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#include "BaseLibInternals.h"
;------------------------------------------------------------------------------
;
; Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
; This program and the accompanying materials
; are licensed and made available under the terms and conditions of the BSD License
; which accompanies this distribution. The full text of the license may be found at
; http://opensource.org/licenses/bsd-license.php.
;
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
;
; Module Name:
;
; Thunk.asm
;
; Abstract:
;
; Real mode thunk
;
;------------------------------------------------------------------------------
global ASM_PFX(m16Size)
global ASM_PFX(mThunk16Attr)
global ASM_PFX(m16Gdt)
global ASM_PFX(m16GdtrBase)
global ASM_PFX(mTransition)
global ASM_PFX(m16Start)
struc IA32_REGS
._EDI: resd 1
._ESI: resd 1
._EBP: resd 1
._ESP: resd 1
._EBX: resd 1
._EDX: resd 1
._ECX: resd 1
._EAX: resd 1
._DS: resw 1
._ES: resw 1
._FS: resw 1
._GS: resw 1
._EFLAGS: resq 1
._EIP: resd 1
._CS: resw 1
._SS: resw 1
.size:
endstruc
SECTION .data
;
; These are global constant to convey information to C code.
;
ASM_PFX(m16Size) DW ASM_PFX(InternalAsmThunk16) - ASM_PFX(m16Start)
ASM_PFX(mThunk16Attr) DW _BackFromUserCode.ThunkAttrEnd - 4 - ASM_PFX(m16Start)
ASM_PFX(m16Gdt) DW _NullSeg - ASM_PFX(m16Start)
ASM_PFX(m16GdtrBase) DW _16GdtrBase - ASM_PFX(m16Start)
ASM_PFX(mTransition) DW _EntryPoint - ASM_PFX(m16Start)
SECTION .text
ASM_PFX(m16Start):
SavedGdt:
dw 0
dq 0
;------------------------------------------------------------------------------
; _BackFromUserCode() takes control in real mode after 'retf' has been executed
; by user code. It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_BackFromUserCode:
;
; The order of saved registers on the stack matches the order they appears
; in IA32_REGS structure. This facilitates wrapper function to extract them
; into that structure.
;
BITS 16
push ss
push cs
;
; Note: We can't use o32 on the next instruction because of a bug
; in NASM 2.09.04 through 2.10rc1.
;
call dword .Base ; push eip
.Base:
push dword 0 ; reserved high order 32 bits of EFlags
pushfd
cli ; disable interrupts
push gs
push fs
push es
push ds
pushad
mov edx, strict dword 0
.ThunkAttrEnd:
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
jz .1
mov ax, 2401h
int 15h
cli ; disable interrupts
jnc .2
.1:
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
jz .2
in al, 92h
or al, 2
out 92h, al ; deactivate A20M#
.2:
xor eax, eax
mov ax, ss
lea ebp, [esp + IA32_REGS.size]
mov [bp - IA32_REGS.size + IA32_REGS._ESP], ebp
mov ebx, [bp - IA32_REGS.size + IA32_REGS._EIP]
shl eax, 4 ; shl eax, 4
add ebp, eax ; add ebp, eax
mov eax, cs
shl eax, 4
lea eax, [eax + ebx + (.X64JmpEnd - .Base)]
mov [cs:bx + (.X64JmpEnd - 6 - .Base)], eax
mov eax, strict dword 0
.SavedCr4End:
mov cr4, eax
o32 lgdt [cs:bx + (SavedGdt - .Base)]
mov ecx, 0c0000080h
rdmsr
or ah, 1
wrmsr
mov eax, strict dword 0
.SavedCr0End:
mov cr0, eax
jmp 0:strict dword 0
.X64JmpEnd:
BITS 64
nop
mov rsp, strict qword 0
.SavedSpEnd:
nop
ret
_EntryPoint:
DD _ToUserCode - ASM_PFX(m16Start)
DW CODE16
_16Gdtr:
DW GDT_SIZE - 1
_16GdtrBase:
DQ 0
_16Idtr:
DW (1 << 10) - 1
DD 0
;------------------------------------------------------------------------------
; _ToUserCode() takes control in real mode before passing control to user code.
; It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_ToUserCode:
BITS 16
mov ss, dx ; set new segment selectors
mov ds, dx
mov es, dx
mov fs, dx
mov gs, dx
mov ecx, 0c0000080h
mov cr0, eax ; real mode starts at next instruction
rdmsr
and ah, ~1
wrmsr
mov cr4, ebp
mov ss, si ; set up 16-bit stack segment
mov esp, ebx ; set up 16-bit stack pointer
call dword .Base ; push eip
.Base:
pop ebp ; ebp <- address of .Base
push word [dword esp + IA32_REGS.size + 2]
lea ax, [bp + (.RealMode - .Base)]
push ax
retf ; execution begins at next instruction
.RealMode:
o32 lidt [cs:bp + (_16Idtr - .Base)]
popad
pop ds
pop es
pop fs
pop gs
popfd
lea esp, [esp + 4] ; skip high order 32 bits of EFlags
o32 retf ; transfer control to user code
ALIGN 8
CODE16 equ _16Code - $
DATA16 equ _16Data - $
DATA32 equ _32Data - $
_NullSeg DQ 0
_16Code:
DW -1
DW 0
DB 0
DB 9bh
DB 8fh ; 16-bit segment, 4GB limit
DB 0
_16Data:
DW -1
DW 0
DB 0
DB 93h
DB 8fh ; 16-bit segment, 4GB limit
DB 0
_32Data:
DW -1
DW 0
DB 0
DB 93h
DB 0cfh ; 16-bit segment, 4GB limit
DB 0
GDT_SIZE equ $ - _NullSeg
;------------------------------------------------------------------------------
; IA32_REGISTER_SET *
; EFIAPI
; InternalAsmThunk16 (
; IN IA32_REGISTER_SET *RegisterSet,
; IN OUT VOID *Transition
; );
;------------------------------------------------------------------------------
global ASM_PFX(InternalAsmThunk16)
ASM_PFX(InternalAsmThunk16):
BITS 64
push rbp
push rbx
push rsi
push rdi
mov ebx, ds
push rbx ; Save ds segment register on the stack
mov ebx, es
push rbx ; Save es segment register on the stack
mov ebx, ss
push rbx ; Save ss segment register on the stack
push fs
push gs
mov rsi, rcx
movzx r8d, word [rsi + IA32_REGS._SS]
mov edi, [rsi + IA32_REGS._ESP]
lea rdi, [edi - (IA32_REGS.size + 4)]
imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
mov ebx, edi ; ebx <- stack for 16-bit code
push IA32_REGS.size / 4
add edi, eax ; edi <- linear address of 16-bit stack
pop rcx
rep movsd ; copy RegSet
lea ecx, [rdx + (_BackFromUserCode.SavedCr4End - ASM_PFX(m16Start))]
mov eax, edx ; eax <- transition code address
and edx, 0fh
shl eax, 12 ; segment address in high order 16 bits
lea ax, [rdx + (_BackFromUserCode - ASM_PFX(m16Start))] ; offset address
stosd ; [edi] <- return address of user code
sgdt [rsp + 60h] ; save GDT stack in argument space
movzx r10, word [rsp + 60h] ; r10 <- GDT limit
lea r11, [rcx + (ASM_PFX(InternalAsmThunk16) - _BackFromUserCode.SavedCr4End) + 0xf]
and r11, ~0xf ; r11 <- 16-byte aligned shadowed GDT table in real mode buffer
mov [rcx + (SavedGdt - _BackFromUserCode.SavedCr4End)], r10w ; save the limit of shadowed GDT table
mov [rcx + (SavedGdt - _BackFromUserCode.SavedCr4End) + 2], r11 ; save the base address of shadowed GDT table
mov rsi, [rsp + 62h] ; rsi <- the original GDT base address
xchg rcx, r10 ; save rcx to r10 and initialize rcx to be the limit of GDT table
inc rcx ; rcx <- the size of memory to copy
xchg rdi, r11 ; save rdi to r11 and initialize rdi to the base address of shadowed GDT table
rep movsb ; perform memory copy to shadow GDT table
mov rcx, r10 ; restore the orignal rcx before memory copy
mov rdi, r11 ; restore the original rdi before memory copy
sidt [rsp + 50h] ; save IDT stack in argument space
mov rax, cr0
mov [rcx + (_BackFromUserCode.SavedCr0End - 4 - _BackFromUserCode.SavedCr4End)], eax
and eax, 7ffffffeh ; clear PE, PG bits
mov rbp, cr4
mov [rcx - 4], ebp ; save CR4 in _BackFromUserCode.SavedCr4End - 4
and ebp, ~30h ; clear PAE, PSE bits
mov esi, r8d ; esi <- 16-bit stack segment
push DATA32
pop rdx ; rdx <- 32-bit data segment selector
lgdt [rcx + (_16Gdtr - _BackFromUserCode.SavedCr4End)]
mov ss, edx
pushfq
lea edx, [rdx + DATA16 - DATA32]
lea r8, [REL .RetFromRealMode]
push r8
mov r8d, cs
mov [rcx + (_BackFromUserCode.X64JmpEnd - 2 - _BackFromUserCode.SavedCr4End)], r8w
mov [rcx + (_BackFromUserCode.SavedSpEnd - 8 - _BackFromUserCode.SavedCr4End)], rsp
jmp dword far [rcx + (_EntryPoint - _BackFromUserCode.SavedCr4End)]
.RetFromRealMode:
popfq
lgdt [rsp + 60h] ; restore protected mode GDTR
lidt [rsp + 50h] ; restore protected mode IDTR
lea eax, [rbp - IA32_REGS.size]
pop gs
pop fs
pop rbx
mov ss, ebx
pop rbx
mov es, ebx
pop rbx
mov ds, ebx
pop rdi
pop rsi
pop rbx
pop rbp
ret
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