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