Extensible Firmware Interface Specification
116 12/12/00 Version 1.02
4.5.1.2 Handoff State, Itanium-based Operating Systems
EFI uses the standard P64 C calling conventions that are defined for Itanium-based operating
systems. Figure 4-2 shows the stack after ImageEntryPoint has been called on Itanium-based
systems. The arguments are also stored in registers: out0 contains EFI_HANDLE and out1
contains the address of the EFI_SYSTEM_TABLE. The gp for the EFI Image will have been
loaded from the plabel pointed to by the AddressOfEntryPoint in the images header.
EFI_SYSTEM_TABLE *
EFI_HANDLE

Stack

SP + 8
SP

Location

out1
out0

Register

Figure 4-2. Stack after ImageEntryPoint Called, Itanium-based Systems
The SAL specification (see Related Information in Chapter 1) defines the state of the system
registers at boot handoff. The SAL specification also defines which system registers can only be
used after EFI boot services have been properly terminated.