mfbt/Assertions.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Implementations of runtime and static assertion macros for C and C++. */
   8
   9 #ifndef mozilla_Assertions_h
  10 #define mozilla_Assertions_h
  11
  12 #if defined(MOZILLA_INTERNAL_API) && defined(__cplusplus)
  13 #define MOZ_DUMP_ASSERTION_STACK
  14 #endif
  15
  16 #include "mozilla/Attributes.h"
  17 #include "mozilla/Compiler.h"
  18 #include "mozilla/Likely.h"
  19 #include "mozilla/MacroArgs.h"
  20 #ifdef MOZ_DUMP_ASSERTION_STACK
  21 #include "nsTraceRefcnt.h"
  22 #endif
  23
  24 #include <stddef.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #ifdef WIN32
  28    /*
  29     * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  30     * further depends on <windef.h>.  We hardcode these few definitions manually
  31     * because those headers clutter the global namespace with a significant
  32     * number of undesired macros and symbols.
  33     */
  34 #  ifdef __cplusplus
  35 extern "C" {
  36 #  endif
  37 __declspec(dllimport) int __stdcall
  38 TerminateProcess(void* hProcess, unsigned int uExitCode);
  39 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  40 #  ifdef __cplusplus
  41 }
  42 #  endif
  43 #else
  44 #  include <signal.h>
  45 #endif
  46 #ifdef ANDROID
  47 #  include <android/log.h>
  48 #endif
  49
  50 /*
  51  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
  52  * In C++11, static_assert is provided by the compiler to the same effect.
  53  * This can be useful when you make certain assumptions about what must hold for
  54  * optimal, or even correct, behavior.  For example, you might assert that the
  55  * size of a struct is a multiple of the target architecture's word size:
  56  *
  57  *   struct S { ... };
  58  *   // C
  59  *   MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
  60  *                     "S should be a multiple of word size for efficiency");
  61  *   // C++11
  62  *   static_assert(sizeof(S) % sizeof(size_t) == 0,
  63  *                 "S should be a multiple of word size for efficiency");
  64  *
  65  * This macro can be used in any location where both an extern declaration and a
  66  * typedef could be used.
  67  */
  68 #ifndef __cplusplus
  69    /*
  70     * Some of the definitions below create an otherwise-unused typedef.  This
  71     * triggers compiler warnings with some versions of gcc, so mark the typedefs
  72     * as permissibly-unused to disable the warnings.
  73     */
  74 #  if defined(__GNUC__)
  75 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
  76 #  else
  77 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
  78 #  endif
  79 #  define MOZ_STATIC_ASSERT_GLUE1(x, y)          x##y
  80 #  define MOZ_STATIC_ASSERT_GLUE(x, y)           MOZ_STATIC_ASSERT_GLUE1(x, y)
  81 #  if defined(__SUNPRO_CC)
  82      /*
  83       * The Sun Studio C++ compiler is buggy when declaring, inside a function,
  84       * another extern'd function with an array argument whose length contains a
  85       * sizeof, triggering the error message "sizeof expression not accepted as
  86       * size of array parameter".  This bug (6688515, not public yet) would hit
  87       * defining moz_static_assert as a function, so we always define an extern
  88       * array for Sun Studio.
  89       *
  90       * We include the line number in the symbol name in a best-effort attempt
  91       * to avoid conflicts (see below).
  92       */
  93 #    define MOZ_STATIC_ASSERT(cond, reason) \
  94        extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]
  95 #  elif defined(__COUNTER__)
  96      /*
  97       * If there was no preferred alternative, use a compiler-agnostic version.
  98       *
  99       * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
 100       * in both |extern "C"| and normal C++ in the same translation unit.  (Alas
 101       * |extern "C"| isn't allowed in a function.)  The only affected compiler
 102       * we really care about is gcc 4.2.  For that compiler and others like it,
 103       * we include the line number in the function name to do the best we can to
 104       * avoid conflicts.  These should be rare: a conflict would require use of
 105       * MOZ_STATIC_ASSERT on the same line in separate files in the same
 106       * translation unit, *and* the uses would have to be in code with
 107       * different linkage, *and* the first observed use must be in C++-linkage
 108       * code.
 109       */
 110 #    define MOZ_STATIC_ASSERT(cond, reason) \
 111        typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 112 #  else
 113 #    define MOZ_STATIC_ASSERT(cond, reason) \
 114        extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 115 #  endif
 116
 117 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
 118 #else
 119 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  static_assert(!(cond) || (expr), reason)
 120 #endif
 121
 122 #ifdef __cplusplus
 123 extern "C" {
 124 #endif
 125
 126 /*
 127  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
 128  * location of the assertion) to the standard debug-output channel.
 129  *
 130  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
 131  * method is primarily for internal use in this header, and only secondarily
 132  * for use in implementing release-build assertions.
 133  */
 134 static MOZ_ALWAYS_INLINE void
 135 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename, int aLine)
 136   MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS
 137 {
 138 #ifdef ANDROID
 139   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
 140                       "Assertion failure: %s, at %s:%d\n",
 141                       aStr, aFilename, aLine);
 142 #else
 143   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 144 #ifdef MOZ_DUMP_ASSERTION_STACK
 145   nsTraceRefcnt::WalkTheStack(stderr);
 146 #endif
 147   fflush(stderr);
 148 #endif
 149 }
 150
 151 static MOZ_ALWAYS_INLINE void
 152 MOZ_ReportCrash(const char* aStr, const char* aFilename, int aLine)
 153   MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS
 154 {
 155 #ifdef ANDROID
 156   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 157                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 158 #else
 159   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 160 #ifdef MOZ_DUMP_ASSERTION_STACK
 161   nsTraceRefcnt::WalkTheStack(stderr);
 162 #endif
 163   fflush(stderr);
 164 #endif
 165 }
 166
 167 /**
 168  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 169  * call MOZ_CRASH instead.
 170  */
 171 #if defined(_MSC_VER)
 172    /*
 173     * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 174     * (not nested in a system function) breakpoint.  This distinctively invokes
 175     * Breakpad without requiring system library symbols on all stack-processing
 176     * machines, as a nested breakpoint would require.
 177     *
 178     * We use TerminateProcess with the exit code aborting would generate
 179     * because we don't want to invoke atexit handlers, destructors, library
 180     * unload handlers, and so on when our process might be in a compromised
 181     * state.
 182     *
 183     * We don't use abort() because it'd cause Windows to annoyingly pop up the
 184     * process error dialog multiple times.  See bug 345118 and bug 426163.
 185     *
 186     * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the
 187     * compiler doesn't hassle us to provide a return statement after a
 188     * MOZ_REALLY_CRASH() call.
 189     *
 190     * (Technically these are Windows requirements, not MSVC requirements.  But
 191     * practically you need MSVC for debugging, and we only ship builds created
 192     * by MSVC, so doing it this way reduces complexity.)
 193     */
 194
 195 __declspec(noreturn) __inline void MOZ_NoReturn() {}
 196
 197 #  ifdef __cplusplus
 198 #    define MOZ_REALLY_CRASH() \
 199        do { \
 200          ::__debugbreak(); \
 201          *((volatile int*) NULL) = __LINE__; \
 202          ::TerminateProcess(::GetCurrentProcess(), 3); \
 203          ::MOZ_NoReturn(); \
 204        } while (0)
 205 #  else
 206 #    define MOZ_REALLY_CRASH() \
 207        do { \
 208          __debugbreak(); \
 209          *((volatile int*) NULL) = __LINE__; \
 210          TerminateProcess(GetCurrentProcess(), 3); \
 211          MOZ_NoReturn(); \
 212        } while (0)
 213 #  endif
 214 #else
 215 #  ifdef __cplusplus
 216 #    define MOZ_REALLY_CRASH() \
 217        do { \
 218          *((volatile int*) NULL) = __LINE__; \
 219          ::abort(); \
 220        } while (0)
 221 #  else
 222 #    define MOZ_REALLY_CRASH() \
 223        do { \
 224          *((volatile int*) NULL) = __LINE__; \
 225          abort(); \
 226        } while (0)
 227 #  endif
 228 #endif
 229
 230 /*
 231  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 232  * Breakpad-compatible way, in both debug and release builds.
 233  *
 234  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 235  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 236  * corruption, and so on.  It's also a good solution if you need safe behavior
 237  * in release builds as well as debug builds.  But if the failure is one that
 238  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 239  *
 240  * The optional explanation-string, if provided, must be a string literal
 241  * explaining why we're crashing.  This argument is intended for use with
 242  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 243  * obvious why we're crashing.
 244  *
 245  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 246  * explanation-string, we print the string to stderr.  Otherwise, we don't
 247  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 248  * builds, and it's hard to print to stderr safely when memory might have been
 249  * corrupted.
 250  */
 251 #ifndef DEBUG
 252 #  define MOZ_CRASH(...) MOZ_REALLY_CRASH()
 253 #else
 254 #  define MOZ_CRASH(...) \
 255      do { \
 256        MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
 257        MOZ_REALLY_CRASH(); \
 258      } while (0)
 259 #endif
 260
 261 #ifdef __cplusplus
 262 } /* extern "C" */
 263 #endif
 264
 265 /*
 266  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 267  * debug builds.  If it is, execution continues.  Otherwise, an error message
 268  * including the expression and the explanation-string (if provided) is printed,
 269  * an attempt is made to invoke any existing debugger, and execution halts.
 270  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 271  * which can correctly be falsy.
 272  *
 273  * The optional explanation-string, if provided, must be a string literal
 274  * explaining the assertion.  It is intended for use with assertions whose
 275  * correctness or rationale is non-obvious, and for assertions where the "real"
 276  * condition being tested is best described prosaically.  Don't provide an
 277  * explanation if it's not actually helpful.
 278  *
 279  *   // No explanation needed: pointer arguments often must not be NULL.
 280  *   MOZ_ASSERT(arg);
 281  *
 282  *   // An explanation can be helpful to explain exactly how we know an
 283  *   // assertion is valid.
 284  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 285  *              "given that <thingA> and <thingB>, we must have...");
 286  *
 287  *   // Or it might disambiguate multiple identical (save for their location)
 288  *   // assertions of the same expression.
 289  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 290  *              "we already set [[PrimitiveThis]] for this Boolean object");
 291  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 292  *              "we already set [[PrimitiveThis]] for this String object");
 293  *
 294  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 295  * *only* during debugging, not "in the field". If you want the latter, use
 296  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 297  *
 298  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 299  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 300  * enough to require real user testing to hit, but is not security-sensitive.
 301  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 302  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 303  * is being investigated, rather than letting users suffer.
 304  */
 305
 306 /*
 307  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 308  * accidentally passing something unintended in lieu of an assertion condition.
 309  */
 310
 311 #ifdef __cplusplus
 312 #  if defined(__clang__)
 313 #    define MOZ_SUPPORT_ASSERT_CONDITION_TYPE_VALIDATION
 314 #  elif defined(__GNUC__)
 315 //   B2G GCC 4.4 has insufficient decltype support.
 316 #    if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)
 317 #      define MOZ_SUPPORT_ASSERT_CONDITION_TYPE_VALIDATION
 318 #    endif
 319 #  elif defined(_MSC_VER)
 320 //   Disabled for now because of insufficient decltype support. Bug 1004028.
 321 #  endif
 322 #endif
 323
 324 #ifdef MOZ_SUPPORT_ASSERT_CONDITION_TYPE_VALIDATION
 325 #  include "mozilla/TypeTraits.h"
 326 namespace mozilla {
 327 namespace detail {
 328
 329 template<typename T>
 330 struct IsFunction
 331 {
 332   static const bool value = false;
 333 };
 334
 335 template<typename R, typename... A>
 336 struct IsFunction<R(A...)>
 337 {
 338   static const bool value = true;
 339 };
 340
 341 template<typename T>
 342 struct AssertionConditionType
 343 {
 344   typedef typename RemoveReference<T>::Type ValueT;
 345   static_assert(!IsArray<ValueT>::value,
 346                 "Expected boolean assertion condition, got an array or a "
 347                 "string!");
 348   static_assert(!IsFunction<ValueT>::value,
 349                 "Expected boolean assertion condition, got a function! Did "
 350                 "you intend to call that function?");
 351   static_assert(!IsFloatingPoint<ValueT>::value,
 352                 "It's often a bad idea to assert that a floating-point number "
 353                 "is nonzero, because such assertions tend to intermittently "
 354                 "fail. Shouldn't your code gracefully handle this case instead "
 355                 "of asserting? Anyway, if you really want to do that, write an "
 356                 "explicit boolean condition, like !!x or x!=0.");
 357
 358   static const bool isValid = true;
 359 };
 360
 361 } // namespace detail
 362 } // namespace mozilla
 363 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x) \
 364      static_assert(mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 365                    "invalid assertion condition")
 366 #else
 367 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 368 #endif
 369
 370 /* First the single-argument form. */
 371 #define MOZ_ASSERT_HELPER1(expr) \
 372   do { \
 373     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr); \
 374     if (MOZ_UNLIKELY(!(expr))) { \
 375       MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \
 376       MOZ_REALLY_CRASH(); \
 377     } \
 378   } while (0)
 379 /* Now the two-argument form. */
 380 #define MOZ_ASSERT_HELPER2(expr, explain) \
 381   do { \
 382     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr); \
 383     if (MOZ_UNLIKELY(!(expr))) { \
 384       MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \
 385       MOZ_REALLY_CRASH(); \
 386     } \
 387   } while (0)
 388
 389 #define MOZ_RELEASE_ASSERT_GLUE(a, b) a b
 390 #define MOZ_RELEASE_ASSERT(...) \
 391   MOZ_RELEASE_ASSERT_GLUE( \
 392     MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 393     (__VA_ARGS__))
 394
 395 #ifdef DEBUG
 396 #  define MOZ_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)
 397 #else
 398 #  define MOZ_ASSERT(...) do { } while (0)
 399 #endif /* DEBUG */
 400
 401 #ifdef RELEASE_BUILD
 402 #  define MOZ_DIAGNOSTIC_ASSERT MOZ_ASSERT
 403 #else
 404 #  define MOZ_DIAGNOSTIC_ASSERT MOZ_RELEASE_ASSERT
 405 #endif
 406
 407 /*
 408  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 409  * true.
 410  *
 411  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 412  *
 413  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 414  * designed to catch bugs during debugging, not "in the field".
 415  */
 416 #ifdef DEBUG
 417 #  define MOZ_ASSERT_IF(cond, expr) \
 418      do { \
 419        if (cond) { \
 420          MOZ_ASSERT(expr); \
 421        } \
 422      } while (0)
 423 #else
 424 #  define MOZ_ASSERT_IF(cond, expr)  do { } while (0)
 425 #endif
 426
 427 /*
 428  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 429  * it is undefined behavior for execution to reach this point.  No guarantees
 430  * are made about what will happen if this is reached at runtime.  Most code
 431  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 432  * asserts.
 433  */
 434 #if defined(__clang__)
 435 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 436 #elif defined(__GNUC__)
 437    /*
 438     * __builtin_unreachable() was implemented in gcc 4.5.  If we don't have
 439     * that, call a noreturn function; abort() will do nicely.  Qualify the call
 440     * in C++ in case there's another abort() visible in local scope.
 441     */
 442 #  if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)
 443 #    define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 444 #  else
 445 #    ifdef __cplusplus
 446 #      define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 447 #    else
 448 #      define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 449 #    endif
 450 #  endif
 451 #elif defined(_MSC_VER)
 452 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 453 #else
 454 #  ifdef __cplusplus
 455 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 456 #  else
 457 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 458 #  endif
 459 #endif
 460
 461 /*
 462  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 463  * can assume that the macro call cannot be reached during execution.  This lets
 464  * the compiler generate better-optimized code under some circumstances, at the
 465  * expense of the program's behavior being undefined if control reaches the
 466  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 467  *
 468  * In Gecko, you probably should not use this macro outside of performance- or
 469  * size-critical code, because it's unsafe.  If you don't care about code size
 470  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 471  *
 472  * SpiderMonkey is a different beast, and there it's acceptable to use
 473  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 474  *
 475  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 476  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 477  * call.
 478  *
 479  * Example usage:
 480  *
 481  *   enum ValueType {
 482  *     VALUE_STRING,
 483  *     VALUE_INT,
 484  *     VALUE_FLOAT
 485  *   };
 486  *
 487  *   int ptrToInt(ValueType type, void* value) {
 488  *   {
 489  *     // We know for sure that type is either INT or FLOAT, and we want this
 490  *     // code to run as quickly as possible.
 491  *     switch (type) {
 492  *     case VALUE_INT:
 493  *       return *(int*) value;
 494  *     case VALUE_FLOAT:
 495  *       return (int) *(float*) value;
 496  *     default:
 497  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 498  *     }
 499  *   }
 500  */
 501
 502 /*
 503  * Unconditional assert in debug builds for (assumed) unreachable code paths
 504  * that have a safe return without crashing in release builds.
 505  */
 506 #define MOZ_ASSERT_UNREACHABLE(reason) \
 507    MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 508
 509 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 510    do { \
 511      MOZ_ASSERT_UNREACHABLE(reason); \
 512      MOZ_ASSUME_UNREACHABLE_MARKER(); \
 513    } while (0)
 514
 515 /*
 516  * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
 517  * expression, in debug builds and in release builds both.  Then, in debug
 518  * builds only, the value of the expression is asserted either true or false
 519  * using MOZ_ASSERT.
 520  */
 521 #ifdef DEBUG
 522 #  define MOZ_ALWAYS_TRUE(expr)      MOZ_ASSERT((expr))
 523 #  define MOZ_ALWAYS_FALSE(expr)     MOZ_ASSERT(!(expr))
 524 #else
 525 #  define MOZ_ALWAYS_TRUE(expr)      ((void)(expr))
 526 #  define MOZ_ALWAYS_FALSE(expr)     ((void)(expr))
 527 #endif
 528
 529 #undef MOZ_DUMP_ASSERTION_STACK
 530
 531 #endif /* mozilla_Assertions_h */