1 ;------------------------------------------------------------------------------
3 ; Copyright (c) 2006, Intel Corporation
4 ; All rights reserved. This program and the accompanying materials
5 ; are licensed and made available under the terms and conditions of the BSD License
6 ; which accompanies this distribution. The full text of the license may be found at
7 ; http://opensource.org/licenses/bsd-license.php
9 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
10 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
20 ;------------------------------------------------------------------------------
22 EXTERNDEF m16Start:BYTE
23 EXTERNDEF m16Size:WORD
24 EXTERNDEF mThunk16Attr:WORD
26 EXTERNDEF m16GdtrBase:WORD
27 EXTERNDEF mTransition:WORD
29 ;THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 EQU 2
30 ;THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL EQU 4
53 m16Size DW offset InternalAsmThunk16 - offset m16Start
54 mThunk16Attr DW offset _ThunkAttr - offset m16Start
55 m16Gdt DW offset _NullSegDesc - offset m16Start
56 m16GdtrBase DW offset _16GdtrBase - offset m16Start
57 mTransition DW offset _EntryPoint - offset m16Start
67 _BackFromUserCode PROC
74 push 0 ; reserved high order 32 bits of EFlags
75 pushf ; pushfd actually
76 cli ; disable interrupts
82 DB 66h, 0bah ; mov edx, imm32
84 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
86 mov eax, 15cd2401h ; mov ax, 2401h & int 15h
87 cli ; disable interrupts
90 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
94 out 92h, al ; deactivate A20M#
97 lea bp, [esp + sizeof (IA32_REGS)]
98 mov word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
99 mov ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
100 shl ax, 4 ; shl eax, 4
101 add bp, ax ; add ebp, eax
102 DB 66h, 0b8h ; mov eax, imm32
106 lgdt fword ptr [rdi + (offset SavedGdt - offset @Base)]
112 DB 66h, 0b8h ; mov eax, imm32
115 DB 0b8h ; mov ax, imm16
118 DB 66h, 0bch ; mov esp, imm32
121 retf ; return to protected mode
122 _BackFromUserCode ENDP
124 _EntryPoint DD offset _ToUserCode - offset m16Start
127 DW offset GdtEnd - offset _NullSegDesc - 1
128 _16GdtrBase DQ offset _NullSegDesc
129 _16Idtr FWORD (1 SHL 10) - 1
133 mov ss, edx ; set new segment selectors
140 mov cr0, rax ; real mode starts at next instruction
145 mov ss, esi ; set up 16-bit stack segment
146 xchg sp, bx ; set up 16-bit stack pointer
148 call @Base ; push eip
150 pop bp ; ebp <- offset @Base
151 push [esp + sizeof (IA32_REGS) + 2]
152 lea eax, [rsi + (offset @RealMode - offset @Base)]
157 mov [rsi + (offset SavedSs - offset @Base)], edi
159 mov [rsi + (offset SavedEsp - offset @Base)], bx
160 DB 66h, 2eh ; CS and operand size override
161 lidt fword ptr [rsi + (offset _16Idtr - offset @Base)]
168 lea sp, [esp + 4] ; skip high order 32 bits of EFlags
170 retf ; transfer control to user code
174 _16CsDesc LABEL QWORD
179 DB 8fh ; 16-bit segment, 4GB limit
181 _16DsDesc LABEL QWORD
186 DB 8fh ; 16-bit segment, 4GB limit
191 ; @param RegSet Pointer to a IA32_DWORD_REGS structure
192 ; @param Transition Pointer to the transition code
193 ; @return The address of the 16-bit stack after returning from user code
195 InternalAsmThunk16 PROC USES rbp rbx rsi rdi
201 movzx r8d, (IA32_REGS ptr [rsi])._SS
202 mov edi, (IA32_REGS ptr [rsi])._ESP
203 lea rdi, [edi - (sizeof (IA32_REGS) + 4)]
204 imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
205 mov ebx, edi ; ebx <- stack offset for 16-bit code
206 push sizeof (IA32_REGS) / 4
207 add edi, eax ; edi <- linear address of 16-bit stack
209 rep movsd ; copy RegSet
210 lea ecx, [rdx + (offset SavedCr4 - offset m16Start)]
211 mov eax, edx ; eax <- transition code address
214 lea edx, [rdx + (offset _BackFromUserCode - offset m16Start)]
216 stosd ; [edi] <- return address of user code
217 sgdt fword ptr [rcx + (offset SavedGdt - offset SavedCr4)]
218 sidt fword ptr [rsp + 38h] ; save IDT stack in argument space
220 mov [rcx + (offset SavedCr0 - offset SavedCr4)], eax
221 and eax, 7ffffffeh ; clear PE, PG bits
223 mov [rcx], ebp ; save CR4 in SavedCr4
224 and ebp, 300h ; clear all but PCE and OSFXSR bits
225 mov esi, r8d ; esi <- 16-bit stack segment
227 pop rdx ; rdx <- selector for data segments
228 lgdt fword ptr [rcx + (offset _16Gdtr - offset SavedCr4)]
230 call fword ptr [rcx + (offset _EntryPoint - offset SavedCr4)]
232 lidt fword ptr [rsp + 38h] ; restore protected mode IDTR
233 lea eax, [rbp - sizeof (IA32_REGS)]
239 InternalAsmThunk16 ENDP