breakpad/src/common/mac/macho_walker.cc

// Copyright (c) 2006, Google Inc.
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// macho_walker.cc: Iterate over the load commands in a mach-o file
//
// See macho_walker.h for documentation
//
// Author: Dan Waylonis

extern "C" {  // necessary for Leopard
  #include <assert.h>
  #include <fcntl.h>
  #include <mach-o/arch.h>
  #include <mach-o/loader.h>
  #include <mach-o/swap.h>
  #include <string.h>
  #include <unistd.h>
}

#include "common/mac/byteswap.h"
#include "common/mac/macho_walker.h"
#include "common/mac/macho_utilities.h"

namespace MacFileUtilities {

MachoWalker::MachoWalker(const char *path, LoadCommandCallback callback,
                         void *context)
    : callback_(callback),
      callback_context_(context) {
  file_ = open(path, O_RDONLY);
}

MachoWalker::~MachoWalker() {
  if (file_ != -1)
    close(file_);
}

int MachoWalker::ValidateCPUType(int cpu_type) {
  // If the user didn't specify, use the local architecture.
  if (cpu_type == 0) {
    const NXArchInfo *arch = NXGetLocalArchInfo();
    assert(arch);
    cpu_type = arch->cputype;
  }

  return cpu_type;
}

bool MachoWalker::WalkHeader(int cpu_type) {
  int valid_cpu_type = ValidateCPUType(cpu_type);
  off_t offset;
  if (FindHeader(valid_cpu_type, offset)) {
    if (cpu_type & CPU_ARCH_ABI64)
      return WalkHeader64AtOffset(offset);

    return WalkHeaderAtOffset(offset);
  }

  return false;
}

bool MachoWalker::ReadBytes(void *buffer, size_t size, off_t offset) {
  return pread(file_, buffer, size, offset) == (ssize_t)size;
}

bool MachoWalker::CurrentHeader(struct mach_header_64 *header, off_t *offset) {
  if (current_header_) {
    memcpy(header, current_header_, sizeof(mach_header_64));
    *offset = current_header_offset_;
    return true;
  }
  
  return false;
}

bool MachoWalker::FindHeader(int cpu_type, off_t &offset) {
  int valid_cpu_type = ValidateCPUType(cpu_type);
  // Read the magic bytes that's common amongst all mach-o files
  uint32_t magic;
  if (!ReadBytes(&magic, sizeof(magic), 0))
    return false;

  offset = sizeof(magic);

  // Figure out what type of file we've got
  bool is_fat = false;
  if (magic == FAT_MAGIC || magic == FAT_CIGAM) {
    is_fat = true;    
  }
  else if (magic != MH_MAGIC && magic != MH_CIGAM && magic != MH_MAGIC_64 &&
           magic != MH_CIGAM_64) {
    return false;
  }

  if (!is_fat) {
    // If we don't have a fat header, check if the cpu type matches the single
    // header
    cpu_type_t header_cpu_type;
    if (!ReadBytes(&header_cpu_type, sizeof(header_cpu_type), offset))
      return false;

    if (magic == MH_CIGAM || magic == MH_CIGAM_64)
      header_cpu_type = ByteSwap(header_cpu_type);

    if (valid_cpu_type != header_cpu_type)
      return false;

    offset = 0;
    return true;
  } else {
    // Read the fat header and find an appropriate architecture
    offset = 0;
    struct fat_header fat;
    if (!ReadBytes(&fat, sizeof(fat), offset))
      return false;

    if (NXHostByteOrder() != NX_BigEndian)
      swap_fat_header(&fat, NXHostByteOrder());

    offset += sizeof(fat);

    // Search each architecture for the desired one
    struct fat_arch arch;
    for (uint32_t i = 0; i < fat.nfat_arch; ++i) {
      if (!ReadBytes(&arch, sizeof(arch), offset))
        return false;

      if (NXHostByteOrder() != NX_BigEndian)
        swap_fat_arch(&arch, 1, NXHostByteOrder());

      if (arch.cputype == valid_cpu_type) {
        offset = arch.offset;
        return true;
      }

      offset += sizeof(arch);
    }
  }

  return false;
}

bool MachoWalker::WalkHeaderAtOffset(off_t offset) {
  struct mach_header header;
  if (!ReadBytes(&header, sizeof(header), offset))
    return false;

  bool swap = (header.magic == MH_CIGAM);
  if (swap)
    swap_mach_header(&header, NXHostByteOrder());
  
  // Copy the data into the mach_header_64 structure.  Since the 32-bit and
  // 64-bit only differ in the last field (reserved), this is safe to do.
  struct mach_header_64 header64;
  memcpy((void *)&header64, (const void *)&header, sizeof(header));
  header64.reserved = 0;
  
  current_header_ = &header64;
  current_header_size_ = sizeof(header); // 32-bit, not 64-bit
  current_header_offset_ = offset;
  offset += current_header_size_;
  bool result = WalkHeaderCore(offset, header.ncmds, swap);
  current_header_ = NULL;
  current_header_size_ = 0;
  current_header_offset_ = 0;
  return result;
}

bool MachoWalker::WalkHeader64AtOffset(off_t offset) {
  struct mach_header_64 header;
  if (!ReadBytes(&header, sizeof(header), offset))
    return false;

  bool swap = (header.magic == MH_CIGAM_64);
  if (swap)
    breakpad_swap_mach_header_64(&header, NXHostByteOrder());

  current_header_ = &header;
  current_header_size_ = sizeof(header);
  current_header_offset_ = offset;
  offset += current_header_size_;
  bool result = WalkHeaderCore(offset, header.ncmds, swap);
  current_header_ = NULL;
  current_header_size_ = 0;
  current_header_offset_ = 0;
  return result;
}

bool MachoWalker::WalkHeaderCore(off_t offset, uint32_t number_of_commands,
                                 bool swap) {
  for (uint32_t i = 0; i < number_of_commands; ++i) {
    struct load_command cmd;
    if (!ReadBytes(&cmd, sizeof(cmd), offset))
      return false;

    if (swap)
      swap_load_command(&cmd, NXHostByteOrder());

    // Call the user callback
    if (callback_ && !callback_(this, &cmd, offset, swap, callback_context_))
      break;

    offset += cmd.cmdsize;
  }

  return true;
}

}  // namespace MacFileUtilities