Intel Extensible Firmware Interface - Manual (Page 126)

Extensible Firmware Interface Specification
5-28 12/01/02 Version 1.10
Description
The GetMemoryMap() function returns a copy of the current memory map. The map is an array
of memory descriptors, each of which describes a contiguous block of memory. The map describes
all of memory, no matter how it is being used. That is, it includes blocks allocated by
AllocatePages() and AllocatePool() , as well as blocks that the firmware is using for its
own purposes. The memory map is only used to describe memory that is present in the system.
Memory descriptors are never used to describe holes in the system memory map.
Until ExitBootServices() is called, the memory map is owned by the firmware and the
currently executing EFI Image should only use memory pages it has explicitly allocated.
If the MemoryMap buffer is too small, the EFI_BUFFER_TOO_SMALL error code is returned and
the MemoryMapSize value contains the size of the buffer needed to contain the current
memory map.
On success a MapKey is returned that identifies the current memory map. The firmware’s key is
changed every time something in the memory map changes. In order to successfully invoke
ExitBootServices() the caller must provide the current memory map key.
The GetMemoryMap() function also returns the size and revision number of the
EFI_MEMORY_DESCRIPTOR . The DescriptorSize represents the size in bytes of an
EFI_MEMORY_DESCRIPTOR array element returned in MemoryMap . The size is returned to
allow for future expansion of the EFI_MEMORY_DESCRIPTOR in response to hardware
innovation. The structure of the EFI_MEMORY_DESCRIPTOR may be extended in the future but
it will remain backwards compatible with the current definition. Thus OS software must use the
DescriptorSize to find the start of each EFI_MEMORY_DESCRIPTOR in the MemoryMap
array.
Status Codes Returned
EFI_SUCCESS The memory map was returned in the MemoryMap buffer.
EFI_BUFFER_TOO_SMALL The MemoryMap buffer was too small. The current buffer size
needed to hold the memory map is returned in MemoryMapSize .
EFI_INVALID_PARAMETER One of the parameters has an invalid value.