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 // It appears that this is sometimes compiled without XP_WIN
  21 #if defined(_WIN32)
  22 #  include <process.h>
  23 #  define MOZ_GET_PID() _getpid()
  24 #elif !defined(__wasi__)
  25 #  include <unistd.h>
  26 #  define MOZ_GET_PID() getpid()
  27 #else
  28 // Prevent compiler warning
  29 #  define MOZ_GET_PID() -1
  30 #endif
  31
  32 #include "mozilla/Attributes.h"
  33 #include "mozilla/Compiler.h"
  34 #include "mozilla/Fuzzing.h"
  35 #include "mozilla/Likely.h"
  36 #include "mozilla/MacroArgs.h"
  37 #include "mozilla/StaticAnalysisFunctions.h"
  38 #include "mozilla/Types.h"
  39 #ifdef MOZ_DUMP_ASSERTION_STACK
  40 #  include "mozilla/StackWalk.h"
  41 #endif
  42
  43 /*
  44  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  45  * if present. It is declared here (and defined in Assertions.cpp) to make it
  46  * available to all code, even libraries that don't link with the crash reporter
  47  * directly.
  48  */
  49 MOZ_BEGIN_EXTERN_C
  50 extern MFBT_DATA const char* gMozCrashReason;
  51 MOZ_END_EXTERN_C
  52
  53 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  54 static inline void AnnotateMozCrashReason(const char* reason) {
  55   gMozCrashReason = reason;
  56   // See bug 1681846, on 32-bit Android ARM the compiler removes the store to
  57   // gMozCrashReason if this barrier is not present.
  58   asm volatile("" ::: "memory");
  59 }
  60 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  61 #else
  62 #  define MOZ_CRASH_ANNOTATE(...) \
  63     do { /* nothing */            \
  64     } while (false)
  65 #endif
  66
  67 #include <stddef.h>
  68 #include <stdio.h>
  69 #include <stdlib.h>
  70 #ifdef _MSC_VER
  71 /*
  72  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  73  * further depends on <windef.h>.  We hardcode these few definitions manually
  74  * because those headers clutter the global namespace with a significant
  75  * number of undesired macros and symbols.
  76  */
  77 MOZ_BEGIN_EXTERN_C
  78 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  79                                                      unsigned int uExitCode);
  80 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  81 MOZ_END_EXTERN_C
  82 #elif defined(__wasi__)
  83 /*
  84  * On Wasm/WASI platforms, we just call __builtin_trap().
  85  */
  86 #else
  87 #  include <signal.h>
  88 #endif
  89 #ifdef ANDROID
  90 #  include <android/log.h>
  91 #endif
  92
  93 MOZ_BEGIN_EXTERN_C
  94
  95 #if defined(ANDROID) && defined(MOZ_DUMP_ASSERTION_STACK)
  96 MOZ_MAYBE_UNUSED static void MOZ_ReportAssertionFailurePrintFrame(
  97     const char* aBuf) {
  98   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s\n", aBuf);
  99 }
 100 #endif
 101
 102 /*
 103  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
 104  * location of the assertion) to the standard debug-output channel.
 105  *
 106  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
 107  * method is primarily for internal use in this header, and only secondarily
 108  * for use in implementing release-build assertions.
 109  */
 110
 111 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
 112 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
 113                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 114   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_ASSERT", aFilename, aLine, aStr);
 115 #ifdef ANDROID
 116   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
 117                       "[%d] Assertion failure: %s, at %s:%d\n", MOZ_GET_PID(),
 118                       aStr, aFilename, aLine);
 119 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 120   MozWalkTheStackWithWriter(MOZ_ReportAssertionFailurePrintFrame, CallerPC(),
 121                             /* aMaxFrames */ 0);
 122 #  endif
 123 #else
 124 #  if defined(MOZ_BUFFER_STDERR)
 125   char msg[1024] = "";
 126   snprintf(msg, sizeof(msg) - 1, "[%d] Assertion failure: %s, at %s:%d\n",
 127            MOZ_GET_PID(), aStr, aFilename, aLine);
 128   fputs(msg, stderr);
 129 #  else
 130   fprintf(stderr, "[%d] Assertion failure: %s, at %s:%d\n", MOZ_GET_PID(), aStr,
 131           aFilename, aLine);
 132 #  endif
 133 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 134   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 135 #  endif
 136   fflush(stderr);
 137 #endif
 138 }
 139
 140 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 141     const char* aStr, const char* aFilename,
 142     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 143 #ifdef ANDROID
 144   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 145                       "[%d] Hit MOZ_CRASH(%s) at %s:%d\n", MOZ_GET_PID(), aStr,
 146                       aFilename, aLine);
 147 #else
 148 #  if defined(MOZ_BUFFER_STDERR)
 149   char msg[1024] = "";
 150   snprintf(msg, sizeof(msg) - 1, "[%d] Hit MOZ_CRASH(%s) at %s:%d\n",
 151            MOZ_GET_PID(), aStr, aFilename, aLine);
 152   fputs(msg, stderr);
 153 #  else
 154   fprintf(stderr, "[%d] Hit MOZ_CRASH(%s) at %s:%d\n", MOZ_GET_PID(), aStr,
 155           aFilename, aLine);
 156 #  endif
 157 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 158   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 159 #  endif
 160   fflush(stderr);
 161 #endif
 162 }
 163
 164 /*
 165  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 166  * it is undefined behavior for execution to reach this point.  No guarantees
 167  * are made about what will happen if this is reached at runtime.  Most code
 168  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 169  * asserts.
 170  */
 171 #if defined(__clang__) || defined(__GNUC__)
 172 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 173 #elif defined(_MSC_VER)
 174 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 175 #else
 176 #  ifdef __cplusplus
 177 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 178 #  else
 179 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 180 #  endif
 181 #endif
 182
 183 /**
 184  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 185  * call MOZ_CRASH instead.
 186  */
 187 #if defined(_MSC_VER)
 188 /*
 189  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 190  * (not nested in a system function) breakpoint.  This distinctively invokes
 191  * Breakpad without requiring system library symbols on all stack-processing
 192  * machines, as a nested breakpoint would require.
 193  *
 194  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 195  * together, which would make crash reports hard to understand.
 196  *
 197  * We use TerminateProcess with the exit code aborting would generate
 198  * because we don't want to invoke atexit handlers, destructors, library
 199  * unload handlers, and so on when our process might be in a compromised
 200  * state.
 201  *
 202  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 203  * process error dialog multiple times.  See bug 345118 and bug 426163.
 204  *
 205  * (Technically these are Windows requirements, not MSVC requirements.  But
 206  * practically you need MSVC for debugging, and we only ship builds created
 207  * by MSVC, so doing it this way reduces complexity.)
 208  */
 209
 210 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 211 MOZ_NoReturn(int aLine) {
 212   *((volatile int*)NULL) = aLine;
 213   TerminateProcess(GetCurrentProcess(), 3);
 214   MOZ_ASSUME_UNREACHABLE_MARKER();
 215 }
 216
 217 #  define MOZ_REALLY_CRASH(line) \
 218     do {                         \
 219       __debugbreak();            \
 220       MOZ_NoReturn(line);        \
 221     } while (false)
 222
 223 #elif __wasi__
 224
 225 #  define MOZ_REALLY_CRASH(line) __builtin_trap()
 226
 227 #else
 228
 229 /*
 230  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 231  * crash. NULL is preferred however if for some reason NULL cannot be used
 232  * this makes choosing another value possible.
 233  *
 234  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 235  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 236  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 237  * SEGV at 0x0.
 238  */
 239 #  ifdef MOZ_UBSAN
 240 #    define MOZ_CRASH_WRITE_ADDR 0x1
 241 #  else
 242 #    define MOZ_CRASH_WRITE_ADDR NULL
 243 #  endif
 244
 245 #  ifdef __cplusplus
 246 #    define MOZ_REALLY_CRASH(line)                                  \
 247       do {                                                          \
 248         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 249         MOZ_NOMERGE ::abort();                                      \
 250       } while (false)
 251 #  else
 252 #    define MOZ_REALLY_CRASH(line)                                  \
 253       do {                                                          \
 254         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 255         MOZ_NOMERGE abort();                                        \
 256       } while (false)
 257 #  endif
 258 #endif
 259
 260 /*
 261  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 262  * Breakpad-compatible way, in both debug and release builds.
 263  *
 264  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 265  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 266  * corruption, and so on.  It's also a good solution if you need safe behavior
 267  * in release builds as well as debug builds.  But if the failure is one that
 268  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 269  *
 270  * The optional explanation-string, if provided, must be a string literal
 271  * explaining why we're crashing.  This argument is intended for use with
 272  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 273  * obvious why we're crashing.
 274  *
 275  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 276  * explanation-string, we print the string to stderr.  Otherwise, we don't
 277  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 278  * builds, and it's hard to print to stderr safely when memory might have been
 279  * corrupted.
 280  */
 281 #if !(defined(DEBUG) || defined(FUZZING))
 282 #  define MOZ_CRASH(...)                                                      \
 283     do {                                                                      \
 284       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 285       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 286       MOZ_REALLY_CRASH(__LINE__);                                             \
 287     } while (false)
 288 #else
 289 #  define MOZ_CRASH(...)                                                      \
 290     do {                                                                      \
 291       MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", __FILE__, __LINE__, NULL); \
 292       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__);                    \
 293       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");                       \
 294       MOZ_REALLY_CRASH(__LINE__);                                             \
 295     } while (false)
 296 #endif
 297
 298 /*
 299  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 300  * cannot be a string literal (but no other processing needs to be done on it).
 301  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 302  * strings from a potentially compromised process is not without risk. If the
 303  * string being passed is the result of a printf-style function, consider using
 304  * MOZ_CRASH_UNSAFE_PRINTF instead.
 305  *
 306  * @note This macro causes data collection because crash strings are annotated
 307  * to crash-stats and are publicly visible. Firefox data stewards must do data
 308  * review on usages of this macro.
 309  */
 310 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 311     const char* aFilename, int aLine, const char* aReason) {
 312   MOZ_FUZZING_HANDLE_CRASH_EVENT4("MOZ_CRASH", aFilename, aLine, aReason);
 313 #if defined(DEBUG) || defined(FUZZING)
 314   MOZ_ReportCrash(aReason, aFilename, aLine);
 315 #endif
 316   MOZ_CRASH_ANNOTATE(aReason);
 317   MOZ_REALLY_CRASH(aLine);
 318 }
 319 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 320
 321 static const size_t sPrintfMaxArgs = 4;
 322 static const size_t sPrintfCrashReasonSize = 1024;
 323
 324 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 325     char* MOZ_CrashPrintf(const char* aFormat, ...);
 326
 327 /*
 328  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 329  * information is desired than a string literal can supply. The caller provides
 330  * a printf-style format string, which must be a string literal and between
 331  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 332  * possible, as passing arbitrary strings to printf from a potentially
 333  * compromised process is not without risk.
 334  *
 335  * @note This macro causes data collection because crash strings are annotated
 336  * to crash-stats and are publicly visible. Firefox data stewards must do data
 337  * review on usages of this macro.
 338  */
 339 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 340   do {                                                                      \
 341     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 342                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 343                   "Or maybe you want MOZ_CRASH instead?");                  \
 344     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 345                   "Only up to 4 additional arguments are allowed!");        \
 346     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 347                   "The supplied format string is too long!");               \
 348     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 349   } while (false)
 350
 351 MOZ_END_EXTERN_C
 352
 353 /*
 354  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 355  * debug builds.  If it is, execution continues.  Otherwise, an error message
 356  * including the expression and the explanation-string (if provided) is printed,
 357  * an attempt is made to invoke any existing debugger, and execution halts.
 358  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 359  * which can correctly be falsy.
 360  *
 361  * The optional explanation-string, if provided, must be a string literal
 362  * explaining the assertion.  It is intended for use with assertions whose
 363  * correctness or rationale is non-obvious, and for assertions where the "real"
 364  * condition being tested is best described prosaically.  Don't provide an
 365  * explanation if it's not actually helpful.
 366  *
 367  *   // No explanation needed: pointer arguments often must not be NULL.
 368  *   MOZ_ASSERT(arg);
 369  *
 370  *   // An explanation can be helpful to explain exactly how we know an
 371  *   // assertion is valid.
 372  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 373  *              "given that <thingA> and <thingB>, we must have...");
 374  *
 375  *   // Or it might disambiguate multiple identical (save for their location)
 376  *   // assertions of the same expression.
 377  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 378  *              "we already set [[PrimitiveThis]] for this Boolean object");
 379  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 380  *              "we already set [[PrimitiveThis]] for this String object");
 381  *
 382  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 383  * *only* during debugging, not "in the field". If you want the latter, use
 384  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 385  *
 386  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly and early beta
 387  * and MOZ_ASSERT in late Beta and Release - use this when a condition is
 388  * potentially rare enough to require real user testing to hit, but is not
 389  * security-sensitive. This can cause user pain, so use it sparingly. If a
 390  * MOZ_DIAGNOSTIC_ASSERT is firing, it should promptly be converted to a
 391  * MOZ_ASSERT while the failure is being investigated, rather than letting users
 392  * suffer.
 393  *
 394  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 395  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 396  */
 397
 398 /*
 399  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 400  * accidentally passing something unintended in lieu of an assertion condition.
 401  */
 402
 403 #ifdef __cplusplus
 404 #  include <type_traits>
 405 namespace mozilla {
 406 namespace detail {
 407
 408 template <typename T>
 409 struct AssertionConditionType {
 410   using ValueT = std::remove_reference_t<T>;
 411   static_assert(!std::is_array_v<ValueT>,
 412                 "Expected boolean assertion condition, got an array or a "
 413                 "string!");
 414   static_assert(!std::is_function_v<ValueT>,
 415                 "Expected boolean assertion condition, got a function! Did "
 416                 "you intend to call that function?");
 417   static_assert(!std::is_floating_point_v<ValueT>,
 418                 "It's often a bad idea to assert that a floating-point number "
 419                 "is nonzero, because such assertions tend to intermittently "
 420                 "fail. Shouldn't your code gracefully handle this case instead "
 421                 "of asserting? Anyway, if you really want to do that, write an "
 422                 "explicit boolean condition, like !!x or x!=0.");
 423
 424   static const bool isValid = true;
 425 };
 426
 427 }  // namespace detail
 428 }  // namespace mozilla
 429 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 430     static_assert(                                                     \
 431         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 432         "invalid assertion condition")
 433 #else
 434 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 435 #endif
 436
 437 #if defined(DEBUG) || defined(MOZ_ASAN)
 438 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 439     MOZ_ReportAssertionFailure(__VA_ARGS__)
 440 #else
 441 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 442     do { /* nothing */                      \
 443     } while (false)
 444 #endif
 445
 446 /* First the single-argument form. */
 447 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 448   do {                                                         \
 449     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 450     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 451       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);            \
 452       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 453       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 454       MOZ_REALLY_CRASH(__LINE__);                              \
 455     }                                                          \
 456   } while (false)
 457 /* Now the two-argument form. */
 458 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 459   do {                                                               \
 460     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 461     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 462       MOZ_FUZZING_HANDLE_CRASH_EVENT2(kind, #expr);                  \
 463       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 464                                    __LINE__);                        \
 465       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 466       MOZ_REALLY_CRASH(__LINE__);                                    \
 467     }                                                                \
 468   } while (false)
 469
 470 #define MOZ_ASSERT_GLUE(a, b) a b
 471 #define MOZ_RELEASE_ASSERT(...)                                       \
 472   MOZ_ASSERT_GLUE(                                                    \
 473       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 474       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 475
 476 #ifdef DEBUG
 477 #  define MOZ_ASSERT(...)                                               \
 478     MOZ_ASSERT_GLUE(                                                    \
 479         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 480         ("MOZ_ASSERT", __VA_ARGS__))
 481 #else
 482 #  define MOZ_ASSERT(...) \
 483     do {                  \
 484     } while (false)
 485 #endif /* DEBUG */
 486
 487 #if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
 488 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 489     MOZ_ASSERT_GLUE(                                                    \
 490         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 491         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 492 #else
 493 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 494     do {                             \
 495     } while (false)
 496 #endif
 497
 498 /*
 499  * MOZ_ASSERT_DEBUG_OR_FUZZING is like a MOZ_ASSERT but also enabled in builds
 500  * that are non-DEBUG but FUZZING. This is useful for checks that are too
 501  * expensive for Nightly in general but are still indicating potentially
 502  * critical bugs.
 503  * In fuzzing builds, the assert is rewritten to be a diagnostic assert because
 504  * we already use this in other sensitive places and fuzzing automation is
 505  * set to act on these under all circumstances.
 506  */
 507 #ifdef FUZZING
 508 #  define MOZ_ASSERT_DEBUG_OR_FUZZING(...) MOZ_DIAGNOSTIC_ASSERT(__VA_ARGS__)
 509 #else
 510 #  define MOZ_ASSERT_DEBUG_OR_FUZZING(...) MOZ_ASSERT(__VA_ARGS__)
 511 #endif
 512
 513 /*
 514  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 515  * true.
 516  *
 517  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 518  *
 519  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 520  * designed to catch bugs during debugging, not "in the field".
 521  */
 522 #ifdef DEBUG
 523 #  define MOZ_ASSERT_IF(cond, expr) \
 524     do {                            \
 525       if (cond) {                   \
 526         MOZ_ASSERT(expr);           \
 527       }                             \
 528     } while (false)
 529 #else
 530 #  define MOZ_ASSERT_IF(cond, expr) \
 531     do {                            \
 532     } while (false)
 533 #endif
 534
 535 /*
 536  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 537  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 538  *
 539  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 540  * diagnostic assertions work and how to use them.
 541  */
 542 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 543 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 544     do {                                       \
 545       if (cond) {                              \
 546         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 547       }                                        \
 548     } while (false)
 549 #else
 550 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 551     do {                                       \
 552     } while (false)
 553 #endif
 554
 555 /*
 556  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 557  * can assume that the macro call cannot be reached during execution.  This lets
 558  * the compiler generate better-optimized code under some circumstances, at the
 559  * expense of the program's behavior being undefined if control reaches the
 560  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 561  *
 562  * In Gecko, you probably should not use this macro outside of performance- or
 563  * size-critical code, because it's unsafe.  If you don't care about code size
 564  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 565  *
 566  * SpiderMonkey is a different beast, and there it's acceptable to use
 567  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 568  *
 569  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 570  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 571  * call.
 572  *
 573  * Example usage:
 574  *
 575  *   enum ValueType {
 576  *     VALUE_STRING,
 577  *     VALUE_INT,
 578  *     VALUE_FLOAT
 579  *   };
 580  *
 581  *   int ptrToInt(ValueType type, void* value) {
 582  *   {
 583  *     // We know for sure that type is either INT or FLOAT, and we want this
 584  *     // code to run as quickly as possible.
 585  *     switch (type) {
 586  *     case VALUE_INT:
 587  *       return *(int*) value;
 588  *     case VALUE_FLOAT:
 589  *       return (int) *(float*) value;
 590  *     default:
 591  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 592  *     }
 593  *   }
 594  */
 595
 596 /*
 597  * Unconditional assert in debug builds for (assumed) unreachable code paths
 598  * that have a safe return without crashing in release builds.
 599  */
 600 #define MOZ_ASSERT_UNREACHABLE(reason) \
 601   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 602
 603 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 604   do {                                                  \
 605     MOZ_ASSERT_UNREACHABLE(reason);                     \
 606     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 607   } while (false)
 608
 609 /**
 610  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 611  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 612  * debug builds, but intentionally fall through in release builds to handle
 613  * unexpected values.
 614  *
 615  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to [[fallthrough]]? In
 616  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 617  * requiring a [[fallthrough]] annotation to suppress a -Wimplicit-fallthrough
 618  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 619  * `if (true) { MOZ_CRASH(); }` and the [[fallthrough]] annotation will cause
 620  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 621  * warning stalemate.
 622  *
 623  * // Example before MOZ_FALLTHROUGH_ASSERT:
 624  * switch (foo) {
 625  *   default:
 626  *     // This case wants to assert in debug builds, fall through in release.
 627  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 628  *     [[fallthrough]];   // but -Wunreachable-code warning in debug builds!
 629  *   case 5:
 630  *     return 5;
 631  * }
 632  *
 633  * // Example with MOZ_FALLTHROUGH_ASSERT:
 634  * switch (foo) {
 635  *   default:
 636  *     // This case asserts in debug builds, falls through in release.
 637  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 638  *   case 5:
 639  *     return 5;
 640  * }
 641  */
 642 #ifdef DEBUG
 643 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 644     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 645 #else
 646 #  define MOZ_FALLTHROUGH_ASSERT(...) [[fallthrough]]
 647 #endif
 648
 649 /*
 650  * MOZ_ALWAYS_TRUE(expr) and friends always evaluate the provided expression,
 651  * in debug builds and in release builds both.  Then, in debug builds and
 652  * Nightly and early beta builds, the value of the expression is
 653  * asserted either true or false using MOZ_DIAGNOSTIC_ASSERT.
 654  */
 655 #define MOZ_ALWAYS_TRUE(expr)              \
 656   do {                                     \
 657     if (MOZ_LIKELY(expr)) {                \
 658       /* Silence [[nodiscard]]. */         \
 659     } else {                               \
 660       MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 661     }                                      \
 662   } while (false)
 663
 664 #define MOZ_ALWAYS_FALSE(expr) MOZ_ALWAYS_TRUE(!(expr))
 665 #define MOZ_ALWAYS_OK(expr) MOZ_ALWAYS_TRUE((expr).isOk())
 666 #define MOZ_ALWAYS_ERR(expr) MOZ_ALWAYS_TRUE((expr).isErr())
 667
 668 /*
 669  * These are disabled when fuzzing
 670  */
 671 #ifdef FUZZING
 672 #  define MOZ_CRASH_UNLESS_FUZZING(...) \
 673     do {                                \
 674     } while (0)
 675 #  define MOZ_ASSERT_UNLESS_FUZZING(...) \
 676     do {                                 \
 677     } while (0)
 678 #else
 679 #  define MOZ_CRASH_UNLESS_FUZZING(...) MOZ_CRASH(__VA_ARGS__)
 680 #  define MOZ_ASSERT_UNLESS_FUZZING(...) MOZ_ASSERT(__VA_ARGS__)
 681 #endif
 682
 683 #undef MOZ_BUFFER_STDERR
 684 #undef MOZ_CRASH_CRASHREPORT
 685 #undef MOZ_DUMP_ASSERTION_STACK
 686
 687 /*
 688  * This is only used by Array and nsTArray classes, therefore it is not
 689  * required when included from C code.
 690  */
 691 #ifdef __cplusplus
 692 namespace mozilla::detail {
 693 MFBT_API MOZ_NORETURN MOZ_COLD void InvalidArrayIndex_CRASH(size_t aIndex,
 694                                                             size_t aLength);
 695 }  // namespace mozilla::detail
 696 #endif  // __cplusplus
 697
 698 /*
 699  * Provide a fake default value to be used when a value is required but none can
 700  * sensibily be provided without adding undefined behavior or security issues.
 701  *
 702  * This function asserts and aborts if it ever executed.
 703  *
 704  * Example usage:
 705  *
 706  *   class Trooper {
 707  *     const Droid& lookFor;
 708  *     Trooper() : lookFor(MakeCompilerAssumeUnreachableFakeValue<
 709                            const Droid&>()) {
 710  *       // The class might be instantiated due to existing caller
 711  *       // but this never happens in practice.
 712  *     }
 713  *   };
 714  *
 715  */
 716 #ifdef __cplusplus
 717 namespace mozilla {
 718 template <typename T>
 719 static inline T MakeCompilerAssumeUnreachableFakeValue() {
 720   MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE();
 721 }
 722 }  // namespace mozilla
 723 #endif  // __cplusplus
 724
 725 #endif /* mozilla_Assertions_h */