mfbt/Assertions.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Implementations of runtime and static assertion macros for C and C++. */
   8
   9 #ifndef mozilla_Assertions_h
  10 #define mozilla_Assertions_h
  11
  12 #if (defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)) && \
  13     !defined(__wasi__)
  14 #  define MOZ_DUMP_ASSERTION_STACK
  15 #endif
  16
  17 #include "mozilla/Attributes.h"
  18 #include "mozilla/Compiler.h"
  19 #include "mozilla/Likely.h"
  20 #include "mozilla/MacroArgs.h"
  21 #include "mozilla/StaticAnalysisFunctions.h"
  22 #include "mozilla/Types.h"
  23 #ifdef MOZ_DUMP_ASSERTION_STACK
  24 #  include "mozilla/StackWalk.h"
  25 #endif
  26
  27 /*
  28  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  29  * if present. It is declared here (and defined in Assertions.cpp) to make it
  30  * available to all code, even libraries that don't link with the crash reporter
  31  * directly.
  32  */
  33 MOZ_BEGIN_EXTERN_C
  34 extern MFBT_DATA const char* gMozCrashReason;
  35 MOZ_END_EXTERN_C
  36
  37 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  38 static inline void AnnotateMozCrashReason(const char* reason) {
  39   gMozCrashReason = reason;
  40 }
  41 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  42 #else
  43 #  define MOZ_CRASH_ANNOTATE(...) \
  44     do { /* nothing */            \
  45     } while (false)
  46 #endif
  47
  48 #include <stddef.h>
  49 #include <stdio.h>
  50 #include <stdlib.h>
  51 #ifdef _MSC_VER
  52 /*
  53  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  54  * further depends on <windef.h>.  We hardcode these few definitions manually
  55  * because those headers clutter the global namespace with a significant
  56  * number of undesired macros and symbols.
  57  */
  58 MOZ_BEGIN_EXTERN_C
  59 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  60                                                      unsigned int uExitCode);
  61 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  62 MOZ_END_EXTERN_C
  63 #elif defined(__wasi__)
  64 /*
  65  * On Wasm/WASI platforms, we just call __builtin_trap().
  66  */
  67 #else
  68 #  include <signal.h>
  69 #endif
  70 #ifdef ANDROID
  71 #  include <android/log.h>
  72 #endif
  73
  74 MOZ_BEGIN_EXTERN_C
  75
  76 #if defined(ANDROID) && defined(MOZ_DUMP_ASSERTION_STACK)
  77 MOZ_MAYBE_UNUSED static void MOZ_ReportAssertionFailurePrintFrame(
  78     const char* aBuf) {
  79   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s\n", aBuf);
  80 }
  81 #endif
  82
  83 /*
  84  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
  85  * location of the assertion) to the standard debug-output channel.
  86  *
  87  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
  88  * method is primarily for internal use in this header, and only secondarily
  89  * for use in implementing release-build assertions.
  90  */
  91 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
  92 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
  93                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
  94 #ifdef ANDROID
  95   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
  96                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
  97                       aLine);
  98 #  if defined(MOZ_DUMP_ASSERTION_STACK)
  99   MozWalkTheStackWithWriter(MOZ_ReportAssertionFailurePrintFrame, CallerPC(),
 100                             /* aMaxFrames */ 0);
 101 #  endif
 102 #else
 103   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 104 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 105   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 106 #  endif
 107   fflush(stderr);
 108 #endif
 109 }
 110
 111 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 112     const char* aStr, const char* aFilename,
 113     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 114 #ifdef ANDROID
 115   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 116                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 117 #else
 118   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 119 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 120   MozWalkTheStack(stderr, CallerPC(), /* aMaxFrames */ 0);
 121 #  endif
 122   fflush(stderr);
 123 #endif
 124 }
 125
 126 /**
 127  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 128  * call MOZ_CRASH instead.
 129  */
 130 #if defined(_MSC_VER)
 131 /*
 132  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 133  * (not nested in a system function) breakpoint.  This distinctively invokes
 134  * Breakpad without requiring system library symbols on all stack-processing
 135  * machines, as a nested breakpoint would require.
 136  *
 137  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 138  * together, which would make crash reports hard to understand.
 139  *
 140  * We use TerminateProcess with the exit code aborting would generate
 141  * because we don't want to invoke atexit handlers, destructors, library
 142  * unload handlers, and so on when our process might be in a compromised
 143  * state.
 144  *
 145  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 146  * process error dialog multiple times.  See bug 345118 and bug 426163.
 147  *
 148  * (Technically these are Windows requirements, not MSVC requirements.  But
 149  * practically you need MSVC for debugging, and we only ship builds created
 150  * by MSVC, so doing it this way reduces complexity.)
 151  */
 152
 153 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 154 MOZ_NoReturn(int aLine) {
 155   *((volatile int*)NULL) = aLine;
 156   TerminateProcess(GetCurrentProcess(), 3);
 157 }
 158
 159 #  define MOZ_REALLY_CRASH(line) \
 160     do {                         \
 161       __debugbreak();            \
 162       MOZ_NoReturn(line);        \
 163     } while (false)
 164
 165 #elif __wasi__
 166
 167 #  define MOZ_REALLY_CRASH(line) __builtin_trap()
 168
 169 #else
 170
 171 /*
 172  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 173  * crash. NULL is preferred however if for some reason NULL cannot be used
 174  * this makes choosing another value possible.
 175  *
 176  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 177  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 178  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 179  * SEGV at 0x0.
 180  */
 181 #  ifdef MOZ_UBSAN
 182 #    define MOZ_CRASH_WRITE_ADDR 0x1
 183 #  else
 184 #    define MOZ_CRASH_WRITE_ADDR NULL
 185 #  endif
 186
 187 #  ifdef __cplusplus
 188 #    define MOZ_REALLY_CRASH(line)                                  \
 189       do {                                                          \
 190         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 191         ::abort();                                                  \
 192       } while (false)
 193 #  else
 194 #    define MOZ_REALLY_CRASH(line)                                  \
 195       do {                                                          \
 196         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 197         abort();                                                    \
 198       } while (false)
 199 #  endif
 200 #endif
 201
 202 /*
 203  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 204  * Breakpad-compatible way, in both debug and release builds.
 205  *
 206  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 207  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 208  * corruption, and so on.  It's also a good solution if you need safe behavior
 209  * in release builds as well as debug builds.  But if the failure is one that
 210  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 211  *
 212  * The optional explanation-string, if provided, must be a string literal
 213  * explaining why we're crashing.  This argument is intended for use with
 214  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 215  * obvious why we're crashing.
 216  *
 217  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 218  * explanation-string, we print the string to stderr.  Otherwise, we don't
 219  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 220  * builds, and it's hard to print to stderr safely when memory might have been
 221  * corrupted.
 222  */
 223 #ifndef DEBUG
 224 #  define MOZ_CRASH(...)                                \
 225     do {                                                \
 226       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")"); \
 227       MOZ_REALLY_CRASH(__LINE__);                       \
 228     } while (false)
 229 #else
 230 #  define MOZ_CRASH(...)                                   \
 231     do {                                                   \
 232       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
 233       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");    \
 234       MOZ_REALLY_CRASH(__LINE__);                          \
 235     } while (false)
 236 #endif
 237
 238 /*
 239  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 240  * cannot be a string literal (but no other processing needs to be done on it).
 241  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 242  * strings from a potentially compromised process is not without risk. If the
 243  * string being passed is the result of a printf-style function, consider using
 244  * MOZ_CRASH_UNSAFE_PRINTF instead.
 245  *
 246  * @note This macro causes data collection because crash strings are annotated
 247  * to crash-stats and are publicly visible. Firefox data stewards must do data
 248  * review on usages of this macro.
 249  */
 250 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 251     const char* aFilename, int aLine, const char* aReason) {
 252 #ifdef DEBUG
 253   MOZ_ReportCrash(aReason, aFilename, aLine);
 254 #endif
 255   MOZ_CRASH_ANNOTATE(aReason);
 256   MOZ_REALLY_CRASH(aLine);
 257 }
 258 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 259
 260 static const size_t sPrintfMaxArgs = 4;
 261 static const size_t sPrintfCrashReasonSize = 1024;
 262
 263 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 264     char* MOZ_CrashPrintf(const char* aFormat, ...);
 265
 266 /*
 267  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 268  * information is desired than a string literal can supply. The caller provides
 269  * a printf-style format string, which must be a string literal and between
 270  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 271  * possible, as passing arbitrary strings to printf from a potentially
 272  * compromised process is not without risk.
 273  *
 274  * @note This macro causes data collection because crash strings are annotated
 275  * to crash-stats and are publicly visible. Firefox data stewards must do data
 276  * review on usages of this macro.
 277  */
 278 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 279   do {                                                                      \
 280     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 281                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 282                   "Or maybe you want MOZ_CRASH instead?");                  \
 283     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 284                   "Only up to 4 additional arguments are allowed!");        \
 285     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 286                   "The supplied format string is too long!");               \
 287     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 288   } while (false)
 289
 290 MOZ_END_EXTERN_C
 291
 292 /*
 293  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 294  * debug builds.  If it is, execution continues.  Otherwise, an error message
 295  * including the expression and the explanation-string (if provided) is printed,
 296  * an attempt is made to invoke any existing debugger, and execution halts.
 297  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 298  * which can correctly be falsy.
 299  *
 300  * The optional explanation-string, if provided, must be a string literal
 301  * explaining the assertion.  It is intended for use with assertions whose
 302  * correctness or rationale is non-obvious, and for assertions where the "real"
 303  * condition being tested is best described prosaically.  Don't provide an
 304  * explanation if it's not actually helpful.
 305  *
 306  *   // No explanation needed: pointer arguments often must not be NULL.
 307  *   MOZ_ASSERT(arg);
 308  *
 309  *   // An explanation can be helpful to explain exactly how we know an
 310  *   // assertion is valid.
 311  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 312  *              "given that <thingA> and <thingB>, we must have...");
 313  *
 314  *   // Or it might disambiguate multiple identical (save for their location)
 315  *   // assertions of the same expression.
 316  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 317  *              "we already set [[PrimitiveThis]] for this Boolean object");
 318  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 319  *              "we already set [[PrimitiveThis]] for this String object");
 320  *
 321  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 322  * *only* during debugging, not "in the field". If you want the latter, use
 323  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 324  *
 325  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 326  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 327  * enough to require real user testing to hit, but is not security-sensitive.
 328  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 329  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 330  * is being investigated, rather than letting users suffer.
 331  *
 332  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 333  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 334  */
 335
 336 /*
 337  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 338  * accidentally passing something unintended in lieu of an assertion condition.
 339  */
 340
 341 #ifdef __cplusplus
 342 #  include <type_traits>
 343 namespace mozilla {
 344 namespace detail {
 345
 346 template <typename T>
 347 struct AssertionConditionType {
 348   using ValueT = std::remove_reference_t<T>;
 349   static_assert(!std::is_array_v<ValueT>,
 350                 "Expected boolean assertion condition, got an array or a "
 351                 "string!");
 352   static_assert(!std::is_function_v<ValueT>,
 353                 "Expected boolean assertion condition, got a function! Did "
 354                 "you intend to call that function?");
 355   static_assert(!std::is_floating_point_v<ValueT>,
 356                 "It's often a bad idea to assert that a floating-point number "
 357                 "is nonzero, because such assertions tend to intermittently "
 358                 "fail. Shouldn't your code gracefully handle this case instead "
 359                 "of asserting? Anyway, if you really want to do that, write an "
 360                 "explicit boolean condition, like !!x or x!=0.");
 361
 362   static const bool isValid = true;
 363 };
 364
 365 }  // namespace detail
 366 }  // namespace mozilla
 367 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 368     static_assert(                                                     \
 369         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 370         "invalid assertion condition")
 371 #else
 372 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 373 #endif
 374
 375 #if defined(DEBUG) || defined(MOZ_ASAN)
 376 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 377     MOZ_ReportAssertionFailure(__VA_ARGS__)
 378 #else
 379 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 380     do { /* nothing */                      \
 381     } while (false)
 382 #endif
 383
 384 /* First the single-argument form. */
 385 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 386   do {                                                         \
 387     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 388     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 389       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 390       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 391       MOZ_REALLY_CRASH(__LINE__);                              \
 392     }                                                          \
 393   } while (false)
 394 /* Now the two-argument form. */
 395 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 396   do {                                                               \
 397     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 398     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 399       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 400                                    __LINE__);                        \
 401       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 402       MOZ_REALLY_CRASH(__LINE__);                                    \
 403     }                                                                \
 404   } while (false)
 405
 406 #define MOZ_ASSERT_GLUE(a, b) a b
 407 #define MOZ_RELEASE_ASSERT(...)                                       \
 408   MOZ_ASSERT_GLUE(                                                    \
 409       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 410       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 411
 412 #ifdef DEBUG
 413 #  define MOZ_ASSERT(...)                                               \
 414     MOZ_ASSERT_GLUE(                                                    \
 415         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 416         ("MOZ_ASSERT", __VA_ARGS__))
 417 #else
 418 #  define MOZ_ASSERT(...) \
 419     do {                  \
 420     } while (false)
 421 #endif /* DEBUG */
 422
 423 #if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION) || defined(DEBUG)
 424 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 425     MOZ_ASSERT_GLUE(                                                    \
 426         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 427         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 428 #  define MOZ_DIAGNOSTIC_ASSERT_ENABLED 1
 429 #else
 430 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 431     do {                             \
 432     } while (false)
 433 #endif
 434
 435 /*
 436  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 437  * true.
 438  *
 439  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 440  *
 441  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 442  * designed to catch bugs during debugging, not "in the field".
 443  */
 444 #ifdef DEBUG
 445 #  define MOZ_ASSERT_IF(cond, expr) \
 446     do {                            \
 447       if (cond) {                   \
 448         MOZ_ASSERT(expr);           \
 449       }                             \
 450     } while (false)
 451 #else
 452 #  define MOZ_ASSERT_IF(cond, expr) \
 453     do {                            \
 454     } while (false)
 455 #endif
 456
 457 /*
 458  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 459  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 460  *
 461  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 462  * diagnostic assertions work and how to use them.
 463  */
 464 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 465 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 466     do {                                       \
 467       if (cond) {                              \
 468         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 469       }                                        \
 470     } while (false)
 471 #else
 472 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 473     do {                                       \
 474     } while (false)
 475 #endif
 476
 477 /*
 478  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 479  * it is undefined behavior for execution to reach this point.  No guarantees
 480  * are made about what will happen if this is reached at runtime.  Most code
 481  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 482  * asserts.
 483  */
 484 #if defined(__clang__) || defined(__GNUC__)
 485 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 486 #elif defined(_MSC_VER)
 487 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 488 #else
 489 #  ifdef __cplusplus
 490 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 491 #  else
 492 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 493 #  endif
 494 #endif
 495
 496 /*
 497  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 498  * can assume that the macro call cannot be reached during execution.  This lets
 499  * the compiler generate better-optimized code under some circumstances, at the
 500  * expense of the program's behavior being undefined if control reaches the
 501  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 502  *
 503  * In Gecko, you probably should not use this macro outside of performance- or
 504  * size-critical code, because it's unsafe.  If you don't care about code size
 505  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 506  *
 507  * SpiderMonkey is a different beast, and there it's acceptable to use
 508  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 509  *
 510  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 511  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 512  * call.
 513  *
 514  * Example usage:
 515  *
 516  *   enum ValueType {
 517  *     VALUE_STRING,
 518  *     VALUE_INT,
 519  *     VALUE_FLOAT
 520  *   };
 521  *
 522  *   int ptrToInt(ValueType type, void* value) {
 523  *   {
 524  *     // We know for sure that type is either INT or FLOAT, and we want this
 525  *     // code to run as quickly as possible.
 526  *     switch (type) {
 527  *     case VALUE_INT:
 528  *       return *(int*) value;
 529  *     case VALUE_FLOAT:
 530  *       return (int) *(float*) value;
 531  *     default:
 532  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 533  *     }
 534  *   }
 535  */
 536
 537 /*
 538  * Unconditional assert in debug builds for (assumed) unreachable code paths
 539  * that have a safe return without crashing in release builds.
 540  */
 541 #define MOZ_ASSERT_UNREACHABLE(reason) \
 542   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 543
 544 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 545   do {                                                  \
 546     MOZ_ASSERT_UNREACHABLE(reason);                     \
 547     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 548   } while (false)
 549
 550 /**
 551  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 552  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 553  * debug builds, but intentionally fall through in release builds to handle
 554  * unexpected values.
 555  *
 556  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to [[fallthrough]]? In
 557  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 558  * requiring a [[fallthrough]] annotation to suppress a -Wimplicit-fallthrough
 559  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 560  * `if (true) { MOZ_CRASH(); }` and the [[fallthrough]] annotation will cause
 561  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 562  * warning stalemate.
 563  *
 564  * // Example before MOZ_FALLTHROUGH_ASSERT:
 565  * switch (foo) {
 566  *   default:
 567  *     // This case wants to assert in debug builds, fall through in release.
 568  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 569  *     [[fallthrough]];   // but -Wunreachable-code warning in debug builds!
 570  *   case 5:
 571  *     return 5;
 572  * }
 573  *
 574  * // Example with MOZ_FALLTHROUGH_ASSERT:
 575  * switch (foo) {
 576  *   default:
 577  *     // This case asserts in debug builds, falls through in release.
 578  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 579  *   case 5:
 580  *     return 5;
 581  * }
 582  */
 583 #ifdef DEBUG
 584 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 585     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 586 #else
 587 #  define MOZ_FALLTHROUGH_ASSERT(...) [[fallthrough]]
 588 #endif
 589
 590 /*
 591  * MOZ_ALWAYS_TRUE(expr) and friends always evaluate the provided expression,
 592  * in debug builds and in release builds both.  Then, in debug builds and
 593  * Nightly and DevEdition release builds, the value of the expression is
 594  * asserted either true or false using MOZ_DIAGNOSTIC_ASSERT.
 595  */
 596 #define MOZ_ALWAYS_TRUE(expr)              \
 597   do {                                     \
 598     if (MOZ_LIKELY(expr)) {                \
 599       /* Silence [[nodiscard]]. */         \
 600     } else {                               \
 601       MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 602     }                                      \
 603   } while (false)
 604
 605 #define MOZ_ALWAYS_FALSE(expr) MOZ_ALWAYS_TRUE(!(expr))
 606 #define MOZ_ALWAYS_OK(expr) MOZ_ALWAYS_TRUE((expr).isOk())
 607 #define MOZ_ALWAYS_ERR(expr) MOZ_ALWAYS_TRUE((expr).isErr())
 608
 609 #undef MOZ_DUMP_ASSERTION_STACK
 610 #undef MOZ_CRASH_CRASHREPORT
 611
 612 #endif /* mozilla_Assertions_h */