1 ; Copyright (c) 2004, Intel Corporation. All rights reserved.<BR>
2 ; This program and the accompanying materials
3 ; are licensed and made available under the terms and conditions of the BSD License
4 ; which accompanies this distribution. The full text of the license may be found at
5 ; http://opensource.org/licenses/bsd-license.php
7 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
8 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
18 ;------------------------------------------------------------------------------
20 EXTERNDEF m16Start:BYTE
21 EXTERNDEF m16Size:WORD
22 EXTERNDEF mThunk16Attr:WORD
24 EXTERNDEF m16GdtrBase:WORD
25 EXTERNDEF mTransition:WORD
27 THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 EQU 2
28 THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL EQU 4
51 m16Size DW InternalAsmThunk16 - m16Start
52 mThunk16Attr DW _ThunkAttr - m16Start
53 m16Gdt DW _NullSeg - m16Start
54 m16GdtrBase DW _16GdtrBase - m16Start
55 mTransition DW _EntryPoint - m16Start
65 ;------------------------------------------------------------------------------
66 ; _BackFromUserCode() takes control in real mode after 'retf' has been executed
67 ; by user code. It will be shadowed to somewhere in memory below 1MB.
68 ;------------------------------------------------------------------------------
69 _BackFromUserCode PROC
71 ; The order of saved registers on the stack matches the order they appears
72 ; in IA32_REGS structure. This facilitates wrapper function to extract them
73 ; into that structure.
75 ; Some instructions for manipulation of segment registers have to be written
76 ; in opcode since 64-bit MASM prevents accesses to those registers.
84 push 0 ; reserved high order 32 bits of EFlags
85 pushf ; pushfd actually
86 cli ; disable interrupts
92 DB 66h, 0bah ; mov edx, imm32
94 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
96 mov eax, 15cd2401h ; mov ax, 2401h & int 15h
97 cli ; disable interrupts
100 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
104 out 92h, al ; deactivate A20M#
107 lea bp, [esp + sizeof (IA32_REGS)]
109 ; rsi in the following 2 instructions is indeed bp in 16-bit code
111 mov word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
113 mov ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
114 shl ax, 4 ; shl eax, 4
115 add bp, ax ; add ebp, eax
118 lea ax, [eax + ebx + (@64BitCode - @Base)]
119 DB 66h, 2eh, 89h, 87h ; mov cs:[bx + (@64Eip - @Base)], eax
121 DB 66h, 0b8h ; mov eax, imm32
125 ; rdi in the instruction below is indeed bx in 16-bit code
127 DB 66h, 2eh ; 2eh is "cs:" segment override
128 lgdt fword ptr [rdi + (SavedGdt - @Base)]
134 DB 66h, 0b8h ; mov eax, imm32
137 DB 66h, 0eah ; jmp far cs:@64Bit
142 db 067h, 0bch ; mov esp, imm32
143 SavedSp DD ? ; restore stack
146 _BackFromUserCode ENDP
148 _EntryPoint DD _ToUserCode - m16Start
152 _16GdtrBase DQ _NullSeg
153 _16Idtr FWORD (1 SHL 10) - 1
155 ;------------------------------------------------------------------------------
156 ; _ToUserCode() takes control in real mode before passing control to user code.
157 ; It will be shadowed to somewhere in memory below 1MB.
158 ;------------------------------------------------------------------------------
160 mov ss, edx ; set new segment selectors
167 mov cr0, rax ; real mode starts at next instruction
172 mov ss, esi ; set up 16-bit stack segment
173 mov sp, bx ; set up 16-bit stack pointer
174 DB 66h ; make the following call 32-bit
175 call @Base ; push eip
177 pop bp ; ebp <- address of @Base
178 push [esp + sizeof (IA32_REGS) + 2]
179 lea eax, [rsi + (@RealMode - @Base)] ; rsi is "bp" in 16-bit code
181 retf ; execution begins at next instruction
183 DB 66h, 2eh ; CS and operand size override
184 lidt fword ptr [rsi + (_16Idtr - @Base)]
191 lea sp, [esp + 4] ; skip high order 32 bits of EFlags
192 DB 66h ; make the following retf 32-bit
193 retf ; transfer control to user code
206 DB 8fh ; 16-bit segment, 4GB limit
213 DB 8fh ; 16-bit segment, 4GB limit
220 DB 0cfh ; 16-bit segment, 4GB limit
223 GDT_SIZE = $ - _NullSeg
225 ;------------------------------------------------------------------------------
226 ; IA32_REGISTER_SET *
228 ; InternalAsmThunk16 (
229 ; IN IA32_REGISTER_SET *RegisterSet,
230 ; IN OUT VOID *Transition
232 ;------------------------------------------------------------------------------
233 InternalAsmThunk16 PROC USES rbp rbx rsi rdi
235 push rbx ; Save ds segment register on the stack
237 push rbx ; Save es segment register on the stack
239 push rbx ; Save ss segment register on the stack
244 movzx r8d, (IA32_REGS ptr [rsi])._SS
245 mov edi, (IA32_REGS ptr [rsi])._ESP
246 lea rdi, [edi - (sizeof (IA32_REGS) + 4)]
247 imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
248 mov ebx, edi ; ebx <- stack for 16-bit code
249 push sizeof (IA32_REGS) / 4
250 add edi, eax ; edi <- linear address of 16-bit stack
252 rep movsd ; copy RegSet
253 lea ecx, [rdx + (SavedCr4 - m16Start)]
254 mov eax, edx ; eax <- transition code address
256 shl eax, 12 ; segment address in high order 16 bits
257 lea ax, [rdx + (_BackFromUserCode - m16Start)] ; offset address
258 stosd ; [edi] <- return address of user code
259 sgdt fword ptr [rcx + (SavedGdt - SavedCr4)]
260 sidt fword ptr [rsp + 50h] ; save IDT stack in argument space
262 mov [rcx + (SavedCr0 - SavedCr4)], eax
263 and eax, 7ffffffeh ; clear PE, PG bits
265 mov [rcx], ebp ; save CR4 in SavedCr4
266 and ebp, 300h ; clear all but PCE and OSFXSR bits
267 mov esi, r8d ; esi <- 16-bit stack segment
268 DB 6ah, DATA32 ; push DATA32
269 pop rdx ; rdx <- 32-bit data segment selector
270 lgdt fword ptr [rcx + (_16Gdtr - SavedCr4)]
273 lea edx, [rdx + DATA16 - DATA32]
274 lea r8, @RetFromRealMode
277 mov [rcx + (SavedCs - SavedCr4)], r8w
278 mov [rcx + (SavedSp - SavedCr4)], esp
279 jmp fword ptr [rcx + (_EntryPoint - SavedCr4)]
282 lidt fword ptr [rsp + 50h] ; restore protected mode IDTR
283 lea eax, [rbp - sizeof (IA32_REGS)]
293 InternalAsmThunk16 ENDP