common/linux/elfutils.cc

// Copyright (c) 2012, Google Inc.
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
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#include "common/linux/elfutils.h"

#include <assert.h>
#include <string.h>

#include "common/linux/linux_libc_support.h"
#include "common/linux/elfutils-inl.h"

#if defined(__FreeBSD__)
#  define ElfW(type) Elf_##type
#endif

namespace google_breakpad {

namespace {

template<typename ElfClass>
void FindElfClassSection(const char *elf_base,
                         const char *section_name,
                         typename ElfClass::Word section_type,
                         const void **section_start,
                         size_t *section_size) {
  typedef typename ElfClass::Ehdr Ehdr;
  typedef typename ElfClass::Shdr Shdr;

  assert(elf_base);
  assert(section_start);
  assert(section_size);

  assert(my_strncmp(elf_base, ELFMAG, SELFMAG) == 0);

  const Ehdr* elf_header = reinterpret_cast<const Ehdr*>(elf_base);
  assert(elf_header->e_ident[EI_CLASS] == ElfClass::kClass);

  const Shdr* sections =
    GetOffset<ElfClass, Shdr>(elf_header, elf_header->e_shoff);
  const Shdr* section_names = sections + elf_header->e_shstrndx;
  const char* names =
    GetOffset<ElfClass, char>(elf_header, section_names->sh_offset);
  const char *names_end = names + section_names->sh_size;

  const Shdr* section =
    FindElfSectionByName<ElfClass>(section_name, section_type,
                                   sections, names, names_end,
                                   elf_header->e_shnum);

  if (section != NULL && section->sh_size > 0) {
    *section_start = elf_base + section->sh_offset;
    *section_size = section->sh_size;
  }
}

template<typename ElfClass>
void FindElfClassSegment(const char *elf_base,
                         typename ElfClass::Word segment_type,
                         wasteful_vector<ElfSegment> *segments) {
  typedef typename ElfClass::Ehdr Ehdr;
  typedef typename ElfClass::Phdr Phdr;

  assert(elf_base);
  assert(segments);

  assert(my_strncmp(elf_base, ELFMAG, SELFMAG) == 0);

  const Ehdr* elf_header = reinterpret_cast<const Ehdr*>(elf_base);
  assert(elf_header->e_ident[EI_CLASS] == ElfClass::kClass);

  const Phdr* phdrs =
    GetOffset<ElfClass, Phdr>(elf_header, elf_header->e_phoff);

  for (int i = 0; i < elf_header->e_phnum; ++i) {
    if (phdrs[i].p_type == segment_type) {
      ElfSegment seg = {};
      seg.start = elf_base + phdrs[i].p_offset;
      seg.size = phdrs[i].p_filesz;
      segments->push_back(seg);
    }
  }
}

}  // namespace

bool IsValidElf(const void* elf_base) {
  return my_strncmp(reinterpret_cast<const char*>(elf_base),
                    ELFMAG, SELFMAG) == 0;
}

int ElfClass(const void* elf_base) {
  const ElfW(Ehdr)* elf_header =
    reinterpret_cast<const ElfW(Ehdr)*>(elf_base);

  return elf_header->e_ident[EI_CLASS];
}

bool FindElfSection(const void *elf_mapped_base,
                    const char *section_name,
                    uint32_t section_type,
                    const void **section_start,
                    size_t *section_size) {
  assert(elf_mapped_base);
  assert(section_start);
  assert(section_size);

  *section_start = NULL;
  *section_size = 0;

  if (!IsValidElf(elf_mapped_base))
    return false;

  int cls = ElfClass(elf_mapped_base);
  const char* elf_base =
    static_cast<const char*>(elf_mapped_base);

  if (cls == ELFCLASS32) {
    FindElfClassSection<ElfClass32>(elf_base, section_name, section_type,
                                    section_start, section_size);
    return *section_start != NULL;
  } else if (cls == ELFCLASS64) {
    FindElfClassSection<ElfClass64>(elf_base, section_name, section_type,
                                    section_start, section_size);
    return *section_start != NULL;
  }

  return false;
}

bool FindElfSegments(const void* elf_mapped_base,
                     uint32_t segment_type,
                     wasteful_vector<ElfSegment>* segments) {
  assert(elf_mapped_base);
  assert(segments);

  if (!IsValidElf(elf_mapped_base))
    return false;

  int cls = ElfClass(elf_mapped_base);
  const char* elf_base =
    static_cast<const char*>(elf_mapped_base);

  if (cls == ELFCLASS32) {
    FindElfClassSegment<ElfClass32>(elf_base, segment_type, segments);
    return true;
  } else if (cls == ELFCLASS64) {
    FindElfClassSegment<ElfClass64>(elf_base, segment_type, segments);
    return true;
  }

  return false;
}

template <typename ElfClass>
bool FindElfSoNameFromDynamicSection(const void* section_start,
                                     size_t section_size,
                                     const void* dynstr_start,
                                     size_t dynstr_size,
                                     char* soname,
                                     size_t soname_size) {
  typedef typename ElfClass::Dyn Dyn;

  auto* dynamic = static_cast<const Dyn*>(section_start);
  size_t dcount = section_size / sizeof(Dyn);
  for (const Dyn* dyn = dynamic; dyn < dynamic + dcount; ++dyn) {
    if (dyn->d_tag == DT_SONAME) {
      const char* dynstr = static_cast<const char*>(dynstr_start);
      if (dyn->d_un.d_val >= dynstr_size) {
        // Beyond the end of the dynstr section
        return false;
      }
      const char* str = dynstr + dyn->d_un.d_val;
      const size_t maxsize = dynstr_size - dyn->d_un.d_val;
      my_strlcpy(soname, str, maxsize < soname_size ? maxsize : soname_size);
      return true;
    }
  }

  return false;
}

bool ElfFileSoNameFromMappedFile(const void* elf_base,
                                 char* soname,
                                 size_t soname_size) {
  if (!IsValidElf(elf_base)) {
    // Not ELF
    return false;
  }

  const void* segment_start;
  size_t segment_size;
  if (!FindElfSection(elf_base, ".dynamic", SHT_DYNAMIC, &segment_start,
                      &segment_size)) {
    // No dynamic section
    return false;
  }

  const void* dynstr_start;
  size_t dynstr_size;
  if (!FindElfSection(elf_base, ".dynstr", SHT_STRTAB, &dynstr_start,
                      &dynstr_size)) {
    // No dynstr section
    return false;
  }

  int cls = ElfClass(elf_base);
  return cls == ELFCLASS32 ? FindElfSoNameFromDynamicSection<ElfClass32>(
                                 segment_start, segment_size, dynstr_start,
                                 dynstr_size, soname, soname_size)
                           : FindElfSoNameFromDynamicSection<ElfClass64>(
                                 segment_start, segment_size, dynstr_start,
                                 dynstr_size, soname, soname_size);
}

}  // namespace google_breakpad