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(MOZILLA_INTERNAL_API) && defined(__cplusplus)
  13 #  define MOZ_DUMP_ASSERTION_STACK
  14 #endif
  15
  16 #include "mozilla/Attributes.h"
  17 #include "mozilla/Compiler.h"
  18 #include "mozilla/Likely.h"
  19 #include "mozilla/MacroArgs.h"
  20 #include "mozilla/StaticAnalysisFunctions.h"
  21 #include "mozilla/Types.h"
  22 #ifdef MOZ_DUMP_ASSERTION_STACK
  23 #  include "nsTraceRefcnt.h"
  24 #  ifdef ANDROID
  25 #    include "mozilla/StackWalk.h"
  26 #    include <algorithm>
  27 #  endif
  28 #endif
  29
  30 /*
  31  * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
  32  * if present. It is declared here (and defined in Assertions.cpp) to make it
  33  * available to all code, even libraries that don't link with the crash reporter
  34  * directly.
  35  */
  36 MOZ_BEGIN_EXTERN_C
  37 extern MFBT_DATA const char* gMozCrashReason;
  38 MOZ_END_EXTERN_C
  39
  40 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
  41 static inline void AnnotateMozCrashReason(const char* reason) {
  42   gMozCrashReason = reason;
  43 }
  44 #  define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
  45 #else
  46 #  define MOZ_CRASH_ANNOTATE(...) \
  47     do { /* nothing */            \
  48     } while (false)
  49 #endif
  50
  51 #include <stddef.h>
  52 #include <stdio.h>
  53 #include <stdlib.h>
  54 #ifdef _MSC_VER
  55 /*
  56  * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  57  * further depends on <windef.h>.  We hardcode these few definitions manually
  58  * because those headers clutter the global namespace with a significant
  59  * number of undesired macros and symbols.
  60  */
  61 MOZ_BEGIN_EXTERN_C
  62 __declspec(dllimport) int __stdcall TerminateProcess(void* hProcess,
  63                                                      unsigned int uExitCode);
  64 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  65 MOZ_END_EXTERN_C
  66 #else
  67 #  include <signal.h>
  68 #endif
  69 #ifdef ANDROID
  70 #  include <android/log.h>
  71 #endif
  72
  73 MOZ_BEGIN_EXTERN_C
  74
  75 /*
  76  * Prints |aStr| as an assertion failure (using aFilename and aLine as the
  77  * location of the assertion) to the standard debug-output channel.
  78  *
  79  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
  80  * method is primarily for internal use in this header, and only secondarily
  81  * for use in implementing release-build assertions.
  82  */
  83 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void
  84 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
  85                            int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
  86 #ifdef ANDROID
  87   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
  88                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
  89                       aLine);
  90 #  if defined(MOZ_DUMP_ASSERTION_STACK)
  91   nsTraceRefcnt::WalkTheStack(
  92       [](uint32_t aFrameNumber, void* aPC, void* aSP, void* aClosure) {
  93         MozCodeAddressDetails details;
  94         static const size_t buflen = 1024;
  95         char buf[buflen + 1];  // 1 for trailing '\n'
  96
  97         MozDescribeCodeAddress(aPC, &details);
  98         MozFormatCodeAddressDetails(buf, buflen, aFrameNumber, aPC, &details);
  99         size_t len = std::min(strlen(buf), buflen + 1 - 2);
 100         buf[len++] = '\n';
 101         buf[len] = '\0';
 102         __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s", buf);
 103       });
 104 #  endif
 105 #else
 106   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 107 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 108   nsTraceRefcnt::WalkTheStack(stderr);
 109 #  endif
 110   fflush(stderr);
 111 #endif
 112 }
 113
 114 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NEVER_INLINE void MOZ_ReportCrash(
 115     const char* aStr, const char* aFilename,
 116     int aLine) MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {
 117 #ifdef ANDROID
 118   __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 119                       "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 120 #else
 121   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
 122 #  if defined(MOZ_DUMP_ASSERTION_STACK)
 123   nsTraceRefcnt::WalkTheStack(stderr);
 124 #  endif
 125   fflush(stderr);
 126 #endif
 127 }
 128
 129 /**
 130  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 131  * call MOZ_CRASH instead.
 132  */
 133 #if defined(_MSC_VER)
 134 /*
 135  * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 136  * (not nested in a system function) breakpoint.  This distinctively invokes
 137  * Breakpad without requiring system library symbols on all stack-processing
 138  * machines, as a nested breakpoint would require.
 139  *
 140  * We use __LINE__ to prevent the compiler from folding multiple crash sites
 141  * together, which would make crash reports hard to understand.
 142  *
 143  * We use TerminateProcess with the exit code aborting would generate
 144  * because we don't want to invoke atexit handlers, destructors, library
 145  * unload handlers, and so on when our process might be in a compromised
 146  * state.
 147  *
 148  * We don't use abort() because it'd cause Windows to annoyingly pop up the
 149  * process error dialog multiple times.  See bug 345118 and bug 426163.
 150  *
 151  * (Technically these are Windows requirements, not MSVC requirements.  But
 152  * practically you need MSVC for debugging, and we only ship builds created
 153  * by MSVC, so doing it this way reduces complexity.)
 154  */
 155
 156 MOZ_MAYBE_UNUSED static MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
 157 MOZ_NoReturn(int aLine) {
 158   *((volatile int*)NULL) = aLine;
 159   TerminateProcess(GetCurrentProcess(), 3);
 160 }
 161
 162 #  define MOZ_REALLY_CRASH(line) \
 163     do {                         \
 164       __debugbreak();            \
 165       MOZ_NoReturn(line);        \
 166     } while (false)
 167 #else
 168
 169 /*
 170  * MOZ_CRASH_WRITE_ADDR is the address to be used when performing a forced
 171  * crash. NULL is preferred however if for some reason NULL cannot be used
 172  * this makes choosing another value possible.
 173  *
 174  * In the case of UBSan certain checks, bounds specifically, cause the compiler
 175  * to emit the 'ud2' instruction when storing to 0x0. This causes forced
 176  * crashes to manifest as ILL (at an arbitrary address) instead of the expected
 177  * SEGV at 0x0.
 178  */
 179 #  ifdef MOZ_UBSAN
 180 #    define MOZ_CRASH_WRITE_ADDR 0x1
 181 #  else
 182 #    define MOZ_CRASH_WRITE_ADDR NULL
 183 #  endif
 184
 185 #  ifdef __cplusplus
 186 #    define MOZ_REALLY_CRASH(line)                                  \
 187       do {                                                          \
 188         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 189         ::abort();                                                  \
 190       } while (false)
 191 #  else
 192 #    define MOZ_REALLY_CRASH(line)                                  \
 193       do {                                                          \
 194         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
 195         abort();                                                    \
 196       } while (false)
 197 #  endif
 198 #endif
 199
 200 /*
 201  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 202  * Breakpad-compatible way, in both debug and release builds.
 203  *
 204  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 205  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 206  * corruption, and so on.  It's also a good solution if you need safe behavior
 207  * in release builds as well as debug builds.  But if the failure is one that
 208  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 209  *
 210  * The optional explanation-string, if provided, must be a string literal
 211  * explaining why we're crashing.  This argument is intended for use with
 212  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 213  * obvious why we're crashing.
 214  *
 215  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 216  * explanation-string, we print the string to stderr.  Otherwise, we don't
 217  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 218  * builds, and it's hard to print to stderr safely when memory might have been
 219  * corrupted.
 220  */
 221 #ifndef DEBUG
 222 #  define MOZ_CRASH(...)                                \
 223     do {                                                \
 224       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")"); \
 225       MOZ_REALLY_CRASH(__LINE__);                       \
 226     } while (false)
 227 #else
 228 #  define MOZ_CRASH(...)                                   \
 229     do {                                                   \
 230       MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
 231       MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")");    \
 232       MOZ_REALLY_CRASH(__LINE__);                          \
 233     } while (false)
 234 #endif
 235
 236 /*
 237  * MOZ_CRASH_UNSAFE(explanation-string) can be used if the explanation string
 238  * cannot be a string literal (but no other processing needs to be done on it).
 239  * A regular MOZ_CRASH() is preferred wherever possible, as passing arbitrary
 240  * strings from a potentially compromised process is not without risk. If the
 241  * string being passed is the result of a printf-style function, consider using
 242  * MOZ_CRASH_UNSAFE_PRINTF instead.
 243  *
 244  * @note This macro causes data collection because crash strings are annotated
 245  * to crash-stats and are publicly visible. Firefox data stewards must do data
 246  * review on usages of this macro.
 247  */
 248 static MOZ_ALWAYS_INLINE_EVEN_DEBUG MOZ_COLD MOZ_NORETURN void MOZ_Crash(
 249     const char* aFilename, int aLine, const char* aReason) {
 250 #ifdef DEBUG
 251   MOZ_ReportCrash(aReason, aFilename, aLine);
 252 #endif
 253   MOZ_CRASH_ANNOTATE(aReason);
 254   MOZ_REALLY_CRASH(aLine);
 255 }
 256 #define MOZ_CRASH_UNSAFE(reason) MOZ_Crash(__FILE__, __LINE__, reason)
 257
 258 static const size_t sPrintfMaxArgs = 4;
 259 static const size_t sPrintfCrashReasonSize = 1024;
 260
 261 MFBT_API MOZ_COLD MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(1, 2) const
 262     char* MOZ_CrashPrintf(const char* aFormat, ...);
 263
 264 /*
 265  * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
 266  * information is desired than a string literal can supply. The caller provides
 267  * a printf-style format string, which must be a string literal and between
 268  * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
 269  * possible, as passing arbitrary strings to printf from a potentially
 270  * compromised process is not without risk.
 271  *
 272  * @note This macro causes data collection because crash strings are annotated
 273  * to crash-stats and are publicly visible. Firefox data stewards must do data
 274  * review on usages of this macro.
 275  */
 276 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...)                                \
 277   do {                                                                      \
 278     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
 279                   "Did you forget arguments to MOZ_CRASH_UNSAFE_PRINTF? "   \
 280                   "Or maybe you want MOZ_CRASH instead?");                  \
 281     static_assert(MOZ_ARG_COUNT(__VA_ARGS__) <= sPrintfMaxArgs,             \
 282                   "Only up to 4 additional arguments are allowed!");        \
 283     static_assert(sizeof(format) <= sPrintfCrashReasonSize,                 \
 284                   "The supplied format string is too long!");               \
 285     MOZ_Crash(__FILE__, __LINE__, MOZ_CrashPrintf("" format, __VA_ARGS__)); \
 286   } while (false)
 287
 288 MOZ_END_EXTERN_C
 289
 290 /*
 291  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 292  * debug builds.  If it is, execution continues.  Otherwise, an error message
 293  * including the expression and the explanation-string (if provided) is printed,
 294  * an attempt is made to invoke any existing debugger, and execution halts.
 295  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 296  * which can correctly be falsy.
 297  *
 298  * The optional explanation-string, if provided, must be a string literal
 299  * explaining the assertion.  It is intended for use with assertions whose
 300  * correctness or rationale is non-obvious, and for assertions where the "real"
 301  * condition being tested is best described prosaically.  Don't provide an
 302  * explanation if it's not actually helpful.
 303  *
 304  *   // No explanation needed: pointer arguments often must not be NULL.
 305  *   MOZ_ASSERT(arg);
 306  *
 307  *   // An explanation can be helpful to explain exactly how we know an
 308  *   // assertion is valid.
 309  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 310  *              "given that <thingA> and <thingB>, we must have...");
 311  *
 312  *   // Or it might disambiguate multiple identical (save for their location)
 313  *   // assertions of the same expression.
 314  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 315  *              "we already set [[PrimitiveThis]] for this Boolean object");
 316  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 317  *              "we already set [[PrimitiveThis]] for this String object");
 318  *
 319  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 320  * *only* during debugging, not "in the field". If you want the latter, use
 321  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
 322  *
 323  * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
 324  * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
 325  * enough to require real user testing to hit, but is not security-sensitive.
 326  * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
 327  * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
 328  * is being investigated, rather than letting users suffer.
 329  *
 330  * MOZ_DIAGNOSTIC_ASSERT_ENABLED is defined when MOZ_DIAGNOSTIC_ASSERT is like
 331  * MOZ_RELEASE_ASSERT rather than MOZ_ASSERT.
 332  */
 333
 334 /*
 335  * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
 336  * accidentally passing something unintended in lieu of an assertion condition.
 337  */
 338
 339 #ifdef __cplusplus
 340 #  include <type_traits>
 341 namespace mozilla {
 342 namespace detail {
 343
 344 template <typename T>
 345 struct AssertionConditionType {
 346   using ValueT = std::remove_reference_t<T>;
 347   static_assert(!std::is_array_v<ValueT>,
 348                 "Expected boolean assertion condition, got an array or a "
 349                 "string!");
 350   static_assert(!std::is_function_v<ValueT>,
 351                 "Expected boolean assertion condition, got a function! Did "
 352                 "you intend to call that function?");
 353   static_assert(!std::is_floating_point_v<ValueT>,
 354                 "It's often a bad idea to assert that a floating-point number "
 355                 "is nonzero, because such assertions tend to intermittently "
 356                 "fail. Shouldn't your code gracefully handle this case instead "
 357                 "of asserting? Anyway, if you really want to do that, write an "
 358                 "explicit boolean condition, like !!x or x!=0.");
 359
 360   static const bool isValid = true;
 361 };
 362
 363 }  // namespace detail
 364 }  // namespace mozilla
 365 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)                        \
 366     static_assert(                                                     \
 367         mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
 368         "invalid assertion condition")
 369 #else
 370 #  define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
 371 #endif
 372
 373 #if defined(DEBUG) || defined(MOZ_ASAN)
 374 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 375     MOZ_ReportAssertionFailure(__VA_ARGS__)
 376 #else
 377 #  define MOZ_REPORT_ASSERTION_FAILURE(...) \
 378     do { /* nothing */                      \
 379     } while (false)
 380 #endif
 381
 382 /* First the single-argument form. */
 383 #define MOZ_ASSERT_HELPER1(kind, expr)                         \
 384   do {                                                         \
 385     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                  \
 386     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {    \
 387       MOZ_REPORT_ASSERTION_FAILURE(#expr, __FILE__, __LINE__); \
 388       MOZ_CRASH_ANNOTATE(kind "(" #expr ")");                  \
 389       MOZ_REALLY_CRASH(__LINE__);                              \
 390     }                                                          \
 391   } while (false)
 392 /* Now the two-argument form. */
 393 #define MOZ_ASSERT_HELPER2(kind, expr, explain)                      \
 394   do {                                                               \
 395     MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr);                        \
 396     if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) {          \
 397       MOZ_REPORT_ASSERTION_FAILURE(#expr " (" explain ")", __FILE__, \
 398                                    __LINE__);                        \
 399       MOZ_CRASH_ANNOTATE(kind "(" #expr ") (" explain ")");          \
 400       MOZ_REALLY_CRASH(__LINE__);                                    \
 401     }                                                                \
 402   } while (false)
 403
 404 #define MOZ_ASSERT_GLUE(a, b) a b
 405 #define MOZ_RELEASE_ASSERT(...)                                       \
 406   MOZ_ASSERT_GLUE(                                                    \
 407       MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 408       ("MOZ_RELEASE_ASSERT", __VA_ARGS__))
 409
 410 #ifdef DEBUG
 411 #  define MOZ_ASSERT(...)                                               \
 412     MOZ_ASSERT_GLUE(                                                    \
 413         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 414         ("MOZ_ASSERT", __VA_ARGS__))
 415 #else
 416 #  define MOZ_ASSERT(...) \
 417     do {                  \
 418     } while (false)
 419 #endif /* DEBUG */
 420
 421 #if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION) || defined(DEBUG)
 422 #  define MOZ_DIAGNOSTIC_ASSERT(...)                                    \
 423     MOZ_ASSERT_GLUE(                                                    \
 424         MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
 425         ("MOZ_DIAGNOSTIC_ASSERT", __VA_ARGS__))
 426 #  define MOZ_DIAGNOSTIC_ASSERT_ENABLED 1
 427 #else
 428 #  define MOZ_DIAGNOSTIC_ASSERT(...) \
 429     do {                             \
 430     } while (false)
 431 #endif
 432
 433 /*
 434  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 435  * true.
 436  *
 437  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 438  *
 439  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 440  * designed to catch bugs during debugging, not "in the field".
 441  */
 442 #ifdef DEBUG
 443 #  define MOZ_ASSERT_IF(cond, expr) \
 444     do {                            \
 445       if (cond) {                   \
 446         MOZ_ASSERT(expr);           \
 447       }                             \
 448     } while (false)
 449 #else
 450 #  define MOZ_ASSERT_IF(cond, expr) \
 451     do {                            \
 452     } while (false)
 453 #endif
 454
 455 /*
 456  * MOZ_DIAGNOSTIC_ASSERT_IF is like MOZ_ASSERT_IF, but using
 457  * MOZ_DIAGNOSTIC_ASSERT as the underlying assert.
 458  *
 459  * See the block comment for MOZ_DIAGNOSTIC_ASSERT above for more details on how
 460  * diagnostic assertions work and how to use them.
 461  */
 462 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 463 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 464     do {                                       \
 465       if (cond) {                              \
 466         MOZ_DIAGNOSTIC_ASSERT(expr);           \
 467       }                                        \
 468     } while (false)
 469 #else
 470 #  define MOZ_DIAGNOSTIC_ASSERT_IF(cond, expr) \
 471     do {                                       \
 472     } while (false)
 473 #endif
 474
 475 /*
 476  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
 477  * it is undefined behavior for execution to reach this point.  No guarantees
 478  * are made about what will happen if this is reached at runtime.  Most code
 479  * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
 480  * asserts.
 481  */
 482 #if defined(__clang__) || defined(__GNUC__)
 483 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 484 #elif defined(_MSC_VER)
 485 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 486 #else
 487 #  ifdef __cplusplus
 488 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 489 #  else
 490 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 491 #  endif
 492 #endif
 493
 494 /*
 495  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
 496  * can assume that the macro call cannot be reached during execution.  This lets
 497  * the compiler generate better-optimized code under some circumstances, at the
 498  * expense of the program's behavior being undefined if control reaches the
 499  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
 500  *
 501  * In Gecko, you probably should not use this macro outside of performance- or
 502  * size-critical code, because it's unsafe.  If you don't care about code size
 503  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 504  *
 505  * SpiderMonkey is a different beast, and there it's acceptable to use
 506  * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
 507  *
 508  * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
 509  * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
 510  * call.
 511  *
 512  * Example usage:
 513  *
 514  *   enum ValueType {
 515  *     VALUE_STRING,
 516  *     VALUE_INT,
 517  *     VALUE_FLOAT
 518  *   };
 519  *
 520  *   int ptrToInt(ValueType type, void* value) {
 521  *   {
 522  *     // We know for sure that type is either INT or FLOAT, and we want this
 523  *     // code to run as quickly as possible.
 524  *     switch (type) {
 525  *     case VALUE_INT:
 526  *       return *(int*) value;
 527  *     case VALUE_FLOAT:
 528  *       return (int) *(float*) value;
 529  *     default:
 530  *       MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
 531  *     }
 532  *   }
 533  */
 534
 535 /*
 536  * Unconditional assert in debug builds for (assumed) unreachable code paths
 537  * that have a safe return without crashing in release builds.
 538  */
 539 #define MOZ_ASSERT_UNREACHABLE(reason) \
 540   MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
 541
 542 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
 543   do {                                                  \
 544     MOZ_ASSERT_UNREACHABLE(reason);                     \
 545     MOZ_ASSUME_UNREACHABLE_MARKER();                    \
 546   } while (false)
 547
 548 /**
 549  * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
 550  * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
 551  * debug builds, but intentionally fall through in release builds to handle
 552  * unexpected values.
 553  *
 554  * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to [[fallthrough]]? In
 555  * release builds, the MOZ_ASSERT(false) will expand to `do { } while (false)`,
 556  * requiring a [[fallthrough]] annotation to suppress a -Wimplicit-fallthrough
 557  * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
 558  * `if (true) { MOZ_CRASH(); }` and the [[fallthrough]] annotation will cause
 559  * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
 560  * warning stalemate.
 561  *
 562  * // Example before MOZ_FALLTHROUGH_ASSERT:
 563  * switch (foo) {
 564  *   default:
 565  *     // This case wants to assert in debug builds, fall through in release.
 566  *     MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
 567  *     [[fallthrough]];   // but -Wunreachable-code warning in debug builds!
 568  *   case 5:
 569  *     return 5;
 570  * }
 571  *
 572  * // Example with MOZ_FALLTHROUGH_ASSERT:
 573  * switch (foo) {
 574  *   default:
 575  *     // This case asserts in debug builds, falls through in release.
 576  *     MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
 577  *   case 5:
 578  *     return 5;
 579  * }
 580  */
 581 #ifdef DEBUG
 582 #  define MOZ_FALLTHROUGH_ASSERT(...) \
 583     MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " __VA_ARGS__)
 584 #else
 585 #  define MOZ_FALLTHROUGH_ASSERT(...) [[fallthrough]]
 586 #endif
 587
 588 /*
 589  * MOZ_ALWAYS_TRUE(expr) and friends always evaluate the provided expression,
 590  * in debug builds and in release builds both.  Then, in debug builds and
 591  * Nightly and DevEdition release builds, the value of the expression is
 592  * asserted either true or false using MOZ_DIAGNOSTIC_ASSERT.
 593  */
 594 #define MOZ_ALWAYS_TRUE(expr)              \
 595   do {                                     \
 596     if (MOZ_LIKELY(expr)) {                \
 597       /* Silence MOZ_MUST_USE. */          \
 598     } else {                               \
 599       MOZ_DIAGNOSTIC_ASSERT(false, #expr); \
 600     }                                      \
 601   } while (false)
 602
 603 #define MOZ_ALWAYS_FALSE(expr) MOZ_ALWAYS_TRUE(!(expr))
 604 #define MOZ_ALWAYS_OK(expr) MOZ_ALWAYS_TRUE((expr).isOk())
 605 #define MOZ_ALWAYS_ERR(expr) MOZ_ALWAYS_TRUE((expr).isErr())
 606
 607 #undef MOZ_DUMP_ASSERTION_STACK
 608 #undef MOZ_CRASH_CRASHREPORT
 609
 610 #endif /* mozilla_Assertions_h */