1 //===- InputSection.cpp ---------------------------------------------------===//
2 //
3 //                             The LLVM Linker
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "InputSection.h"
11 #include "Config.h"
12 #include "Error.h"
13 #include "InputFiles.h"
14 #include "OutputSections.h"
15 #include "Target.h"
16 
17 using namespace llvm;
18 using namespace llvm::ELF;
19 using namespace llvm::object;
20 
21 using namespace lld;
22 using namespace lld::elf2;
23 
24 template <class ELFT>
25 InputSectionBase<ELFT>::InputSectionBase(ObjectFile<ELFT> *File,
26                                          const Elf_Shdr *Header,
27                                          Kind SectionKind)
28     : Header(Header), File(File), SectionKind(SectionKind) {}
29 
30 template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
31   ErrorOr<StringRef> Name = File->getObj().getSectionName(this->Header);
32   error(Name);
33   return *Name;
34 }
35 
36 template <class ELFT>
37 ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
38   ErrorOr<ArrayRef<uint8_t>> Ret =
39       this->File->getObj().getSectionContents(this->Header);
40   error(Ret);
41   return *Ret;
42 }
43 
44 template <class ELFT>
45 typename ELFFile<ELFT>::uintX_t
46 InputSectionBase<ELFT>::getOffset(uintX_t Offset) {
47   switch (SectionKind) {
48   case Regular:
49     return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
50   case EHFrame:
51     return cast<EHInputSection<ELFT>>(this)->getOffset(Offset);
52   case Merge:
53     return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
54   }
55   llvm_unreachable("Invalid section kind");
56 }
57 
58 template <class ELFT>
59 typename ELFFile<ELFT>::uintX_t
60 InputSectionBase<ELFT>::getOffset(const Elf_Sym &Sym) {
61   return getOffset(Sym.st_value);
62 }
63 
64 // Returns a section that Rel relocation is pointing to.
65 template <class ELFT>
66 InputSectionBase<ELFT> *
67 InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) {
68   // Global symbol
69   uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
70   if (SymbolBody *B = File->getSymbolBody(SymIndex))
71     if (auto *D = dyn_cast<DefinedRegular<ELFT>>(B->repl()))
72       return &D->Section;
73   // Local symbol
74   if (const Elf_Sym *Sym = File->getLocalSymbol(SymIndex))
75     if (InputSectionBase<ELFT> *Sec = File->getSection(*Sym))
76       return Sec;
77   return nullptr;
78 }
79 
80 template <class ELFT>
81 InputSectionBase<ELFT> *
82 InputSectionBase<ELFT>::getRelocTarget(const Elf_Rela &Rel) {
83   return getRelocTarget(reinterpret_cast<const Elf_Rel &>(Rel));
84 }
85 
86 template <class ELFT>
87 InputSection<ELFT>::InputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header)
88     : InputSectionBase<ELFT>(F, Header, Base::Regular) {}
89 
90 template <class ELFT>
91 bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
92   return S->SectionKind == Base::Regular;
93 }
94 
95 template <class ELFT>
96 template <bool isRela>
97 uint8_t *
98 InputSectionBase<ELFT>::findMipsPairedReloc(uint8_t *Buf, uint32_t Type,
99                                             RelIteratorRange<isRela> Rels) {
100   // Some MIPS relocations use addend calculated from addend of the relocation
101   // itself and addend of paired relocation. ABI requires to compute such
102   // combined addend in case of REL relocation record format only.
103   // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
104   if (isRela || Config->EMachine != EM_MIPS)
105     return nullptr;
106   if (Type == R_MIPS_HI16)
107     Type = R_MIPS_LO16;
108   else if (Type == R_MIPS_PCHI16)
109     Type = R_MIPS_PCLO16;
110   else if (Type == R_MICROMIPS_HI16)
111     Type = R_MICROMIPS_LO16;
112   else
113     return nullptr;
114   for (const auto &RI : Rels) {
115     if (RI.getType(Config->Mips64EL) != Type)
116       continue;
117     uintX_t Offset = getOffset(RI.r_offset);
118     if (Offset == (uintX_t)-1)
119       return nullptr;
120     return Buf + Offset;
121   }
122   return nullptr;
123 }
124 
125 template <class ELFT>
126 template <bool isRela>
127 void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd,
128                                       RelIteratorRange<isRela> Rels) {
129   typedef Elf_Rel_Impl<ELFT, isRela> RelType;
130   size_t Num = Rels.end() - Rels.begin();
131   for (size_t I = 0; I < Num; ++I) {
132     const RelType &RI = *(Rels.begin() + I);
133     uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
134     uint32_t Type = RI.getType(Config->Mips64EL);
135     uintX_t Offset = getOffset(RI.r_offset);
136     if (Offset == (uintX_t)-1)
137       continue;
138 
139     uint8_t *BufLoc = Buf + Offset;
140     uintX_t AddrLoc = OutSec->getVA() + Offset;
141     auto NextRelocs = llvm::make_range(&RI, Rels.end());
142 
143     if (Target->isTlsLocalDynamicReloc(Type) &&
144         !Target->isTlsOptimized(Type, nullptr)) {
145       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
146                           Out<ELFT>::Got->getLocalTlsIndexVA() +
147                               getAddend<ELFT>(RI));
148       continue;
149     }
150 
151     // Handle relocations for local symbols -- they never get
152     // resolved so we don't allocate a SymbolBody.
153     const Elf_Shdr *SymTab = File->getSymbolTable();
154     if (SymIndex < SymTab->sh_info) {
155       uintX_t SymVA = getLocalRelTarget(*File, RI);
156       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA,
157                           findMipsPairedReloc(Buf, Type, NextRelocs));
158       continue;
159     }
160 
161     SymbolBody &Body = *File->getSymbolBody(SymIndex)->repl();
162 
163     if (Target->isTlsGlobalDynamicReloc(Type) &&
164         !Target->isTlsOptimized(Type, &Body)) {
165       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
166                           Out<ELFT>::Got->getGlobalDynAddr(Body) +
167                               getAddend<ELFT>(RI));
168       continue;
169     }
170 
171     if (Target->isTlsOptimized(Type, &Body)) {
172       uintX_t SymVA = Target->relocNeedsGot(Type, Body)
173                           ? Out<ELFT>::Got->getEntryAddr(Body)
174                           : getSymVA<ELFT>(Body);
175       // By optimizing TLS relocations, it is sometimes needed to skip
176       // relocations that immediately follow TLS relocations. This function
177       // knows how many slots we need to skip.
178       I += Target->relocateTlsOptimize(BufLoc, BufEnd, Type, AddrLoc, SymVA,
179                                        Body);
180       continue;
181     }
182 
183     uintX_t SymVA = getSymVA<ELFT>(Body);
184     if (Target->relocNeedsPlt(Type, Body)) {
185       SymVA = Out<ELFT>::Plt->getEntryAddr(Body);
186       Type = Target->getPltRefReloc(Type);
187     } else if (Target->relocNeedsGot(Type, Body)) {
188       SymVA = Out<ELFT>::Got->getEntryAddr(Body);
189       if (Body.isTLS())
190         Type = Target->getTlsGotReloc();
191     } else if (!Target->relocNeedsCopy(Type, Body) &&
192                isa<SharedSymbol<ELFT>>(Body)) {
193       continue;
194     } else if (Target->isTlsDynReloc(Type)) {
195       continue;
196     }
197     Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
198                         SymVA + getAddend<ELFT>(RI),
199                         findMipsPairedReloc(Buf, Type, NextRelocs));
200   }
201 }
202 
203 template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
204   if (this->Header->sh_type == SHT_NOBITS)
205     return;
206   // Copy section contents from source object file to output file.
207   ArrayRef<uint8_t> Data = this->getSectionData();
208   memcpy(Buf + OutSecOff, Data.data(), Data.size());
209 
210   ELFFile<ELFT> &EObj = this->File->getObj();
211   uint8_t *BufEnd = Buf + OutSecOff + Data.size();
212   // Iterate over all relocation sections that apply to this section.
213   for (const Elf_Shdr *RelSec : this->RelocSections) {
214     if (RelSec->sh_type == SHT_RELA)
215       this->relocate(Buf, BufEnd, EObj.relas(RelSec));
216     else
217       this->relocate(Buf, BufEnd, EObj.rels(RelSec));
218   }
219 }
220 
221 template <class ELFT>
222 SplitInputSection<ELFT>::SplitInputSection(
223     ObjectFile<ELFT> *File, const Elf_Shdr *Header,
224     typename InputSectionBase<ELFT>::Kind SectionKind)
225     : InputSectionBase<ELFT>(File, Header, SectionKind) {}
226 
227 template <class ELFT>
228 EHInputSection<ELFT>::EHInputSection(ObjectFile<ELFT> *F,
229                                      const Elf_Shdr *Header)
230     : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {}
231 
232 template <class ELFT>
233 bool EHInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
234   return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
235 }
236 
237 template <class ELFT>
238 typename EHInputSection<ELFT>::uintX_t
239 EHInputSection<ELFT>::getOffset(uintX_t Offset) {
240   std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
241   uintX_t Base = I->second;
242   if (Base == uintX_t(-1))
243     return -1; // Not in the output
244 
245   uintX_t Addend = Offset - I->first;
246   return Base + Addend;
247 }
248 
249 template <class ELFT>
250 MergeInputSection<ELFT>::MergeInputSection(ObjectFile<ELFT> *F,
251                                            const Elf_Shdr *Header)
252     : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}
253 
254 template <class ELFT>
255 bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
256   return S->SectionKind == InputSectionBase<ELFT>::Merge;
257 }
258 
259 template <class ELFT>
260 std::pair<std::pair<typename ELFFile<ELFT>::uintX_t,
261                     typename ELFFile<ELFT>::uintX_t> *,
262           typename ELFFile<ELFT>::uintX_t>
263 SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
264   ArrayRef<uint8_t> D = this->getSectionData();
265   StringRef Data((const char *)D.data(), D.size());
266   uintX_t Size = Data.size();
267   if (Offset >= Size)
268     error("Entry is past the end of the section");
269 
270   // Find the element this offset points to.
271   auto I = std::upper_bound(
272       Offsets.begin(), Offsets.end(), Offset,
273       [](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
274         return A < B.first;
275       });
276   uintX_t End = I == Offsets.end() ? Data.size() : I->first;
277   --I;
278   return std::make_pair(&*I, End);
279 }
280 
281 template <class ELFT>
282 typename MergeInputSection<ELFT>::uintX_t
283 MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
284   std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
285       this->getRangeAndSize(Offset);
286   std::pair<uintX_t, uintX_t> *I = T.first;
287   uintX_t End = T.second;
288   uintX_t Start = I->first;
289 
290   // Compute the Addend and if the Base is cached, return.
291   uintX_t Addend = Offset - Start;
292   uintX_t &Base = I->second;
293   if (Base != uintX_t(-1))
294     return Base + Addend;
295 
296   // Map the base to the offset in the output section and cache it.
297   ArrayRef<uint8_t> D = this->getSectionData();
298   StringRef Data((const char *)D.data(), D.size());
299   StringRef Entry = Data.substr(Start, End - Start);
300   Base =
301       static_cast<MergeOutputSection<ELFT> *>(this->OutSec)->getOffset(Entry);
302   return Base + Addend;
303 }
304 
305 namespace lld {
306 namespace elf2 {
307 template class InputSectionBase<object::ELF32LE>;
308 template class InputSectionBase<object::ELF32BE>;
309 template class InputSectionBase<object::ELF64LE>;
310 template class InputSectionBase<object::ELF64BE>;
311 
312 template class InputSection<object::ELF32LE>;
313 template class InputSection<object::ELF32BE>;
314 template class InputSection<object::ELF64LE>;
315 template class InputSection<object::ELF64BE>;
316 
317 template class EHInputSection<object::ELF32LE>;
318 template class EHInputSection<object::ELF32BE>;
319 template class EHInputSection<object::ELF64LE>;
320 template class EHInputSection<object::ELF64BE>;
321 
322 template class MergeInputSection<object::ELF32LE>;
323 template class MergeInputSection<object::ELF32BE>;
324 template class MergeInputSection<object::ELF64LE>;
325 template class MergeInputSection<object::ELF64BE>;
326 }
327 }
328