The Tor Browser / file revision

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

 /* vim: set ts=8 sts=2 et sw=2 tw=80: */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 /* Implementations of runtime and static assertion macros for C and C++. */

 #ifndef mozilla_Assertions_h

 #define mozilla_Assertions_h

 #include "mozilla/Attributes.h"

 #include "mozilla/Compiler.h"

 #include "mozilla/Likely.h"

 #include "mozilla/MacroArgs.h"

 #include <stddef.h>

 #include <stdio.h>

 #include <stdlib.h>

 #ifdef WIN32

    /*

     * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which

     * further depends on <windef.h>.  We hardcode these few definitions manually

     * because those headers clutter the global namespace with a significant

     * number of undesired macros and symbols.

     */

 #  ifdef __cplusplus

    extern "C" {

 #  endif

    __declspec(dllimport) int __stdcall

    TerminateProcess(void* hProcess, unsigned int uExitCode);

    __declspec(dllimport) void* __stdcall GetCurrentProcess(void);

 #  ifdef __cplusplus

    }

 #  endif

 #else

 #  include <signal.h>

 #endif

 #ifdef ANDROID

 #  include <android/log.h>

 #endif

 /*

  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.

  * In C++11, static_assert is provided by the compiler to the same effect.

  * This can be useful when you make certain assumptions about what must hold for

  * optimal, or even correct, behavior.  For example, you might assert that the

  * size of a struct is a multiple of the target architecture's word size:

  *

  *   struct S { ... };

  *   // C

  *   MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,

  *                     "S should be a multiple of word size for efficiency");

  *   // C++11

  *   static_assert(sizeof(S) % sizeof(size_t) == 0,

  *                 "S should be a multiple of word size for efficiency");

  *

  * This macro can be used in any location where both an extern declaration and a

  * typedef could be used.

  */

 #ifndef __cplusplus

    /*

     * Some of the definitions below create an otherwise-unused typedef.  This

     * triggers compiler warnings with some versions of gcc, so mark the typedefs

     * as permissibly-unused to disable the warnings.

     */

 #  if defined(__GNUC__)

 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))

 #  else

 #    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */

 #  endif

 #  define MOZ_STATIC_ASSERT_GLUE1(x, y)          x##y

 #  define MOZ_STATIC_ASSERT_GLUE(x, y)           MOZ_STATIC_ASSERT_GLUE1(x, y)

 #  if defined(__SUNPRO_CC)

      /*

       * The Sun Studio C++ compiler is buggy when declaring, inside a function,

       * another extern'd function with an array argument whose length contains a

       * sizeof, triggering the error message "sizeof expression not accepted as

       * size of array parameter".  This bug (6688515, not public yet) would hit

       * defining moz_static_assert as a function, so we always define an extern

       * array for Sun Studio.

       *

       * We include the line number in the symbol name in a best-effort attempt

       * to avoid conflicts (see below).

       */

 #    define MOZ_STATIC_ASSERT(cond, reason) \

        extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]

 #  elif defined(__COUNTER__)

      /*

       * If there was no preferred alternative, use a compiler-agnostic version.

       *

       * Note that the non-__COUNTER__ version has a bug in C++: it can't be used

       * in both |extern "C"| and normal C++ in the same translation unit.  (Alas

       * |extern "C"| isn't allowed in a function.)  The only affected compiler

       * we really care about is gcc 4.2.  For that compiler and others like it,

       * we include the line number in the function name to do the best we can to

       * avoid conflicts.  These should be rare: a conflict would require use of

       * MOZ_STATIC_ASSERT on the same line in separate files in the same

       * translation unit, *and* the uses would have to be in code with

       * different linkage, *and* the first observed use must be in C++-linkage

       * code.

       */

 #    define MOZ_STATIC_ASSERT(cond, reason) \

        typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE

 #  else

 #    define MOZ_STATIC_ASSERT(cond, reason) \

        extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE

 #  endif

 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  MOZ_STATIC_ASSERT(!(cond) || (expr), reason)

 #else

 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  static_assert(!(cond) || (expr), reason)

 #endif

 #ifdef __cplusplus

 extern "C" {

 #endif

 /*

  * Prints |s| as an assertion failure (using file and ln as the location of the

  * assertion) to the standard debug-output channel.

  *

  * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method.  This

  * method is primarily for internal use in this header, and only secondarily

  * for use in implementing release-build assertions.

  */

 static MOZ_ALWAYS_INLINE void

 MOZ_ReportAssertionFailure(const char* s, const char* file, int ln)

 {

 #ifdef ANDROID

   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",

                       "Assertion failure: %s, at %s:%d\n", s, file, ln);

 #else

   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", s, file, ln);

   fflush(stderr);

 #endif

 }

 static MOZ_ALWAYS_INLINE void

 MOZ_ReportCrash(const char* s, const char* file, int ln)

 {

 #ifdef ANDROID

     __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",

                         "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);

 #else

   fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);

   fflush(stderr);

 #endif

 }

 /**

  * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH().  You should

  * call MOZ_CRASH instead.

  */

 #if defined(_MSC_VER)

    /*

     * On MSVC use the __debugbreak compiler intrinsic, which produces an inline

     * (not nested in a system function) breakpoint.  This distinctively invokes

     * Breakpad without requiring system library symbols on all stack-processing

     * machines, as a nested breakpoint would require.

     *

     * We use TerminateProcess with the exit code aborting would generate

     * because we don't want to invoke atexit handlers, destructors, library

     * unload handlers, and so on when our process might be in a compromised

     * state.

     *

     * We don't use abort() because it'd cause Windows to annoyingly pop up the

     * process error dialog multiple times.  See bug 345118 and bug 426163.

     *

     * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the

     * compiler doesn't hassle us to provide a return statement after a

     * MOZ_REALLY_CRASH() call.

     *

     * (Technically these are Windows requirements, not MSVC requirements.  But

     * practically you need MSVC for debugging, and we only ship builds created

     * by MSVC, so doing it this way reduces complexity.)

     */

 __declspec(noreturn) __inline void MOZ_NoReturn() {}

 #  ifdef __cplusplus

 #    define MOZ_REALLY_CRASH() \

        do { \

          ::__debugbreak(); \

          *((volatile int*) NULL) = 123; \

          ::TerminateProcess(::GetCurrentProcess(), 3); \

          ::MOZ_NoReturn(); \

        } while (0)

 #  else

 #    define MOZ_REALLY_CRASH() \

        do { \

          __debugbreak(); \

          *((volatile int*) NULL) = 123; \

          TerminateProcess(GetCurrentProcess(), 3); \

          MOZ_NoReturn(); \

        } while (0)

 #  endif

 #else

 #  ifdef __cplusplus

 #    define MOZ_REALLY_CRASH() \

        do { \

          *((volatile int*) NULL) = 123; \

          ::abort(); \

        } while (0)

 #  else

 #    define MOZ_REALLY_CRASH() \

        do { \

          *((volatile int*) NULL) = 123; \

          abort(); \

        } while (0)

 #  endif

 #endif

 /*

  * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a

  * Breakpad-compatible way, in both debug and release builds.

  *

  * MOZ_CRASH is a good solution for "handling" failure cases when you're

  * unwilling or unable to handle them more cleanly -- for OOM, for likely memory

  * corruption, and so on.  It's also a good solution if you need safe behavior

  * in release builds as well as debug builds.  But if the failure is one that

  * should be debugged and fixed, MOZ_ASSERT is generally preferable.

  *

  * The optional explanation-string, if provided, must be a string literal

  * explaining why we're crashing.  This argument is intended for use with

  * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's

  * obvious why we're crashing.

  *

  * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an

  * explanation-string, we print the string to stderr.  Otherwise, we don't

  * print anything; this is because we want MOZ_CRASH to be 100% safe in release

  * builds, and it's hard to print to stderr safely when memory might have been

  * corrupted.

  */

 #ifndef DEBUG

 #  define MOZ_CRASH(...) MOZ_REALLY_CRASH()

 #else

 #  define MOZ_CRASH(...) \

      do { \

        MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \

        MOZ_REALLY_CRASH(); \

      } while(0)

 #endif

 #ifdef __cplusplus

 } /* extern "C" */

 #endif

 /*

  * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in

  * debug builds.  If it is, execution continues.  Otherwise, an error message

  * including the expression and the explanation-string (if provided) is printed,

  * an attempt is made to invoke any existing debugger, and execution halts.

  * MOZ_ASSERT is fatal: no recovery is possible.  Do not assert a condition

  * which can correctly be falsy.

  *

  * The optional explanation-string, if provided, must be a string literal

  * explaining the assertion.  It is intended for use with assertions whose

  * correctness or rationale is non-obvious, and for assertions where the "real"

  * condition being tested is best described prosaically.  Don't provide an

  * explanation if it's not actually helpful.

  *

  *   // No explanation needed: pointer arguments often must not be NULL.

  *   MOZ_ASSERT(arg);

  *

  *   // An explanation can be helpful to explain exactly how we know an

  *   // assertion is valid.

  *   MOZ_ASSERT(state == WAITING_FOR_RESPONSE,

  *              "given that <thingA> and <thingB>, we must have...");

  *

  *   // Or it might disambiguate multiple identical (save for their location)

  *   // assertions of the same expression.

  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),

  *              "we already set [[PrimitiveThis]] for this Boolean object");

  *   MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),

  *              "we already set [[PrimitiveThis]] for this String object");

  *

  * MOZ_ASSERT has no effect in non-debug builds.  It is designed to catch bugs

  * *only* during debugging, not "in the field". If you want the latter, use

  * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.

  */

 /* First the single-argument form. */

 #define MOZ_ASSERT_HELPER1(expr) \

    do { \

      if (MOZ_UNLIKELY(!(expr))) { \

        MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \

        MOZ_REALLY_CRASH(); \

      } \

    } while (0)

 /* Now the two-argument form. */

 #define MOZ_ASSERT_HELPER2(expr, explain) \

    do { \

      if (MOZ_UNLIKELY(!(expr))) { \

        MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \

        MOZ_REALLY_CRASH(); \

      } \

    } while (0)

 #define MOZ_RELEASE_ASSERT_GLUE(a, b) a b

 #define MOZ_RELEASE_ASSERT(...) \

    MOZ_RELEASE_ASSERT_GLUE( \

      MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \

      (__VA_ARGS__))

 #ifdef DEBUG

 #  define MOZ_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)

 #else

 #  define MOZ_ASSERT(...) do { } while(0)

 #endif /* DEBUG */

 /*

  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is

  * true.

  *

  *   MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));

  *

  * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds.  It is

  * designed to catch bugs during debugging, not "in the field".

  */

 #ifdef DEBUG

 #  define MOZ_ASSERT_IF(cond, expr) \

      do { \

        if (cond) \

          MOZ_ASSERT(expr); \

      } while (0)

 #else

 #  define MOZ_ASSERT_IF(cond, expr)  do { } while (0)

 #endif

 /*

  * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that it is

  * undefined behavior for execution to reach this point.  No guarantees are made

  * about what will happen if this is reached at runtime.  Most code should

  * probably use the higher level MOZ_ASSUME_UNREACHABLE, which uses this when

  * appropriate.

  */

 #if defined(__clang__)

 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()

 #elif defined(__GNUC__)

    /*

     * __builtin_unreachable() was implemented in gcc 4.5.  If we don't have

     * that, call a noreturn function; abort() will do nicely.  Qualify the call

     * in C++ in case there's another abort() visible in local scope.

     */

 #  if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)

 #    define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()

 #  else

 #    ifdef __cplusplus

 #      define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()

 #    else

 #      define MOZ_ASSUME_UNREACHABLE_MARKER() abort()

 #    endif

 #  endif

 #elif defined(_MSC_VER)

 #  define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)

 #else

 #  ifdef __cplusplus

 #    define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()

 #  else

 #    define MOZ_ASSUME_UNREACHABLE_MARKER() abort()

 #  endif

 #endif

 /*

  * MOZ_ASSUME_UNREACHABLE([reason]) tells the compiler that it can assume that

  * the macro call cannot be reached during execution.  This lets the compiler

  * generate better-optimized code under some circumstances, at the expense of

  * the program's behavior being undefined if control reaches the

  * MOZ_ASSUME_UNREACHABLE.

  *

  * In Gecko, you probably should not use this macro outside of performance- or

  * size-critical code, because it's unsafe.  If you don't care about code size

  * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.

  *

  * SpiderMonkey is a different beast, and there it's acceptable to use

  * MOZ_ASSUME_UNREACHABLE more widely.

  *

  * Note that MOZ_ASSUME_UNREACHABLE is noreturn, so it's valid not to return a

  * value following a MOZ_ASSUME_UNREACHABLE call.

  *

  * Example usage:

  *

  *   enum ValueType {

  *     VALUE_STRING,

  *     VALUE_INT,

  *     VALUE_FLOAT

  *   };

  *

  *   int ptrToInt(ValueType type, void* value) {

  *   {

  *     // We know for sure that type is either INT or FLOAT, and we want this

  *     // code to run as quickly as possible.

  *     switch (type) {

  *     case VALUE_INT:

  *       return *(int*) value;

  *     case VALUE_FLOAT:

  *       return (int) *(float*) value;

  *     default:

  *       MOZ_ASSUME_UNREACHABLE("can only handle VALUE_INT and VALUE_FLOAT");

  *     }

  *   }

  */

 #if defined(DEBUG)

 #  define MOZ_ASSUME_UNREACHABLE(...) \

      do { \

        MOZ_ASSERT(false, "MOZ_ASSUME_UNREACHABLE(" __VA_ARGS__ ")"); \

        MOZ_ASSUME_UNREACHABLE_MARKER(); \

      } while (0)

 #else

 #  define MOZ_ASSUME_UNREACHABLE(reason)  MOZ_ASSUME_UNREACHABLE_MARKER()

 #endif

 /*

  * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided

  * expression, in debug builds and in release builds both.  Then, in debug

  * builds only, the value of the expression is asserted either true or false

  * using MOZ_ASSERT.

  */

 #ifdef DEBUG

 #  define MOZ_ALWAYS_TRUE(expr)      MOZ_ASSERT((expr))

 #  define MOZ_ALWAYS_FALSE(expr)     MOZ_ASSERT(!(expr))

 #else

 #  define MOZ_ALWAYS_TRUE(expr)      ((void)(expr))

 #  define MOZ_ALWAYS_FALSE(expr)     ((void)(expr))

 #endif

 #endif /* mozilla_Assertions_h */