elf_mem_image.h - mozsearch

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/*

 * Copyright 2017 The Abseil Authors.

 * 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

 *      https://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.

*/

// Allow dynamic symbol lookup for in-memory Elf images.

#ifndef ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_

#define ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_

// Including this will define the __GLIBC__ macro if glibc is being

// used.

#include <climits>

#include "absl/base/config.h"

// Maybe one day we can rewrite this file not to require the elf

// symbol extensions in glibc, but for right now we need them.

#ifdef ABSL_HAVE_ELF_MEM_IMAGE

#error ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set

#endif

#if defined(__ELF__) && !defined(__OpenBSD__) && !defined(__QNX__) && \

    !defined(__native_client__) && !defined(__asmjs__) &&             \

    !defined(__wasm__) && !defined(__HAIKU__) && !defined(__sun) &&   \

    !defined(__VXWORKS__) && !defined(__hexagon__)

#define ABSL_HAVE_ELF_MEM_IMAGE 1

#endif

#ifdef ABSL_HAVE_ELF_MEM_IMAGE

#include <link.h>  // for ElfW

#if defined(__FreeBSD__) && !defined(ElfW)

#define ElfW(x) __ElfN(x)

#endif

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace debugging_internal {

// An in-memory ELF image (may not exist on disk).

class ElfMemImage {

 private:

  // Sentinel: there could never be an elf image at &kInvalidBaseSentinel.

  static const int kInvalidBaseSentinel;

 public:

  // Sentinel: there could never be an elf image at this address.

  static constexpr const void *const kInvalidBase =

    static_cast<const void*>(&kInvalidBaseSentinel);

  // Information about a single vdso symbol.

  // All pointers are into .dynsym, .dynstr, or .text of the VDSO.

  // Do not free() them or modify through them.

  struct SymbolInfo {

    const char      *name;      // E.g. "__vdso_getcpu"

    const char      *version;   // E.g. "LINUX_2.6", could be ""

                                // for unversioned symbol.

    const void      *address;   // Relocated symbol address.

    const ElfW(Sym) *symbol;    // Symbol in the dynamic symbol table.

};

  // Supports iteration over all dynamic symbols.

  class SymbolIterator {

   public:

    friend class ElfMemImage;

    const SymbolInfo *operator->() const;

    const SymbolInfo &operator*() const;

    SymbolIterator& operator++();

    bool operator!=(const SymbolIterator &rhs) const;

    bool operator==(const SymbolIterator &rhs) const;

   private:

    SymbolIterator(const void *const image, int index);

    void Update(int incr);

    SymbolInfo info_;

    int index_;

    const void *const image_;

};

  explicit ElfMemImage(const void *base);

  void                 Init(const void *base);

  bool                 IsPresent() const { return ehdr_ != nullptr; }

  const ElfW(Phdr)*    GetPhdr(int index) const;

  const ElfW(Sym)*     GetDynsym(int index) const;

  const ElfW(Versym)*  GetVersym(int index) const;

  const ElfW(Verdef)*  GetVerdef(int index) const;

  const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const;

  const char*          GetDynstr(ElfW(Word) offset) const;

  const void*          GetSymAddr(const ElfW(Sym) *sym) const;

  const char*          GetVerstr(ElfW(Word) offset) const;

  int                  GetNumSymbols() const;

  SymbolIterator begin() const;

  SymbolIterator end() const;

  // Look up versioned dynamic symbol in the image.

  // Returns false if image is not present, or doesn't contain given

  // symbol/version/type combination.

  // If info_out is non-null, additional details are filled in.

  bool LookupSymbol(const char *name, const char *version,

                    int symbol_type, SymbolInfo *info_out) const;

  // Find info about symbol (if any) which overlaps given address.

  // Returns true if symbol was found; false if image isn't present

  // or doesn't have a symbol overlapping given address.

  // If info_out is non-null, additional details are filled in.

  bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;

 private:

  const ElfW(Ehdr) *ehdr_;

  const ElfW(Sym) *dynsym_;

  const ElfW(Versym) *versym_;

  const ElfW(Verdef) *verdef_;

  const ElfW(Word) *hash_;

  const char *dynstr_;

  size_t strsize_;

  size_t verdefnum_;

  ElfW(Addr) link_base_;     // Link-time base (p_vaddr of first PT_LOAD).

};

}  // namespace debugging_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_HAVE_ELF_MEM_IMAGE

#endif  // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_