root/third_party/tcmalloc/chromium/src/base/elf_mem_image.cc

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DEFINITIONS

This source file includes following definitions.
  1. ElfBind
  2. ElfType
  3. ElfBind
  4. ElfType
  5. ElfBind
  6. ElfType
  7. GetTableElement
  8. GetNumSymbols
  9. ElfW
  10. ElfW
  11. ElfW
  12. GetDynstr
  13. GetSymAddr
  14. ElfW
  15. ElfW
  16. GetVerstr
  17. Init
  18. LookupSymbol
  19. LookupSymbolByAddress
  20. image_
  21. begin
  22. end
  23. Update

// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// 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.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Paul Pluzhnikov
//
// Allow dynamic symbol lookup in an in-memory Elf image.
//

#include "base/elf_mem_image.h"

#ifdef HAVE_ELF_MEM_IMAGE  // defined in elf_mem_image.h

#include <stddef.h>   // for size_t, ptrdiff_t
#include "base/logging.h"

// From binutils/include/elf/common.h (this doesn't appear to be documented
// anywhere else).
//
//   /* This flag appears in a Versym structure.  It means that the symbol
//      is hidden, and is only visible with an explicit version number.
//      This is a GNU extension.  */
//   #define VERSYM_HIDDEN           0x8000
//
//   /* This is the mask for the rest of the Versym information.  */
//   #define VERSYM_VERSION          0x7fff

#define VERSYM_VERSION 0x7fff

namespace base {

namespace {
template <int N> class ElfClass {
 public:
  static const int kElfClass = -1;
  static int ElfBind(const ElfW(Sym) *) {
    CHECK(false); // << "Unexpected word size";
    return 0;
  }
  static int ElfType(const ElfW(Sym) *) {
    CHECK(false); // << "Unexpected word size";
    return 0;
  }
};

template <> class ElfClass<32> {
 public:
  static const int kElfClass = ELFCLASS32;
  static int ElfBind(const ElfW(Sym) *symbol) {
    return ELF32_ST_BIND(symbol->st_info);
  }
  static int ElfType(const ElfW(Sym) *symbol) {
    return ELF32_ST_TYPE(symbol->st_info);
  }
};

template <> class ElfClass<64> {
 public:
  static const int kElfClass = ELFCLASS64;
  static int ElfBind(const ElfW(Sym) *symbol) {
    return ELF64_ST_BIND(symbol->st_info);
  }
  static int ElfType(const ElfW(Sym) *symbol) {
    return ELF64_ST_TYPE(symbol->st_info);
  }
};

typedef ElfClass<__WORDSIZE> CurrentElfClass;

// Extract an element from one of the ELF tables, cast it to desired type.
// This is just a simple arithmetic and a glorified cast.
// Callers are responsible for bounds checking.
template <class T>
const T* GetTableElement(const ElfW(Ehdr) *ehdr,
                         ElfW(Off) table_offset,
                         ElfW(Word) element_size,
                         size_t index) {
  return reinterpret_cast<const T*>(reinterpret_cast<const char *>(ehdr)
                                    + table_offset
                                    + index * element_size);
}
}  // namespace

const void *const ElfMemImage::kInvalidBase =
    reinterpret_cast<const void *>(~0L);

ElfMemImage::ElfMemImage(const void *base) {
  CHECK(base != kInvalidBase);
  Init(base);
}

int ElfMemImage::GetNumSymbols() const {
  if (!hash_) {
    return 0;
  }
  // See http://www.caldera.com/developers/gabi/latest/ch5.dynamic.html#hash
  return hash_[1];
}

const ElfW(Sym) *ElfMemImage::GetDynsym(int index) const {
  CHECK_LT(index, GetNumSymbols());
  return dynsym_ + index;
}

const ElfW(Versym) *ElfMemImage::GetVersym(int index) const {
  CHECK_LT(index, GetNumSymbols());
  return versym_ + index;
}

const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const {
  CHECK_LT(index, ehdr_->e_phnum);
  return GetTableElement<ElfW(Phdr)>(ehdr_,
                                     ehdr_->e_phoff,
                                     ehdr_->e_phentsize,
                                     index);
}

const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const {
  CHECK_LT(offset, strsize_);
  return dynstr_ + offset;
}

const void *ElfMemImage::GetSymAddr(const ElfW(Sym) *sym) const {
  if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) {
    // Symbol corresponds to "special" (e.g. SHN_ABS) section.
    return reinterpret_cast<const void *>(sym->st_value);
  }
  CHECK_LT(link_base_, sym->st_value);
  return GetTableElement<char>(ehdr_, 0, 1, sym->st_value) - link_base_;
}

const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const {
  CHECK_LE(index, verdefnum_);
  const ElfW(Verdef) *version_definition = verdef_;
  while (version_definition->vd_ndx < index && version_definition->vd_next) {
    const char *const version_definition_as_char =
        reinterpret_cast<const char *>(version_definition);
    version_definition =
        reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char +
                                               version_definition->vd_next);
  }
  return version_definition->vd_ndx == index ? version_definition : NULL;
}

const ElfW(Verdaux) *ElfMemImage::GetVerdefAux(
    const ElfW(Verdef) *verdef) const {
  return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1);
}

const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const {
  CHECK_LT(offset, strsize_);
  return dynstr_ + offset;
}

void ElfMemImage::Init(const void *base) {
  ehdr_      = NULL;
  dynsym_    = NULL;
  dynstr_    = NULL;
  versym_    = NULL;
  verdef_    = NULL;
  hash_      = NULL;
  strsize_   = 0;
  verdefnum_ = 0;
  link_base_ = ~0L;  // Sentinel: PT_LOAD .p_vaddr can't possibly be this.
  if (!base) {
    return;
  }
  const intptr_t base_as_uintptr_t = reinterpret_cast<uintptr_t>(base);
  // Fake VDSO has low bit set.
  const bool fake_vdso = ((base_as_uintptr_t & 1) != 0);
  base = reinterpret_cast<const void *>(base_as_uintptr_t & ~1);
  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) {
    RAW_DCHECK(false, "no ELF magic"); // at %p", base);
    return;
  }
  int elf_class = base_as_char[EI_CLASS];
  if (elf_class != CurrentElfClass::kElfClass) {
    DCHECK_EQ(elf_class, CurrentElfClass::kElfClass);
    return;
  }
  switch (base_as_char[EI_DATA]) {
    case ELFDATA2LSB: {
      if (__LITTLE_ENDIAN != __BYTE_ORDER) {
        DCHECK_EQ(__LITTLE_ENDIAN, __BYTE_ORDER); // << ": wrong byte order";
        return;
      }
      break;
    }
    case ELFDATA2MSB: {
      if (__BIG_ENDIAN != __BYTE_ORDER) {
        DCHECK_EQ(__BIG_ENDIAN, __BYTE_ORDER); // << ": wrong byte order";
        return;
      }
      break;
    }
    default: {
      RAW_DCHECK(false, "unexpected data encoding"); // << base_as_char[EI_DATA];
      return;
    }
  }

  ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
  const ElfW(Phdr) *dynamic_program_header = NULL;
  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_ == ~0L) {
          link_base_ = program_header->p_vaddr;
        }
        break;
      case PT_DYNAMIC:
        dynamic_program_header = program_header;
        break;
    }
  }
  if (link_base_ == ~0L || !dynamic_program_header) {
    RAW_DCHECK(~0L != link_base_, "no PT_LOADs in VDSO");
    RAW_DCHECK(dynamic_program_header, "no PT_DYNAMIC in VDSO");
    // Mark this image as not present. Can not recur infinitely.
    Init(0);
    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) {
    ElfW(Xword) value = dynamic_entry->d_un.d_val;
    if (fake_vdso) {
      // A complication: in the real VDSO, dynamic entries are not relocated
      // (it wasn't loaded by a dynamic loader). But when testing with a
      // "fake" dlopen()ed vdso library, the loader relocates some (but
      // not all!) of them before we get here.
      if (dynamic_entry->d_tag == DT_VERDEF) {
        // The only dynamic entry (of the ones we care about) libc-2.3.6
        // loader doesn't relocate.
        value += relocation;
      }
    } else {
      // Real VDSO. Everything needs to be relocated.
      value += 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_) {
    RAW_DCHECK(hash_, "invalid VDSO (no DT_HASH)");
    RAW_DCHECK(dynsym_, "invalid VDSO (no DT_SYMTAB)");
    RAW_DCHECK(dynstr_, "invalid VDSO (no DT_STRTAB)");
    RAW_DCHECK(versym_, "invalid VDSO (no DT_VERSYM)");
    RAW_DCHECK(verdef_, "invalid VDSO (no DT_VERDEF)");
    RAW_DCHECK(verdefnum_, "invalid VDSO (no DT_VERDEFNUM)");
    RAW_DCHECK(strsize_, "invalid VDSO (no DT_STRSZ)");
    // Mark this image as not present. Can not recur infinitely.
    Init(0);
    return;
  }
}

bool ElfMemImage::LookupSymbol(const char *name,
                               const char *version,
                               int type,
                               SymbolInfo *info) const {
  for (SymbolIterator it = begin(); it != end(); ++it) {
    if (strcmp(it->name, name) == 0 && strcmp(it->version, version) == 0 &&
        CurrentElfClass::ElfType(it->symbol) == type) {
      if (info) {
        *info = *it;
      }
      return true;
    }
  }
  return false;
}

bool ElfMemImage::LookupSymbolByAddress(const void *address,
                                        SymbolInfo *info_out) const {
  for (SymbolIterator it = begin(); it != end(); ++it) {
    const char *const symbol_start =
        reinterpret_cast<const char *>(it->address);
    const char *const symbol_end = symbol_start + it->symbol->st_size;
    if (symbol_start <= address && address < symbol_end) {
      if (info_out) {
        // Client wants to know details for that symbol (the usual case).
        if (CurrentElfClass::ElfBind(it->symbol) == STB_GLOBAL) {
          // Strong symbol; just return it.
          *info_out = *it;
          return true;
        } else {
          // Weak or local. Record it, but keep looking for a strong one.
          *info_out = *it;
        }
      } else {
        // Client only cares if there is an overlapping symbol.
        return true;
      }
    }
  }
  return false;
}

ElfMemImage::SymbolIterator::SymbolIterator(const void *const image, int index)
    : index_(index), image_(image) {
}

const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const {
  return &info_;
}

const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const {
  return info_;
}

bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const {
  return this->image_ == rhs.image_ && this->index_ == rhs.index_;
}

bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const {
  return !(*this == rhs);
}

ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() {
  this->Update(1);
  return *this;
}

ElfMemImage::SymbolIterator ElfMemImage::begin() const {
  SymbolIterator it(this, 0);
  it.Update(0);
  return it;
}

ElfMemImage::SymbolIterator ElfMemImage::end() const {
  return SymbolIterator(this, GetNumSymbols());
}

void ElfMemImage::SymbolIterator::Update(int increment) {
  const ElfMemImage *image = reinterpret_cast<const ElfMemImage *>(image_);
  CHECK(image->IsPresent() || increment == 0);
  if (!image->IsPresent()) {
    return;
  }
  index_ += increment;
  if (index_ >= image->GetNumSymbols()) {
    index_ = image->GetNumSymbols();
    return;
  }
  const ElfW(Sym)    *symbol = image->GetDynsym(index_);
  const ElfW(Versym) *version_symbol = image->GetVersym(index_);
  CHECK(symbol && version_symbol);
  const char *const symbol_name = image->GetDynstr(symbol->st_name);
  const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
  const ElfW(Verdef) *version_definition = NULL;
  const char *version_name = "";
  if (symbol->st_shndx == SHN_UNDEF) {
    // Undefined symbols reference DT_VERNEED, not DT_VERDEF, and
    // version_index could well be greater than verdefnum_, so calling
    // GetVerdef(version_index) may trigger assertion.
  } else {
    version_definition = image->GetVerdef(version_index);
  }
  if (version_definition) {
    // I am expecting 1 or 2 auxiliary entries: 1 for the version itself,
    // optional 2nd if the version has a parent.
    CHECK_LE(1, version_definition->vd_cnt);
    CHECK_LE(version_definition->vd_cnt, 2);
    const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition);
    version_name = image->GetVerstr(version_aux->vda_name);
  }
  info_.name    = symbol_name;
  info_.version = version_name;
  info_.address = image->GetSymAddr(symbol);
  info_.symbol  = symbol;
}

}  // namespace base

#endif  // HAVE_ELF_MEM_IMAGE

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