1 //===- ELFObjHandler.cpp --------------------------------------------------===//
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/InterfaceStub/ELFObjHandler.h"
10 #include "llvm/InterfaceStub/ELFStub.h"
11 #include "llvm/MC/StringTableBuilder.h"
12 #include "llvm/Object/Binary.h"
13 #include "llvm/Object/ELFObjectFile.h"
14 #include "llvm/Object/ELFTypes.h"
15 #include "llvm/Support/Errc.h"
16 #include "llvm/Support/Error.h"
17 #include "llvm/Support/FileOutputBuffer.h"
18 #include "llvm/Support/MathExtras.h"
19 #include "llvm/Support/MemoryBuffer.h"
20 #include "llvm/Support/Process.h"
21
22 using llvm::MemoryBufferRef;
23 using llvm::object::ELFObjectFile;
24
25 using namespace llvm;
26 using namespace llvm::object;
27 using namespace llvm::ELF;
28
29 namespace llvm {
30 namespace elfabi {
31
32 // Simple struct to hold relevant .dynamic entries.
33 struct DynamicEntries {
34 uint64_t StrTabAddr = 0;
35 uint64_t StrSize = 0;
36 Optional<uint64_t> SONameOffset;
37 std::vector<uint64_t> NeededLibNames;
38 // Symbol table:
39 uint64_t DynSymAddr = 0;
40 // Hash tables:
41 Optional<uint64_t> ElfHash;
42 Optional<uint64_t> GnuHash;
43 };
44
45 /// This initializes an ELF file header with information specific to a binary
46 /// dynamic shared object.
47 /// Offsets, indexes, links, etc. for section and program headers are just
48 /// zero-initialized as they will be updated elsewhere.
49 ///
50 /// @param ElfHeader Target ELFT::Ehdr to populate.
51 /// @param Machine Target architecture (e_machine from ELF specifications).
52 template <class ELFT>
initELFHeader(typename ELFT::Ehdr & ElfHeader,uint16_t Machine)53 static void initELFHeader(typename ELFT::Ehdr &ElfHeader, uint16_t Machine) {
54 memset(&ElfHeader, 0, sizeof(ElfHeader));
55 // ELF identification.
56 ElfHeader.e_ident[EI_MAG0] = ElfMagic[EI_MAG0];
57 ElfHeader.e_ident[EI_MAG1] = ElfMagic[EI_MAG1];
58 ElfHeader.e_ident[EI_MAG2] = ElfMagic[EI_MAG2];
59 ElfHeader.e_ident[EI_MAG3] = ElfMagic[EI_MAG3];
60 ElfHeader.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
61 bool IsLittleEndian = ELFT::TargetEndianness == support::little;
62 ElfHeader.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
63 ElfHeader.e_ident[EI_VERSION] = EV_CURRENT;
64 ElfHeader.e_ident[EI_OSABI] = ELFOSABI_NONE;
65
66 // Remainder of ELF header.
67 ElfHeader.e_type = ET_DYN;
68 ElfHeader.e_machine = Machine;
69 ElfHeader.e_version = EV_CURRENT;
70 ElfHeader.e_ehsize = sizeof(typename ELFT::Ehdr);
71 ElfHeader.e_phentsize = sizeof(typename ELFT::Phdr);
72 ElfHeader.e_shentsize = sizeof(typename ELFT::Shdr);
73 }
74
75 namespace {
76 template <class ELFT> struct OutputSection {
77 using Elf_Shdr = typename ELFT::Shdr;
78 std::string Name;
79 Elf_Shdr Shdr;
80 uint64_t Addr;
81 uint64_t Offset;
82 uint64_t Size;
83 uint64_t Align;
84 uint32_t Index;
85 bool NoBits = true;
86 };
87
88 template <class T, class ELFT>
89 struct ContentSection : public OutputSection<ELFT> {
90 T Content;
ContentSectionllvm::elfabi::__anon5a3844aa0111::ContentSection91 ContentSection() { this->NoBits = false; }
92 };
93
94 // This class just wraps StringTableBuilder for the purpose of adding a
95 // default constructor.
96 class ELFStringTableBuilder : public StringTableBuilder {
97 public:
ELFStringTableBuilder()98 ELFStringTableBuilder() : StringTableBuilder(StringTableBuilder::ELF) {}
99 };
100
101 template <class ELFT> class ELFSymbolTableBuilder {
102 public:
103 using Elf_Sym = typename ELFT::Sym;
104
ELFSymbolTableBuilder()105 ELFSymbolTableBuilder() { Symbols.push_back({}); }
106
add(size_t StNameOffset,uint64_t StSize,uint8_t StBind,uint8_t StType,uint8_t StOther,uint16_t StShndx)107 void add(size_t StNameOffset, uint64_t StSize, uint8_t StBind, uint8_t StType,
108 uint8_t StOther, uint16_t StShndx) {
109 Elf_Sym S{};
110 S.st_name = StNameOffset;
111 S.st_size = StSize;
112 S.st_info = (StBind << 4) | (StType & 0xf);
113 S.st_other = StOther;
114 S.st_shndx = StShndx;
115 Symbols.push_back(S);
116 }
117
getSize() const118 size_t getSize() const { return Symbols.size() * sizeof(Elf_Sym); }
119
write(uint8_t * Buf) const120 void write(uint8_t *Buf) const {
121 memcpy(Buf, Symbols.data(), sizeof(Elf_Sym) * Symbols.size());
122 }
123
124 private:
125 llvm::SmallVector<Elf_Sym, 8> Symbols;
126 };
127
128 template <class ELFT> class ELFDynamicTableBuilder {
129 public:
130 using Elf_Dyn = typename ELFT::Dyn;
131
addAddr(uint64_t Tag,uint64_t Addr)132 size_t addAddr(uint64_t Tag, uint64_t Addr) {
133 Elf_Dyn Entry;
134 Entry.d_tag = Tag;
135 Entry.d_un.d_ptr = Addr;
136 Entries.push_back(Entry);
137 return Entries.size() - 1;
138 }
139
modifyAddr(size_t Index,uint64_t Addr)140 void modifyAddr(size_t Index, uint64_t Addr) {
141 Entries[Index].d_un.d_ptr = Addr;
142 }
143
addValue(uint64_t Tag,uint64_t Value)144 size_t addValue(uint64_t Tag, uint64_t Value) {
145 Elf_Dyn Entry;
146 Entry.d_tag = Tag;
147 Entry.d_un.d_val = Value;
148 Entries.push_back(Entry);
149 return Entries.size() - 1;
150 }
151
modifyValue(size_t Index,uint64_t Value)152 void modifyValue(size_t Index, uint64_t Value) {
153 Entries[Index].d_un.d_val = Value;
154 }
155
getSize() const156 size_t getSize() const {
157 // Add DT_NULL entry at the end.
158 return (Entries.size() + 1) * sizeof(Elf_Dyn);
159 }
160
write(uint8_t * Buf) const161 void write(uint8_t *Buf) const {
162 memcpy(Buf, Entries.data(), sizeof(Elf_Dyn) * Entries.size());
163 // Add DT_NULL entry at the end.
164 memset(Buf + sizeof(Elf_Dyn) * Entries.size(), 0, sizeof(Elf_Dyn));
165 }
166
167 private:
168 llvm::SmallVector<Elf_Dyn, 8> Entries;
169 };
170
171 template <class ELFT> class ELFStubBuilder {
172 public:
173 using Elf_Ehdr = typename ELFT::Ehdr;
174 using Elf_Shdr = typename ELFT::Shdr;
175 using Elf_Phdr = typename ELFT::Phdr;
176 using Elf_Sym = typename ELFT::Sym;
177 using Elf_Addr = typename ELFT::Addr;
178 using Elf_Dyn = typename ELFT::Dyn;
179
180 ELFStubBuilder(const ELFStubBuilder &) = delete;
181 ELFStubBuilder(ELFStubBuilder &&) = default;
182
ELFStubBuilder(const ELFStub & Stub)183 explicit ELFStubBuilder(const ELFStub &Stub) {
184 DynSym.Name = ".dynsym";
185 DynSym.Align = sizeof(Elf_Addr);
186 DynStr.Name = ".dynstr";
187 DynStr.Align = 1;
188 DynTab.Name = ".dynamic";
189 DynTab.Align = sizeof(Elf_Addr);
190 ShStrTab.Name = ".shstrtab";
191 ShStrTab.Align = 1;
192
193 // Populate string tables.
194 for (const ELFSymbol &Sym : Stub.Symbols)
195 DynStr.Content.add(Sym.Name);
196 for (const std::string &Lib : Stub.NeededLibs)
197 DynStr.Content.add(Lib);
198 if (Stub.SoName)
199 DynStr.Content.add(Stub.SoName.getValue());
200
201 std::vector<OutputSection<ELFT> *> Sections = {&DynSym, &DynStr, &DynTab,
202 &ShStrTab};
203 const OutputSection<ELFT> *LastSection = Sections.back();
204 // Now set the Index and put sections names into ".shstrtab".
205 uint64_t Index = 1;
206 for (OutputSection<ELFT> *Sec : Sections) {
207 Sec->Index = Index++;
208 ShStrTab.Content.add(Sec->Name);
209 }
210 ShStrTab.Content.finalize();
211 ShStrTab.Size = ShStrTab.Content.getSize();
212 DynStr.Content.finalize();
213 DynStr.Size = DynStr.Content.getSize();
214
215 // Populate dynamic symbol table.
216 for (const ELFSymbol &Sym : Stub.Symbols) {
217 uint8_t Bind = Sym.Weak ? STB_WEAK : STB_GLOBAL;
218 // For non-undefined symbols, value of the shndx is not relevant at link
219 // time as long as it is not SHN_UNDEF. Set shndx to 1, which
220 // points to ".dynsym".
221 uint16_t Shndx = Sym.Undefined ? SHN_UNDEF : 1;
222 DynSym.Content.add(DynStr.Content.getOffset(Sym.Name), Sym.Size, Bind,
223 (uint8_t)Sym.Type, 0, Shndx);
224 }
225 DynSym.Size = DynSym.Content.getSize();
226
227 // Poplulate dynamic table.
228 size_t DynSymIndex = DynTab.Content.addAddr(DT_SYMTAB, 0);
229 size_t DynStrIndex = DynTab.Content.addAddr(DT_STRTAB, 0);
230 for (const std::string &Lib : Stub.NeededLibs)
231 DynTab.Content.addValue(DT_NEEDED, DynStr.Content.getOffset(Lib));
232 if (Stub.SoName)
233 DynTab.Content.addValue(DT_SONAME,
234 DynStr.Content.getOffset(Stub.SoName.getValue()));
235 DynTab.Size = DynTab.Content.getSize();
236 // Calculate sections' addresses and offsets.
237 uint64_t CurrentOffset = sizeof(Elf_Ehdr);
238 for (OutputSection<ELFT> *Sec : Sections) {
239 Sec->Offset = alignTo(CurrentOffset, Sec->Align);
240 Sec->Addr = Sec->Offset;
241 CurrentOffset = Sec->Offset + Sec->Size;
242 }
243 // Fill Addr back to dynamic table.
244 DynTab.Content.modifyAddr(DynSymIndex, DynSym.Addr);
245 DynTab.Content.modifyAddr(DynStrIndex, DynStr.Addr);
246 // Write section headers of string tables.
247 fillSymTabShdr(DynSym, SHT_DYNSYM);
248 fillStrTabShdr(DynStr, SHF_ALLOC);
249 fillDynTabShdr(DynTab);
250 fillStrTabShdr(ShStrTab);
251
252 // Finish initializing the ELF header.
253 initELFHeader<ELFT>(ElfHeader, Stub.Arch);
254 ElfHeader.e_shstrndx = ShStrTab.Index;
255 ElfHeader.e_shnum = LastSection->Index + 1;
256 ElfHeader.e_shoff =
257 alignTo(LastSection->Offset + LastSection->Size, sizeof(Elf_Addr));
258 }
259
getSize() const260 size_t getSize() const {
261 return ElfHeader.e_shoff + ElfHeader.e_shnum * sizeof(Elf_Shdr);
262 }
263
write(uint8_t * Data) const264 void write(uint8_t *Data) const {
265 write(Data, ElfHeader);
266 DynSym.Content.write(Data + DynSym.Shdr.sh_offset);
267 DynStr.Content.write(Data + DynStr.Shdr.sh_offset);
268 DynTab.Content.write(Data + DynTab.Shdr.sh_offset);
269 ShStrTab.Content.write(Data + ShStrTab.Shdr.sh_offset);
270 writeShdr(Data, DynSym);
271 writeShdr(Data, DynStr);
272 writeShdr(Data, DynTab);
273 writeShdr(Data, ShStrTab);
274 }
275
276 private:
277 Elf_Ehdr ElfHeader;
278 ContentSection<ELFStringTableBuilder, ELFT> DynStr;
279 ContentSection<ELFStringTableBuilder, ELFT> ShStrTab;
280 ContentSection<ELFSymbolTableBuilder<ELFT>, ELFT> DynSym;
281 ContentSection<ELFDynamicTableBuilder<ELFT>, ELFT> DynTab;
282
write(uint8_t * Data,const T & Value)283 template <class T> static void write(uint8_t *Data, const T &Value) {
284 *reinterpret_cast<T *>(Data) = Value;
285 }
286
fillStrTabShdr(ContentSection<ELFStringTableBuilder,ELFT> & StrTab,uint32_t ShFlags=0) const287 void fillStrTabShdr(ContentSection<ELFStringTableBuilder, ELFT> &StrTab,
288 uint32_t ShFlags = 0) const {
289 StrTab.Shdr.sh_type = SHT_STRTAB;
290 StrTab.Shdr.sh_flags = ShFlags;
291 StrTab.Shdr.sh_addr = StrTab.Addr;
292 StrTab.Shdr.sh_offset = StrTab.Offset;
293 StrTab.Shdr.sh_info = 0;
294 StrTab.Shdr.sh_size = StrTab.Size;
295 StrTab.Shdr.sh_name = ShStrTab.Content.getOffset(StrTab.Name);
296 StrTab.Shdr.sh_addralign = StrTab.Align;
297 StrTab.Shdr.sh_entsize = 0;
298 StrTab.Shdr.sh_link = 0;
299 }
fillSymTabShdr(ContentSection<ELFSymbolTableBuilder<ELFT>,ELFT> & SymTab,uint32_t ShType) const300 void fillSymTabShdr(ContentSection<ELFSymbolTableBuilder<ELFT>, ELFT> &SymTab,
301 uint32_t ShType) const {
302 SymTab.Shdr.sh_type = ShType;
303 SymTab.Shdr.sh_flags = SHF_ALLOC;
304 SymTab.Shdr.sh_addr = SymTab.Addr;
305 SymTab.Shdr.sh_offset = SymTab.Offset;
306 SymTab.Shdr.sh_info = SymTab.Size / sizeof(Elf_Sym) > 1 ? 1 : 0;
307 SymTab.Shdr.sh_size = SymTab.Size;
308 SymTab.Shdr.sh_name = this->ShStrTab.Content.getOffset(SymTab.Name);
309 SymTab.Shdr.sh_addralign = SymTab.Align;
310 SymTab.Shdr.sh_entsize = sizeof(Elf_Sym);
311 SymTab.Shdr.sh_link = this->DynStr.Index;
312 }
fillDynTabShdr(ContentSection<ELFDynamicTableBuilder<ELFT>,ELFT> & DynTab) const313 void fillDynTabShdr(
314 ContentSection<ELFDynamicTableBuilder<ELFT>, ELFT> &DynTab) const {
315 DynTab.Shdr.sh_type = SHT_DYNAMIC;
316 DynTab.Shdr.sh_flags = SHF_ALLOC;
317 DynTab.Shdr.sh_addr = DynTab.Addr;
318 DynTab.Shdr.sh_offset = DynTab.Offset;
319 DynTab.Shdr.sh_info = 0;
320 DynTab.Shdr.sh_size = DynTab.Size;
321 DynTab.Shdr.sh_name = this->ShStrTab.Content.getOffset(DynTab.Name);
322 DynTab.Shdr.sh_addralign = DynTab.Align;
323 DynTab.Shdr.sh_entsize = sizeof(Elf_Dyn);
324 DynTab.Shdr.sh_link = this->DynStr.Index;
325 }
shdrOffset(const OutputSection<ELFT> & Sec) const326 uint64_t shdrOffset(const OutputSection<ELFT> &Sec) const {
327 return ElfHeader.e_shoff + Sec.Index * sizeof(Elf_Shdr);
328 }
329
writeShdr(uint8_t * Data,const OutputSection<ELFT> & Sec) const330 void writeShdr(uint8_t *Data, const OutputSection<ELFT> &Sec) const {
331 write(Data + shdrOffset(Sec), Sec.Shdr);
332 }
333 };
334 } // end anonymous namespace
335
336 /// This function behaves similarly to StringRef::substr(), but attempts to
337 /// terminate the returned StringRef at the first null terminator. If no null
338 /// terminator is found, an error is returned.
339 ///
340 /// @param Str Source string to create a substring from.
341 /// @param Offset The start index of the desired substring.
terminatedSubstr(StringRef Str,size_t Offset)342 static Expected<StringRef> terminatedSubstr(StringRef Str, size_t Offset) {
343 size_t StrEnd = Str.find('\0', Offset);
344 if (StrEnd == StringLiteral::npos) {
345 return createError(
346 "String overran bounds of string table (no null terminator)");
347 }
348
349 size_t StrLen = StrEnd - Offset;
350 return Str.substr(Offset, StrLen);
351 }
352
353 /// This function takes an error, and appends a string of text to the end of
354 /// that error. Since "appending" to an Error isn't supported behavior of an
355 /// Error, this function technically creates a new error with the combined
356 /// message and consumes the old error.
357 ///
358 /// @param Err Source error.
359 /// @param After Text to append at the end of Err's error message.
appendToError(Error Err,StringRef After)360 Error appendToError(Error Err, StringRef After) {
361 std::string Message;
362 raw_string_ostream Stream(Message);
363 Stream << Err;
364 Stream << " " << After;
365 consumeError(std::move(Err));
366 return createError(Stream.str().c_str());
367 }
368
369 /// This function populates a DynamicEntries struct using an ELFT::DynRange.
370 /// After populating the struct, the members are validated with
371 /// some basic sanity checks.
372 ///
373 /// @param Dyn Target DynamicEntries struct to populate.
374 /// @param DynTable Source dynamic table.
375 template <class ELFT>
populateDynamic(DynamicEntries & Dyn,typename ELFT::DynRange DynTable)376 static Error populateDynamic(DynamicEntries &Dyn,
377 typename ELFT::DynRange DynTable) {
378 if (DynTable.empty())
379 return createError("No .dynamic section found");
380
381 // Search .dynamic for relevant entries.
382 bool FoundDynStr = false;
383 bool FoundDynStrSz = false;
384 bool FoundDynSym = false;
385 for (auto &Entry : DynTable) {
386 switch (Entry.d_tag) {
387 case DT_SONAME:
388 Dyn.SONameOffset = Entry.d_un.d_val;
389 break;
390 case DT_STRTAB:
391 Dyn.StrTabAddr = Entry.d_un.d_ptr;
392 FoundDynStr = true;
393 break;
394 case DT_STRSZ:
395 Dyn.StrSize = Entry.d_un.d_val;
396 FoundDynStrSz = true;
397 break;
398 case DT_NEEDED:
399 Dyn.NeededLibNames.push_back(Entry.d_un.d_val);
400 break;
401 case DT_SYMTAB:
402 Dyn.DynSymAddr = Entry.d_un.d_ptr;
403 FoundDynSym = true;
404 break;
405 case DT_HASH:
406 Dyn.ElfHash = Entry.d_un.d_ptr;
407 break;
408 case DT_GNU_HASH:
409 Dyn.GnuHash = Entry.d_un.d_ptr;
410 }
411 }
412
413 if (!FoundDynStr) {
414 return createError(
415 "Couldn't locate dynamic string table (no DT_STRTAB entry)");
416 }
417 if (!FoundDynStrSz) {
418 return createError(
419 "Couldn't determine dynamic string table size (no DT_STRSZ entry)");
420 }
421 if (!FoundDynSym) {
422 return createError(
423 "Couldn't locate dynamic symbol table (no DT_SYMTAB entry)");
424 }
425 if (Dyn.SONameOffset.hasValue() && *Dyn.SONameOffset >= Dyn.StrSize) {
426 return createStringError(object_error::parse_failed,
427 "DT_SONAME string offset (0x%016" PRIx64
428 ") outside of dynamic string table",
429 *Dyn.SONameOffset);
430 }
431 for (uint64_t Offset : Dyn.NeededLibNames) {
432 if (Offset >= Dyn.StrSize) {
433 return createStringError(object_error::parse_failed,
434 "DT_NEEDED string offset (0x%016" PRIx64
435 ") outside of dynamic string table",
436 Offset);
437 }
438 }
439
440 return Error::success();
441 }
442
443 /// This function extracts symbol type from a symbol's st_info member and
444 /// maps it to an ELFSymbolType enum.
445 /// Currently, STT_NOTYPE, STT_OBJECT, STT_FUNC, and STT_TLS are supported.
446 /// Other symbol types are mapped to ELFSymbolType::Unknown.
447 ///
448 /// @param Info Binary symbol st_info to extract symbol type from.
convertInfoToType(uint8_t Info)449 static ELFSymbolType convertInfoToType(uint8_t Info) {
450 Info = Info & 0xf;
451 switch (Info) {
452 case ELF::STT_NOTYPE:
453 return ELFSymbolType::NoType;
454 case ELF::STT_OBJECT:
455 return ELFSymbolType::Object;
456 case ELF::STT_FUNC:
457 return ELFSymbolType::Func;
458 case ELF::STT_TLS:
459 return ELFSymbolType::TLS;
460 default:
461 return ELFSymbolType::Unknown;
462 }
463 }
464
465 /// This function creates an ELFSymbol and populates all members using
466 /// information from a binary ELFT::Sym.
467 ///
468 /// @param SymName The desired name of the ELFSymbol.
469 /// @param RawSym ELFT::Sym to extract symbol information from.
470 template <class ELFT>
createELFSym(StringRef SymName,const typename ELFT::Sym & RawSym)471 static ELFSymbol createELFSym(StringRef SymName,
472 const typename ELFT::Sym &RawSym) {
473 ELFSymbol TargetSym{std::string(SymName)};
474 uint8_t Binding = RawSym.getBinding();
475 if (Binding == STB_WEAK)
476 TargetSym.Weak = true;
477 else
478 TargetSym.Weak = false;
479
480 TargetSym.Undefined = RawSym.isUndefined();
481 TargetSym.Type = convertInfoToType(RawSym.st_info);
482
483 if (TargetSym.Type == ELFSymbolType::Func) {
484 TargetSym.Size = 0;
485 } else {
486 TargetSym.Size = RawSym.st_size;
487 }
488 return TargetSym;
489 }
490
491 /// This function populates an ELFStub with symbols using information read
492 /// from an ELF binary.
493 ///
494 /// @param TargetStub ELFStub to add symbols to.
495 /// @param DynSym Range of dynamic symbols to add to TargetStub.
496 /// @param DynStr StringRef to the dynamic string table.
497 template <class ELFT>
populateSymbols(ELFStub & TargetStub,const typename ELFT::SymRange DynSym,StringRef DynStr)498 static Error populateSymbols(ELFStub &TargetStub,
499 const typename ELFT::SymRange DynSym,
500 StringRef DynStr) {
501 // Skips the first symbol since it's the NULL symbol.
502 for (auto RawSym : DynSym.drop_front(1)) {
503 // If a symbol does not have global or weak binding, ignore it.
504 uint8_t Binding = RawSym.getBinding();
505 if (!(Binding == STB_GLOBAL || Binding == STB_WEAK))
506 continue;
507 // If a symbol doesn't have default or protected visibility, ignore it.
508 uint8_t Visibility = RawSym.getVisibility();
509 if (!(Visibility == STV_DEFAULT || Visibility == STV_PROTECTED))
510 continue;
511 // Create an ELFSymbol and populate it with information from the symbol
512 // table entry.
513 Expected<StringRef> SymName = terminatedSubstr(DynStr, RawSym.st_name);
514 if (!SymName)
515 return SymName.takeError();
516 ELFSymbol Sym = createELFSym<ELFT>(*SymName, RawSym);
517 TargetStub.Symbols.insert(std::move(Sym));
518 // TODO: Populate symbol warning.
519 }
520 return Error::success();
521 }
522
523 /// Returns a new ELFStub with all members populated from an ELFObjectFile.
524 /// @param ElfObj Source ELFObjectFile.
525 template <class ELFT>
526 static Expected<std::unique_ptr<ELFStub>>
buildStub(const ELFObjectFile<ELFT> & ElfObj)527 buildStub(const ELFObjectFile<ELFT> &ElfObj) {
528 using Elf_Dyn_Range = typename ELFT::DynRange;
529 using Elf_Phdr_Range = typename ELFT::PhdrRange;
530 using Elf_Sym_Range = typename ELFT::SymRange;
531 using Elf_Sym = typename ELFT::Sym;
532 std::unique_ptr<ELFStub> DestStub = std::make_unique<ELFStub>();
533 const ELFFile<ELFT> &ElfFile = ElfObj.getELFFile();
534 // Fetch .dynamic table.
535 Expected<Elf_Dyn_Range> DynTable = ElfFile.dynamicEntries();
536 if (!DynTable) {
537 return DynTable.takeError();
538 }
539
540 // Fetch program headers.
541 Expected<Elf_Phdr_Range> PHdrs = ElfFile.program_headers();
542 if (!PHdrs) {
543 return PHdrs.takeError();
544 }
545
546 // Collect relevant .dynamic entries.
547 DynamicEntries DynEnt;
548 if (Error Err = populateDynamic<ELFT>(DynEnt, *DynTable))
549 return std::move(Err);
550
551 // Get pointer to in-memory location of .dynstr section.
552 Expected<const uint8_t *> DynStrPtr = ElfFile.toMappedAddr(DynEnt.StrTabAddr);
553 if (!DynStrPtr)
554 return appendToError(DynStrPtr.takeError(),
555 "when locating .dynstr section contents");
556
557 StringRef DynStr(reinterpret_cast<const char *>(DynStrPtr.get()),
558 DynEnt.StrSize);
559
560 // Populate Arch from ELF header.
561 DestStub->Arch = ElfFile.getHeader().e_machine;
562
563 // Populate SoName from .dynamic entries and dynamic string table.
564 if (DynEnt.SONameOffset.hasValue()) {
565 Expected<StringRef> NameOrErr =
566 terminatedSubstr(DynStr, *DynEnt.SONameOffset);
567 if (!NameOrErr) {
568 return appendToError(NameOrErr.takeError(), "when reading DT_SONAME");
569 }
570 DestStub->SoName = std::string(*NameOrErr);
571 }
572
573 // Populate NeededLibs from .dynamic entries and dynamic string table.
574 for (uint64_t NeededStrOffset : DynEnt.NeededLibNames) {
575 Expected<StringRef> LibNameOrErr =
576 terminatedSubstr(DynStr, NeededStrOffset);
577 if (!LibNameOrErr) {
578 return appendToError(LibNameOrErr.takeError(), "when reading DT_NEEDED");
579 }
580 DestStub->NeededLibs.push_back(std::string(*LibNameOrErr));
581 }
582
583 // Populate Symbols from .dynsym table and dynamic string table.
584 Expected<uint64_t> SymCount = ElfFile.getDynSymtabSize();
585 if (!SymCount)
586 return SymCount.takeError();
587 if (*SymCount > 0) {
588 // Get pointer to in-memory location of .dynsym section.
589 Expected<const uint8_t *> DynSymPtr =
590 ElfFile.toMappedAddr(DynEnt.DynSymAddr);
591 if (!DynSymPtr)
592 return appendToError(DynSymPtr.takeError(),
593 "when locating .dynsym section contents");
594 Elf_Sym_Range DynSyms = ArrayRef<Elf_Sym>(
595 reinterpret_cast<const Elf_Sym *>(*DynSymPtr), *SymCount);
596 Error SymReadError = populateSymbols<ELFT>(*DestStub, DynSyms, DynStr);
597 if (SymReadError)
598 return appendToError(std::move(SymReadError),
599 "when reading dynamic symbols");
600 }
601
602 return std::move(DestStub);
603 }
604
605 /// This function opens a file for writing and then writes a binary ELF stub to
606 /// the file.
607 ///
608 /// @param FilePath File path for writing the ELF binary.
609 /// @param Stub Source ELFStub to generate a binary ELF stub from.
610 template <class ELFT>
writeELFBinaryToFile(StringRef FilePath,const ELFStub & Stub,bool WriteIfChanged)611 static Error writeELFBinaryToFile(StringRef FilePath, const ELFStub &Stub,
612 bool WriteIfChanged) {
613 ELFStubBuilder<ELFT> Builder{Stub};
614 // Write Stub to memory first.
615 std::vector<uint8_t> Buf(Builder.getSize());
616 Builder.write(Buf.data());
617
618 if (WriteIfChanged) {
619 if (ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrError =
620 MemoryBuffer::getFile(FilePath)) {
621 // Compare Stub output with existing Stub file.
622 // If Stub file unchanged, abort updating.
623 if ((*BufOrError)->getBufferSize() == Builder.getSize() &&
624 !memcmp((*BufOrError)->getBufferStart(), Buf.data(),
625 Builder.getSize()))
626 return Error::success();
627 }
628 }
629
630 Expected<std::unique_ptr<FileOutputBuffer>> BufOrError =
631 FileOutputBuffer::create(FilePath, Builder.getSize());
632 if (!BufOrError)
633 return createStringError(errc::invalid_argument,
634 toString(BufOrError.takeError()) +
635 " when trying to open `" + FilePath +
636 "` for writing");
637
638 // Write binary to file.
639 std::unique_ptr<FileOutputBuffer> FileBuf = std::move(*BufOrError);
640 memcpy(FileBuf->getBufferStart(), Buf.data(), Buf.size());
641
642 return FileBuf->commit();
643 }
644
readELFFile(MemoryBufferRef Buf)645 Expected<std::unique_ptr<ELFStub>> readELFFile(MemoryBufferRef Buf) {
646 Expected<std::unique_ptr<Binary>> BinOrErr = createBinary(Buf);
647 if (!BinOrErr) {
648 return BinOrErr.takeError();
649 }
650
651 Binary *Bin = BinOrErr->get();
652 if (auto Obj = dyn_cast<ELFObjectFile<ELF32LE>>(Bin)) {
653 return buildStub(*Obj);
654 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF64LE>>(Bin)) {
655 return buildStub(*Obj);
656 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF32BE>>(Bin)) {
657 return buildStub(*Obj);
658 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF64BE>>(Bin)) {
659 return buildStub(*Obj);
660 }
661 return createStringError(errc::not_supported, "unsupported binary format");
662 }
663
664 // This function wraps the ELFT writeELFBinaryToFile() so writeBinaryStub()
665 // can be called without having to use ELFType templates directly.
writeBinaryStub(StringRef FilePath,const ELFStub & Stub,ELFTarget OutputFormat,bool WriteIfChanged)666 Error writeBinaryStub(StringRef FilePath, const ELFStub &Stub,
667 ELFTarget OutputFormat, bool WriteIfChanged) {
668 if (OutputFormat == ELFTarget::ELF32LE)
669 return writeELFBinaryToFile<ELF32LE>(FilePath, Stub, WriteIfChanged);
670 if (OutputFormat == ELFTarget::ELF32BE)
671 return writeELFBinaryToFile<ELF32BE>(FilePath, Stub, WriteIfChanged);
672 if (OutputFormat == ELFTarget::ELF64LE)
673 return writeELFBinaryToFile<ELF64LE>(FilePath, Stub, WriteIfChanged);
674 if (OutputFormat == ELFTarget::ELF64BE)
675 return writeELFBinaryToFile<ELF64BE>(FilePath, Stub, WriteIfChanged);
676 llvm_unreachable("invalid binary output target");
677 }
678
679 } // end namespace elfabi
680 } // end namespace llvm
681