elf_builder.h revision 625a64aad13905d8a2454bf3cc0e874487b110d5
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 "elf_utils.h" 27#include "leb128.h" 28#include "linker/error_delaying_output_stream.h" 29#include "utils/array_ref.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 // Start writing of this section. 104 void Start() { 105 CHECK(!started_); 106 CHECK(!finished_); 107 started_ = true; 108 auto& sections = owner_->sections_; 109 // Check that the previous section is complete. 110 CHECK(sections.empty() || sections.back()->finished_); 111 // The first ELF section index is 1. Index 0 is reserved for NULL. 112 section_index_ = sections.size() + 1; 113 // Push this section on the list of written sections. 114 sections.push_back(this); 115 // Align file position. 116 if (header_.sh_type != SHT_NOBITS) { 117 header_.sh_offset = RoundUp(owner_->stream_.Seek(0, kSeekCurrent), header_.sh_addralign); 118 owner_->stream_.Seek(header_.sh_offset, kSeekSet); 119 } 120 // Align virtual memory address. 121 if ((header_.sh_flags & SHF_ALLOC) != 0) { 122 header_.sh_addr = RoundUp(owner_->virtual_address_, header_.sh_addralign); 123 owner_->virtual_address_ = header_.sh_addr; 124 } 125 } 126 127 // Finish writing of this section. 128 void End() { 129 CHECK(started_); 130 CHECK(!finished_); 131 finished_ = true; 132 if (header_.sh_type == SHT_NOBITS) { 133 CHECK_GT(header_.sh_size, 0u); 134 } else { 135 // Use the current file position to determine section size. 136 off_t file_offset = owner_->stream_.Seek(0, kSeekCurrent); 137 CHECK_GE(file_offset, (off_t)header_.sh_offset); 138 header_.sh_size = file_offset - header_.sh_offset; 139 } 140 if ((header_.sh_flags & SHF_ALLOC) != 0) { 141 owner_->virtual_address_ += header_.sh_size; 142 } 143 } 144 145 // Returns true if the section was written to disk. 146 // (Used to check whether we have .text when writing JIT debug info) 147 bool Exists() const { 148 return finished_; 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_->stream_.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 return owner_->stream_.WriteFully(buffer, byte_count); 180 } 181 182 // This function always succeeds to simplify code. 183 // Use builder's Good() to check the actual status. 184 off_t Seek(off_t offset, Whence whence) OVERRIDE { 185 // Forward the seek as-is and trust the caller to use it reasonably. 186 return owner_->stream_.Seek(offset, whence); 187 } 188 189 // This function flushes the output and returns whether it succeeded. 190 // If there was a previous failure, this does nothing and returns false, i.e. failed. 191 bool Flush() OVERRIDE { 192 return owner_->stream_.Flush(); 193 } 194 195 Elf_Word GetSectionIndex() const { 196 DCHECK(started_); 197 DCHECK_NE(section_index_, 0u); 198 return section_index_; 199 } 200 201 private: 202 ElfBuilder<ElfTypes>* owner_; 203 Elf_Shdr header_; 204 Elf_Word section_index_; 205 const std::string name_; 206 const Section* const link_; 207 bool started_; 208 bool finished_; 209 Elf_Word phdr_flags_; 210 Elf_Word phdr_type_; 211 212 friend class ElfBuilder; 213 214 DISALLOW_COPY_AND_ASSIGN(Section); 215 }; 216 217 // Writer of .dynstr .strtab and .shstrtab sections. 218 class StringSection FINAL : public Section { 219 public: 220 StringSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 221 Elf_Word flags, Elf_Word align) 222 : Section(owner, name, SHT_STRTAB, flags, nullptr, 0, align, 0), 223 current_offset_(0) { 224 } 225 226 Elf_Word Write(const std::string& name) { 227 if (current_offset_ == 0) { 228 DCHECK(name.empty()); 229 } 230 Elf_Word offset = current_offset_; 231 this->WriteFully(name.c_str(), name.length() + 1); 232 current_offset_ += name.length() + 1; 233 return offset; 234 } 235 236 private: 237 Elf_Word current_offset_; 238 }; 239 240 // Writer of .dynsym and .symtab sections. 241 class SymbolSection FINAL : public Section { 242 public: 243 SymbolSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 244 Elf_Word type, Elf_Word flags, StringSection* strtab) 245 : Section(owner, name, type, flags, strtab, 0, 246 sizeof(Elf_Off), sizeof(Elf_Sym)) { 247 } 248 249 // Buffer symbol for this section. It will be written later. 250 // If the symbol's section is null, it will be considered absolute (SHN_ABS). 251 // (we use this in JIT to reference code which is stored outside the debug ELF file) 252 void Add(Elf_Word name, const Section* section, 253 Elf_Addr addr, bool is_relative, Elf_Word size, 254 uint8_t binding, uint8_t type, uint8_t other = 0) { 255 Elf_Sym sym = Elf_Sym(); 256 sym.st_name = name; 257 sym.st_value = addr + (is_relative ? section->GetAddress() : 0); 258 sym.st_size = size; 259 sym.st_other = other; 260 sym.st_shndx = (section != nullptr ? section->GetSectionIndex() 261 : static_cast<Elf_Word>(SHN_ABS)); 262 sym.st_info = (binding << 4) + (type & 0xf); 263 symbols_.push_back(sym); 264 } 265 266 void Write() { 267 // The symbol table always has to start with NULL symbol. 268 Elf_Sym null_symbol = Elf_Sym(); 269 this->WriteFully(&null_symbol, sizeof(null_symbol)); 270 this->WriteFully(symbols_.data(), symbols_.size() * sizeof(symbols_[0])); 271 symbols_.clear(); 272 symbols_.shrink_to_fit(); 273 } 274 275 private: 276 std::vector<Elf_Sym> symbols_; 277 }; 278 279 ElfBuilder(InstructionSet isa, OutputStream* output) 280 : isa_(isa), 281 stream_(output), 282 rodata_(this, ".rodata", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 283 text_(this, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, nullptr, 0, kPageSize, 0), 284 bss_(this, ".bss", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 285 dynstr_(this, ".dynstr", SHF_ALLOC, kPageSize), 286 dynsym_(this, ".dynsym", SHT_DYNSYM, SHF_ALLOC, &dynstr_), 287 hash_(this, ".hash", SHT_HASH, SHF_ALLOC, &dynsym_, 0, sizeof(Elf_Word), sizeof(Elf_Word)), 288 dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), 289 eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 290 eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), 291 strtab_(this, ".strtab", 0, kPageSize), 292 symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), 293 debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), 294 debug_info_(this, ".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 295 debug_line_(this, ".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 296 shstrtab_(this, ".shstrtab", 0, 1), 297 virtual_address_(0) { 298 text_.phdr_flags_ = PF_R | PF_X; 299 bss_.phdr_flags_ = PF_R | PF_W; 300 dynamic_.phdr_flags_ = PF_R | PF_W; 301 dynamic_.phdr_type_ = PT_DYNAMIC; 302 eh_frame_hdr_.phdr_type_ = PT_GNU_EH_FRAME; 303 } 304 ~ElfBuilder() {} 305 306 InstructionSet GetIsa() { return isa_; } 307 Section* GetRoData() { return &rodata_; } 308 Section* GetText() { return &text_; } 309 Section* GetBss() { return &bss_; } 310 StringSection* GetStrTab() { return &strtab_; } 311 SymbolSection* GetSymTab() { return &symtab_; } 312 Section* GetEhFrame() { return &eh_frame_; } 313 Section* GetEhFrameHdr() { return &eh_frame_hdr_; } 314 Section* GetDebugFrame() { return &debug_frame_; } 315 Section* GetDebugInfo() { return &debug_info_; } 316 Section* GetDebugLine() { return &debug_line_; } 317 318 // Encode patch locations as LEB128 list of deltas between consecutive addresses. 319 // (exposed publicly for tests) 320 static void EncodeOatPatches(const ArrayRef<const uintptr_t>& locations, 321 std::vector<uint8_t>* buffer) { 322 buffer->reserve(buffer->size() + locations.size() * 2); // guess 2 bytes per ULEB128. 323 uintptr_t address = 0; // relative to start of section. 324 for (uintptr_t location : locations) { 325 DCHECK_GE(location, address) << "Patch locations are not in sorted order"; 326 EncodeUnsignedLeb128(buffer, dchecked_integral_cast<uint32_t>(location - address)); 327 address = location; 328 } 329 } 330 331 void WritePatches(const char* name, const ArrayRef<const uintptr_t>& patch_locations) { 332 std::vector<uint8_t> buffer; 333 EncodeOatPatches(patch_locations, &buffer); 334 std::unique_ptr<Section> s(new Section(this, name, SHT_OAT_PATCH, 0, nullptr, 0, 1, 0)); 335 s->Start(); 336 s->WriteFully(buffer.data(), buffer.size()); 337 s->End(); 338 other_sections_.push_back(std::move(s)); 339 } 340 341 void WriteSection(const char* name, const std::vector<uint8_t>* buffer) { 342 std::unique_ptr<Section> s(new Section(this, name, SHT_PROGBITS, 0, nullptr, 0, 1, 0)); 343 s->Start(); 344 s->WriteFully(buffer->data(), buffer->size()); 345 s->End(); 346 other_sections_.push_back(std::move(s)); 347 } 348 349 void Start() { 350 // Reserve space for ELF header and program headers. 351 // We do not know the number of headers until later, so 352 // it is easiest to just reserve a fixed amount of space. 353 int size = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; 354 stream_.Seek(size, kSeekSet); 355 virtual_address_ += size; 356 } 357 358 void End() { 359 // Write section names and finish the section headers. 360 shstrtab_.Start(); 361 shstrtab_.Write(""); 362 for (auto* section : sections_) { 363 section->header_.sh_name = shstrtab_.Write(section->name_); 364 if (section->link_ != nullptr) { 365 section->header_.sh_link = section->link_->GetSectionIndex(); 366 } 367 } 368 shstrtab_.End(); 369 370 // Write section headers at the end of the ELF file. 371 std::vector<Elf_Shdr> shdrs; 372 shdrs.reserve(1u + sections_.size()); 373 shdrs.push_back(Elf_Shdr()); // NULL at index 0. 374 for (auto* section : sections_) { 375 shdrs.push_back(section->header_); 376 } 377 Elf_Off section_headers_offset; 378 section_headers_offset = RoundUp(stream_.Seek(0, kSeekCurrent), sizeof(Elf_Off)); 379 stream_.Seek(section_headers_offset, kSeekSet); 380 stream_.WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); 381 382 // Flush everything else before writing the program headers. This should prevent 383 // the OS from reordering writes, so that we don't end up with valid headers 384 // and partially written data if we suddenly lose power, for example. 385 stream_.Flush(); 386 387 // Write the initial file headers. 388 std::vector<Elf_Phdr> phdrs = MakeProgramHeaders(); 389 Elf_Ehdr elf_header = MakeElfHeader(isa_); 390 elf_header.e_phoff = sizeof(Elf_Ehdr); 391 elf_header.e_shoff = section_headers_offset; 392 elf_header.e_phnum = phdrs.size(); 393 elf_header.e_shnum = shdrs.size(); 394 elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); 395 stream_.Seek(0, kSeekSet); 396 stream_.WriteFully(&elf_header, sizeof(elf_header)); 397 stream_.WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); 398 stream_.Flush(); 399 } 400 401 // The running program does not have access to section headers 402 // and the loader is not supposed to use them either. 403 // The dynamic sections therefore replicates some of the layout 404 // information like the address and size of .rodata and .text. 405 // It also contains other metadata like the SONAME. 406 // The .dynamic section is found using the PT_DYNAMIC program header. 407 void WriteDynamicSection(const std::string& elf_file_path) { 408 std::string soname(elf_file_path); 409 size_t directory_separator_pos = soname.rfind('/'); 410 if (directory_separator_pos != std::string::npos) { 411 soname = soname.substr(directory_separator_pos + 1); 412 } 413 414 dynstr_.Start(); 415 dynstr_.Write(""); // dynstr should start with empty string. 416 dynsym_.Add(dynstr_.Write("oatdata"), &rodata_, 0, true, 417 rodata_.GetSize(), STB_GLOBAL, STT_OBJECT); 418 if (text_.GetSize() != 0u) { 419 dynsym_.Add(dynstr_.Write("oatexec"), &text_, 0, true, 420 text_.GetSize(), STB_GLOBAL, STT_OBJECT); 421 dynsym_.Add(dynstr_.Write("oatlastword"), &text_, text_.GetSize() - 4, 422 true, 4, STB_GLOBAL, STT_OBJECT); 423 } else if (rodata_.GetSize() != 0) { 424 // rodata_ can be size 0 for dwarf_test. 425 dynsym_.Add(dynstr_.Write("oatlastword"), &rodata_, rodata_.GetSize() - 4, 426 true, 4, STB_GLOBAL, STT_OBJECT); 427 } 428 if (bss_.finished_) { 429 dynsym_.Add(dynstr_.Write("oatbss"), &bss_, 430 0, true, bss_.GetSize(), STB_GLOBAL, STT_OBJECT); 431 dynsym_.Add(dynstr_.Write("oatbsslastword"), &bss_, 432 bss_.GetSize() - 4, true, 4, STB_GLOBAL, STT_OBJECT); 433 } 434 Elf_Word soname_offset = dynstr_.Write(soname); 435 dynstr_.End(); 436 437 dynsym_.Start(); 438 dynsym_.Write(); 439 dynsym_.End(); 440 441 // We do not really need a hash-table since there is so few entries. 442 // However, the hash-table is the only way the linker can actually 443 // determine the number of symbols in .dynsym so it is required. 444 hash_.Start(); 445 int count = dynsym_.GetSize() / sizeof(Elf_Sym); // Includes NULL. 446 std::vector<Elf_Word> hash; 447 hash.push_back(1); // Number of buckets. 448 hash.push_back(count); // Number of chains. 449 // Buckets. Having just one makes it linear search. 450 hash.push_back(1); // Point to first non-NULL symbol. 451 // Chains. This creates linked list of symbols. 452 hash.push_back(0); // Dummy entry for the NULL symbol. 453 for (int i = 1; i < count - 1; i++) { 454 hash.push_back(i + 1); // Each symbol points to the next one. 455 } 456 hash.push_back(0); // Last symbol terminates the chain. 457 hash_.WriteFully(hash.data(), hash.size() * sizeof(hash[0])); 458 hash_.End(); 459 460 dynamic_.Start(); 461 Elf_Dyn dyns[] = { 462 { DT_HASH, { hash_.GetAddress() } }, 463 { DT_STRTAB, { dynstr_.GetAddress() } }, 464 { DT_SYMTAB, { dynsym_.GetAddress() } }, 465 { DT_SYMENT, { sizeof(Elf_Sym) } }, 466 { DT_STRSZ, { dynstr_.GetSize() } }, 467 { DT_SONAME, { soname_offset } }, 468 { DT_NULL, { 0 } }, 469 }; 470 dynamic_.WriteFully(&dyns, sizeof(dyns)); 471 dynamic_.End(); 472 } 473 474 // Returns true if all writes and seeks on the output stream succeeded. 475 bool Good() { 476 return stream_.Good(); 477 } 478 479 // Returns the builder's internal stream. 480 OutputStream* GetStream() { 481 return &stream_; 482 } 483 484 private: 485 static Elf_Ehdr MakeElfHeader(InstructionSet isa) { 486 Elf_Ehdr elf_header = Elf_Ehdr(); 487 switch (isa) { 488 case kArm: 489 // Fall through. 490 case kThumb2: { 491 elf_header.e_machine = EM_ARM; 492 elf_header.e_flags = EF_ARM_EABI_VER5; 493 break; 494 } 495 case kArm64: { 496 elf_header.e_machine = EM_AARCH64; 497 elf_header.e_flags = 0; 498 break; 499 } 500 case kX86: { 501 elf_header.e_machine = EM_386; 502 elf_header.e_flags = 0; 503 break; 504 } 505 case kX86_64: { 506 elf_header.e_machine = EM_X86_64; 507 elf_header.e_flags = 0; 508 break; 509 } 510 case kMips: { 511 elf_header.e_machine = EM_MIPS; 512 elf_header.e_flags = (EF_MIPS_NOREORDER | 513 EF_MIPS_PIC | 514 EF_MIPS_CPIC | 515 EF_MIPS_ABI_O32 | 516 EF_MIPS_ARCH_32R2); 517 break; 518 } 519 case kMips64: { 520 elf_header.e_machine = EM_MIPS; 521 elf_header.e_flags = (EF_MIPS_NOREORDER | 522 EF_MIPS_PIC | 523 EF_MIPS_CPIC | 524 EF_MIPS_ARCH_64R6); 525 break; 526 } 527 case kNone: { 528 LOG(FATAL) << "No instruction set"; 529 break; 530 } 531 default: { 532 LOG(FATAL) << "Unknown instruction set " << isa; 533 } 534 } 535 536 elf_header.e_ident[EI_MAG0] = ELFMAG0; 537 elf_header.e_ident[EI_MAG1] = ELFMAG1; 538 elf_header.e_ident[EI_MAG2] = ELFMAG2; 539 elf_header.e_ident[EI_MAG3] = ELFMAG3; 540 elf_header.e_ident[EI_CLASS] = (sizeof(Elf_Addr) == sizeof(Elf32_Addr)) 541 ? ELFCLASS32 : ELFCLASS64;; 542 elf_header.e_ident[EI_DATA] = ELFDATA2LSB; 543 elf_header.e_ident[EI_VERSION] = EV_CURRENT; 544 elf_header.e_ident[EI_OSABI] = ELFOSABI_LINUX; 545 elf_header.e_ident[EI_ABIVERSION] = 0; 546 elf_header.e_type = ET_DYN; 547 elf_header.e_version = 1; 548 elf_header.e_entry = 0; 549 elf_header.e_ehsize = sizeof(Elf_Ehdr); 550 elf_header.e_phentsize = sizeof(Elf_Phdr); 551 elf_header.e_shentsize = sizeof(Elf_Shdr); 552 elf_header.e_phoff = sizeof(Elf_Ehdr); 553 return elf_header; 554 } 555 556 // Create program headers based on written sections. 557 std::vector<Elf_Phdr> MakeProgramHeaders() { 558 CHECK(!sections_.empty()); 559 std::vector<Elf_Phdr> phdrs; 560 { 561 // The program headers must start with PT_PHDR which is used in 562 // loaded process to determine the number of program headers. 563 Elf_Phdr phdr = Elf_Phdr(); 564 phdr.p_type = PT_PHDR; 565 phdr.p_flags = PF_R; 566 phdr.p_offset = phdr.p_vaddr = phdr.p_paddr = sizeof(Elf_Ehdr); 567 phdr.p_filesz = phdr.p_memsz = 0; // We need to fill this later. 568 phdr.p_align = sizeof(Elf_Off); 569 phdrs.push_back(phdr); 570 // Tell the linker to mmap the start of file to memory. 571 Elf_Phdr load = Elf_Phdr(); 572 load.p_type = PT_LOAD; 573 load.p_flags = PF_R; 574 load.p_offset = load.p_vaddr = load.p_paddr = 0; 575 load.p_filesz = load.p_memsz = sections_[0]->header_.sh_offset; 576 load.p_align = kPageSize; 577 phdrs.push_back(load); 578 } 579 // Create program headers for sections. 580 for (auto* section : sections_) { 581 const Elf_Shdr& shdr = section->header_; 582 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 583 // PT_LOAD tells the linker to mmap part of the file. 584 // The linker can only mmap page-aligned sections. 585 // Single PT_LOAD may contain several ELF sections. 586 Elf_Phdr& prev = phdrs.back(); 587 Elf_Phdr load = Elf_Phdr(); 588 load.p_type = PT_LOAD; 589 load.p_flags = section->phdr_flags_; 590 load.p_offset = shdr.sh_offset; 591 load.p_vaddr = load.p_paddr = shdr.sh_addr; 592 load.p_filesz = (shdr.sh_type != SHT_NOBITS ? shdr.sh_size : 0u); 593 load.p_memsz = shdr.sh_size; 594 load.p_align = shdr.sh_addralign; 595 if (prev.p_type == load.p_type && 596 prev.p_flags == load.p_flags && 597 prev.p_filesz == prev.p_memsz && // Do not merge .bss 598 load.p_filesz == load.p_memsz) { // Do not merge .bss 599 // Merge this PT_LOAD with the previous one. 600 Elf_Word size = shdr.sh_offset + shdr.sh_size - prev.p_offset; 601 prev.p_filesz = size; 602 prev.p_memsz = size; 603 } else { 604 // If we are adding new load, it must be aligned. 605 CHECK_EQ(shdr.sh_addralign, (Elf_Word)kPageSize); 606 phdrs.push_back(load); 607 } 608 } 609 } 610 for (auto* section : sections_) { 611 const Elf_Shdr& shdr = section->header_; 612 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 613 // Other PT_* types allow the program to locate interesting 614 // parts of memory at runtime. They must overlap with PT_LOAD. 615 if (section->phdr_type_ != 0) { 616 Elf_Phdr phdr = Elf_Phdr(); 617 phdr.p_type = section->phdr_type_; 618 phdr.p_flags = section->phdr_flags_; 619 phdr.p_offset = shdr.sh_offset; 620 phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr; 621 phdr.p_filesz = phdr.p_memsz = shdr.sh_size; 622 phdr.p_align = shdr.sh_addralign; 623 phdrs.push_back(phdr); 624 } 625 } 626 } 627 // Set the size of the initial PT_PHDR. 628 CHECK_EQ(phdrs[0].p_type, (Elf_Word)PT_PHDR); 629 phdrs[0].p_filesz = phdrs[0].p_memsz = phdrs.size() * sizeof(Elf_Phdr); 630 631 return phdrs; 632 } 633 634 InstructionSet isa_; 635 636 ErrorDelayingOutputStream stream_; 637 638 Section rodata_; 639 Section text_; 640 Section bss_; 641 StringSection dynstr_; 642 SymbolSection dynsym_; 643 Section hash_; 644 Section dynamic_; 645 Section eh_frame_; 646 Section eh_frame_hdr_; 647 StringSection strtab_; 648 SymbolSection symtab_; 649 Section debug_frame_; 650 Section debug_info_; 651 Section debug_line_; 652 StringSection shstrtab_; 653 std::vector<std::unique_ptr<Section>> other_sections_; 654 655 // List of used section in the order in which they were written. 656 std::vector<Section*> sections_; 657 658 // Used for allocation of virtual address space. 659 Elf_Addr virtual_address_; 660 661 DISALLOW_COPY_AND_ASSIGN(ElfBuilder); 662}; 663 664} // namespace art 665 666#endif // ART_COMPILER_ELF_BUILDER_H_ 667