void ElfMemImage::Init()

in absl/debugging/internal/elf_mem_image.cc [153:260]

• 104 lines of code
• 30 McCabe index (conditional complexity)

void ElfMemImage::Init(const void *base) {
  ehdr_      = nullptr;
  dynsym_    = nullptr;
  dynstr_    = nullptr;
  versym_    = nullptr;
  verdef_    = nullptr;
  hash_      = nullptr;
  strsize_   = 0;
  verdefnum_ = 0;
  link_base_ = ~0L;  // Sentinel: PT_LOAD .p_vaddr can't possibly be this.
  if (!base) {
    return;
  }
  const char *const base_as_char = reinterpret_cast<const char *>(base);
  if (base_as_char[EI_MAG0] != ELFMAG0 || base_as_char[EI_MAG1] != ELFMAG1 ||
      base_as_char[EI_MAG2] != ELFMAG2 || base_as_char[EI_MAG3] != ELFMAG3) {
    assert(false);
    return;
  }
  int elf_class = base_as_char[EI_CLASS];
  if (elf_class != kElfClass) {
    assert(false);
    return;
  }
  switch (base_as_char[EI_DATA]) {
    case ELFDATA2LSB: {
#ifndef ABSL_IS_LITTLE_ENDIAN
      assert(false);
      return;
#endif
      break;
    }
    case ELFDATA2MSB: {
#ifndef ABSL_IS_BIG_ENDIAN
      assert(false);
      return;
#endif
      break;
    }
    default: {
      assert(false);
      return;
    }
  }

  ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
  const ElfW(Phdr) *dynamic_program_header = nullptr;
  for (int i = 0; i < ehdr_->e_phnum; ++i) {
    const ElfW(Phdr) *const program_header = GetPhdr(i);
    switch (program_header->p_type) {
      case PT_LOAD:
        if (!~link_base_) {
          link_base_ = program_header->p_vaddr;
        }
        break;
      case PT_DYNAMIC:
        dynamic_program_header = program_header;
        break;
    }
  }
  if (!~link_base_ || !dynamic_program_header) {
    assert(false);
    // Mark this image as not present. Can not recur infinitely.
    Init(nullptr);
    return;
  }
  ptrdiff_t relocation =
      base_as_char - reinterpret_cast<const char *>(link_base_);
  ElfW(Dyn) *dynamic_entry =
      reinterpret_cast<ElfW(Dyn) *>(dynamic_program_header->p_vaddr +
                                    relocation);
  for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) {
    const auto value = dynamic_entry->d_un.d_val + relocation;
    switch (dynamic_entry->d_tag) {
      case DT_HASH:
        hash_ = reinterpret_cast<ElfW(Word) *>(value);
        break;
      case DT_SYMTAB:
        dynsym_ = reinterpret_cast<ElfW(Sym) *>(value);
        break;
      case DT_STRTAB:
        dynstr_ = reinterpret_cast<const char *>(value);
        break;
      case DT_VERSYM:
        versym_ = reinterpret_cast<ElfW(Versym) *>(value);
        break;
      case DT_VERDEF:
        verdef_ = reinterpret_cast<ElfW(Verdef) *>(value);
        break;
      case DT_VERDEFNUM:
        verdefnum_ = dynamic_entry->d_un.d_val;
        break;
      case DT_STRSZ:
        strsize_ = dynamic_entry->d_un.d_val;
        break;
      default:
        // Unrecognized entries explicitly ignored.
        break;
    }
  }
  if (!hash_ || !dynsym_ || !dynstr_ || !versym_ ||
      !verdef_ || !verdefnum_ || !strsize_) {
    assert(false);  // invalid VDSO
    // Mark this image as not present. Can not recur infinitely.
    Init(nullptr);
    return;
  }
}