mirror of https://github.com/acidanthera/audk.git
172 lines
5.3 KiB
ArmAsm
172 lines
5.3 KiB
ArmAsm
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#------------------------------------------------------------------------------
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#
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# Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
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# This program and the accompanying materials
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# are licensed and made available under the terms and conditions of the BSD License
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# which accompanies this distribution. The full text of the license may be found at
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# http://opensource.org/licenses/bsd-license.php.
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#
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# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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#
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# Abstract:
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#
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# This is the code that goes from real-mode to protected mode.
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# It consumes the reset vector, configures the stack.
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#
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#------------------------------------------------------------------------------
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#
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# Contrary to the name, this file contains 16 bit code as well.
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#
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.text
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#----------------------------------------------------------------------------
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#
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# Procedure: _ModuleEntryPoint
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#
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# Input: None
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#
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# Output: None
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#
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# Destroys: Assume all registers
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#
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# Description:
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#
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# Transition to non-paged flat-model protected mode from a
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# hard-coded GDT that provides exactly two descriptors.
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# This is a bare bones transition to protected mode only
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# used for a while in PEI and possibly DXE.
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#
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# After enabling protected mode, a far jump is executed to
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# transfer to PEI using the newly loaded GDT.
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#
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# Return: None
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#
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#----------------------------------------------------------------------------
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ASM_GLOBAL ASM_PFX(_ModuleEntryPoint)
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ASM_PFX(_ModuleEntryPoint):
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#
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# Load the GDT table in GdtDesc
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#
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.byte 0x66,0xbe #movl $GdtDesc, %esi
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.long GdtDesc
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.byte 0x66,0x2e,0x0f,0x01,0x14 #lgdt %cs:(%si)
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#
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# Transition to 16 bit protected mode
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#
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.byte 0x0f,0x20,0xc0 #movl %cr0, %eax # Get control register 0
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.byte 0x66,0x83,0xc8,0x03 #orl $0x0000003, %eax # Set PE bit (bit #0) & MP bit (bit #1)
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.byte 0x0f,0x22,0xc0 #movl %eax, %cr0 # Activate protected mode
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#
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# Now we're in 16 bit protected mode
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# Set up the selectors for 32 bit protected mode entry
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#
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.byte 0xb8 #movw SYS_DATA_SEL, %ax
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.word SYS_DATA_SEL
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.byte 0x8e,0xd8 #movw %ax, %ds
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.byte 0x8e,0xc0 #movw %ax, %es
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.byte 0x8e,0xe0 #movw %ax, %fs
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.byte 0x8e,0xe8 #movw %ax, %gs
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.byte 0x8e,0xd0 #movw %ax, %ss
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#
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# Transition to Flat 32 bit protected mode
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# The jump to a far pointer causes the transition to 32 bit mode
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#
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.byte 0x66,0xbe #movl ProtectedModeEntryLinearAddress, %esi
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.long ProtectedModeEntryLinearAddress
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.byte 0x66,0x2e,0xff,0x2c #jmp %cs:(%esi)
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#
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# Protected mode portion initializes stack, configures cache, and calls C entry point
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#
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#----------------------------------------------------------------------------
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#
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# Procedure: ProtectedModeEntryPoint
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#
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# Input: Executing in 32 Bit Protected (flat) mode
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# cs: 0-4GB
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# ds: 0-4GB
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# es: 0-4GB
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# fs: 0-4GB
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# gs: 0-4GB
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# ss: 0-4GB
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#
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# Output: This function never returns
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#
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# Destroys:
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# ecx
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# edi
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# esi
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# esp
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#
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# Description:
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# Perform any essential early platform initilaisation
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# Setup a stack
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#
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#----------------------------------------------------------------------------
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ProtectedModeEntryPoint:
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#
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# Dummy function. Consume 2 API to make sure they can be linked.
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#
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movl ASM_PFX(TempRamInitApi), %eax
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movl ASM_PFX(FspInitApi), %eax
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#
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# Should never return
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#
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jmp . #'$'
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#
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# ROM-based Global-Descriptor Table for the PEI Phase
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#
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.align 16
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#
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# GDT[0]: 000h: Null entry, never used.
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#
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.equ NULL_SEL, . - GDT_BASE # Selector [0]
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GDT_BASE:
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BootGdtTable:
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.long 0
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.long 0
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#
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# Linear code segment descriptor
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#
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.equ LINEAR_CODE_SEL, . - GDT_BASE # Selector [08h]
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.word 0xFFFF # limit 0FFFFh
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.word 0 # base 0
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.byte 0
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.byte 0x9B # present, ring 0, data, expand-up, not-writable
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.byte 0xCF # page-granular, 32-bit
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.byte 0
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#
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# System data segment descriptor
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#
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.equ SYS_DATA_SEL, . - GDT_BASE # Selector [010h]
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.word 0xFFFF # limit 0FFFFh
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.word 0 # base 0
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.byte 0
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.byte 0x93 # present, ring 0, data, expand-up, not-writable
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.byte 0xCF # page-granular, 32-bit
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.byte 0
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.equ GDT_SIZE, . - BootGdtTable # Size, in bytes
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#
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# GDT Descriptor
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#
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GdtDesc: # GDT descriptor
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.word GDT_SIZE - 1
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.long BootGdtTable
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ProtectedModeEntryLinearAddress:
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ProtectedModeEntryLinearOffset:
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.long ProtectedModeEntryPoint
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.word LINEAR_CODE_SEL
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