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 <sys/types.h>
#include <unistd.h>

#include "base/logging.h"
#include "base/stringprintf.h"
#include "base/stl_util.h"
#include "dwarf.h"
#include "leb128.h"
#include "utils.h"
#include "instruction_set.h"

namespace art {

// -------------------------------------------------------------------
// Binary GDB JIT Interface as described in
//   http://sourceware.org/gdb/onlinedocs/gdb/Declarations.html
extern "C" {
  typedef enum {
    JIT_NOACTION = 0,
    JIT_REGISTER_FN,
    JIT_UNREGISTER_FN
  } JITAction;

  struct JITCodeEntry {
    JITCodeEntry* next_;
    JITCodeEntry* prev_;
    const byte *symfile_addr_;
    uint64_t symfile_size_;
  };

  struct JITDescriptor {
    uint32_t version_;
    uint32_t action_flag_;
    JITCodeEntry* relevant_entry_;
    JITCodeEntry* first_entry_;
  };

  // GDB will place breakpoint into this function.
  // To prevent GCC from inlining or removing it we place noinline attribute
  // and inline assembler statement inside.
  void __attribute__((noinline)) __jit_debug_register_code() {
    __asm__("");
  }

  // GDB will inspect contents of this descriptor.
  // Static initialization is necessary to prevent GDB from seeing
  // uninitialized descriptor.
  JITDescriptor __jit_debug_descriptor = { 1, JIT_NOACTION, nullptr, nullptr };
}


static JITCodeEntry* CreateCodeEntry(const byte *symfile_addr,
                                     uintptr_t symfile_size) {
  JITCodeEntry* entry = new JITCodeEntry;
  entry->symfile_addr_ = symfile_addr;
  entry->symfile_size_ = symfile_size;
  entry->prev_ = nullptr;

  // TODO: Do we need a lock here?
  entry->next_ = __jit_debug_descriptor.first_entry_;
  if (entry->next_ != nullptr) {
    entry->next_->prev_ = entry;
  }
  __jit_debug_descriptor.first_entry_ = entry;
  __jit_debug_descriptor.relevant_entry_ = entry;

  __jit_debug_descriptor.action_flag_ = JIT_REGISTER_FN;
  __jit_debug_register_code();
  return entry;
}


static void UnregisterCodeEntry(JITCodeEntry* entry) {
  // TODO: Do we need a lock here?
  if (entry->prev_ != nullptr) {
    entry->prev_->next_ = entry->next_;
  } else {
    __jit_debug_descriptor.first_entry_ = entry->next_;
  }

  if (entry->next_ != nullptr) {
    entry->next_->prev_ = entry->prev_;
  }

  __jit_debug_descriptor.relevant_entry_ = entry;
  __jit_debug_descriptor.action_flag_ = JIT_UNREGISTER_FN;
  __jit_debug_register_code();
  delete entry;
}

ElfFile::ElfFile(File* file, bool writable, bool program_header_only, uint8_t* requested_base)
  : file_(file),
    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),
    jit_elf_image_(nullptr),
    jit_gdb_entry_(nullptr),
    requested_base_(requested_base) {
  CHECK(file != nullptr);
}

ElfFile* ElfFile::Open(File* file, bool writable, bool program_header_only,
                       std::string* error_msg, uint8_t* requested_base) {
  std::unique_ptr<ElfFile> elf_file(new ElfFile(file, writable, program_header_only,
                                    requested_base));
  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(prot, flags, error_msg)) {
    return nullptr;
  }
  return elf_file.release();
}

ElfFile* ElfFile::Open(File* file, int prot, int flags, std::string* error_msg) {
  std::unique_ptr<ElfFile> elf_file(new ElfFile(file, (prot & PROT_WRITE) == PROT_WRITE, false,
                                    /*requested_base*/nullptr));
  if (!elf_file->Setup(prot, flags, error_msg)) {
    return nullptr;
  }
  return elf_file.release();
}

bool ElfFile::Setup(int prot, int flags, 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(Elf32_Ehdr)) {
    *error_msg = StringPrintf("File size of %zd bytes not large enough to contain ELF header of "
                              "%zd bytes: '%s'", file_length, sizeof(Elf32_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(Elf32_Ehdr);
    if (!SetMap(MemMap::MapFile(elf_header_size, prot, flags, file_->Fd(), 0,
                                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(Elf32_Ehdr), file_->GetPath().c_str());
      return false;
    }
    if (!SetMap(MemMap::MapFile(program_header_size, prot, flags, file_->Fd(), 0,
                                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(MemMap::MapFile(file_->GetLength(), prot, flags, file_->Fd(), 0,
                                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.
    Elf32_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<byte**>(&dynamic_section_start_), error_msg)) {
      return false;
    }

    // Find other sections from section headers
    for (Elf32_Word i = 0; i < GetSectionHeaderNum(); i++) {
      Elf32_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<byte**>(&symtab_section_start_), error_msg)) {
            return false;
          }
          break;
        }
        case SHT_DYNSYM: {
          if (!CheckAndSet(section_header->sh_offset, "dynsym",
                           reinterpret_cast<byte**>(&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<byte**>(&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<byte**>(&strtab_section_start_), error_msg)) {
                return false;
              }
            }
          }
          break;
        }
        case SHT_DYNAMIC: {
          if (reinterpret_cast<byte*>(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<byte**>(&hash_section_start_), error_msg)) {
            return false;
          }
          break;
        }
      }
    }

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

  return true;
}

ElfFile::~ElfFile() {
  STLDeleteElements(&segments_);
  delete symtab_symbol_table_;
  delete dynsym_symbol_table_;
  delete jit_elf_image_;
  if (jit_gdb_entry_) {
    UnregisterCodeEntry(jit_gdb_entry_);
  }
}

bool ElfFile::CheckAndSet(Elf32_Off offset, const char* label,
                          byte** 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_->GetPath().c_str());
    return false;
  }
  *target = Begin() + offset;
  return true;
}

bool ElfFile::CheckSectionsLinked(const byte* source, const byte* 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;
  }

  Elf32_Shdr* source_section = nullptr;
  Elf32_Word target_index = 0;
  bool target_found = false;
  for (Elf32_Word i = 0; i < GetSectionHeaderNum(); i++) {
    Elf32_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;
}

bool ElfFile::CheckSectionsExist(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 byte*>(symtab_section_start_),
                             reinterpret_cast<const byte*>(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 byte*>(hash_section_start_),
                           reinterpret_cast<const byte*>(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;
}

bool ElfFile::SetMap(MemMap* map, std::string* error_msg) {
  if (map == nullptr) {
    // MemMap::Open should have already set an error.
    DCHECK(!error_msg->empty());
    return false;
  }
  map_.reset(map);
  CHECK(map_.get() != nullptr) << file_->GetPath();
  CHECK(map_->Begin() != nullptr) << file_->GetPath();

  header_ = reinterpret_cast<Elf32_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;
  }
  if (ELFCLASS32 != header_->e_ident[EI_CLASS]) {
    *error_msg = StringPrintf("Failed to find expected EI_CLASS value %d in %s, found %d",
                              ELFCLASS32,
                              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(),
                              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 %d less than %zd in %s",
                                header_->e_phoff,
                                Size(),
                                file_->GetPath().c_str());
      return false;
    }
    if (header_->e_shoff >= Size()) {
      *error_msg = StringPrintf("Failed to find e_shoff value %d less than %zd in %s",
                                header_->e_shoff,
                                Size(),
                                file_->GetPath().c_str());
      return false;
    }
  }
  return true;
}


Elf32_Ehdr& ElfFile::GetHeader() const {
  CHECK(header_ != nullptr);  // Header has been checked in SetMap. This is a sanity check.
  return *header_;
}

byte* ElfFile::GetProgramHeadersStart() const {
  CHECK(program_headers_start_ != nullptr);  // Header has been set in Setup. This is a sanity
                                             // check.
  return program_headers_start_;
}

byte* ElfFile::GetSectionHeadersStart() const {
  CHECK(!program_header_only_);              // Only used in "full" mode.
  CHECK(section_headers_start_ != nullptr);  // Is checked in CheckSectionsExist. Sanity check.
  return section_headers_start_;
}

Elf32_Phdr& ElfFile::GetDynamicProgramHeader() const {
  CHECK(dynamic_program_header_ != nullptr);  // Is checked in CheckSectionsExist. Sanity check.
  return *dynamic_program_header_;
}

Elf32_Dyn* ElfFile::GetDynamicSectionStart() const {
  CHECK(dynamic_section_start_ != nullptr);  // Is checked in CheckSectionsExist. Sanity check.
  return dynamic_section_start_;
}

static bool IsSymbolSectionType(Elf32_Word section_type) {
  return ((section_type == SHT_SYMTAB) || (section_type == SHT_DYNSYM));
}

Elf32_Sym* ElfFile::GetSymbolSectionStart(Elf32_Word section_type) const {
  CHECK(IsSymbolSectionType(section_type)) << file_->GetPath() << " " << 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;
    }
  }
}

const char* ElfFile::GetStringSectionStart(Elf32_Word section_type) const {
  CHECK(IsSymbolSectionType(section_type)) << file_->GetPath() << " " << 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;
    }
  }
}

const char* ElfFile::GetString(Elf32_Word section_type, Elf32_Word i) const {
  CHECK(IsSymbolSectionType(section_type)) << file_->GetPath() << " " << 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.

Elf32_Word* ElfFile::GetHashSectionStart() const {
  return hash_section_start_;
}

Elf32_Word ElfFile::GetHashBucketNum() const {
  return GetHashSectionStart()[0];
}

Elf32_Word ElfFile::GetHashChainNum() const {
  return GetHashSectionStart()[1];
}

Elf32_Word ElfFile::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];
}

Elf32_Word ElfFile::GetHashChain(size_t i, bool* ok) const {
  if (i >= GetHashBucketNum()) {
    *ok = false;
    return 0;
  }
  *ok = true;
  // 0 is nbucket, 1 is nchain, & chains are after buckets
  return GetHashSectionStart()[2 + GetHashBucketNum() + i];
}

Elf32_Word ElfFile::GetProgramHeaderNum() const {
  return GetHeader().e_phnum;
}

Elf32_Phdr* ElfFile::GetProgramHeader(Elf32_Word i) const {
  CHECK_LT(i, GetProgramHeaderNum()) << file_->GetPath();  // Sanity check for caller.
  byte* program_header = GetProgramHeadersStart() + (i * GetHeader().e_phentsize);
  if (program_header >= End()) {
    return nullptr;  // Failure condition.
  }
  return reinterpret_cast<Elf32_Phdr*>(program_header);
}

Elf32_Phdr* ElfFile::FindProgamHeaderByType(Elf32_Word type) const {
  for (Elf32_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf32_Phdr* program_header = GetProgramHeader(i);
    if (program_header->p_type == type) {
      return program_header;
    }
  }
  return nullptr;
}

Elf32_Word ElfFile::GetSectionHeaderNum() const {
  return GetHeader().e_shnum;
}

Elf32_Shdr* ElfFile::GetSectionHeader(Elf32_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_->GetPath();
  if (i >= GetSectionHeaderNum()) {
    return nullptr;  // Failure condition.
  }
  byte* section_header = GetSectionHeadersStart() + (i * GetHeader().e_shentsize);
  if (section_header >= End()) {
    return nullptr;  // Failure condition.
  }
  return reinterpret_cast<Elf32_Shdr*>(section_header);
}

Elf32_Shdr* ElfFile::FindSectionByType(Elf32_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_->GetPath();
  for (Elf32_Word i = 0; i < GetSectionHeaderNum(); i++) {
    Elf32_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;
}

Elf32_Shdr* ElfFile::GetSectionNameStringSection() const {
  return GetSectionHeader(GetHeader().e_shstrndx);
}

const byte* ElfFile::FindDynamicSymbolAddress(const std::string& symbol_name) const {
  // Check that we have a hash section.
  if (GetHashSectionStart() == nullptr) {
    return nullptr;  // Failure condition.
  }
  const Elf32_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.
const Elf32_Sym* ElfFile::FindDynamicSymbol(const std::string& symbol_name) const {
  if (GetHashBucketNum() == 0) {
    // No dynamic symbols at all.
    return nullptr;
  }
  Elf32_Word hash = elfhash(symbol_name.c_str());
  Elf32_Word bucket_index = hash % GetHashBucketNum();
  bool ok;
  Elf32_Word symbol_and_chain_index = GetHashBucket(bucket_index, &ok);
  if (!ok) {
    return nullptr;
  }
  while (symbol_and_chain_index != 0 /* STN_UNDEF */) {
    Elf32_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;
}

Elf32_Word ElfFile::GetSymbolNum(Elf32_Shdr& section_header) const {
  CHECK(IsSymbolSectionType(section_header.sh_type))
      << file_->GetPath() << " " << section_header.sh_type;
  CHECK_NE(0U, section_header.sh_entsize) << file_->GetPath();
  return section_header.sh_size / section_header.sh_entsize;
}

Elf32_Sym* ElfFile::GetSymbol(Elf32_Word section_type,
                              Elf32_Word i) const {
  Elf32_Sym* sym_start = GetSymbolSectionStart(section_type);
  if (sym_start == nullptr) {
    return nullptr;
  }
  return sym_start + i;
}

ElfFile::SymbolTable** ElfFile::GetSymbolTable(Elf32_Word section_type) {
  CHECK(IsSymbolSectionType(section_type)) << file_->GetPath() << " " << 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;
    }
  }
}

Elf32_Sym* ElfFile::FindSymbolByName(Elf32_Word section_type,
                                     const std::string& symbol_name,
                                     bool build_map) {
  CHECK(!program_header_only_) << file_->GetPath();
  CHECK(IsSymbolSectionType(section_type)) << file_->GetPath() << " " << 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;
      Elf32_Shdr* symbol_section = FindSectionByType(section_type);
      if (symbol_section == nullptr) {
        return nullptr;  // Failure condition.
      }
      Elf32_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++) {
        Elf32_Sym* symbol = GetSymbol(section_type, i);
        if (symbol == nullptr) {
          return nullptr;  // Failure condition.
        }
        unsigned char type = 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<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);
    SymbolTable::const_iterator it = (*symbol_table)->find(symbol_name);
    if (it == (*symbol_table)->end()) {
      return nullptr;
    }
    return it->second;
  }

  // Fall back to linear search
  Elf32_Shdr* symbol_section = FindSectionByType(section_type);
  if (symbol_section == nullptr) {
    return nullptr;
  }
  Elf32_Shdr* string_section = GetSectionHeader(symbol_section->sh_link);
  if (string_section == nullptr) {
    return nullptr;
  }
  for (uint32_t i = 0; i < GetSymbolNum(*symbol_section); i++) {
    Elf32_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;
}

Elf32_Addr ElfFile::FindSymbolAddress(Elf32_Word section_type,
                                      const std::string& symbol_name,
                                      bool build_map) {
  Elf32_Sym* symbol = FindSymbolByName(section_type, symbol_name, build_map);
  if (symbol == nullptr) {
    return 0;
  }
  return symbol->st_value;
}

const char* ElfFile::GetString(Elf32_Shdr& string_section, Elf32_Word i) const {
  CHECK(!program_header_only_) << file_->GetPath();
  // TODO: remove this static_cast from enum when using -std=gnu++0x
  if (static_cast<Elf32_Word>(SHT_STRTAB) != string_section.sh_type) {
    return nullptr;  // Failure condition.
  }
  if (i >= string_section.sh_size) {
    return nullptr;
  }
  if (i == 0) {
    return nullptr;
  }
  byte* strings = Begin() + string_section.sh_offset;
  byte* string = strings + i;
  if (string >= End()) {
    return nullptr;
  }
  return reinterpret_cast<const char*>(string);
}

Elf32_Word ElfFile::GetDynamicNum() const {
  return GetDynamicProgramHeader().p_filesz / sizeof(Elf32_Dyn);
}

Elf32_Dyn& ElfFile::GetDynamic(Elf32_Word i) const {
  CHECK_LT(i, GetDynamicNum()) << file_->GetPath();
  return *(GetDynamicSectionStart() + i);
}

Elf32_Dyn* ElfFile::FindDynamicByType(Elf32_Sword type) const {
  for (Elf32_Word i = 0; i < GetDynamicNum(); i++) {
    Elf32_Dyn* dyn = &GetDynamic(i);
    if (dyn->d_tag == type) {
      return dyn;
    }
  }
  return NULL;
}

Elf32_Word ElfFile::FindDynamicValueByType(Elf32_Sword type) const {
  Elf32_Dyn* dyn = FindDynamicByType(type);
  if (dyn == NULL) {
    return 0;
  } else {
    return dyn->d_un.d_val;
  }
}

Elf32_Rel* ElfFile::GetRelSectionStart(Elf32_Shdr& section_header) const {
  CHECK(SHT_REL == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  return reinterpret_cast<Elf32_Rel*>(Begin() + section_header.sh_offset);
}

Elf32_Word ElfFile::GetRelNum(Elf32_Shdr& section_header) const {
  CHECK(SHT_REL == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  CHECK_NE(0U, section_header.sh_entsize) << file_->GetPath();
  return section_header.sh_size / section_header.sh_entsize;
}

Elf32_Rel& ElfFile::GetRel(Elf32_Shdr& section_header, Elf32_Word i) const {
  CHECK(SHT_REL == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  CHECK_LT(i, GetRelNum(section_header)) << file_->GetPath();
  return *(GetRelSectionStart(section_header) + i);
}

Elf32_Rela* ElfFile::GetRelaSectionStart(Elf32_Shdr& section_header) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  return reinterpret_cast<Elf32_Rela*>(Begin() + section_header.sh_offset);
}

Elf32_Word ElfFile::GetRelaNum(Elf32_Shdr& section_header) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  return section_header.sh_size / section_header.sh_entsize;
}

Elf32_Rela& ElfFile::GetRela(Elf32_Shdr& section_header, Elf32_Word i) const {
  CHECK(SHT_RELA == section_header.sh_type) << file_->GetPath() << " " << section_header.sh_type;
  CHECK_LT(i, GetRelaNum(section_header)) << file_->GetPath();
  return *(GetRelaSectionStart(section_header) + i);
}

// Base on bionic phdr_table_get_load_size
size_t ElfFile::GetLoadedSize() const {
  Elf32_Addr min_vaddr = 0xFFFFFFFFu;
  Elf32_Addr max_vaddr = 0x00000000u;
  for (Elf32_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf32_Phdr* program_header = GetProgramHeader(i);
    if (program_header->p_type != PT_LOAD) {
      continue;
    }
    Elf32_Addr begin_vaddr = program_header->p_vaddr;
    if (begin_vaddr < min_vaddr) {
       min_vaddr = begin_vaddr;
    }
    Elf32_Addr end_vaddr = program_header->p_vaddr + program_header->p_memsz;
    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_->GetPath();
  size_t loaded_size = max_vaddr - min_vaddr;
  return loaded_size;
}

bool ElfFile::Load(bool executable, std::string* error_msg) {
  CHECK(program_header_only_) << file_->GetPath();

  if (executable) {
    InstructionSet elf_ISA = kNone;
    switch (GetHeader().e_machine) {
      case EM_ARM: {
        elf_ISA = kArm;
        break;
      }
      case EM_AARCH64: {
        elf_ISA = kArm64;
        break;
      }
      case EM_386: {
        elf_ISA = kX86;
        break;
      }
      case EM_X86_64: {
        elf_ISA = kX86_64;
        break;
      }
      case EM_MIPS: {
        elf_ISA = kMips;
        break;
      }
    }

    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 (Elf32_Word i = 0; i < GetProgramHeaderNum(); i++) {
    Elf32_Phdr* program_header = GetProgramHeader(i);
    if (program_header == nullptr) {
      *error_msg = StringPrintf("No program header for entry %d in ELF file %s.",
                                i, file_->GetPath().c_str());
      return false;
    }

    // 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* reserve_base = reinterpret_cast<uint8_t*>(program_header->p_vaddr);
      uint8_t* reserve_base_override = reserve_base;
      // Override the base (e.g. when compiling with --compile-pic)
      if (requested_base_ != nullptr) {
        reserve_base_override = requested_base_;
      }
      std::string reservation_name("ElfFile reservation for ");
      reservation_name += file_->GetPath();
      std::unique_ptr<MemMap> reserve(MemMap::MapAnonymous(reservation_name.c_str(),
                                                           reserve_base_override,
                                                           GetLoadedSize(), PROT_NONE, false,
                                                           error_msg));
      if (reserve.get() == nullptr) {
        *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 p_vaddr
      base_address_ = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(reserve->Begin())
                       - reinterpret_cast<uintptr_t>(reserve_base));
      // 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(reserve.release());
    }
    // empty segment, nothing to map
    if (program_header->p_memsz == 0) {
      continue;
    }
    byte* 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 (file_length < (program_header->p_offset + program_header->p_memsz)) {
      *error_msg = StringPrintf("File size of %zd bytes not large enough to contain ELF segment "
                                "%d of %d bytes: '%s'", file_length, i,
                                program_header->p_offset + program_header->p_memsz,
                                file_->GetPath().c_str());
      return false;
    }
    std::unique_ptr<MemMap> segment(MemMap::MapFileAtAddress(p_vaddr,
                                                       program_header->p_memsz,
                                                       prot, flags, file_->Fd(),
                                                       program_header->p_offset,
                                                       true,  // implies MAP_FIXED
                                                       file_->GetPath().c_str(),
                                                       error_msg));
    if (segment.get() == nullptr) {
      *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(segment.release());
  }

  // Now that we are done loading, .dynamic should be in memory to find .dynstr, .dynsym, .hash
  byte* 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<Elf32_Dyn*>(dsptr);

  for (Elf32_Word i = 0; i < GetDynamicNum(); i++) {
    Elf32_Dyn& elf_dyn = GetDynamic(i);
    byte* 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<Elf32_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<Elf32_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(error_msg)) {
    return false;
  }

  // Use GDB JIT support to do stack backtrace, etc.
  if (executable) {
    GdbJITSupport();
  }

  return true;
}

bool ElfFile::ValidPointer(const byte* start) const {
  for (size_t i = 0; i < segments_.size(); ++i) {
    const MemMap* segment = segments_[i];
    if (segment->Begin() <= start && start < segment->End()) {
      return true;
    }
  }
  return false;
}


Elf32_Shdr* ElfFile::FindSectionByName(const std::string& name) const {
  CHECK(!program_header_only_);
  Elf32_Shdr* shstrtab_sec = GetSectionNameStringSection();
  if (shstrtab_sec == nullptr) {
    return nullptr;
  }
  for (uint32_t i = 0; i < GetSectionHeaderNum(); i++) {
    Elf32_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;
}

struct PACKED(1) FDE {
  uint32_t raw_length_;
  uint32_t GetLength() {
    return raw_length_ + sizeof(raw_length_);
  }
  uint32_t CIE_pointer;
  uint32_t initial_location;
  uint32_t address_range;
  uint8_t instructions[0];
};

static FDE* NextFDE(FDE* frame) {
  byte* fde_bytes = reinterpret_cast<byte*>(frame);
  fde_bytes += frame->GetLength();
  return reinterpret_cast<FDE*>(fde_bytes);
}

static bool IsFDE(FDE* frame) {
  return frame->CIE_pointer != 0;
}

// TODO This only works for 32-bit Elf Files.
static bool FixupEHFrame(uintptr_t text_start, byte* eh_frame, size_t eh_frame_size) {
  FDE* last_frame = reinterpret_cast<FDE*>(eh_frame + eh_frame_size);
  FDE* frame = NextFDE(reinterpret_cast<FDE*>(eh_frame));
  for (; frame < last_frame; frame = NextFDE(frame)) {
    if (!IsFDE(frame)) {
      return false;
    }
    frame->initial_location += text_start;
  }
  return true;
}

struct PACKED(1) DebugInfoHeader {
  uint32_t unit_length;  // TODO 32-bit specific size
  uint16_t version;
  uint32_t debug_abbrev_offset;  // TODO 32-bit specific size
  uint8_t  address_size;
};

// Returns -1 if it is variable length, which we will just disallow for now.
static int32_t FormLength(uint32_t att) {
  switch (att) {
    case DW_FORM_data1:
    case DW_FORM_flag:
    case DW_FORM_flag_present:
    case DW_FORM_ref1:
      return 1;

    case DW_FORM_data2:
    case DW_FORM_ref2:
      return 2;

    case DW_FORM_addr:        // TODO 32-bit only
    case DW_FORM_ref_addr:    // TODO 32-bit only
    case DW_FORM_sec_offset:  // TODO 32-bit only
    case DW_FORM_strp:        // TODO 32-bit only
    case DW_FORM_data4:
    case DW_FORM_ref4:
      return 4;

    case DW_FORM_data8:
    case DW_FORM_ref8:
    case DW_FORM_ref_sig8:
      return 8;

    case DW_FORM_block:
    case DW_FORM_block1:
    case DW_FORM_block2:
    case DW_FORM_block4:
    case DW_FORM_exprloc:
    case DW_FORM_indirect:
    case DW_FORM_ref_udata:
    case DW_FORM_sdata:
    case DW_FORM_string:
    case DW_FORM_udata:
    default:
      return -1;
  }
}

class DebugTag {
 public:
  const uint32_t index_;
  ~DebugTag() {}
  // Creates a new tag and moves data pointer up to the start of the next one.
  // nullptr means error.
  static DebugTag* Create(const byte** data_pointer) {
    const byte* data = *data_pointer;
    uint32_t index = DecodeUnsignedLeb128(&data);
    std::unique_ptr<DebugTag> tag(new DebugTag(index));
    tag->size_ = static_cast<uint32_t>(
        reinterpret_cast<uintptr_t>(data) - reinterpret_cast<uintptr_t>(*data_pointer));
    // skip the abbrev
    tag->tag_ = DecodeUnsignedLeb128(&data);
    tag->has_child_ = (*data == 0);
    data++;
    while (true) {
      uint32_t attr = DecodeUnsignedLeb128(&data);
      uint32_t form = DecodeUnsignedLeb128(&data);
      if (attr == 0 && form == 0) {
        break;
      } else if (attr == 0 || form == 0) {
        // Bad abbrev.
        return nullptr;
      }
      int32_t size = FormLength(form);
      if (size == -1) {
        return nullptr;
      }
      tag->AddAttribute(attr, static_cast<uint32_t>(size));
    }
    *data_pointer = data;
    return tag.release();
  }

  uint32_t GetSize() const {
    return size_;
  }

  bool HasChild() {
    return has_child_;
  }

  uint32_t GetTagNumber() {
    return tag_;
  }

  // Gets the offset of a particular attribute in this tag structure.
  // Interpretation of the data is left to the consumer. 0 is returned if the
  // tag does not contain the attribute.
  uint32_t GetOffsetOf(uint32_t dwarf_attribute) const {
    auto it = off_map_.find(dwarf_attribute);
    if (it == off_map_.end()) {
      return 0;
    } else {
      return it->second;
    }
  }

  // Gets the size of attribute
  uint32_t GetAttrSize(uint32_t dwarf_attribute) const {
    auto it = size_map_.find(dwarf_attribute);
    if (it == size_map_.end()) {
      return 0;
    } else {
      return it->second;
    }
  }

 private:
  explicit DebugTag(uint32_t index) : index_(index), size_(0), tag_(0), has_child_(false) {}
  void AddAttribute(uint32_t type, uint32_t attr_size) {
    off_map_.insert(std::pair<uint32_t, uint32_t>(type, size_));
    size_map_.insert(std::pair<uint32_t, uint32_t>(type, attr_size));
    size_ += attr_size;
  }
  std::map<uint32_t, uint32_t> off_map_;
  std::map<uint32_t, uint32_t> size_map_;
  uint32_t size_;
  uint32_t tag_;
  bool has_child_;
};

class DebugAbbrev {
 public:
  ~DebugAbbrev() {}
  static DebugAbbrev* Create(const byte* dbg_abbrev, size_t dbg_abbrev_size) {
    std::unique_ptr<DebugAbbrev> abbrev(new DebugAbbrev);
    const byte* last = dbg_abbrev + dbg_abbrev_size;
    while (dbg_abbrev < last) {
      std::unique_ptr<DebugTag> tag(DebugTag::Create(&dbg_abbrev));
      if (tag.get() == nullptr) {
        return nullptr;
      } else {
        abbrev->tags_.insert(std::pair<uint32_t, uint32_t>(tag->index_, abbrev->tag_list_.size()));
        abbrev->tag_list_.push_back(std::move(tag));
      }
    }
    return abbrev.release();
  }

  DebugTag* ReadTag(const byte* entry) {
    uint32_t tag_num = DecodeUnsignedLeb128(&entry);
    auto it = tags_.find(tag_num);
    if (it == tags_.end()) {
      return nullptr;
    } else {
      CHECK_GT(tag_list_.size(), it->second);
      return tag_list_.at(it->second).get();
    }
  }

 private:
  DebugAbbrev() {}
  std::map<uint32_t, uint32_t> tags_;
  std::vector<std::unique_ptr<DebugTag>> tag_list_;
};

class DebugInfoIterator {
 public:
  static DebugInfoIterator* Create(DebugInfoHeader* header, size_t frame_size,
                                   DebugAbbrev* abbrev) {
    std::unique_ptr<DebugInfoIterator> iter(new DebugInfoIterator(header, frame_size, abbrev));
    if (iter->GetCurrentTag() == nullptr) {
      return nullptr;
    } else {
      return iter.release();
    }
  }
  ~DebugInfoIterator() {}

  // Moves to the next DIE. Returns false if at last entry.
  // TODO Handle variable length attributes.
  bool next() {
    if (current_entry_ == nullptr || current_tag_ == nullptr) {
      return false;
    }
    current_entry_ += current_tag_->GetSize();
    if (current_entry_ >= last_entry_) {
      current_entry_ = nullptr;
      return false;
    }
    current_tag_ = abbrev_->ReadTag(current_entry_);
    if (current_tag_ == nullptr) {
      current_entry_ = nullptr;
      return false;
    } else {
      return true;
    }
  }

  const DebugTag* GetCurrentTag() {
    return const_cast<DebugTag*>(current_tag_);
  }
  byte* GetPointerToField(uint8_t dwarf_field) {
    if (current_tag_ == nullptr || current_entry_ == nullptr || current_entry_ >= last_entry_) {
      return nullptr;
    }
    uint32_t off = current_tag_->GetOffsetOf(dwarf_field);
    if (off == 0) {
      // tag does not have that field.
      return nullptr;
    } else {
      DCHECK_LT(off, current_tag_->GetSize());
      return current_entry_ + off;
    }
  }

 private:
  DebugInfoIterator(DebugInfoHeader* header, size_t frame_size, DebugAbbrev* abbrev)
      : abbrev_(abbrev),
        last_entry_(reinterpret_cast<byte*>(header) + frame_size),
        current_entry_(reinterpret_cast<byte*>(header) + sizeof(DebugInfoHeader)),
        current_tag_(abbrev_->ReadTag(current_entry_)) {}
  DebugAbbrev* abbrev_;
  byte* last_entry_;
  byte* current_entry_;
  DebugTag* current_tag_;
};

static bool FixupDebugInfo(uint32_t text_start, DebugInfoIterator* iter) {
  do {
    if (iter->GetCurrentTag()->GetAttrSize(DW_AT_low_pc) != sizeof(int32_t) ||
        iter->GetCurrentTag()->GetAttrSize(DW_AT_high_pc) != sizeof(int32_t)) {
      return false;
    }
    uint32_t* PC_low = reinterpret_cast<uint32_t*>(iter->GetPointerToField(DW_AT_low_pc));
    uint32_t* PC_high = reinterpret_cast<uint32_t*>(iter->GetPointerToField(DW_AT_high_pc));
    if (PC_low != nullptr && PC_high != nullptr) {
      *PC_low  += text_start;
      *PC_high += text_start;
    }
  } while (iter->next());
  return true;
}

static bool FixupDebugSections(const byte* dbg_abbrev, size_t dbg_abbrev_size,
                               uintptr_t text_start,
                               byte* dbg_info, size_t dbg_info_size,
                               byte* eh_frame, size_t eh_frame_size) {
  std::unique_ptr<DebugAbbrev> abbrev(DebugAbbrev::Create(dbg_abbrev, dbg_abbrev_size));
  if (abbrev.get() == nullptr) {
    return false;
  }
  std::unique_ptr<DebugInfoIterator> iter(
      DebugInfoIterator::Create(reinterpret_cast<DebugInfoHeader*>(dbg_info),
                                dbg_info_size, abbrev.get()));
  if (iter.get() == nullptr) {
    return false;
  }
  return FixupDebugInfo(text_start, iter.get())
      && FixupEHFrame(text_start, eh_frame, eh_frame_size);
}

void ElfFile::GdbJITSupport() {
  // We only get here if we only are mapping the program header.
  DCHECK(program_header_only_);

  // Well, we need the whole file to do this.
  std::string error_msg;
  // Make it MAP_PRIVATE so we can just give it to gdb if all the necessary
  // sections are there.
  std::unique_ptr<ElfFile> all_ptr(Open(const_cast<File*>(file_), PROT_READ | PROT_WRITE,
                                        MAP_PRIVATE, &error_msg));
  if (all_ptr.get() == nullptr) {
    return;
  }
  ElfFile& all = *all_ptr;

  // Do we have interesting sections?
  const Elf32_Shdr* debug_info = all.FindSectionByName(".debug_info");
  const Elf32_Shdr* debug_abbrev = all.FindSectionByName(".debug_abbrev");
  const Elf32_Shdr* eh_frame = all.FindSectionByName(".eh_frame");
  const Elf32_Shdr* debug_str = all.FindSectionByName(".debug_str");
  const Elf32_Shdr* strtab_sec = all.FindSectionByName(".strtab");
  const Elf32_Shdr* symtab_sec = all.FindSectionByName(".symtab");
  Elf32_Shdr* text_sec = all.FindSectionByName(".text");
  if (debug_info == nullptr || debug_abbrev == nullptr || eh_frame == nullptr ||
      debug_str == nullptr || text_sec == nullptr || strtab_sec == nullptr ||
      symtab_sec == nullptr) {
    return;
  }
  // We need to add in a strtab and symtab to the image.
  // all is MAP_PRIVATE so it can be written to freely.
  // We also already have strtab and symtab so we are fine there.
  Elf32_Ehdr& elf_hdr = all.GetHeader();
  elf_hdr.e_entry = 0;
  elf_hdr.e_phoff = 0;
  elf_hdr.e_phnum = 0;
  elf_hdr.e_phentsize = 0;
  elf_hdr.e_type = ET_EXEC;

  text_sec->sh_type = SHT_NOBITS;
  text_sec->sh_offset = 0;

  if (!FixupDebugSections(
        all.Begin() + debug_abbrev->sh_offset, debug_abbrev->sh_size, text_sec->sh_addr,
        all.Begin() + debug_info->sh_offset, debug_info->sh_size,
        all.Begin() + eh_frame->sh_offset, eh_frame->sh_size)) {
    LOG(ERROR) << "Failed to load GDB data";
    return;
  }

  jit_gdb_entry_ = CreateCodeEntry(all.Begin(), all.Size());
  gdb_file_mapping_.reset(all_ptr.release());
}

}  // namespace art