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 #if defined(XP_WIN) && (defined(DEBUG) || defined(FUZZING))
  17 #  define MOZ_BUFFER_STDERR
  18 #endif
  19
  20 #include "mozilla/Attributes.h"
  21 #include "mozilla/Compiler.h"
  22 #include "mozilla/Fuzzing.h"
  23 #include "mozilla/Likely.h"
  24 #include "mozilla/MacroArgs.h"
  25 #include "mozilla/StaticAnalysisFunctions.h"
  26 #include "mozilla/Types.h"
  27 #ifdef MOZ_DUMP_ASSERTION_STACK
  28 #  include "mozilla/StackWalk.h"
  29 #endif
  30
  31 /*
  32  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  33  * if present. It is declared here (and defined in Assertions.cpp) to make it
  34  * available to all code, even libraries that don't link with the crash reporter
  35  * directly.
  36  */
  37 MOZ_BEGIN_EXTERN_C
  38 extern MFBT_DATA const char* gMozCrashReason;
  39 MOZ_END_EXTERN_C
  40
  41 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  42 static inline void AnnotateMozCrashReason(const char* reason) {
  43   gMozCrashReason = reason;
  44   // See bug 1681846, on 32-bit Android ARM the compiler removes the store to
  45   // gMozCrashReason if this barrier is not present.
  46   asm volatile("" ::: "memory");
  47 }
  48 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  49 #else
  50 #  define MOZ_CRASH_ANNOTATE(...) \
  51     do { /* nothing */            \
  52     } while (false)
  53 #endif
  54
  55 #include <stddef.h>
  56 #include <stdio.h>
  57 #include <stdlib.h>
  58 #ifdef _MSC_VER
  59 /*
  60  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  61  * further depends on <windef.h>.  We hardcode these few definitions manually
  62  * because those headers clutter the global namespace with a significant
  63  * number of undesired macros and symbols.
  64  */
  65 MOZ_BEGIN_EXTERN_C
  66 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  67                                                      unsigned int uExitCode);
  68 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  69 MOZ_END_EXTERN_C
  70 #elif defined(__wasi__)
  71 /*
  72  * On Wasm/WASI platforms, we just call __builtin_trap().
  73  */
  74 #else
  75 #  include <signal.h>
  76 #endif
  77 #ifdef ANDROID
  78 #  include <android/log.h>
  79 #endif
  80
  81 MOZ_BEGIN_EXTERN_C
  82
  83 #if defined(ANDROID) && defined(MOZ_DUMP_ASSERTION_STACK)
  84 MOZ_MAYBE_UNUSED static void MOZ_ReportAssertionFailurePrintFrame(
  85     const char* aBuf) {
  86   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s\n", aBuf);
  87 }
  88 #endif
  89
  90 /*
  91  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
  92  * location of the assertion) to the standard debug-output channel.
  93  *
  94  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
  95  * method is primarily for internal use in this header, and only secondarily
  96  * for use in implementing release-build assertions.
  97  */
  98 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
  99 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
 100                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 101   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_ASSERT", aFilename, aLine, aStr);
 102 #ifdef ANDROID
 103   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
 104                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
 105                       aLine);
 106 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 107   MozWalkTheStackWithWriter(MOZ_ReportAssertionFailurePrintFrame, CallerPC(),
 108                             /* aMaxFrames */ 0);
 109 #  endif
 110 #else
 111 #  if defined(MOZ_BUFFER_STDERR)
 112   char msg[1024] = "";
 113   snprintf(msg, sizeof(msg) - 1, "Assertion failure: %s, at %s:%d\n", aStr,
 114            aFilename, aLine);
 115   fputs(msg, stderr);
 116 #  else
 117   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 118 #  endif
 119 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 120   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 121 #  endif
 122   fflush(stderr);
 123 #endif
 124 }
 125
 126 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 127     const char* aStr, const char* aFilename,
 128     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 129 #ifdef ANDROID
 130   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 131                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 132 #else
 133 #  if defined(MOZ_BUFFER_STDERR)
 134   char msg[1024] = "";
 135   snprintf(msg, sizeof(msg) - 1, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr,
 136            aFilename, aLine);
 137   fputs(msg, stderr);
 138 #  else
 139   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 140 #  endif
 141 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 142   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 143 #  endif
 144   fflush(stderr);
 145 #endif
 146 }
 147
 148 /**
 149  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 150  * call MOZ_CRASH instead.
 151  */
 152 #if defined(_MSC_VER)
 153 /*
 154  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 155  * (not nested in a system function) breakpoint.  This distinctively invokes
 156  * Breakpad without requiring system library symbols on all stack-processing
 157  * machines, as a nested breakpoint would require.
 158  *
 159  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 160  * together, which would make crash reports hard to understand.
 161  *
 162  * We use TerminateProcess with the exit code aborting would generate
 163  * because we don't want to invoke atexit handlers, destructors, library
 164  * unload handlers, and so on when our process might be in a compromised
 165  * state.
 166  *
 167  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 168  * process error dialog multiple times.  See bug 345118 and bug 426163.
 169  *
 170  * (Technically these are Windows requirements, not MSVC requirements.  But
 171  * practically you need MSVC for debugging, and we only ship builds created
 172  * by MSVC, so doing it this way reduces complexity.)
 173  */
 174
 175 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 176 MOZ_NoReturn(int aLine) {
 177   *((volatile int*)NULL) = aLine;
 178   TerminateProcess(GetCurrentProcess(), 3);
 179 }
 180
 181 #  define MOZ_REALLY_CRASH(line) \
 182     do {                         \
 183       __debugbreak();            \
 184       MOZ_NoReturn(line);        \
 185     } while (false)
 186
 187 #elif __wasi__
 188
 189 #  define MOZ_REALLY_CRASH(line) __builtin_trap()
 190
 191 #else
 192
 193 /*
 194  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 195  * crash. NULL is preferred however if for some reason NULL cannot be used
 196  * this makes choosing another value possible.
 197  *
 198  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 199  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 200  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 201  * SEGV at 0x0.
 202  */
 203 #  ifdef MOZ_UBSAN
 204 #    define MOZ_CRASH_WRITE_ADDR 0x1
 205 #  else
 206 #    define MOZ_CRASH_WRITE_ADDR NULL
 207 #  endif
 208
 209 #  ifdef __cplusplus
 210 #    define MOZ_REALLY_CRASH(line)                                  \
 211       do {                                                          \
 212         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 213         ::abort();                                                  \
 214       } while (false)
 215 #  else
 216 #    define MOZ_REALLY_CRASH(line)                                  \
 217       do {                                                          \
 218         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 219         abort();                                                    \
 220       } while (false)
 221 #  endif
 222 #endif
 223
 224 /*
 225  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 226  * Breakpad-compatible way, in both debug and release builds.
 227  *
 228  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 229  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 230  * corruption, and so on.  It's also a good solution if you need safe behavior
 231  * in release builds as well as debug builds.  But if the failure is one that
 232  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 233  *
 234  * The optional explanation-string, if provided, must be a string literal
 235  * explaining why we're crashing.  This argument is intended for use with
 236  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 237  * obvious why we're crashing.
 238  *
 239  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 240  * explanation-string, we print the string to stderr.  Otherwise, we don't
 241  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 242  * builds, and it's hard to print to stderr safely when memory might have been
 243  * corrupted.
 244  */
 245 #if !(defined(DEBUG) || defined(FUZZING))
 246 #  define MOZ_CRASH(...)                                                      \
 247     do {                                                                      \
 248       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 249       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 250       MOZ_REALLY_CRASH(__LINE__);                                             \
 251     } while (false)
 252 #else
 253 #  define MOZ_CRASH(...)                                                      \
 254     do {                                                                      \
 255       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 256       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__);                    \
 257       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 258       MOZ_REALLY_CRASH(__LINE__);                                             \
 259     } while (false)
 260 #endif
 261
 262 /*
 263  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 264  * cannot be a string literal (but no other processing needs to be done on it).
 265  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 266  * strings from a potentially compromised process is not without risk. If the
 267  * string being passed is the result of a printf-style function, consider using
 268  * MOZ_CRASH_UNSAFE_PRINTF instead.
 269  *
 270  * @note This macro causes data collection because crash strings are annotated
 271  * to crash-stats and are publicly visible. Firefox data stewards must do data
 272  * review on usages of this macro.
 273  */
 274 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 275     const char* aFilename, int aLine, const char* aReason) {
 276   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", aFilename, aLine, aReason);
 277 #if defined(DEBUG) || defined(FUZZING)
 278   MOZ_ReportCrash(aReason, aFilename, aLine);
 279 #endif
 280   MOZ_CRASH_ANNOTATE(aReason);
 281   MOZ_REALLY_CRASH(aLine);
 282 }
 283 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 284
 285 static const size_t sPrintfMaxArgs = 4;
 286 static const size_t sPrintfCrashReasonSize = 1024;
 287
 288 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 289     char* MOZ_CrashPrintf(const char* aFormat, ...);
 290
 291 /*
 292  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 293  * information is desired than a string literal can supply. The caller provides
 294  * a printf-style format string, which must be a string literal and between
 295  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 296  * possible, as passing arbitrary strings to printf from a potentially
 297  * compromised process is not without risk.
 298  *
 299  * @note This macro causes data collection because crash strings are annotated
 300  * to crash-stats and are publicly visible. Firefox data stewards must do data
 301  * review on usages of this macro.
 302  */
 303 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 304   do {                                                                      \
 305     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 306                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 307                   "Or maybe you want MOZ_CRASH instead?");                  \
 308     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 309                   "Only up to 4 additional arguments are allowed!");        \
 310     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 311                   "The supplied format string is too long!");               \
 312     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 313   } while (false)
 314
 315 MOZ_END_EXTERN_C
 316
 317 /*
 318  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 319  * debug builds.  If it is, execution continues.  Otherwise, an error message
 320  * including the expression and the explanation-string (if provided) is printed,
 321  * an attempt is made to invoke any existing debugger, and execution halts.
 322  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 323  * which can correctly be falsy.
 324  *
 325  * The optional explanation-string, if provided, must be a string literal
 326  * explaining the assertion.  It is intended for use with assertions whose
 327  * correctness or rationale is non-obvious, and for assertions where the "real"
 328  * condition being tested is best described prosaically.  Don't provide an
 329  * explanation if it's not actually helpful.
 330  *
 331  *   // No explanation needed: pointer arguments often must not be NULL.
 332  *   MOZ_ASSERT(arg);
 333  *
 334  *   // An explanation can be helpful to explain exactly how we know an
 335  *   // assertion is valid.
 336  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 337  *              "given that <thingA> and <thingB>, we must have...");
 338  *
 339  *   // Or it might disambiguate multiple identical (save for their location)
 340  *   // assertions of the same expression.
 341  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 342  *              "we already set [[PrimitiveThis]] for this Boolean object");
 343  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 344  *              "we already set [[PrimitiveThis]] for this String object");
 345  *
 346  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 347  * *only* during debugging, not "in the field". If you want the latter, use
 348  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 349  *
 350  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly and early beta
 351  * and MOZ_ASSERT in late Beta and Release - use this when a condition is
 352  * potentially rare enough to require real user testing to hit, but is not
 353  * security-sensitive. This can cause user pain, so use it sparingly. If a
 354  * MOZ_DIAGNOSTIC_ASSERT is firing, it should promptly be converted to a
 355  * MOZ_ASSERT while the failure is being investigated, rather than letting users
 356  * suffer.
 357  *
 358  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 359  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 360  */
 361
 362 /*
 363  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 364  * accidentally passing something unintended in lieu of an assertion condition.
 365  */
 366
 367 #ifdef __cplusplus
 368 #  include <type_traits>
 369 namespace mozilla {
 370 namespace detail {
 371
 372 template <typename T>
 373 struct AssertionConditionType {
 374   using ValueT = std::remove_reference_t<T>;
 375   static_assert(!std::is_array_v<ValueT>,
 376                 "Expected boolean assertion condition, got an array or a "
 377                 "string!");
 378   static_assert(!std::is_function_v<ValueT>,
 379                 "Expected boolean assertion condition, got a function! Did "
 380                 "you intend to call that function?");
 381   static_assert(!std::is_floating_point_v<ValueT>,
 382                 "It's often a bad idea to assert that a floating-point number "
 383                 "is nonzero, because such assertions tend to intermittently "
 384                 "fail. Shouldn't your code gracefully handle this case instead "
 385                 "of asserting? Anyway, if you really want to do that, write an "
 386                 "explicit boolean condition, like !!x or x!=0.");
 387
 388   static const bool isValid = true;
 389 };
 390
 391 }  // namespace detail
 392 }  // namespace mozilla
 393 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 394     static_assert(                                                     \
 395         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 396         "invalid assertion condition")
 397 #else
 398 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 399 #endif
 400
 401 #if defined(DEBUG) || defined(MOZ_ASAN)
 402 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 403     MOZ_ReportAssertionFailure(__VA_ARGS__)
 404 #else
 405 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 406     do { /* nothing */                      \
 407     } while (false)
 408 #endif
 409
 410 /* First the single-argument form. */
 411 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 412   do {                                                         \
 413     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 414     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 415       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);            \
 416       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 417       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 418       MOZ_REALLY_CRASH(__LINE__);                              \
 419     }                                                          \
 420   } while (false)
 421 /* Now the two-argument form. */
 422 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 423   do {                                                               \
 424     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 425     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 426       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);                  \
 427       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 428                                    __LINE__);                        \
 429       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 430       MOZ_REALLY_CRASH(__LINE__);                                    \
 431     }                                                                \
 432   } while (false)
 433
 434 #define MOZ_ASSERT_GLUE(a, b) a b
 435 #define MOZ_RELEASE_ASSERT(...)                                       \
 436   MOZ_ASSERT_GLUE(                                                    \
 437       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 438       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 439
 440 #ifdef DEBUG
 441 #  define MOZ_ASSERT(...)                                               \
 442     MOZ_ASSERT_GLUE(                                                    \
 443         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 444         ("MOZ_ASSERT", __VA_ARGS__))
 445 #else
 446 #  define MOZ_ASSERT(...) \
 447     do {                  \
 448     } while (false)
 449 #endif /* DEBUG */
 450
 451 #if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
 452 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 453     MOZ_ASSERT_GLUE(                                                    \
 454         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 455         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 456 #else
 457 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 458     do {                             \
 459     } while (false)
 460 #endif
 461
 462 /*
 463  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 464  * true.
 465  *
 466  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 467  *
 468  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 469  * designed to catch bugs during debugging, not "in the field".
 470  */
 471 #ifdef DEBUG
 472 #  define MOZ_ASSERT_IF(cond, expr) \
 473     do {                            \
 474       if (cond) {                   \
 475         MOZ_ASSERT(expr);           \
 476       }                             \
 477     } while (false)
 478 #else
 479 #  define MOZ_ASSERT_IF(cond, expr) \
 480     do {                            \
 481     } while (false)
 482 #endif
 483
 484 /*
 485  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 486  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 487  *
 488  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 489  * diagnostic assertions work and how to use them.
 490  */
 491 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 492 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 493     do {                                       \
 494       if (cond) {                              \
 495         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 496       }                                        \
 497     } while (false)
 498 #else
 499 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 500     do {                                       \
 501     } while (false)
 502 #endif
 503
 504 /*
 505  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 506  * it is undefined behavior for execution to reach this point.  No guarantees
 507  * are made about what will happen if this is reached at runtime.  Most code
 508  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 509  * asserts.
 510  */
 511 #if defined(__clang__) || defined(__GNUC__)
 512 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 513 #elif defined(_MSC_VER)
 514 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 515 #else
 516 #  ifdef __cplusplus
 517 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 518 #  else
 519 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 520 #  endif
 521 #endif
 522
 523 /*
 524  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 525  * can assume that the macro call cannot be reached during execution.  This lets
 526  * the compiler generate better-optimized code under some circumstances, at the
 527  * expense of the program's behavior being undefined if control reaches the
 528  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 529  *
 530  * In Gecko, you probably should not use this macro outside of performance- or
 531  * size-critical code, because it's unsafe.  If you don't care about code size
 532  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 533  *
 534  * SpiderMonkey is a different beast, and there it's acceptable to use
 535  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 536  *
 537  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 538  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 539  * call.
 540  *
 541  * Example usage:
 542  *
 543  *   enum ValueType {
 544  *     VALUE_STRING,
 545  *     VALUE_INT,
 546  *     VALUE_FLOAT
 547  *   };
 548  *
 549  *   int ptrToInt(ValueType type, void* value) {
 550  *   {
 551  *     // We know for sure that type is either INT or FLOAT, and we want this
 552  *     // code to run as quickly as possible.
 553  *     switch (type) {
 554  *     case VALUE_INT:
 555  *       return *(int*) value;
 556  *     case VALUE_FLOAT:
 557  *       return (int) *(float*) value;
 558  *     default:
 559  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 560  *     }
 561  *   }
 562  */
 563
 564 /*
 565  * Unconditional assert in debug builds for (assumed) unreachable code paths
 566  * that have a safe return without crashing in release builds.
 567  */
 568 #define MOZ_ASSERT_UNREACHABLE(reason) \
 569   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 570
 571 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 572   do {                                                  \
 573     MOZ_ASSERT_UNREACHABLE(reason);                     \
 574     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 575   } while (false)
 576
 577 /**
 578  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 579  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 580  * debug builds, but intentionally fall through in release builds to handle
 581  * unexpected values.
 582  *
 583  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to [[fallthrough]]? In
 584  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 585  * requiring a [[fallthrough]] annotation to suppress a -Wimplicit-fallthrough
 586  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 587  * `if (true) { MOZ_CRASH(); }` and the [[fallthrough]] annotation will cause
 588  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 589  * warning stalemate.
 590  *
 591  * // Example before MOZ_FALLTHROUGH_ASSERT:
 592  * switch (foo) {
 593  *   default:
 594  *     // This case wants to assert in debug builds, fall through in release.
 595  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 596  *     [[fallthrough]];   // but -Wunreachable-code warning in debug builds!
 597  *   case 5:
 598  *     return 5;
 599  * }
 600  *
 601  * // Example with MOZ_FALLTHROUGH_ASSERT:
 602  * switch (foo) {
 603  *   default:
 604  *     // This case asserts in debug builds, falls through in release.
 605  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 606  *   case 5:
 607  *     return 5;
 608  * }
 609  */
 610 #ifdef DEBUG
 611 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 612     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 613 #else
 614 #  define MOZ_FALLTHROUGH_ASSERT(...) [[fallthrough]]
 615 #endif
 616
 617 /*
 618  * MOZ_ALWAYS_TRUE(expr) and friends always evaluate the provided expression,
 619  * in debug builds and in release builds both.  Then, in debug builds and
 620  * Nightly and early beta builds, the value of the expression is
 621  * asserted either true or false using MOZ_DIAGNOSTIC_ASSERT.
 622  */
 623 #define MOZ_ALWAYS_TRUE(expr)              \
 624   do {                                     \
 625     if (MOZ_LIKELY(expr)) {                \
 626       /* Silence [[nodiscard]]. */         \
 627     } else {                               \
 628       MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 629     }                                      \
 630   } while (false)
 631
 632 #define MOZ_ALWAYS_FALSE(expr) MOZ_ALWAYS_TRUE(!(expr))
 633 #define MOZ_ALWAYS_OK(expr) MOZ_ALWAYS_TRUE((expr).isOk())
 634 #define MOZ_ALWAYS_ERR(expr) MOZ_ALWAYS_TRUE((expr).isErr())
 635
 636 /*
 637  * These are disabled when fuzzing
 638  */
 639 #ifdef FUZZING
 640 #  define MOZ_CRASH_UNLESS_FUZZING(...) \
 641     do {                                \
 642     } while (0)
 643 #  define MOZ_ASSERT_UNLESS_FUZZING(...) \
 644     do {                                 \
 645     } while (0)
 646 #else
 647 #  define MOZ_CRASH_UNLESS_FUZZING(...) MOZ_CRASH(__VA_ARGS__)
 648 #  define MOZ_ASSERT_UNLESS_FUZZING(...) MOZ_ASSERT(__VA_ARGS__)
 649 #endif
 650
 651 #undef MOZ_BUFFER_STDERR
 652 #undef MOZ_CRASH_CRASHREPORT
 653 #undef MOZ_DUMP_ASSERTION_STACK
 654
 655 /*
 656  * This is only used by Array and nsTArray classes, therefore it is not
 657  * required when included from C code.
 658  */
 659 #ifdef __cplusplus
 660 namespace mozilla::detail {
 661 MFBT_API MOZ_NORETURN MOZ_COLD void InvalidArrayIndex_CRASH(size_t aIndex,
 662                                                             size_t aLength);
 663 }  // namespace mozilla::detail
 664 #endif  // __cplusplus
 665
 666 /*
 667  * Provide a fake default value to be used when a value is required but none can
 668  * sensibily be provided without adding undefined behavior or security issues.
 669  *
 670  * This function asserts and aborts if it ever executed.
 671  *
 672  * Example usage:
 673  *
 674  *   class Trooper {
 675  *     const Droid& lookFor;
 676  *     Trooper() : lookFor(MakeCompilerAssumeUnreachableFakeValue<
 677                            const Droid&>()) {
 678  *       // The class might be instantiated due to existing caller
 679  *       // but this never happens in practice.
 680  *     }
 681  *   };
 682  *
 683  */
 684 #ifdef __cplusplus
 685 namespace mozilla {
 686 template <typename T>
 687 static inline T MakeCompilerAssumeUnreachableFakeValue() {
 688   MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE();
 689 }
 690 }  // namespace mozilla
 691 #endif  // __cplusplus
 692
 693 #endif /* mozilla_Assertions_h */