elf_builder.h revision b851b49eee0a77720347a4f777c07d4531302655
1/* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#ifndef ART_COMPILER_ELF_BUILDER_H_ 18#define ART_COMPILER_ELF_BUILDER_H_ 19 20#include <vector> 21 22#include "arch/instruction_set.h" 23#include "base/bit_utils.h" 24#include "base/casts.h" 25#include "base/unix_file/fd_file.h" 26#include "buffered_output_stream.h" 27#include "elf_utils.h" 28#include "file_output_stream.h" 29#include "leb128.h" 30 31namespace art { 32 33// Writes ELF file. 34// 35// The basic layout of the elf file: 36// Elf_Ehdr - The ELF header. 37// Elf_Phdr[] - Program headers for the linker. 38// .rodata - DEX files and oat metadata. 39// .text - Compiled code. 40// .bss - Zero-initialized writeable section. 41// .dynstr - Names for .dynsym. 42// .dynsym - A few oat-specific dynamic symbols. 43// .hash - Hash-table for .dynsym. 44// .dynamic - Tags which let the linker locate .dynsym. 45// .strtab - Names for .symtab. 46// .symtab - Debug symbols. 47// .eh_frame - Unwind information (CFI). 48// .eh_frame_hdr - Index of .eh_frame. 49// .debug_frame - Unwind information (CFI). 50// .debug_frame.oat_patches - Addresses for relocation. 51// .debug_info - Debug information. 52// .debug_info.oat_patches - Addresses for relocation. 53// .debug_abbrev - Decoding information for .debug_info. 54// .debug_str - Strings for .debug_info. 55// .debug_line - Line number tables. 56// .debug_line.oat_patches - Addresses for relocation. 57// .text.oat_patches - Addresses for relocation. 58// .shstrtab - Names of ELF sections. 59// Elf_Shdr[] - Section headers. 60// 61// Some section are optional (the debug sections in particular). 62// 63// We try write the section data directly into the file without much 64// in-memory buffering. This means we generally write sections based on the 65// dependency order (e.g. .dynamic points to .dynsym which points to .text). 66// 67// In the cases where we need to buffer, we write the larger section first 68// and buffer the smaller one (e.g. .strtab is bigger than .symtab). 69// 70// The debug sections are written last for easier stripping. 71// 72template <typename ElfTypes> 73class ElfBuilder FINAL { 74 public: 75 static constexpr size_t kMaxProgramHeaders = 16; 76 using Elf_Addr = typename ElfTypes::Addr; 77 using Elf_Off = typename ElfTypes::Off; 78 using Elf_Word = typename ElfTypes::Word; 79 using Elf_Sword = typename ElfTypes::Sword; 80 using Elf_Ehdr = typename ElfTypes::Ehdr; 81 using Elf_Shdr = typename ElfTypes::Shdr; 82 using Elf_Sym = typename ElfTypes::Sym; 83 using Elf_Phdr = typename ElfTypes::Phdr; 84 using Elf_Dyn = typename ElfTypes::Dyn; 85 86 // Base class of all sections. 87 class Section : public OutputStream { 88 public: 89 Section(ElfBuilder<ElfTypes>* owner, const std::string& name, 90 Elf_Word type, Elf_Word flags, const Section* link, 91 Elf_Word info, Elf_Word align, Elf_Word entsize) 92 : OutputStream(name), owner_(owner), header_(), 93 section_index_(0), name_(name), link_(link), 94 started_(false), finished_(false), phdr_flags_(PF_R), phdr_type_(0) { 95 DCHECK_GE(align, 1u); 96 header_.sh_type = type; 97 header_.sh_flags = flags; 98 header_.sh_info = info; 99 header_.sh_addralign = align; 100 header_.sh_entsize = entsize; 101 } 102 103 virtual ~Section() { 104 if (started_) { 105 CHECK(finished_); 106 } 107 } 108 109 // Start writing of this section. 110 void Start() { 111 CHECK(!started_); 112 CHECK(!finished_); 113 started_ = true; 114 auto& sections = owner_->sections_; 115 // Check that the previous section is complete. 116 CHECK(sections.empty() || sections.back()->finished_); 117 // The first ELF section index is 1. Index 0 is reserved for NULL. 118 section_index_ = sections.size() + 1; 119 // Push this section on the list of written sections. 120 sections.push_back(this); 121 // Align file position. 122 if (header_.sh_type != SHT_NOBITS) { 123 header_.sh_offset = RoundUp(owner_->Seek(0, kSeekCurrent), header_.sh_addralign); 124 owner_->Seek(header_.sh_offset, kSeekSet); 125 } 126 // Align virtual memory address. 127 if ((header_.sh_flags & SHF_ALLOC) != 0) { 128 header_.sh_addr = RoundUp(owner_->virtual_address_, header_.sh_addralign); 129 owner_->virtual_address_ = header_.sh_addr; 130 } 131 } 132 133 // Finish writing of this section. 134 void End() { 135 CHECK(started_); 136 CHECK(!finished_); 137 finished_ = true; 138 if (header_.sh_type == SHT_NOBITS) { 139 CHECK_GT(header_.sh_size, 0u); 140 } else { 141 // Use the current file position to determine section size. 142 off_t file_offset = owner_->Seek(0, kSeekCurrent); 143 CHECK_GE(file_offset, (off_t)header_.sh_offset); 144 header_.sh_size = file_offset - header_.sh_offset; 145 } 146 if ((header_.sh_flags & SHF_ALLOC) != 0) { 147 owner_->virtual_address_ += header_.sh_size; 148 } 149 } 150 151 // Get the location of this section in virtual memory. 152 Elf_Addr GetAddress() const { 153 CHECK(started_); 154 return header_.sh_addr; 155 } 156 157 // Returns the size of the content of this section. 158 Elf_Word GetSize() const { 159 if (finished_) { 160 return header_.sh_size; 161 } else { 162 CHECK(started_); 163 CHECK_NE(header_.sh_type, (Elf_Word)SHT_NOBITS); 164 return owner_->Seek(0, kSeekCurrent) - header_.sh_offset; 165 } 166 } 167 168 // Set desired allocation size for .bss section. 169 void SetSize(Elf_Word size) { 170 CHECK_EQ(header_.sh_type, (Elf_Word)SHT_NOBITS); 171 header_.sh_size = size; 172 } 173 174 // This function always succeeds to simplify code. 175 // Use builder's Good() to check the actual status. 176 bool WriteFully(const void* buffer, size_t byte_count) OVERRIDE { 177 CHECK(started_); 178 CHECK(!finished_); 179 owner_->WriteFully(buffer, byte_count); 180 return true; 181 } 182 183 // This function always succeeds to simplify code. 184 // Use builder's Good() to check the actual status. 185 off_t Seek(off_t offset, Whence whence) OVERRIDE { 186 // Forward the seek as-is and trust the caller to use it reasonably. 187 return owner_->Seek(offset, whence); 188 } 189 190 Elf_Word GetSectionIndex() const { 191 DCHECK(started_); 192 DCHECK_NE(section_index_, 0u); 193 return section_index_; 194 } 195 196 private: 197 ElfBuilder<ElfTypes>* owner_; 198 Elf_Shdr header_; 199 Elf_Word section_index_; 200 const std::string name_; 201 const Section* const link_; 202 bool started_; 203 bool finished_; 204 Elf_Word phdr_flags_; 205 Elf_Word phdr_type_; 206 207 friend class ElfBuilder; 208 209 DISALLOW_COPY_AND_ASSIGN(Section); 210 }; 211 212 // Writer of .dynstr .strtab and .shstrtab sections. 213 class StringSection FINAL : public Section { 214 public: 215 StringSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 216 Elf_Word flags, Elf_Word align) 217 : Section(owner, name, SHT_STRTAB, flags, nullptr, 0, align, 0), 218 current_offset_(0) { 219 } 220 221 Elf_Word Write(const std::string& name) { 222 if (current_offset_ == 0) { 223 DCHECK(name.empty()); 224 } 225 Elf_Word offset = current_offset_; 226 this->WriteFully(name.c_str(), name.length() + 1); 227 current_offset_ += name.length() + 1; 228 return offset; 229 } 230 231 private: 232 Elf_Word current_offset_; 233 }; 234 235 // Writer of .dynsym and .symtab sections. 236 class SymbolSection FINAL : public Section { 237 public: 238 SymbolSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 239 Elf_Word type, Elf_Word flags, StringSection* strtab) 240 : Section(owner, name, type, flags, strtab, 0, 241 sizeof(Elf_Off), sizeof(Elf_Sym)) { 242 } 243 244 // Buffer symbol for this section. It will be written later. 245 void Add(Elf_Word name, const Section* section, 246 Elf_Addr addr, bool is_relative, Elf_Word size, 247 uint8_t binding, uint8_t type, uint8_t other = 0) { 248 CHECK(section != nullptr); 249 Elf_Sym sym = Elf_Sym(); 250 sym.st_name = name; 251 sym.st_value = addr + (is_relative ? section->GetAddress() : 0); 252 sym.st_size = size; 253 sym.st_other = other; 254 sym.st_shndx = section->GetSectionIndex(); 255 sym.st_info = (binding << 4) + (type & 0xf); 256 symbols_.push_back(sym); 257 } 258 259 void Write() { 260 // The symbol table always has to start with NULL symbol. 261 Elf_Sym null_symbol = Elf_Sym(); 262 this->WriteFully(&null_symbol, sizeof(null_symbol)); 263 this->WriteFully(symbols_.data(), symbols_.size() * sizeof(symbols_[0])); 264 symbols_.clear(); 265 symbols_.shrink_to_fit(); 266 } 267 268 private: 269 std::vector<Elf_Sym> symbols_; 270 }; 271 272 ElfBuilder(InstructionSet isa, OutputStream* output) 273 : isa_(isa), 274 output_(output), 275 output_good_(true), 276 output_offset_(0), 277 rodata_(this, ".rodata", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 278 text_(this, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, nullptr, 0, kPageSize, 0), 279 bss_(this, ".bss", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 280 dynstr_(this, ".dynstr", SHF_ALLOC, kPageSize), 281 dynsym_(this, ".dynsym", SHT_DYNSYM, SHF_ALLOC, &dynstr_), 282 hash_(this, ".hash", SHT_HASH, SHF_ALLOC, &dynsym_, 0, sizeof(Elf_Word), sizeof(Elf_Word)), 283 dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), 284 eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 285 eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), 286 strtab_(this, ".strtab", 0, kPageSize), 287 symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), 288 debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), 289 debug_info_(this, ".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 290 debug_line_(this, ".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 291 shstrtab_(this, ".shstrtab", 0, 1), 292 virtual_address_(0) { 293 text_.phdr_flags_ = PF_R | PF_X; 294 bss_.phdr_flags_ = PF_R | PF_W; 295 dynamic_.phdr_flags_ = PF_R | PF_W; 296 dynamic_.phdr_type_ = PT_DYNAMIC; 297 eh_frame_hdr_.phdr_type_ = PT_GNU_EH_FRAME; 298 } 299 ~ElfBuilder() {} 300 301 InstructionSet GetIsa() { return isa_; } 302 Section* GetRoData() { return &rodata_; } 303 Section* GetText() { return &text_; } 304 Section* GetBss() { return &bss_; } 305 StringSection* GetStrTab() { return &strtab_; } 306 SymbolSection* GetSymTab() { return &symtab_; } 307 Section* GetEhFrame() { return &eh_frame_; } 308 Section* GetEhFrameHdr() { return &eh_frame_hdr_; } 309 Section* GetDebugFrame() { return &debug_frame_; } 310 Section* GetDebugInfo() { return &debug_info_; } 311 Section* GetDebugLine() { return &debug_line_; } 312 313 // Encode patch locations as LEB128 list of deltas between consecutive addresses. 314 // (exposed publicly for tests) 315 static void EncodeOatPatches(const std::vector<uintptr_t>& locations, 316 std::vector<uint8_t>* buffer) { 317 buffer->reserve(buffer->size() + locations.size() * 2); // guess 2 bytes per ULEB128. 318 uintptr_t address = 0; // relative to start of section. 319 for (uintptr_t location : locations) { 320 DCHECK_GE(location, address) << "Patch locations are not in sorted order"; 321 EncodeUnsignedLeb128(buffer, dchecked_integral_cast<uint32_t>(location - address)); 322 address = location; 323 } 324 } 325 326 void WritePatches(const char* name, const std::vector<uintptr_t>* patch_locations) { 327 std::vector<uint8_t> buffer; 328 EncodeOatPatches(*patch_locations, &buffer); 329 std::unique_ptr<Section> s(new Section(this, name, SHT_OAT_PATCH, 0, nullptr, 0, 1, 0)); 330 s->Start(); 331 s->WriteFully(buffer.data(), buffer.size()); 332 s->End(); 333 other_sections_.push_back(std::move(s)); 334 } 335 336 void WriteSection(const char* name, const std::vector<uint8_t>* buffer) { 337 std::unique_ptr<Section> s(new Section(this, name, SHT_PROGBITS, 0, nullptr, 0, 1, 0)); 338 s->Start(); 339 s->WriteFully(buffer->data(), buffer->size()); 340 s->End(); 341 other_sections_.push_back(std::move(s)); 342 } 343 344 void Start() { 345 // Reserve space for ELF header and program headers. 346 // We do not know the number of headers until later, so 347 // it is easiest to just reserve a fixed amount of space. 348 int size = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; 349 Seek(size, kSeekSet); 350 virtual_address_ += size; 351 } 352 353 void End() { 354 // Write section names and finish the section headers. 355 shstrtab_.Start(); 356 shstrtab_.Write(""); 357 for (auto* section : sections_) { 358 section->header_.sh_name = shstrtab_.Write(section->name_); 359 if (section->link_ != nullptr) { 360 section->header_.sh_link = section->link_->GetSectionIndex(); 361 } 362 } 363 shstrtab_.End(); 364 365 // Write section headers at the end of the ELF file. 366 std::vector<Elf_Shdr> shdrs; 367 shdrs.reserve(1u + sections_.size()); 368 shdrs.push_back(Elf_Shdr()); // NULL at index 0. 369 for (auto* section : sections_) { 370 shdrs.push_back(section->header_); 371 } 372 Elf_Off section_headers_offset; 373 section_headers_offset = RoundUp(Seek(0, kSeekCurrent), sizeof(Elf_Off)); 374 Seek(section_headers_offset, kSeekSet); 375 WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); 376 377 // Write the initial file headers. 378 std::vector<Elf_Phdr> phdrs = MakeProgramHeaders(); 379 Elf_Ehdr elf_header = MakeElfHeader(isa_); 380 elf_header.e_phoff = sizeof(Elf_Ehdr); 381 elf_header.e_shoff = section_headers_offset; 382 elf_header.e_phnum = phdrs.size(); 383 elf_header.e_shnum = shdrs.size(); 384 elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); 385 Seek(0, kSeekSet); 386 WriteFully(&elf_header, sizeof(elf_header)); 387 WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); 388 } 389 390 // The running program does not have access to section headers 391 // and the loader is not supposed to use them either. 392 // The dynamic sections therefore replicates some of the layout 393 // information like the address and size of .rodata and .text. 394 // It also contains other metadata like the SONAME. 395 // The .dynamic section is found using the PT_DYNAMIC program header. 396 void WriteDynamicSection(const std::string& elf_file_path) { 397 std::string soname(elf_file_path); 398 size_t directory_separator_pos = soname.rfind('/'); 399 if (directory_separator_pos != std::string::npos) { 400 soname = soname.substr(directory_separator_pos + 1); 401 } 402 403 dynstr_.Start(); 404 dynstr_.Write(""); // dynstr should start with empty string. 405 dynsym_.Add(dynstr_.Write("oatdata"), &rodata_, 0, true, 406 rodata_.GetSize(), STB_GLOBAL, STT_OBJECT); 407 if (text_.GetSize() != 0u) { 408 dynsym_.Add(dynstr_.Write("oatexec"), &text_, 0, true, 409 text_.GetSize(), STB_GLOBAL, STT_OBJECT); 410 dynsym_.Add(dynstr_.Write("oatlastword"), &text_, text_.GetSize() - 4, 411 true, 4, STB_GLOBAL, STT_OBJECT); 412 } else if (rodata_.GetSize() != 0) { 413 // rodata_ can be size 0 for dwarf_test. 414 dynsym_.Add(dynstr_.Write("oatlastword"), &rodata_, rodata_.GetSize() - 4, 415 true, 4, STB_GLOBAL, STT_OBJECT); 416 } 417 if (bss_.finished_) { 418 dynsym_.Add(dynstr_.Write("oatbss"), &bss_, 419 0, true, bss_.GetSize(), STB_GLOBAL, STT_OBJECT); 420 dynsym_.Add(dynstr_.Write("oatbsslastword"), &bss_, 421 bss_.GetSize() - 4, true, 4, STB_GLOBAL, STT_OBJECT); 422 } 423 Elf_Word soname_offset = dynstr_.Write(soname); 424 dynstr_.End(); 425 426 dynsym_.Start(); 427 dynsym_.Write(); 428 dynsym_.End(); 429 430 // We do not really need a hash-table since there is so few entries. 431 // However, the hash-table is the only way the linker can actually 432 // determine the number of symbols in .dynsym so it is required. 433 hash_.Start(); 434 int count = dynsym_.GetSize() / sizeof(Elf_Sym); // Includes NULL. 435 std::vector<Elf_Word> hash; 436 hash.push_back(1); // Number of buckets. 437 hash.push_back(count); // Number of chains. 438 // Buckets. Having just one makes it linear search. 439 hash.push_back(1); // Point to first non-NULL symbol. 440 // Chains. This creates linked list of symbols. 441 hash.push_back(0); // Dummy entry for the NULL symbol. 442 for (int i = 1; i < count - 1; i++) { 443 hash.push_back(i + 1); // Each symbol points to the next one. 444 } 445 hash.push_back(0); // Last symbol terminates the chain. 446 hash_.WriteFully(hash.data(), hash.size() * sizeof(hash[0])); 447 hash_.End(); 448 449 dynamic_.Start(); 450 Elf_Dyn dyns[] = { 451 { DT_HASH, { hash_.GetAddress() } }, 452 { DT_STRTAB, { dynstr_.GetAddress() } }, 453 { DT_SYMTAB, { dynsym_.GetAddress() } }, 454 { DT_SYMENT, { sizeof(Elf_Sym) } }, 455 { DT_STRSZ, { dynstr_.GetSize() } }, 456 { DT_SONAME, { soname_offset } }, 457 { DT_NULL, { 0 } }, 458 }; 459 dynamic_.WriteFully(&dyns, sizeof(dyns)); 460 dynamic_.End(); 461 } 462 463 // Returns true if all writes and seeks on the output stream succeeded. 464 bool Good() { 465 return output_good_; 466 } 467 468 private: 469 // This function always succeeds to simplify code. 470 // Use Good() to check the actual status of the output stream. 471 void WriteFully(const void* buffer, size_t byte_count) { 472 if (output_good_) { 473 if (!output_->WriteFully(buffer, byte_count)) { 474 PLOG(ERROR) << "Failed to write " << byte_count 475 << " bytes to ELF file at offset " << output_offset_; 476 output_good_ = false; 477 } 478 } 479 output_offset_ += byte_count; 480 } 481 482 // This function always succeeds to simplify code. 483 // Use Good() to check the actual status of the output stream. 484 off_t Seek(off_t offset, Whence whence) { 485 // We keep shadow copy of the offset so that we return 486 // the expected value even if the output stream failed. 487 off_t new_offset; 488 switch (whence) { 489 case kSeekSet: 490 new_offset = offset; 491 break; 492 case kSeekCurrent: 493 new_offset = output_offset_ + offset; 494 break; 495 default: 496 LOG(FATAL) << "Unsupported seek type: " << whence; 497 UNREACHABLE(); 498 } 499 if (output_good_) { 500 off_t actual_offset = output_->Seek(offset, whence); 501 if (actual_offset == (off_t)-1) { 502 PLOG(ERROR) << "Failed to seek in ELF file. Offset=" << offset 503 << " whence=" << whence << " new_offset=" << new_offset; 504 output_good_ = false; 505 } 506 DCHECK_EQ(actual_offset, new_offset); 507 } 508 output_offset_ = new_offset; 509 return new_offset; 510 } 511 512 static Elf_Ehdr MakeElfHeader(InstructionSet isa) { 513 Elf_Ehdr elf_header = Elf_Ehdr(); 514 switch (isa) { 515 case kArm: 516 // Fall through. 517 case kThumb2: { 518 elf_header.e_machine = EM_ARM; 519 elf_header.e_flags = EF_ARM_EABI_VER5; 520 break; 521 } 522 case kArm64: { 523 elf_header.e_machine = EM_AARCH64; 524 elf_header.e_flags = 0; 525 break; 526 } 527 case kX86: { 528 elf_header.e_machine = EM_386; 529 elf_header.e_flags = 0; 530 break; 531 } 532 case kX86_64: { 533 elf_header.e_machine = EM_X86_64; 534 elf_header.e_flags = 0; 535 break; 536 } 537 case kMips: { 538 elf_header.e_machine = EM_MIPS; 539 elf_header.e_flags = (EF_MIPS_NOREORDER | 540 EF_MIPS_PIC | 541 EF_MIPS_CPIC | 542 EF_MIPS_ABI_O32 | 543 EF_MIPS_ARCH_32R2); 544 break; 545 } 546 case kMips64: { 547 elf_header.e_machine = EM_MIPS; 548 elf_header.e_flags = (EF_MIPS_NOREORDER | 549 EF_MIPS_PIC | 550 EF_MIPS_CPIC | 551 EF_MIPS_ARCH_64R6); 552 break; 553 } 554 case kNone: { 555 LOG(FATAL) << "No instruction set"; 556 break; 557 } 558 default: { 559 LOG(FATAL) << "Unknown instruction set " << isa; 560 } 561 } 562 563 elf_header.e_ident[EI_MAG0] = ELFMAG0; 564 elf_header.e_ident[EI_MAG1] = ELFMAG1; 565 elf_header.e_ident[EI_MAG2] = ELFMAG2; 566 elf_header.e_ident[EI_MAG3] = ELFMAG3; 567 elf_header.e_ident[EI_CLASS] = (sizeof(Elf_Addr) == sizeof(Elf32_Addr)) 568 ? ELFCLASS32 : ELFCLASS64;; 569 elf_header.e_ident[EI_DATA] = ELFDATA2LSB; 570 elf_header.e_ident[EI_VERSION] = EV_CURRENT; 571 elf_header.e_ident[EI_OSABI] = ELFOSABI_LINUX; 572 elf_header.e_ident[EI_ABIVERSION] = 0; 573 elf_header.e_type = ET_DYN; 574 elf_header.e_version = 1; 575 elf_header.e_entry = 0; 576 elf_header.e_ehsize = sizeof(Elf_Ehdr); 577 elf_header.e_phentsize = sizeof(Elf_Phdr); 578 elf_header.e_shentsize = sizeof(Elf_Shdr); 579 elf_header.e_phoff = sizeof(Elf_Ehdr); 580 return elf_header; 581 } 582 583 // Create program headers based on written sections. 584 std::vector<Elf_Phdr> MakeProgramHeaders() { 585 CHECK(!sections_.empty()); 586 std::vector<Elf_Phdr> phdrs; 587 { 588 // The program headers must start with PT_PHDR which is used in 589 // loaded process to determine the number of program headers. 590 Elf_Phdr phdr = Elf_Phdr(); 591 phdr.p_type = PT_PHDR; 592 phdr.p_flags = PF_R; 593 phdr.p_offset = phdr.p_vaddr = phdr.p_paddr = sizeof(Elf_Ehdr); 594 phdr.p_filesz = phdr.p_memsz = 0; // We need to fill this later. 595 phdr.p_align = sizeof(Elf_Off); 596 phdrs.push_back(phdr); 597 // Tell the linker to mmap the start of file to memory. 598 Elf_Phdr load = Elf_Phdr(); 599 load.p_type = PT_LOAD; 600 load.p_flags = PF_R; 601 load.p_offset = load.p_vaddr = load.p_paddr = 0; 602 load.p_filesz = load.p_memsz = sections_[0]->header_.sh_offset; 603 load.p_align = kPageSize; 604 phdrs.push_back(load); 605 } 606 // Create program headers for sections. 607 for (auto* section : sections_) { 608 const Elf_Shdr& shdr = section->header_; 609 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 610 // PT_LOAD tells the linker to mmap part of the file. 611 // The linker can only mmap page-aligned sections. 612 // Single PT_LOAD may contain several ELF sections. 613 Elf_Phdr& prev = phdrs.back(); 614 Elf_Phdr load = Elf_Phdr(); 615 load.p_type = PT_LOAD; 616 load.p_flags = section->phdr_flags_; 617 load.p_offset = shdr.sh_offset; 618 load.p_vaddr = load.p_paddr = shdr.sh_addr; 619 load.p_filesz = (shdr.sh_type != SHT_NOBITS ? shdr.sh_size : 0u); 620 load.p_memsz = shdr.sh_size; 621 load.p_align = shdr.sh_addralign; 622 if (prev.p_type == load.p_type && 623 prev.p_flags == load.p_flags && 624 prev.p_filesz == prev.p_memsz && // Do not merge .bss 625 load.p_filesz == load.p_memsz) { // Do not merge .bss 626 // Merge this PT_LOAD with the previous one. 627 Elf_Word size = shdr.sh_offset + shdr.sh_size - prev.p_offset; 628 prev.p_filesz = size; 629 prev.p_memsz = size; 630 } else { 631 // If we are adding new load, it must be aligned. 632 CHECK_EQ(shdr.sh_addralign, (Elf_Word)kPageSize); 633 phdrs.push_back(load); 634 } 635 } 636 } 637 for (auto* section : sections_) { 638 const Elf_Shdr& shdr = section->header_; 639 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 640 // Other PT_* types allow the program to locate interesting 641 // parts of memory at runtime. They must overlap with PT_LOAD. 642 if (section->phdr_type_ != 0) { 643 Elf_Phdr phdr = Elf_Phdr(); 644 phdr.p_type = section->phdr_type_; 645 phdr.p_flags = section->phdr_flags_; 646 phdr.p_offset = shdr.sh_offset; 647 phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr; 648 phdr.p_filesz = phdr.p_memsz = shdr.sh_size; 649 phdr.p_align = shdr.sh_addralign; 650 phdrs.push_back(phdr); 651 } 652 } 653 } 654 // Set the size of the initial PT_PHDR. 655 CHECK_EQ(phdrs[0].p_type, (Elf_Word)PT_PHDR); 656 phdrs[0].p_filesz = phdrs[0].p_memsz = phdrs.size() * sizeof(Elf_Phdr); 657 658 return phdrs; 659 } 660 661 InstructionSet isa_; 662 663 OutputStream* output_; 664 bool output_good_; // True if all writes to output succeeded. 665 off_t output_offset_; // Keep track of the current position in the stream. 666 667 Section rodata_; 668 Section text_; 669 Section bss_; 670 StringSection dynstr_; 671 SymbolSection dynsym_; 672 Section hash_; 673 Section dynamic_; 674 Section eh_frame_; 675 Section eh_frame_hdr_; 676 StringSection strtab_; 677 SymbolSection symtab_; 678 Section debug_frame_; 679 Section debug_info_; 680 Section debug_line_; 681 StringSection shstrtab_; 682 std::vector<std::unique_ptr<Section>> other_sections_; 683 684 // List of used section in the order in which they were written. 685 std::vector<Section*> sections_; 686 687 // Used for allocation of virtual address space. 688 Elf_Addr virtual_address_; 689 690 DISALLOW_COPY_AND_ASSIGN(ElfBuilder); 691}; 692 693} // namespace art 694 695#endif // ART_COMPILER_ELF_BUILDER_H_ 696