2 ; Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
3 ; This program and the accompanying materials
4 ; are licensed and made available under the terms and conditions of the BSD License
5 ; which accompanies this distribution. The full text of the license may be found at
6 ; http://opensource.org/licenses/bsd-license.php.
8 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
9 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
18 ; This is the assembly code to transition from long mode to compatibility mode to execute 32-bit code and then
19 ; transit back to long mode.
21 ;-------------------------------------------------------------------------------
24 ;----------------------------------------------------------------------------
25 ; Procedure: AsmExecute32BitCode
32 ; AsmExecute32BitCode (
36 ; IN IA32_DESCRIPTOR *InternalGdtr
40 ; Description: A thunk function to execute 32-bit code in long mode.
42 ;----------------------------------------------------------------------------
43 global ASM_PFX(AsmExecute32BitCode)
44 ASM_PFX(AsmExecute32BitCode):
46 ; save IFLAG and disable it
52 ; save orignal GDTR and CS
65 ; Save general purpose register and rflag register
80 ; Prepare the CS and return address for the transition from 32-bit to 64-bit mode
82 mov rax, dword 0x10 ; load long mode selector
84 lea r9, [ReloadCS] ;Assume the ReloadCS is under 4G
88 ; Save parameters for 32-bit function call
95 ; save the 32-bit function entry and the return address into stack which will be
96 ; retrieve in compatibility mode.
98 lea rax, [ReturnBack] ;Assume the ReloadCS is under 4G
109 ; Change to Compatible Segment
111 mov rcx, dword 0x8 ; load compatible mode selector
113 lea rdx, [Compatible] ; assume address < 4G
119 ; reload DS/ES/SS to make sure they are correct referred to current GDT
138 ; Now we are in protected mode
140 ; Call 32-bit function. Assume the function entry address and parameter value is less than 4G
142 pop rax ; Here is the function entry
144 ; Now the parameter is at the bottom of the stack, then call in to IA32 function.
148 mov ebx, eax ; save return status
149 pop rcx ; drop param1
150 pop rcx ; drop param2
166 ; Set EFER.LME to re-enable ia32-e
178 ; Now we are in compatible mode
186 ; Now we're in Long Mode
189 ; Restore C register and eax hold the return status from 32-bit function.
190 ; Note: Do not touch rax from now which hold the return value from IA32 function
192 mov eax, ebx ; put return status to EAX
199 ; Switch to orignal GDT and CS. here rsp is pointer to the orignal GDT descriptor.
203 ; drop GDT descriptor in stack
207 ; switch to orignal CS and GDTR
210 shl r9, 32 ; rcx[32..47] <- Cs
217 ; Reload original DS/ES/SS