1 //===- Relocations.cpp ----------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains platform-independent functions to process relocations.
11 // I'll describe the overview of this file here.
13 // Simple relocations are easy to handle for the linker. For example,
14 // for R_X86_64_PC64 relocs, the linker just has to fix up locations
15 // with the relative offsets to the target symbols. It would just be
16 // reading records from relocation sections and applying them to output.
18 // But not all relocations are that easy to handle. For example, for
19 // R_386_GOTOFF relocs, the linker has to create new GOT entries for
20 // symbols if they don't exist, and fix up locations with GOT entry
21 // offsets from the beginning of GOT section. So there is more than
22 // fixing addresses in relocation processing.
24 // ELF defines a large number of complex relocations.
26 // The functions in this file analyze relocations and do whatever needs
27 // to be done. It includes, but not limited to, the following.
29 // - create GOT/PLT entries
30 // - create new relocations in .dynsym to let the dynamic linker resolve
31 // them at runtime (since ELF supports dynamic linking, not all
32 // relocations can be resolved at link-time)
33 // - create COPY relocs and reserve space in .bss
34 // - replace expensive relocs (in terms of runtime cost) with cheap ones
35 // - error out infeasible combinations such as PIC and non-relative relocs
37 // Note that the functions in this file don't actually apply relocations
38 // because it doesn't know about the output file nor the output file buffer.
39 // It instead stores Relocation objects to InputSection's Relocations
40 // vector to let it apply later in InputSection::writeTo.
42 //===----------------------------------------------------------------------===//
44 #include "Relocations.h"
46 #include "OutputSections.h"
48 #include "SymbolTable.h"
49 #include "SyntheticSections.h"
53 #include "llvm/Support/Endian.h"
54 #include "llvm/Support/raw_ostream.h"
57 using namespace llvm::ELF;
58 using namespace llvm::object;
59 using namespace llvm::support::endian;
64 static bool refersToGotEntry(RelExpr Expr) {
65 return isRelExprOneOf<R_GOT, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE, R_MIPS_GOT_OFF,
66 R_MIPS_GOT_OFF32, R_MIPS_TLSGD, R_MIPS_TLSLD,
67 R_GOT_PAGE_PC, R_GOT_PC, R_GOT_FROM_END, R_TLSGD,
68 R_TLSGD_PC, R_TLSDESC, R_TLSDESC_PAGE>(Expr);
71 static bool isPreemptible(const SymbolBody &Body, uint32_t Type) {
72 // In case of MIPS GP-relative relocations always resolve to a definition
73 // in a regular input file, ignoring the one-definition rule. So we,
74 // for example, should not attempt to create a dynamic relocation even
75 // if the target symbol is preemptible. There are two two MIPS GP-relative
76 // relocations R_MIPS_GPREL16 and R_MIPS_GPREL32. But only R_MIPS_GPREL16
77 // can be against a preemptible symbol.
78 // To get MIPS relocation type we apply 0xff mask. In case of O32 ABI all
79 // relocation types occupy eight bit. In case of N64 ABI we extract first
80 // relocation from 3-in-1 packet because only the first relocation can
81 // be against a real symbol.
82 if (Config->EMachine == EM_MIPS && (Type & 0xff) == R_MIPS_GPREL16)
84 return Body.isPreemptible();
87 // This function is similar to the `handleTlsRelocation`. ARM and MIPS do not
88 // support any relaxations for TLS relocations so by factoring out ARM and MIPS
89 // handling in to the separate function we can simplify the code and do not
90 // pollute `handleTlsRelocation` by ARM and MIPS `ifs` statements.
91 template <class ELFT, class GOT>
92 static unsigned handleNoRelaxTlsRelocation(
93 GOT *Got, uint32_t Type, SymbolBody &Body, InputSectionBase<ELFT> &C,
94 typename ELFT::uint Offset, typename ELFT::uint Addend, RelExpr Expr) {
95 typedef typename ELFT::uint uintX_t;
96 auto addModuleReloc = [](SymbolBody &Body, GOT *Got, uintX_t Off, bool LD) {
97 // The Dynamic TLS Module Index Relocation can be statically resolved to 1
98 // if we know that we are linking an executable. For ARM we resolve the
99 // relocation when writing the Got. MIPS has a custom Got implementation
100 // that writes the Module index in directly.
101 if (!Body.isPreemptible() && !Config->Pic && Config->EMachine == EM_ARM)
102 Got->Relocations.push_back(
103 {R_ABS, Target->TlsModuleIndexRel, Off, 0, &Body});
105 SymbolBody *Dest = LD ? nullptr : &Body;
106 In<ELFT>::RelaDyn->addReloc(
107 {Target->TlsModuleIndexRel, Got, Off, false, Dest, 0});
110 if (Expr == R_MIPS_TLSLD || Expr == R_TLSLD_PC) {
111 if (Got->addTlsIndex() && (Config->Pic || Config->EMachine == EM_ARM))
112 addModuleReloc(Body, Got, Got->getTlsIndexOff(), true);
113 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
116 if (Target->isTlsGlobalDynamicRel(Type)) {
117 if (Got->addDynTlsEntry(Body) &&
118 (Body.isPreemptible() || Config->EMachine == EM_ARM)) {
119 uintX_t Off = Got->getGlobalDynOffset(Body);
120 addModuleReloc(Body, Got, Off, false);
121 if (Body.isPreemptible())
122 In<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, Got,
123 Off + (uintX_t)sizeof(uintX_t), false,
126 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
132 // Returns the number of relocations processed.
133 template <class ELFT>
134 static unsigned handleTlsRelocation(uint32_t Type, SymbolBody &Body,
135 InputSectionBase<ELFT> &C,
136 typename ELFT::uint Offset,
137 typename ELFT::uint Addend, RelExpr Expr) {
138 if (!(C.Flags & SHF_ALLOC))
144 typedef typename ELFT::uint uintX_t;
146 if (Config->EMachine == EM_ARM)
147 return handleNoRelaxTlsRelocation<ELFT>(In<ELFT>::Got, Type, Body, C,
148 Offset, Addend, Expr);
149 if (Config->EMachine == EM_MIPS)
150 return handleNoRelaxTlsRelocation<ELFT>(In<ELFT>::MipsGot, Type, Body, C,
151 Offset, Addend, Expr);
153 bool IsPreemptible = isPreemptible(Body, Type);
154 if ((Expr == R_TLSDESC || Expr == R_TLSDESC_PAGE || Expr == R_TLSDESC_CALL) &&
156 if (In<ELFT>::Got->addDynTlsEntry(Body)) {
157 uintX_t Off = In<ELFT>::Got->getGlobalDynOffset(Body);
158 In<ELFT>::RelaDyn->addReloc({Target->TlsDescRel, In<ELFT>::Got, Off,
159 !IsPreemptible, &Body, 0});
161 if (Expr != R_TLSDESC_CALL)
162 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
166 if (Expr == R_TLSLD_PC || Expr == R_TLSLD) {
167 // Local-Dynamic relocs can be relaxed to Local-Exec.
168 if (!Config->Shared) {
169 C.Relocations.push_back(
170 {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
173 if (In<ELFT>::Got->addTlsIndex())
174 In<ELFT>::RelaDyn->addReloc({Target->TlsModuleIndexRel, In<ELFT>::Got,
175 In<ELFT>::Got->getTlsIndexOff(), false,
177 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
181 // Local-Dynamic relocs can be relaxed to Local-Exec.
182 if (Target->isTlsLocalDynamicRel(Type) && !Config->Shared) {
183 C.Relocations.push_back(
184 {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
188 if (Expr == R_TLSDESC_PAGE || Expr == R_TLSDESC || Expr == R_TLSDESC_CALL ||
189 Target->isTlsGlobalDynamicRel(Type)) {
190 if (Config->Shared) {
191 if (In<ELFT>::Got->addDynTlsEntry(Body)) {
192 uintX_t Off = In<ELFT>::Got->getGlobalDynOffset(Body);
193 In<ELFT>::RelaDyn->addReloc(
194 {Target->TlsModuleIndexRel, In<ELFT>::Got, Off, false, &Body, 0});
196 // If the symbol is preemptible we need the dynamic linker to write
198 uintX_t OffsetOff = Off + (uintX_t)sizeof(uintX_t);
200 In<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, In<ELFT>::Got,
201 OffsetOff, false, &Body, 0});
203 In<ELFT>::Got->Relocations.push_back(
204 {R_ABS, Target->TlsOffsetRel, OffsetOff, 0, &Body});
206 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
210 // Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
211 // depending on the symbol being locally defined or not.
213 C.Relocations.push_back(
214 {Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_GD_TO_IE), Type,
215 Offset, Addend, &Body});
216 if (!Body.isInGot()) {
217 In<ELFT>::Got->addEntry(Body);
218 In<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, In<ELFT>::Got,
219 Body.getGotOffset<ELFT>(), false, &Body,
222 return Target->TlsGdRelaxSkip;
224 C.Relocations.push_back(
225 {Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_GD_TO_LE), Type,
226 Offset, Addend, &Body});
227 return Target->TlsGdRelaxSkip;
230 // Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
232 if (Target->isTlsInitialExecRel(Type) && !Config->Shared && !IsPreemptible) {
233 C.Relocations.push_back(
234 {R_RELAX_TLS_IE_TO_LE, Type, Offset, Addend, &Body});
240 template <endianness E> static int16_t readSignedLo16(const uint8_t *Loc) {
241 return read32<E>(Loc) & 0xffff;
244 template <class RelTy>
245 static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
246 switch (Rel->getType(Config->Mips64EL)) {
250 return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
252 return R_MIPS_PCLO16;
253 case R_MICROMIPS_HI16:
254 return R_MICROMIPS_LO16;
260 template <class ELFT, class RelTy>
261 static int32_t findMipsPairedAddend(const uint8_t *Buf, const uint8_t *BufLoc,
262 SymbolBody &Sym, const RelTy *Rel,
264 uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
265 uint32_t Type = getMipsPairType(Rel, Sym);
267 // Some MIPS relocations use addend calculated from addend of the relocation
268 // itself and addend of paired relocation. ABI requires to compute such
269 // combined addend in case of REL relocation record format only.
270 // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
271 if (RelTy::IsRela || Type == R_MIPS_NONE)
274 for (const RelTy *RI = Rel; RI != End; ++RI) {
275 if (RI->getType(Config->Mips64EL) != Type)
277 if (RI->getSymbol(Config->Mips64EL) != SymIndex)
279 const endianness E = ELFT::TargetEndianness;
280 return ((read32<E>(BufLoc) & 0xffff) << 16) +
281 readSignedLo16<E>(Buf + RI->r_offset);
283 warn("can't find matching " + toString(Type) + " relocation for " +
284 toString(Rel->getType(Config->Mips64EL)));
288 // True if non-preemptable symbol always has the same value regardless of where
289 // the DSO is loaded.
290 template <class ELFT> static bool isAbsolute(const SymbolBody &Body) {
291 if (Body.isUndefined())
292 return !Body.isLocal() && Body.symbol()->isWeak();
293 if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(&Body))
294 return DR->Section == nullptr; // Absolute symbol.
298 template <class ELFT> static bool isAbsoluteValue(const SymbolBody &Body) {
299 return isAbsolute<ELFT>(Body) || Body.isTls();
302 static bool needsPlt(RelExpr Expr) {
303 return isRelExprOneOf<R_PLT_PC, R_PPC_PLT_OPD, R_PLT, R_PLT_PAGE_PC,
304 R_THUNK_PLT_PC>(Expr);
307 // True if this expression is of the form Sym - X, where X is a position in the
308 // file (PC, or GOT for example).
309 static bool isRelExpr(RelExpr Expr) {
310 return isRelExprOneOf<R_PC, R_GOTREL, R_GOTREL_FROM_END, R_MIPS_GOTREL,
311 R_PAGE_PC, R_RELAX_GOT_PC, R_THUNK_PC, R_THUNK_PLT_PC>(
315 template <class ELFT>
316 static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
317 const SymbolBody &Body,
318 InputSectionBase<ELFT> &S,
319 typename ELFT::uint RelOff) {
320 // These expressions always compute a constant
321 if (isRelExprOneOf<R_SIZE, R_GOT_FROM_END, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE,
322 R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_TLSGD,
323 R_GOT_PAGE_PC, R_GOT_PC, R_PLT_PC, R_TLSGD_PC, R_TLSGD,
324 R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT,
325 R_THUNK_PC, R_THUNK_PLT_PC>(E))
328 // These never do, except if the entire file is position dependent or if
329 // only the low bits are used.
330 if (E == R_GOT || E == R_PLT || E == R_TLSDESC)
331 return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
333 if (isPreemptible(Body, Type))
339 bool AbsVal = isAbsoluteValue<ELFT>(Body);
340 bool RelE = isRelExpr(E);
346 // Relative relocation to an absolute value. This is normally unrepresentable,
347 // but if the relocation refers to a weak undefined symbol, we allow it to
348 // resolve to the image base. This is a little strange, but it allows us to
349 // link function calls to such symbols. Normally such a call will be guarded
350 // with a comparison, which will load a zero from the GOT.
351 // Another special case is MIPS _gp_disp symbol which represents offset
352 // between start of a function and '_gp' value and defined as absolute just
353 // to simplify the code.
354 if (AbsVal && RelE) {
355 if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
357 if (&Body == ElfSym<ELFT>::MipsGpDisp)
359 error(S.getLocation(RelOff) + ": relocation " + toString(Type) +
360 " cannot refer to absolute symbol '" + toString(Body) +
361 "' defined in " + toString(Body.File));
365 return Target->usesOnlyLowPageBits(Type);
368 static RelExpr toPlt(RelExpr Expr) {
369 if (Expr == R_PPC_OPD)
370 return R_PPC_PLT_OPD;
373 if (Expr == R_PAGE_PC)
374 return R_PLT_PAGE_PC;
380 static RelExpr fromPlt(RelExpr Expr) {
381 // We decided not to use a plt. Optimize a reference to the plt to a
382 // reference to the symbol itself.
383 if (Expr == R_PLT_PC)
385 if (Expr == R_PPC_PLT_OPD)
392 template <class ELFT> static uint32_t getAlignment(SharedSymbol<ELFT> *SS) {
393 typedef typename ELFT::uint uintX_t;
395 uintX_t SecAlign = SS->file()->getSection(SS->Sym)->sh_addralign;
396 uintX_t SymValue = SS->Sym.st_value;
398 std::min(countTrailingZeros(SecAlign), countTrailingZeros(SymValue));
399 return 1 << TrailingZeros;
402 // Reserve space in .bss for copy relocation.
403 template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
404 typedef typename ELFT::uint uintX_t;
405 typedef typename ELFT::Sym Elf_Sym;
407 // Copy relocation against zero-sized symbol doesn't make sense.
408 uintX_t SymSize = SS->template getSize<ELFT>();
410 fatal("cannot create a copy relocation for symbol " + toString(*SS));
412 uintX_t Alignment = getAlignment(SS);
413 uintX_t Off = alignTo(Out<ELFT>::Bss->Size, Alignment);
414 Out<ELFT>::Bss->Size = Off + SymSize;
415 Out<ELFT>::Bss->updateAlignment(Alignment);
416 uintX_t Shndx = SS->Sym.st_shndx;
417 uintX_t Value = SS->Sym.st_value;
418 // Look through the DSO's dynamic symbol table for aliases and create a
419 // dynamic symbol for each one. This causes the copy relocation to correctly
420 // interpose any aliases.
421 for (const Elf_Sym &S : SS->file()->getGlobalSymbols()) {
422 if (S.st_shndx != Shndx || S.st_value != Value)
424 auto *Alias = dyn_cast_or_null<SharedSymbol<ELFT>>(
425 Symtab<ELFT>::X->find(check(S.getName(SS->file()->getStringTable()))));
428 Alias->OffsetInBss = Off;
429 Alias->NeedsCopyOrPltAddr = true;
430 Alias->symbol()->IsUsedInRegularObj = true;
432 In<ELFT>::RelaDyn->addReloc(
433 {Target->CopyRel, Out<ELFT>::Bss, SS->OffsetInBss, false, SS, 0});
436 template <class ELFT>
437 static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
438 bool IsWrite, RelExpr Expr, uint32_t Type,
439 const uint8_t *Data, InputSectionBase<ELFT> &S,
440 typename ELFT::uint RelOff) {
441 bool Preemptible = isPreemptible(Body, Type);
442 if (Body.isGnuIFunc()) {
444 } else if (!Preemptible) {
446 Expr = fromPlt(Expr);
447 if (Expr == R_GOT_PC && !isAbsoluteValue<ELFT>(Body))
448 Expr = Target->adjustRelaxExpr(Type, Data, Expr);
450 Expr = Target->getThunkExpr(Expr, Type, File, Body);
452 if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body, S, RelOff))
455 // This relocation would require the dynamic linker to write a value to read
456 // only memory. We can hack around it if we are producing an executable and
457 // the refered symbol can be preemepted to refer to the executable.
458 if (Config->Shared || (Config->Pic && !isRelExpr(Expr))) {
459 error(S.getLocation(RelOff) + ": can't create dynamic relocation " +
460 toString(Type) + " against " +
461 (Body.getName().empty() ? "local symbol in readonly segment"
462 : "symbol '" + toString(Body) + "'") +
463 " defined in " + toString(Body.File));
466 if (Body.getVisibility() != STV_DEFAULT) {
467 error(S.getLocation(RelOff) + ": cannot preempt symbol '" + toString(Body) +
468 "' defined in " + toString(Body.File));
471 if (Body.isObject()) {
472 // Produce a copy relocation.
473 auto *B = cast<SharedSymbol<ELFT>>(&Body);
479 // This handles a non PIC program call to function in a shared library. In
480 // an ideal world, we could just report an error saying the relocation can
481 // overflow at runtime. In the real world with glibc, crt1.o has a
482 // R_X86_64_PC32 pointing to libc.so.
484 // The general idea on how to handle such cases is to create a PLT entry and
485 // use that as the function value.
487 // For the static linking part, we just return a plt expr and everything
488 // else will use the the PLT entry as the address.
490 // The remaining problem is making sure pointer equality still works. We
491 // need the help of the dynamic linker for that. We let it know that we have
492 // a direct reference to a so symbol by creating an undefined symbol with a
493 // non zero st_value. Seeing that, the dynamic linker resolves the symbol to
494 // the value of the symbol we created. This is true even for got entries, so
495 // pointer equality is maintained. To avoid an infinite loop, the only entry
496 // that points to the real function is a dedicated got entry used by the
497 // plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
498 // R_386_JMP_SLOT, etc).
499 Body.NeedsCopyOrPltAddr = true;
502 error("symbol '" + toString(Body) + "' defined in " + toString(Body.File) +
508 template <class ELFT, class RelTy>
509 static typename ELFT::uint computeAddend(const elf::ObjectFile<ELFT> &File,
510 const uint8_t *SectionData,
511 const RelTy *End, const RelTy &RI,
512 RelExpr Expr, SymbolBody &Body) {
513 typedef typename ELFT::uint uintX_t;
515 uint32_t Type = RI.getType(Config->Mips64EL);
516 uintX_t Addend = getAddend<ELFT>(RI);
517 const uint8_t *BufLoc = SectionData + RI.r_offset;
519 Addend += Target->getImplicitAddend(BufLoc, Type);
520 if (Config->EMachine == EM_MIPS) {
521 Addend += findMipsPairedAddend<ELFT>(SectionData, BufLoc, Body, &RI, End);
522 if (Type == R_MIPS_LO16 && Expr == R_PC)
523 // R_MIPS_LO16 expression has R_PC type iif the target is _gp_disp
524 // symbol. In that case we should use the following formula for
525 // calculation "AHL + GP - P + 4". Let's add 4 right here.
526 // For details see p. 4-19 at
527 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
529 if (Expr == R_MIPS_GOTREL && Body.isLocal())
530 Addend += File.MipsGp0;
532 if (Config->Pic && Config->EMachine == EM_PPC64 && Type == R_PPC64_TOC)
533 Addend += getPPC64TocBase();
537 template <class ELFT>
538 static void reportUndefined(SymbolBody &Sym, InputSectionBase<ELFT> &S,
539 typename ELFT::uint Offset) {
540 if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore)
543 if (Config->Shared && Sym.symbol()->Visibility == STV_DEFAULT &&
544 Config->UnresolvedSymbols != UnresolvedPolicy::NoUndef)
548 S.getLocation(Offset) + ": undefined symbol '" + toString(Sym) + "'";
550 if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn)
556 template <class RelTy>
557 static std::pair<uint32_t, uint32_t>
558 mergeMipsN32RelTypes(uint32_t Type, uint32_t Offset, RelTy *I, RelTy *E) {
559 // MIPS N32 ABI treats series of successive relocations with the same offset
560 // as a single relocation. The similar approach used by N64 ABI, but this ABI
561 // packs all relocations into the single relocation record. Here we emulate
562 // this for the N32 ABI. Iterate over relocation with the same offset and put
563 // theirs types into the single bit-set.
564 uint32_t Processed = 0;
565 for (; I != E && Offset == I->r_offset; ++I) {
567 Type |= I->getType(Config->Mips64EL) << (8 * Processed);
569 return std::make_pair(Type, Processed);
572 // The reason we have to do this early scan is as follows
573 // * To mmap the output file, we need to know the size
574 // * For that, we need to know how many dynamic relocs we will have.
575 // It might be possible to avoid this by outputting the file with write:
576 // * Write the allocated output sections, computing addresses.
577 // * Apply relocations, recording which ones require a dynamic reloc.
578 // * Write the dynamic relocations.
579 // * Write the rest of the file.
580 // This would have some drawbacks. For example, we would only know if .rela.dyn
581 // is needed after applying relocations. If it is, it will go after rw and rx
582 // sections. Given that it is ro, we will need an extra PT_LOAD. This
583 // complicates things for the dynamic linker and means we would have to reserve
584 // space for the extra PT_LOAD even if we end up not using it.
585 template <class ELFT, class RelTy>
586 static void scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
587 typedef typename ELFT::uint uintX_t;
589 bool IsWrite = C.Flags & SHF_WRITE;
591 auto AddDyn = [=](const DynamicReloc<ELFT> &Reloc) {
592 In<ELFT>::RelaDyn->addReloc(Reloc);
595 const elf::ObjectFile<ELFT> *File = C.getFile();
596 ArrayRef<uint8_t> SectionData = C.Data;
597 const uint8_t *Buf = SectionData.begin();
599 ArrayRef<EhSectionPiece> Pieces;
600 if (auto *Eh = dyn_cast<EhInputSection<ELFT>>(&C))
603 ArrayRef<EhSectionPiece>::iterator PieceI = Pieces.begin();
604 ArrayRef<EhSectionPiece>::iterator PieceE = Pieces.end();
606 for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
607 const RelTy &RI = *I;
608 SymbolBody &Body = File->getRelocTargetSym(RI);
609 uint32_t Type = RI.getType(Config->Mips64EL);
611 if (Config->MipsN32Abi) {
613 std::tie(Type, Processed) =
614 mergeMipsN32RelTypes(Type, RI.r_offset, I + 1, E);
618 // We only report undefined symbols if they are referenced somewhere in the
620 if (!Body.isLocal() && Body.isUndefined() && !Body.symbol()->isWeak())
621 reportUndefined(Body, C, RI.r_offset);
623 RelExpr Expr = Target->getRelExpr(Type, Body);
624 bool Preemptible = isPreemptible(Body, Type);
625 Expr = adjustExpr(*File, Body, IsWrite, Expr, Type, Buf + RI.r_offset, C,
630 // Skip a relocation that points to a dead piece
631 // in a eh_frame section.
632 while (PieceI != PieceE &&
633 (PieceI->InputOff + PieceI->size() <= RI.r_offset))
636 // Compute the offset of this section in the output section. We do it here
637 // to try to compute it only once.
639 if (PieceI != PieceE) {
640 assert(PieceI->InputOff <= RI.r_offset && "Relocation not in any piece");
641 if (PieceI->OutputOff == -1)
643 Offset = PieceI->OutputOff + RI.r_offset - PieceI->InputOff;
645 Offset = RI.r_offset;
648 // This relocation does not require got entry, but it is relative to got and
649 // needs it to be created. Here we request for that.
650 if (Expr == R_GOTONLY_PC || Expr == R_GOTONLY_PC_FROM_END ||
651 Expr == R_GOTREL || Expr == R_GOTREL_FROM_END || Expr == R_PPC_TOC)
652 In<ELFT>::Got->HasGotOffRel = true;
654 uintX_t Addend = computeAddend(*File, Buf, E, RI, Expr, Body);
656 if (unsigned Processed =
657 handleTlsRelocation<ELFT>(Type, Body, C, Offset, Addend, Expr)) {
658 I += (Processed - 1);
662 // Ignore "hint" and TLS Descriptor call relocation because they are
663 // only markers for relaxation.
664 if (isRelExprOneOf<R_HINT, R_TLSDESC_CALL>(Expr))
667 if (needsPlt(Expr) ||
668 isRelExprOneOf<R_THUNK_ABS, R_THUNK_PC, R_THUNK_PLT_PC>(Expr) ||
669 refersToGotEntry(Expr) || !isPreemptible(Body, Type)) {
670 // If the relocation points to something in the file, we can process it.
672 isStaticLinkTimeConstant<ELFT>(Expr, Type, Body, C, RI.r_offset);
674 // If the output being produced is position independent, the final value
675 // is still not known. In that case we still need some help from the
676 // dynamic linker. We can however do better than just copying the incoming
677 // relocation. We can process some of it and and just ask the dynamic
678 // linker to add the load address.
680 AddDyn({Target->RelativeRel, &C, Offset, true, &Body, Addend});
682 // If the produced value is a constant, we just remember to write it
683 // when outputting this section. We also have to do it if the format
684 // uses Elf_Rel, since in that case the written value is the addend.
685 if (Constant || !RelTy::IsRela)
686 C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
688 // We don't know anything about the finaly symbol. Just ask the dynamic
689 // linker to handle the relocation for us.
690 if (!Target->isPicRel(Type))
691 error(C.getLocation(Offset) + ": relocation " + toString(Type) +
692 " cannot be used against shared object; recompile with -fPIC.");
693 AddDyn({Target->getDynRel(Type), &C, Offset, false, &Body, Addend});
695 // MIPS ABI turns using of GOT and dynamic relocations inside out.
696 // While regular ABI uses dynamic relocations to fill up GOT entries
697 // MIPS ABI requires dynamic linker to fills up GOT entries using
698 // specially sorted dynamic symbol table. This affects even dynamic
699 // relocations against symbols which do not require GOT entries
700 // creation explicitly, i.e. do not have any GOT-relocations. So if
701 // a preemptible symbol has a dynamic relocation we anyway have
702 // to create a GOT entry for it.
703 // If a non-preemptible symbol has a dynamic relocation against it,
704 // dynamic linker takes it st_value, adds offset and writes down
705 // result of the dynamic relocation. In case of preemptible symbol
706 // dynamic linker performs symbol resolution, writes the symbol value
707 // to the GOT entry and reads the GOT entry when it needs to perform
708 // a dynamic relocation.
709 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
710 if (Config->EMachine == EM_MIPS)
711 In<ELFT>::MipsGot->addEntry(Body, Addend, Expr);
715 // At this point we are done with the relocated position. Some relocations
716 // also require us to create a got or plt entry.
718 // If a relocation needs PLT, we create a PLT and a GOT slot for the symbol.
719 if (needsPlt(Expr)) {
723 if (Body.isGnuIFunc() && !Preemptible) {
724 In<ELFT>::Iplt->addEntry(Body);
725 In<ELFT>::IgotPlt->addEntry(Body);
726 In<ELFT>::RelaIplt->addReloc({Target->IRelativeRel, In<ELFT>::IgotPlt,
727 Body.getGotPltOffset<ELFT>(),
728 !Preemptible, &Body, 0});
730 In<ELFT>::Plt->addEntry(Body);
731 In<ELFT>::GotPlt->addEntry(Body);
732 In<ELFT>::RelaPlt->addReloc({Target->PltRel, In<ELFT>::GotPlt,
733 Body.getGotPltOffset<ELFT>(), !Preemptible,
739 if (refersToGotEntry(Expr)) {
740 if (Config->EMachine == EM_MIPS) {
741 // MIPS ABI has special rules to process GOT entries and doesn't
742 // require relocation entries for them. A special case is TLS
743 // relocations. In that case dynamic loader applies dynamic
744 // relocations to initialize TLS GOT entries.
745 // See "Global Offset Table" in Chapter 5 in the following document
746 // for detailed description:
747 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
748 In<ELFT>::MipsGot->addEntry(Body, Addend, Expr);
749 if (Body.isTls() && Body.isPreemptible())
750 AddDyn({Target->TlsGotRel, In<ELFT>::MipsGot,
751 Body.getGotOffset<ELFT>(), false, &Body, 0});
758 In<ELFT>::Got->addEntry(Body);
759 uintX_t Off = Body.getGotOffset<ELFT>();
761 RelExpr GotRE = R_ABS;
763 DynType = Target->TlsGotRel;
765 } else if (!Preemptible && Config->Pic && !isAbsolute<ELFT>(Body))
766 DynType = Target->RelativeRel;
768 DynType = Target->GotRel;
770 // FIXME: this logic is almost duplicated above.
771 bool Constant = !Preemptible && !(Config->Pic && !isAbsolute<ELFT>(Body));
773 AddDyn({DynType, In<ELFT>::Got, Off, !Preemptible, &Body, 0});
774 if (Constant || (!RelTy::IsRela && !Preemptible))
775 In<ELFT>::Got->Relocations.push_back({GotRE, DynType, Off, 0, &Body});
781 template <class ELFT> void scanRelocations(InputSectionBase<ELFT> &S) {
783 scanRelocs(S, S.relas());
785 scanRelocs(S, S.rels());
788 template <class ELFT, class RelTy>
789 static void createThunks(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
790 const elf::ObjectFile<ELFT> *File = C.getFile();
791 for (const RelTy &Rel : Rels) {
792 SymbolBody &Body = File->getRelocTargetSym(Rel);
793 uint32_t Type = Rel.getType(Config->Mips64EL);
794 RelExpr Expr = Target->getRelExpr(Type, Body);
795 if (!isPreemptible(Body, Type) && needsPlt(Expr))
796 Expr = fromPlt(Expr);
797 Expr = Target->getThunkExpr(Expr, Type, *File, Body);
798 // Some targets might require creation of thunks for relocations.
799 // Now we support only MIPS which requires LA25 thunk to call PIC
800 // code from non-PIC one, and ARM which requires interworking.
801 if (Expr == R_THUNK_ABS || Expr == R_THUNK_PC || Expr == R_THUNK_PLT_PC) {
802 auto *Sec = cast<InputSection<ELFT>>(&C);
803 addThunk<ELFT>(Type, Body, *Sec);
808 template <class ELFT> void createThunks(InputSectionBase<ELFT> &S) {
810 createThunks(S, S.relas());
812 createThunks(S, S.rels());
815 template void scanRelocations<ELF32LE>(InputSectionBase<ELF32LE> &);
816 template void scanRelocations<ELF32BE>(InputSectionBase<ELF32BE> &);
817 template void scanRelocations<ELF64LE>(InputSectionBase<ELF64LE> &);
818 template void scanRelocations<ELF64BE>(InputSectionBase<ELF64BE> &);
820 template void createThunks<ELF32LE>(InputSectionBase<ELF32LE> &);
821 template void createThunks<ELF32BE>(InputSectionBase<ELF32BE> &);
822 template void createThunks<ELF64LE>(InputSectionBase<ELF64LE> &);
823 template void createThunks<ELF64BE>(InputSectionBase<ELF64BE> &);