Intel Extensible Firmware Interface - Manual (Page 80)

Extensible Firmware Interface Specification
4-2 12/01/02 Version 1.10
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 nonzero 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 Chapter 7.
If the EFI image is an EFI Application, then the EFI Application executes and either returns or calls
the EFI Boot Services
Exit() . An EFI Application is always unloaded from memory when it
exits, and its return status is returned to the component that started the EFI Application.
If the EFI image is an EFI OS Loader, then the EFI OS Loader executes and either returns, calls the
EFI Boot Service
Exit(), or calls the EFI Boot Service ExitBootServices() . If the EFI
OS Loader returns or calls Exit() , then the load of the OS has failed, and the EFI OS Loader is
unloaded from memory and control is returned to the component that attempted to boot the EFI OS
Loader. If
ExitBootServices() is called, then the OS Loader has taken control of the
platform, and EFI will not regain control of the system until the platform is reset. One method of
resetting the platform is through the EFI Runtime Service
ResetSystem() .
If the EFI image is an EFI Driver, then the EFI Driver executes and either returns or calls the EFI
Boot Service
Exit() . If an EFI driver returns an error, then the driver is unloaded from memory.
If the EFI driver returns EFI_SUCCESS , then it stays resident in memory. If the EFI Driver does
not follow the EFI Driver Model, then it performs any required initialization and installs its
protocol services before returning. If the EFI driver does follow the EFI Driver Model, then the
entry point is not allowed to touch any device hardware. Instead, the entry point is required to
create and install the
EFI_DRIVER_BINDING_PROTOCOL (Chapter 9) on the ImageHandle
of the EFI Driver. If this process is completed, then EFI_SUCCESS is returned. If the resources
are not available to complete the driver initialization, then EFI_OUT_OF_RESOURCES
is returned.
Status Codes Returned
EFI_SUCCESS The driver was initialized .
EFI_OUT_OF_RESOURCES The request could not be completed due to a lack of resources.