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; \
 248     ::abort();                                     \
 249   } while (false)
 250 #else
 251 #define MOZ_REALLY_CRASH(line)                     \
 252   do {                                             \
 253     *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; \
 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_OOL(explanation-string) can be used if the explanation
 297  * string cannot be a string literal (but no other processing needs to be done
 298  * on it). A regular MOZ_CRASH() is preferred wherever possible, as passing
 299  * arbitrary strings from a potentially compromised process is not without risk.
 300  * If the string being passed is the result of a printf-style function,
 301  * consider using 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 inline MOZ_COLD MOZ_NORETURN void MOZ_CrashOOL(const char* aFilename,
 308                                                       int aLine,
 309                                                       const char* aReason) {
 310 #ifdef DEBUG
 311   MOZ_ReportCrash(aReason, aFilename, aLine);
 312 #endif
 313   MOZ_CRASH_ANNOTATE(aReason);
 314   MOZ_REALLY_CRASH(aLine);
 315 }
 316 #define MOZ_CRASH_UNSAFE_OOL(reason) MOZ_CrashOOL(__FILE__, __LINE__, reason)
 317
 318 static const size_t sPrintfMaxArgs = 4;
 319 static const size_t sPrintfCrashReasonSize = 1024;
 320
 321 #ifndef DEBUG
 322 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(
 323     2, 3) void MOZ_CrashPrintf(int aLine, const char* aFormat, ...);
 324 #define MOZ_CALL_CRASH_PRINTF(format, ...) \
 325   MOZ_CrashPrintf(__LINE__, format, __VA_ARGS__)
 326 #else
 327 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(
 328     3, 4) void MOZ_CrashPrintf(const char* aFilename, int aLine,
 329                                const char* aFormat, ...);
 330 #define MOZ_CALL_CRASH_PRINTF(format, ...) \
 331   MOZ_CrashPrintf(__FILE__, __LINE__, format, __VA_ARGS__)
 332 #endif
 333
 334 /*
 335  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 336  * information is desired than a string literal can supply. The caller provides
 337  * a printf-style format string, which must be a string literal and between
 338  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 339  * possible, as passing arbitrary strings to printf from a potentially
 340  * compromised process is not without risk.
 341  *
 342  * @note This macro causes data collection because crash strings are annotated
 343  * to crash-stats and are publicly visible. Firefox data stewards must do data
 344  * review on usages of this macro.
 345  */
 346 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                              \
 347   do {                                                                    \
 348     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                         \
 349                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? " \
 350                   "Or maybe you want MOZ_CRASH instead?");                \
 351     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,           \
 352                   "Only up to 4 additional arguments are allowed!");      \
 353     static_assert(sizeof(format) <= sPrintfCrashReasonSize,               \
 354                   "The supplied format string is too long!");             \
 355     MOZ_CALL_CRASH_PRINTF("" format, __VA_ARGS__);                        \
 356   } while (false)
 357
 358 MOZ_END_EXTERN_C
 359
 360 /*
 361  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 362  * debug builds.  If it is, execution continues.  Otherwise, an error message
 363  * including the expression and the explanation-string (if provided) is printed,
 364  * an attempt is made to invoke any existing debugger, and execution halts.
 365  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 366  * which can correctly be falsy.
 367  *
 368  * The optional explanation-string, if provided, must be a string literal
 369  * explaining the assertion.  It is intended for use with assertions whose
 370  * correctness or rationale is non-obvious, and for assertions where the "real"
 371  * condition being tested is best described prosaically.  Don't provide an
 372  * explanation if it's not actually helpful.
 373  *
 374  *   // No explanation needed: pointer arguments often must not be NULL.
 375  *   MOZ_ASSERT(arg);
 376  *
 377  *   // An explanation can be helpful to explain exactly how we know an
 378  *   // assertion is valid.
 379  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 380  *              "given that <thingA> and <thingB>, we must have...");
 381  *
 382  *   // Or it might disambiguate multiple identical (save for their location)
 383  *   // assertions of the same expression.
 384  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 385  *              "we already set [[PrimitiveThis]] for this Boolean object");
 386  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 387  *              "we already set [[PrimitiveThis]] for this String object");
 388  *
 389  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 390  * *only* during debugging, not "in the field". If you want the latter, use
 391  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 392  *
 393  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 394  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 395  * enough to require real user testing to hit, but is not security-sensitive.
 396  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 397  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 398  * is being investigated, rather than letting users suffer.
 399  *
 400  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 401  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 402  */
 403
 404 /*
 405  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 406  * accidentally passing something unintended in lieu of an assertion condition.
 407  */
 408
 409 #ifdef __cplusplus
 410 #include "mozilla/TypeTraits.h"
 411 namespace mozilla {
 412 namespace detail {
 413
 414 template <typename T>
 415 struct AssertionConditionType {
 416   typedef typename RemoveReference<T>::Type ValueT;
 417   static_assert(!IsArray<ValueT>::value,
 418                 "Expected boolean assertion condition, got an array or a "
 419                 "string!");
 420   static_assert(!IsFunction<ValueT>::value,
 421                 "Expected boolean assertion condition, got a function! Did "
 422                 "you intend to call that function?");
 423   static_assert(!IsFloatingPoint<ValueT>::value,
 424                 "It's often a bad idea to assert that a floating-point number "
 425                 "is nonzero, because such assertions tend to intermittently "
 426                 "fail. Shouldn't your code gracefully handle this case instead "
 427                 "of asserting? Anyway, if you really want to do that, write an "
 428                 "explicit boolean condition, like !!x or x!=0.");
 429
 430   static const bool isValid = true;
 431 };
 432
 433 }  // namespace detail
 434 }  // namespace mozilla
 435 #define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                                  \
 436   static_assert(mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 437                 "invalid assertion condition")
 438 #else
 439 #define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 440 #endif
 441
 442 #if defined(DEBUG) || defined(MOZ_ASAN)
 443 #define MOZ_REPORT_ASSERTION_FAILURE(...) \
 444   MOZ_ReportAssertionFailure(__VA_ARGS__)
 445 #else
 446 #define MOZ_REPORT_ASSERTION_FAILURE(...) \
 447   do { /* nothing */                      \
 448   } while (false)
 449 #endif
 450
 451 /* First the single-argument form. */
 452 #define MOZ_ASSERT_HELPER1(expr)                               \
 453   do {                                                         \
 454     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 455     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 456       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 457       MOZ_CRASH_ANNOTATE("MOZ_RELEASE_ASSERT(" #expr ")");     \
 458       MOZ_REALLY_CRASH(__LINE__);                              \
 459     }                                                          \
 460   } while (false)
 461 /* Now the two-argument form. */
 462 #define MOZ_ASSERT_HELPER2(expr, explain)                                \
 463   do {                                                                   \
 464     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                            \
 465     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {              \
 466       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__,     \
 467                                    __LINE__);                            \
 468       MOZ_CRASH_ANNOTATE("MOZ_RELEASE_ASSERT(" #expr ") (" explain ")"); \
 469       MOZ_REALLY_CRASH(__LINE__);                                        \
 470     }                                                                    \
 471   } while (false)
 472
 473 #define MOZ_RELEASE_ASSERT_GLUE(a, b) a b
 474 #define MOZ_RELEASE_ASSERT(...)                                       \
 475   MOZ_RELEASE_ASSERT_GLUE(                                            \
 476       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 477       (__VA_ARGS__))
 478
 479 #ifdef DEBUG
 480 #define MOZ_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)
 481 #else
 482 #define MOZ_ASSERT(...) \
 483   do {                  \
 484   } while (false)
 485 #endif /* DEBUG */
 486
 487 #if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION)
 488 #define MOZ_DIAGNOSTIC_ASSERT MOZ_RELEASE_ASSERT
 489 #define MOZ_DIAGNOSTIC_ASSERT_ENABLED 1
 490 #else
 491 #define MOZ_DIAGNOSTIC_ASSERT MOZ_ASSERT
 492 #ifdef DEBUG
 493 #define MOZ_DIAGNOSTIC_ASSERT_ENABLED 1
 494 #endif
 495 #endif
 496
 497 /*
 498  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 499  * true.
 500  *
 501  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 502  *
 503  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 504  * designed to catch bugs during debugging, not "in the field".
 505  */
 506 #ifdef DEBUG
 507 #define MOZ_ASSERT_IF(cond, expr) \
 508   do {                            \
 509     if (cond) {                   \
 510       MOZ_ASSERT(expr);           \
 511     }                             \
 512   } while (false)
 513 #else
 514 #define MOZ_ASSERT_IF(cond, expr) \
 515   do {                            \
 516   } while (false)
 517 #endif
 518
 519 /*
 520  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 521  * it is undefined behavior for execution to reach this point.  No guarantees
 522  * are made about what will happen if this is reached at runtime.  Most code
 523  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 524  * asserts.
 525  */
 526 #if defined(__clang__) || defined(__GNUC__)
 527 #define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 528 #elif defined(_MSC_VER)
 529 #define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 530 #else
 531 #ifdef __cplusplus
 532 #define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 533 #else
 534 #define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 535 #endif
 536 #endif
 537
 538 /*
 539  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 540  * can assume that the macro call cannot be reached during execution.  This lets
 541  * the compiler generate better-optimized code under some circumstances, at the
 542  * expense of the program's behavior being undefined if control reaches the
 543  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 544  *
 545  * In Gecko, you probably should not use this macro outside of performance- or
 546  * size-critical code, because it's unsafe.  If you don't care about code size
 547  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 548  *
 549  * SpiderMonkey is a different beast, and there it's acceptable to use
 550  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 551  *
 552  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 553  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 554  * call.
 555  *
 556  * Example usage:
 557  *
 558  *   enum ValueType {
 559  *     VALUE_STRING,
 560  *     VALUE_INT,
 561  *     VALUE_FLOAT
 562  *   };
 563  *
 564  *   int ptrToInt(ValueType type, void* value) {
 565  *   {
 566  *     // We know for sure that type is either INT or FLOAT, and we want this
 567  *     // code to run as quickly as possible.
 568  *     switch (type) {
 569  *     case VALUE_INT:
 570  *       return *(int*) value;
 571  *     case VALUE_FLOAT:
 572  *       return (int) *(float*) value;
 573  *     default:
 574  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 575  *     }
 576  *   }
 577  */
 578
 579 /*
 580  * Unconditional assert in debug builds for (assumed) unreachable code paths
 581  * that have a safe return without crashing in release builds.
 582  */
 583 #define MOZ_ASSERT_UNREACHABLE(reason) \
 584   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 585
 586 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 587   do {                                                  \
 588     MOZ_ASSERT_UNREACHABLE(reason);                     \
 589     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 590   } while (false)
 591
 592 /**
 593  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 594  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 595  * debug builds, but intentionally fall through in release builds to handle
 596  * unexpected values.
 597  *
 598  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to MOZ_FALLTHROUGH? In
 599  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 600  * requiring a MOZ_FALLTHROUGH annotation to suppress a -Wimplicit-fallthrough
 601  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 602  * `if (true) { MOZ_CRASH(); }` and the MOZ_FALLTHROUGH annotation will cause
 603  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 604  * warning stalemate.
 605  *
 606  * // Example before MOZ_FALLTHROUGH_ASSERT:
 607  * switch (foo) {
 608  *   default:
 609  *     // This case wants to assert in debug builds, fall through in release.
 610  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 611  *     MOZ_FALLTHROUGH;   // but -Wunreachable-code warning in debug builds!
 612  *   case 5:
 613  *     return 5;
 614  * }
 615  *
 616  * // Example with MOZ_FALLTHROUGH_ASSERT:
 617  * switch (foo) {
 618  *   default:
 619  *     // This case asserts in debug builds, falls through in release.
 620  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 621  *   case 5:
 622  *     return 5;
 623  * }
 624  */
 625 #ifdef DEBUG
 626 #define MOZ_FALLTHROUGH_ASSERT(...) \
 627   MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 628 #else
 629 #define MOZ_FALLTHROUGH_ASSERT(...) MOZ_FALLTHROUGH
 630 #endif
 631
 632 /*
 633  * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
 634  * expression, in debug builds and in release builds both.  Then, in debug
 635  * builds only, the value of the expression is asserted either true or false
 636  * using MOZ_ASSERT.
 637  */
 638 #ifdef DEBUG
 639 #define MOZ_ALWAYS_TRUE(expr)   \
 640   do {                          \
 641     if ((expr)) {               \
 642       /* Do nothing. */         \
 643     } else {                    \
 644       MOZ_ASSERT(false, #expr); \
 645     }                           \
 646   } while (false)
 647 #define MOZ_ALWAYS_FALSE(expr)  \
 648   do {                          \
 649     if ((expr)) {               \
 650       MOZ_ASSERT(false, #expr); \
 651     } else {                    \
 652       /* Do nothing. */         \
 653     }                           \
 654   } while (false)
 655 #define MOZ_ALWAYS_OK(expr) MOZ_ASSERT((expr).isOk())
 656 #define MOZ_ALWAYS_ERR(expr) MOZ_ASSERT((expr).isErr())
 657 #else
 658 #define MOZ_ALWAYS_TRUE(expr)     \
 659   do {                            \
 660     if ((expr)) {                 \
 661       /* Silence MOZ_MUST_USE. */ \
 662     }                             \
 663   } while (false)
 664 #define MOZ_ALWAYS_FALSE(expr)    \
 665   do {                            \
 666     if ((expr)) {                 \
 667       /* Silence MOZ_MUST_USE. */ \
 668     }                             \
 669   } while (false)
 670 #define MOZ_ALWAYS_OK(expr)       \
 671   do {                            \
 672     if ((expr).isOk()) {          \
 673       /* Silence MOZ_MUST_USE. */ \
 674     }                             \
 675   } while (false)
 676 #define MOZ_ALWAYS_ERR(expr)      \
 677   do {                            \
 678     if ((expr).isErr()) {         \
 679       /* Silence MOZ_MUST_USE. */ \
 680     }                             \
 681   } while (false)
 682 #endif
 683
 684 #undef MOZ_DUMP_ASSERTION_STACK
 685 #undef MOZ_CRASH_CRASHREPORT
 686
 687 #endif /* mozilla_Assertions_h */