Intel Extensible Firmware Interface, Specification

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EFI Image
Version 1.02 12/12/00 111
When the boot manager loads a driver, the image handle may be used to locate the “load options”
for the driver. The load options are those options that were stored in the
LoadOptions
field of
the
EFI_LOADED_IMAGE
information for the driver.
4.5.1 EFI Image Handoff State
Control is transferred to a loaded image at the
AddressOfEntryPoint
reference according to
the normal indirect calling conventions for the image’s
Machine
type. The entry point is a
function of type
EFI_IMAGE_ENTRY_POINT
. All other linkage to and from an EFI image is
done programmatically. See Chapter 3 for the full definition of
EFI_IMAGE_ENTRY_POINT
. Its
prototype is repeated below, along with some additional comments.
typedef
EFI_STATUS
(EFIAPI *EFI_IMAGE_ENTRY_POINT) (
IN EFI_HANDLE ImageHandle,
IN EFI_SYSTEM_TABLE *SystemTable
);
The first argument is the image’s image handle. The second argument is a pointer to the image’s
system table. The system table contains the standard output and input handles, plus pointers to the
EFI_BOOT_SERVICES
and
EFI_RUNTIME_SERVICES
tables. The service tables contain the
entry points in the firmware for accessing the core EFI system functionality. The handles in the
system table are used to obtain basic access to the console. In addition, the EFI system table
contains pointers to other standard tables that a loaded image may use if the associated pointers are
initialized to non-zero values. Examples of such tables are ACPI, SMBIOS, SAL System
Table, etc.
The
ImageHandle
is a firmware-allocated handle that is used to identify the image on various
functions. The handle also supports one or more protocols that the image can use. All images
support the
EFI_LOADED_IMAGE
protocol that returns the source location of the image, the
memory location of the image, the load options for the image, etc. The exact
EFI_LOADED_IMAGE
structure is defined in Section 4.1.
The following code shows the definition for the EFI system table. The EFI system table is provided
as the second argument to a loaded image’s entry point.