runtime/elf_file.cc

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "elf_file.h"

#include <inttypes.h>
#include <sys/mman.h>  // For the PROT_* and MAP_* constants.
#include <sys/types.h>
#include <unistd.h>

#include "android-base/stringprintf.h"
#include "android-base/strings.h"

#include "arch/instruction_set.h"
#include "base/leb128.h"
#include "base/stl_util.h"
#include "base/unix_file/fd_file.h"
#include "base/utils.h"
#include "elf/elf_utils.h"
#include "elf_file_impl.h"

namespace art {

using android::base::StringPrintf;

template <typename ElfTypes>
ElfFileImpl<ElfTypes>::ElfFileImpl(File* file, bool writable, bool program_header_only)
  : writable_(writable),
    program_header_only_(program_header_only),
    header_(nullptr),
    base_address_(nullptr),
    program_headers_start_(nullptr),
    section_headers_start_(nullptr),
    dynamic_program_header_(nullptr),
    dynamic_section_start_(nullptr),
    symtab_section_start_(nullptr),
    dynsym_section_start_(nullptr),
    strtab_section_start_(nullptr),
    dynstr_section_start_(nullptr),
    hash_section_start_(nullptr),
    symtab_symbol_table_(nullptr),
    dynsym_symbol_table_(nullptr) {
  CHECK(file != nullptr);
}

template <typename ElfTypes>
ElfFileImpl<ElfTypes>* ElfFileImpl<ElfTypes>::Open(File* file,
                                                   bool writable,
                                                   bool program_header_only,
                                                   bool low_4gb,
                                                   std::string* error_msg) {
  std::unique_ptr<ElfFileImpl<ElfTypes>> elf_file(
      new ElfFileImpl<ElfTypes>(file, writable, program_header_only));
  int prot;
  int flags;
  if (writable) {
    prot = PROT_READ | PROT_WRITE;
    flags = MAP_SHARED;
  } else {
    prot = PROT_READ;
    flags = MAP_PRIVATE;
  }
  if (!elf_file->Setup(file, prot, flags, low_4gb, error_msg)) {
    return nullptr;
  }
  return elf_file.release();
}

template <typename ElfTypes>
ElfFileImpl<ElfTypes>* ElfFileImpl<ElfTypes>::Open(File* file,
                                                   int prot,
                                                   int flags,
                                                   bool low_4gb,
                                                   std::string* error_msg) {
  std::unique_ptr<ElfFileImpl<ElfTypes>> elf_file(
      new ElfFileImpl<ElfTypes>(file, (prot & PROT_WRITE) != 0, /* program_header_only= */ false));
  if (!elf_file->Setup(file, prot, flags, low_4gb, error_msg)) {
    return nullptr;
  }
  return elf_file.release();
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::Setup(File* file,
                                  int prot,
                                  int flags,
                                  bool low_4gb,
                                  std::string* error_msg) {
  int64_t temp_file_length = file->GetLength();
  if (temp_file_length < 0) {
    errno = -temp_file_length;
    *error_msg = StringPrintf("Failed to get length of file: '%s' fd=%d: %s",
                              file->GetPath().c_str(), file->Fd(), strerror(errno));
    return false;
  }
  size_t file_length = static_cast<size_t>(temp_file_length);
  if (file_length < sizeof(Elf_Ehdr)) {
    *error_msg = StringPrintf("File size of %zd bytes not large enough to contain ELF header of "
                              "%zd bytes: '%s'", file_length, sizeof(Elf_Ehdr),
                              file->GetPath().c_str());
    return false;
  }

  if (program_header_only_) {
    // first just map ELF header to get program header size information
    size_t elf_header_size = sizeof(Elf_Ehdr);
    if (!SetMap(file,
                MemMap::MapFile(elf_header_size,
                                prot,
                                flags,
                                file->Fd(),
                                0,
                                low_4gb,
                                file->GetPath().c_str(),
                                error_msg),
                error_msg)) {
      return false;
    }
    // then remap to cover program header
    size_t program_header_size = header_->e_phoff + (header_->e_phentsize * header_->e_phnum);
    if (file_length < program_header_size) {
      *error_msg = StringPrintf("File size of %zd bytes not large enough to contain ELF program "
                                "header of %zd bytes: '%s'", file_length,
                                sizeof(Elf_Ehdr), file->GetPath().c_str());
      return false;
    }
    if (!SetMap(file,
                MemMap::MapFile(program_header_size,
                                prot,
                                flags,
                                file->Fd(),
                                0,
                                low_4gb,
                                file->GetPath().c_str(),
                                error_msg),
                error_msg)) {
      *error_msg = StringPrintf("Failed to map ELF program headers: %s", error_msg->c_str());
      return false;
    }
  } else {
    // otherwise map entire file
    if (!SetMap(file,
                MemMap::MapFile(file->GetLength(),
                                prot,
                                flags,
                                file->Fd(),
                                0,
                                low_4gb,
                                file->GetPath().c_str(),
                                error_msg),
                error_msg)) {
      *error_msg = StringPrintf("Failed to map ELF file: %s", error_msg->c_str());
      return false;
    }
  }

  if (program_header_only_) {
    program_headers_start_ = Begin() + GetHeader().e_phoff;
  } else {
    if (!CheckAndSet(GetHeader().e_phoff, "program headers", &program_headers_start_, error_msg)) {
      return false;
    }

    // Setup section headers.
    if (!CheckAndSet(GetHeader().e_shoff, "section headers", &section_headers_start_, error_msg)) {
      return false;
    }

    // Find shstrtab.
    Elf_Shdr* shstrtab_section_header = GetSectionNameStringSection();
    if (shstrtab_section_header == nullptr) {
      *error_msg = StringPrintf("Failed to find shstrtab section header in ELF file: '%s'",
                                file->GetPath().c_str());
      return false;
    }

    // Find .dynamic section info from program header
    dynamic_program_header_ = FindProgamHeaderByType(PT_DYNAMIC);
    if (dynamic_program_header_ == nullptr) {
      *error_msg = StringPrintf("Failed to find PT_DYNAMIC program header in ELF file: '%s'",
                                file->GetPath().c_str());
      return false;
    }

    if (!CheckAndSet(GetDynamicProgramHeader().p_offset, "dynamic section",
                     reinterpret_cast<uint8_t**>(&dynamic_section_start_), error_msg)) {
      return false;
    }

    // Find other sections from section headers
    for (Elf_Word i = 0; i < GetSectionHeaderNum(); i++) {
      Elf_Shdr* section_header = GetSectionHeader(i);
      if (section_header == nullptr) {
        *error_msg = StringPrintf("Failed to find section header for section %d in ELF file: '%s'",
                                  i, file->GetPath().c_str());
        return false;
      }
      switch (section_header->sh_type) {
        case SHT_SYMTAB: {
          if (!CheckAndSet(section_header->sh_offset, "symtab",
                           reinterpret_cast<uint8_t**>(&symtab_section_start_), error_msg)) {
            return false;
          }
          break;
        }
        case SHT_DYNSYM: {
          if (!CheckAndSet(section_header->sh_offset, "dynsym",
                           reinterpret_cast<uint8_t**>(&dynsym_section_start_), error_msg)) {
            return false;
          }
          break;
        }
        case SHT_STRTAB: {
          // TODO: base these off of sh_link from .symtab and .dynsym above
          if ((section_header->sh_flags & SHF_ALLOC) != 0) {
            // Check that this is named ".dynstr" and ignore otherwise.
            const char* header_name = GetString(*shstrtab_section_header, section_header->sh_name);
            if (strncmp(".dynstr", header_name, 8) == 0) {
              if (!CheckAndSet(section_header->sh_offset, "dynstr",
                               reinterpret_cast<uint8_t**>(&dynstr_section_start_), error_msg)) {
                return false;
              }
            }
          } else {
            // Check that this is named ".strtab" and ignore otherwise.
            const char* header_name = GetString(*shstrtab_section_header, section_header->sh_name);
            if (strncmp(".strtab", header_name, 8) == 0) {
              if (!CheckAndSet(section_header->sh_offset, "strtab",
                               reinterpret_cast<uint8_t**>(&strtab_section_start_), error_msg)) {
                return false;
              }
            }
          }
          break;
        }
        case SHT_DYNAMIC: {
          if (reinterpret_cast<uint8_t*>(dynamic_section_start_) !=
              Begin() + section_header->sh_offset) {
            LOG(WARNING) << "Failed to find matching SHT_DYNAMIC for PT_DYNAMIC in "
                         << file->GetPath() << ": " << std::hex
                         << reinterpret_cast<void*>(dynamic_section_start_)
                         << " != " << reinterpret_cast<void*>(Begin() + section_header->sh_offset);
            return false;
          }
          break;
        }
        case SHT_HASH: {
          if (!CheckAndSet(section_header->sh_offset, "hash section",
                           reinterpret_cast<uint8_t**>(&hash_section_start_), error_msg)) {
            return false;
          }
          break;
        }
      }
    }

    // Check for the existence of some sections.
    if (!CheckSectionsExist(file, error_msg)) {
      return false;
    }
  }

  return true;
}

template <typename ElfTypes>
ElfFileImpl<ElfTypes>::~ElfFileImpl() {
  delete symtab_symbol_table_;
  delete dynsym_symbol_table_;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::CheckAndSet(Elf32_Off offset, const char* label,
                                        uint8_t** target, std::string* error_msg) {
  if (Begin() + offset >= End()) {
    *error_msg = StringPrintf("Offset %d is out of range for %s in ELF file: '%s'", offset, label,
                              file_path_.c_str());
    return false;
  }
  *target = Begin() + offset;
  return true;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::CheckSectionsLinked(const uint8_t* source,
                                                const uint8_t* target) const {
  // Only works in whole-program mode, as we need to iterate over the sections.
  // Note that we normally can't search by type, as duplicates are allowed for most section types.
  if (program_header_only_) {
    return true;
  }

  Elf_Shdr* source_section = nullptr;
  Elf_Word target_index = 0;
  bool target_found = false;
  for (Elf_Word i = 0; i < GetSectionHeaderNum(); i++) {
    Elf_Shdr* section_header = GetSectionHeader(i);

    if (Begin() + section_header->sh_offset == source) {
      // Found the source.
      source_section = section_header;
      if (target_index) {
        break;
      }
    } else if (Begin() + section_header->sh_offset == target) {
      target_index = i;
      target_found = true;
      if (source_section != nullptr) {
        break;
      }
    }
  }

  return target_found && source_section != nullptr && source_section->sh_link == target_index;
}

template <typename ElfTypes>
  bool ElfFileImpl<ElfTypes>::CheckSectionsExist(File* file, std::string* error_msg) const {
  if (!program_header_only_) {
    // If in full mode, need section headers.
    if (section_headers_start_ == nullptr) {
      *error_msg = StringPrintf("No section headers in ELF file: '%s'", file->GetPath().c_str());
      return false;
    }
  }

  // This is redundant, but defensive.
  if (dynamic_program_header_ == nullptr) {
    *error_msg = StringPrintf("Failed to find PT_DYNAMIC program header in ELF file: '%s'",
                              file->GetPath().c_str());
    return false;
  }

  // Need a dynamic section. This is redundant, but defensive.
  if (dynamic_section_start_ == nullptr) {
    *error_msg = StringPrintf("Failed to find dynamic section in ELF file: '%s'",
                              file->GetPath().c_str());
    return false;
  }

  // Symtab validation. These is not really a hard failure, as we are currently not using the
  // symtab internally, but it's nice to be defensive.
  if (symtab_section_start_ != nullptr) {
    // When there's a symtab, there should be a strtab.
    if (strtab_section_start_ == nullptr) {
      *error_msg = StringPrintf("No strtab for symtab in ELF file: '%s'", file->GetPath().c_str());
      return false;
    }

    // The symtab should link to the strtab.
    if (!CheckSectionsLinked(reinterpret_cast<const uint8_t*>(symtab_section_start_),
                             reinterpret_cast<const uint8_t*>(strtab_section_start_))) {
      *error_msg = StringPrintf("Symtab is not linked to the strtab in ELF file: '%s'",
                                file->GetPath().c_str());
      return false;
    }
  }

  // We always need a dynstr & dynsym.
  if (dynstr_section_start_ == nullptr) {
    *error_msg = StringPrintf("No dynstr in ELF file: '%s'", file->GetPath().c_str());
    return false;
  }
  if (dynsym_section_start_ == nullptr) {
    *error_msg = StringPrintf("No dynsym in ELF file: '%s'", file->GetPath().c_str());
    return false;
  }

  // Need a hash section for dynamic symbol lookup.
  if (hash_section_start_ == nullptr) {
    *error_msg = StringPrintf("Failed to find hash section in ELF file: '%s'",
                              file->GetPath().c_str());
    return false;
  }

  // And the hash section should be linking to the dynsym.
  if (!CheckSectionsLinked(reinterpret_cast<const uint8_t*>(hash_section_start_),
                           reinterpret_cast<const uint8_t*>(dynsym_section_start_))) {
    *error_msg = StringPrintf("Hash section is not linked to the dynstr in ELF file: '%s'",
                              file->GetPath().c_str());
    return false;
  }

  // We'd also like to confirm a shstrtab in program_header_only_ mode (else Open() does this for
  // us). This is usually the last in an oat file, and a good indicator of whether writing was
  // successful (or the process crashed and left garbage).
  if (program_header_only_) {
    // It might not be mapped, but we can compare against the file size.
    int64_t offset = static_cast<int64_t>(GetHeader().e_shoff +
                                          (GetHeader().e_shstrndx * GetHeader().e_shentsize));
    if (offset >= file->GetLength()) {
      *error_msg = StringPrintf("Shstrtab is not in the mapped ELF file: '%s'",
                                file->GetPath().c_str());
      return false;
    }
  }

  return true;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::SetMap(File* file, MemMap&& map, std::string* error_msg) {
  if (!map.IsValid()) {
    // MemMap::Open should have already set an error.
    DCHECK(!error_msg->empty());
    return false;
  }
  map_ = std::move(map);
  CHECK(map_.IsValid()) << file->GetPath();
  CHECK(map_.Begin() != nullptr) << file->GetPath();

  header_ = reinterpret_cast<Elf_Ehdr*>(map_.Begin());
  if ((ELFMAG0 != header_->e_ident[EI_MAG0])
      || (ELFMAG1 != header_->e_ident[EI_MAG1])
      || (ELFMAG2 != header_->e_ident[EI_MAG2])
      || (ELFMAG3 != header_->e_ident[EI_MAG3])) {
    *error_msg = StringPrintf("Failed to find ELF magic value %d %d %d %d in %s, found %d %d %d %d",
                              ELFMAG0, ELFMAG1, ELFMAG2, ELFMAG3,
                              file->GetPath().c_str(),
                              header_->e_ident[EI_MAG0],
                              header_->e_ident[EI_MAG1],
                              header_->e_ident[EI_MAG2],
                              header_->e_ident[EI_MAG3]);
    return false;
  }
  uint8_t elf_class = (sizeof(Elf_Addr) == sizeof(Elf64_Addr)) ? ELFCLASS64 : ELFCLASS32;
  if (elf_class != header_->e_ident[EI_CLASS]) {
    *error_msg = StringPrintf("Failed to find expected EI_CLASS value %d in %s, found %d",
                              elf_class,
                              file->GetPath().c_str(),
                              header_->e_ident[EI_CLASS]);
    return false;
  }
  if (ELFDATA2LSB != header_->e_ident[EI_DATA]) {
    *error_msg = StringPrintf("Failed to find expected EI_DATA value %d in %s, found %d",
                              ELFDATA2LSB,
                              file->GetPath().c_str(),
                              header_->e_ident[EI_CLASS]);
    return false;
  }
  if (EV_CURRENT != header_->e_ident[EI_VERSION]) {
    *error_msg = StringPrintf("Failed to find expected EI_VERSION value %d in %s, found %d",
                              EV_CURRENT,
                              file->GetPath().c_str(),
                              header_->e_ident[EI_CLASS]);
    return false;
  }
  if (ET_DYN != header_->e_type) {
    *error_msg = StringPrintf("Failed to find expected e_type value %d in %s, found %d",
                              ET_DYN,
                              file->GetPath().c_str(),
                              header_->e_type);
    return false;
  }
  if (EV_CURRENT != header_->e_version) {
    *error_msg = StringPrintf("Failed to find expected e_version value %d in %s, found %d",
                              EV_CURRENT,
                              file->GetPath().c_str(),
                              header_->e_version);
    return false;
  }
  if (0 != header_->e_entry) {
    *error_msg = StringPrintf("Failed to find expected e_entry value %d in %s, found %d",
                              0,
                              file->GetPath().c_str(),
                              static_cast<int32_t>(header_->e_entry));
    return false;
  }
  if (0 == header_->e_phoff) {
    *error_msg = StringPrintf("Failed to find non-zero e_phoff value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_shoff) {
    *error_msg = StringPrintf("Failed to find non-zero e_shoff value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_ehsize) {
    *error_msg = StringPrintf("Failed to find non-zero e_ehsize value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_phentsize) {
    *error_msg = StringPrintf("Failed to find non-zero e_phentsize value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_phnum) {
    *error_msg = StringPrintf("Failed to find non-zero e_phnum value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_shentsize) {
    *error_msg = StringPrintf("Failed to find non-zero e_shentsize value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_shnum) {
    *error_msg = StringPrintf("Failed to find non-zero e_shnum value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (0 == header_->e_shstrndx) {
    *error_msg = StringPrintf("Failed to find non-zero e_shstrndx value in %s",
                              file->GetPath().c_str());
    return false;
  }
  if (header_->e_shstrndx >= header_->e_shnum) {
    *error_msg = StringPrintf("Failed to find e_shnum value %d less than %d in %s",
                              header_->e_shstrndx,
                              header_->e_shnum,
                              file->GetPath().c_str());
    return false;
  }

  if (!program_header_only_) {
    if (header_->e_phoff >= Size()) {
      *error_msg = StringPrintf("Failed to find e_phoff value %" PRIu64 " less than %zd in %s",
                                static_cast<uint64_t>(header_->e_phoff),
                                Size(),
                                file->GetPath().c_str());
      return false;
    }
    if (header_->e_shoff >= Size()) {
      *error_msg = StringPrintf("Failed to find e_shoff value %" PRIu64 " less than %zd in %s",
                                static_cast<uint64_t>(header_->e_shoff),
                                Size(),
                                file->GetPath().c_str());
      return false;
    }
  }
  return true;
}

template <typename ElfTypes>
typename ElfTypes::Ehdr& ElfFileImpl<ElfTypes>::GetHeader() const {
  CHECK(header_ != nullptr);  // Header has been checked in SetMap
  return *header_;
}

template <typename ElfTypes>
uint8_t* ElfFileImpl<ElfTypes>::GetProgramHeadersStart() const {
  CHECK(program_headers_start_ != nullptr);  // Header has been set in Setup
  return program_headers_start_;
}

template <typename ElfTypes>
uint8_t* ElfFileImpl<ElfTypes>::GetSectionHeadersStart() const {
  CHECK(!program_header_only_);              // Only used in "full" mode.
  CHECK(section_headers_start_ != nullptr);  // Is checked in CheckSectionsExist
  return section_headers_start_;
}

template <typename ElfTypes>
typename ElfTypes::Phdr& ElfFileImpl<ElfTypes>::GetDynamicProgramHeader() const {
  CHECK(dynamic_program_header_ != nullptr);  // Is checked in CheckSectionsExist
  return *dynamic_program_header_;
}

template <typename ElfTypes>
typename ElfTypes::Dyn* ElfFileImpl<ElfTypes>::GetDynamicSectionStart() const {
  CHECK(dynamic_section_start_ != nullptr);  // Is checked in CheckSectionsExist
  return dynamic_section_start_;
}

template <typename ElfTypes>
typename ElfTypes::Sym* ElfFileImpl<ElfTypes>::GetSymbolSectionStart(
    Elf_Word section_type) const {
  CHECK(IsSymbolSectionType(section_type)) << file_path_ << " " << section_type;
  switch (section_type) {
    case SHT_SYMTAB: {
      return symtab_section_start_;
      break;
    }
    case SHT_DYNSYM: {
      return dynsym_section_start_;
      break;
    }
    default: {
      LOG(FATAL) << section_type;
      return nullptr;
    }
  }
}

template <typename ElfTypes>
const char* ElfFileImpl<ElfTypes>::GetStringSectionStart(
    Elf_Word section_type) const {
  CHECK(IsSymbolSectionType(section_type)) << file_path_ << " " << section_type;
  switch (section_type) {
    case SHT_SYMTAB: {
      return strtab_section_start_;
    }
    case SHT_DYNSYM: {
      return dynstr_section_start_;
    }
    default: {
      LOG(FATAL) << section_type;
      return nullptr;
    }
  }
}

template <typename ElfTypes>
const char* ElfFileImpl<ElfTypes>::GetString(Elf_Word section_type,
                                             Elf_Word i) const {
  CHECK(IsSymbolSectionType(section_type)) << file_path_ << " " << section_type;
  if (i == 0) {
    return nullptr;
  }
  const char* string_section_start = GetStringSectionStart(section_type);
  if (string_section_start == nullptr) {
    return nullptr;
  }
  return string_section_start + i;
}

// WARNING: The following methods do not check for an error condition (non-existent hash section).
//          It is the caller's job to do this.

template <typename ElfTypes>
typename ElfTypes::Word* ElfFileImpl<ElfTypes>::GetHashSectionStart() const {
  return hash_section_start_;
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetHashBucketNum() const {
  return GetHashSectionStart()[0];
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetHashChainNum() const {
  return GetHashSectionStart()[1];
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetHashBucket(size_t i, bool* ok) const {
  if (i >= GetHashBucketNum()) {
    *ok = false;
    return 0;
  }
  *ok = true;
  // 0 is nbucket, 1 is nchain
  return GetHashSectionStart()[2 + i];
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetHashChain(size_t i, bool* ok) const {
  if (i >= GetHashChainNum()) {
    *ok = false;
    return 0;
  }
  *ok = true;
  // 0 is nbucket, 1 is nchain, & chains are after buckets
  return GetHashSectionStart()[2 + GetHashBucketNum() + i];
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetProgramHeaderNum() const {
  return GetHeader().e_phnum;
}

template <typename ElfTypes>
typename ElfTypes::Phdr* ElfFileImpl<ElfTypes>::GetProgramHeader(Elf_Word i) const {
  CHECK_LT(i, GetProgramHeaderNum()) << file_path_;  // Validity check for caller.
  uint8_t* program_header = GetProgramHeadersStart() + (i * GetHeader().e_phentsize);
  CHECK_LT(program_header, End());
  return reinterpret_cast<Elf_Phdr*>(program_header);
}

template <typename ElfTypes>
typename ElfTypes::Phdr* ElfFileImpl<ElfTypes>::FindProgamHeaderByType(Elf_Word type) const {
  for (Elf_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf_Phdr* program_header = GetProgramHeader(i);
    if (program_header->p_type == type) {
      return program_header;
    }
  }
  return nullptr;
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetSectionHeaderNum() const {
  return GetHeader().e_shnum;
}

template <typename ElfTypes>
typename ElfTypes::Shdr* ElfFileImpl<ElfTypes>::GetSectionHeader(Elf_Word i) const {
  // Can only access arbitrary sections when we have the whole file, not just program header.
  // Even if we Load(), it doesn't bring in all the sections.
  CHECK(!program_header_only_) << file_path_;
  if (i >= GetSectionHeaderNum()) {
    return nullptr;  // Failure condition.
  }
  uint8_t* section_header = GetSectionHeadersStart() + (i * GetHeader().e_shentsize);
  if (section_header >= End()) {
    return nullptr;  // Failure condition.
  }
  return reinterpret_cast<Elf_Shdr*>(section_header);
}

template <typename ElfTypes>
typename ElfTypes::Shdr* ElfFileImpl<ElfTypes>::FindSectionByType(Elf_Word type) const {
  // Can only access arbitrary sections when we have the whole file, not just program header.
  // We could change this to switch on known types if they were detected during loading.
  CHECK(!program_header_only_) << file_path_;
  for (Elf_Word i = 0; i < GetSectionHeaderNum(); i++) {
    Elf_Shdr* section_header = GetSectionHeader(i);
    if (section_header->sh_type == type) {
      return section_header;
    }
  }
  return nullptr;
}

// from bionic
static unsigned elfhash(const char *_name) {
  const unsigned char *name = (const unsigned char *) _name;
  unsigned h = 0, g;

  while (*name) {
    h = (h << 4) + *name++;
    g = h & 0xf0000000;
    h ^= g;
    h ^= g >> 24;
  }
  return h;
}

template <typename ElfTypes>
typename ElfTypes::Shdr* ElfFileImpl<ElfTypes>::GetSectionNameStringSection() const {
  return GetSectionHeader(GetHeader().e_shstrndx);
}

template <typename ElfTypes>
const uint8_t* ElfFileImpl<ElfTypes>::FindDynamicSymbolAddress(
    const std::string& symbol_name) const {
  // Check that we have a hash section.
  if (GetHashSectionStart() == nullptr) {
    return nullptr;  // Failure condition.
  }
  const Elf_Sym* sym = FindDynamicSymbol(symbol_name);
  if (sym != nullptr) {
    // TODO: we need to change this to calculate base_address_ in ::Open,
    // otherwise it will be wrongly 0 if ::Load has not yet been called.
    return base_address_ + sym->st_value;
  } else {
    return nullptr;
  }
}

// WARNING: Only called from FindDynamicSymbolAddress. Elides check for hash section.
template <typename ElfTypes>
const typename ElfTypes::Sym* ElfFileImpl<ElfTypes>::FindDynamicSymbol(
    const std::string& symbol_name) const {
  if (GetHashBucketNum() == 0) {
    // No dynamic symbols at all.
    return nullptr;
  }
  Elf_Word hash = elfhash(symbol_name.c_str());
  Elf_Word bucket_index = hash % GetHashBucketNum();
  bool ok;
  Elf_Word symbol_and_chain_index = GetHashBucket(bucket_index, &ok);
  if (!ok) {
    return nullptr;
  }
  while (symbol_and_chain_index != 0 /* STN_UNDEF */) {
    Elf_Sym* symbol = GetSymbol(SHT_DYNSYM, symbol_and_chain_index);
    if (symbol == nullptr) {
      return nullptr;  // Failure condition.
    }
    const char* name = GetString(SHT_DYNSYM, symbol->st_name);
    if (symbol_name == name) {
      return symbol;
    }
    symbol_and_chain_index = GetHashChain(symbol_and_chain_index, &ok);
    if (!ok) {
      return nullptr;
    }
  }
  return nullptr;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::IsSymbolSectionType(Elf_Word section_type) {
  return ((section_type == SHT_SYMTAB) || (section_type == SHT_DYNSYM));
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetSymbolNum(Elf_Shdr& section_header) const {
  CHECK(IsSymbolSectionType(section_header.sh_type))
      << file_path_ << " " << section_header.sh_type;
  CHECK_NE(0U, section_header.sh_entsize) << file_path_;
  return section_header.sh_size / section_header.sh_entsize;
}

template <typename ElfTypes>
typename ElfTypes::Sym* ElfFileImpl<ElfTypes>::GetSymbol(Elf_Word section_type, Elf_Word i) const {
  Elf_Sym* sym_start = GetSymbolSectionStart(section_type);
  if (sym_start == nullptr) {
    return nullptr;
  }
  return sym_start + i;
}

template <typename ElfTypes>
typename ElfFileImpl<ElfTypes>::SymbolTable**
ElfFileImpl<ElfTypes>::GetSymbolTable(Elf_Word section_type) {
  CHECK(IsSymbolSectionType(section_type)) << file_path_ << " " << section_type;
  switch (section_type) {
    case SHT_SYMTAB: {
      return &symtab_symbol_table_;
    }
    case SHT_DYNSYM: {
      return &dynsym_symbol_table_;
    }
    default: {
      LOG(FATAL) << section_type;
      return nullptr;
    }
  }
}

template <typename ElfTypes>
typename ElfTypes::Sym* ElfFileImpl<ElfTypes>::FindSymbolByName(
    Elf_Word section_type, const std::string& symbol_name, bool build_map) {
  CHECK(!program_header_only_) << file_path_;
  CHECK(IsSymbolSectionType(section_type)) << file_path_ << " " << section_type;

  SymbolTable** symbol_table = GetSymbolTable(section_type);
  if (*symbol_table != nullptr || build_map) {
    if (*symbol_table == nullptr) {
      DCHECK(build_map);
      *symbol_table = new SymbolTable;
      Elf_Shdr* symbol_section = FindSectionByType(section_type);
      if (symbol_section == nullptr) {
        return nullptr;  // Failure condition.
      }
      Elf_Shdr* string_section = GetSectionHeader(symbol_section->sh_link);
      if (string_section == nullptr) {
        return nullptr;  // Failure condition.
      }
      for (uint32_t i = 0; i < GetSymbolNum(*symbol_section); i++) {
        Elf_Sym* symbol = GetSymbol(section_type, i);
        if (symbol == nullptr) {
          return nullptr;  // Failure condition.
        }
        unsigned char type = (sizeof(Elf_Addr) == sizeof(Elf64_Addr))
                             ? ELF64_ST_TYPE(symbol->st_info)
                             : ELF32_ST_TYPE(symbol->st_info);
        if (type == STT_NOTYPE) {
          continue;
        }
        const char* name = GetString(*string_section, symbol->st_name);
        if (name == nullptr) {
          continue;
        }
        std::pair<typename SymbolTable::iterator, bool> result =
            (*symbol_table)->insert(std::make_pair(name, symbol));
        if (!result.second) {
          // If a duplicate, make sure it has the same logical value. Seen on x86.
          if ((symbol->st_value != result.first->second->st_value) ||
              (symbol->st_size != result.first->second->st_size) ||
              (symbol->st_info != result.first->second->st_info) ||
              (symbol->st_other != result.first->second->st_other) ||
              (symbol->st_shndx != result.first->second->st_shndx)) {
            return nullptr;  // Failure condition.
          }
        }
      }
    }
    CHECK(*symbol_table != nullptr);
    typename SymbolTable::const_iterator it = (*symbol_table)->find(symbol_name);
    if (it == (*symbol_table)->end()) {
      return nullptr;
    }
    return it->second;
  }

  // Fall back to linear search
  Elf_Shdr* symbol_section = FindSectionByType(section_type);
  if (symbol_section == nullptr) {
    return nullptr;
  }
  Elf_Shdr* string_section = GetSectionHeader(symbol_section->sh_link);
  if (string_section == nullptr) {
    return nullptr;
  }
  for (uint32_t i = 0; i < GetSymbolNum(*symbol_section); i++) {
    Elf_Sym* symbol = GetSymbol(section_type, i);
    if (symbol == nullptr) {
      return nullptr;  // Failure condition.
    }
    const char* name = GetString(*string_section, symbol->st_name);
    if (name == nullptr) {
      continue;
    }
    if (symbol_name == name) {
      return symbol;
    }
  }
  return nullptr;
}

template <typename ElfTypes>
typename ElfTypes::Addr ElfFileImpl<ElfTypes>::FindSymbolAddress(
    Elf_Word section_type, const std::string& symbol_name, bool build_map) {
  Elf_Sym* symbol = FindSymbolByName(section_type, symbol_name, build_map);
  if (symbol == nullptr) {
    return 0;
  }
  return symbol->st_value;
}

template <typename ElfTypes>
const char* ElfFileImpl<ElfTypes>::GetString(Elf_Shdr& string_section,
                                             Elf_Word i) const {
  CHECK(!program_header_only_) << file_path_;
  // TODO: remove this static_cast from enum when using -std=gnu++0x
  if (static_cast<Elf_Word>(SHT_STRTAB) != string_section.sh_type) {
    return nullptr;  // Failure condition.
  }
  if (i >= string_section.sh_size) {
    return nullptr;
  }
  if (i == 0) {
    return nullptr;
  }
  uint8_t* strings = Begin() + string_section.sh_offset;
  uint8_t* string = strings + i;
  if (string >= End()) {
    return nullptr;
  }
  return reinterpret_cast<const char*>(string);
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetDynamicNum() const {
  return GetDynamicProgramHeader().p_filesz / sizeof(Elf_Dyn);
}

template <typename ElfTypes>
typename ElfTypes::Dyn& ElfFileImpl<ElfTypes>::GetDynamic(Elf_Word i) const {
  CHECK_LT(i, GetDynamicNum()) << file_path_;
  return *(GetDynamicSectionStart() + i);
}

template <typename ElfTypes>
typename ElfTypes::Dyn* ElfFileImpl<ElfTypes>::FindDynamicByType(Elf_Sword type) const {
  for (Elf_Word i = 0; i < GetDynamicNum(); i++) {
    Elf_Dyn* dyn = &GetDynamic(i);
    if (dyn->d_tag == type) {
      return dyn;
    }
  }
  return nullptr;
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::FindDynamicValueByType(Elf_Sword type) const {
  Elf_Dyn* dyn = FindDynamicByType(type);
  if (dyn == nullptr) {
    return 0;
  } else {
    return dyn->d_un.d_val;
  }
}

template <typename ElfTypes>
typename ElfTypes::Rel* ElfFileImpl<ElfTypes>::GetRelSectionStart(Elf_Shdr& section_header) const {
  CHECK(SHT_REL == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  return reinterpret_cast<Elf_Rel*>(Begin() + section_header.sh_offset);
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetRelNum(Elf_Shdr& section_header) const {
  CHECK(SHT_REL == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  CHECK_NE(0U, section_header.sh_entsize) << file_path_;
  return section_header.sh_size / section_header.sh_entsize;
}

template <typename ElfTypes>
typename ElfTypes::Rel& ElfFileImpl<ElfTypes>::GetRel(Elf_Shdr& section_header, Elf_Word i) const {
  CHECK(SHT_REL == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  CHECK_LT(i, GetRelNum(section_header)) << file_path_;
  return *(GetRelSectionStart(section_header) + i);
}

template <typename ElfTypes>
typename ElfTypes::Rela* ElfFileImpl<ElfTypes>::GetRelaSectionStart(Elf_Shdr& section_header) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  return reinterpret_cast<Elf_Rela*>(Begin() + section_header.sh_offset);
}

template <typename ElfTypes>
typename ElfTypes::Word ElfFileImpl<ElfTypes>::GetRelaNum(Elf_Shdr& section_header) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  return section_header.sh_size / section_header.sh_entsize;
}

template <typename ElfTypes>
typename ElfTypes::Rela& ElfFileImpl<ElfTypes>::GetRela(Elf_Shdr& section_header, Elf_Word i) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_path_ << " " << section_header.sh_type;
  CHECK_LT(i, GetRelaNum(section_header)) << file_path_;
  return *(GetRelaSectionStart(section_header) + i);
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::GetLoadedSize(size_t* size, std::string* error_msg) const {
  uint8_t* vaddr_begin;
  return GetLoadedAddressRange(&vaddr_begin, size, error_msg);
}

// Base on bionic phdr_table_get_load_size
template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::GetLoadedAddressRange(/*out*/uint8_t** vaddr_begin,
                                                  /*out*/size_t* vaddr_size,
                                                  /*out*/std::string* error_msg) const {
  Elf_Addr min_vaddr = static_cast<Elf_Addr>(-1);
  Elf_Addr max_vaddr = 0u;
  for (Elf_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf_Phdr* program_header = GetProgramHeader(i);
    if (program_header->p_type != PT_LOAD) {
      continue;
    }
    Elf_Addr begin_vaddr = program_header->p_vaddr;
    if (begin_vaddr < min_vaddr) {
       min_vaddr = begin_vaddr;
    }
    Elf_Addr end_vaddr = program_header->p_vaddr + program_header->p_memsz;
    if (UNLIKELY(begin_vaddr > end_vaddr)) {
      std::ostringstream oss;
      oss << "Program header #" << i << " has overflow in p_vaddr+p_memsz: 0x" << std::hex
          << program_header->p_vaddr << "+0x" << program_header->p_memsz << "=0x" << end_vaddr
          << " in ELF file \"" << file_path_ << "\"";
      *error_msg = oss.str();
      *vaddr_begin = nullptr;
      *vaddr_size = static_cast<size_t>(-1);
      return false;
    }
    if (end_vaddr > max_vaddr) {
      max_vaddr = end_vaddr;
    }
  }
  min_vaddr = RoundDown(min_vaddr, kPageSize);
  max_vaddr = RoundUp(max_vaddr, kPageSize);
  CHECK_LT(min_vaddr, max_vaddr) << file_path_;
  // Check that the range fits into the runtime address space.
  if (UNLIKELY(max_vaddr - 1u > std::numeric_limits<size_t>::max())) {
    std::ostringstream oss;
    oss << "Loaded range is 0x" << std::hex << min_vaddr << "-0x" << max_vaddr
        << " but maximum size_t is 0x" << std::numeric_limits<size_t>::max()
        << " for ELF file \"" << file_path_ << "\"";
    *error_msg = oss.str();
    *vaddr_begin = nullptr;
    *vaddr_size = static_cast<size_t>(-1);
    return false;
  }
  *vaddr_begin = reinterpret_cast<uint8_t*>(min_vaddr);
  *vaddr_size = dchecked_integral_cast<size_t>(max_vaddr - min_vaddr);
  return true;
}

static InstructionSet GetInstructionSetFromELF(uint16_t e_machine,
                                               uint32_t e_flags ATTRIBUTE_UNUSED) {
  switch (e_machine) {
    case EM_ARM:
      return InstructionSet::kArm;
    case EM_AARCH64:
      return InstructionSet::kArm64;
    case EM_386:
      return InstructionSet::kX86;
    case EM_X86_64:
      return InstructionSet::kX86_64;
  }
  return InstructionSet::kNone;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::Load(File* file,
                                 bool executable,
                                 bool low_4gb,
                                 /*inout*/MemMap* reservation,
                                 /*out*/std::string* error_msg) {
  CHECK(program_header_only_) << file->GetPath();

  if (executable) {
    InstructionSet elf_ISA = GetInstructionSetFromELF(GetHeader().e_machine, GetHeader().e_flags);
    if (elf_ISA != kRuntimeISA) {
      std::ostringstream oss;
      oss << "Expected ISA " << kRuntimeISA << " but found " << elf_ISA;
      *error_msg = oss.str();
      return false;
    }
  }

  bool reserved = false;
  for (Elf_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf_Phdr* program_header = GetProgramHeader(i);

    // Record .dynamic header information for later use
    if (program_header->p_type == PT_DYNAMIC) {
      dynamic_program_header_ = program_header;
      continue;
    }

    // Not something to load, move on.
    if (program_header->p_type != PT_LOAD) {
      continue;
    }

    // Found something to load.

    // Before load the actual segments, reserve a contiguous chunk
    // of required size and address for all segments, but with no
    // permissions. We'll then carve that up with the proper
    // permissions as we load the actual segments. If p_vaddr is
    // non-zero, the segments require the specific address specified,
    // which either was specified in the file because we already set
    // base_address_ after the first zero segment).
    int64_t temp_file_length = file->GetLength();
    if (temp_file_length < 0) {
      errno = -temp_file_length;
      *error_msg = StringPrintf("Failed to get length of file: '%s' fd=%d: %s",
                                file->GetPath().c_str(), file->Fd(), strerror(errno));
      return false;
    }
    size_t file_length = static_cast<size_t>(temp_file_length);
    if (!reserved) {
      uint8_t* vaddr_begin;
      size_t vaddr_size;
      if (!GetLoadedAddressRange(&vaddr_begin, &vaddr_size, error_msg)) {
        DCHECK(!error_msg->empty());
        return false;
      }
      std::string reservation_name = "ElfFile reservation for " + file->GetPath();
      MemMap local_reservation = MemMap::MapAnonymous(
          reservation_name.c_str(),
          (reservation != nullptr) ? reservation->Begin() : nullptr,
          vaddr_size,
          PROT_NONE,
          low_4gb,
          /* reuse= */ false,
          reservation,
          error_msg);
      if (!local_reservation.IsValid()) {
        *error_msg = StringPrintf("Failed to allocate %s: %s",
                                  reservation_name.c_str(),
                                  error_msg->c_str());
        return false;
      }
      reserved = true;

      // Base address is the difference of actual mapped location and the vaddr_begin.
      base_address_ = reinterpret_cast<uint8_t*>(
          static_cast<uintptr_t>(local_reservation.Begin() - vaddr_begin));
      // By adding the p_vaddr of a section/symbol to base_address_ we will always get the
      // dynamic memory address of where that object is actually mapped
      //
      // TODO: base_address_ needs to be calculated in ::Open, otherwise
      // FindDynamicSymbolAddress returns the wrong values until Load is called.
      segments_.push_back(std::move(local_reservation));
    }
    // empty segment, nothing to map
    if (program_header->p_memsz == 0) {
      continue;
    }
    uint8_t* p_vaddr = base_address_ + program_header->p_vaddr;
    int prot = 0;
    if (executable && ((program_header->p_flags & PF_X) != 0)) {
      prot |= PROT_EXEC;
    }
    if ((program_header->p_flags & PF_W) != 0) {
      prot |= PROT_WRITE;
    }
    if ((program_header->p_flags & PF_R) != 0) {
      prot |= PROT_READ;
    }
    int flags = 0;
    if (writable_) {
      prot |= PROT_WRITE;
      flags |= MAP_SHARED;
    } else {
      flags |= MAP_PRIVATE;
    }
    if (program_header->p_filesz > program_header->p_memsz) {
      *error_msg = StringPrintf("Invalid p_filesz > p_memsz (%" PRIu64 " > %" PRIu64 "): %s",
                                static_cast<uint64_t>(program_header->p_filesz),
                                static_cast<uint64_t>(program_header->p_memsz),
                                file->GetPath().c_str());
      return false;
    }
    if (program_header->p_filesz < program_header->p_memsz &&
        !IsAligned<kPageSize>(program_header->p_filesz)) {
      *error_msg = StringPrintf("Unsupported unaligned p_filesz < p_memsz (%" PRIu64
                                " < %" PRIu64 "): %s",
                                static_cast<uint64_t>(program_header->p_filesz),
                                static_cast<uint64_t>(program_header->p_memsz),
                                file->GetPath().c_str());
      return false;
    }
    if (file_length < (program_header->p_offset + program_header->p_filesz)) {
      *error_msg = StringPrintf("File size of %zd bytes not large enough to contain ELF segment "
                                "%d of %" PRIu64 " bytes: '%s'", file_length, i,
                                static_cast<uint64_t>(program_header->p_offset + program_header->p_filesz),
                                file->GetPath().c_str());
      return false;
    }
    if (program_header->p_filesz != 0u) {
      MemMap segment =
          MemMap::MapFileAtAddress(p_vaddr,
                                   program_header->p_filesz,
                                   prot,
                                   flags,
                                   file->Fd(),
                                   program_header->p_offset,
                                   /* low_4gb= */ false,
                                   file->GetPath().c_str(),
                                   /* reuse= */ true,  // implies MAP_FIXED
                                   /* reservation= */ nullptr,
                                   error_msg);
      if (!segment.IsValid()) {
        *error_msg = StringPrintf("Failed to map ELF file segment %d from %s: %s",
                                  i, file->GetPath().c_str(), error_msg->c_str());
        return false;
      }
      if (segment.Begin() != p_vaddr) {
        *error_msg = StringPrintf("Failed to map ELF file segment %d from %s at expected address %p, "
                                  "instead mapped to %p",
                                  i, file->GetPath().c_str(), p_vaddr, segment.Begin());
        return false;
      }
      segments_.push_back(std::move(segment));
    }
    if (program_header->p_filesz < program_header->p_memsz) {
      std::string name = StringPrintf("Zero-initialized segment %" PRIu64 " of ELF file %s",
                                      static_cast<uint64_t>(i), file->GetPath().c_str());
      MemMap segment = MemMap::MapAnonymous(name.c_str(),
                                            p_vaddr + program_header->p_filesz,
                                            program_header->p_memsz - program_header->p_filesz,
                                            prot,
                                            /* low_4gb= */ false,
                                            /* reuse= */ true,
                                            /* reservation= */ nullptr,
                                            error_msg);
      if (!segment.IsValid()) {
        *error_msg = StringPrintf("Failed to map zero-initialized ELF file segment %d from %s: %s",
                                  i, file->GetPath().c_str(), error_msg->c_str());
        return false;
      }
      if (segment.Begin() != p_vaddr) {
        *error_msg = StringPrintf("Failed to map zero-initialized ELF file segment %d from %s "
                                  "at expected address %p, instead mapped to %p",
                                  i, file->GetPath().c_str(), p_vaddr, segment.Begin());
        return false;
      }
      segments_.push_back(std::move(segment));
    }
  }

  // Now that we are done loading, .dynamic should be in memory to find .dynstr, .dynsym, .hash
  uint8_t* dsptr = base_address_ + GetDynamicProgramHeader().p_vaddr;
  if ((dsptr < Begin() || dsptr >= End()) && !ValidPointer(dsptr)) {
    *error_msg = StringPrintf("dynamic section address invalid in ELF file %s",
                              file->GetPath().c_str());
    return false;
  }
  dynamic_section_start_ = reinterpret_cast<Elf_Dyn*>(dsptr);

  for (Elf_Word i = 0; i < GetDynamicNum(); i++) {
    Elf_Dyn& elf_dyn = GetDynamic(i);
    uint8_t* d_ptr = base_address_ + elf_dyn.d_un.d_ptr;
    switch (elf_dyn.d_tag) {
      case DT_HASH: {
        if (!ValidPointer(d_ptr)) {
          *error_msg = StringPrintf("DT_HASH value %p does not refer to a loaded ELF segment of %s",
                                    d_ptr, file->GetPath().c_str());
          return false;
        }
        hash_section_start_ = reinterpret_cast<Elf_Word*>(d_ptr);
        break;
      }
      case DT_STRTAB: {
        if (!ValidPointer(d_ptr)) {
          *error_msg = StringPrintf("DT_HASH value %p does not refer to a loaded ELF segment of %s",
                                    d_ptr, file->GetPath().c_str());
          return false;
        }
        dynstr_section_start_ = reinterpret_cast<char*>(d_ptr);
        break;
      }
      case DT_SYMTAB: {
        if (!ValidPointer(d_ptr)) {
          *error_msg = StringPrintf("DT_HASH value %p does not refer to a loaded ELF segment of %s",
                                    d_ptr, file->GetPath().c_str());
          return false;
        }
        dynsym_section_start_ = reinterpret_cast<Elf_Sym*>(d_ptr);
        break;
      }
      case DT_NULL: {
        if (GetDynamicNum() != i+1) {
          *error_msg = StringPrintf("DT_NULL found after %d .dynamic entries, "
                                    "expected %d as implied by size of PT_DYNAMIC segment in %s",
                                    i + 1, GetDynamicNum(), file->GetPath().c_str());
          return false;
        }
        break;
      }
    }
  }

  // Check for the existence of some sections.
  if (!CheckSectionsExist(file, error_msg)) {
    return false;
  }

  return true;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::ValidPointer(const uint8_t* start) const {
  for (const MemMap& segment : segments_) {
    if (segment.Begin() <= start && start < segment.End()) {
      return true;
    }
  }
  return false;
}


template <typename ElfTypes>
typename ElfTypes::Shdr* ElfFileImpl<ElfTypes>::FindSectionByName(
    const std::string& name) const {
  CHECK(!program_header_only_);
  Elf_Shdr* shstrtab_sec = GetSectionNameStringSection();
  if (shstrtab_sec == nullptr) {
    return nullptr;
  }
  for (uint32_t i = 0; i < GetSectionHeaderNum(); i++) {
    Elf_Shdr* shdr = GetSectionHeader(i);
    if (shdr == nullptr) {
      return nullptr;
    }
    const char* sec_name = GetString(*shstrtab_sec, shdr->sh_name);
    if (sec_name == nullptr) {
      continue;
    }
    if (name == sec_name) {
      return shdr;
    }
  }
  return nullptr;
}

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::Strip(File* file, std::string* error_msg) {
  // ELF files produced by MCLinker look roughly like this
  //
  // +------------+
  // | Elf_Ehdr   | contains number of Elf_Shdr and offset to first
  // +------------+
  // | Elf_Phdr   | program headers
  // | Elf_Phdr   |
  // | ...        |
  // | Elf_Phdr   |
  // +------------+
  // | section    | mixture of needed and unneeded sections
  // +------------+
  // | section    |
  // +------------+
  // | ...        |
  // +------------+
  // | section    |
  // +------------+
  // | Elf_Shdr   | section headers
  // | Elf_Shdr   |
  // | ...        | contains offset to section start
  // | Elf_Shdr   |
  // +------------+
  //
  // To strip:
  // - leave the Elf_Ehdr and Elf_Phdr values in place.
  // - walk the sections making a new set of Elf_Shdr section headers for what we want to keep
  // - move the sections are keeping up to fill in gaps of sections we want to strip
  // - write new Elf_Shdr section headers to end of file, updating Elf_Ehdr
  // - truncate rest of file
  //

  std::vector<Elf_Shdr> section_headers;
  std::vector<Elf_Word> section_headers_original_indexes;
  section_headers.reserve(GetSectionHeaderNum());


  Elf_Shdr* string_section = GetSectionNameStringSection();
  CHECK(string_section != nullptr);
  for (Elf_Word i = 0; i < GetSectionHeaderNum(); i++) {
    Elf_Shdr* sh = GetSectionHeader(i);
    CHECK(sh != nullptr);
    const char* name = GetString(*string_section, sh->sh_name);
    if (name == nullptr) {
      CHECK_EQ(0U, i);
      section_headers.push_back(*sh);
      section_headers_original_indexes.push_back(0);
      continue;
    }
    if (android::base::StartsWith(name, ".debug")
        || (strcmp(name, ".strtab") == 0)
        || (strcmp(name, ".symtab") == 0)) {
      continue;
    }
    section_headers.push_back(*sh);
    section_headers_original_indexes.push_back(i);
  }
  CHECK_NE(0U, section_headers.size());
  CHECK_EQ(section_headers.size(), section_headers_original_indexes.size());

  // section 0 is the null section, sections start at offset of first section
  CHECK(GetSectionHeader(1) != nullptr);
  Elf_Off offset = GetSectionHeader(1)->sh_offset;
  for (size_t i = 1; i < section_headers.size(); i++) {
    Elf_Shdr& new_sh = section_headers[i];
    Elf_Shdr* old_sh = GetSectionHeader(section_headers_original_indexes[i]);
    CHECK(old_sh != nullptr);
    CHECK_EQ(new_sh.sh_name, old_sh->sh_name);
    if (old_sh->sh_addralign > 1) {
      offset = RoundUp(offset, old_sh->sh_addralign);
    }
    if (old_sh->sh_offset == offset) {
      // already in place
      offset += old_sh->sh_size;
      continue;
    }
    // shift section earlier
    memmove(Begin() + offset,
            Begin() + old_sh->sh_offset,
            old_sh->sh_size);
    new_sh.sh_offset = offset;
    offset += old_sh->sh_size;
  }

  Elf_Off shoff = offset;
  size_t section_headers_size_in_bytes = section_headers.size() * sizeof(Elf_Shdr);
  memcpy(Begin() + offset, &section_headers[0], section_headers_size_in_bytes);
  offset += section_headers_size_in_bytes;

  GetHeader().e_shnum = section_headers.size();
  GetHeader().e_shoff = shoff;
  int result = ftruncate(file->Fd(), offset);
  if (result != 0) {
    *error_msg = StringPrintf("Failed to truncate while stripping ELF file: '%s': %s",
                              file->GetPath().c_str(), strerror(errno));
    return false;
  }
  return true;
}

// Explicit instantiations
template class ElfFileImpl<ElfTypes32>;
template class ElfFileImpl<ElfTypes64>;

ElfFile::ElfFile(ElfFileImpl32* elf32) : elf32_(elf32), elf64_(nullptr) {
}

ElfFile::ElfFile(ElfFileImpl64* elf64) : elf32_(nullptr), elf64_(elf64) {
}

ElfFile::~ElfFile() {
  // Should never have 32 and 64-bit impls.
  CHECK_NE(elf32_.get() == nullptr, elf64_.get() == nullptr);
}

ElfFile* ElfFile::Open(File* file,
                       bool writable,
                       bool program_header_only,
                       bool low_4gb,
                       /*out*/std::string* error_msg) {
  if (file->GetLength() < EI_NIDENT) {
    *error_msg = StringPrintf("File %s is too short to be a valid ELF file",
                              file->GetPath().c_str());
    return nullptr;
  }
  MemMap map = MemMap::MapFile(EI_NIDENT,
                               PROT_READ,
                               MAP_PRIVATE,
                               file->Fd(),
                               0,
                               low_4gb,
                               file->GetPath().c_str(),
                               error_msg);
  if (!map.IsValid() || map.Size() != EI_NIDENT) {
    return nullptr;
  }
  uint8_t* header = map.Begin();
  if (header[EI_CLASS] == ELFCLASS64) {
    ElfFileImpl64* elf_file_impl = ElfFileImpl64::Open(file,
                                                       writable,
                                                       program_header_only,
                                                       low_4gb,
                                                       error_msg);
    if (elf_file_impl == nullptr) {
      return nullptr;
    }
    return new ElfFile(elf_file_impl);
  } else if (header[EI_CLASS] == ELFCLASS32) {
    ElfFileImpl32* elf_file_impl = ElfFileImpl32::Open(file,
                                                       writable,
                                                       program_header_only,
                                                       low_4gb,
                                                       error_msg);
    if (elf_file_impl == nullptr) {
      return nullptr;
    }
    return new ElfFile(elf_file_impl);
  } else {
    *error_msg = StringPrintf("Failed to find expected EI_CLASS value %d or %d in %s, found %d",
                              ELFCLASS32, ELFCLASS64,
                              file->GetPath().c_str(),
                              header[EI_CLASS]);
    return nullptr;
  }
}

ElfFile* ElfFile::Open(File* file, int mmap_prot, int mmap_flags, /*out*/std::string* error_msg) {
  // low_4gb support not required for this path.
  constexpr bool low_4gb = false;
  if (file->GetLength() < EI_NIDENT) {
    *error_msg = StringPrintf("File %s is too short to be a valid ELF file",
                              file->GetPath().c_str());
    return nullptr;
  }
  MemMap map = MemMap::MapFile(EI_NIDENT,
                               PROT_READ,
                               MAP_PRIVATE,
                               file->Fd(),
                               /* start= */ 0,
                               low_4gb,
                               file->GetPath().c_str(),
                               error_msg);
  if (!map.IsValid() || map.Size() != EI_NIDENT) {
    return nullptr;
  }
  uint8_t* header = map.Begin();
  if (header[EI_CLASS] == ELFCLASS64) {
    ElfFileImpl64* elf_file_impl = ElfFileImpl64::Open(file,
                                                       mmap_prot,
                                                       mmap_flags,
                                                       low_4gb,
                                                       error_msg);
    if (elf_file_impl == nullptr) {
      return nullptr;
    }
    return new ElfFile(elf_file_impl);
  } else if (header[EI_CLASS] == ELFCLASS32) {
    ElfFileImpl32* elf_file_impl = ElfFileImpl32::Open(file,
                                                       mmap_prot,
                                                       mmap_flags,
                                                       low_4gb,
                                                       error_msg);
    if (elf_file_impl == nullptr) {
      return nullptr;
    }
    return new ElfFile(elf_file_impl);
  } else {
    *error_msg = StringPrintf("Failed to find expected EI_CLASS value %d or %d in %s, found %d",
                              ELFCLASS32, ELFCLASS64,
                              file->GetPath().c_str(),
                              header[EI_CLASS]);
    return nullptr;
  }
}

#define DELEGATE_TO_IMPL(func, ...) \
  if (elf64_.get() != nullptr) { \
    return elf64_->func(__VA_ARGS__); \
  } else { \
    DCHECK(elf32_.get() != nullptr); \
    return elf32_->func(__VA_ARGS__); \
  }

bool ElfFile::Load(File* file,
                   bool executable,
                   bool low_4gb,
                   /*inout*/MemMap* reservation,
                   /*out*/std::string* error_msg) {
  DELEGATE_TO_IMPL(Load, file, executable, low_4gb, reservation, error_msg);
}

const uint8_t* ElfFile::FindDynamicSymbolAddress(const std::string& symbol_name) const {
  DELEGATE_TO_IMPL(FindDynamicSymbolAddress, symbol_name);
}

size_t ElfFile::Size() const {
  DELEGATE_TO_IMPL(Size);
}

uint8_t* ElfFile::Begin() const {
  DELEGATE_TO_IMPL(Begin);
}

uint8_t* ElfFile::End() const {
  DELEGATE_TO_IMPL(End);
}

const std::string& ElfFile::GetFilePath() const {
  DELEGATE_TO_IMPL(GetFilePath);
}

bool ElfFile::GetSectionOffsetAndSize(const char* section_name, uint64_t* offset,
                                      uint64_t* size) const {
  if (elf32_.get() == nullptr) {
    CHECK(elf64_.get() != nullptr);

    Elf64_Shdr *shdr = elf64_->FindSectionByName(section_name);
    if (shdr == nullptr) {
      return false;
    }
    if (offset != nullptr) {
      *offset = shdr->sh_offset;
    }
    if (size != nullptr) {
      *size = shdr->sh_size;
    }
    return true;
  } else {
    Elf32_Shdr *shdr = elf32_->FindSectionByName(section_name);
    if (shdr == nullptr) {
      return false;
    }
    if (offset != nullptr) {
      *offset = shdr->sh_offset;
    }
    if (size != nullptr) {
      *size = shdr->sh_size;
    }
    return true;
  }
}

bool ElfFile::HasSection(const std::string& name) const {
  if (elf64_.get() != nullptr) {
    return elf64_->FindSectionByName(name) != nullptr;
  } else {
    return elf32_->FindSectionByName(name) != nullptr;
  }
}

uint64_t ElfFile::FindSymbolAddress(unsigned section_type,
                                    const std::string& symbol_name,
                                    bool build_map) {
  DELEGATE_TO_IMPL(FindSymbolAddress, section_type, symbol_name, build_map);
}

bool ElfFile::GetLoadedSize(size_t* size, std::string* error_msg) const {
  DELEGATE_TO_IMPL(GetLoadedSize, size, error_msg);
}

bool ElfFile::Strip(File* file, std::string* error_msg) {
  std::unique_ptr<ElfFile> elf_file(ElfFile::Open(file, true, false, /*low_4gb=*/false, error_msg));
  if (elf_file.get() == nullptr) {
    return false;
  }

  if (elf_file->elf64_.get() != nullptr) {
    return elf_file->elf64_->Strip(file, error_msg);
  } else {
    return elf_file->elf32_->Strip(file, error_msg);
  }
}

}  // namespace art