elf_builder.h revision 5cc349f3dd578e974f78314c50b6a0267c23e591
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 ~Section() OVERRIDE { 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_->stream_.Seek(0, kSeekCurrent), header_.sh_addralign); 124 owner_->stream_.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_->stream_.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 // Returns true if the section was written to disk. 152 // (Used to check whether we have .text when writing JIT debug info) 153 bool Exists() const { 154 return finished_; 155 } 156 157 // Get the location of this section in virtual memory. 158 Elf_Addr GetAddress() const { 159 CHECK(started_); 160 return header_.sh_addr; 161 } 162 163 // Returns the size of the content of this section. 164 Elf_Word GetSize() const { 165 if (finished_) { 166 return header_.sh_size; 167 } else { 168 CHECK(started_); 169 CHECK_NE(header_.sh_type, (Elf_Word)SHT_NOBITS); 170 return owner_->stream_.Seek(0, kSeekCurrent) - header_.sh_offset; 171 } 172 } 173 174 // Set desired allocation size for .bss section. 175 void SetSize(Elf_Word size) { 176 CHECK_EQ(header_.sh_type, (Elf_Word)SHT_NOBITS); 177 header_.sh_size = size; 178 } 179 180 // This function always succeeds to simplify code. 181 // Use builder's Good() to check the actual status. 182 bool WriteFully(const void* buffer, size_t byte_count) OVERRIDE { 183 CHECK(started_); 184 CHECK(!finished_); 185 return owner_->stream_.WriteFully(buffer, byte_count); 186 } 187 188 // This function always succeeds to simplify code. 189 // Use builder's Good() to check the actual status. 190 off_t Seek(off_t offset, Whence whence) OVERRIDE { 191 // Forward the seek as-is and trust the caller to use it reasonably. 192 return owner_->stream_.Seek(offset, whence); 193 } 194 195 // This function flushes the output and returns whether it succeeded. 196 // If there was a previous failure, this does nothing and returns false, i.e. failed. 197 bool Flush() OVERRIDE { 198 return owner_->stream_.Flush(); 199 } 200 201 Elf_Word GetSectionIndex() const { 202 DCHECK(started_); 203 DCHECK_NE(section_index_, 0u); 204 return section_index_; 205 } 206 207 private: 208 ElfBuilder<ElfTypes>* owner_; 209 Elf_Shdr header_; 210 Elf_Word section_index_; 211 const std::string name_; 212 const Section* const link_; 213 bool started_; 214 bool finished_; 215 Elf_Word phdr_flags_; 216 Elf_Word phdr_type_; 217 218 friend class ElfBuilder; 219 220 DISALLOW_COPY_AND_ASSIGN(Section); 221 }; 222 223 // Writer of .dynstr .strtab and .shstrtab sections. 224 class StringSection FINAL : public Section { 225 public: 226 StringSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 227 Elf_Word flags, Elf_Word align) 228 : Section(owner, name, SHT_STRTAB, flags, nullptr, 0, align, 0), 229 current_offset_(0) { 230 } 231 232 Elf_Word Write(const std::string& name) { 233 if (current_offset_ == 0) { 234 DCHECK(name.empty()); 235 } 236 Elf_Word offset = current_offset_; 237 this->WriteFully(name.c_str(), name.length() + 1); 238 current_offset_ += name.length() + 1; 239 return offset; 240 } 241 242 private: 243 Elf_Word current_offset_; 244 }; 245 246 // Writer of .dynsym and .symtab sections. 247 class SymbolSection FINAL : public Section { 248 public: 249 SymbolSection(ElfBuilder<ElfTypes>* owner, const std::string& name, 250 Elf_Word type, Elf_Word flags, StringSection* strtab) 251 : Section(owner, name, type, flags, strtab, 0, 252 sizeof(Elf_Off), sizeof(Elf_Sym)) { 253 } 254 255 // Buffer symbol for this section. It will be written later. 256 // If the symbol's section is null, it will be considered absolute (SHN_ABS). 257 // (we use this in JIT to reference code which is stored outside the debug ELF file) 258 void Add(Elf_Word name, const Section* section, 259 Elf_Addr addr, bool is_relative, Elf_Word size, 260 uint8_t binding, uint8_t type, uint8_t other = 0) { 261 Elf_Sym sym = Elf_Sym(); 262 sym.st_name = name; 263 sym.st_value = addr + (is_relative ? section->GetAddress() : 0); 264 sym.st_size = size; 265 sym.st_other = other; 266 sym.st_shndx = (section != nullptr ? section->GetSectionIndex() 267 : static_cast<Elf_Word>(SHN_ABS)); 268 sym.st_info = (binding << 4) + (type & 0xf); 269 symbols_.push_back(sym); 270 } 271 272 void Write() { 273 // The symbol table always has to start with NULL symbol. 274 Elf_Sym null_symbol = Elf_Sym(); 275 this->WriteFully(&null_symbol, sizeof(null_symbol)); 276 this->WriteFully(symbols_.data(), symbols_.size() * sizeof(symbols_[0])); 277 symbols_.clear(); 278 symbols_.shrink_to_fit(); 279 } 280 281 private: 282 std::vector<Elf_Sym> symbols_; 283 }; 284 285 ElfBuilder(InstructionSet isa, OutputStream* output) 286 : isa_(isa), 287 stream_(output), 288 rodata_(this, ".rodata", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 289 text_(this, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, nullptr, 0, kPageSize, 0), 290 bss_(this, ".bss", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 291 dynstr_(this, ".dynstr", SHF_ALLOC, kPageSize), 292 dynsym_(this, ".dynsym", SHT_DYNSYM, SHF_ALLOC, &dynstr_), 293 hash_(this, ".hash", SHT_HASH, SHF_ALLOC, &dynsym_, 0, sizeof(Elf_Word), sizeof(Elf_Word)), 294 dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), 295 eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), 296 eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), 297 strtab_(this, ".strtab", 0, kPageSize), 298 symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), 299 debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), 300 debug_info_(this, ".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 301 debug_line_(this, ".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0), 302 shstrtab_(this, ".shstrtab", 0, 1), 303 virtual_address_(0) { 304 text_.phdr_flags_ = PF_R | PF_X; 305 bss_.phdr_flags_ = PF_R | PF_W; 306 dynamic_.phdr_flags_ = PF_R | PF_W; 307 dynamic_.phdr_type_ = PT_DYNAMIC; 308 eh_frame_hdr_.phdr_type_ = PT_GNU_EH_FRAME; 309 } 310 ~ElfBuilder() {} 311 312 InstructionSet GetIsa() { return isa_; } 313 Section* GetRoData() { return &rodata_; } 314 Section* GetText() { return &text_; } 315 Section* GetBss() { return &bss_; } 316 StringSection* GetStrTab() { return &strtab_; } 317 SymbolSection* GetSymTab() { return &symtab_; } 318 Section* GetEhFrame() { return &eh_frame_; } 319 Section* GetEhFrameHdr() { return &eh_frame_hdr_; } 320 Section* GetDebugFrame() { return &debug_frame_; } 321 Section* GetDebugInfo() { return &debug_info_; } 322 Section* GetDebugLine() { return &debug_line_; } 323 324 // Encode patch locations as LEB128 list of deltas between consecutive addresses. 325 // (exposed publicly for tests) 326 static void EncodeOatPatches(const ArrayRef<const uintptr_t>& locations, 327 std::vector<uint8_t>* buffer) { 328 buffer->reserve(buffer->size() + locations.size() * 2); // guess 2 bytes per ULEB128. 329 uintptr_t address = 0; // relative to start of section. 330 for (uintptr_t location : locations) { 331 DCHECK_GE(location, address) << "Patch locations are not in sorted order"; 332 EncodeUnsignedLeb128(buffer, dchecked_integral_cast<uint32_t>(location - address)); 333 address = location; 334 } 335 } 336 337 void WritePatches(const char* name, const ArrayRef<const uintptr_t>& patch_locations) { 338 std::vector<uint8_t> buffer; 339 EncodeOatPatches(patch_locations, &buffer); 340 std::unique_ptr<Section> s(new Section(this, name, SHT_OAT_PATCH, 0, nullptr, 0, 1, 0)); 341 s->Start(); 342 s->WriteFully(buffer.data(), buffer.size()); 343 s->End(); 344 other_sections_.push_back(std::move(s)); 345 } 346 347 void WriteSection(const char* name, const std::vector<uint8_t>* buffer) { 348 std::unique_ptr<Section> s(new Section(this, name, SHT_PROGBITS, 0, nullptr, 0, 1, 0)); 349 s->Start(); 350 s->WriteFully(buffer->data(), buffer->size()); 351 s->End(); 352 other_sections_.push_back(std::move(s)); 353 } 354 355 void Start() { 356 // Reserve space for ELF header and program headers. 357 // We do not know the number of headers until later, so 358 // it is easiest to just reserve a fixed amount of space. 359 int size = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; 360 stream_.Seek(size, kSeekSet); 361 virtual_address_ += size; 362 } 363 364 void End() { 365 // Write section names and finish the section headers. 366 shstrtab_.Start(); 367 shstrtab_.Write(""); 368 for (auto* section : sections_) { 369 section->header_.sh_name = shstrtab_.Write(section->name_); 370 if (section->link_ != nullptr) { 371 section->header_.sh_link = section->link_->GetSectionIndex(); 372 } 373 } 374 shstrtab_.End(); 375 376 // Write section headers at the end of the ELF file. 377 std::vector<Elf_Shdr> shdrs; 378 shdrs.reserve(1u + sections_.size()); 379 shdrs.push_back(Elf_Shdr()); // NULL at index 0. 380 for (auto* section : sections_) { 381 shdrs.push_back(section->header_); 382 } 383 Elf_Off section_headers_offset; 384 section_headers_offset = RoundUp(stream_.Seek(0, kSeekCurrent), sizeof(Elf_Off)); 385 stream_.Seek(section_headers_offset, kSeekSet); 386 stream_.WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); 387 388 // Flush everything else before writing the program headers. This should prevent 389 // the OS from reordering writes, so that we don't end up with valid headers 390 // and partially written data if we suddenly lose power, for example. 391 stream_.Flush(); 392 393 // Write the initial file headers. 394 std::vector<Elf_Phdr> phdrs = MakeProgramHeaders(); 395 Elf_Ehdr elf_header = MakeElfHeader(isa_); 396 elf_header.e_phoff = sizeof(Elf_Ehdr); 397 elf_header.e_shoff = section_headers_offset; 398 elf_header.e_phnum = phdrs.size(); 399 elf_header.e_shnum = shdrs.size(); 400 elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); 401 stream_.Seek(0, kSeekSet); 402 stream_.WriteFully(&elf_header, sizeof(elf_header)); 403 stream_.WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); 404 stream_.Flush(); 405 } 406 407 // The running program does not have access to section headers 408 // and the loader is not supposed to use them either. 409 // The dynamic sections therefore replicates some of the layout 410 // information like the address and size of .rodata and .text. 411 // It also contains other metadata like the SONAME. 412 // The .dynamic section is found using the PT_DYNAMIC program header. 413 void WriteDynamicSection(const std::string& elf_file_path) { 414 std::string soname(elf_file_path); 415 size_t directory_separator_pos = soname.rfind('/'); 416 if (directory_separator_pos != std::string::npos) { 417 soname = soname.substr(directory_separator_pos + 1); 418 } 419 420 dynstr_.Start(); 421 dynstr_.Write(""); // dynstr should start with empty string. 422 dynsym_.Add(dynstr_.Write("oatdata"), &rodata_, 0, true, 423 rodata_.GetSize(), STB_GLOBAL, STT_OBJECT); 424 if (text_.GetSize() != 0u) { 425 dynsym_.Add(dynstr_.Write("oatexec"), &text_, 0, true, 426 text_.GetSize(), STB_GLOBAL, STT_OBJECT); 427 dynsym_.Add(dynstr_.Write("oatlastword"), &text_, text_.GetSize() - 4, 428 true, 4, STB_GLOBAL, STT_OBJECT); 429 } else if (rodata_.GetSize() != 0) { 430 // rodata_ can be size 0 for dwarf_test. 431 dynsym_.Add(dynstr_.Write("oatlastword"), &rodata_, rodata_.GetSize() - 4, 432 true, 4, STB_GLOBAL, STT_OBJECT); 433 } 434 if (bss_.finished_) { 435 dynsym_.Add(dynstr_.Write("oatbss"), &bss_, 436 0, true, bss_.GetSize(), STB_GLOBAL, STT_OBJECT); 437 dynsym_.Add(dynstr_.Write("oatbsslastword"), &bss_, 438 bss_.GetSize() - 4, true, 4, STB_GLOBAL, STT_OBJECT); 439 } 440 Elf_Word soname_offset = dynstr_.Write(soname); 441 dynstr_.End(); 442 443 dynsym_.Start(); 444 dynsym_.Write(); 445 dynsym_.End(); 446 447 // We do not really need a hash-table since there is so few entries. 448 // However, the hash-table is the only way the linker can actually 449 // determine the number of symbols in .dynsym so it is required. 450 hash_.Start(); 451 int count = dynsym_.GetSize() / sizeof(Elf_Sym); // Includes NULL. 452 std::vector<Elf_Word> hash; 453 hash.push_back(1); // Number of buckets. 454 hash.push_back(count); // Number of chains. 455 // Buckets. Having just one makes it linear search. 456 hash.push_back(1); // Point to first non-NULL symbol. 457 // Chains. This creates linked list of symbols. 458 hash.push_back(0); // Dummy entry for the NULL symbol. 459 for (int i = 1; i < count - 1; i++) { 460 hash.push_back(i + 1); // Each symbol points to the next one. 461 } 462 hash.push_back(0); // Last symbol terminates the chain. 463 hash_.WriteFully(hash.data(), hash.size() * sizeof(hash[0])); 464 hash_.End(); 465 466 dynamic_.Start(); 467 Elf_Dyn dyns[] = { 468 { DT_HASH, { hash_.GetAddress() } }, 469 { DT_STRTAB, { dynstr_.GetAddress() } }, 470 { DT_SYMTAB, { dynsym_.GetAddress() } }, 471 { DT_SYMENT, { sizeof(Elf_Sym) } }, 472 { DT_STRSZ, { dynstr_.GetSize() } }, 473 { DT_SONAME, { soname_offset } }, 474 { DT_NULL, { 0 } }, 475 }; 476 dynamic_.WriteFully(&dyns, sizeof(dyns)); 477 dynamic_.End(); 478 } 479 480 // Returns true if all writes and seeks on the output stream succeeded. 481 bool Good() { 482 return stream_.Good(); 483 } 484 485 // Returns the builder's internal stream. 486 OutputStream* GetStream() { 487 return &stream_; 488 } 489 490 private: 491 static Elf_Ehdr MakeElfHeader(InstructionSet isa) { 492 Elf_Ehdr elf_header = Elf_Ehdr(); 493 switch (isa) { 494 case kArm: 495 // Fall through. 496 case kThumb2: { 497 elf_header.e_machine = EM_ARM; 498 elf_header.e_flags = EF_ARM_EABI_VER5; 499 break; 500 } 501 case kArm64: { 502 elf_header.e_machine = EM_AARCH64; 503 elf_header.e_flags = 0; 504 break; 505 } 506 case kX86: { 507 elf_header.e_machine = EM_386; 508 elf_header.e_flags = 0; 509 break; 510 } 511 case kX86_64: { 512 elf_header.e_machine = EM_X86_64; 513 elf_header.e_flags = 0; 514 break; 515 } 516 case kMips: { 517 elf_header.e_machine = EM_MIPS; 518 elf_header.e_flags = (EF_MIPS_NOREORDER | 519 EF_MIPS_PIC | 520 EF_MIPS_CPIC | 521 EF_MIPS_ABI_O32 | 522 EF_MIPS_ARCH_32R2); 523 break; 524 } 525 case kMips64: { 526 elf_header.e_machine = EM_MIPS; 527 elf_header.e_flags = (EF_MIPS_NOREORDER | 528 EF_MIPS_PIC | 529 EF_MIPS_CPIC | 530 EF_MIPS_ARCH_64R6); 531 break; 532 } 533 case kNone: { 534 LOG(FATAL) << "No instruction set"; 535 break; 536 } 537 default: { 538 LOG(FATAL) << "Unknown instruction set " << isa; 539 } 540 } 541 542 elf_header.e_ident[EI_MAG0] = ELFMAG0; 543 elf_header.e_ident[EI_MAG1] = ELFMAG1; 544 elf_header.e_ident[EI_MAG2] = ELFMAG2; 545 elf_header.e_ident[EI_MAG3] = ELFMAG3; 546 elf_header.e_ident[EI_CLASS] = (sizeof(Elf_Addr) == sizeof(Elf32_Addr)) 547 ? ELFCLASS32 : ELFCLASS64;; 548 elf_header.e_ident[EI_DATA] = ELFDATA2LSB; 549 elf_header.e_ident[EI_VERSION] = EV_CURRENT; 550 elf_header.e_ident[EI_OSABI] = ELFOSABI_LINUX; 551 elf_header.e_ident[EI_ABIVERSION] = 0; 552 elf_header.e_type = ET_DYN; 553 elf_header.e_version = 1; 554 elf_header.e_entry = 0; 555 elf_header.e_ehsize = sizeof(Elf_Ehdr); 556 elf_header.e_phentsize = sizeof(Elf_Phdr); 557 elf_header.e_shentsize = sizeof(Elf_Shdr); 558 elf_header.e_phoff = sizeof(Elf_Ehdr); 559 return elf_header; 560 } 561 562 // Create program headers based on written sections. 563 std::vector<Elf_Phdr> MakeProgramHeaders() { 564 CHECK(!sections_.empty()); 565 std::vector<Elf_Phdr> phdrs; 566 { 567 // The program headers must start with PT_PHDR which is used in 568 // loaded process to determine the number of program headers. 569 Elf_Phdr phdr = Elf_Phdr(); 570 phdr.p_type = PT_PHDR; 571 phdr.p_flags = PF_R; 572 phdr.p_offset = phdr.p_vaddr = phdr.p_paddr = sizeof(Elf_Ehdr); 573 phdr.p_filesz = phdr.p_memsz = 0; // We need to fill this later. 574 phdr.p_align = sizeof(Elf_Off); 575 phdrs.push_back(phdr); 576 // Tell the linker to mmap the start of file to memory. 577 Elf_Phdr load = Elf_Phdr(); 578 load.p_type = PT_LOAD; 579 load.p_flags = PF_R; 580 load.p_offset = load.p_vaddr = load.p_paddr = 0; 581 load.p_filesz = load.p_memsz = sections_[0]->header_.sh_offset; 582 load.p_align = kPageSize; 583 phdrs.push_back(load); 584 } 585 // Create program headers for sections. 586 for (auto* section : sections_) { 587 const Elf_Shdr& shdr = section->header_; 588 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 589 // PT_LOAD tells the linker to mmap part of the file. 590 // The linker can only mmap page-aligned sections. 591 // Single PT_LOAD may contain several ELF sections. 592 Elf_Phdr& prev = phdrs.back(); 593 Elf_Phdr load = Elf_Phdr(); 594 load.p_type = PT_LOAD; 595 load.p_flags = section->phdr_flags_; 596 load.p_offset = shdr.sh_offset; 597 load.p_vaddr = load.p_paddr = shdr.sh_addr; 598 load.p_filesz = (shdr.sh_type != SHT_NOBITS ? shdr.sh_size : 0u); 599 load.p_memsz = shdr.sh_size; 600 load.p_align = shdr.sh_addralign; 601 if (prev.p_type == load.p_type && 602 prev.p_flags == load.p_flags && 603 prev.p_filesz == prev.p_memsz && // Do not merge .bss 604 load.p_filesz == load.p_memsz) { // Do not merge .bss 605 // Merge this PT_LOAD with the previous one. 606 Elf_Word size = shdr.sh_offset + shdr.sh_size - prev.p_offset; 607 prev.p_filesz = size; 608 prev.p_memsz = size; 609 } else { 610 // If we are adding new load, it must be aligned. 611 CHECK_EQ(shdr.sh_addralign, (Elf_Word)kPageSize); 612 phdrs.push_back(load); 613 } 614 } 615 } 616 for (auto* section : sections_) { 617 const Elf_Shdr& shdr = section->header_; 618 if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { 619 // Other PT_* types allow the program to locate interesting 620 // parts of memory at runtime. They must overlap with PT_LOAD. 621 if (section->phdr_type_ != 0) { 622 Elf_Phdr phdr = Elf_Phdr(); 623 phdr.p_type = section->phdr_type_; 624 phdr.p_flags = section->phdr_flags_; 625 phdr.p_offset = shdr.sh_offset; 626 phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr; 627 phdr.p_filesz = phdr.p_memsz = shdr.sh_size; 628 phdr.p_align = shdr.sh_addralign; 629 phdrs.push_back(phdr); 630 } 631 } 632 } 633 // Set the size of the initial PT_PHDR. 634 CHECK_EQ(phdrs[0].p_type, (Elf_Word)PT_PHDR); 635 phdrs[0].p_filesz = phdrs[0].p_memsz = phdrs.size() * sizeof(Elf_Phdr); 636 637 return phdrs; 638 } 639 640 InstructionSet isa_; 641 642 ErrorDelayingOutputStream stream_; 643 644 Section rodata_; 645 Section text_; 646 Section bss_; 647 StringSection dynstr_; 648 SymbolSection dynsym_; 649 Section hash_; 650 Section dynamic_; 651 Section eh_frame_; 652 Section eh_frame_hdr_; 653 StringSection strtab_; 654 SymbolSection symtab_; 655 Section debug_frame_; 656 Section debug_info_; 657 Section debug_line_; 658 StringSection shstrtab_; 659 std::vector<std::unique_ptr<Section>> other_sections_; 660 661 // List of used section in the order in which they were written. 662 std::vector<Section*> sections_; 663 664 // Used for allocation of virtual address space. 665 Elf_Addr virtual_address_; 666 667 DISALLOW_COPY_AND_ASSIGN(ElfBuilder); 668}; 669 670} // namespace art 671 672#endif // ART_COMPILER_ELF_BUILDER_H_ 673