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 #include "mozilla/StaticAnalysisFunctions.h"
  21 #include "mozilla/Types.h"
  22 #ifdef MOZ_DUMP_ASSERTION_STACK
  23 #  include "nsTraceRefcnt.h"
  24 #endif
  25
  26 /*
  27  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  28  * if present. It is declared here (and defined in Assertions.cpp) to make it
  29  * available to all code, even libraries that don't link with the crash reporter
  30  * directly.
  31  */
  32 MOZ_BEGIN_EXTERN_C
  33 extern MFBT_DATA const char* gMozCrashReason;
  34 MOZ_END_EXTERN_C
  35
  36 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  37 static inline void AnnotateMozCrashReason(const char* reason) {
  38   gMozCrashReason = reason;
  39 }
  40 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  41 #else
  42 #  define MOZ_CRASH_ANNOTATE(...) \
  43     do { /* nothing */            \
  44     } while (false)
  45 #endif
  46
  47 #include <stddef.h>
  48 #include <stdio.h>
  49 #include <stdlib.h>
  50 #ifdef _MSC_VER
  51 /*
  52  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  53  * further depends on <windef.h>.  We hardcode these few definitions manually
  54  * because those headers clutter the global namespace with a significant
  55  * number of undesired macros and symbols.
  56  */
  57 MOZ_BEGIN_EXTERN_C
  58 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  59                                                      unsigned int uExitCode);
  60 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  61 MOZ_END_EXTERN_C
  62 #else
  63 #  include <signal.h>
  64 #endif
  65 #ifdef ANDROID
  66 #  include <android/log.h>
  67 #endif
  68
  69 /*
  70  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
  71  * In C++11, static_assert is provided by the compiler to the same effect.
  72  * This can be useful when you make certain assumptions about what must hold for
  73  * optimal, or even correct, behavior.  For example, you might assert that the
  74  * size of a struct is a multiple of the target architecture's word size:
  75  *
  76  *   struct S { ... };
  77  *   // C
  78  *   MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
  79  *                     "S should be a multiple of word size for efficiency");
  80  *   // C++11
  81  *   static_assert(sizeof(S) % sizeof(size_t) == 0,
  82  *                 "S should be a multiple of word size for efficiency");
  83  *
  84  * This macro can be used in any location where both an extern declaration and a
  85  * typedef could be used.
  86  */
  87 #ifndef __cplusplus
  88 /*
  89  * Some of the definitions below create an otherwise-unused typedef.  This
  90  * triggers compiler warnings with some versions of gcc, so mark the typedefs
  91  * as permissibly-unused to disable the warnings.
  92  */
  93 #  if defined(__GNUC__)
  94 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
  95 #  else
  96 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
  97 #  endif
  98 #  define MOZ_STATIC_ASSERT_GLUE1(x, y) x##y
  99 #  define MOZ_STATIC_ASSERT_GLUE(x, y) MOZ_STATIC_ASSERT_GLUE1(x, y)
 100 #  if defined(__SUNPRO_CC)
 101 /*
 102  * The Sun Studio C++ compiler is buggy when declaring, inside a function,
 103  * another extern'd function with an array argument whose length contains a
 104  * sizeof, triggering the error message "sizeof expression not accepted as
 105  * size of array parameter".  This bug (6688515, not public yet) would hit
 106  * defining moz_static_assert as a function, so we always define an extern
 107  * array for Sun Studio.
 108  *
 109  * We include the line number in the symbol name in a best-effort attempt
 110  * to avoid conflicts (see below).
 111  */
 112 #    define MOZ_STATIC_ASSERT(cond, reason)                 \
 113       extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, \
 114                                          __LINE__)[(cond) ? 1 : -1]
 115 #  elif defined(__COUNTER__)
 116 /*
 117  * If there was no preferred alternative, use a compiler-agnostic version.
 118  *
 119  * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
 120  * in both |extern "C"| and normal C++ in the same translation unit.  (Alas
 121  * |extern "C"| isn't allowed in a function.)  The only affected compiler
 122  * we really care about is gcc 4.2.  For that compiler and others like it,
 123  * we include the line number in the function name to do the best we can to
 124  * avoid conflicts.  These should be rare: a conflict would require use of
 125  * MOZ_STATIC_ASSERT on the same line in separate files in the same
 126  * translation unit, *and* the uses would have to be in code with
 127  * different linkage, *and* the first observed use must be in C++-linkage
 128  * code.
 129  */
 130 #    define MOZ_STATIC_ASSERT(cond, reason) \
 131       typedef int MOZ_STATIC_ASSERT_GLUE(   \
 132           moz_static_assert,                \
 133           __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 134 #  else
 135 #    define MOZ_STATIC_ASSERT(cond, reason)                            \
 136       extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)( \
 137           int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 138 #  endif
 139
 140 #  define MOZ_STATIC_ASSERT_IF(cond, expr, reason) \
 141     MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
 142 #else
 143 #  define MOZ_STATIC_ASSERT_IF(cond, expr, reason) \
 144     static_assert(!(cond) || (expr), reason)
 145 #endif
 146
 147 MOZ_BEGIN_EXTERN_C
 148
 149 /*
 150  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
 151  * location of the assertion) to the standard debug-output channel.
 152  *
 153  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
 154  * method is primarily for internal use in this header, and only secondarily
 155  * for use in implementing release-build assertions.
 156  */
 157 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
 158 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
 159                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 160 #ifdef ANDROID
 161   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
 162                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
 163                       aLine);
 164 #else
 165   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 166 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 167   nsTraceRefcnt::WalkTheStack(stderr);
 168 #  endif
 169   fflush(stderr);
 170 #endif
 171 }
 172
 173 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 174     const char* aStr, const char* aFilename,
 175     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 176 #ifdef ANDROID
 177   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 178                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 179 #else
 180   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 181 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 182   nsTraceRefcnt::WalkTheStack(stderr);
 183 #  endif
 184   fflush(stderr);
 185 #endif
 186 }
 187
 188 /**
 189  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 190  * call MOZ_CRASH instead.
 191  */
 192 #if defined(_MSC_VER)
 193 /*
 194  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 195  * (not nested in a system function) breakpoint.  This distinctively invokes
 196  * Breakpad without requiring system library symbols on all stack-processing
 197  * machines, as a nested breakpoint would require.
 198  *
 199  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 200  * together, which would make crash reports hard to understand.
 201  *
 202  * We use TerminateProcess with the exit code aborting would generate
 203  * because we don't want to invoke atexit handlers, destructors, library
 204  * unload handlers, and so on when our process might be in a compromised
 205  * state.
 206  *
 207  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 208  * process error dialog multiple times.  See bug 345118 and bug 426163.
 209  *
 210  * (Technically these are Windows requirements, not MSVC requirements.  But
 211  * practically you need MSVC for debugging, and we only ship builds created
 212  * by MSVC, so doing it this way reduces complexity.)
 213  */
 214
 215 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 216 MOZ_NoReturn(int aLine) {
 217   *((volatile int*)NULL) = aLine;
 218   TerminateProcess(GetCurrentProcess(), 3);
 219 }
 220
 221 #  define MOZ_REALLY_CRASH(line) \
 222     do {                         \
 223       __debugbreak();            \
 224       MOZ_NoReturn(line);        \
 225     } while (false)
 226 #else
 227
 228 /*
 229  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 230  * crash. NULL is preferred however if for some reason NULL cannot be used
 231  * this makes choosing another value possible.
 232  *
 233  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 234  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 235  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 236  * SEGV at 0x0.
 237  */
 238 #  ifdef MOZ_UBSAN
 239 #    define MOZ_CRASH_WRITE_ADDR 0x1
 240 #  else
 241 #    define MOZ_CRASH_WRITE_ADDR NULL
 242 #  endif
 243
 244 #  ifdef __cplusplus
 245 #    define MOZ_REALLY_CRASH(line)                                  \
 246       do {                                                          \
 247         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 248         ::abort();                                                  \
 249       } while (false)
 250 #  else
 251 #    define MOZ_REALLY_CRASH(line)                                  \
 252       do {                                                          \
 253         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 254         abort();                                                    \
 255       } while (false)
 256 #  endif
 257 #endif
 258
 259 /*
 260  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 261  * Breakpad-compatible way, in both debug and release builds.
 262  *
 263  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 264  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 265  * corruption, and so on.  It's also a good solution if you need safe behavior
 266  * in release builds as well as debug builds.  But if the failure is one that
 267  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 268  *
 269  * The optional explanation-string, if provided, must be a string literal
 270  * explaining why we're crashing.  This argument is intended for use with
 271  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 272  * obvious why we're crashing.
 273  *
 274  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 275  * explanation-string, we print the string to stderr.  Otherwise, we don't
 276  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 277  * builds, and it's hard to print to stderr safely when memory might have been
 278  * corrupted.
 279  */
 280 #ifndef DEBUG
 281 #  define MOZ_CRASH(...)                                \
 282     do {                                                \
 283       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")"); \
 284       MOZ_REALLY_CRASH(__LINE__);                       \
 285     } while (false)
 286 #else
 287 #  define MOZ_CRASH(...)                                   \
 288     do {                                                   \
 289       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
 290       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");    \
 291       MOZ_REALLY_CRASH(__LINE__);                          \
 292     } while (false)
 293 #endif
 294
 295 /*
 296  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 297  * cannot be a string literal (but no other processing needs to be done on it).
 298  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 299  * strings from a potentially compromised process is not without risk. If the
 300  * string being passed is the result of a printf-style function, consider using
 301  * MOZ_CRASH_UNSAFE_PRINTF instead.
 302  *
 303  * @note This macro causes data collection because crash strings are annotated
 304  * to crash-stats and are publicly visible. Firefox data stewards must do data
 305  * review on usages of this macro.
 306  */
 307 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 308     const char* aFilename, int aLine, const char* aReason) {
 309 #ifdef DEBUG
 310   MOZ_ReportCrash(aReason, aFilename, aLine);
 311 #endif
 312   MOZ_CRASH_ANNOTATE(aReason);
 313   MOZ_REALLY_CRASH(aLine);
 314 }
 315 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 316
 317 static const size_t sPrintfMaxArgs = 4;
 318 static const size_t sPrintfCrashReasonSize = 1024;
 319
 320 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 321     char* MOZ_CrashPrintf(const char* aFormat, ...);
 322
 323 /*
 324  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 325  * information is desired than a string literal can supply. The caller provides
 326  * a printf-style format string, which must be a string literal and between
 327  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 328  * possible, as passing arbitrary strings to printf from a potentially
 329  * compromised process is not without risk.
 330  *
 331  * @note This macro causes data collection because crash strings are annotated
 332  * to crash-stats and are publicly visible. Firefox data stewards must do data
 333  * review on usages of this macro.
 334  */
 335 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 336   do {                                                                      \
 337     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 338                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 339                   "Or maybe you want MOZ_CRASH instead?");                  \
 340     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 341                   "Only up to 4 additional arguments are allowed!");        \
 342     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 343                   "The supplied format string is too long!");               \
 344     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 345   } while (false)
 346
 347 MOZ_END_EXTERN_C
 348
 349 /*
 350  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 351  * debug builds.  If it is, execution continues.  Otherwise, an error message
 352  * including the expression and the explanation-string (if provided) is printed,
 353  * an attempt is made to invoke any existing debugger, and execution halts.
 354  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 355  * which can correctly be falsy.
 356  *
 357  * The optional explanation-string, if provided, must be a string literal
 358  * explaining the assertion.  It is intended for use with assertions whose
 359  * correctness or rationale is non-obvious, and for assertions where the "real"
 360  * condition being tested is best described prosaically.  Don't provide an
 361  * explanation if it's not actually helpful.
 362  *
 363  *   // No explanation needed: pointer arguments often must not be NULL.
 364  *   MOZ_ASSERT(arg);
 365  *
 366  *   // An explanation can be helpful to explain exactly how we know an
 367  *   // assertion is valid.
 368  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 369  *              "given that <thingA> and <thingB>, we must have...");
 370  *
 371  *   // Or it might disambiguate multiple identical (save for their location)
 372  *   // assertions of the same expression.
 373  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 374  *              "we already set [[PrimitiveThis]] for this Boolean object");
 375  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 376  *              "we already set [[PrimitiveThis]] for this String object");
 377  *
 378  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 379  * *only* during debugging, not "in the field". If you want the latter, use
 380  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 381  *
 382  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 383  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 384  * enough to require real user testing to hit, but is not security-sensitive.
 385  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 386  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 387  * is being investigated, rather than letting users suffer.
 388  *
 389  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 390  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 391  */
 392
 393 /*
 394  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 395  * accidentally passing something unintended in lieu of an assertion condition.
 396  */
 397
 398 #ifdef __cplusplus
 399 #  include "mozilla/TypeTraits.h"
 400 namespace mozilla {
 401 namespace detail {
 402
 403 template <typename T>
 404 struct AssertionConditionType {
 405   typedef typename RemoveReference<T>::Type ValueT;
 406   static_assert(!IsArray<ValueT>::value,
 407                 "Expected boolean assertion condition, got an array or a "
 408                 "string!");
 409   static_assert(!IsFunction<ValueT>::value,
 410                 "Expected boolean assertion condition, got a function! Did "
 411                 "you intend to call that function?");
 412   static_assert(!IsFloatingPoint<ValueT>::value,
 413                 "It's often a bad idea to assert that a floating-point number "
 414                 "is nonzero, because such assertions tend to intermittently "
 415                 "fail. Shouldn't your code gracefully handle this case instead "
 416                 "of asserting? Anyway, if you really want to do that, write an "
 417                 "explicit boolean condition, like !!x or x!=0.");
 418
 419   static const bool isValid = true;
 420 };
 421
 422 }  // namespace detail
 423 }  // namespace mozilla
 424 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 425     static_assert(                                                     \
 426         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 427         "invalid assertion condition")
 428 #else
 429 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 430 #endif
 431
 432 #if defined(DEBUG) || defined(MOZ_ASAN)
 433 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 434     MOZ_ReportAssertionFailure(__VA_ARGS__)
 435 #else
 436 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 437     do { /* nothing */                      \
 438     } while (false)
 439 #endif
 440
 441 /* First the single-argument form. */
 442 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 443   do {                                                         \
 444     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 445     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 446       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 447       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 448       MOZ_REALLY_CRASH(__LINE__);                              \
 449     }                                                          \
 450   } while (false)
 451 /* Now the two-argument form. */
 452 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 453   do {                                                               \
 454     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 455     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 456       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 457                                    __LINE__);                        \
 458       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 459       MOZ_REALLY_CRASH(__LINE__);                                    \
 460     }                                                                \
 461   } while (false)
 462
 463 #define MOZ_ASSERT_GLUE(a, b) a b
 464 #define MOZ_RELEASE_ASSERT(...)                                       \
 465   MOZ_ASSERT_GLUE(                                                    \
 466       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 467       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 468
 469 #ifdef DEBUG
 470 #  define MOZ_ASSERT(...)                                               \
 471     MOZ_ASSERT_GLUE(                                                    \
 472         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 473         ("MOZ_ASSERT", __VA_ARGS__))
 474 #else
 475 #  define MOZ_ASSERT(...) \
 476     do {                  \
 477     } while (false)
 478 #endif /* DEBUG */
 479
 480 #if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION) || defined(DEBUG)
 481 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 482     MOZ_ASSERT_GLUE(                                                    \
 483         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 484         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 485 #  define MOZ_DIAGNOSTIC_ASSERT_ENABLED 1
 486 #else
 487 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 488     do {                             \
 489     } while (false)
 490 #endif
 491
 492 /*
 493  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 494  * true.
 495  *
 496  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 497  *
 498  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 499  * designed to catch bugs during debugging, not "in the field".
 500  */
 501 #ifdef DEBUG
 502 #  define MOZ_ASSERT_IF(cond, expr) \
 503     do {                            \
 504       if (cond) {                   \
 505         MOZ_ASSERT(expr);           \
 506       }                             \
 507     } while (false)
 508 #else
 509 #  define MOZ_ASSERT_IF(cond, expr) \
 510     do {                            \
 511     } while (false)
 512 #endif
 513
 514 /*
 515  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 516  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 517  *
 518  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 519  * diagnostic assertions work and how to use them.
 520  */
 521 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 522 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 523     do {                                       \
 524       if (cond) {                              \
 525         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 526       }                                        \
 527     } while (false)
 528 #else
 529 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 530     do {                                       \
 531     } while (false)
 532 #endif
 533
 534 /*
 535  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 536  * it is undefined behavior for execution to reach this point.  No guarantees
 537  * are made about what will happen if this is reached at runtime.  Most code
 538  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 539  * asserts.
 540  */
 541 #if defined(__clang__) || defined(__GNUC__)
 542 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 543 #elif defined(_MSC_VER)
 544 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 545 #else
 546 #  ifdef __cplusplus
 547 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 548 #  else
 549 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 550 #  endif
 551 #endif
 552
 553 /*
 554  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 555  * can assume that the macro call cannot be reached during execution.  This lets
 556  * the compiler generate better-optimized code under some circumstances, at the
 557  * expense of the program's behavior being undefined if control reaches the
 558  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 559  *
 560  * In Gecko, you probably should not use this macro outside of performance- or
 561  * size-critical code, because it's unsafe.  If you don't care about code size
 562  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 563  *
 564  * SpiderMonkey is a different beast, and there it's acceptable to use
 565  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 566  *
 567  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 568  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 569  * call.
 570  *
 571  * Example usage:
 572  *
 573  *   enum ValueType {
 574  *     VALUE_STRING,
 575  *     VALUE_INT,
 576  *     VALUE_FLOAT
 577  *   };
 578  *
 579  *   int ptrToInt(ValueType type, void* value) {
 580  *   {
 581  *     // We know for sure that type is either INT or FLOAT, and we want this
 582  *     // code to run as quickly as possible.
 583  *     switch (type) {
 584  *     case VALUE_INT:
 585  *       return *(int*) value;
 586  *     case VALUE_FLOAT:
 587  *       return (int) *(float*) value;
 588  *     default:
 589  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 590  *     }
 591  *   }
 592  */
 593
 594 /*
 595  * Unconditional assert in debug builds for (assumed) unreachable code paths
 596  * that have a safe return without crashing in release builds.
 597  */
 598 #define MOZ_ASSERT_UNREACHABLE(reason) \
 599   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 600
 601 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 602   do {                                                  \
 603     MOZ_ASSERT_UNREACHABLE(reason);                     \
 604     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 605   } while (false)
 606
 607 /**
 608  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 609  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 610  * debug builds, but intentionally fall through in release builds to handle
 611  * unexpected values.
 612  *
 613  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to MOZ_FALLTHROUGH? In
 614  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 615  * requiring a MOZ_FALLTHROUGH annotation to suppress a -Wimplicit-fallthrough
 616  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 617  * `if (true) { MOZ_CRASH(); }` and the MOZ_FALLTHROUGH annotation will cause
 618  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 619  * warning stalemate.
 620  *
 621  * // Example before MOZ_FALLTHROUGH_ASSERT:
 622  * switch (foo) {
 623  *   default:
 624  *     // This case wants to assert in debug builds, fall through in release.
 625  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 626  *     MOZ_FALLTHROUGH;   // but -Wunreachable-code warning in debug builds!
 627  *   case 5:
 628  *     return 5;
 629  * }
 630  *
 631  * // Example with MOZ_FALLTHROUGH_ASSERT:
 632  * switch (foo) {
 633  *   default:
 634  *     // This case asserts in debug builds, falls through in release.
 635  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 636  *   case 5:
 637  *     return 5;
 638  * }
 639  */
 640 #ifdef DEBUG
 641 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 642     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 643 #else
 644 #  define MOZ_FALLTHROUGH_ASSERT(...) MOZ_FALLTHROUGH
 645 #endif
 646
 647 /*
 648  * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
 649  * expression, in debug builds and in release builds both.  Then, in debug
 650  * builds only, the value of the expression is asserted either true or false
 651  * using MOZ_ASSERT.
 652  */
 653 #ifdef DEBUG
 654 #  define MOZ_ALWAYS_TRUE(expr)   \
 655     do {                          \
 656       if ((expr)) {               \
 657         /* Do nothing. */         \
 658       } else {                    \
 659         MOZ_ASSERT(false, #expr); \
 660       }                           \
 661     } while (false)
 662 #  define MOZ_ALWAYS_FALSE(expr)  \
 663     do {                          \
 664       if ((expr)) {               \
 665         MOZ_ASSERT(false, #expr); \
 666       } else {                    \
 667         /* Do nothing. */         \
 668       }                           \
 669     } while (false)
 670 #  define MOZ_ALWAYS_OK(expr) MOZ_ASSERT((expr).isOk())
 671 #  define MOZ_ALWAYS_ERR(expr) MOZ_ASSERT((expr).isErr())
 672 #else
 673 #  define MOZ_ALWAYS_TRUE(expr)     \
 674     do {                            \
 675       if ((expr)) {                 \
 676         /* Silence MOZ_MUST_USE. */ \
 677       }                             \
 678     } while (false)
 679 #  define MOZ_ALWAYS_FALSE(expr)    \
 680     do {                            \
 681       if ((expr)) {                 \
 682         /* Silence MOZ_MUST_USE. */ \
 683       }                             \
 684     } while (false)
 685 #  define MOZ_ALWAYS_OK(expr)       \
 686     do {                            \
 687       if ((expr).isOk()) {          \
 688         /* Silence MOZ_MUST_USE. */ \
 689       }                             \
 690     } while (false)
 691 #  define MOZ_ALWAYS_ERR(expr)      \
 692     do {                            \
 693       if ((expr).isErr()) {         \
 694         /* Silence MOZ_MUST_USE. */ \
 695       }                             \
 696     } while (false)
 697 #endif
 698
 699 /*
 700  * MOZ_DIAGNOSTIC_ALWAYS_TRUE is like MOZ_ALWAYS_TRUE, but using
 701  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 702  *
 703  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 704  * diagnostic assertions work and how to use them.
 705  */
 706 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 707 #  define MOZ_DIAGNOSTIC_ALWAYS_TRUE(expr)   \
 708     do {                                     \
 709       if ((expr)) {                          \
 710         /* Do nothing. */                    \
 711       } else {                               \
 712         MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 713       }                                      \
 714     } while (false)
 715 #else
 716 #  define MOZ_DIAGNOSTIC_ALWAYS_TRUE(expr) \
 717     do {                                   \
 718       if ((expr)) {                        \
 719         /* Silence MOZ_MUST_USE. */        \
 720       }                                    \
 721     } while (false)
 722 #endif
 723
 724 #undef MOZ_DUMP_ASSERTION_STACK
 725 #undef MOZ_CRASH_CRASHREPORT
 726
 727 #endif /* mozilla_Assertions_h */