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29
30// macho_walker.cc: Iterate over the load commands in a mach-o file
31//
32// See macho_walker.h for documentation
33//
34// Author: Dan Waylonis
35
36extern "C" {  // necessary for Leopard
37  #include <assert.h>
38  #include <fcntl.h>
39  #include <mach-o/arch.h>
40  #include <mach-o/loader.h>
41  #include <mach-o/swap.h>
42  #include <string.h>
43  #include <unistd.h>
44}
45
46#include "common/mac/byteswap.h"
47#include "common/mac/macho_walker.h"
48#include "common/mac/macho_utilities.h"
49
50namespace MacFileUtilities {
51
52MachoWalker::MachoWalker(const char *path, LoadCommandCallback callback,
53                         void *context)
54    : file_(-1),
55      memory_(NULL),
56      memory_size_(0),
57      callback_(callback),
58      callback_context_(context),
59      current_header_(NULL),
60      current_header_size_(0),
61      current_header_offset_(0) {
62  file_ = open(path, O_RDONLY);
63}
64
65MachoWalker::MachoWalker(void *memory, size_t size,
66                         LoadCommandCallback callback, void *context)
67    : file_(-1),
68      memory_(memory),
69      memory_size_(size),
70      callback_(callback),
71      callback_context_(context),
72      current_header_(NULL),
73      current_header_size_(0),
74      current_header_offset_(0) {
75}
76
77MachoWalker::~MachoWalker() {
78  if (file_ != -1)
79    close(file_);
80}
81
82bool MachoWalker::WalkHeader(cpu_type_t cpu_type, cpu_subtype_t cpu_subtype) {
83  cpu_type_t valid_cpu_type = cpu_type;
84  cpu_subtype_t valid_cpu_subtype = cpu_subtype;
85  // if |cpu_type| is 0, use the native cpu type.
86  if (cpu_type == 0) {
87    const NXArchInfo *arch = NXGetLocalArchInfo();
88    assert(arch);
89    valid_cpu_type = arch->cputype;
90    valid_cpu_subtype = CPU_SUBTYPE_MULTIPLE;
91  }
92  off_t offset;
93  if (FindHeader(valid_cpu_type, valid_cpu_subtype, offset)) {
94    if (cpu_type & CPU_ARCH_ABI64)
95      return WalkHeader64AtOffset(offset);
96
97    return WalkHeaderAtOffset(offset);
98  }
99
100  return false;
101}
102
103bool MachoWalker::ReadBytes(void *buffer, size_t size, off_t offset) {
104  if (memory_) {
105    if (offset < 0)
106      return false;
107    bool result = true;
108    if (offset + size > memory_size_) {
109      if (static_cast<size_t>(offset) >= memory_size_)
110        return false;
111      size = memory_size_ - static_cast<size_t>(offset);
112      result = false;
113    }
114    memcpy(buffer, static_cast<char *>(memory_) + offset, size);
115    return result;
116  } else {
117    return pread(file_, buffer, size, offset) == (ssize_t)size;
118  }
119}
120
121bool MachoWalker::CurrentHeader(struct mach_header_64 *header, off_t *offset) {
122  if (current_header_) {
123    memcpy(header, current_header_, sizeof(mach_header_64));
124    *offset = current_header_offset_;
125    return true;
126  }
127
128  return false;
129}
130
131bool MachoWalker::FindHeader(cpu_type_t cpu_type,
132                             cpu_subtype_t cpu_subtype,
133                             off_t &offset) {
134  // Read the magic bytes that's common amongst all mach-o files
135  uint32_t magic;
136  if (!ReadBytes(&magic, sizeof(magic), 0))
137    return false;
138
139  offset = sizeof(magic);
140
141  // Figure out what type of file we've got
142  bool is_fat = false;
143  if (magic == FAT_MAGIC || magic == FAT_CIGAM) {
144    is_fat = true;
145  }
146  else if (magic != MH_MAGIC && magic != MH_CIGAM && magic != MH_MAGIC_64 &&
147           magic != MH_CIGAM_64) {
148    return false;
149  }
150
151  if (!is_fat) {
152    // If we don't have a fat header, check if the cpu type matches the single
153    // header
154    struct mach_header header;
155    if (!ReadBytes(&header, sizeof(header), 0))
156      return false;
157
158    if (magic == MH_CIGAM || magic == MH_CIGAM_64)
159      swap_mach_header(&header, NXHostByteOrder());
160
161    if (cpu_type != header.cputype ||
162        (cpu_subtype != CPU_SUBTYPE_MULTIPLE &&
163         cpu_subtype != header.cpusubtype)) {
164      return false;
165    }
166
167    offset = 0;
168    return true;
169  } else {
170    // Read the fat header and find an appropriate architecture
171    offset = 0;
172    struct fat_header fat;
173    if (!ReadBytes(&fat, sizeof(fat), offset))
174      return false;
175
176    if (NXHostByteOrder() != NX_BigEndian)
177      swap_fat_header(&fat, NXHostByteOrder());
178
179    offset += sizeof(fat);
180
181    // Search each architecture for the desired one
182    struct fat_arch arch;
183    for (uint32_t i = 0; i < fat.nfat_arch; ++i) {
184      if (!ReadBytes(&arch, sizeof(arch), offset))
185        return false;
186
187      if (NXHostByteOrder() != NX_BigEndian)
188        swap_fat_arch(&arch, 1, NXHostByteOrder());
189
190      if (arch.cputype == cpu_type &&
191          (cpu_subtype == CPU_SUBTYPE_MULTIPLE ||
192           arch.cpusubtype == cpu_subtype)) {
193        offset = arch.offset;
194        return true;
195      }
196
197      offset += sizeof(arch);
198    }
199  }
200
201  return false;
202}
203
204bool MachoWalker::WalkHeaderAtOffset(off_t offset) {
205  struct mach_header header;
206  if (!ReadBytes(&header, sizeof(header), offset))
207    return false;
208
209  bool swap = (header.magic == MH_CIGAM);
210  if (swap)
211    swap_mach_header(&header, NXHostByteOrder());
212
213  // Copy the data into the mach_header_64 structure.  Since the 32-bit and
214  // 64-bit only differ in the last field (reserved), this is safe to do.
215  struct mach_header_64 header64;
216  memcpy((void *)&header64, (const void *)&header, sizeof(header));
217  header64.reserved = 0;
218
219  current_header_ = &header64;
220  current_header_size_ = sizeof(header); // 32-bit, not 64-bit
221  current_header_offset_ = offset;
222  offset += current_header_size_;
223  bool result = WalkHeaderCore(offset, header.ncmds, swap);
224  current_header_ = NULL;
225  current_header_size_ = 0;
226  current_header_offset_ = 0;
227  return result;
228}
229
230bool MachoWalker::WalkHeader64AtOffset(off_t offset) {
231  struct mach_header_64 header;
232  if (!ReadBytes(&header, sizeof(header), offset))
233    return false;
234
235  bool swap = (header.magic == MH_CIGAM_64);
236  if (swap)
237    breakpad_swap_mach_header_64(&header, NXHostByteOrder());
238
239  current_header_ = &header;
240  current_header_size_ = sizeof(header);
241  current_header_offset_ = offset;
242  offset += current_header_size_;
243  bool result = WalkHeaderCore(offset, header.ncmds, swap);
244  current_header_ = NULL;
245  current_header_size_ = 0;
246  current_header_offset_ = 0;
247  return result;
248}
249
250bool MachoWalker::WalkHeaderCore(off_t offset, uint32_t number_of_commands,
251                                 bool swap) {
252  for (uint32_t i = 0; i < number_of_commands; ++i) {
253    struct load_command cmd;
254    if (!ReadBytes(&cmd, sizeof(cmd), offset))
255      return false;
256
257    if (swap)
258      swap_load_command(&cmd, NXHostByteOrder());
259
260    // Call the user callback
261    if (callback_ && !callback_(this, &cmd, offset, swap, callback_context_))
262      break;
263
264    offset += cmd.cmdsize;
265  }
266
267  return true;
268}
269
270}  // namespace MacFileUtilities
271