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
70 ; The order of saved registers on the stack matches the order they appears
71 ; in IA32_REGS structure. This facilitates wrapper function to extract them
72 ; into that structure.
74 ; Some instructions for manipulation of segment registers have to be written
75 ; in opcode since 64-bit MASM prevents accesses to those registers.
83 push 0 ; reserved high order 32 bits of EFlags
84 pushf ; pushfd actually
85 cli ; disable interrupts
91 DB 66h, 0bah ; mov edx, imm32
93 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
95 mov eax, 15cd2401h ; mov ax, 2401h & int 15h
96 cli ; disable interrupts
99 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
103 out 92h, al ; deactivate A20M#
106 lea bp, [esp + sizeof (IA32_REGS)]
108 ; rsi in the following 2 instructions is indeed bp in 16-bit code
110 mov word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
112 mov ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
113 shl ax, 4 ; shl eax, 4
114 add bp, ax ; add ebp, eax
117 lea ax, [eax + ebx + (@64BitCode - @Base)]
118 DB 66h, 2eh, 89h, 87h ; mov cs:[bx + (@64Eip - @Base)], eax
120 DB 66h, 0b8h ; mov eax, imm32
124 ; rdi in the instruction below is indeed bx in 16-bit code
126 DB 66h, 2eh ; 2eh is "cs:" segment override
127 lgdt fword ptr [rdi + (SavedGdt - @Base)]
133 DB 66h, 0b8h ; mov eax, imm32
136 DB 66h, 0eah ; jmp far cs:@64Bit
140 mov rsp, r8 ; restore stack
142 _BackFromUserCode ENDP
144 _EntryPoint DD _ToUserCode - m16Start
148 _16GdtrBase DQ _NullSeg
149 _16Idtr FWORD (1 SHL 10) - 1
151 ;------------------------------------------------------------------------------
152 ; _ToUserCode() takes control in real mode before passing control to user code.
153 ; It will be shadowed to somewhere in memory below 1MB.
154 ;------------------------------------------------------------------------------
156 mov ss, edx ; set new segment selectors
163 mov cr0, rax ; real mode starts at next instruction
168 mov ss, esi ; set up 16-bit stack segment
169 mov sp, bx ; set up 16-bit stack pointer
170 DB 66h ; make the following call 32-bit
171 call @Base ; push eip
173 pop bp ; ebp <- address of @Base
174 push [esp + sizeof (IA32_REGS) + 2]
175 lea eax, [rsi + (@RealMode - @Base)] ; rsi is "bp" in 16-bit code
177 retf ; execution begins at next instruction
179 DB 66h, 2eh ; CS and operand size override
180 lidt fword ptr [rsi + (_16Idtr - @Base)]
187 lea sp, [esp + 4] ; skip high order 32 bits of EFlags
188 DB 66h ; make the following retf 32-bit
189 retf ; transfer control to user code
202 DB 8fh ; 16-bit segment, 4GB limit
209 DB 8fh ; 16-bit segment, 4GB limit
216 DB 0cfh ; 16-bit segment, 4GB limit
219 GDT_SIZE = $ - _NullSeg
221 ;------------------------------------------------------------------------------
222 ; IA32_REGISTER_SET *
224 ; InternalAsmThunk16 (
225 ; IN IA32_REGISTER_SET *RegisterSet,
226 ; IN OUT VOID *Transition
228 ;------------------------------------------------------------------------------
229 InternalAsmThunk16 PROC USES rbp rbx rsi rdi
230 mov r10d, ds ; r9 ~ r11 are not accessible in 16-bit
231 mov r11d, es ; so use them for saving seg registers
236 movzx r8d, (IA32_REGS ptr [rsi])._SS
237 mov edi, (IA32_REGS ptr [rsi])._ESP
238 lea rdi, [edi - (sizeof (IA32_REGS) + 4)]
239 imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
240 mov ebx, edi ; ebx <- stack for 16-bit code
241 push sizeof (IA32_REGS) / 4
242 add edi, eax ; edi <- linear address of 16-bit stack
244 rep movsd ; copy RegSet
245 lea ecx, [rdx + (SavedCr4 - m16Start)]
246 mov eax, edx ; eax <- transition code address
248 shl eax, 12 ; segment address in high order 16 bits
249 lea ax, [rdx + (_BackFromUserCode - m16Start)] ; offset address
250 stosd ; [edi] <- return address of user code
251 sgdt fword ptr [rcx + (SavedGdt - SavedCr4)]
252 sidt fword ptr [rsp + 38h] ; save IDT stack in argument space
254 mov [rcx + (SavedCr0 - SavedCr4)], eax
255 and eax, 7ffffffeh ; clear PE, PG bits
257 mov [rcx], ebp ; save CR4 in SavedCr4
258 and ebp, 300h ; clear all but PCE and OSFXSR bits
259 mov esi, r8d ; esi <- 16-bit stack segment
260 DB 6ah, DATA32 ; push DATA32
261 pop rdx ; rdx <- 32-bit data segment selector
262 lgdt fword ptr [rcx + (_16Gdtr - SavedCr4)]
265 lea edx, [rdx + DATA16 - DATA32]
266 lea r8, @RetFromRealMode
269 mov [rcx + (SavedCs - SavedCr4)], r8w
271 jmp fword ptr [rcx + (_EntryPoint - SavedCr4)]
274 lidt fword ptr [rsp + 38h] ; restore protected mode IDTR
275 lea eax, [rbp - sizeof (IA32_REGS)]
282 InternalAsmThunk16 ENDP