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 #include "mozilla/Attributes.h"
  13 #include "mozilla/Compiler.h"
  14 #include "mozilla/Likely.h"
  15
  16 #include <stddef.h>
  17 #include <stdio.h>
  18 #include <stdlib.h>
  19 #ifdef WIN32
  20    /*
  21     * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
  22     * further depends on <windef.h>.  We hardcode these few definitions manually
  23     * because those headers clutter the global namespace with a significant
  24     * number of undesired macros and symbols.
  25     */
  26 #  ifdef __cplusplus
  27    extern "C" {
  28 #  endif
  29    __declspec(dllimport) int __stdcall
  30    TerminateProcess(void* hProcess, unsigned int uExitCode);
  31    __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
  32 #  ifdef __cplusplus
  33    }
  34 #  endif
  35 #else
  36 #  include <signal.h>
  37 #endif
  38 #ifdef ANDROID
  39 #  include <android/log.h>
  40 #endif
  41
  42 /*
  43  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
  44  * In C++11, static_assert is provided by the compiler to the same effect.
  45  * This can be useful when you make certain assumptions about what must hold for
  46  * optimal, or even correct, behavior.  For example, you might assert that the
  47  * size of a struct is a multiple of the target architecture's word size:
  48  *
  49  *   struct S { ... };
  50  *   // C
  51  *   MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
  52  *                     "S should be a multiple of word size for efficiency");
  53  *   // C++11
  54  *   static_assert(sizeof(S) % sizeof(size_t) == 0,
  55  *                 "S should be a multiple of word size for efficiency");
  56  *
  57  * This macro can be used in any location where both an extern declaration and a
  58  * typedef could be used.
  59  */
  60 #ifndef __cplusplus
  61    /*
  62     * Some of the definitions below create an otherwise-unused typedef.  This
  63     * triggers compiler warnings with some versions of gcc, so mark the typedefs
  64     * as permissibly-unused to disable the warnings.
  65     */
  66 #  if defined(__GNUC__)
  67 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
  68 #  else
  69 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
  70 #  endif
  71 #  define MOZ_STATIC_ASSERT_GLUE1(x, y)          x##y
  72 #  define MOZ_STATIC_ASSERT_GLUE(x, y)           MOZ_STATIC_ASSERT_GLUE1(x, y)
  73 #  if defined(__SUNPRO_CC)
  74      /*
  75       * The Sun Studio C++ compiler is buggy when declaring, inside a function,
  76       * another extern'd function with an array argument whose length contains a
  77       * sizeof, triggering the error message "sizeof expression not accepted as
  78       * size of array parameter".  This bug (6688515, not public yet) would hit
  79       * defining moz_static_assert as a function, so we always define an extern
  80       * array for Sun Studio.
  81       *
  82       * We include the line number in the symbol name in a best-effort attempt
  83       * to avoid conflicts (see below).
  84       */
  85 #    define MOZ_STATIC_ASSERT(cond, reason) \
  86        extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]
  87 #  elif defined(__COUNTER__)
  88      /*
  89       * If there was no preferred alternative, use a compiler-agnostic version.
  90       *
  91       * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
  92       * in both |extern "C"| and normal C++ in the same translation unit.  (Alas
  93       * |extern "C"| isn't allowed in a function.)  The only affected compiler
  94       * we really care about is gcc 4.2.  For that compiler and others like it,
  95       * we include the line number in the function name to do the best we can to
  96       * avoid conflicts.  These should be rare: a conflict would require use of
  97       * MOZ_STATIC_ASSERT on the same line in separate files in the same
  98       * translation unit, *and* the uses would have to be in code with
  99       * different linkage, *and* the first observed use must be in C++-linkage
 100       * code.
 101       */
 102 #    define MOZ_STATIC_ASSERT(cond, reason) \
 103        typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 104 #  else
 105 #    define MOZ_STATIC_ASSERT(cond, reason) \
 106        extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 107 #  endif
 108
 109 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
 110 #else
 111 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  static_assert(!(cond) || (expr), reason)
 112 #endif
 113
 114 #ifdef __cplusplus
 115 extern "C" {
 116 #endif
 117
 118 /*
 119  * Prints |s| as an assertion failure (using file and ln as the location of the
 120  * assertion) to the standard debug-output channel.
 121  *
 122  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This
 123  * method is primarily for internal use in this header, and only secondarily
 124  * for use in implementing release-build assertions.
 125  */
 126 static MOZ_ALWAYS_INLINE void
 127 MOZ_ReportAssertionFailure(const char* s, const char* file, int ln)
 128 {
 129 #ifdef ANDROID
 130   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
 131                       "Assertion failure: %s, at %s:%d\n", s, file, ln);
 132 #else
 133   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", s, file, ln);
 134   fflush(stderr);
 135 #endif
 136 }
 137
 138 static MOZ_ALWAYS_INLINE void
 139 MOZ_ReportCrash(const char* s, const char* file, int ln)
 140 {
 141 #ifdef ANDROID
 142     __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
 143                         "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
 144 #else
 145   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
 146   fflush(stderr);
 147 #endif
 148 }
 149
 150 /**
 151  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should
 152  * call MOZ_CRASH instead.
 153  */
 154 #if defined(_MSC_VER)
 155    /*
 156     * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
 157     * (not nested in a system function) breakpoint.  This distinctively invokes
 158     * Breakpad without requiring system library symbols on all stack-processing
 159     * machines, as a nested breakpoint would require.
 160     *
 161     * We use TerminateProcess with the exit code aborting would generate
 162     * because we don't want to invoke atexit handlers, destructors, library
 163     * unload handlers, and so on when our process might be in a compromised
 164     * state.
 165     *
 166     * We don't use abort() because it'd cause Windows to annoyingly pop up the
 167     * process error dialog multiple times.  See bug 345118 and bug 426163.
 168     *
 169     * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the
 170     * compiler doesn't hassle us to provide a return statement after a
 171     * MOZ_REALLY_CRASH() call.
 172     *
 173     * (Technically these are Windows requirements, not MSVC requirements.  But
 174     * practically you need MSVC for debugging, and we only ship builds created
 175     * by MSVC, so doing it this way reduces complexity.)
 176     */
 177
 178 __declspec(noreturn) __inline void MOZ_NoReturn() {}
 179
 180 #  ifdef __cplusplus
 181 #    define MOZ_REALLY_CRASH() \
 182        do { \
 183          ::__debugbreak(); \
 184          *((volatile int*) NULL) = 123; \
 185          ::TerminateProcess(::GetCurrentProcess(), 3); \
 186          ::MOZ_NoReturn(); \
 187        } while (0)
 188 #  else
 189 #    define MOZ_REALLY_CRASH() \
 190        do { \
 191          __debugbreak(); \
 192          *((volatile int*) NULL) = 123; \
 193          TerminateProcess(GetCurrentProcess(), 3); \
 194          MOZ_NoReturn(); \
 195        } while (0)
 196 #  endif
 197 #else
 198 #  ifdef __cplusplus
 199 #    define MOZ_REALLY_CRASH() \
 200        do { \
 201          *((volatile int*) NULL) = 123; \
 202          ::abort(); \
 203        } while (0)
 204 #  else
 205 #    define MOZ_REALLY_CRASH() \
 206        do { \
 207          *((volatile int*) NULL) = 123; \
 208          abort(); \
 209        } while (0)
 210 #  endif
 211 #endif
 212
 213 /*
 214  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
 215  * Breakpad-compatible way, in both debug and release builds.
 216  *
 217  * MOZ_CRASH is a good solution for "handling" failure cases when you're
 218  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
 219  * corruption, and so on.  It's also a good solution if you need safe behavior
 220  * in release builds as well as debug builds.  But if the failure is one that
 221  * should be debugged and fixed, MOZ_ASSERT is generally preferable.
 222  *
 223  * The optional explanation-string, if provided, must be a string literal
 224  * explaining why we're crashing.  This argument is intended for use with
 225  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
 226  * obvious why we're crashing.
 227  *
 228  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
 229  * explanation-string, we print the string to stderr.  Otherwise, we don't
 230  * print anything; this is because we want MOZ_CRASH to be 100% safe in release
 231  * builds, and it's hard to print to stderr safely when memory might have been
 232  * corrupted.
 233  */
 234 #ifndef DEBUG
 235 #  define MOZ_CRASH(...) MOZ_REALLY_CRASH()
 236 #else
 237 #  define MOZ_CRASH(...) \
 238      do { \
 239        MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
 240        MOZ_REALLY_CRASH(); \
 241      } while(0)
 242 #endif
 243
 244 #ifdef __cplusplus
 245 } /* extern "C" */
 246 #endif
 247
 248 /*
 249  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
 250  * debug builds.  If it is, execution continues.  Otherwise, an error message
 251  * including the expression and the explanation-string (if provided) is printed,
 252  * an attempt is made to invoke any existing debugger, and execution halts.
 253  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition
 254  * which can correctly be falsy.
 255  *
 256  * The optional explanation-string, if provided, must be a string literal
 257  * explaining the assertion.  It is intended for use with assertions whose
 258  * correctness or rationale is non-obvious, and for assertions where the "real"
 259  * condition being tested is best described prosaically.  Don't provide an
 260  * explanation if it's not actually helpful.
 261  *
 262  *   // No explanation needed: pointer arguments often must not be NULL.
 263  *   MOZ_ASSERT(arg);
 264  *
 265  *   // An explanation can be helpful to explain exactly how we know an
 266  *   // assertion is valid.
 267  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
 268  *              "given that <thingA> and <thingB>, we must have...");
 269  *
 270  *   // Or it might disambiguate multiple identical (save for their location)
 271  *   // assertions of the same expression.
 272  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 273  *              "we already set [[PrimitiveThis]] for this Boolean object");
 274  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
 275  *              "we already set [[PrimitiveThis]] for this String object");
 276  *
 277  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs
 278  * *only* during debugging, not "in the field".
 279  */
 280 #ifdef DEBUG
 281    /* First the single-argument form. */
 282 #  define MOZ_ASSERT_HELPER1(expr) \
 283      do { \
 284        if (MOZ_UNLIKELY(!(expr))) { \
 285          MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \
 286          MOZ_REALLY_CRASH(); \
 287        } \
 288      } while (0)
 289    /* Now the two-argument form. */
 290 #  define MOZ_ASSERT_HELPER2(expr, explain) \
 291      do { \
 292        if (MOZ_UNLIKELY(!(expr))) { \
 293          MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \
 294          MOZ_REALLY_CRASH(); \
 295        } \
 296      } while (0)
 297    /* And now, helper macrology up the wazoo. */
 298    /*
 299     * Count the number of arguments passed to MOZ_ASSERT, very carefully
 300     * tiptoeing around an MSVC bug where it improperly expands __VA_ARGS__ as a
 301     * single token in argument lists.  See these URLs for details:
 302     *
 303     *   http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
 304     *   http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
 305     */
 306 #  define MOZ_COUNT_ASSERT_ARGS_IMPL2(_1, _2, count, ...) \
 307      count
 308 #  define MOZ_COUNT_ASSERT_ARGS_IMPL(args) \
 309          MOZ_COUNT_ASSERT_ARGS_IMPL2 args
 310 #  define MOZ_COUNT_ASSERT_ARGS(...) \
 311      MOZ_COUNT_ASSERT_ARGS_IMPL((__VA_ARGS__, 2, 1, 0))
 312    /* Pick the right helper macro to invoke. */
 313 #  define MOZ_ASSERT_CHOOSE_HELPER2(count) MOZ_ASSERT_HELPER##count
 314 #  define MOZ_ASSERT_CHOOSE_HELPER1(count) MOZ_ASSERT_CHOOSE_HELPER2(count)
 315 #  define MOZ_ASSERT_CHOOSE_HELPER(count) MOZ_ASSERT_CHOOSE_HELPER1(count)
 316    /* The actual macro. */
 317 #  define MOZ_ASSERT_GLUE(x, y) x y
 318 #  define MOZ_ASSERT(...) \
 319      MOZ_ASSERT_GLUE(MOZ_ASSERT_CHOOSE_HELPER(MOZ_COUNT_ASSERT_ARGS(__VA_ARGS__)), \
 320                      (__VA_ARGS__))
 321 #else
 322 #  define MOZ_ASSERT(...) do { } while(0)
 323 #endif /* DEBUG */
 324
 325 /*
 326  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
 327  * true.
 328  *
 329  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
 330  *
 331  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is
 332  * designed to catch bugs during debugging, not "in the field".
 333  */
 334 #ifdef DEBUG
 335 #  define MOZ_ASSERT_IF(cond, expr) \
 336      do { \
 337        if (cond) \
 338          MOZ_ASSERT(expr); \
 339      } while (0)
 340 #else
 341 #  define MOZ_ASSERT_IF(cond, expr)  do { } while (0)
 342 #endif
 343
 344 /*
 345  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that it is
 346  * undefined behavior for execution to reach this point.  No guarantees are made
 347  * about what will happen if this is reached at runtime.  Most code should
 348  * probably use the higher level MOZ_ASSUME_UNREACHABLE, which uses this when
 349  * appropriate.
 350  */
 351 #if defined(__clang__)
 352 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 353 #elif defined(__GNUC__)
 354    /*
 355     * __builtin_unreachable() was implemented in gcc 4.5.  If we don't have
 356     * that, call a noreturn function; abort() will do nicely.  Qualify the call
 357     * in C++ in case there's another abort() visible in local scope.
 358     */
 359 #  if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)
 360 #    define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
 361 #  else
 362 #    ifdef __cplusplus
 363 #      define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 364 #    else
 365 #      define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 366 #    endif
 367 #  endif
 368 #elif defined(_MSC_VER)
 369 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
 370 #else
 371 #  ifdef __cplusplus
 372 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
 373 #  else
 374 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
 375 #  endif
 376 #endif
 377
 378 /*
 379  * MOZ_ASSUME_UNREACHABLE([reason]) tells the compiler that it can assume that
 380  * the macro call cannot be reached during execution.  This lets the compiler
 381  * generate better-optimized code under some circumstances, at the expense of
 382  * the program's behavior being undefined if control reaches the
 383  * MOZ_ASSUME_UNREACHABLE.
 384  *
 385  * In Gecko, you probably should not use this macro outside of performance- or
 386  * size-critical code, because it's unsafe.  If you don't care about code size
 387  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
 388  *
 389  * SpiderMonkey is a different beast, and there it's acceptable to use
 390  * MOZ_ASSUME_UNREACHABLE more widely.
 391  *
 392  * Note that MOZ_ASSUME_UNREACHABLE is noreturn, so it's valid not to return a
 393  * value following a MOZ_ASSUME_UNREACHABLE call.
 394  *
 395  * Example usage:
 396  *
 397  *   enum ValueType {
 398  *     VALUE_STRING,
 399  *     VALUE_INT,
 400  *     VALUE_FLOAT
 401  *   };
 402  *
 403  *   int ptrToInt(ValueType type, void* value) {
 404  *   {
 405  *     // We know for sure that type is either INT or FLOAT, and we want this
 406  *     // code to run as quickly as possible.
 407  *     switch (type) {
 408  *     case VALUE_INT:
 409  *       return *(int*) value;
 410  *     case VALUE_FLOAT:
 411  *       return (int) *(float*) value;
 412  *     default:
 413  *       MOZ_ASSUME_UNREACHABLE("can only handle VALUE_INT and VALUE_FLOAT");
 414  *     }
 415  *   }
 416  */
 417 #if defined(DEBUG)
 418 #  define MOZ_ASSUME_UNREACHABLE(...) \
 419      do { \
 420        MOZ_ASSERT(false, "MOZ_ASSUME_UNREACHABLE(" __VA_ARGS__ ")"); \
 421        MOZ_ASSUME_UNREACHABLE_MARKER(); \
 422      } while (0)
 423 #else
 424 #  define MOZ_ASSUME_UNREACHABLE(reason)  MOZ_ASSUME_UNREACHABLE_MARKER()
 425 #endif
 426
 427 /*
 428  * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
 429  * expression, in debug builds and in release builds both.  Then, in debug
 430  * builds only, the value of the expression is asserted either true or false
 431  * using MOZ_ASSERT.
 432  */
 433 #ifdef DEBUG
 434 #  define MOZ_ALWAYS_TRUE(expr)      MOZ_ASSERT((expr))
 435 #  define MOZ_ALWAYS_FALSE(expr)     MOZ_ASSERT(!(expr))
 436 #else
 437 #  define MOZ_ALWAYS_TRUE(expr)      ((void)(expr))
 438 #  define MOZ_ALWAYS_FALSE(expr)     ((void)(expr))
 439 #endif
 440
 441 #endif /* mozilla_Assertions_h */