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/IFSStub.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 <optional>
21
22 using llvm::object::ELFObjectFile;
23
24 using namespace llvm;
25 using namespace llvm::object;
26 using namespace llvm::ELF;
27
28 namespace llvm {
29 namespace ifs {
30
31 // Simple struct to hold relevant .dynamic entries.
32 struct DynamicEntries {
33 uint64_t StrTabAddr = 0;
34 uint64_t StrSize = 0;
35 std::optional<uint64_t> SONameOffset;
36 std::vector<uint64_t> NeededLibNames;
37 // Symbol table:
38 uint64_t DynSymAddr = 0;
39 // Hash tables:
40 std::optional<uint64_t> ElfHash;
41 std::optional<uint64_t> GnuHash;
42 };
43
44 /// This initializes an ELF file header with information specific to a binary
45 /// dynamic shared object.
46 /// Offsets, indexes, links, etc. for section and program headers are just
47 /// zero-initialized as they will be updated elsewhere.
48 ///
49 /// @param ElfHeader Target ELFT::Ehdr to populate.
50 /// @param Machine Target architecture (e_machine from ELF specifications).
51 template <class ELFT>
initELFHeader(typename ELFT::Ehdr & ElfHeader,uint16_t Machine)52 static void initELFHeader(typename ELFT::Ehdr &ElfHeader, uint16_t Machine) {
53 memset(&ElfHeader, 0, sizeof(ElfHeader));
54 // ELF identification.
55 ElfHeader.e_ident[EI_MAG0] = ElfMagic[EI_MAG0];
56 ElfHeader.e_ident[EI_MAG1] = ElfMagic[EI_MAG1];
57 ElfHeader.e_ident[EI_MAG2] = ElfMagic[EI_MAG2];
58 ElfHeader.e_ident[EI_MAG3] = ElfMagic[EI_MAG3];
59 ElfHeader.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
60 bool IsLittleEndian = ELFT::TargetEndianness == llvm::endianness::little;
61 ElfHeader.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
62 ElfHeader.e_ident[EI_VERSION] = EV_CURRENT;
63 ElfHeader.e_ident[EI_OSABI] = ELFOSABI_NONE;
64
65 // Remainder of ELF header.
66 ElfHeader.e_type = ET_DYN;
67 ElfHeader.e_machine = Machine;
68 ElfHeader.e_version = EV_CURRENT;
69 ElfHeader.e_ehsize = sizeof(typename ELFT::Ehdr);
70 ElfHeader.e_phentsize = sizeof(typename ELFT::Phdr);
71 ElfHeader.e_shentsize = sizeof(typename ELFT::Shdr);
72 }
73
74 namespace {
75 template <class ELFT> struct OutputSection {
76 using Elf_Shdr = typename ELFT::Shdr;
77 std::string Name;
78 Elf_Shdr Shdr;
79 uint64_t Addr;
80 uint64_t Offset;
81 uint64_t Size;
82 uint64_t Align;
83 uint32_t Index;
84 bool NoBits = true;
85 };
86
87 template <class T, class ELFT>
88 struct ContentSection : public OutputSection<ELFT> {
89 T Content;
ContentSectionllvm::ifs::__anon7b42d4660111::ContentSection90 ContentSection() { this->NoBits = false; }
91 };
92
93 // This class just wraps StringTableBuilder for the purpose of adding a
94 // default constructor.
95 class ELFStringTableBuilder : public StringTableBuilder {
96 public:
ELFStringTableBuilder()97 ELFStringTableBuilder() : StringTableBuilder(StringTableBuilder::ELF) {}
98 };
99
100 template <class ELFT> class ELFSymbolTableBuilder {
101 public:
102 using Elf_Sym = typename ELFT::Sym;
103
ELFSymbolTableBuilder()104 ELFSymbolTableBuilder() { Symbols.push_back({}); }
105
add(size_t StNameOffset,uint64_t StSize,uint8_t StBind,uint8_t StType,uint8_t StOther,uint16_t StShndx)106 void add(size_t StNameOffset, uint64_t StSize, uint8_t StBind, uint8_t StType,
107 uint8_t StOther, uint16_t StShndx) {
108 Elf_Sym S{};
109 S.st_name = StNameOffset;
110 S.st_size = StSize;
111 S.st_info = (StBind << 4) | (StType & 0xf);
112 S.st_other = StOther;
113 S.st_shndx = StShndx;
114 Symbols.push_back(S);
115 }
116
getSize() const117 size_t getSize() const { return Symbols.size() * sizeof(Elf_Sym); }
118
write(uint8_t * Buf) const119 void write(uint8_t *Buf) const {
120 memcpy(Buf, Symbols.data(), sizeof(Elf_Sym) * Symbols.size());
121 }
122
123 private:
124 llvm::SmallVector<Elf_Sym, 8> Symbols;
125 };
126
127 template <class ELFT> class ELFDynamicTableBuilder {
128 public:
129 using Elf_Dyn = typename ELFT::Dyn;
130
addAddr(uint64_t Tag,uint64_t Addr)131 size_t addAddr(uint64_t Tag, uint64_t Addr) {
132 Elf_Dyn Entry;
133 Entry.d_tag = Tag;
134 Entry.d_un.d_ptr = Addr;
135 Entries.push_back(Entry);
136 return Entries.size() - 1;
137 }
138
modifyAddr(size_t Index,uint64_t Addr)139 void modifyAddr(size_t Index, uint64_t Addr) {
140 Entries[Index].d_un.d_ptr = Addr;
141 }
142
addValue(uint64_t Tag,uint64_t Value)143 size_t addValue(uint64_t Tag, uint64_t Value) {
144 Elf_Dyn Entry;
145 Entry.d_tag = Tag;
146 Entry.d_un.d_val = Value;
147 Entries.push_back(Entry);
148 return Entries.size() - 1;
149 }
150
modifyValue(size_t Index,uint64_t Value)151 void modifyValue(size_t Index, uint64_t Value) {
152 Entries[Index].d_un.d_val = Value;
153 }
154
getSize() const155 size_t getSize() const {
156 // Add DT_NULL entry at the end.
157 return (Entries.size() + 1) * sizeof(Elf_Dyn);
158 }
159
write(uint8_t * Buf) const160 void write(uint8_t *Buf) const {
161 memcpy(Buf, Entries.data(), sizeof(Elf_Dyn) * Entries.size());
162 // Add DT_NULL entry at the end.
163 memset(Buf + sizeof(Elf_Dyn) * Entries.size(), 0, sizeof(Elf_Dyn));
164 }
165
166 private:
167 llvm::SmallVector<Elf_Dyn, 8> Entries;
168 };
169
170 template <class ELFT> class ELFStubBuilder {
171 public:
172 using Elf_Ehdr = typename ELFT::Ehdr;
173 using Elf_Shdr = typename ELFT::Shdr;
174 using Elf_Phdr = typename ELFT::Phdr;
175 using Elf_Sym = typename ELFT::Sym;
176 using Elf_Addr = typename ELFT::Addr;
177 using Elf_Dyn = typename ELFT::Dyn;
178
179 ELFStubBuilder(const ELFStubBuilder &) = delete;
180 ELFStubBuilder(ELFStubBuilder &&) = default;
181
ELFStubBuilder(const IFSStub & Stub)182 explicit ELFStubBuilder(const IFSStub &Stub) {
183 DynSym.Name = ".dynsym";
184 DynSym.Align = sizeof(Elf_Addr);
185 DynStr.Name = ".dynstr";
186 DynStr.Align = 1;
187 DynTab.Name = ".dynamic";
188 DynTab.Align = sizeof(Elf_Addr);
189 ShStrTab.Name = ".shstrtab";
190 ShStrTab.Align = 1;
191
192 // Populate string tables.
193 for (const IFSSymbol &Sym : Stub.Symbols)
194 DynStr.Content.add(Sym.Name);
195 for (const std::string &Lib : Stub.NeededLibs)
196 DynStr.Content.add(Lib);
197 if (Stub.SoName)
198 DynStr.Content.add(*Stub.SoName);
199
200 std::vector<OutputSection<ELFT> *> Sections = {&DynSym, &DynStr, &DynTab,
201 &ShStrTab};
202 const OutputSection<ELFT> *LastSection = Sections.back();
203 // Now set the Index and put sections names into ".shstrtab".
204 uint64_t Index = 1;
205 for (OutputSection<ELFT> *Sec : Sections) {
206 Sec->Index = Index++;
207 ShStrTab.Content.add(Sec->Name);
208 }
209 ShStrTab.Content.finalize();
210 ShStrTab.Size = ShStrTab.Content.getSize();
211 DynStr.Content.finalize();
212 DynStr.Size = DynStr.Content.getSize();
213
214 // Populate dynamic symbol table.
215 for (const IFSSymbol &Sym : Stub.Symbols) {
216 uint8_t Bind = Sym.Weak ? STB_WEAK : STB_GLOBAL;
217 // For non-undefined symbols, value of the shndx is not relevant at link
218 // time as long as it is not SHN_UNDEF. Set shndx to 1, which
219 // points to ".dynsym".
220 uint16_t Shndx = Sym.Undefined ? SHN_UNDEF : 1;
221 uint64_t Size = Sym.Size.value_or(0);
222 DynSym.Content.add(DynStr.Content.getOffset(Sym.Name), Size, Bind,
223 convertIFSSymbolTypeToELF(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 DynTab.Content.addValue(DT_STRSZ, DynSym.Size);
231 for (const std::string &Lib : Stub.NeededLibs)
232 DynTab.Content.addValue(DT_NEEDED, DynStr.Content.getOffset(Lib));
233 if (Stub.SoName)
234 DynTab.Content.addValue(DT_SONAME,
235 DynStr.Content.getOffset(*Stub.SoName));
236 DynTab.Size = DynTab.Content.getSize();
237 // Calculate sections' addresses and offsets.
238 uint64_t CurrentOffset = sizeof(Elf_Ehdr);
239 for (OutputSection<ELFT> *Sec : Sections) {
240 Sec->Offset = alignTo(CurrentOffset, Sec->Align);
241 Sec->Addr = Sec->Offset;
242 CurrentOffset = Sec->Offset + Sec->Size;
243 }
244 // Fill Addr back to dynamic table.
245 DynTab.Content.modifyAddr(DynSymIndex, DynSym.Addr);
246 DynTab.Content.modifyAddr(DynStrIndex, DynStr.Addr);
247 // Write section headers of string tables.
248 fillSymTabShdr(DynSym, SHT_DYNSYM);
249 fillStrTabShdr(DynStr, SHF_ALLOC);
250 fillDynTabShdr(DynTab);
251 fillStrTabShdr(ShStrTab);
252
253 // Finish initializing the ELF header.
254 initELFHeader<ELFT>(ElfHeader, static_cast<uint16_t>(*Stub.Target.Arch));
255 ElfHeader.e_shstrndx = ShStrTab.Index;
256 ElfHeader.e_shnum = LastSection->Index + 1;
257 ElfHeader.e_shoff =
258 alignTo(LastSection->Offset + LastSection->Size, sizeof(Elf_Addr));
259 }
260
getSize() const261 size_t getSize() const {
262 return ElfHeader.e_shoff + ElfHeader.e_shnum * sizeof(Elf_Shdr);
263 }
264
write(uint8_t * Data) const265 void write(uint8_t *Data) const {
266 write(Data, ElfHeader);
267 DynSym.Content.write(Data + DynSym.Shdr.sh_offset);
268 DynStr.Content.write(Data + DynStr.Shdr.sh_offset);
269 DynTab.Content.write(Data + DynTab.Shdr.sh_offset);
270 ShStrTab.Content.write(Data + ShStrTab.Shdr.sh_offset);
271 writeShdr(Data, DynSym);
272 writeShdr(Data, DynStr);
273 writeShdr(Data, DynTab);
274 writeShdr(Data, ShStrTab);
275 }
276
277 private:
278 Elf_Ehdr ElfHeader;
279 ContentSection<ELFStringTableBuilder, ELFT> DynStr;
280 ContentSection<ELFStringTableBuilder, ELFT> ShStrTab;
281 ContentSection<ELFSymbolTableBuilder<ELFT>, ELFT> DynSym;
282 ContentSection<ELFDynamicTableBuilder<ELFT>, ELFT> DynTab;
283
write(uint8_t * Data,const T & Value)284 template <class T> static void write(uint8_t *Data, const T &Value) {
285 *reinterpret_cast<T *>(Data) = Value;
286 }
287
fillStrTabShdr(ContentSection<ELFStringTableBuilder,ELFT> & StrTab,uint32_t ShFlags=0) const288 void fillStrTabShdr(ContentSection<ELFStringTableBuilder, ELFT> &StrTab,
289 uint32_t ShFlags = 0) const {
290 StrTab.Shdr.sh_type = SHT_STRTAB;
291 StrTab.Shdr.sh_flags = ShFlags;
292 StrTab.Shdr.sh_addr = StrTab.Addr;
293 StrTab.Shdr.sh_offset = StrTab.Offset;
294 StrTab.Shdr.sh_info = 0;
295 StrTab.Shdr.sh_size = StrTab.Size;
296 StrTab.Shdr.sh_name = ShStrTab.Content.getOffset(StrTab.Name);
297 StrTab.Shdr.sh_addralign = StrTab.Align;
298 StrTab.Shdr.sh_entsize = 0;
299 StrTab.Shdr.sh_link = 0;
300 }
fillSymTabShdr(ContentSection<ELFSymbolTableBuilder<ELFT>,ELFT> & SymTab,uint32_t ShType) const301 void fillSymTabShdr(ContentSection<ELFSymbolTableBuilder<ELFT>, ELFT> &SymTab,
302 uint32_t ShType) const {
303 SymTab.Shdr.sh_type = ShType;
304 SymTab.Shdr.sh_flags = SHF_ALLOC;
305 SymTab.Shdr.sh_addr = SymTab.Addr;
306 SymTab.Shdr.sh_offset = SymTab.Offset;
307 // Only non-local symbols are included in the tbe file, so .dynsym only
308 // contains 1 local symbol (the undefined symbol at index 0). The sh_info
309 // should always be 1.
310 SymTab.Shdr.sh_info = 1;
311 SymTab.Shdr.sh_size = SymTab.Size;
312 SymTab.Shdr.sh_name = this->ShStrTab.Content.getOffset(SymTab.Name);
313 SymTab.Shdr.sh_addralign = SymTab.Align;
314 SymTab.Shdr.sh_entsize = sizeof(Elf_Sym);
315 SymTab.Shdr.sh_link = this->DynStr.Index;
316 }
fillDynTabShdr(ContentSection<ELFDynamicTableBuilder<ELFT>,ELFT> & DynTab) const317 void fillDynTabShdr(
318 ContentSection<ELFDynamicTableBuilder<ELFT>, ELFT> &DynTab) const {
319 DynTab.Shdr.sh_type = SHT_DYNAMIC;
320 DynTab.Shdr.sh_flags = SHF_ALLOC;
321 DynTab.Shdr.sh_addr = DynTab.Addr;
322 DynTab.Shdr.sh_offset = DynTab.Offset;
323 DynTab.Shdr.sh_info = 0;
324 DynTab.Shdr.sh_size = DynTab.Size;
325 DynTab.Shdr.sh_name = this->ShStrTab.Content.getOffset(DynTab.Name);
326 DynTab.Shdr.sh_addralign = DynTab.Align;
327 DynTab.Shdr.sh_entsize = sizeof(Elf_Dyn);
328 DynTab.Shdr.sh_link = this->DynStr.Index;
329 }
shdrOffset(const OutputSection<ELFT> & Sec) const330 uint64_t shdrOffset(const OutputSection<ELFT> &Sec) const {
331 return ElfHeader.e_shoff + Sec.Index * sizeof(Elf_Shdr);
332 }
333
writeShdr(uint8_t * Data,const OutputSection<ELFT> & Sec) const334 void writeShdr(uint8_t *Data, const OutputSection<ELFT> &Sec) const {
335 write(Data + shdrOffset(Sec), Sec.Shdr);
336 }
337 };
338
339 /// This function takes an error, and appends a string of text to the end of
340 /// that error. Since "appending" to an Error isn't supported behavior of an
341 /// Error, this function technically creates a new error with the combined
342 /// message and consumes the old error.
343 ///
344 /// @param Err Source error.
345 /// @param After Text to append at the end of Err's error message.
appendToError(Error Err,StringRef After)346 Error appendToError(Error Err, StringRef After) {
347 std::string Message;
348 raw_string_ostream Stream(Message);
349 Stream << Err;
350 Stream << " " << After;
351 consumeError(std::move(Err));
352 return createError(Stream.str());
353 }
354
355 template <class ELFT> class DynSym {
356 using Elf_Shdr_Range = typename ELFT::ShdrRange;
357 using Elf_Shdr = typename ELFT::Shdr;
358
359 public:
create(const ELFFile<ELFT> & ElfFile,const DynamicEntries & DynEnt)360 static Expected<DynSym> create(const ELFFile<ELFT> &ElfFile,
361 const DynamicEntries &DynEnt) {
362 Expected<Elf_Shdr_Range> Shdrs = ElfFile.sections();
363 if (!Shdrs)
364 return Shdrs.takeError();
365 return DynSym(ElfFile, DynEnt, *Shdrs);
366 }
367
getDynSym()368 Expected<const uint8_t *> getDynSym() {
369 if (DynSymHdr)
370 return ElfFile.base() + DynSymHdr->sh_offset;
371 return getDynamicData(DynEnt.DynSymAddr, "dynamic symbol table");
372 }
373
getDynStr()374 Expected<StringRef> getDynStr() {
375 if (DynSymHdr)
376 return ElfFile.getStringTableForSymtab(*DynSymHdr, Shdrs);
377 Expected<const uint8_t *> DataOrErr = getDynamicData(
378 DynEnt.StrTabAddr, "dynamic string table", DynEnt.StrSize);
379 if (!DataOrErr)
380 return DataOrErr.takeError();
381 return StringRef(reinterpret_cast<const char *>(*DataOrErr),
382 DynEnt.StrSize);
383 }
384
385 private:
DynSym(const ELFFile<ELFT> & ElfFile,const DynamicEntries & DynEnt,Elf_Shdr_Range Shdrs)386 DynSym(const ELFFile<ELFT> &ElfFile, const DynamicEntries &DynEnt,
387 Elf_Shdr_Range Shdrs)
388 : ElfFile(ElfFile), DynEnt(DynEnt), Shdrs(Shdrs),
389 DynSymHdr(findDynSymHdr()) {}
390
findDynSymHdr()391 const Elf_Shdr *findDynSymHdr() {
392 for (const Elf_Shdr &Sec : Shdrs)
393 if (Sec.sh_type == SHT_DYNSYM) {
394 // If multiple .dynsym are present, use the first one.
395 // This behavior aligns with llvm::object::ELFFile::getDynSymtabSize()
396 return &Sec;
397 }
398 return nullptr;
399 }
400
getDynamicData(uint64_t EntAddr,StringRef Name,uint64_t Size=0)401 Expected<const uint8_t *> getDynamicData(uint64_t EntAddr, StringRef Name,
402 uint64_t Size = 0) {
403 Expected<const uint8_t *> SecPtr = ElfFile.toMappedAddr(EntAddr);
404 if (!SecPtr)
405 return appendToError(
406 SecPtr.takeError(),
407 ("when locating " + Name + " section contents").str());
408 Expected<const uint8_t *> SecEndPtr = ElfFile.toMappedAddr(EntAddr + Size);
409 if (!SecEndPtr)
410 return appendToError(
411 SecEndPtr.takeError(),
412 ("when locating " + Name + " section contents").str());
413 return *SecPtr;
414 }
415
416 const ELFFile<ELFT> &ElfFile;
417 const DynamicEntries &DynEnt;
418 Elf_Shdr_Range Shdrs;
419 const Elf_Shdr *DynSymHdr;
420 };
421 } // end anonymous namespace
422
423 /// This function behaves similarly to StringRef::substr(), but attempts to
424 /// terminate the returned StringRef at the first null terminator. If no null
425 /// terminator is found, an error is returned.
426 ///
427 /// @param Str Source string to create a substring from.
428 /// @param Offset The start index of the desired substring.
terminatedSubstr(StringRef Str,size_t Offset)429 static Expected<StringRef> terminatedSubstr(StringRef Str, size_t Offset) {
430 size_t StrEnd = Str.find('\0', Offset);
431 if (StrEnd == StringLiteral::npos) {
432 return createError(
433 "String overran bounds of string table (no null terminator)");
434 }
435
436 size_t StrLen = StrEnd - Offset;
437 return Str.substr(Offset, StrLen);
438 }
439
440 /// This function populates a DynamicEntries struct using an ELFT::DynRange.
441 /// After populating the struct, the members are validated with
442 /// some basic correctness checks.
443 ///
444 /// @param Dyn Target DynamicEntries struct to populate.
445 /// @param DynTable Source dynamic table.
446 template <class ELFT>
populateDynamic(DynamicEntries & Dyn,typename ELFT::DynRange DynTable)447 static Error populateDynamic(DynamicEntries &Dyn,
448 typename ELFT::DynRange DynTable) {
449 if (DynTable.empty())
450 return createError("No .dynamic section found");
451
452 // Search .dynamic for relevant entries.
453 bool FoundDynStr = false;
454 bool FoundDynStrSz = false;
455 bool FoundDynSym = false;
456 for (auto &Entry : DynTable) {
457 switch (Entry.d_tag) {
458 case DT_SONAME:
459 Dyn.SONameOffset = Entry.d_un.d_val;
460 break;
461 case DT_STRTAB:
462 Dyn.StrTabAddr = Entry.d_un.d_ptr;
463 FoundDynStr = true;
464 break;
465 case DT_STRSZ:
466 Dyn.StrSize = Entry.d_un.d_val;
467 FoundDynStrSz = true;
468 break;
469 case DT_NEEDED:
470 Dyn.NeededLibNames.push_back(Entry.d_un.d_val);
471 break;
472 case DT_SYMTAB:
473 Dyn.DynSymAddr = Entry.d_un.d_ptr;
474 FoundDynSym = true;
475 break;
476 case DT_HASH:
477 Dyn.ElfHash = Entry.d_un.d_ptr;
478 break;
479 case DT_GNU_HASH:
480 Dyn.GnuHash = Entry.d_un.d_ptr;
481 }
482 }
483
484 if (!FoundDynStr) {
485 return createError(
486 "Couldn't locate dynamic string table (no DT_STRTAB entry)");
487 }
488 if (!FoundDynStrSz) {
489 return createError(
490 "Couldn't determine dynamic string table size (no DT_STRSZ entry)");
491 }
492 if (!FoundDynSym) {
493 return createError(
494 "Couldn't locate dynamic symbol table (no DT_SYMTAB entry)");
495 }
496 if (Dyn.SONameOffset && *Dyn.SONameOffset >= Dyn.StrSize) {
497 return createStringError(object_error::parse_failed,
498 "DT_SONAME string offset (0x%016" PRIx64
499 ") outside of dynamic string table",
500 *Dyn.SONameOffset);
501 }
502 for (uint64_t Offset : Dyn.NeededLibNames) {
503 if (Offset >= Dyn.StrSize) {
504 return createStringError(object_error::parse_failed,
505 "DT_NEEDED string offset (0x%016" PRIx64
506 ") outside of dynamic string table",
507 Offset);
508 }
509 }
510
511 return Error::success();
512 }
513
514 /// This function creates an IFSSymbol and populates all members using
515 /// information from a binary ELFT::Sym.
516 ///
517 /// @param SymName The desired name of the IFSSymbol.
518 /// @param RawSym ELFT::Sym to extract symbol information from.
519 template <class ELFT>
createELFSym(StringRef SymName,const typename ELFT::Sym & RawSym)520 static IFSSymbol createELFSym(StringRef SymName,
521 const typename ELFT::Sym &RawSym) {
522 IFSSymbol TargetSym{std::string(SymName)};
523 uint8_t Binding = RawSym.getBinding();
524 if (Binding == STB_WEAK)
525 TargetSym.Weak = true;
526 else
527 TargetSym.Weak = false;
528
529 TargetSym.Undefined = RawSym.isUndefined();
530 TargetSym.Type = convertELFSymbolTypeToIFS(RawSym.st_info);
531
532 if (TargetSym.Type == IFSSymbolType::Func) {
533 TargetSym.Size = 0;
534 } else {
535 TargetSym.Size = RawSym.st_size;
536 }
537 return TargetSym;
538 }
539
540 /// This function populates an IFSStub with symbols using information read
541 /// from an ELF binary.
542 ///
543 /// @param TargetStub IFSStub to add symbols to.
544 /// @param DynSym Range of dynamic symbols to add to TargetStub.
545 /// @param DynStr StringRef to the dynamic string table.
546 template <class ELFT>
populateSymbols(IFSStub & TargetStub,const typename ELFT::SymRange DynSym,StringRef DynStr)547 static Error populateSymbols(IFSStub &TargetStub,
548 const typename ELFT::SymRange DynSym,
549 StringRef DynStr) {
550 // Skips the first symbol since it's the NULL symbol.
551 for (auto RawSym : DynSym.drop_front(1)) {
552 // If a symbol does not have global or weak binding, ignore it.
553 uint8_t Binding = RawSym.getBinding();
554 if (!(Binding == STB_GLOBAL || Binding == STB_WEAK))
555 continue;
556 // If a symbol doesn't have default or protected visibility, ignore it.
557 uint8_t Visibility = RawSym.getVisibility();
558 if (!(Visibility == STV_DEFAULT || Visibility == STV_PROTECTED))
559 continue;
560 // Create an IFSSymbol and populate it with information from the symbol
561 // table entry.
562 Expected<StringRef> SymName = terminatedSubstr(DynStr, RawSym.st_name);
563 if (!SymName)
564 return SymName.takeError();
565 IFSSymbol Sym = createELFSym<ELFT>(*SymName, RawSym);
566 TargetStub.Symbols.push_back(std::move(Sym));
567 // TODO: Populate symbol warning.
568 }
569 return Error::success();
570 }
571
572 /// Returns a new IFSStub with all members populated from an ELFObjectFile.
573 /// @param ElfObj Source ELFObjectFile.
574 template <class ELFT>
575 static Expected<std::unique_ptr<IFSStub>>
buildStub(const ELFObjectFile<ELFT> & ElfObj)576 buildStub(const ELFObjectFile<ELFT> &ElfObj) {
577 using Elf_Dyn_Range = typename ELFT::DynRange;
578 using Elf_Sym_Range = typename ELFT::SymRange;
579 using Elf_Sym = typename ELFT::Sym;
580 std::unique_ptr<IFSStub> DestStub = std::make_unique<IFSStub>();
581 const ELFFile<ELFT> &ElfFile = ElfObj.getELFFile();
582 // Fetch .dynamic table.
583 Expected<Elf_Dyn_Range> DynTable = ElfFile.dynamicEntries();
584 if (!DynTable) {
585 return DynTable.takeError();
586 }
587
588 // Collect relevant .dynamic entries.
589 DynamicEntries DynEnt;
590 if (Error Err = populateDynamic<ELFT>(DynEnt, *DynTable))
591 return std::move(Err);
592 Expected<DynSym<ELFT>> EDynSym = DynSym<ELFT>::create(ElfFile, DynEnt);
593 if (!EDynSym)
594 return EDynSym.takeError();
595
596 Expected<StringRef> EDynStr = EDynSym->getDynStr();
597 if (!EDynStr)
598 return EDynStr.takeError();
599
600 StringRef DynStr = *EDynStr;
601
602 // Populate Arch from ELF header.
603 DestStub->Target.Arch = static_cast<IFSArch>(ElfFile.getHeader().e_machine);
604 DestStub->Target.BitWidth =
605 convertELFBitWidthToIFS(ElfFile.getHeader().e_ident[EI_CLASS]);
606 DestStub->Target.Endianness =
607 convertELFEndiannessToIFS(ElfFile.getHeader().e_ident[EI_DATA]);
608 DestStub->Target.ObjectFormat = "ELF";
609
610 // Populate SoName from .dynamic entries and dynamic string table.
611 if (DynEnt.SONameOffset) {
612 Expected<StringRef> NameOrErr =
613 terminatedSubstr(DynStr, *DynEnt.SONameOffset);
614 if (!NameOrErr) {
615 return appendToError(NameOrErr.takeError(), "when reading DT_SONAME");
616 }
617 DestStub->SoName = std::string(*NameOrErr);
618 }
619
620 // Populate NeededLibs from .dynamic entries and dynamic string table.
621 for (uint64_t NeededStrOffset : DynEnt.NeededLibNames) {
622 Expected<StringRef> LibNameOrErr =
623 terminatedSubstr(DynStr, NeededStrOffset);
624 if (!LibNameOrErr) {
625 return appendToError(LibNameOrErr.takeError(), "when reading DT_NEEDED");
626 }
627 DestStub->NeededLibs.push_back(std::string(*LibNameOrErr));
628 }
629
630 // Populate Symbols from .dynsym table and dynamic string table.
631 Expected<uint64_t> SymCount = ElfFile.getDynSymtabSize();
632 if (!SymCount)
633 return SymCount.takeError();
634 if (*SymCount > 0) {
635 // Get pointer to in-memory location of .dynsym section.
636 Expected<const uint8_t *> DynSymPtr = EDynSym->getDynSym();
637 if (!DynSymPtr)
638 return appendToError(DynSymPtr.takeError(),
639 "when locating .dynsym section contents");
640 Elf_Sym_Range DynSyms = ArrayRef<Elf_Sym>(
641 reinterpret_cast<const Elf_Sym *>(*DynSymPtr), *SymCount);
642 Error SymReadError = populateSymbols<ELFT>(*DestStub, DynSyms, DynStr);
643 if (SymReadError)
644 return appendToError(std::move(SymReadError),
645 "when reading dynamic symbols");
646 }
647
648 return std::move(DestStub);
649 }
650
651 /// This function opens a file for writing and then writes a binary ELF stub to
652 /// the file.
653 ///
654 /// @param FilePath File path for writing the ELF binary.
655 /// @param Stub Source InterFace Stub to generate a binary ELF stub from.
656 template <class ELFT>
writeELFBinaryToFile(StringRef FilePath,const IFSStub & Stub,bool WriteIfChanged)657 static Error writeELFBinaryToFile(StringRef FilePath, const IFSStub &Stub,
658 bool WriteIfChanged) {
659 ELFStubBuilder<ELFT> Builder{Stub};
660 // Write Stub to memory first.
661 std::vector<uint8_t> Buf(Builder.getSize());
662 Builder.write(Buf.data());
663
664 if (WriteIfChanged) {
665 if (ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrError =
666 MemoryBuffer::getFile(FilePath)) {
667 // Compare Stub output with existing Stub file.
668 // If Stub file unchanged, abort updating.
669 if ((*BufOrError)->getBufferSize() == Builder.getSize() &&
670 !memcmp((*BufOrError)->getBufferStart(), Buf.data(),
671 Builder.getSize()))
672 return Error::success();
673 }
674 }
675
676 Expected<std::unique_ptr<FileOutputBuffer>> BufOrError =
677 FileOutputBuffer::create(FilePath, Builder.getSize());
678 if (!BufOrError)
679 return createStringError(errc::invalid_argument,
680 toString(BufOrError.takeError()) +
681 " when trying to open `" + FilePath +
682 "` for writing");
683
684 // Write binary to file.
685 std::unique_ptr<FileOutputBuffer> FileBuf = std::move(*BufOrError);
686 memcpy(FileBuf->getBufferStart(), Buf.data(), Buf.size());
687
688 return FileBuf->commit();
689 }
690
readELFFile(MemoryBufferRef Buf)691 Expected<std::unique_ptr<IFSStub>> readELFFile(MemoryBufferRef Buf) {
692 Expected<std::unique_ptr<Binary>> BinOrErr = createBinary(Buf);
693 if (!BinOrErr) {
694 return BinOrErr.takeError();
695 }
696
697 Binary *Bin = BinOrErr->get();
698 if (auto Obj = dyn_cast<ELFObjectFile<ELF32LE>>(Bin)) {
699 return buildStub(*Obj);
700 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF64LE>>(Bin)) {
701 return buildStub(*Obj);
702 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF32BE>>(Bin)) {
703 return buildStub(*Obj);
704 } else if (auto Obj = dyn_cast<ELFObjectFile<ELF64BE>>(Bin)) {
705 return buildStub(*Obj);
706 }
707 return createStringError(errc::not_supported, "unsupported binary format");
708 }
709
710 // This function wraps the ELFT writeELFBinaryToFile() so writeBinaryStub()
711 // can be called without having to use ELFType templates directly.
writeBinaryStub(StringRef FilePath,const IFSStub & Stub,bool WriteIfChanged)712 Error writeBinaryStub(StringRef FilePath, const IFSStub &Stub,
713 bool WriteIfChanged) {
714 assert(Stub.Target.Arch);
715 assert(Stub.Target.BitWidth);
716 assert(Stub.Target.Endianness);
717 if (Stub.Target.BitWidth == IFSBitWidthType::IFS32) {
718 if (Stub.Target.Endianness == IFSEndiannessType::Little) {
719 return writeELFBinaryToFile<ELF32LE>(FilePath, Stub, WriteIfChanged);
720 } else {
721 return writeELFBinaryToFile<ELF32BE>(FilePath, Stub, WriteIfChanged);
722 }
723 } else {
724 if (Stub.Target.Endianness == IFSEndiannessType::Little) {
725 return writeELFBinaryToFile<ELF64LE>(FilePath, Stub, WriteIfChanged);
726 } else {
727 return writeELFBinaryToFile<ELF64BE>(FilePath, Stub, WriteIfChanged);
728 }
729 }
730 llvm_unreachable("invalid binary output target");
731 }
732
733 } // end namespace ifs
734 } // end namespace llvm
735