gecko-dev/mfbt/Attributes.h

553 lines
22 KiB
C

/* -*- 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 various class and method modifier attributes. */
#ifndef mozilla_Attributes_h
#define mozilla_Attributes_h
#include "mozilla/Compiler.h"
/*
* MOZ_ALWAYS_INLINE is a macro which expands to tell the compiler that the
* method decorated with it must be inlined, even if the compiler thinks
* otherwise. This is only a (much) stronger version of the inline hint:
* compilers are not guaranteed to respect it (although they're much more likely
* to do so).
*
* The MOZ_ALWAYS_INLINE_EVEN_DEBUG macro is yet stronger. It tells the
* compiler to inline even in DEBUG builds. It should be used very rarely.
*/
#if defined(_MSC_VER)
# define MOZ_ALWAYS_INLINE_EVEN_DEBUG __forceinline
#elif defined(__GNUC__)
# define MOZ_ALWAYS_INLINE_EVEN_DEBUG __attribute__((always_inline)) inline
#else
# define MOZ_ALWAYS_INLINE_EVEN_DEBUG inline
#endif
#if !defined(DEBUG)
# define MOZ_ALWAYS_INLINE MOZ_ALWAYS_INLINE_EVEN_DEBUG
#elif defined(_MSC_VER) && !defined(__cplusplus)
# define MOZ_ALWAYS_INLINE __inline
#else
# define MOZ_ALWAYS_INLINE inline
#endif
#if defined(_MSC_VER)
/*
* g++ requires -std=c++0x or -std=gnu++0x to support C++11 functionality
* without warnings (functionality used by the macros below). These modes are
* detectable by checking whether __GXX_EXPERIMENTAL_CXX0X__ is defined or, more
* standardly, by checking whether __cplusplus has a C++11 or greater value.
* Current versions of g++ do not correctly set __cplusplus, so we check both
* for forward compatibility.
*
* Even though some versions of MSVC support explicit conversion operators, we
* don't indicate support for them here, due to
* http://stackoverflow.com/questions/20498142/visual-studio-2013-explicit-keyword-bug
*/
# define MOZ_HAVE_CXX11_FINAL final
# define MOZ_HAVE_CXX11_OVERRIDE
# define MOZ_HAVE_NEVER_INLINE __declspec(noinline)
# define MOZ_HAVE_NORETURN __declspec(noreturn)
# ifdef __clang__
/* clang-cl probably supports constexpr and explicit conversions. */
# if __has_extension(cxx_constexpr)
# define MOZ_HAVE_CXX11_CONSTEXPR
# endif
# if __has_extension(cxx_explicit_conversions)
# define MOZ_HAVE_EXPLICIT_CONVERSION
# endif
# endif
#elif defined(__clang__)
/*
* Per Clang documentation, "Note that marketing version numbers should not
* be used to check for language features, as different vendors use different
* numbering schemes. Instead, use the feature checking macros."
*/
# ifndef __has_extension
# define __has_extension __has_feature /* compatibility, for older versions of clang */
# endif
# if __has_extension(cxx_constexpr)
# define MOZ_HAVE_CXX11_CONSTEXPR
# endif
# if __has_extension(cxx_explicit_conversions)
# define MOZ_HAVE_EXPLICIT_CONVERSION
# endif
# if __has_extension(cxx_override_control)
# define MOZ_HAVE_CXX11_OVERRIDE
# define MOZ_HAVE_CXX11_FINAL final
# endif
# if __has_attribute(noinline)
# define MOZ_HAVE_NEVER_INLINE __attribute__((noinline))
# endif
# if __has_attribute(noreturn)
# define MOZ_HAVE_NORETURN __attribute__((noreturn))
# endif
#elif defined(__GNUC__)
# if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
# if MOZ_GCC_VERSION_AT_LEAST(4, 7, 0)
# define MOZ_HAVE_CXX11_OVERRIDE
# define MOZ_HAVE_CXX11_FINAL final
# endif
# define MOZ_HAVE_CXX11_CONSTEXPR
# define MOZ_HAVE_EXPLICIT_CONVERSION
# else
/* __final is a non-C++11 GCC synonym for 'final', per GCC r176655. */
# if MOZ_GCC_VERSION_AT_LEAST(4, 7, 0)
# define MOZ_HAVE_CXX11_FINAL __final
# endif
# endif
# define MOZ_HAVE_NEVER_INLINE __attribute__((noinline))
# define MOZ_HAVE_NORETURN __attribute__((noreturn))
#endif
/*
* When built with clang analyzer (a.k.a scan-build), define MOZ_HAVE_NORETURN
* to mark some false positives
*/
#ifdef __clang_analyzer__
# if __has_extension(attribute_analyzer_noreturn)
# define MOZ_HAVE_ANALYZER_NORETURN __attribute__((analyzer_noreturn))
# endif
#endif
/*
* The MOZ_CONSTEXPR specifier declares that a C++11 compiler can evaluate a
* function at compile time. A constexpr function cannot examine any values
* except its arguments and can have no side effects except its return value.
* The MOZ_CONSTEXPR_VAR specifier tells a C++11 compiler that a variable's
* value may be computed at compile time. It should be prefered to just
* marking variables as MOZ_CONSTEXPR because if the compiler does not support
* constexpr it will fall back to making the variable const, and some compilers
* do not accept variables being marked both const and constexpr.
*/
#ifdef MOZ_HAVE_CXX11_CONSTEXPR
# define MOZ_CONSTEXPR constexpr
# define MOZ_CONSTEXPR_VAR constexpr
#else
# define MOZ_CONSTEXPR /* no support */
# define MOZ_CONSTEXPR_VAR const
#endif
/*
* MOZ_EXPLICIT_CONVERSION is a specifier on a type conversion
* overloaded operator that declares that a C++11 compiler should restrict
* this operator to allow only explicit type conversions, disallowing
* implicit conversions.
*
* Example:
*
* template<typename T>
* class Ptr
* {
* T* mPtr;
* MOZ_EXPLICIT_CONVERSION operator bool() const
* {
* return mPtr != nullptr;
* }
* };
*
*/
#ifdef MOZ_HAVE_EXPLICIT_CONVERSION
# define MOZ_EXPLICIT_CONVERSION explicit
#else
# define MOZ_EXPLICIT_CONVERSION /* no support */
#endif
/*
* MOZ_NEVER_INLINE is a macro which expands to tell the compiler that the
* method decorated with it must never be inlined, even if the compiler would
* otherwise choose to inline the method. Compilers aren't absolutely
* guaranteed to support this, but most do.
*/
#if defined(MOZ_HAVE_NEVER_INLINE)
# define MOZ_NEVER_INLINE MOZ_HAVE_NEVER_INLINE
#else
# define MOZ_NEVER_INLINE /* no support */
#endif
/*
* MOZ_NORETURN, specified at the start of a function declaration, indicates
* that the given function does not return. (The function definition does not
* need to be annotated.)
*
* MOZ_NORETURN void abort(const char* msg);
*
* This modifier permits the compiler to optimize code assuming a call to such a
* function will never return. It also enables the compiler to avoid spurious
* warnings about not initializing variables, or about any other seemingly-dodgy
* operations performed after the function returns.
*
* This modifier does not affect the corresponding function's linking behavior.
*/
#if defined(MOZ_HAVE_NORETURN)
# define MOZ_NORETURN MOZ_HAVE_NORETURN
#else
# define MOZ_NORETURN /* no support */
#endif
/**
* MOZ_COLD tells the compiler that a function is "cold", meaning infrequently
* executed. This may lead it to optimize for size more aggressively than speed,
* or to allocate the body of the function in a distant part of the text segment
* to help keep it from taking up unnecessary icache when it isn't in use.
*
* Place this attribute at the very beginning of a function definition. For
* example, write
*
* MOZ_COLD int foo();
*
* or
*
* MOZ_COLD int foo() { return 42; }
*/
#if defined(__GNUC__) || defined(__clang__)
# define MOZ_COLD __attribute__ ((cold))
#else
# define MOZ_COLD
#endif
/*
* MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS, specified at the end of a function
* declaration, indicates that for the purposes of static analysis, this
* function does not return. (The function definition does not need to be
* annotated.)
*
* MOZ_ReportCrash(const char* s, const char* file, int ln)
* MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS
*
* Some static analyzers, like scan-build from clang, can use this information
* to eliminate false positives. From the upstream documentation of scan-build:
* "This attribute is useful for annotating assertion handlers that actually
* can return, but for the purpose of using the analyzer we want to pretend
* that such functions do not return."
*
*/
#if defined(MOZ_HAVE_ANALYZER_NORETURN)
# define MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS MOZ_HAVE_ANALYZER_NORETURN
#else
# define MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS /* no support */
#endif
/*
* MOZ_ASAN_BLACKLIST is a macro to tell AddressSanitizer (a compile-time
* instrumentation shipped with Clang and GCC) to not instrument the annotated
* function. Furthermore, it will prevent the compiler from inlining the
* function because inlining currently breaks the blacklisting mechanism of
* AddressSanitizer.
*/
#if defined(__has_feature)
# if __has_feature(address_sanitizer)
# define MOZ_HAVE_ASAN_BLACKLIST
# endif
#elif defined(__GNUC__)
# if defined(__SANITIZE_ADDRESS__)
# define MOZ_HAVE_ASAN_BLACKLIST
# endif
#endif
#if defined(MOZ_HAVE_ASAN_BLACKLIST)
# define MOZ_ASAN_BLACKLIST MOZ_NEVER_INLINE __attribute__((no_sanitize_address))
#else
# define MOZ_ASAN_BLACKLIST /* nothing */
#endif
/*
* MOZ_TSAN_BLACKLIST is a macro to tell ThreadSanitizer (a compile-time
* instrumentation shipped with Clang) to not instrument the annotated function.
* Furthermore, it will prevent the compiler from inlining the function because
* inlining currently breaks the blacklisting mechanism of ThreadSanitizer.
*/
#if defined(__has_feature)
# if __has_feature(thread_sanitizer)
# define MOZ_TSAN_BLACKLIST MOZ_NEVER_INLINE __attribute__((no_sanitize_thread))
# else
# define MOZ_TSAN_BLACKLIST /* nothing */
# endif
#else
# define MOZ_TSAN_BLACKLIST /* nothing */
#endif
#ifdef __cplusplus
/*
* MOZ_OVERRIDE explicitly indicates that a virtual member function in a class
* overrides a member function of a base class, rather than potentially being a
* new member function. MOZ_OVERRIDE should be placed immediately before the
* ';' terminating the member function's declaration, or before '= 0;' if the
* member function is pure. If the member function is defined in the class
* definition, it should appear before the opening brace of the function body.
*
* class Base
* {
* public:
* virtual void f() = 0;
* };
* class Derived1 : public Base
* {
* public:
* virtual void f() MOZ_OVERRIDE;
* };
* class Derived2 : public Base
* {
* public:
* virtual void f() MOZ_OVERRIDE = 0;
* };
* class Derived3 : public Base
* {
* public:
* virtual void f() MOZ_OVERRIDE { }
* };
*
* In compilers supporting C++11 override controls, MOZ_OVERRIDE *requires* that
* the function marked with it override a member function of a base class: it
* is a compile error if it does not. Otherwise MOZ_OVERRIDE does not affect
* semantics and merely documents the override relationship to the reader (but
* of course must still be used correctly to not break C++11 compilers).
*/
#if defined(MOZ_HAVE_CXX11_OVERRIDE)
# define MOZ_OVERRIDE override
#else
# define MOZ_OVERRIDE /* no support */
#endif
/*
* MOZ_FINAL indicates that some functionality cannot be overridden through
* inheritance. It can be used to annotate either classes/structs or virtual
* member functions.
*
* To annotate a class/struct with MOZ_FINAL, place MOZ_FINAL immediately after
* the name of the class, before the list of classes from which it derives (if
* any) and before its opening brace. MOZ_FINAL must not be used to annotate
* unnamed classes or structs. (With some compilers, and with C++11 proper, the
* underlying expansion is ambiguous with specifying a class name.)
*
* class Base MOZ_FINAL
* {
* public:
* Base();
* ~Base();
* virtual void f() { }
* };
* // This will be an error in some compilers:
* class Derived : public Base
* {
* public:
* ~Derived() { }
* };
*
* One particularly common reason to specify MOZ_FINAL upon a class is to tell
* the compiler that it's not dangerous for it to have a non-virtual destructor
* yet have one or more virtual functions, silencing the warning it might emit
* in this case. Suppose Base above weren't annotated with MOZ_FINAL. Because
* ~Base() is non-virtual, an attempt to delete a Derived* through a Base*
* wouldn't call ~Derived(), so any cleanup ~Derived() might do wouldn't happen.
* (Formally C++ says behavior is undefined, but compilers will likely just call
* ~Base() and not ~Derived().) Specifying MOZ_FINAL tells the compiler that
* it's safe for the destructor to be non-virtual.
*
* In compilers implementing final controls, it is an error to inherit from a
* class annotated with MOZ_FINAL. In other compilers it serves only as
* documentation.
*
* To annotate a virtual member function with MOZ_FINAL, place MOZ_FINAL
* immediately before the ';' terminating the member function's declaration, or
* before '= 0;' if the member function is pure. If the member function is
* defined in the class definition, it should appear before the opening brace of
* the function body. (This placement is identical to that for MOZ_OVERRIDE.
* If both are used, they should appear in the order 'MOZ_FINAL MOZ_OVERRIDE'
* for consistency.)
*
* class Base
* {
* public:
* virtual void f() MOZ_FINAL;
* };
* class Derived
* {
* public:
* // This will be an error in some compilers:
* virtual void f();
* };
*
* In compilers implementing final controls, it is an error for a derived class
* to override a method annotated with MOZ_FINAL. In other compilers it serves
* only as documentation.
*/
#if defined(MOZ_HAVE_CXX11_FINAL)
# define MOZ_FINAL MOZ_HAVE_CXX11_FINAL
#else
# define MOZ_FINAL /* no support */
#endif
/**
* MOZ_WARN_UNUSED_RESULT tells the compiler to emit a warning if a function's
* return value is not used by the caller.
*
* Place this attribute at the very beginning of a function definition. For
* example, write
*
* MOZ_WARN_UNUSED_RESULT int foo();
*
* or
*
* MOZ_WARN_UNUSED_RESULT int foo() { return 42; }
*/
#if defined(__GNUC__) || defined(__clang__)
# define MOZ_WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
#else
# define MOZ_WARN_UNUSED_RESULT
#endif
/*
* The following macros are attributes that support the static analysis plugin
* included with Mozilla, and will be implemented (when such support is enabled)
* as C++11 attributes. Since such attributes are legal pretty much everywhere
* and have subtly different semantics depending on their placement, the
* following is a guide on where to place the attributes.
*
* Attributes that apply to a struct or class precede the name of the class:
* (Note that this is different from the placement of MOZ_FINAL for classes!)
*
* class MOZ_CLASS_ATTRIBUTE SomeClass {};
*
* Attributes that apply to functions follow the parentheses and const
* qualifiers but precede MOZ_FINAL, MOZ_OVERRIDE and the function body:
*
* void DeclaredFunction() MOZ_FUNCTION_ATTRIBUTE;
* void SomeFunction() MOZ_FUNCTION_ATTRIBUTE {}
* void PureFunction() const MOZ_FUNCTION_ATTRIBUTE = 0;
* void OverriddenFunction() MOZ_FUNCTION_ATTIRBUTE MOZ_OVERRIDE;
*
* Attributes that apply to variables or parameters follow the variable's name:
*
* int variable MOZ_VARIABLE_ATTRIBUTE;
*
* Attributes that apply to types follow the type name:
*
* typedef int MOZ_TYPE_ATTRIBUTE MagicInt;
* int MOZ_TYPE_ATTRIBUTE someVariable;
* int* MOZ_TYPE_ATTRIBUTE magicPtrInt;
* int MOZ_TYPE_ATTRIBUTE* ptrToMagicInt;
*
* Attributes that apply to statements precede the statement:
*
* MOZ_IF_ATTRIBUTE if (x == 0)
* MOZ_DO_ATTRIBUTE do { } while (0);
*
* Attributes that apply to labels precede the label:
*
* MOZ_LABEL_ATTRIBUTE target:
* goto target;
* MOZ_CASE_ATTRIBUTE case 5:
* MOZ_DEFAULT_ATTRIBUTE default:
*
* The static analyses that are performed by the plugin are as follows:
*
* MOZ_MUST_OVERRIDE: Applies to all C++ member functions. All immediate
* subclasses must provide an exact override of this method; if a subclass
* does not override this method, the compiler will emit an error. This
* attribute is not limited to virtual methods, so if it is applied to a
* nonvirtual method and the subclass does not provide an equivalent
* definition, the compiler will emit an error.
* MOZ_STACK_CLASS: Applies to all classes. Any class with this annotation is
* expected to live on the stack, so it is a compile-time error to use it, or
* an array of such objects, as a global or static variable, or as the type of
* a new expression (unless placement new is being used). If a member of
* another class uses this class, or if another class inherits from this
* class, then it is considered to be a stack class as well, although this
* attribute need not be provided in such cases.
* MOZ_NONHEAP_CLASS: Applies to all classes. Any class with this annotation is
* expected to live on the stack or in static storage, so it is a compile-time
* error to use it, or an array of such objects, as the type of a new
* expression (unless placement new is being used). If a member of another
* class uses this class, or if another class inherits from this class, then
* it is considered to be a non-heap class as well, although this attribute
* need not be provided in such cases.
* MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS: Applies to all classes that are
* intended to prevent introducing static initializers. This attribute
* currently makes it a compile-time error to instantiate these classes
* anywhere other than at the global scope, or as a static member of a class.
* MOZ_TRIVIAL_CTOR_DTOR: Applies to all classes that must have both a trivial
* constructor and a trivial destructor. Setting this attribute on a class
* makes it a compile-time error for that class to get a non-trivial
* constructor or destructor for any reason.
* MOZ_HEAP_ALLOCATOR: Applies to any function. This indicates that the return
* value is allocated on the heap, and will as a result check such allocations
* during MOZ_STACK_CLASS and MOZ_NONHEAP_CLASS annotation checking.
* MOZ_IMPLICIT: Applies to constructors. Implicit conversion constructors
* are disallowed by default unless they are marked as MOZ_IMPLICIT. This
* attribute must be used for constructors which intend to provide implicit
* conversions.
* MOZ_NO_ARITHMETIC_EXPR_IN_ARGUMENT: Applies to functions. Makes it a compile
* time error to pass arithmetic expressions on variables to the function.
* MOZ_OWNING_REF: Applies to declarations of pointer types. This attribute
* tells the compiler that the raw pointer is a strong reference, and that
* property is somehow enforced by the code. This can make the compiler
* ignore these pointers when validating the usage of pointers otherwise.
* MOZ_NON_OWNING_REF: Applies to declarations of pointer types. This attribute
* tells the compiler that the raw pointer is a weak reference, and that
* property is somehow enforced by the code. This can make the compiler
* ignore these pointers when validating the usage of pointers otherwise.
* MOZ_UNSAFE_REF: Applies to declarations of pointer types. This attribute
* should be used for non-owning references that can be unsafe, and their
* safety needs to be validated through code inspection. The string argument
* passed to this macro documents the safety conditions.
* MOZ_NO_ADDREF_RELEASE_ON_RETURN: Applies to function declarations. Makes it
* a compile time error to call AddRef or Release on the return value of a
* function. This is intended to be used with operator->() of our smart
* pointer classes to ensure that the refcount of an object wrapped in a
* smart pointer is not manipulated directly.
*/
#ifdef MOZ_CLANG_PLUGIN
# define MOZ_MUST_OVERRIDE __attribute__((annotate("moz_must_override")))
# define MOZ_STACK_CLASS __attribute__((annotate("moz_stack_class")))
# define MOZ_NONHEAP_CLASS __attribute__((annotate("moz_nonheap_class")))
# define MOZ_TRIVIAL_CTOR_DTOR __attribute__((annotate("moz_trivial_ctor_dtor")))
# ifdef DEBUG
/* in debug builds, these classes do have non-trivial constructors. */
# define MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS __attribute__((annotate("moz_global_class")))
# else
# define MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS __attribute__((annotate("moz_global_class"))) \
MOZ_TRIVIAL_CTOR_DTOR
# endif
# define MOZ_IMPLICIT __attribute__((annotate("moz_implicit")))
# define MOZ_NO_ARITHMETIC_EXPR_IN_ARGUMENT __attribute__((annotate("moz_no_arith_expr_in_arg")))
# define MOZ_OWNING_REF __attribute__((annotate("moz_strong_ref")))
# define MOZ_NON_OWNING_REF __attribute__((annotate("moz_weak_ref")))
# define MOZ_UNSAFE_REF(reason) __attribute__((annotate("moz_strong_ref")))
# define MOZ_NO_ADDREF_RELEASE_ON_RETURN __attribute__((annotate("moz_no_addref_release_on_return")))
/*
* It turns out that clang doesn't like void func() __attribute__ {} without a
* warning, so use pragmas to disable the warning. This code won't work on GCC
* anyways, so the warning is safe to ignore.
*/
# define MOZ_HEAP_ALLOCATOR \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wgcc-compat\"") \
__attribute__((annotate("moz_heap_allocator"))) \
_Pragma("clang diagnostic pop")
#else
# define MOZ_MUST_OVERRIDE /* nothing */
# define MOZ_STACK_CLASS /* nothing */
# define MOZ_NONHEAP_CLASS /* nothing */
# define MOZ_TRIVIAL_CTOR_DTOR /* nothing */
# define MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS /* nothing */
# define MOZ_IMPLICIT /* nothing */
# define MOZ_NO_ARITHMETIC_EXPR_IN_ARGUMENT /* nothing */
# define MOZ_HEAP_ALLOCATOR /* nothing */
# define MOZ_OWNING_REF /* nothing */
# define MOZ_NON_OWNING_REF /* nothing */
# define MOZ_UNSAFE_REF(reason) /* nothing */
# define MOZ_NO_ADDREF_RELEASE_ON_RETURN /* nothing */
#endif /* MOZ_CLANG_PLUGIN */
#endif /* __cplusplus */
#endif /* mozilla_Attributes_h */