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(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)) && \
  13     !defined(__wasi__)
  14 #  define MOZ_DUMP_ASSERTION_STACK
  15 #endif
  16
  17 #include "mozilla/Attributes.h"
  18 #include "mozilla/Compiler.h"
  19 #include "mozilla/Fuzzing.h"
  20 #include "mozilla/Likely.h"
  21 #include "mozilla/MacroArgs.h"
  22 #include "mozilla/StaticAnalysisFunctions.h"
  23 #include "mozilla/Types.h"
  24 #ifdef MOZ_DUMP_ASSERTION_STACK
  25 #  include "mozilla/StackWalk.h"
  26 #endif
  27
  28 /*
  29  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  30  * if present. It is declared here (and defined in Assertions.cpp) to make it
  31  * available to all code, even libraries that don't link with the crash reporter
  32  * directly.
  33  */
  34 MOZ_BEGIN_EXTERN_C
  35 extern MFBT_DATA const char* gMozCrashReason;
  36 MOZ_END_EXTERN_C
  37
  38 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  39 static inline void AnnotateMozCrashReason(const char* reason) {
  40   gMozCrashReason = reason;
  41 }
  42 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  43 #else
  44 #  define MOZ_CRASH_ANNOTATE(...) \
  45     do { /* nothing */            \
  46     } while (false)
  47 #endif
  48
  49 #include <stddef.h>
  50 #include <stdio.h>
  51 #include <stdlib.h>
  52 #ifdef _MSC_VER
  53 /*
  54  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  55  * further depends on <windef.h>.  We hardcode these few definitions manually
  56  * because those headers clutter the global namespace with a significant
  57  * number of undesired macros and symbols.
  58  */
  59 MOZ_BEGIN_EXTERN_C
  60 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  61                                                      unsigned int uExitCode);
  62 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  63 MOZ_END_EXTERN_C
  64 #elif defined(__wasi__)
  65 /*
  66  * On Wasm/WASI platforms, we just call __builtin_trap().
  67  */
  68 #else
  69 #  include <signal.h>
  70 #endif
  71 #ifdef ANDROID
  72 #  include <android/log.h>
  73 #endif
  74
  75 MOZ_BEGIN_EXTERN_C
  76
  77 #if defined(ANDROID) && defined(MOZ_DUMP_ASSERTION_STACK)
  78 MOZ_MAYBE_UNUSED static void MOZ_ReportAssertionFailurePrintFrame(
  79     const char* aBuf) {
  80   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s\n", aBuf);
  81 }
  82 #endif
  83
  84 /*
  85  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
  86  * location of the assertion) to the standard debug-output channel.
  87  *
  88  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
  89  * method is primarily for internal use in this header, and only secondarily
  90  * for use in implementing release-build assertions.
  91  */
  92 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
  93 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
  94                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
  95   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_ASSERT", aFilename, aLine, aStr);
  96 #ifdef ANDROID
  97   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
  98                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
  99                       aLine);
 100 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 101   MozWalkTheStackWithWriter(MOZ_ReportAssertionFailurePrintFrame, CallerPC(),
 102                             /* aMaxFrames */ 0);
 103 #  endif
 104 #else
 105   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 106 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 107   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 108 #  endif
 109   fflush(stderr);
 110 #endif
 111 }
 112
 113 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 114     const char* aStr, const char* aFilename,
 115     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 116 #ifdef ANDROID
 117   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 118                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 119 #else
 120   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 121 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 122   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 123 #  endif
 124   fflush(stderr);
 125 #endif
 126 }
 127
 128 /**
 129  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 130  * call MOZ_CRASH instead.
 131  */
 132 #if defined(_MSC_VER)
 133 /*
 134  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 135  * (not nested in a system function) breakpoint.  This distinctively invokes
 136  * Breakpad without requiring system library symbols on all stack-processing
 137  * machines, as a nested breakpoint would require.
 138  *
 139  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 140  * together, which would make crash reports hard to understand.
 141  *
 142  * We use TerminateProcess with the exit code aborting would generate
 143  * because we don't want to invoke atexit handlers, destructors, library
 144  * unload handlers, and so on when our process might be in a compromised
 145  * state.
 146  *
 147  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 148  * process error dialog multiple times.  See bug 345118 and bug 426163.
 149  *
 150  * (Technically these are Windows requirements, not MSVC requirements.  But
 151  * practically you need MSVC for debugging, and we only ship builds created
 152  * by MSVC, so doing it this way reduces complexity.)
 153  */
 154
 155 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 156 MOZ_NoReturn(int aLine) {
 157   *((volatile int*)NULL) = aLine;
 158   TerminateProcess(GetCurrentProcess(), 3);
 159 }
 160
 161 #  define MOZ_REALLY_CRASH(line) \
 162     do {                         \
 163       __debugbreak();            \
 164       MOZ_NoReturn(line);        \
 165     } while (false)
 166
 167 #elif __wasi__
 168
 169 #  define MOZ_REALLY_CRASH(line) __builtin_trap()
 170
 171 #else
 172
 173 /*
 174  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 175  * crash. NULL is preferred however if for some reason NULL cannot be used
 176  * this makes choosing another value possible.
 177  *
 178  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 179  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 180  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 181  * SEGV at 0x0.
 182  */
 183 #  ifdef MOZ_UBSAN
 184 #    define MOZ_CRASH_WRITE_ADDR 0x1
 185 #  else
 186 #    define MOZ_CRASH_WRITE_ADDR NULL
 187 #  endif
 188
 189 #  ifdef __cplusplus
 190 #    define MOZ_REALLY_CRASH(line)                                  \
 191       do {                                                          \
 192         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 193         ::abort();                                                  \
 194       } while (false)
 195 #  else
 196 #    define MOZ_REALLY_CRASH(line)                                  \
 197       do {                                                          \
 198         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 199         abort();                                                    \
 200       } while (false)
 201 #  endif
 202 #endif
 203
 204 /*
 205  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 206  * Breakpad-compatible way, in both debug and release builds.
 207  *
 208  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 209  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 210  * corruption, and so on.  It's also a good solution if you need safe behavior
 211  * in release builds as well as debug builds.  But if the failure is one that
 212  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 213  *
 214  * The optional explanation-string, if provided, must be a string literal
 215  * explaining why we're crashing.  This argument is intended for use with
 216  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 217  * obvious why we're crashing.
 218  *
 219  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 220  * explanation-string, we print the string to stderr.  Otherwise, we don't
 221  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 222  * builds, and it's hard to print to stderr safely when memory might have been
 223  * corrupted.
 224  */
 225 #if !(defined(DEBUG) || defined(FUZZING))
 226 #  define MOZ_CRASH(...)                                                      \
 227     do {                                                                      \
 228       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 229       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 230       MOZ_REALLY_CRASH(__LINE__);                                             \
 231     } while (false)
 232 #else
 233 #  define MOZ_CRASH(...)                                                      \
 234     do {                                                                      \
 235       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 236       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__);                    \
 237       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 238       MOZ_REALLY_CRASH(__LINE__);                                             \
 239     } while (false)
 240 #endif
 241
 242 /*
 243  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 244  * cannot be a string literal (but no other processing needs to be done on it).
 245  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 246  * strings from a potentially compromised process is not without risk. If the
 247  * string being passed is the result of a printf-style function, consider using
 248  * MOZ_CRASH_UNSAFE_PRINTF instead.
 249  *
 250  * @note This macro causes data collection because crash strings are annotated
 251  * to crash-stats and are publicly visible. Firefox data stewards must do data
 252  * review on usages of this macro.
 253  */
 254 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 255     const char* aFilename, int aLine, const char* aReason) {
 256   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", aFilename, aLine, aReason);
 257 #if defined(DEBUG) || defined(FUZZING)
 258   MOZ_ReportCrash(aReason, aFilename, aLine);
 259 #endif
 260   MOZ_CRASH_ANNOTATE(aReason);
 261   MOZ_REALLY_CRASH(aLine);
 262 }
 263 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 264
 265 static const size_t sPrintfMaxArgs = 4;
 266 static const size_t sPrintfCrashReasonSize = 1024;
 267
 268 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 269     char* MOZ_CrashPrintf(const char* aFormat, ...);
 270
 271 /*
 272  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 273  * information is desired than a string literal can supply. The caller provides
 274  * a printf-style format string, which must be a string literal and between
 275  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 276  * possible, as passing arbitrary strings to printf from a potentially
 277  * compromised process is not without risk.
 278  *
 279  * @note This macro causes data collection because crash strings are annotated
 280  * to crash-stats and are publicly visible. Firefox data stewards must do data
 281  * review on usages of this macro.
 282  */
 283 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 284   do {                                                                      \
 285     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 286                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 287                   "Or maybe you want MOZ_CRASH instead?");                  \
 288     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 289                   "Only up to 4 additional arguments are allowed!");        \
 290     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 291                   "The supplied format string is too long!");               \
 292     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 293   } while (false)
 294
 295 MOZ_END_EXTERN_C
 296
 297 /*
 298  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 299  * debug builds.  If it is, execution continues.  Otherwise, an error message
 300  * including the expression and the explanation-string (if provided) is printed,
 301  * an attempt is made to invoke any existing debugger, and execution halts.
 302  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 303  * which can correctly be falsy.
 304  *
 305  * The optional explanation-string, if provided, must be a string literal
 306  * explaining the assertion.  It is intended for use with assertions whose
 307  * correctness or rationale is non-obvious, and for assertions where the "real"
 308  * condition being tested is best described prosaically.  Don't provide an
 309  * explanation if it's not actually helpful.
 310  *
 311  *   // No explanation needed: pointer arguments often must not be NULL.
 312  *   MOZ_ASSERT(arg);
 313  *
 314  *   // An explanation can be helpful to explain exactly how we know an
 315  *   // assertion is valid.
 316  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 317  *              "given that <thingA> and <thingB>, we must have...");
 318  *
 319  *   // Or it might disambiguate multiple identical (save for their location)
 320  *   // assertions of the same expression.
 321  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 322  *              "we already set [[PrimitiveThis]] for this Boolean object");
 323  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 324  *              "we already set [[PrimitiveThis]] for this String object");
 325  *
 326  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 327  * *only* during debugging, not "in the field". If you want the latter, use
 328  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 329  *
 330  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 331  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 332  * enough to require real user testing to hit, but is not security-sensitive.
 333  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 334  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 335  * is being investigated, rather than letting users suffer.
 336  *
 337  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 338  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 339  */
 340
 341 /*
 342  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 343  * accidentally passing something unintended in lieu of an assertion condition.
 344  */
 345
 346 #ifdef __cplusplus
 347 #  include <type_traits>
 348 namespace mozilla {
 349 namespace detail {
 350
 351 template <typename T>
 352 struct AssertionConditionType {
 353   using ValueT = std::remove_reference_t<T>;
 354   static_assert(!std::is_array_v<ValueT>,
 355                 "Expected boolean assertion condition, got an array or a "
 356                 "string!");
 357   static_assert(!std::is_function_v<ValueT>,
 358                 "Expected boolean assertion condition, got a function! Did "
 359                 "you intend to call that function?");
 360   static_assert(!std::is_floating_point_v<ValueT>,
 361                 "It's often a bad idea to assert that a floating-point number "
 362                 "is nonzero, because such assertions tend to intermittently "
 363                 "fail. Shouldn't your code gracefully handle this case instead "
 364                 "of asserting? Anyway, if you really want to do that, write an "
 365                 "explicit boolean condition, like !!x or x!=0.");
 366
 367   static const bool isValid = true;
 368 };
 369
 370 }  // namespace detail
 371 }  // namespace mozilla
 372 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 373     static_assert(                                                     \
 374         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 375         "invalid assertion condition")
 376 #else
 377 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 378 #endif
 379
 380 #if defined(DEBUG) || defined(MOZ_ASAN)
 381 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 382     MOZ_ReportAssertionFailure(__VA_ARGS__)
 383 #else
 384 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 385     do { /* nothing */                      \
 386     } while (false)
 387 #endif
 388
 389 /* First the single-argument form. */
 390 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 391   do {                                                         \
 392     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 393     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 394       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);            \
 395       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 396       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 397       MOZ_REALLY_CRASH(__LINE__);                              \
 398     }                                                          \
 399   } while (false)
 400 /* Now the two-argument form. */
 401 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 402   do {                                                               \
 403     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 404     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 405       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);                  \
 406       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 407                                    __LINE__);                        \
 408       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 409       MOZ_REALLY_CRASH(__LINE__);                                    \
 410     }                                                                \
 411   } while (false)
 412
 413 #define MOZ_ASSERT_GLUE(a, b) a b
 414 #define MOZ_RELEASE_ASSERT(...)                                       \
 415   MOZ_ASSERT_GLUE(                                                    \
 416       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 417       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 418
 419 #ifdef DEBUG
 420 #  define MOZ_ASSERT(...)                                               \
 421     MOZ_ASSERT_GLUE(                                                    \
 422         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 423         ("MOZ_ASSERT", __VA_ARGS__))
 424 #else
 425 #  define MOZ_ASSERT(...) \
 426     do {                  \
 427     } while (false)
 428 #endif /* DEBUG */
 429
 430 #if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
 431 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 432     MOZ_ASSERT_GLUE(                                                    \
 433         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 434         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 435 #else
 436 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 437     do {                             \
 438     } while (false)
 439 #endif
 440
 441 /*
 442  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 443  * true.
 444  *
 445  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 446  *
 447  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 448  * designed to catch bugs during debugging, not "in the field".
 449  */
 450 #ifdef DEBUG
 451 #  define MOZ_ASSERT_IF(cond, expr) \
 452     do {                            \
 453       if (cond) {                   \
 454         MOZ_ASSERT(expr);           \
 455       }                             \
 456     } while (false)
 457 #else
 458 #  define MOZ_ASSERT_IF(cond, expr) \
 459     do {                            \
 460     } while (false)
 461 #endif
 462
 463 /*
 464  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 465  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 466  *
 467  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 468  * diagnostic assertions work and how to use them.
 469  */
 470 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 471 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 472     do {                                       \
 473       if (cond) {                              \
 474         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 475       }                                        \
 476     } while (false)
 477 #else
 478 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 479     do {                                       \
 480     } while (false)
 481 #endif
 482
 483 /*
 484  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 485  * it is undefined behavior for execution to reach this point.  No guarantees
 486  * are made about what will happen if this is reached at runtime.  Most code
 487  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 488  * asserts.
 489  */
 490 #if defined(__clang__) || defined(__GNUC__)
 491 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 492 #elif defined(_MSC_VER)
 493 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 494 #else
 495 #  ifdef __cplusplus
 496 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 497 #  else
 498 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 499 #  endif
 500 #endif
 501
 502 /*
 503  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 504  * can assume that the macro call cannot be reached during execution.  This lets
 505  * the compiler generate better-optimized code under some circumstances, at the
 506  * expense of the program's behavior being undefined if control reaches the
 507  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 508  *
 509  * In Gecko, you probably should not use this macro outside of performance- or
 510  * size-critical code, because it's unsafe.  If you don't care about code size
 511  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 512  *
 513  * SpiderMonkey is a different beast, and there it's acceptable to use
 514  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 515  *
 516  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 517  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 518  * call.
 519  *
 520  * Example usage:
 521  *
 522  *   enum ValueType {
 523  *     VALUE_STRING,
 524  *     VALUE_INT,
 525  *     VALUE_FLOAT
 526  *   };
 527  *
 528  *   int ptrToInt(ValueType type, void* value) {
 529  *   {
 530  *     // We know for sure that type is either INT or FLOAT, and we want this
 531  *     // code to run as quickly as possible.
 532  *     switch (type) {
 533  *     case VALUE_INT:
 534  *       return *(int*) value;
 535  *     case VALUE_FLOAT:
 536  *       return (int) *(float*) value;
 537  *     default:
 538  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 539  *     }
 540  *   }
 541  */
 542
 543 /*
 544  * Unconditional assert in debug builds for (assumed) unreachable code paths
 545  * that have a safe return without crashing in release builds.
 546  */
 547 #define MOZ_ASSERT_UNREACHABLE(reason) \
 548   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 549
 550 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 551   do {                                                  \
 552     MOZ_ASSERT_UNREACHABLE(reason);                     \
 553     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 554   } while (false)
 555
 556 /**
 557  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 558  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 559  * debug builds, but intentionally fall through in release builds to handle
 560  * unexpected values.
 561  *
 562  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to [[fallthrough]]? In
 563  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 564  * requiring a [[fallthrough]] annotation to suppress a -Wimplicit-fallthrough
 565  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 566  * `if (true) { MOZ_CRASH(); }` and the [[fallthrough]] annotation will cause
 567  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 568  * warning stalemate.
 569  *
 570  * // Example before MOZ_FALLTHROUGH_ASSERT:
 571  * switch (foo) {
 572  *   default:
 573  *     // This case wants to assert in debug builds, fall through in release.
 574  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 575  *     [[fallthrough]];   // but -Wunreachable-code warning in debug builds!
 576  *   case 5:
 577  *     return 5;
 578  * }
 579  *
 580  * // Example with MOZ_FALLTHROUGH_ASSERT:
 581  * switch (foo) {
 582  *   default:
 583  *     // This case asserts in debug builds, falls through in release.
 584  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 585  *   case 5:
 586  *     return 5;
 587  * }
 588  */
 589 #ifdef DEBUG
 590 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 591     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 592 #else
 593 #  define MOZ_FALLTHROUGH_ASSERT(...) [[fallthrough]]
 594 #endif
 595
 596 /*
 597  * MOZ_ALWAYS_TRUE(expr) and friends always evaluate the provided expression,
 598  * in debug builds and in release builds both.  Then, in debug builds and
 599  * Nightly and DevEdition release builds, the value of the expression is
 600  * asserted either true or false using MOZ_DIAGNOSTIC_ASSERT.
 601  */
 602 #define MOZ_ALWAYS_TRUE(expr)              \
 603   do {                                     \
 604     if (MOZ_LIKELY(expr)) {                \
 605       /* Silence [[nodiscard]]. */         \
 606     } else {                               \
 607       MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 608     }                                      \
 609   } while (false)
 610
 611 #define MOZ_ALWAYS_FALSE(expr) MOZ_ALWAYS_TRUE(!(expr))
 612 #define MOZ_ALWAYS_OK(expr) MOZ_ALWAYS_TRUE((expr).isOk())
 613 #define MOZ_ALWAYS_ERR(expr) MOZ_ALWAYS_TRUE((expr).isErr())
 614
 615 /*
 616  * These are disabled when fuzzing
 617  */
 618 #ifdef FUZZING
 619 #  define MOZ_CRASH_UNLESS_FUZZING(...) \
 620     do {                                \
 621     } while (0)
 622 #  define MOZ_ASSERT_UNLESS_FUZZING(...) \
 623     do {                                 \
 624     } while (0)
 625 #else
 626 #  define MOZ_CRASH_UNLESS_FUZZING(...) MOZ_CRASH(__VA_ARGS__)
 627 #  define MOZ_ASSERT_UNLESS_FUZZING(...) MOZ_ASSERT(__VA_ARGS__)
 628 #endif
 629
 630 #undef MOZ_DUMP_ASSERTION_STACK
 631 #undef MOZ_CRASH_CRASHREPORT
 632
 633 /*
 634  * This is only used by Array and nsTArray classes, therefore it is not
 635  * required when included from C code.
 636  */
 637 #ifdef __cplusplus
 638 namespace mozilla::detail {
 639 MFBT_API MOZ_NORETURN MOZ_COLD void InvalidArrayIndex_CRASH(size_t aIndex,
 640                                                             size_t aLength);
 641 }  // namespace mozilla::detail
 642 #endif  // __cplusplus
 643
 644 #endif /* mozilla_Assertions_h */