2 #include "BaseLibInternals.h"
4 ;------------------------------------------------------------------------------
6 ; Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
7 ; This program and the accompanying materials
8 ; are licensed and made available under the terms and conditions of the BSD License
9 ; which accompanies this distribution. The full text of the license may be found at
10 ; http://opensource.org/licenses/bsd-license.php.
12 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
13 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
23 ;------------------------------------------------------------------------------
25 global ASM_PFX(m16Size)
26 global ASM_PFX(mThunk16Attr)
27 global ASM_PFX(m16Gdt)
28 global ASM_PFX(m16GdtrBase)
29 global ASM_PFX(mTransition)
30 global ASM_PFX(m16Start)
57 ; These are global constant to convey information to C code.
59 ASM_PFX(m16Size) DW ASM_PFX(InternalAsmThunk16) - ASM_PFX(m16Start)
60 ASM_PFX(mThunk16Attr) DW _BackFromUserCode.ThunkAttrEnd - 4 - ASM_PFX(m16Start)
61 ASM_PFX(m16Gdt) DW _NullSeg - ASM_PFX(m16Start)
62 ASM_PFX(m16GdtrBase) DW _16GdtrBase - ASM_PFX(m16Start)
63 ASM_PFX(mTransition) DW _EntryPoint - ASM_PFX(m16Start)
73 ;------------------------------------------------------------------------------
74 ; _BackFromUserCode() takes control in real mode after 'retf' has been executed
75 ; by user code. It will be shadowed to somewhere in memory below 1MB.
76 ;------------------------------------------------------------------------------
79 ; The order of saved registers on the stack matches the order they appears
80 ; in IA32_REGS structure. This facilitates wrapper function to extract them
81 ; into that structure.
87 ; Note: We can't use o32 on the next instruction because of a bug
88 ; in NASM 2.09.04 through 2.10rc1.
90 call dword .Base ; push eip
92 push dword 0 ; reserved high order 32 bits of EFlags
94 cli ; disable interrupts
100 mov edx, strict dword 0
102 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
106 cli ; disable interrupts
109 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
113 out 92h, al ; deactivate A20M#
117 lea ebp, [esp + IA32_REGS.size]
118 mov [bp - IA32_REGS.size + IA32_REGS._ESP], ebp
119 mov ebx, [bp - IA32_REGS.size + IA32_REGS._EIP]
120 shl eax, 4 ; shl eax, 4
121 add ebp, eax ; add ebp, eax
124 lea eax, [eax + ebx + (.X64JmpEnd - .Base)]
125 mov [cs:bx + (.X64JmpEnd - 6 - .Base)], eax
126 mov eax, strict dword 0
129 o32 lgdt [cs:bx + (SavedGdt - .Base)]
134 mov eax, strict dword 0
141 mov rsp, strict qword 0
147 DD _ToUserCode - ASM_PFX(m16Start)
157 ;------------------------------------------------------------------------------
158 ; _ToUserCode() takes control in real mode before passing control to user code.
159 ; It will be shadowed to somewhere in memory below 1MB.
160 ;------------------------------------------------------------------------------
163 mov ss, dx ; set new segment selectors
169 mov cr0, eax ; real mode starts at next instruction
174 mov ss, si ; set up 16-bit stack segment
175 mov esp, ebx ; set up 16-bit stack pointer
176 call dword .Base ; push eip
178 pop ebp ; ebp <- address of .Base
179 push word [dword esp + IA32_REGS.size + 2]
180 lea ax, [bp + (.RealMode - .Base)]
182 retf ; execution begins at next instruction
185 o32 lidt [cs:bp + (_16Idtr - .Base)]
193 lea esp, [esp + 4] ; skip high order 32 bits of EFlags
195 o32 retf ; transfer control to user code
199 CODE16 equ _16Code - $
200 DATA16 equ _16Data - $
201 DATA32 equ _32Data - $
209 DB 8fh ; 16-bit segment, 4GB limit
216 DB 8fh ; 16-bit segment, 4GB limit
223 DB 0cfh ; 16-bit segment, 4GB limit
226 GDT_SIZE equ $ - _NullSeg
228 ;------------------------------------------------------------------------------
229 ; IA32_REGISTER_SET *
231 ; InternalAsmThunk16 (
232 ; IN IA32_REGISTER_SET *RegisterSet,
233 ; IN OUT VOID *Transition
235 ;------------------------------------------------------------------------------
236 global ASM_PFX(InternalAsmThunk16)
237 ASM_PFX(InternalAsmThunk16):
245 push rbx ; Save ds segment register on the stack
247 push rbx ; Save es segment register on the stack
249 push rbx ; Save ss segment register on the stack
254 movzx r8d, word [rsi + IA32_REGS._SS]
255 mov edi, [rsi + IA32_REGS._ESP]
256 lea rdi, [edi - (IA32_REGS.size + 4)]
257 imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
258 mov ebx, edi ; ebx <- stack for 16-bit code
259 push IA32_REGS.size / 4
260 add edi, eax ; edi <- linear address of 16-bit stack
262 rep movsd ; copy RegSet
263 lea ecx, [rdx + (_BackFromUserCode.SavedCr4End - ASM_PFX(m16Start))]
264 mov eax, edx ; eax <- transition code address
266 shl eax, 12 ; segment address in high order 16 bits
267 lea ax, [rdx + (_BackFromUserCode - ASM_PFX(m16Start))] ; offset address
268 stosd ; [edi] <- return address of user code
270 sgdt [rsp + 60h] ; save GDT stack in argument space
271 movzx r10, word [rsp + 60h] ; r10 <- GDT limit
272 lea r11, [rcx + (ASM_PFX(InternalAsmThunk16) - _BackFromUserCode.SavedCr4End) + 0xf]
273 and r11, ~0xf ; r11 <- 16-byte aligned shadowed GDT table in real mode buffer
275 mov [rcx + (SavedGdt - _BackFromUserCode.SavedCr4End)], r10w ; save the limit of shadowed GDT table
276 mov [rcx + (SavedGdt - _BackFromUserCode.SavedCr4End) + 2], r11 ; save the base address of shadowed GDT table
278 mov rsi, [rsp + 62h] ; rsi <- the original GDT base address
279 xchg rcx, r10 ; save rcx to r10 and initialize rcx to be the limit of GDT table
280 inc rcx ; rcx <- the size of memory to copy
281 xchg rdi, r11 ; save rdi to r11 and initialize rdi to the base address of shadowed GDT table
282 rep movsb ; perform memory copy to shadow GDT table
283 mov rcx, r10 ; restore the orignal rcx before memory copy
284 mov rdi, r11 ; restore the original rdi before memory copy
286 sidt [rsp + 50h] ; save IDT stack in argument space
288 mov [rcx + (_BackFromUserCode.SavedCr0End - 4 - _BackFromUserCode.SavedCr4End)], eax
289 and eax, 7ffffffeh ; clear PE, PG bits
291 mov [rcx - 4], ebp ; save CR4 in _BackFromUserCode.SavedCr4End - 4
292 and ebp, ~30h ; clear PAE, PSE bits
293 mov esi, r8d ; esi <- 16-bit stack segment
295 pop rdx ; rdx <- 32-bit data segment selector
296 lgdt [rcx + (_16Gdtr - _BackFromUserCode.SavedCr4End)]
299 lea edx, [rdx + DATA16 - DATA32]
300 lea r8, [REL .RetFromRealMode]
303 mov [rcx + (_BackFromUserCode.X64JmpEnd - 2 - _BackFromUserCode.SavedCr4End)], r8w
304 mov [rcx + (_BackFromUserCode.SavedSpEnd - 8 - _BackFromUserCode.SavedCr4End)], rsp
305 jmp dword far [rcx + (_EntryPoint - _BackFromUserCode.SavedCr4End)]
308 lgdt [rsp + 60h] ; restore protected mode GDTR
309 lidt [rsp + 50h] ; restore protected mode IDTR
310 lea eax, [rbp - IA32_REGS.size]