library.h

// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef LIBRARY_H__
#define LIBRARY_H__

#include <elf.h>
#include <functional>
#include <map>
#include <set>
#include <string>
#include <string.h>
#include <sys/mman.h>

#include "maps.h"

#if defined(__x86_64__)
typedef Elf64_Ehdr Elf_Ehdr;
typedef Elf64_Shdr Elf_Shdr;
typedef Elf64_Sym  Elf_Sym;
typedef Elf64_Addr Elf_Addr;
#elif defined(__i386__)
typedef Elf32_Ehdr Elf_Ehdr;
typedef Elf32_Shdr Elf_Shdr;
typedef Elf32_Sym  Elf_Sym;
typedef Elf32_Addr Elf_Addr;
#else
#error Unsupported target platform
#endif

struct SyscallTable;
namespace playground {

class Library {
  friend class Maps;
 public:
  typedef Maps::string string;

  Library();
  ~Library();

  void setLibraryInfo(Maps* maps) {
    if (!maps_) {
      maps_ = maps;
    }
  }

  void addMemoryRange(void* start, void* stop, Elf_Addr offset,
                      int prot, int isVDSO) {
    isVDSO_ = isVDSO;
    RangeMap::const_iterator iter = memory_ranges_.find(offset);
    if (iter != memory_ranges_.end()) {
      // It is possible to have overlapping mappings. This is particularly
      // likely to happen with very small programs or libraries. If it does
      // happen, we really only care about the text segment. Look for a
      // mapping that is mapped executable.
      if ((prot & PROT_EXEC) == 0) {
        return;
      }
    }
    memory_ranges_.insert(std::make_pair(offset, Range(start, stop, prot)));
  }

  char *get(Elf_Addr offset, char *buf, size_t len);
  string get(Elf_Addr offset);
  char *getOriginal(Elf_Addr offset, char *buf, size_t len);
  string getOriginal(Elf_Addr offset);

  template<class T>T* get(Elf_Addr offset, T* t) {
    if (!valid_) {
      memset(t, 0, sizeof(T));
      return NULL;
    }
    return reinterpret_cast<T *>(get(offset, reinterpret_cast<char *>(t),
                                     sizeof(T)));
  }

  template<class T>T* getOriginal(Elf_Addr offset, T* t) {
    if (!valid_) {
      memset(t, 0, sizeof(T));
      return NULL;
    }
    return reinterpret_cast<T *>(getOriginal(offset,
                                             reinterpret_cast<char *>(t),
                                             sizeof(T)));
  }

  template<class T>bool set(void *addr, T* value) {
    if (!valid_) {
      return false;
    }
    *reinterpret_cast<T *>(addr) = *value;
    return true;
  }

  template<class T>bool set(Elf_Addr offset, T* value) {
    if (!valid_) {
      return false;
    }
    RangeMap::const_iterator iter = memory_ranges_.lower_bound(offset);
    if (iter == memory_ranges_.end()) {
      return false;
    }
    offset -= iter->first;
    if (offset >
        reinterpret_cast<char *>(iter->second.stop) -
        reinterpret_cast<char *>(iter->second.start) -
        sizeof(T)) {
      return false;
    }
    *reinterpret_cast<T *>(
        reinterpret_cast<char *>(iter->second.start) + offset) = *value;
    return true;
  }

  bool parseElf();
  const Elf_Ehdr* getEhdr();
  const Elf_Shdr* getSection(const string& section);
  void makeWritable(bool state) const;
  void patchSystemCalls();
  void patchSystemCallsInRange(char* start, char* stop,
                               char** extraSpace, int* extraLength);
  bool isVDSO() const { return isVDSO_; }

 protected:
  bool parseSymbols();

 private:
  class GreaterThan : public std::binary_function<Elf_Addr, Elf_Addr, bool> {
    // We create the RangeMap with a GreaterThan rather than the default
    // comparator, as that allows us to use lower_bound() to find memory
    // mappings.
   public:
    bool operator() (Elf_Addr s1, Elf_Addr s2) const {
      return s1 > s2;
    }
  };

  struct Range {
    Range(void* start, void* stop, int prot) :
        start(start), stop(stop), prot(prot) { }
    void* start;
    void* stop;
    int   prot;
  };

  typedef std::map<Elf_Addr, Range, GreaterThan,
                   SystemAllocator<std::pair<const Elf_Addr,
                                             Range> > > RangeMap;
  typedef std::map<string, std::pair<int, Elf_Shdr>, std::less<string>,
                   SystemAllocator<std::pair<const string,
                                             std::pair<int, Elf_Shdr> > > >
                   SectionTable;
  typedef std::map<string, Elf_Sym, std::less<string>,
                   SystemAllocator<std::pair<const string,
                                             Elf_Sym> > > SymbolTable;

  char* getBytes(char* dst, const char* src, ssize_t len);
  static bool isSafeInsn(unsigned short insn);
  static char* getScratchSpace(const Maps* maps, char* near, int needed,
                               char** extraSpace, int* extraLength);
  static void patchSystemCallsInFunction(const Maps* maps, int vsys_offset,
                                         char* start, char* end,
                                         char** extraSpace, int* extraLength);
  int  patchVSystemCalls();
  void patchVDSO(char** extraSpace, int* extraLength);

  RangeMap        memory_ranges_;
  bool            valid_;
  bool            isVDSO_;
  char*           asr_offset_;
  int             vsys_offset_;
  Elf_Ehdr        ehdr_;
  SectionTable    section_table_;
  SymbolTable     symbols_;
  char*           image_;
  size_t          image_size_;
  Maps*           maps_;
  static char*    __kernel_vsyscall;
  static char*    __kernel_sigreturn;
  static char*    __kernel_rt_sigreturn;
};

} // namespace

#endif // LIBRARY_H__