private:
1250 size_t size = 0;
1251
1252 // Instead of storing pointers to the .ARM.exidx InputSections from
1253 // InputObjects, we store pointers to the executable sections that need
1254 // .ARM.exidx sections. We can then use the dependentSections of these to
1255 // either find the .ARM.exidx section or know that we need to generate one.
1256 SmallVector<InputSection *, 0> executableSections;
1257
1258 // The executable InputSection with the highest address to use for the
1259 // sentinel. We store separately from ExecutableSections as merging of
1260 // duplicate entries may mean this InputSection is removed from
1261 // ExecutableSections.
1262 InputSection *sentinel = nullptr;
1263};
1264
1265// A container for one or more linker generated thunks. Instances of these
1266// thunks including ARM interworking and Mips LA25 PI to non-PI thunks.
1267class ThunkSection final : public SyntheticSection {
1268public:
1269 // ThunkSection in OS, with desired outSecOff of Off
1270 ThunkSection(OutputSection *os, uint64_t off);
1271
1272 // Add a newly created Thunk to this container:
1273 // Thunk is given offset from start of this InputSection
1274 // Thunk defines a symbol in this InputSection that can be used as target
1275 // of a relocation
1276 void addThunk(Thunk *t);
1277 size_t getSize() const override;
1278 void writeTo(uint8_t *buf) override;
1279 InputSection *getTargetInputSection() const;
1280 bool assignOffsets();
1281
1282 // When true, round up reported size of section to 4 KiB. See comment
1283 // in addThunkSection() for more details.
1284 bool roundUpSizeForErrata = false;
1285
1286private:
1287 SmallVector<Thunk *, 0> thunks;
1288 size_t size = 0;
1289};
1290
1291// Cortex-M Security Extensions. Prefix for functions that should be exported
1292// for the non-secure world.
1293const char ACLESESYM_PREFIX[] = "__acle_se_";
1294const int ACLESESYM_SIZE = 8;
1295
1296class ArmCmseSGVeneer;
1297
1298class ArmCmseSGSection final : public SyntheticSection {
1299public:
1300 ArmCmseSGSection();
1301 bool isNeeded() const override { return !entries.empty(); }
1302 size_t getSize() const override;
1303 void writeTo(uint8_t *buf) override;
1304 void addSGVeneer(Symbol *sym, Symbol *ext_sym);
1305 void addMappingSymbol();
1306 void finalizeContents() override;
1307 void exportEntries(SymbolTableBaseSection *symTab);
1308 uint64_t impLibMaxAddr = 0;
1309
1310private:
1311 SmallVector<std::pair<Symbol *, Symbol *>, 0> entries;
1312 SmallVector<ArmCmseSGVeneer *, 0> sgVeneers;
1313 uint64_t newEntries = 0;
1314};
1315
1316// Used to compute outSecOff of .got2 in each object file. This is needed to
1317// synthesize PLT entries for PPC32 Secure PLT ABI.
1318class PPC32Got2Section final : public SyntheticSection {
1319public:
1320 PPC32Got2Section();
1321 size_t getSize() const override { return 0; }
1322 bool isNeeded() const override;
1323 void finalizeContents() override;
1324 void writeTo(uint8_t *buf) override {}
1325};
1326
1327// This section is used to store the addresses of functions that are called
1328// in range-extending thunks on PowerPC64. When producing position dependent
1329// code the addresses are link-time constants and the table is written out to
1330// the binary. When producing position-dependent code the table is allocated and
1331// filled in by the dynamic linker.
1332class PPC64LongBranchTargetSection final : public SyntheticSection {
1333public:
1334 PPC64LongBranchTargetSection();
1335 uint64_t getEntryVA(const Symbol *sym, int64_t addend);
1336 std::optional<uint32_t> addEntry(const Symbol *sym, int64_t addend);
1337 size_t getSize() const override;
1338 void writeTo(uint8_t *buf) override;
1339 bool isNeeded() const override;
1340 void finalizeContents() override { finalized = true; }
1341
1342private:
1343 SmallVector<std::pair<const Symbol *, int64_t>, 0> entries;
1344 llvm::DenseMap<std::pair<const Symbol *, int64_t>, uint32_t> entry_index;
1345 bool finalized = false;
1346};
1347
1348template <typename ELFT>
1349class PartitionElfHeaderSection final : public SyntheticSection {
1350public:
1351 PartitionElfHeaderSection();
1352 size_t getSize() const override;
1353 void writeTo(uint8_t *buf) override;
1354};
1355
1356template <typename ELFT>
1357class PartitionProgramHeadersSection final : public SyntheticSection {
1358public:
1359 PartitionProgramHeadersSection();
1360 size_t getSize() const override;
1361 void writeTo(uint8_t *buf) override;
1362};
1363
1364class PartitionIndexSection final : public SyntheticSection {
1365public:
1366 PartitionIndexSection();
1367 size_t getSize() const override;
1368 void finalizeContents() override;
1369 void writeTo(uint8_t *buf) override;
1370};
1371
1372// See the following link for the Android-specific loader code that operates on
1373// this section:
1374// https://cs.android.com/android/platform/superproject/+/master:bionic/libc/bionic/libc_init_static.cpp;drc=9425b16978f9c5aa8f2c50c873db470819480d1d;l=192
1375class MemtagAndroidNote final : public SyntheticSection {
1376public:
1377 MemtagAndroidNote()
1378 : SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE,
1379 /*alignment=*/4, ".note.android.memtag") {}
1380 void writeTo(uint8_t *buf) override;
1381 size_t getSize() const override;
1382};
1383
1384class PackageMetadataNote final : public SyntheticSection {
1385public:
1386 PackageMetadataNote()
1387 : SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE,
1388 /*alignment=*/4, ".note.package") {}
1389 void writeTo(uint8_t *buf) override;
1390 size_t getSize() const override;
1391};
1392
1393class MemtagGlobalDescriptors final : public SyntheticSection {
1394public:
1395 MemtagGlobalDescriptors()
1396 : SyntheticSection(llvm::ELF::SHF_ALLOC,
1397 llvm::ELF::SHT_AARCH64_MEMTAG_GLOBALS_DYNAMIC,
1398 /*alignment=*/4, ".memtag.globals.dynamic") {}
1399 void writeTo(uint8_t *buf) override;
1400 // The size of the section is non-computable until all addresses are
1401 // synthetized, because the section's contents contain a sorted
1402 // varint-compressed list of pointers to global variables. We only know the
1403 // final size after `finalizeAddressDependentContent()`.
1404 size_t getSize() const override;
1405 bool updateAllocSize() override;
1406
1407 void addSymbol(const Symbol &sym) {
1408 symbols.push_back(Elt: &sym);
1409 }
1410
1411 bool isNeeded() const override {
1412 return !symbols.empty();
1413 }
1414
1415private:
1416 SmallVector<const Symbol *, 0> symbols;
1417};
1418
1419template <class ELFT> void createSyntheticSections();
1420InputSection *createInterpSection();
1421MergeInputSection *createCommentSection();
1422template <class ELFT> void splitSections();
1423void combineEhSections();
1424
1425bool hasMemtag();
1426bool canHaveMemtagGlobals();
1427
1428template <typename ELFT> void writeEhdr(uint8_t *buf, Partition &part);
1429template <typename ELFT> void writePhdrs(uint8_t *buf, Partition &part);
1430
1431Defined *addSyntheticLocal(StringRef name, uint8_t type, uint64_t value,
1432 uint64_t size, InputSectionBase &section);
1433
1434void addVerneed(Symbol *ss);
1435
1436// Linker generated per-partition sections.
1437struct Partition {
1438 StringRef name;
1439 uint64_t nameStrTab;
1440
1441 std::unique_ptr<SyntheticSection> elfHeader;
1442 std::unique_ptr<SyntheticSection> programHeaders;
1443 SmallVector<PhdrEntry *, 0> phdrs;
1444
1445 std::unique_ptr<ARMExidxSyntheticSection> armExidx;
1446 std::unique_ptr<BuildIdSection> buildId;
1447 std::unique_ptr<SyntheticSection> dynamic;
1448 std::unique_ptr<StringTableSection> dynStrTab;
1449 std::unique_ptr<SymbolTableBaseSection> dynSymTab;
1450 std::unique_ptr<EhFrameHeader> ehFrameHdr;
1451 std::unique_ptr<EhFrameSection> ehFrame;
1452 std::unique_ptr<GnuHashTableSection> gnuHashTab;
1453 std::unique_ptr<HashTableSection> hashTab;
1454 std::unique_ptr<MemtagAndroidNote> memtagAndroidNote;
1455 std::unique_ptr<MemtagGlobalDescriptors> memtagGlobalDescriptors;
1456 std::unique_ptr<PackageMetadataNote> packageMetadataNote;
1457 std::unique_ptr<RelocationBaseSection> relaDyn;
1458 std::unique_ptr<RelrBaseSection> relrDyn;
1459 std::unique_ptr<VersionDefinitionSection> verDef;
1460 std::unique_ptr<SyntheticSection> verNeed;
1461 std::unique_ptr<VersionTableSection> verSym;
1462
1463 unsigned getNumber() const { return this - &partitions[0] + 1; }
1464};
1465
1466LLVM_LIBRARY_VISIBILITY extern Partition *mainPart;
1467
1468inline Partition &SectionBase::getPartition() const {
1469 assert(isLive());
1470 return partitions[partition - 1];
1471}
1472
1473// Linker generated sections which can be used as inputs and are not specific to
1474// a partition.
1475struct InStruct {
1476 std::unique_ptr<InputSection> attributes;
1477 std::unique_ptr<SyntheticSection> riscvAttributes;
1478 std::unique_ptr<BssSection> bss;
1479 std::unique_ptr<BssSection> bssRelRo;
1480 std::unique_ptr<GotSection> got;
1481 std::unique_ptr<GotPltSection> gotPlt;
1482 std::unique_ptr<IgotPltSection> igotPlt;
1483 std::unique_ptr<RelroPaddingSection> relroPadding;
1484 std::unique_ptr<SyntheticSection> armCmseSGSection;
1485 std::unique_ptr<PPC64LongBranchTargetSection> ppc64LongBranchTarget;
1486 std::unique_ptr<SyntheticSection> mipsAbiFlags;
1487 std::unique_ptr<MipsGotSection> mipsGot;
1488 std::unique_ptr<SyntheticSection> mipsOptions;
1489 std::unique_ptr<SyntheticSection> mipsReginfo;
1490 std::unique_ptr<MipsRldMapSection> mipsRldMap;
1491 std::unique_ptr<SyntheticSection> partEnd;
1492 std::unique_ptr<SyntheticSection> partIndex;
1493 std::unique_ptr<PltSection> plt;
1494 std::unique_ptr<IpltSection> iplt;
1495 std::unique_ptr<PPC32Got2Section> ppc32Got2;
1496 std::unique_ptr<IBTPltSection> ibtPlt;
1497 std::unique_ptr<RelocationBaseSection> relaPlt;
1498 // Non-SHF_ALLOC sections
1499 std::unique_ptr<SyntheticSection> debugNames;
1500 std::unique_ptr<GdbIndexSection> gdbIndex;
1501 std::unique_ptr<StringTableSection> shStrTab;
1502 std::unique_ptr<StringTableSection> strTab;
1503 std::unique_ptr<SymbolTableBaseSection> symTab;
1504 std::unique_ptr<SymtabShndxSection> symTabShndx;
1505
1506 void reset();
1507};
1508
1509LLVM_LIBRARY_VISIBILITY extern InStruct in;
1510
1511} // namespace lld::elf
1512
1513#endif
1514

source code of lld/ELF/SyntheticSections.h