--- /dev/null
+;; @file\r
+; This is the code that goes from real-mode to protected mode.\r
+; It consumes the reset vector, configures the stack.\r
+;\r
+; Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>\r
+; This program and the accompanying materials\r
+; are licensed and made available under the terms and conditions of the BSD License\r
+; which accompanies this distribution. The full text of the license may be found at\r
+; http://opensource.org/licenses/bsd-license.php.\r
+;\r
+; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
+; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
+;;\r
+\r
+;\r
+; Define assembler characteristics\r
+;\r
+.586p\r
+.xmm\r
+.model flat, c\r
+\r
+EXTRN TempRamInitApi:NEAR\r
+EXTRN FspInitApi:NEAR\r
+\r
+;\r
+; Contrary to the name, this file contains 16 bit code as well.\r
+;\r
+_TEXT_REALMODE SEGMENT PARA PUBLIC USE16 'CODE'\r
+ ASSUME CS:_TEXT_REALMODE, DS:_TEXT_REALMODE\r
+\r
+;----------------------------------------------------------------------------\r
+;\r
+; Procedure: _ModuleEntryPoint\r
+;\r
+; Input: None\r
+;\r
+; Output: None\r
+;\r
+; Destroys: Assume all registers\r
+;\r
+; Description:\r
+;\r
+; Transition to non-paged flat-model protected mode from a\r
+; hard-coded GDT that provides exactly two descriptors.\r
+; This is a bare bones transition to protected mode only\r
+; used for a while in PEI and possibly DXE.\r
+;\r
+; After enabling protected mode, a far jump is executed to\r
+; transfer to PEI using the newly loaded GDT.\r
+;\r
+; Return: None\r
+;\r
+;----------------------------------------------------------------------------\r
+align 16\r
+_ModuleEntryPoint PROC C PUBLIC\r
+ ;\r
+ ; Load the GDT table in GdtDesc\r
+ ;\r
+ mov esi, OFFSET GdtDesc\r
+ db 66h\r
+ lgdt fword ptr cs:[si]\r
+\r
+ ;\r
+ ; Transition to 16 bit protected mode\r
+ ;\r
+ mov eax, cr0 ; Get control register 0\r
+ or eax, 00000003h ; Set PE bit (bit #0) & MP bit (bit #1)\r
+ mov cr0, eax ; Activate protected mode\r
+\r
+ ;\r
+ ; Now we're in 16 bit protected mode\r
+ ; Set up the selectors for 32 bit protected mode entry\r
+ ; \r
+ mov ax, SYS_DATA_SEL\r
+ mov ds, ax\r
+ mov es, ax\r
+ mov fs, ax\r
+ mov gs, ax\r
+ mov ss, ax\r
+\r
+ ;\r
+ ; Transition to Flat 32 bit protected mode\r
+ ; The jump to a far pointer causes the transition to 32 bit mode\r
+ ;\r
+ mov esi, offset ProtectedModeEntryLinearAddress\r
+ jmp fword ptr cs:[si]\r
+\r
+_ModuleEntryPoint ENDP\r
+\r
+_TEXT_REALMODE ENDS\r
+\r
+.code \r
+;\r
+; Protected mode portion initializes stack, configures cache, and calls C entry point\r
+;\r
+\r
+;----------------------------------------------------------------------------\r
+;\r
+; Procedure: ProtectedModeEntryPoint\r
+;\r
+; Input: Executing in 32 Bit Protected (flat) mode\r
+; cs: 0-4GB\r
+; ds: 0-4GB\r
+; es: 0-4GB\r
+; fs: 0-4GB\r
+; gs: 0-4GB\r
+; ss: 0-4GB\r
+;\r
+; Output: This function never returns\r
+;\r
+; Destroys:\r
+; ecx\r
+; edi\r
+; esi\r
+; esp\r
+;\r
+; Description:\r
+; Perform any essential early platform initilaisation\r
+; Setup a stack\r
+;\r
+;----------------------------------------------------------------------------\r
+\r
+ProtectedModeEntryPoint PROC NEAR C PUBLIC\r
+ ;\r
+ ; Dummy function. Consume 2 API to make sure they can be linked.\r
+ ;\r
+ mov eax, TempRamInitApi\r
+ mov eax, FspInitApi\r
+\r
+ ; Should never return\r
+ jmp $\r
+\r
+ProtectedModeEntryPoint ENDP\r
+\r
+;\r
+; ROM-based Global-Descriptor Table for the PEI Phase\r
+;\r
+align 16\r
+PUBLIC BootGdtTable\r
+\r
+;\r
+; GDT[0]: 0x00: Null entry, never used.\r
+;\r
+NULL_SEL equ $ - GDT_BASE ; Selector [0]\r
+GDT_BASE:\r
+BootGdtTable DD 0\r
+ DD 0\r
+;\r
+; Linear code segment descriptor\r
+;\r
+LINEAR_CODE_SEL equ $ - GDT_BASE ; Selector [0x8]\r
+ DW 0FFFFh ; limit 0xFFFF\r
+ DW 0 ; base 0\r
+ DB 0\r
+ DB 09Bh ; present, ring 0, data, expand-up, not-writable\r
+ DB 0CFh ; page-granular, 32-bit\r
+ DB 0\r
+;\r
+; System data segment descriptor\r
+;\r
+SYS_DATA_SEL equ $ - GDT_BASE ; Selector [0x10]\r
+ DW 0FFFFh ; limit 0xFFFF\r
+ DW 0 ; base 0\r
+ DB 0\r
+ DB 093h ; present, ring 0, data, expand-up, not-writable\r
+ DB 0CFh ; page-granular, 32-bit\r
+ DB 0\r
+\r
+GDT_SIZE EQU $ - BootGDTtable ; Size, in bytes\r
+\r
+;\r
+; GDT Descriptor\r
+;\r
+GdtDesc: ; GDT descriptor\r
+ DW GDT_SIZE - 1 ; GDT limit\r
+ DD OFFSET BootGdtTable ; GDT base address\r
+\r
+ProtectedModeEntryLinearAddress LABEL FWORD\r
+ProtectedModeEntryLinearOffset LABEL DWORD\r
+ DD OFFSET ProtectedModeEntryPoint ; Offset of our 32 bit code\r
+ DW LINEAR_CODE_SEL\r
+ \r
+END\r
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