1/* 2 * U-boot - x86 Startup Code 3 * 4 * (C) Copyright 2008-2011 5 * Graeme Russ, <graeme.russ@gmail.com> 6 * 7 * (C) Copyright 2002,2003 8 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se> 9 * 10 * SPDX-License-Identifier: GPL-2.0+ 11 */ 12 13#include <asm/global_data.h> 14#include <asm/processor-flags.h> 15 16#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ 17#define a32 .byte 0x67; 18#define o32 .byte 0x66; 19 20.section .start16, "ax" 21.code16 22.globl start16 23start16: 24 /* Set the Cold Boot / Hard Reset flag */ 25 movl $GD_FLG_COLD_BOOT, %ebx 26 27 xorl %eax, %eax 28 movl %eax, %cr3 /* Invalidate TLB */ 29 30 /* Turn off cache (this might require a 486-class CPU) */ 31 movl %cr0, %eax 32 orl $(X86_CR0_NW | X86_CR0_CD), %eax 33 movl %eax, %cr0 34 wbinvd 35 36 /* load the temporary Global Descriptor Table */ 37o32 cs lidt idt_ptr 38o32 cs lgdt gdt_ptr 39 40 /* Now, we enter protected mode */ 41 movl %cr0, %eax 42 orl $X86_CR0_PE, %eax 43 movl %eax, %cr0 44 45 /* Flush the prefetch queue */ 46 jmp ff 47ff: 48 /* Finally jump to the 32bit initialization code */ 49 movw $code32start, %ax 50 movw %ax, %bp 51o32 cs ljmp *(%bp) 52 53 /* 48-bit far pointer */ 54code32start: 55 .long _start /* offset */ 56 .word 0x10 /* segment */ 57 58idt_ptr: 59 .word 0 /* limit */ 60 .long 0 /* base */ 61 62/* 63 * The following Global Descriptor Table is just enough to get us into 64 * 'Flat Protected Mode' - It will be discarded as soon as the final 65 * GDT is setup in a safe location in RAM 66 */ 67gdt_ptr: 68 .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */ 69 .long BOOT_SEG + gdt /* base */ 70 71/* Some CPUs are picky about GDT alignment... */ 72.align 16 73gdt: 74 /* 75 * The GDT table ... 76 * 77 * Selector Type 78 * 0x00 NULL 79 * 0x08 Unused 80 * 0x10 32bit code 81 * 0x18 32bit data/stack 82 */ 83 /* The NULL Desciptor - Mandatory */ 84 .word 0x0000 /* limit_low */ 85 .word 0x0000 /* base_low */ 86 .byte 0x00 /* base_middle */ 87 .byte 0x00 /* access */ 88 .byte 0x00 /* flags + limit_high */ 89 .byte 0x00 /* base_high */ 90 91 /* Unused Desciptor - (matches Linux) */ 92 .word 0x0000 /* limit_low */ 93 .word 0x0000 /* base_low */ 94 .byte 0x00 /* base_middle */ 95 .byte 0x00 /* access */ 96 .byte 0x00 /* flags + limit_high */ 97 .byte 0x00 /* base_high */ 98 99 /* 100 * The Code Segment Descriptor: 101 * - Base = 0x00000000 102 * - Size = 4GB 103 * - Access = Present, Ring 0, Exec (Code), Readable 104 * - Flags = 4kB Granularity, 32-bit 105 */ 106 .word 0xffff /* limit_low */ 107 .word 0x0000 /* base_low */ 108 .byte 0x00 /* base_middle */ 109 .byte 0x9b /* access */ 110 .byte 0xcf /* flags + limit_high */ 111 .byte 0x00 /* base_high */ 112 113 /* 114 * The Data Segment Descriptor: 115 * - Base = 0x00000000 116 * - Size = 4GB 117 * - Access = Present, Ring 0, Non-Exec (Data), Writable 118 * - Flags = 4kB Granularity, 32-bit 119 */ 120 .word 0xffff /* limit_low */ 121 .word 0x0000 /* base_low */ 122 .byte 0x00 /* base_middle */ 123 .byte 0x93 /* access */ 124 .byte 0xcf /* flags + limit_high */ 125 .byte 0x00 /* base_high */ 126