gecko-dev/mfbt/Assertions.h
Justin Lebar 3da6ed220e Bug 820686 - Follow-up: s/MOZ_ASSUME_NOT_REACHED/MOZ_ASSUME_UNREACHABLE/. rs=waldo
I'd meant to do this, but I only got as far as the comment in mfbt.  Oops!

--HG--
extra : rebase_source : 3cfe3ef1bf401eb7d9a10fcabcfb39008e9553a4
2013-06-28 19:20:12 -07:00

459 lines
17 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 <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*. 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 { ... };
* MOZ_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.
*
* Be aware of the gcc 4.2 concerns noted further down when writing patches that
* use this macro, particularly if a patch only bounces on OS X.
*/
#ifdef __cplusplus
# if defined(__clang__)
# ifndef __has_extension
# define __has_extension __has_feature /* compatibility, for older versions of clang */
# endif
# if __has_extension(cxx_static_assert)
# define MOZ_STATIC_ASSERT(cond, reason) static_assert((cond), reason)
# endif
# elif defined(__GNUC__)
# if (defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L)
# define MOZ_STATIC_ASSERT(cond, reason) static_assert((cond), reason)
# endif
# elif defined(_MSC_VER)
# if _MSC_VER >= 1600 /* MSVC 10 */
# define MOZ_STATIC_ASSERT(cond, reason) static_assert((cond), reason)
# endif
# elif defined(__HP_aCC)
# if __HP_aCC >= 62500 && defined(_HP_CXX0x_SOURCE)
# define MOZ_STATIC_ASSERT(cond, reason) static_assert((cond), reason)
# endif
# endif
#endif
#ifndef MOZ_STATIC_ASSERT
/*
* 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
#endif
#define MOZ_STATIC_ASSERT_IF(cond, expr, reason) MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
#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".
*/
#ifdef DEBUG
/* 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)
/* And now, helper macrology up the wazoo. */
/*
* Count the number of arguments passed to MOZ_ASSERT, very carefully
* tiptoeing around an MSVC bug where it improperly expands __VA_ARGS__ as a
* single token in argument lists. See these URLs for details:
*
* http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
* http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
*/
# define MOZ_COUNT_ASSERT_ARGS_IMPL2(_1, _2, count, ...) \
count
# define MOZ_COUNT_ASSERT_ARGS_IMPL(args) \
MOZ_COUNT_ASSERT_ARGS_IMPL2 args
# define MOZ_COUNT_ASSERT_ARGS(...) \
MOZ_COUNT_ASSERT_ARGS_IMPL((__VA_ARGS__, 2, 1, 0))
/* Pick the right helper macro to invoke. */
# define MOZ_ASSERT_CHOOSE_HELPER2(count) MOZ_ASSERT_HELPER##count
# define MOZ_ASSERT_CHOOSE_HELPER1(count) MOZ_ASSERT_CHOOSE_HELPER2(count)
# define MOZ_ASSERT_CHOOSE_HELPER(count) MOZ_ASSERT_CHOOSE_HELPER1(count)
/* The actual macro. */
# define MOZ_ASSERT_GLUE(x, y) x y
# define MOZ_ASSERT(...) \
MOZ_ASSERT_GLUE(MOZ_ASSERT_CHOOSE_HELPER(MOZ_COUNT_ASSERT_ARGS(__VA_ARGS__)), \
(__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_ */