1 //===- ELF.cpp - ELF object file implementation ---------------------------===//
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 #include "llvm/Object/ELF.h"
10 #include "llvm/BinaryFormat/ELF.h"
11 #include "llvm/Support/LEB128.h"
12 
13 using namespace llvm;
14 using namespace object;
15 
16 #define STRINGIFY_ENUM_CASE(ns, name)                                          \
17   case ns::name:                                                               \
18     return #name;
19 
20 #define ELF_RELOC(name, value) STRINGIFY_ENUM_CASE(ELF, name)
21 
22 StringRef llvm::object::getELFRelocationTypeName(uint32_t Machine,
23                                                  uint32_t Type) {
24   switch (Machine) {
25   case ELF::EM_X86_64:
26     switch (Type) {
27 #include "llvm/BinaryFormat/ELFRelocs/x86_64.def"
28     default:
29       break;
30     }
31     break;
32   case ELF::EM_386:
33   case ELF::EM_IAMCU:
34     switch (Type) {
35 #include "llvm/BinaryFormat/ELFRelocs/i386.def"
36     default:
37       break;
38     }
39     break;
40   case ELF::EM_MIPS:
41     switch (Type) {
42 #include "llvm/BinaryFormat/ELFRelocs/Mips.def"
43     default:
44       break;
45     }
46     break;
47   case ELF::EM_AARCH64:
48     switch (Type) {
49 #include "llvm/BinaryFormat/ELFRelocs/AArch64.def"
50     default:
51       break;
52     }
53     break;
54   case ELF::EM_ARM:
55     switch (Type) {
56 #include "llvm/BinaryFormat/ELFRelocs/ARM.def"
57     default:
58       break;
59     }
60     break;
61   case ELF::EM_ARC_COMPACT:
62   case ELF::EM_ARC_COMPACT2:
63     switch (Type) {
64 #include "llvm/BinaryFormat/ELFRelocs/ARC.def"
65     default:
66       break;
67     }
68     break;
69   case ELF::EM_AVR:
70     switch (Type) {
71 #include "llvm/BinaryFormat/ELFRelocs/AVR.def"
72     default:
73       break;
74     }
75     break;
76   case ELF::EM_HEXAGON:
77     switch (Type) {
78 #include "llvm/BinaryFormat/ELFRelocs/Hexagon.def"
79     default:
80       break;
81     }
82     break;
83   case ELF::EM_LANAI:
84     switch (Type) {
85 #include "llvm/BinaryFormat/ELFRelocs/Lanai.def"
86     default:
87       break;
88     }
89     break;
90   case ELF::EM_PPC:
91     switch (Type) {
92 #include "llvm/BinaryFormat/ELFRelocs/PowerPC.def"
93     default:
94       break;
95     }
96     break;
97   case ELF::EM_PPC64:
98     switch (Type) {
99 #include "llvm/BinaryFormat/ELFRelocs/PowerPC64.def"
100     default:
101       break;
102     }
103     break;
104   case ELF::EM_RISCV:
105     switch (Type) {
106 #include "llvm/BinaryFormat/ELFRelocs/RISCV.def"
107     default:
108       break;
109     }
110     break;
111   case ELF::EM_S390:
112     switch (Type) {
113 #include "llvm/BinaryFormat/ELFRelocs/SystemZ.def"
114     default:
115       break;
116     }
117     break;
118   case ELF::EM_SPARC:
119   case ELF::EM_SPARC32PLUS:
120   case ELF::EM_SPARCV9:
121     switch (Type) {
122 #include "llvm/BinaryFormat/ELFRelocs/Sparc.def"
123     default:
124       break;
125     }
126     break;
127   case ELF::EM_AMDGPU:
128     switch (Type) {
129 #include "llvm/BinaryFormat/ELFRelocs/AMDGPU.def"
130     default:
131       break;
132     }
133     break;
134   case ELF::EM_BPF:
135     switch (Type) {
136 #include "llvm/BinaryFormat/ELFRelocs/BPF.def"
137     default:
138       break;
139     }
140     break;
141   case ELF::EM_MSP430:
142     switch (Type) {
143 #include "llvm/BinaryFormat/ELFRelocs/MSP430.def"
144     default:
145       break;
146     }
147     break;
148   default:
149     break;
150   }
151   return "Unknown";
152 }
153 
154 #undef ELF_RELOC
155 
156 uint32_t llvm::object::getELFRelativeRelocationType(uint32_t Machine) {
157   switch (Machine) {
158   case ELF::EM_X86_64:
159     return ELF::R_X86_64_RELATIVE;
160   case ELF::EM_386:
161   case ELF::EM_IAMCU:
162     return ELF::R_386_RELATIVE;
163   case ELF::EM_MIPS:
164     break;
165   case ELF::EM_AARCH64:
166     return ELF::R_AARCH64_RELATIVE;
167   case ELF::EM_ARM:
168     return ELF::R_ARM_RELATIVE;
169   case ELF::EM_ARC_COMPACT:
170   case ELF::EM_ARC_COMPACT2:
171     return ELF::R_ARC_RELATIVE;
172   case ELF::EM_AVR:
173     break;
174   case ELF::EM_HEXAGON:
175     return ELF::R_HEX_RELATIVE;
176   case ELF::EM_LANAI:
177     break;
178   case ELF::EM_PPC:
179     break;
180   case ELF::EM_PPC64:
181     return ELF::R_PPC64_RELATIVE;
182   case ELF::EM_RISCV:
183     return ELF::R_RISCV_RELATIVE;
184   case ELF::EM_S390:
185     return ELF::R_390_RELATIVE;
186   case ELF::EM_SPARC:
187   case ELF::EM_SPARC32PLUS:
188   case ELF::EM_SPARCV9:
189     return ELF::R_SPARC_RELATIVE;
190   case ELF::EM_AMDGPU:
191     break;
192   case ELF::EM_BPF:
193     break;
194   default:
195     break;
196   }
197   return 0;
198 }
199 
200 StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
201   switch (Machine) {
202   case ELF::EM_ARM:
203     switch (Type) {
204       STRINGIFY_ENUM_CASE(ELF, SHT_ARM_EXIDX);
205       STRINGIFY_ENUM_CASE(ELF, SHT_ARM_PREEMPTMAP);
206       STRINGIFY_ENUM_CASE(ELF, SHT_ARM_ATTRIBUTES);
207       STRINGIFY_ENUM_CASE(ELF, SHT_ARM_DEBUGOVERLAY);
208       STRINGIFY_ENUM_CASE(ELF, SHT_ARM_OVERLAYSECTION);
209     }
210     break;
211   case ELF::EM_HEXAGON:
212     switch (Type) { STRINGIFY_ENUM_CASE(ELF, SHT_HEX_ORDERED); }
213     break;
214   case ELF::EM_X86_64:
215     switch (Type) { STRINGIFY_ENUM_CASE(ELF, SHT_X86_64_UNWIND); }
216     break;
217   case ELF::EM_MIPS:
218   case ELF::EM_MIPS_RS3_LE:
219     switch (Type) {
220       STRINGIFY_ENUM_CASE(ELF, SHT_MIPS_REGINFO);
221       STRINGIFY_ENUM_CASE(ELF, SHT_MIPS_OPTIONS);
222       STRINGIFY_ENUM_CASE(ELF, SHT_MIPS_DWARF);
223       STRINGIFY_ENUM_CASE(ELF, SHT_MIPS_ABIFLAGS);
224     }
225     break;
226   default:
227     break;
228   }
229 
230   switch (Type) {
231     STRINGIFY_ENUM_CASE(ELF, SHT_NULL);
232     STRINGIFY_ENUM_CASE(ELF, SHT_PROGBITS);
233     STRINGIFY_ENUM_CASE(ELF, SHT_SYMTAB);
234     STRINGIFY_ENUM_CASE(ELF, SHT_STRTAB);
235     STRINGIFY_ENUM_CASE(ELF, SHT_RELA);
236     STRINGIFY_ENUM_CASE(ELF, SHT_HASH);
237     STRINGIFY_ENUM_CASE(ELF, SHT_DYNAMIC);
238     STRINGIFY_ENUM_CASE(ELF, SHT_NOTE);
239     STRINGIFY_ENUM_CASE(ELF, SHT_NOBITS);
240     STRINGIFY_ENUM_CASE(ELF, SHT_REL);
241     STRINGIFY_ENUM_CASE(ELF, SHT_SHLIB);
242     STRINGIFY_ENUM_CASE(ELF, SHT_DYNSYM);
243     STRINGIFY_ENUM_CASE(ELF, SHT_INIT_ARRAY);
244     STRINGIFY_ENUM_CASE(ELF, SHT_FINI_ARRAY);
245     STRINGIFY_ENUM_CASE(ELF, SHT_PREINIT_ARRAY);
246     STRINGIFY_ENUM_CASE(ELF, SHT_GROUP);
247     STRINGIFY_ENUM_CASE(ELF, SHT_SYMTAB_SHNDX);
248     STRINGIFY_ENUM_CASE(ELF, SHT_RELR);
249     STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_REL);
250     STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_RELA);
251     STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_RELR);
252     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ODRTAB);
253     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LINKER_OPTIONS);
254     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_CALL_GRAPH_PROFILE);
255     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ADDRSIG);
256     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_DEPENDENT_LIBRARIES);
257     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_SYMPART);
258     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_PART_EHDR);
259     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_PART_PHDR);
260     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
261     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
262     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);
263     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verneed);
264     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_versym);
265   default:
266     return "Unknown";
267   }
268 }
269 
270 template <class ELFT>
271 Expected<std::vector<typename ELFT::Rela>>
272 ELFFile<ELFT>::decode_relrs(Elf_Relr_Range relrs) const {
273   // This function decodes the contents of an SHT_RELR packed relocation
274   // section.
275   //
276   // Proposal for adding SHT_RELR sections to generic-abi is here:
277   //   https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
278   //
279   // The encoded sequence of Elf64_Relr entries in a SHT_RELR section looks
280   // like [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
281   //
282   // i.e. start with an address, followed by any number of bitmaps. The address
283   // entry encodes 1 relocation. The subsequent bitmap entries encode up to 63
284   // relocations each, at subsequent offsets following the last address entry.
285   //
286   // The bitmap entries must have 1 in the least significant bit. The assumption
287   // here is that an address cannot have 1 in lsb. Odd addresses are not
288   // supported.
289   //
290   // Excluding the least significant bit in the bitmap, each non-zero bit in
291   // the bitmap represents a relocation to be applied to a corresponding machine
292   // word that follows the base address word. The second least significant bit
293   // represents the machine word immediately following the initial address, and
294   // each bit that follows represents the next word, in linear order. As such,
295   // a single bitmap can encode up to 31 relocations in a 32-bit object, and
296   // 63 relocations in a 64-bit object.
297   //
298   // This encoding has a couple of interesting properties:
299   // 1. Looking at any entry, it is clear whether it's an address or a bitmap:
300   //    even means address, odd means bitmap.
301   // 2. Just a simple list of addresses is a valid encoding.
302 
303   Elf_Rela Rela;
304   Rela.r_info = 0;
305   Rela.r_addend = 0;
306   Rela.setType(getRelativeRelocationType(), false);
307   std::vector<Elf_Rela> Relocs;
308 
309   // Word type: uint32_t for Elf32, and uint64_t for Elf64.
310   typedef typename ELFT::uint Word;
311 
312   // Word size in number of bytes.
313   const size_t WordSize = sizeof(Word);
314 
315   // Number of bits used for the relocation offsets bitmap.
316   // These many relative relocations can be encoded in a single entry.
317   const size_t NBits = 8*WordSize - 1;
318 
319   Word Base = 0;
320   for (const Elf_Relr &R : relrs) {
321     Word Entry = R;
322     if ((Entry&1) == 0) {
323       // Even entry: encodes the offset for next relocation.
324       Rela.r_offset = Entry;
325       Relocs.push_back(Rela);
326       // Set base offset for subsequent bitmap entries.
327       Base = Entry + WordSize;
328       continue;
329     }
330 
331     // Odd entry: encodes bitmap for relocations starting at base.
332     Word Offset = Base;
333     while (Entry != 0) {
334       Entry >>= 1;
335       if ((Entry&1) != 0) {
336         Rela.r_offset = Offset;
337         Relocs.push_back(Rela);
338       }
339       Offset += WordSize;
340     }
341 
342     // Advance base offset by NBits words.
343     Base += NBits * WordSize;
344   }
345 
346   return Relocs;
347 }
348 
349 template <class ELFT>
350 Expected<std::vector<typename ELFT::Rela>>
351 ELFFile<ELFT>::android_relas(const Elf_Shdr *Sec) const {
352   // This function reads relocations in Android's packed relocation format,
353   // which is based on SLEB128 and delta encoding.
354   Expected<ArrayRef<uint8_t>> ContentsOrErr = getSectionContents(Sec);
355   if (!ContentsOrErr)
356     return ContentsOrErr.takeError();
357   const uint8_t *Cur = ContentsOrErr->begin();
358   const uint8_t *End = ContentsOrErr->end();
359   if (ContentsOrErr->size() < 4 || Cur[0] != 'A' || Cur[1] != 'P' ||
360       Cur[2] != 'S' || Cur[3] != '2')
361     return createError("invalid packed relocation header");
362   Cur += 4;
363 
364   const char *ErrStr = nullptr;
365   auto ReadSLEB = [&]() -> int64_t {
366     if (ErrStr)
367       return 0;
368     unsigned Len;
369     int64_t Result = decodeSLEB128(Cur, &Len, End, &ErrStr);
370     Cur += Len;
371     return Result;
372   };
373 
374   uint64_t NumRelocs = ReadSLEB();
375   uint64_t Offset = ReadSLEB();
376   uint64_t Addend = 0;
377 
378   if (ErrStr)
379     return createError(ErrStr);
380 
381   std::vector<Elf_Rela> Relocs;
382   Relocs.reserve(NumRelocs);
383   while (NumRelocs) {
384     uint64_t NumRelocsInGroup = ReadSLEB();
385     if (NumRelocsInGroup > NumRelocs)
386       return createError("relocation group unexpectedly large");
387     NumRelocs -= NumRelocsInGroup;
388 
389     uint64_t GroupFlags = ReadSLEB();
390     bool GroupedByInfo = GroupFlags & ELF::RELOCATION_GROUPED_BY_INFO_FLAG;
391     bool GroupedByOffsetDelta = GroupFlags & ELF::RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG;
392     bool GroupedByAddend = GroupFlags & ELF::RELOCATION_GROUPED_BY_ADDEND_FLAG;
393     bool GroupHasAddend = GroupFlags & ELF::RELOCATION_GROUP_HAS_ADDEND_FLAG;
394 
395     uint64_t GroupOffsetDelta;
396     if (GroupedByOffsetDelta)
397       GroupOffsetDelta = ReadSLEB();
398 
399     uint64_t GroupRInfo;
400     if (GroupedByInfo)
401       GroupRInfo = ReadSLEB();
402 
403     if (GroupedByAddend && GroupHasAddend)
404       Addend += ReadSLEB();
405 
406     if (!GroupHasAddend)
407       Addend = 0;
408 
409     for (uint64_t I = 0; I != NumRelocsInGroup; ++I) {
410       Elf_Rela R;
411       Offset += GroupedByOffsetDelta ? GroupOffsetDelta : ReadSLEB();
412       R.r_offset = Offset;
413       R.r_info = GroupedByInfo ? GroupRInfo : ReadSLEB();
414       if (GroupHasAddend && !GroupedByAddend)
415         Addend += ReadSLEB();
416       R.r_addend = Addend;
417       Relocs.push_back(R);
418 
419       if (ErrStr)
420         return createError(ErrStr);
421     }
422 
423     if (ErrStr)
424       return createError(ErrStr);
425   }
426 
427   return Relocs;
428 }
429 
430 template <class ELFT>
431 std::string ELFFile<ELFT>::getDynamicTagAsString(unsigned Arch,
432                                                  uint64_t Type) const {
433 #define DYNAMIC_STRINGIFY_ENUM(tag, value)                                     \
434   case value:                                                                  \
435     return #tag;
436 
437 #define DYNAMIC_TAG(n, v)
438   switch (Arch) {
439   case ELF::EM_AARCH64:
440     switch (Type) {
441 #define AARCH64_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value)
442 #include "llvm/BinaryFormat/DynamicTags.def"
443 #undef AARCH64_DYNAMIC_TAG
444     }
445     break;
446 
447   case ELF::EM_HEXAGON:
448     switch (Type) {
449 #define HEXAGON_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value)
450 #include "llvm/BinaryFormat/DynamicTags.def"
451 #undef HEXAGON_DYNAMIC_TAG
452     }
453     break;
454 
455   case ELF::EM_MIPS:
456     switch (Type) {
457 #define MIPS_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value)
458 #include "llvm/BinaryFormat/DynamicTags.def"
459 #undef MIPS_DYNAMIC_TAG
460     }
461     break;
462 
463   case ELF::EM_PPC64:
464     switch (Type) {
465 #define PPC64_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value)
466 #include "llvm/BinaryFormat/DynamicTags.def"
467 #undef PPC64_DYNAMIC_TAG
468     }
469     break;
470   }
471 #undef DYNAMIC_TAG
472   switch (Type) {
473 // Now handle all dynamic tags except the architecture specific ones
474 #define AARCH64_DYNAMIC_TAG(name, value)
475 #define MIPS_DYNAMIC_TAG(name, value)
476 #define HEXAGON_DYNAMIC_TAG(name, value)
477 #define PPC64_DYNAMIC_TAG(name, value)
478 // Also ignore marker tags such as DT_HIOS (maps to DT_VERNEEDNUM), etc.
479 #define DYNAMIC_TAG_MARKER(name, value)
480 #define DYNAMIC_TAG(name, value) case value: return #name;
481 #include "llvm/BinaryFormat/DynamicTags.def"
482 #undef DYNAMIC_TAG
483 #undef AARCH64_DYNAMIC_TAG
484 #undef MIPS_DYNAMIC_TAG
485 #undef HEXAGON_DYNAMIC_TAG
486 #undef PPC64_DYNAMIC_TAG
487 #undef DYNAMIC_TAG_MARKER
488 #undef DYNAMIC_STRINGIFY_ENUM
489   default:
490     return "<unknown:>0x" + utohexstr(Type, true);
491   }
492 }
493 
494 template <class ELFT>
495 std::string ELFFile<ELFT>::getDynamicTagAsString(uint64_t Type) const {
496   return getDynamicTagAsString(getHeader()->e_machine, Type);
497 }
498 
499 template <class ELFT>
500 Expected<typename ELFT::DynRange> ELFFile<ELFT>::dynamicEntries() const {
501   ArrayRef<Elf_Dyn> Dyn;
502   size_t DynSecSize = 0;
503 
504   auto ProgramHeadersOrError = program_headers();
505   if (!ProgramHeadersOrError)
506     return ProgramHeadersOrError.takeError();
507 
508   for (const Elf_Phdr &Phdr : *ProgramHeadersOrError) {
509     if (Phdr.p_type == ELF::PT_DYNAMIC) {
510       Dyn = makeArrayRef(
511           reinterpret_cast<const Elf_Dyn *>(base() + Phdr.p_offset),
512           Phdr.p_filesz / sizeof(Elf_Dyn));
513       DynSecSize = Phdr.p_filesz;
514       break;
515     }
516   }
517 
518   // If we can't find the dynamic section in the program headers, we just fall
519   // back on the sections.
520   if (Dyn.empty()) {
521     auto SectionsOrError = sections();
522     if (!SectionsOrError)
523       return SectionsOrError.takeError();
524 
525     for (const Elf_Shdr &Sec : *SectionsOrError) {
526       if (Sec.sh_type == ELF::SHT_DYNAMIC) {
527         Expected<ArrayRef<Elf_Dyn>> DynOrError =
528             getSectionContentsAsArray<Elf_Dyn>(&Sec);
529         if (!DynOrError)
530           return DynOrError.takeError();
531         Dyn = *DynOrError;
532         DynSecSize = Sec.sh_size;
533         break;
534       }
535     }
536 
537     if (!Dyn.data())
538       return ArrayRef<Elf_Dyn>();
539   }
540 
541   if (Dyn.empty())
542     // TODO: this error is untested.
543     return createError("invalid empty dynamic section");
544 
545   if (DynSecSize % sizeof(Elf_Dyn) != 0)
546     // TODO: this error is untested.
547     return createError("malformed dynamic section");
548 
549   if (Dyn.back().d_tag != ELF::DT_NULL)
550     // TODO: this error is untested.
551     return createError("dynamic sections must be DT_NULL terminated");
552 
553   return Dyn;
554 }
555 
556 template <class ELFT>
557 Expected<const uint8_t *> ELFFile<ELFT>::toMappedAddr(uint64_t VAddr) const {
558   auto ProgramHeadersOrError = program_headers();
559   if (!ProgramHeadersOrError)
560     return ProgramHeadersOrError.takeError();
561 
562   llvm::SmallVector<Elf_Phdr *, 4> LoadSegments;
563 
564   for (const Elf_Phdr &Phdr : *ProgramHeadersOrError)
565     if (Phdr.p_type == ELF::PT_LOAD)
566       LoadSegments.push_back(const_cast<Elf_Phdr *>(&Phdr));
567 
568   const Elf_Phdr *const *I =
569       std::upper_bound(LoadSegments.begin(), LoadSegments.end(), VAddr,
570                        [](uint64_t VAddr, const Elf_Phdr_Impl<ELFT> *Phdr) {
571                          return VAddr < Phdr->p_vaddr;
572                        });
573 
574   if (I == LoadSegments.begin())
575     return createError("virtual address is not in any segment: 0x" +
576                        Twine::utohexstr(VAddr));
577   --I;
578   const Elf_Phdr &Phdr = **I;
579   uint64_t Delta = VAddr - Phdr.p_vaddr;
580   if (Delta >= Phdr.p_filesz)
581     return createError("virtual address is not in any segment: 0x" +
582                        Twine::utohexstr(VAddr));
583   return base() + Phdr.p_offset + Delta;
584 }
585 
586 template class llvm::object::ELFFile<ELF32LE>;
587 template class llvm::object::ELFFile<ELF32BE>;
588 template class llvm::object::ELFFile<ELF64LE>;
589 template class llvm::object::ELFFile<ELF64BE>;
590