mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-23 04:41:11 +00:00
14ca007916
Also adds missing includes in some files, these were previously only transivitely included through mozilla/TypeTraits.h. Differential Revision: https://phabricator.services.mozilla.com/D68561 --HG-- extra : moz-landing-system : lando
126 lines
4.5 KiB
C++
126 lines
4.5 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/. */
|
|
|
|
#ifndef mozilla_NonDereferenceable_h
|
|
#define mozilla_NonDereferenceable_h
|
|
|
|
/* A pointer wrapper indicating that the pointer should not be dereferenced. */
|
|
|
|
#include "mozilla/Attributes.h"
|
|
|
|
#include <cstdint>
|
|
|
|
// Macro indicating that a function manipulates a pointer that will not be
|
|
// dereferenced, and therefore there is no need to check the object.
|
|
#if defined(__clang__)
|
|
# define NO_POINTEE_CHECKS __attribute__((no_sanitize("vptr")))
|
|
#else
|
|
# define NO_POINTEE_CHECKS /* nothing */
|
|
#endif
|
|
|
|
namespace mozilla {
|
|
|
|
// NonDereferenceable<T> wraps a raw pointer value of type T*, but prevents
|
|
// dereferencing.
|
|
//
|
|
// The main use case is for pointers that referencing memory that may not
|
|
// contain a valid object, either because the object has already been freed, or
|
|
// is under active construction or destruction (and hence parts of it may be
|
|
// uninitialized or destructed.)
|
|
// Such a pointer may still be useful, e.g., for its numeric value for
|
|
// logging/debugging purposes, which may be accessed with `value()`.
|
|
// Using NonDereferenceable with such pointers will make this intent clearer,
|
|
// and prevent misuses.
|
|
//
|
|
// Note that NonDereferenceable is only a wrapper and is NOT an owning pointer,
|
|
// i.e., it will not release/free the object.
|
|
//
|
|
// NonDereferenceable allows conversions between compatible pointer types, e.g.,
|
|
// to navigate a class hierarchy and identify parent/sub-objects. Note that the
|
|
// converted pointers stay safely NonDereferenceable.
|
|
//
|
|
// Use of NonDereferenceable is required to avoid errors from sanitization tools
|
|
// like `clang++ -fsanitize=vptr`, and should prevent false positives while
|
|
// pointers are manipulated within NonDereferenceable objects.
|
|
//
|
|
template <typename T>
|
|
class NonDereferenceable {
|
|
public:
|
|
// Default construction with a null value.
|
|
NonDereferenceable() : mPtr(nullptr) {}
|
|
|
|
// Default copy construction and assignment.
|
|
NO_POINTEE_CHECKS
|
|
NonDereferenceable(const NonDereferenceable&) = default;
|
|
NO_POINTEE_CHECKS
|
|
NonDereferenceable<T>& operator=(const NonDereferenceable&) = default;
|
|
// No move operations, as we're only carrying a non-owning pointer, so
|
|
// copying is most efficient.
|
|
|
|
// Construct/assign from a T* raw pointer.
|
|
// A raw pointer should usually point at a valid object, however we want to
|
|
// leave the ability to the user to create a NonDereferenceable from any
|
|
// pointer. Also, strictly speaking, in a constructor or destructor, `this`
|
|
// points at an object still being constructed or already partially
|
|
// destructed, which some very sensitive sanitizers could complain about.
|
|
NO_POINTEE_CHECKS
|
|
explicit NonDereferenceable(T* aPtr) : mPtr(aPtr) {}
|
|
NO_POINTEE_CHECKS
|
|
NonDereferenceable& operator=(T* aPtr) {
|
|
mPtr = aPtr;
|
|
return *this;
|
|
}
|
|
|
|
// Construct/assign from a compatible pointer type.
|
|
template <typename U>
|
|
NO_POINTEE_CHECKS explicit NonDereferenceable(U* aOther)
|
|
: mPtr(static_cast<T*>(aOther)) {}
|
|
template <typename U>
|
|
NO_POINTEE_CHECKS NonDereferenceable& operator=(U* aOther) {
|
|
mPtr = static_cast<T*>(aOther);
|
|
return *this;
|
|
}
|
|
|
|
// Construct/assign from a NonDereferenceable with a compatible pointer type.
|
|
template <typename U>
|
|
NO_POINTEE_CHECKS MOZ_IMPLICIT
|
|
NonDereferenceable(const NonDereferenceable<U>& aOther)
|
|
: mPtr(static_cast<T*>(aOther.mPtr)) {}
|
|
template <typename U>
|
|
NO_POINTEE_CHECKS NonDereferenceable& operator=(
|
|
const NonDereferenceable<U>& aOther) {
|
|
mPtr = static_cast<T*>(aOther.mPtr);
|
|
return *this;
|
|
}
|
|
|
|
// Explicitly disallow dereference operators, so that compiler errors point
|
|
// at these lines:
|
|
T& operator*() = delete; // Cannot dereference NonDereferenceable!
|
|
T* operator->() = delete; // Cannot dereference NonDereferenceable!
|
|
|
|
// Null check.
|
|
NO_POINTEE_CHECKS
|
|
explicit operator bool() const { return !!mPtr; }
|
|
|
|
// Extract the pointer value, untyped.
|
|
NO_POINTEE_CHECKS
|
|
uintptr_t value() const { return reinterpret_cast<uintptr_t>(mPtr); }
|
|
|
|
private:
|
|
// Let other NonDereferenceable templates access mPtr, to permit construction/
|
|
// assignment from compatible pointer types.
|
|
template <typename>
|
|
friend class NonDereferenceable;
|
|
|
|
T* MOZ_NON_OWNING_REF mPtr;
|
|
};
|
|
|
|
} // namespace mozilla
|
|
|
|
#undef NO_POINTEE_CHECKS
|
|
|
|
#endif /* mozilla_NonDereferenceable_h */
|