Source code
Revision control
Copy as Markdown
Other Tools
/* -*- 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
#ifndef mozilla_ipc_SharedMemoryMapping_h
#define mozilla_ipc_SharedMemoryMapping_h
#include <tuple>
#include <utility>
#include "mozilla/Assertions.h"
#include "mozilla/Span.h"
#include "SharedMemoryHandle.h"
namespace mozilla::ipc {
namespace shared_memory {
/**
* A leaked memory mapping.
*
* This memory will never be unmapped.
*/
struct LeakedMapping : Span<uint8_t> {
using Span::Span;
};
class MappingBase {
public:
/**
* The size of the mapping.
*/
size_t Size() const { return mSize; }
/**
* The pointer to the mapping in memory.
*/
void* Data() const;
/**
* Get a `Span<T>` over the mapping.
*
* The mapping data must meet the alignment requirements of @p T.
*
* @tparam T The type of data in the mapping.
*
* @return A span of type @p T covering as much of the mapping as possible.
*/
template <typename T>
Span<T> DataAsSpan() const {
MOZ_ASSERT((reinterpret_cast<uintptr_t>(Data()) % alignof(T)) == 0,
"memory map does not meet alignment requirements of type");
size_t count = Size() / sizeof(T);
return {static_cast<T*>(Data()), count};
}
/**
* Whether this shared memory mapping is valid.
*/
bool IsValid() const { return (bool)*this; }
/**
* Whether this shared memory mapping is valid.
*/
explicit operator bool() const { return (bool)mMemory; }
protected:
/**
* Create an empty Mapping.
*/
MappingBase();
MOZ_IMPLICIT MappingBase(std::nullptr_t) {}
~MappingBase();
/**
* Mappings are movable (but not copyable).
*/
MappingBase(MappingBase&& aOther)
: mMemory(std::exchange(aOther.mMemory, nullptr)),
mSize(std::exchange(aOther.mSize, 0)) {}
MappingBase& operator=(MappingBase&& aOther) {
mMemory = std::exchange(aOther.mMemory, nullptr);
mSize = std::exchange(aOther.mSize, 0);
return *this;
}
bool Map(const HandleBase& aHandle, void* aFixedAddress, bool aReadOnly);
template <typename Derived>
Derived ConvertTo() && {
Derived d;
static_cast<MappingBase&>(d) = std::move(*this);
return d;
}
/**
* Leak this mapping's memory.
*
* This will cause the memory to be mapped until the process exits.
*/
LeakedMapping release() &&;
private:
void* mMemory = nullptr;
size_t mSize = 0;
};
/**
* A shared memory mapping.
*/
struct Mapping : MappingBase {
/**
* Create an empty Mapping.
*/
Mapping() = default;
MOZ_IMPLICIT Mapping(std::nullptr_t) {}
explicit Mapping(const Handle& aHandle, void* aFixedAddress = nullptr);
using MappingBase::release;
};
/**
* A read-only shared memory mapping.
*/
struct ReadOnlyMapping : MappingBase {
/**
* Create an empty ReadOnlyMapping.
*/
ReadOnlyMapping() = default;
MOZ_IMPLICIT ReadOnlyMapping(std::nullptr_t) {}
explicit ReadOnlyMapping(const ReadOnlyHandle& aHandle,
void* aFixedAddress = nullptr);
};
/**
* A freezable shared memory mapping.
*/
struct FreezableMapping : MappingBase {
/**
* Create an empty FreezableMapping.
*/
FreezableMapping() = default;
MOZ_IMPLICIT FreezableMapping(std::nullptr_t) {}
/**
* Freezable mappings take ownership of a handle to ensure there is only one
* writeable mapping at a time.
*
* Call `Unmap()` to get the handle back.
*/
explicit FreezableMapping(FreezableHandle&& aHandle,
void* aFixedAddress = nullptr);
/**
* Freeze the shared memory region.
*
* The returned Mapping will still be valid and writable until it is deleted,
* however no new writable mappings can be created.
*/
std::tuple<Mapping, ReadOnlyHandle> Freeze() &&;
/**
* Unmap the shared memory, returning the freezable handle.
*
* It is only necessary to call this if you need to get the FreezableHandle
* back.
*/
FreezableHandle Unmap() &&;
private:
FreezableHandle mHandle;
};
// The access level permitted for memory protection.
enum Access {
AccessNone = 0,
AccessRead = 1 << 0,
AccessWrite = 1 << 1,
AccessReadWrite = AccessRead | AccessWrite,
};
/**
* Protect the given memory region.
*
* This protection extends only to the local memory mapping. It doesn't change
* the permissions of other mappings nor the associated handle.
*
* @param aAddr The address at the beginning of the memory region.
* @param aSize The size of the region to protect.
* @param aAccess The access level to allow.
*
* @returns Whether protection was successful.
*/
bool LocalProtect(char* aAddr, size_t aSize, Access aAccess);
/**
* Find a region of free memory.
*
* @param aSize The size of the region to locate.
*
* @returns The start of the memory region, or nullptr on error.
*/
void* FindFreeAddressSpace(size_t aSize);
/**
* Get the system page size.
*/
size_t SystemPageSize();
/**
* Return a size which is page-aligned and can fit at least `minimum` bytes.
*
* @param aMinimum The minimum number of bytes required.
*
* @returns The page-aligned size that can hold `minimum` bytes.
*/
size_t PageAlignedSize(size_t aMinimum);
} // namespace shared_memory
using SharedMemoryMapping = shared_memory::Mapping;
using ReadOnlySharedMemoryMapping = shared_memory::ReadOnlyMapping;
using FreezableSharedMemoryMapping = shared_memory::FreezableMapping;
} // namespace mozilla::ipc
#endif