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
50 m16Size DW InternalAsmThunk16 - m16Start
51 mThunk16Attr DW _ThunkAttr - m16Start
52 m16Gdt DW _NullSeg - m16Start
53 m16GdtrBase DW _16GdtrBase - m16Start
54 mTransition DW _EntryPoint - m16Start
64 ;------------------------------------------------------------------------------
65 ; _BackFromUserCode() takes control in real mode after 'retf' has been executed
66 ; by user code. It will be shadowed to somewhere in memory below 1MB.
67 ;------------------------------------------------------------------------------
68 _BackFromUserCode PROC
75 push 0 ; reserved high order 32 bits of EFlags
76 pushf ; pushfd actually
77 cli ; disable interrupts
83 DB 66h, 0bah ; mov edx, imm32
85 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
87 mov eax, 15cd2401h ; mov ax, 2401h & int 15h
88 cli ; disable interrupts
91 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
95 out 92h, al ; deactivate A20M#
98 lea bp, [esp + sizeof (IA32_REGS)]
99 mov word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
100 mov ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
101 shl ax, 4 ; shl eax, 4
102 add bp, ax ; add ebp, eax
103 DB 66h, 0b8h ; mov eax, imm32
107 lgdt fword ptr [rdi + (SavedGdt - @Base)]
113 DB 66h, 0b8h ; mov eax, imm32
116 DB 0b8h ; mov ax, imm16
119 DB 66h, 0bch ; mov esp, imm32
122 retf ; return to protected mode
123 _BackFromUserCode ENDP
125 _EntryPoint DD _ToUserCode - m16Start
129 _16GdtrBase DQ _NullSeg
130 _16Idtr FWORD (1 SHL 10) - 1
132 ;------------------------------------------------------------------------------
133 ; _ToUserCode() takes control in real mode before passing control to user code.
134 ; It will be shadowed to somewhere in memory below 1MB.
135 ;------------------------------------------------------------------------------
137 mov ss, edx ; set new segment selectors
144 mov cr0, rax ; real mode starts at next instruction
149 mov ss, esi ; set up 16-bit stack segment
150 xchg sp, bx ; set up 16-bit stack pointer
152 call @Base ; push eip
154 pop bp ; ebp <- address of @Base
155 push [esp + sizeof (IA32_REGS) + 2]
156 lea eax, [rsi + (@RealMode - @Base)]
162 pop [rsi + (SavedSs - @Base)]
164 mov [rsi + (SavedEsp - @Base)], bx
165 DB 66h, 2eh ; CS and operand size override
166 lidt fword ptr [rsi + (_16Idtr - @Base)]
173 lea sp, [esp + 4] ; skip high order 32 bits of EFlags
175 retf ; transfer control to user code
188 DB 8fh ; 16-bit segment, 4GB limit
195 DB 8fh ; 16-bit segment, 4GB limit
202 DB 0cfh ; 16-bit segment, 4GB limit
205 GDT_SIZE = $ - _NullSeg
207 ;------------------------------------------------------------------------------
208 ; IA32_REGISTER_SET *
210 ; InternalAsmThunk16 (
211 ; IN IA32_REGISTER_SET *RegisterSet,
212 ; IN OUT VOID *Transition
214 ;------------------------------------------------------------------------------
215 InternalAsmThunk16 PROC USES rbp rbx rsi rdi
222 movzx r8d, (IA32_REGS ptr [rsi])._SS
223 mov edi, (IA32_REGS ptr [rsi])._ESP
224 lea rdi, [edi - (sizeof (IA32_REGS) + 4)]
225 imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
226 mov ebx, edi ; ebx <- stack for 16-bit code
227 push sizeof (IA32_REGS) / 4
228 add edi, eax ; edi <- linear address of 16-bit stack
230 rep movsd ; copy RegSet
231 lea ecx, [rdx + (SavedCr4 - m16Start)]
232 mov eax, edx ; eax <- transition code address
235 lea edx, [rdx + (_BackFromUserCode - m16Start)]
237 stosd ; [edi] <- return address of user code
238 sgdt fword ptr [rcx + (SavedGdt - SavedCr4)]
239 sidt fword ptr [rsp + 38h] ; save IDT stack in argument space
241 mov [rcx + (SavedCr0 - SavedCr4)], eax
242 and eax, 7ffffffeh ; clear PE, PG bits
244 mov [rcx], ebp ; save CR4 in SavedCr4
245 and ebp, 300h ; clear all but PCE and OSFXSR bits
246 mov esi, r8d ; esi <- 16-bit stack segment
247 DB 6ah, DATA32 ; push DATA32
248 pop rdx ; rdx <- 32-bit data segment selector
249 lgdt fword ptr [rcx + (_16Gdtr - SavedCr4)]
252 lea edx, [rdx + DATA16 - DATA32]
253 call fword ptr [rcx + (_EntryPoint - SavedCr4)]
255 lidt fword ptr [rsp + 38h] ; restore protected mode IDTR
256 lea eax, [rbp - sizeof (IA32_REGS)]
263 InternalAsmThunk16 ENDP