elf_builder.h revision 6d8c8f0344a706df651567387ede683ab3ec1b5f
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 CHECK(finished_); 160 return header_.sh_size; 161 } 162 163 // Set desired allocation size for .bss section. 164 void SetSize(Elf_Word size) { 165 CHECK_EQ(header_.sh_type, (Elf_Word)SHT_NOBITS); 166 header_.sh_size = size; 167 } 168 169 // This function always succeeds to simplify code. 170 // Use builder's Good() to check the actual status. 171 bool WriteFully(const void* buffer, size_t byte_count) OVERRIDE { 172 CHECK(started_); 173 CHECK(!finished_); 174 owner_->WriteFully(buffer, byte_count); 175 return true; 176 } 177 178 // This function always succeeds to simplify code. 179 // Use builder's Good() to check the actual status. 180 off_t Seek(off_t offset, Whence whence) OVERRIDE { 181 // Forward the seek as-is and trust the caller to use it reasonably. 182 return owner_->Seek(offset, whence); 183 } 184 185 Elf_Word GetSectionIndex() const { 186 DCHECK(started_); 187 DCHECK_NE(section_index_, 0u); 188 return section_index_; 189 } 190 191 private: 192 ElfBuilder<ElfTypes>* owner_; 193 Elf_Shdr header_; 194 Elf_Word section_index_; 195 const std::string name_; 196 const Section* const link_; 197 bool started_; 198 bool finished_; 199 Elf_Word phdr_flags_; 200 Elf_Word phdr_type_; 201 202 DISALLOW_COPY_AND_ASSIGN(Section); 203 204 friend class ElfBuilder; 205 }; 206 207 // Writer of .dynstr .strtab and .shstrtab sections. 208 class StringSection FINAL : public Section { 209 public: 210 StringSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 211 Elf_Word flags, Elf_Word align) 212 : Section(owner, name, SHT_STRTAB, flags, nullptr, 0, align, 0), 213 current_offset_(0) { 214 } 215 216 Elf_Word Write(const std::string& name) { 217 if (current_offset_ == 0) { 218 DCHECK(name.empty()); 219 } 220 Elf_Word offset = current_offset_; 221 this->WriteFully(name.c_str(), name.length() + 1); 222 current_offset_ += name.length() + 1; 223 return offset; 224 } 225 226 private: 227 Elf_Word current_offset_; 228 }; 229 230 // Writer of .dynsym and .symtab sections. 231 class SymbolSection FINAL : public Section { 232 public: 233 SymbolSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 234 Elf_Word type, Elf_Word flags, StringSection* strtab) 235 : Section(owner, name, type, flags, strtab, 0, 236 sizeof(Elf_Off), sizeof(Elf_Sym)) { 237 } 238 239 // Buffer symbol for this section. It will be written later. 240 void Add(Elf_Word name, const Section* section, 241 Elf_Addr addr, bool is_relative, Elf_Word size, 242 uint8_t binding, uint8_t type, uint8_t other = 0) { 243 CHECK(section != nullptr); 244 Elf_Sym sym = Elf_Sym(); 245 sym.st_name = name; 246 sym.st_value = addr + (is_relative ? section->GetAddress() : 0); 247 sym.st_size = size; 248 sym.st_other = other; 249 sym.st_shndx = section->GetSectionIndex(); 250 sym.st_info = (binding << 4) + (type & 0xf); 251 symbols_.push_back(sym); 252 } 253 254 void Write() { 255 // The symbol table always has to start with NULL symbol. 256 Elf_Sym null_symbol = Elf_Sym(); 257 this->WriteFully(&null_symbol, sizeof(null_symbol)); 258 this->WriteFully(symbols_.data(), symbols_.size() * sizeof(symbols_[0])); 259 symbols_.clear(); 260 symbols_.shrink_to_fit(); 261 } 262 263 private: 264 std::vector<Elf_Sym> symbols_; 265 }; 266 267 ElfBuilder(InstructionSet isa, OutputStream* output) 268 : isa_(isa), 269 output_(output), 270 output_good_(true), 271 output_offset_(0), 272 rodata_(this, ".rodata", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 273 text_(this, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, nullptr, 0, kPageSize, 0), 274 bss_(this, ".bss", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 275 dynstr_(this, ".dynstr", SHF_ALLOC, kPageSize), 276 dynsym_(this, ".dynsym", SHT_DYNSYM, SHF_ALLOC, &dynstr_), 277 hash_(this, ".hash", SHT_HASH, SHF_ALLOC, &dynsym_, 0, sizeof(Elf_Word), sizeof(Elf_Word)), 278 dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), 279 eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 280 eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), 281 strtab_(this, ".strtab", 0, kPageSize), 282 symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), 283 debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), 284 shstrtab_(this, ".shstrtab", 0, 1), 285 virtual_address_(0) { 286 text_.phdr_flags_ = PF_R | PF_X; 287 bss_.phdr_flags_ = PF_R | PF_W; 288 dynamic_.phdr_flags_ = PF_R | PF_W; 289 dynamic_.phdr_type_ = PT_DYNAMIC; 290 eh_frame_hdr_.phdr_type_ = PT_GNU_EH_FRAME; 291 } 292 ~ElfBuilder() {} 293 294 InstructionSet GetIsa() { return isa_; } 295 Section* GetRoData() { return &rodata_; } 296 Section* GetText() { return &text_; } 297 Section* GetBss() { return &bss_; } 298 StringSection* GetStrTab() { return &strtab_; } 299 SymbolSection* GetSymTab() { return &symtab_; } 300 Section* GetEhFrame() { return &eh_frame_; } 301 Section* GetEhFrameHdr() { return &eh_frame_hdr_; } 302 Section* GetDebugFrame() { return &debug_frame_; } 303 304 // Encode patch locations as LEB128 list of deltas between consecutive addresses. 305 // (exposed publicly for tests) 306 static void EncodeOatPatches(const std::vector<uintptr_t>& locations, 307 std::vector<uint8_t>* buffer) { 308 buffer->reserve(buffer->size() + locations.size() * 2); // guess 2 bytes per ULEB128. 309 uintptr_t address = 0; // relative to start of section. 310 for (uintptr_t location : locations) { 311 DCHECK_GE(location, address) << "Patch locations are not in sorted order"; 312 EncodeUnsignedLeb128(buffer, dchecked_integral_cast<uint32_t>(location - address)); 313 address = location; 314 } 315 } 316 317 void WritePatches(const char* name, const std::vector<uintptr_t>* patch_locations) { 318 std::vector<uint8_t> buffer; 319 EncodeOatPatches(*patch_locations, &buffer); 320 std::unique_ptr<Section> s(new Section(this, name, SHT_OAT_PATCH, 0, nullptr, 0, 1, 0)); 321 s->Start(); 322 s->WriteFully(buffer.data(), buffer.size()); 323 s->End(); 324 other_sections_.push_back(std::move(s)); 325 } 326 327 void WriteSection(const char* name, const std::vector<uint8_t>* buffer) { 328 std::unique_ptr<Section> s(new Section(this, name, SHT_PROGBITS, 0, nullptr, 0, 1, 0)); 329 s->Start(); 330 s->WriteFully(buffer->data(), buffer->size()); 331 s->End(); 332 other_sections_.push_back(std::move(s)); 333 } 334 335 void Start() { 336 // Reserve space for ELF header and program headers. 337 // We do not know the number of headers until later, so 338 // it is easiest to just reserve a fixed amount of space. 339 int size = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; 340 Seek(size, kSeekSet); 341 virtual_address_ += size; 342 } 343 344 void End() { 345 // Write section names and finish the section headers. 346 shstrtab_.Start(); 347 shstrtab_.Write(""); 348 for (auto* section : sections_) { 349 section->header_.sh_name = shstrtab_.Write(section->name_); 350 if (section->link_ != nullptr) { 351 section->header_.sh_link = section->link_->GetSectionIndex(); 352 } 353 } 354 shstrtab_.End(); 355 356 // Write section headers at the end of the ELF file. 357 std::vector<Elf_Shdr> shdrs; 358 shdrs.reserve(1u + sections_.size()); 359 shdrs.push_back(Elf_Shdr()); // NULL at index 0. 360 for (auto* section : sections_) { 361 shdrs.push_back(section->header_); 362 } 363 Elf_Off section_headers_offset; 364 section_headers_offset = RoundUp(Seek(0, kSeekCurrent), sizeof(Elf_Off)); 365 Seek(section_headers_offset, kSeekSet); 366 WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); 367 368 // Write the initial file headers. 369 std::vector<Elf_Phdr> phdrs = MakeProgramHeaders(); 370 Elf_Ehdr elf_header = MakeElfHeader(isa_); 371 elf_header.e_phoff = sizeof(Elf_Ehdr); 372 elf_header.e_shoff = section_headers_offset; 373 elf_header.e_phnum = phdrs.size(); 374 elf_header.e_shnum = shdrs.size(); 375 elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); 376 Seek(0, kSeekSet); 377 WriteFully(&elf_header, sizeof(elf_header)); 378 WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); 379 } 380 381 // The running program does not have access to section headers 382 // and the loader is not supposed to use them either. 383 // The dynamic sections therefore replicates some of the layout 384 // information like the address and size of .rodata and .text. 385 // It also contains other metadata like the SONAME. 386 // The .dynamic section is found using the PT_DYNAMIC program header. 387 void WriteDynamicSection(const std::string& elf_file_path) { 388 std::string soname(elf_file_path); 389 size_t directory_separator_pos = soname.rfind('/'); 390 if (directory_separator_pos != std::string::npos) { 391 soname = soname.substr(directory_separator_pos + 1); 392 } 393 394 dynstr_.Start(); 395 dynstr_.Write(""); // dynstr should start with empty string. 396 dynsym_.Add(dynstr_.Write("oatdata"), &rodata_, 0, true, 397 rodata_.GetSize(), STB_GLOBAL, STT_OBJECT); 398 if (text_.GetSize() != 0u) { 399 dynsym_.Add(dynstr_.Write("oatexec"), &text_, 0, true, 400 text_.GetSize(), STB_GLOBAL, STT_OBJECT); 401 dynsym_.Add(dynstr_.Write("oatlastword"), &text_, text_.GetSize() - 4, 402 true, 4, STB_GLOBAL, STT_OBJECT); 403 } else if (rodata_.GetSize() != 0) { 404 // rodata_ can be size 0 for dwarf_test. 405 dynsym_.Add(dynstr_.Write("oatlastword"), &rodata_, rodata_.GetSize() - 4, 406 true, 4, STB_GLOBAL, STT_OBJECT); 407 } 408 if (bss_.finished_) { 409 dynsym_.Add(dynstr_.Write("oatbss"), &bss_, 410 0, true, bss_.GetSize(), STB_GLOBAL, STT_OBJECT); 411 dynsym_.Add(dynstr_.Write("oatbsslastword"), &bss_, 412 bss_.GetSize() - 4, true, 4, STB_GLOBAL, STT_OBJECT); 413 } 414 Elf_Word soname_offset = dynstr_.Write(soname); 415 dynstr_.End(); 416 417 dynsym_.Start(); 418 dynsym_.Write(); 419 dynsym_.End(); 420 421 // We do not really need a hash-table since there is so few entries. 422 // However, the hash-table is the only way the linker can actually 423 // determine the number of symbols in .dynsym so it is required. 424 hash_.Start(); 425 int count = dynsym_.GetSize() / sizeof(Elf_Sym); // Includes NULL. 426 std::vector<Elf_Word> hash; 427 hash.push_back(1); // Number of buckets. 428 hash.push_back(count); // Number of chains. 429 // Buckets. Having just one makes it linear search. 430 hash.push_back(1); // Point to first non-NULL symbol. 431 // Chains. This creates linked list of symbols. 432 hash.push_back(0); // Dummy entry for the NULL symbol. 433 for (int i = 1; i < count - 1; i++) { 434 hash.push_back(i + 1); // Each symbol points to the next one. 435 } 436 hash.push_back(0); // Last symbol terminates the chain. 437 hash_.WriteFully(hash.data(), hash.size() * sizeof(hash[0])); 438 hash_.End(); 439 440 dynamic_.Start(); 441 Elf_Dyn dyns[] = { 442 { DT_HASH, { hash_.GetAddress() } }, 443 { DT_STRTAB, { dynstr_.GetAddress() } }, 444 { DT_SYMTAB, { dynsym_.GetAddress() } }, 445 { DT_SYMENT, { sizeof(Elf_Sym) } }, 446 { DT_STRSZ, { dynstr_.GetSize() } }, 447 { DT_SONAME, { soname_offset } }, 448 { DT_NULL, { 0 } }, 449 }; 450 dynamic_.WriteFully(&dyns, sizeof(dyns)); 451 dynamic_.End(); 452 } 453 454 // Returns true if all writes and seeks on the output stream succeeded. 455 bool Good() { 456 return output_good_; 457 } 458 459 private: 460 // This function always succeeds to simplify code. 461 // Use Good() to check the actual status of the output stream. 462 void WriteFully(const void* buffer, size_t byte_count) { 463 if (output_good_) { 464 if (!output_->WriteFully(buffer, byte_count)) { 465 PLOG(ERROR) << "Failed to write " << byte_count 466 << " bytes to ELF file at offset " << output_offset_; 467 output_good_ = false; 468 } 469 } 470 output_offset_ += byte_count; 471 } 472 473 // This function always succeeds to simplify code. 474 // Use Good() to check the actual status of the output stream. 475 off_t Seek(off_t offset, Whence whence) { 476 // We keep shadow copy of the offset so that we return 477 // the expected value even if the output stream failed. 478 off_t new_offset; 479 switch (whence) { 480 case kSeekSet: 481 new_offset = offset; 482 break; 483 case kSeekCurrent: 484 new_offset = output_offset_ + offset; 485 break; 486 default: 487 LOG(FATAL) << "Unsupported seek type: " << whence; 488 UNREACHABLE(); 489 } 490 if (output_good_) { 491 off_t actual_offset = output_->Seek(offset, whence); 492 if (actual_offset == (off_t)-1) { 493 PLOG(ERROR) << "Failed to seek in ELF file. Offset=" << offset 494 << " whence=" << whence << " new_offset=" << new_offset; 495 output_good_ = false; 496 } 497 DCHECK_EQ(actual_offset, new_offset); 498 } 499 output_offset_ = new_offset; 500 return new_offset; 501 } 502 503 static Elf_Ehdr MakeElfHeader(InstructionSet isa) { 504 Elf_Ehdr elf_header = Elf_Ehdr(); 505 switch (isa) { 506 case kArm: 507 // Fall through. 508 case kThumb2: { 509 elf_header.e_machine = EM_ARM; 510 elf_header.e_flags = EF_ARM_EABI_VER5; 511 break; 512 } 513 case kArm64: { 514 elf_header.e_machine = EM_AARCH64; 515 elf_header.e_flags = 0; 516 break; 517 } 518 case kX86: { 519 elf_header.e_machine = EM_386; 520 elf_header.e_flags = 0; 521 break; 522 } 523 case kX86_64: { 524 elf_header.e_machine = EM_X86_64; 525 elf_header.e_flags = 0; 526 break; 527 } 528 case kMips: { 529 elf_header.e_machine = EM_MIPS; 530 elf_header.e_flags = (EF_MIPS_NOREORDER | 531 EF_MIPS_PIC | 532 EF_MIPS_CPIC | 533 EF_MIPS_ABI_O32 | 534 EF_MIPS_ARCH_32R2); 535 break; 536 } 537 case kMips64: { 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_ARCH_64R6); 543 break; 544 } 545 case kNone: { 546 LOG(FATAL) << "No instruction set"; 547 break; 548 } 549 default: { 550 LOG(FATAL) << "Unknown instruction set " << isa; 551 } 552 } 553 554 elf_header.e_ident[EI_MAG0] = ELFMAG0; 555 elf_header.e_ident[EI_MAG1] = ELFMAG1; 556 elf_header.e_ident[EI_MAG2] = ELFMAG2; 557 elf_header.e_ident[EI_MAG3] = ELFMAG3; 558 elf_header.e_ident[EI_CLASS] = (sizeof(Elf_Addr) == sizeof(Elf32_Addr)) 559 ? ELFCLASS32 : ELFCLASS64;; 560 elf_header.e_ident[EI_DATA] = ELFDATA2LSB; 561 elf_header.e_ident[EI_VERSION] = EV_CURRENT; 562 elf_header.e_ident[EI_OSABI] = ELFOSABI_LINUX; 563 elf_header.e_ident[EI_ABIVERSION] = 0; 564 elf_header.e_type = ET_DYN; 565 elf_header.e_version = 1; 566 elf_header.e_entry = 0; 567 elf_header.e_ehsize = sizeof(Elf_Ehdr); 568 elf_header.e_phentsize = sizeof(Elf_Phdr); 569 elf_header.e_shentsize = sizeof(Elf_Shdr); 570 elf_header.e_phoff = sizeof(Elf_Ehdr); 571 return elf_header; 572 } 573 574 // Create program headers based on written sections. 575 std::vector<Elf_Phdr> MakeProgramHeaders() { 576 CHECK(!sections_.empty()); 577 std::vector<Elf_Phdr> phdrs; 578 { 579 // The program headers must start with PT_PHDR which is used in 580 // loaded process to determine the number of program headers. 581 Elf_Phdr phdr = Elf_Phdr(); 582 phdr.p_type = PT_PHDR; 583 phdr.p_flags = PF_R; 584 phdr.p_offset = phdr.p_vaddr = phdr.p_paddr = sizeof(Elf_Ehdr); 585 phdr.p_filesz = phdr.p_memsz = 0; // We need to fill this later. 586 phdr.p_align = sizeof(Elf_Off); 587 phdrs.push_back(phdr); 588 // Tell the linker to mmap the start of file to memory. 589 Elf_Phdr load = Elf_Phdr(); 590 load.p_type = PT_LOAD; 591 load.p_flags = PF_R; 592 load.p_offset = load.p_vaddr = load.p_paddr = 0; 593 load.p_filesz = load.p_memsz = sections_[0]->header_.sh_offset; 594 load.p_align = kPageSize; 595 phdrs.push_back(load); 596 } 597 // Create program headers for sections. 598 for (auto* section : sections_) { 599 const Elf_Shdr& shdr = section->header_; 600 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 601 // PT_LOAD tells the linker to mmap part of the file. 602 // The linker can only mmap page-aligned sections. 603 // Single PT_LOAD may contain several ELF sections. 604 Elf_Phdr& prev = phdrs.back(); 605 Elf_Phdr load = Elf_Phdr(); 606 load.p_type = PT_LOAD; 607 load.p_flags = section->phdr_flags_; 608 load.p_offset = shdr.sh_offset; 609 load.p_vaddr = load.p_paddr = shdr.sh_addr; 610 load.p_filesz = (shdr.sh_type != SHT_NOBITS ? shdr.sh_size : 0u); 611 load.p_memsz = shdr.sh_size; 612 load.p_align = shdr.sh_addralign; 613 if (prev.p_type == load.p_type && 614 prev.p_flags == load.p_flags && 615 prev.p_filesz == prev.p_memsz && // Do not merge .bss 616 load.p_filesz == load.p_memsz) { // Do not merge .bss 617 // Merge this PT_LOAD with the previous one. 618 Elf_Word size = shdr.sh_offset + shdr.sh_size - prev.p_offset; 619 prev.p_filesz = size; 620 prev.p_memsz = size; 621 } else { 622 // If we are adding new load, it must be aligned. 623 CHECK_EQ(shdr.sh_addralign, (Elf_Word)kPageSize); 624 phdrs.push_back(load); 625 } 626 } 627 } 628 for (auto* section : sections_) { 629 const Elf_Shdr& shdr = section->header_; 630 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 631 // Other PT_* types allow the program to locate interesting 632 // parts of memory at runtime. They must overlap with PT_LOAD. 633 if (section->phdr_type_ != 0) { 634 Elf_Phdr phdr = Elf_Phdr(); 635 phdr.p_type = section->phdr_type_; 636 phdr.p_flags = section->phdr_flags_; 637 phdr.p_offset = shdr.sh_offset; 638 phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr; 639 phdr.p_filesz = phdr.p_memsz = shdr.sh_size; 640 phdr.p_align = shdr.sh_addralign; 641 phdrs.push_back(phdr); 642 } 643 } 644 } 645 // Set the size of the initial PT_PHDR. 646 CHECK_EQ(phdrs[0].p_type, (Elf_Word)PT_PHDR); 647 phdrs[0].p_filesz = phdrs[0].p_memsz = phdrs.size() * sizeof(Elf_Phdr); 648 649 return phdrs; 650 } 651 652 InstructionSet isa_; 653 654 OutputStream* output_; 655 bool output_good_; // True if all writes to output succeeded. 656 off_t output_offset_; // Keep track of the current position in the stream. 657 658 Section rodata_; 659 Section text_; 660 Section bss_; 661 StringSection dynstr_; 662 SymbolSection dynsym_; 663 Section hash_; 664 Section dynamic_; 665 Section eh_frame_; 666 Section eh_frame_hdr_; 667 StringSection strtab_; 668 SymbolSection symtab_; 669 Section debug_frame_; 670 StringSection shstrtab_; 671 std::vector<std::unique_ptr<Section>> other_sections_; 672 673 // List of used section in the order in which they were written. 674 std::vector<Section*> sections_; 675 676 // Used for allocation of virtual address space. 677 Elf_Addr virtual_address_; 678 679 DISALLOW_COPY_AND_ASSIGN(ElfBuilder); 680}; 681 682} // namespace art 683 684#endif // ART_COMPILER_ELF_BUILDER_H_ 685