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#------------------------------------------------------------------------------
#
# Copyright (c) 2006 - 2009, Intel Corporation
# All rights reserved. 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:
#
# Thunk16.S
#
# Abstract:
#
# Real mode thunk
#
#------------------------------------------------------------------------------
#include <Library/BaseLib.h>
ASM_GLOBAL ASM_PFX(m16Start)
ASM_GLOBAL ASM_PFX(m16Size)
ASM_GLOBAL ASM_PFX(mThunk16Attr)
ASM_GLOBAL ASM_PFX(m16Gdt)
ASM_GLOBAL ASM_PFX(m16GdtrBase)
ASM_GLOBAL ASM_PFX(mTransition)
ASM_GLOBAL ASM_PFX(InternalAsmThunk16)
# define the structure of IA32_REGS
.equ _EDI, 0 #size 4
.equ _ESI, 4 #size 4
.equ _EBP, 8 #size 4
.equ _ESP, 12 #size 4
.equ _EBX, 16 #size 4
.equ _EDX, 20 #size 4
.equ _ECX, 24 #size 4
.equ _EAX, 28 #size 4
.equ _DS, 32 #size 2
.equ _ES, 34 #size 2
.equ _FS, 36 #size 2
.equ _GS, 38 #size 2
.equ _EFLAGS, 40 #size 8
.equ _EIP, 48 #size 4
.equ _CS, 52 #size 2
.equ _SS, 54 #size 2
.equ IA32_REGS_SIZE, 56
.data
ASM_PFX(m16Size): .word ASM_PFX(InternalAsmThunk16) - ASM_PFX(m16Start)
ASM_PFX(mThunk16Attr): .word _ThunkAttr - ASM_PFX(m16Start)
ASM_PFX(m16Gdt): .word ASM_PFX(NullSeg) - ASM_PFX(m16Start)
ASM_PFX(m16GdtrBase): .word _16GdtrBase - ASM_PFX(m16Start)
ASM_PFX(mTransition): .word _EntryPoint - ASM_PFX(m16Start)
.text
ASM_PFX(m16Start):
SavedGdt: .space 10
#------------------------------------------------------------------------------
# _BackFromUserCode() takes control in real mode after 'retf' has been executed
# by user code. It will be shadowed to somewhere in memory below 1MB.
#------------------------------------------------------------------------------
ASM_GLOBAL ASM_PFX(BackFromUserCode)
ASM_PFX(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.
#
# Some instructions for manipulation of segment registers have to be written
# in opcode since 64-bit MASM prevents accesses to those registers.
#
.byte 0x16 # push ss
.byte 0xe # push cs
.byte 0x66
call L_Base # push eip
L_Base:
.byte 0x66
pushq $0 # reserved high order 32 bits of EFlags
.byte 0x66, 0x9c # pushfd actually
cli # disable interrupts
push %gs
push %fs
.byte 6 # push es
.byte 0x1e # push ds
.byte 0x66,0x60 # pushad
.byte 0x66,0xba # mov edx, imm32
_ThunkAttr: .space 4
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
jz L_1
movl $0x15cd2401,%eax # mov ax, 2401h & int 15h
cli # disable interrupts
jnc L_2
L_1:
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
jz L_2
inb $0x92,%al
orb $2,%al
outb %al, $0x92 # deactivate A20M#
L_2:
movl %ss,%eax
lea IA32_REGS_SIZE(%esp), %bp
#
# rsi in the following 2 instructions is indeed bp in 16-bit code
#
movw %bp, (_ESP - IA32_REGS_SIZE)(%rsi)
.byte 0x66
movl (_EIP - IA32_REGS_SIZE)(%rsi), %ebx
shlw $4,%ax # shl eax, 4
addw %ax,%bp # add ebp, eax
movw %cs,%ax
shlw $4,%ax
lea (L_64BitCode - L_Base)(%ebx, %eax), %ax
.byte 0x66,0x2e,0x89,0x87 # mov cs:[bx + (L_64Eip - L_Base)], eax
.word L_64Eip - L_Base
.byte 0x66,0xb8 # mov eax, imm32
SavedCr4: .space 4
movq %rax, %cr4
#
# rdi in the instruction below is indeed bx in 16-bit code
#
.byte 0x66,0x2e # 2eh is "cs:" segment override
lgdt (SavedGdt - L_Base)(%rdi)
.byte 0x66
movl $0xc0000080,%ecx
rdmsr
orb $1,%ah
wrmsr
.byte 0x66,0xb8 # mov eax, imm32
SavedCr0: .space 4
movq %rax, %cr0
.byte 0x66,0xea # jmp far cs:L_64Bit
L_64Eip: .space 4
SavedCs: .space 2
L_64BitCode:
.byte 0x90
.byte 0x67,0xbc # mov esp, imm32
SavedSp: .space 4 # restore stack
nop
ret
_EntryPoint: .long ASM_PFX(ToUserCode) - ASM_PFX(m16Start)
.word CODE16
_16Gdtr: .word GDT_SIZE - 1
_16GdtrBase: .quad ASM_PFX(NullSeg)
_16Idtr: .word 0x3ff
.long 0
#------------------------------------------------------------------------------
# _ToUserCode() takes control in real mode before passing control to user code.
# It will be shadowed to somewhere in memory below 1MB.
#------------------------------------------------------------------------------
ASM_GLOBAL ASM_PFX(ToUserCode)
ASM_PFX(ToUserCode):
movl %edx,%ss # set new segment selectors
movl %edx,%ds
movl %edx,%es
movl %edx,%fs
movl %edx,%gs
.byte 0x66
movl $0xc0000080,%ecx
movq %rax, %cr0
rdmsr
andb $0b11111110, %ah
wrmsr
movq %rbp, %cr4
movl %esi,%ss # set up 16-bit stack segment
movw %bx,%sp # set up 16-bit stack pointer
.byte 0x66 # make the following call 32-bit
call L_Base1 # push eip
L_Base1:
popw %bp # ebp <- address of L_Base1
pushq (IA32_REGS_SIZE + 2)(%esp)
lea 0x0c(%rsi), %eax
pushq %rax
lret # execution begins at next instruction
L_RealMode:
.byte 0x66,0x2e # CS and operand size override
lidt (_16Idtr - L_Base1)(%rsi)
.byte 0x66,0x61 # popad
.byte 0x1f # pop ds
.byte 0x7 # pop es
.byte 0x0f, 0xa1 # pop fs
.byte 0x0f, 0xa9 # pop gs
.byte 0x66, 0x9d # popfd
leaw 4(%esp),%sp # skip high order 32 bits of EFlags
.byte 0x66 # make the following retf 32-bit
lret # transfer control to user code
.equ CODE16, ASM_PFX(_16Code) - .
.equ DATA16, ASM_PFX(_16Data) - .
.equ DATA32, ASM_PFX(_32Data) - .
ASM_PFX(NullSeg): .quad 0
ASM_PFX(_16Code):
.word -1
.word 0
.byte 0
.byte 0x9b
.byte 0x8f # 16-bit segment, 4GB limit
.byte 0
ASM_PFX(_16Data):
.word -1
.word 0
.byte 0
.byte 0x93
.byte 0x8f # 16-bit segment, 4GB limit
.byte 0
ASM_PFX(_32Data):
.word -1
.word 0
.byte 0
.byte 0x93
.byte 0xcf # 16-bit segment, 4GB limit
.byte 0
.equ GDT_SIZE, . - ASM_PFX(NullSeg)
#------------------------------------------------------------------------------
# IA32_REGISTER_SET *
# EFIAPI
# InternalAsmThunk16 (
# IN IA32_REGISTER_SET *RegisterSet,
# IN OUT VOID *Transition
# );
#------------------------------------------------------------------------------
ASM_GLOBAL ASM_PFX(InternalAsmThunk16)
ASM_PFX(InternalAsmThunk16):
pushq %rbp
pushq %rbx
pushq %rsi
pushq %rdi
movq %ds, %rbx
pushq %rbx # Save ds segment register on the stack
movq %es, %rbx
pushq %rbx # Save es segment register on the stack
movq %ss, %rbx
pushq %rbx # Save ss segment register on the stack
.byte 0x0f, 0xa0 #push fs
.byte 0x0f, 0xa8 #push gs
movq %rcx, %rsi
movzwl _SS(%rsi), %r8d
movl _ESP(%rsi), %edi
lea -(IA32_REGS_SIZE + 4)(%edi), %rdi
imul $16, %r8d, %eax
movl %edi,%ebx # ebx <- stack for 16-bit code
pushq $(IA32_REGS_SIZE / 4)
addl %eax,%edi # edi <- linear address of 16-bit stack
popq %rcx
rep
movsl # copy RegSet
lea (SavedCr4 - ASM_PFX(m16Start))(%rdx), %ecx
movl %edx,%eax # eax <- transition code address
andl $0xf,%edx
shll $12,%eax # segment address in high order 16 bits
lea (_BackFromUserCode - ASM_PFX(m16Start))(%rdx), %ax
stosl # [edi] <- return address of user code
sgdt 0x60(%rsp) # save GDT stack in argument space
movzwq 0x60(%rsp), %r10 # r10 <- GDT limit
lea ((ASM_PFX(InternalAsmThunk16) - SavedCr4) + 0xf)(%rcx), %r11
andq $0xfffffff0, %r11 # r11 <- 16-byte aligned shadowed GDT table in real mode buffer
movw %r10w, (SavedGdt - SavedCr4)(%rcx) # save the limit of shadowed GDT table
movq %r11, (SavedGdt - SavedCr4 + 0x2)(%rcx) # save the base address of shadowed GDT table
movq 0x62(%rsp) ,%rsi # rsi <- the original GDT base address
xchg %r10, %rcx # save rcx to r10 and initialize rcx to be the limit of GDT table
incq %rcx # rcx <- the size of memory to copy
xchg %r11, %rdi # save rdi to r11 and initialize rdi to the base address of shadowed GDT table
rep
movsb # perform memory copy to shadow GDT table
movq %r10, %rcx # restore the orignal rcx before memory copy
movq %r11, %rdi # restore the original rdi before memory copy
sidt 0x50(%rsp)
movq %cr0, %rax
movl %eax, (SavedCr0 - SavedCr4)(%rcx)
andl $0x7ffffffe,%eax # clear PE, PG bits
movq %cr4, %rbp
movl %ebp, (%rcx) # save CR4 in SavedCr4
andl $0x300,%ebp # clear all but PCE and OSFXSR bits
movl %r8d, %esi # esi <- 16-bit stack segment
.byte 0x6a, DATA32
popq %rdx
lgdt (_16Gdtr - SavedCr4)(%rcx)
movl %edx,%ss
pushfq
lea -8(%rdx), %edx
lea L_RetFromRealMode(%rip), %r8
pushq %r8
movl %cs, %r8d
movw %r8w, (SavedCs - SavedCr4)(%rcx)
movl %esp, (SavedSp - SavedCr4)(%rcx)
.byte 0xff, 0x69 # jmp (_EntryPoint - SavedCr4)(%rcx)
.byte _EntryPoint - SavedCr4
L_RetFromRealMode:
popfq
lgdt 0x60(%rsp) # restore protected mode GDTR
lidt 0x50(%rsp) # restore protected mode IDTR
lea -IA32_REGS_SIZE(%rbp), %eax
.byte 0x0f, 0xa9 # pop gs
.byte 0x0f, 0xa1 # pop fs
popq %rbx
movq %rbx, %ss
popq %rbx
movq %rbx, %es
popq %rbx
movq %rbx, %ds
popq %rdi
popq %rsi
popq %rbx
popq %rbp
ret
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