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#------------------------------------------------------------------------------
#
# Copyright (c) 2015, 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.
#
# Abstract:
#
# This is the code that goes from real-mode to protected mode.
# It consumes the reset vector, configures the stack.
#
#------------------------------------------------------------------------------
#
# Contrary to the name, this file contains 16 bit code as well.
#
.text
#----------------------------------------------------------------------------
#
# Procedure: _ModuleEntryPoint
#
# Input: None
#
# Output: None
#
# Destroys: Assume all registers
#
# Description:
#
# Transition to non-paged flat-model protected mode from a
# hard-coded GDT that provides exactly two descriptors.
# This is a bare bones transition to protected mode only
# used for a while in PEI and possibly DXE.
#
# After enabling protected mode, a far jump is executed to
# transfer to PEI using the newly loaded GDT.
#
# Return: None
#
#----------------------------------------------------------------------------
ASM_GLOBAL ASM_PFX(_ModuleEntryPoint)
ASM_PFX(_ModuleEntryPoint):
#
# Load the GDT table in GdtDesc
#
.byte 0x66,0xbe #movl $GdtDesc, %esi
.long GdtDesc
.byte 0x66,0x2e,0x0f,0x01,0x14 #lgdt %cs:(%si)
#
# Transition to 16 bit protected mode
#
.byte 0x0f,0x20,0xc0 #movl %cr0, %eax # Get control register 0
.byte 0x66,0x83,0xc8,0x03 #orl $0x0000003, %eax # Set PE bit (bit #0) & MP bit (bit #1)
.byte 0x0f,0x22,0xc0 #movl %eax, %cr0 # Activate protected mode
#
# Now we're in 16 bit protected mode
# Set up the selectors for 32 bit protected mode entry
#
.byte 0xb8 #movw SYS_DATA_SEL, %ax
.word SYS_DATA_SEL
.byte 0x8e,0xd8 #movw %ax, %ds
.byte 0x8e,0xc0 #movw %ax, %es
.byte 0x8e,0xe0 #movw %ax, %fs
.byte 0x8e,0xe8 #movw %ax, %gs
.byte 0x8e,0xd0 #movw %ax, %ss
#
# Transition to Flat 32 bit protected mode
# The jump to a far pointer causes the transition to 32 bit mode
#
.byte 0x66,0xbe #movl ProtectedModeEntryLinearAddress, %esi
.long ProtectedModeEntryLinearAddress
.byte 0x66,0x2e,0xff,0x2c #jmp %cs:(%esi)
#
# Protected mode portion initializes stack, configures cache, and calls C entry point
#
#----------------------------------------------------------------------------
#
# Procedure: ProtectedModeEntryPoint
#
# Input: Executing in 32 Bit Protected (flat) mode
# cs: 0-4GB
# ds: 0-4GB
# es: 0-4GB
# fs: 0-4GB
# gs: 0-4GB
# ss: 0-4GB
#
# Output: This function never returns
#
# Destroys:
# ecx
# edi
# esi
# esp
#
# Description:
# Perform any essential early platform initilaisation
# Setup a stack
#
#----------------------------------------------------------------------------
ProtectedModeEntryPoint:
#
# Dummy function. Consume 2 API to make sure they can be linked.
#
movl ASM_PFX(TempRamInitApi), %eax
movl ASM_PFX(FspInitApi), %eax
#
# Should never return
#
jmp . #'$'
#
# ROM-based Global-Descriptor Table for the PEI Phase
#
.align 16
#
# GDT[0]: 000h: Null entry, never used.
#
.equ NULL_SEL, . - GDT_BASE # Selector [0]
GDT_BASE:
BootGdtTable:
.long 0
.long 0
#
# Linear code segment descriptor
#
.equ LINEAR_CODE_SEL, . - GDT_BASE # Selector [08h]
.word 0xFFFF # limit 0FFFFh
.word 0 # base 0
.byte 0
.byte 0x9B # present, ring 0, data, expand-up, not-writable
.byte 0xCF # page-granular, 32-bit
.byte 0
#
# System data segment descriptor
#
.equ SYS_DATA_SEL, . - GDT_BASE # Selector [010h]
.word 0xFFFF # limit 0FFFFh
.word 0 # base 0
.byte 0
.byte 0x93 # present, ring 0, data, expand-up, not-writable
.byte 0xCF # page-granular, 32-bit
.byte 0
.equ GDT_SIZE, . - BootGdtTable # Size, in bytes
#
# GDT Descriptor
#
GdtDesc: # GDT descriptor
.word GDT_SIZE - 1
.long BootGdtTable
ProtectedModeEntryLinearAddress:
ProtectedModeEntryLinearOffset:
.long ProtectedModeEntryPoint
.word LINEAR_CODE_SEL
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