#include <v8-platform.h>

Public Types
using	Address = uintptr_t

Public Member Functions
	VirtualAddressSpace (size_t page_size, size_t allocation_granularity, Address base, size_t size, PagePermissions max_page_permissions)

virtual	~VirtualAddressSpace ()=default

size_t	page_size () const

size_t	allocation_granularity () const

Address	base () const

size_t	size () const

PagePermissions	max_page_permissions () const

bool	Contains (Address address) const

virtual void	SetRandomSeed (int64_t seed)=0

virtual Address	RandomPageAddress ()=0

virtual V8_WARN_UNUSED_RESULT Address	AllocatePages (Address hint, size_t size, size_t alignment, PagePermissions permissions)=0

virtual void	FreePages (Address address, size_t size)=0

virtual V8_WARN_UNUSED_RESULT bool	SetPagePermissions (Address address, size_t size, PagePermissions permissions)=0

virtual V8_WARN_UNUSED_RESULT bool	AllocateGuardRegion (Address address, size_t size)=0

virtual void	FreeGuardRegion (Address address, size_t size)=0

virtual V8_WARN_UNUSED_RESULT Address	AllocateSharedPages (Address hint, size_t size, PagePermissions permissions, PlatformSharedMemoryHandle handle, uint64_t offset)=0

virtual void	FreeSharedPages (Address address, size_t size)=0

virtual bool	CanAllocateSubspaces ()=0

virtual std::unique_ptr< VirtualAddressSpace >	AllocateSubspace (Address hint, size_t size, size_t alignment, PagePermissions max_page_permissions)=0

virtual V8_WARN_UNUSED_RESULT bool	RecommitPages (Address address, size_t size, PagePermissions permissions)=0

virtual V8_WARN_UNUSED_RESULT bool	DiscardSystemPages (Address address, size_t size)

virtual V8_WARN_UNUSED_RESULT bool	DecommitPages (Address address, size_t size)=0

Static Public Attributes
static constexpr Address	kNoHint = 0

Detailed Description

Class to manage a virtual memory address space.

This class represents a contiguous region of virtual address space in which sub-spaces and (private or shared) memory pages can be allocated, freed, and modified. This interface is meant to eventually replace the PageAllocator interface, and can be used as an alternative in the meantime.

This API is not yet stable and may change without notice!

Definition at line 722 of file v8-platform.h.

Member Typedef Documentation

◆ Address

using Address = uintptr_t

Definition at line 724 of file v8-platform.h.

Constructor & Destructor Documentation

◆ VirtualAddressSpace()

VirtualAddressSpace	(	size_t	page_size,
		size_t	allocation_granularity,
		Address	base,
		size_t	size,
		PagePermissions	max_page_permissions
	)

inline

Definition at line 726 of file v8-platform.h.

◆ ~VirtualAddressSpace()

virtual ~VirtualAddressSpace ( )

virtualdefault

Member Function Documentation

◆ AllocateGuardRegion()

virtual V8_WARN_UNUSED_RESULT bool AllocateGuardRegion	(	Address	address,
		size_t	size
	)

pure virtual

Creates a guard region at the specified address.

Guard regions are guaranteed to cause a fault when accessed and generally do not count towards any memory consumption limits. Further, allocating guard regions can usually not fail in subspaces if the region does not overlap with another region, subspace, or page allocation.

Parameters

address	The start address of the guard region. Must be aligned to the allocation_granularity().
size	The size of the guard region in bytes. Must be a multiple of the allocation_granularity().

Returns: true on success, false otherwise.

◆ AllocatePages()

virtual V8_WARN_UNUSED_RESULT Address AllocatePages	(	Address	hint,
		size_t	size,
		size_t	alignment,
		PagePermissions	permissions
	)

pure virtual

◆ AllocateSharedPages()

virtual V8_WARN_UNUSED_RESULT Address AllocateSharedPages	(	Address	hint,
		size_t	size,
		PagePermissions	permissions,
		PlatformSharedMemoryHandle	handle,
		uint64_t	offset
	)

pure virtual

Allocates shared memory pages with the given permissions.

Parameters

hint	Placement hint. See AllocatePages.
size	The size of the allocation in bytes. Must be a multiple of the allocation_granularity().
permissions	The page permissions of the newly allocated pages.
handle	A platform-specific handle to a shared memory object. See the SharedMemoryHandleFromX routines above for ways to obtain these.
offset	The offset in the shared memory object at which the mapping should start. Must be a multiple of the allocation_granularity().

Returns: the start address of the allocated pages on success, zero on failure.

◆ AllocateSubspace()

virtual std::unique_ptr< VirtualAddressSpace > AllocateSubspace	(	Address	hint,
		size_t	size,
		size_t	alignment,
		PagePermissions	max_page_permissions
	)

pure virtual

◆ allocation_granularity()

size_t allocation_granularity ( ) const

inline

The granularity of page allocations and, by extension, of subspace allocations. This is guaranteed to be a power of two and a multiple of the page_size(). In practice, this is equal to the page size on most OSes, but on Windows it is usually 64KB, while the page size is 4KB.

Returns: the allocation granularity in bytes.

Definition at line 754 of file v8-platform.h.

◆ base()

Address base ( ) const

inline

The base address of the address space managed by this instance.

Returns: the base address of this address space.

Definition at line 761 of file v8-platform.h.

Referenced by VirtualAddressSpace::Contains().

◆ CanAllocateSubspaces()

virtual bool CanAllocateSubspaces ( )

pure virtual

Whether this instance can allocate subspaces or not.

Returns: true if subspaces can be allocated, false if not.

◆ Contains()

bool Contains ( Address address ) const

inline

Whether the |address| is inside the address space managed by this instance.

Returns: true if it is inside the address space, false if not.

Definition at line 783 of file v8-platform.h.

References VirtualAddressSpace::base(), and VirtualAddressSpace::size().

◆ DecommitPages()

virtual V8_WARN_UNUSED_RESULT bool DecommitPages	(	Address	address,
		size_t	size
	)

pure virtual

Decommits any wired memory pages in the given range, allowing the OS to reclaim them, and marks the region as inacessible (kNoAccess). The address range stays reserved and can be accessed again later by changing its permissions. However, in that case the memory content is guaranteed to be zero-initialized again. The memory must have been previously allocated by a call to AllocatePages.

Returns: true on success, false otherwise.

◆ DiscardSystemPages()

virtual V8_WARN_UNUSED_RESULT bool DiscardSystemPages	(	Address	address,
		size_t	size
	)

inlinevirtual

Frees memory in the given [address, address + size) range. address and size should be aligned to the page_size(). The next write to this memory area brings the memory transparently back. This should be treated as a hint to the OS that the pages are no longer needed. It does not guarantee that the pages will be discarded immediately or at all.

Returns: true on success, false otherwise. Since this method is only a hint, a successful invocation does not imply that pages have been removed.

Definition at line 999 of file v8-platform.h.

◆ FreeGuardRegion()

virtual void FreeGuardRegion	(	Address	address,
		size_t	size
	)

pure virtual

Frees an existing guard region.

This function will terminate the process on failure as this implies a bug in the client. As such, there is no return value.

Parameters

address	The start address of the guard region to free. This address must have previously been used as address parameter in a successful invocation of AllocateGuardRegion.
size	The size in bytes of the guard region to free. This must match the size passed to AllocateGuardRegion when the region was created.

◆ FreePages()

virtual void FreePages	(	Address	address,
		size_t	size
	)

pure virtual

Frees previously allocated pages.

This function will terminate the process on failure as this implies a bug in the client. As such, there is no return value.

Parameters

address	The start address of the pages to free. This address must have been obtained through a call to AllocatePages.
size	The size in bytes of the region to free. This must match the size passed to AllocatePages when the pages were allocated.

◆ FreeSharedPages()

virtual void FreeSharedPages	(	Address	address,
		size_t	size
	)

pure virtual

Frees previously allocated shared pages.

This function will terminate the process on failure as this implies a bug in the client. As such, there is no return value.

Parameters

address	The start address of the pages to free. This address must have been obtained through a call to AllocateSharedPages.
size	The size in bytes of the region to free. This must match the size passed to AllocateSharedPages when the pages were allocated.

◆ max_page_permissions()

PagePermissions max_page_permissions ( ) const

inline

The maximum page permissions that pages allocated inside this space can obtain.

Returns: the maximum page permissions.

Definition at line 776 of file v8-platform.h.

◆ page_size()

size_t page_size ( ) const

inline

The page size used inside this space. Guaranteed to be a power of two. Used as granularity for all page-related operations except for allocation, which use the allocation_granularity(), see below.

Returns: the page size in bytes.

Definition at line 744 of file v8-platform.h.

◆ RandomPageAddress()

virtual Address RandomPageAddress ( )

pure virtual

Returns a random address inside this address space, suitable for page allocations hints.

Returns: a random address aligned to allocation_granularity().

◆ RecommitPages()

virtual V8_WARN_UNUSED_RESULT bool RecommitPages	(	Address	address,
		size_t	size,
		PagePermissions	permissions
	)

pure virtual

Recommits discarded pages in the given range with given permissions. Discarded pages must be recommitted with their original permissions before they are used again.

Parameters

address	The start address of the range. Must be aligned to page_size().
size	The size in bytes of the range. Must be a multiple of page_size().
permissions	The permissions for the range that the pages must have.

Returns: true on success, false otherwise.

◆ SetPagePermissions()

virtual V8_WARN_UNUSED_RESULT bool SetPagePermissions	(	Address	address,
		size_t	size,
		PagePermissions	permissions
	)

pure virtual

Sets permissions of all allocated pages in the given range.

This operation can fail due to OOM, in which case false is returned. If the operation fails for a reason other than OOM, this function will terminate the process as this implies a bug in the client.

Parameters

address	The start address of the range. Must be aligned to page_size().
size	The size in bytes of the range. Must be a multiple of page_size().
permissions	The new permissions for the range.

Returns: true on success, false on OOM.

◆ SetRandomSeed()

virtual void SetRandomSeed ( int64_t seed )

pure virtual

Sets the random seed so that GetRandomPageAddress() will generate repeatable sequences of random addresses.

Parameters

The	seed for the PRNG.

◆ size()

size_t size ( ) const

inline

The size of the address space managed by this instance.

Returns: the size of this address space in bytes.

Definition at line 768 of file v8-platform.h.

Referenced by VirtualAddressSpace::Contains().

Field Documentation

◆ kNoHint

constexpr Address kNoHint = 0

staticconstexpr

Allocates private memory pages with the given alignment and permissions.

Parameters

hint	If nonzero, the allocation is attempted to be placed at the given address first. If that fails, the allocation is attempted to be placed elsewhere, possibly nearby, but that is not guaranteed. Specifying zero for the hint always causes this function to choose a random address. The hint, if specified, must be aligned to the specified alignment.
size	The size of the allocation in bytes. Must be a multiple of the allocation_granularity().
alignment	The alignment of the allocation in bytes. Must be a multiple of the allocation_granularity() and should be a power of two.
permissions	The page permissions of the newly allocated pages.

Returns: the start address of the allocated pages on success, zero on failure.

Definition at line 823 of file v8-platform.h.

The documentation for this class was generated from the following file:

include/v8-platform.h

Public Types

Public Member Functions

Static Public Attributes

Detailed Description

Member Typedef Documentation

◆ Address

Constructor & Destructor Documentation

◆ VirtualAddressSpace()

◆ ~VirtualAddressSpace()

Member Function Documentation

◆ AllocateGuardRegion()

◆ AllocatePages()

◆ AllocateSharedPages()

◆ AllocateSubspace()

◆ allocation_granularity()

◆ base()

◆ CanAllocateSubspaces()

◆ Contains()

◆ DecommitPages()

◆ DiscardSystemPages()

◆ FreeGuardRegion()

◆ FreePages()

◆ FreeSharedPages()

◆ max_page_permissions()

◆ page_size()

◆ RandomPageAddress()

◆ RecommitPages()

◆ SetPagePermissions()

◆ SetRandomSeed()

◆ size()

Field Documentation

◆ kNoHint