summaryrefslogtreecommitdiffstats
path: root/mozglue/linker/ElfLoader.h
blob: 033805460514764e10dfb83f1b110ec97728d3b7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef ElfLoader_h
#define ElfLoader_h

#include <vector>
#include <dlfcn.h>
#include <signal.h>
#include "mozilla/RefCounted.h"
#include "mozilla/RefPtr.h"
#include "mozilla/UniquePtr.h"
#include "Zip.h"
#include "Elfxx.h"
#include "Mappable.h"

/**
 * dlfcn.h replacement functions
 */
extern "C" {
  void *__wrap_dlopen(const char *path, int flags);
  const char *__wrap_dlerror(void);
  void *__wrap_dlsym(void *handle, const char *symbol);
  int __wrap_dlclose(void *handle);

#ifndef HAVE_DLADDR
  typedef struct {
    const char *dli_fname;
    void *dli_fbase;
    const char *dli_sname;
    void *dli_saddr;
  } Dl_info;
#endif
  int __wrap_dladdr(void *addr, Dl_info *info);

  struct dl_phdr_info {
    Elf::Addr dlpi_addr;
    const char *dlpi_name;
    const Elf::Phdr *dlpi_phdr;
    Elf::Half dlpi_phnum;
  };

  typedef int (*dl_phdr_cb)(struct dl_phdr_info *, size_t, void *);
  int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data);

#ifdef __ARM_EABI__
  const void *__wrap___gnu_Unwind_Find_exidx(void *pc, int *pcount);
#endif

/**
 * faulty.lib public API
 */
MFBT_API size_t
__dl_get_mappable_length(void *handle);

MFBT_API void *
__dl_mmap(void *handle, void *addr, size_t length, off_t offset);

MFBT_API void
__dl_munmap(void *handle, void *addr, size_t length);

MFBT_API bool
IsSignalHandlingBroken();

}

/* Forward declarations for use in LibHandle */
class BaseElf;
class CustomElf;
class SystemElf;

/**
 * Specialize RefCounted template for LibHandle. We may get references to
 * LibHandles during the execution of their destructor, so we need
 * RefCounted<LibHandle>::Release to support some reentrancy. See further
 * below.
 */
class LibHandle;

namespace mozilla {
namespace detail {

template <> inline void RefCounted<LibHandle, AtomicRefCount>::Release() const;

template <> inline RefCounted<LibHandle, AtomicRefCount>::~RefCounted()
{
  MOZ_ASSERT(mRefCnt == 0x7fffdead);
}

} /* namespace detail */
} /* namespace mozilla */

/**
 * Abstract class for loaded libraries. Libraries may be loaded through the
 * system linker or this linker, both cases will be derived from this class.
 */
class LibHandle: public mozilla::external::AtomicRefCounted<LibHandle>
{
public:
  MOZ_DECLARE_REFCOUNTED_TYPENAME(LibHandle)
  /**
   * Constructor. Takes the path of the loaded library and will store a copy
   * of the leaf name.
   */
  LibHandle(const char *path)
  : directRefCnt(0), path(path ? strdup(path) : nullptr), mappable(nullptr) { }

  /**
   * Destructor.
   */
  virtual ~LibHandle();

  /**
   * Returns the pointer to the address to which the given symbol resolves
   * inside the library. It is not supposed to resolve the symbol in other
   * libraries, although in practice, it will for system libraries.
   */
  virtual void *GetSymbolPtr(const char *symbol) const = 0;

  /**
   * Returns whether the given address is part of the virtual address space
   * covered by the loaded library.
   */
  virtual bool Contains(void *addr) const = 0;

  /**
   * Returns the base address of the loaded library.
   */
  virtual void *GetBase() const = 0;

  /**
   * Returns the file name of the library without the containing directory.
   */
  const char *GetName() const;

  /**
   * Returns the full path of the library, when available. Otherwise, returns
   * the file name.
   */
  const char *GetPath() const
  {
    return path;
  }

  /**
   * Library handles can be referenced from other library handles or
   * externally (when dlopen()ing using this linker). We need to be
   * able to distinguish between the two kind of referencing for better
   * bookkeeping.
   */
  void AddDirectRef()
  {
    ++directRefCnt;
    mozilla::external::AtomicRefCounted<LibHandle>::AddRef();
  }

  /**
   * Releases a direct reference, and returns whether there are any direct
   * references left.
   */
  bool ReleaseDirectRef()
  {
    bool ret = false;
    if (directRefCnt) {
      MOZ_ASSERT(directRefCnt <=
                 mozilla::external::AtomicRefCounted<LibHandle>::refCount());
      if (--directRefCnt)
        ret = true;
      mozilla::external::AtomicRefCounted<LibHandle>::Release();
    }
    return ret;
  }

  /**
   * Returns the number of direct references
   */
  MozRefCountType DirectRefCount()
  {
    return directRefCnt;
  }

  /**
   * Returns the complete size of the file or stream behind the library
   * handle.
   */
  size_t GetMappableLength() const;

  /**
   * Returns a memory mapping of the file or stream behind the library
   * handle.
   */
  void *MappableMMap(void *addr, size_t length, off_t offset) const;

  /**
   * Unmaps a memory mapping of the file or stream behind the library
   * handle.
   */
  void MappableMUnmap(void *addr, size_t length) const;

#ifdef __ARM_EABI__
  /**
   * Find the address and entry count of the ARM.exidx section
   * associated with the library
   */
  virtual const void *FindExidx(int *pcount) const = 0;
#endif

  /**
   * Shows some stats about the Mappable instance. The when argument is to be
   * used by the caller to give an identifier of the when the stats call is
   * made.
   */
  virtual void stats(const char *when) const { };

protected:
  /**
   * Returns a mappable object for use by MappableMMap and related functions.
   */
  virtual Mappable *GetMappable() const = 0;

  /**
   * Returns the instance, casted as the wanted type. Returns nullptr if
   * that's not the actual type. (short of a better way to do this without
   * RTTI)
   */
  friend class ElfLoader;
  friend class CustomElf;
  friend class SEGVHandler;
  virtual BaseElf *AsBaseElf() { return nullptr; }
  virtual SystemElf *AsSystemElf() { return nullptr; }

private:
  MozRefCountType directRefCnt;
  char *path;

  /* Mappable object keeping the result of GetMappable() */
  mutable RefPtr<Mappable> mappable;
};

/**
 * Specialized RefCounted<LibHandle>::Release. Under normal operation, when
 * mRefCnt reaches 0, the LibHandle is deleted. Its mRefCnt is however
 * increased to 1 on normal builds, and 0x7fffdead on debug builds so that the
 * LibHandle can still be referenced while the destructor is executing. The
 * mRefCnt is allowed to grow > 0x7fffdead, but not to decrease under that
 * value, which would mean too many Releases from within the destructor.
 */
namespace mozilla {
namespace detail {

template <> inline void RefCounted<LibHandle, AtomicRefCount>::Release() const {
#ifdef DEBUG
  if (mRefCnt > 0x7fff0000)
    MOZ_ASSERT(mRefCnt > 0x7fffdead);
#endif
  MOZ_ASSERT(mRefCnt > 0);
  if (mRefCnt > 0) {
    if (0 == --mRefCnt) {
#ifdef DEBUG
      mRefCnt = 0x7fffdead;
#else
      mRefCnt = 1;
#endif
      delete static_cast<const LibHandle*>(this);
    }
  }
}

} /* namespace detail */
} /* namespace mozilla */

/**
 * Class handling libraries loaded by the system linker
 */
class SystemElf: public LibHandle
{
public:
  /**
   * Returns a new SystemElf for the given path. The given flags are passed
   * to dlopen().
   */
  static already_AddRefed<LibHandle> Load(const char *path, int flags);

  /**
   * Inherited from LibHandle
   */
  virtual ~SystemElf();
  virtual void *GetSymbolPtr(const char *symbol) const;
  virtual bool Contains(void *addr) const { return false; /* UNIMPLEMENTED */ }
  virtual void *GetBase() const { return nullptr; /* UNIMPLEMENTED */ }

#ifdef __ARM_EABI__
  virtual const void *FindExidx(int *pcount) const;
#endif

protected:
  virtual Mappable *GetMappable() const;

  /**
   * Returns the instance, casted as SystemElf. (short of a better way to do
   * this without RTTI)
   */
  friend class ElfLoader;
  virtual SystemElf *AsSystemElf() { return this; }

  /**
   * Remove the reference to the system linker handle. This avoids dlclose()
   * being called when the instance is destroyed.
   */
  void Forget()
  {
    dlhandle = nullptr;
  }

private:
  /**
   * Private constructor
   */
  SystemElf(const char *path, void *handle)
  : LibHandle(path), dlhandle(handle) { }

  /* Handle as returned by system dlopen() */
  void *dlhandle;
};

/**
 * The ElfLoader registers its own SIGSEGV handler to handle segmentation
 * faults within the address space of the loaded libraries. It however
 * allows a handler to be set for faults in other places, and redispatches
 * to the handler set through signal() or sigaction().
 */
class SEGVHandler
{
public:
  bool hasRegisteredHandler() {
    if (! initialized)
      FinishInitialization();
    return registeredHandler;
  }

  bool isSignalHandlingBroken() {
    return signalHandlingBroken;
  }

  static int __wrap_sigaction(int signum, const struct sigaction *act,
                              struct sigaction *oldact);

protected:
  SEGVHandler();
  ~SEGVHandler();

private:

  /**
   * The constructor doesn't do all initialization, and the tail is done
   * at a later time.
   */
  void FinishInitialization();

  /**
   * SIGSEGV handler registered with __wrap_signal or __wrap_sigaction.
   */
  struct sigaction action;
  
  /**
   * ElfLoader SIGSEGV handler.
   */
  static void handler(int signum, siginfo_t *info, void *context);

  /**
   * Temporary test handler.
   */
  static void test_handler(int signum, siginfo_t *info, void *context);

  /**
   * Size of the alternative stack. The printf family requires more than 8KB
   * of stack, and our signal handler may print a few things.
   */
  static const size_t stackSize = 12 * 1024;

  /**
   * Alternative stack information used before initialization.
   */
  stack_t oldStack;

  /**
   * Pointer to an alternative stack for signals. Only set if oldStack is
   * not set or not big enough.
   */
  MappedPtr stackPtr;

  bool initialized;
  bool registeredHandler;
  bool signalHandlingBroken;
  bool signalHandlingSlow;
};

/**
 * Elf Loader class in charge of loading and bookkeeping libraries.
 */
class ElfLoader: public SEGVHandler
{
public:
  /**
   * The Elf Loader instance
   */
  static ElfLoader Singleton;

  /**
   * Loads the given library with the given flags. Equivalent to dlopen()
   * The extra "parent" argument optionally gives the handle of the library
   * requesting the given library to be loaded. The loader may look in the
   * directory containing that parent library for the library to load.
   */
  already_AddRefed<LibHandle> Load(const char *path, int flags,
                                        LibHandle *parent = nullptr);

  /**
   * Returns the handle of the library containing the given address in
   * its virtual address space, i.e. the library handle for which
   * LibHandle::Contains returns true. Its purpose is to allow to
   * implement dladdr().
   */
  already_AddRefed<LibHandle> GetHandleByPtr(void *addr);

  /**
   * Returns a Mappable object for the path. Paths in the form
   *   /foo/bar/baz/archive!/directory/lib.so
   * try to load the directory/lib.so in /foo/bar/baz/archive, provided
   * that file is a Zip archive.
   */
  static Mappable *GetMappableFromPath(const char *path);

  void ExpectShutdown(bool val) { expect_shutdown = val; }
  bool IsShutdownExpected() { return expect_shutdown; }

private:
  bool expect_shutdown;

protected:
  /**
   * Registers the given handle. This method is meant to be called by
   * LibHandle subclass creators.
   */
  void Register(LibHandle *handle);
  void Register(CustomElf *handle);

  /**
   * Forget about the given handle. This method is meant to be called by
   * LibHandle subclass destructors.
   */
  void Forget(LibHandle *handle);
  void Forget(CustomElf *handle);

  /* Last error. Used for dlerror() */
  friend class SystemElf;
  friend const char *__wrap_dlerror(void);
  friend void *__wrap_dlsym(void *handle, const char *symbol);
  friend int __wrap_dlclose(void *handle);
  const char *lastError;

private:
  ElfLoader() : expect_shutdown(true) {}
  ~ElfLoader();

  /* Initialization code that can't run during static initialization. */
  void Init();

  /* System loader handle for the library/program containing our code. This
   * is used to resolve wrapped functions. */
  RefPtr<LibHandle> self_elf;

  /* Bookkeeping */
  typedef std::vector<LibHandle *> LibHandleList;
  LibHandleList handles;

protected:
  friend class CustomElf;
  friend class LoadedElf;
  /**
   * Show some stats about Mappables in CustomElfs. The when argument is to
   * be used by the caller to give an identifier of the when the stats call
   * is made.
   */
  static void stats(const char *when);

  /* Definition of static destructors as to be used for C++ ABI compatibility */
  typedef void (*Destructor)(void *object);

  /**
   * C++ ABI makes static initializers register destructors through a specific
   * atexit interface. On glibc/linux systems, the dso_handle is a pointer
   * within a given library. On bionic/android systems, it is an undefined
   * symbol. Making sense of the value is not really important, and all that
   * is really important is that it is different for each loaded library, so
   * that they can be discriminated when shutting down. For convenience, on
   * systems where the dso handle is a symbol, that symbol is resolved to
   * point at corresponding CustomElf.
   *
   * Destructors are registered with __*_atexit with an associated object to
   * be passed as argument when it is called.
   *
   * When __cxa_finalize is called, destructors registered for the given
   * DSO handle are called in the reverse order they were registered.
   */
#ifdef __ARM_EABI__
  static int __wrap_aeabi_atexit(void *that, Destructor destructor,
                                 void *dso_handle);
#else
  static int __wrap_cxa_atexit(Destructor destructor, void *that,
                               void *dso_handle);
#endif

  static void __wrap_cxa_finalize(void *dso_handle);

  /**
   * Registered destructor. Keeps track of the destructor function pointer,
   * associated object to call it with, and DSO handle.
   */
  class DestructorCaller {
  public:
    DestructorCaller(Destructor destructor, void *object, void *dso_handle)
    : destructor(destructor), object(object), dso_handle(dso_handle) { }

    /**
     * Call the destructor function with the associated object.
     * Call only once, see CustomElf::~CustomElf.
     */
    void Call();

    /**
     * Returns whether the destructor is associated to the given DSO handle
     */
    bool IsForHandle(void *handle) const
    {
      return handle == dso_handle;
    }

  private:
    Destructor destructor;
    void *object;
    void *dso_handle;
  };

private:
  /* Keep track of all registered destructors */
  std::vector<DestructorCaller> destructors;

  /* Forward declaration, see further below */
  class DebuggerHelper;
public:
  /* Loaded object descriptor for the debugger interface below*/
  struct link_map {
    /* Base address of the loaded object. */
    const void *l_addr;
    /* File name */
    const char *l_name;
    /* Address of the PT_DYNAMIC segment. */
    const void *l_ld;

  private:
    friend class ElfLoader::DebuggerHelper;
    /* Double linked list of loaded objects. */
    link_map *l_next, *l_prev;
  };

private:
  /* Data structure used by the linker to give details about shared objects it
   * loaded to debuggers. This is normally defined in link.h, but Android
   * headers lack this file. */
  struct r_debug {
    /* Version number of the protocol. */
    int r_version;

    /* Head of the linked list of loaded objects. */
    link_map *r_map;

    /* Function to be called when updates to the linked list of loaded objects
     * are going to occur. The function is to be called before and after
     * changes. */
    void (*r_brk)(void);

    /* Indicates to the debugger what state the linked list of loaded objects
     * is in when the function above is called. */
    enum {
      RT_CONSISTENT, /* Changes are complete */
      RT_ADD,        /* Beginning to add a new object */
      RT_DELETE      /* Beginning to remove an object */
    } r_state;
  };

  /* Memory representation of ELF Auxiliary Vectors */
  struct AuxVector {
    Elf::Addr type;
    Elf::Addr value;
  };

  /* Helper class used to integrate libraries loaded by this linker in
   * r_debug */
  class DebuggerHelper
  {
  public:
    DebuggerHelper();

    void Init(AuxVector *auvx);

    operator bool()
    {
      return dbg;
    }

    /* Make the debugger aware of a new loaded object */
    void Add(link_map *map);

    /* Make the debugger aware of the unloading of an object */
    void Remove(link_map *map);

    /* Iterates over all link_maps */
    class iterator
    {
    public:
      const link_map *operator ->() const
      {
        return item;
      }

      const link_map &operator ++()
      {
        item = item->l_next;
        return *item;
      }

      bool operator<(const iterator &other) const
      {
        if (other.item == nullptr)
          return item ? true : false;
        MOZ_CRASH("DebuggerHelper::iterator::operator< called with something else than DebuggerHelper::end()");
      }
    protected:
      friend class DebuggerHelper;
      iterator(const link_map *item): item(item) { }

    private:
      const link_map *item;
    };

    iterator begin() const
    {
      return iterator(dbg ? dbg->r_map : nullptr);
    }

    iterator end() const
    {
      return iterator(nullptr);
    }

  private:
    r_debug *dbg;
    link_map *firstAdded;
  };
  friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data);
  DebuggerHelper dbg;
};

#endif /* ElfLoader_h */