103 lines
2.5 KiB
C
103 lines
2.5 KiB
C
/* vim: tabstop=4 shiftwidth=4 noexpandtab
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* This file is part of ToaruOS and is released under the terms
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* of the NCSA / University of Illinois License - see LICENSE.md
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* Copyright (C) 2011-2018 K Lange
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* Copyright (C) 2015 Dale Weiler
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*
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* Global Descriptor Tables module
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*
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*/
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#include <kernel/system.h>
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#include <kernel/logging.h>
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#include <kernel/tss.h>
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typedef struct {
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/* Limits */
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uint16_t limit_low;
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/* Segment address */
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uint16_t base_low;
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uint8_t base_middle;
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/* Access modes */
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uint8_t access;
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uint8_t granularity;
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uint8_t base_high;
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} __attribute__((packed)) gdt_entry_t;
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typedef struct {
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uint16_t limit;
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uintptr_t base;
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} __attribute__((packed)) gdt_pointer_t;
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/* In the future we may need to put a lock on the access of this */
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static struct {
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gdt_entry_t entries[6];
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gdt_pointer_t pointer;
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tss_entry_t tss;
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} gdt __attribute__((used));
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extern void gdt_flush(uintptr_t);
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#define ENTRY(X) (gdt.entries[(X)])
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void gdt_set_gate(uint8_t num, uint64_t base, uint64_t limit, uint8_t access, uint8_t gran) {
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/* Base Address */
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ENTRY(num).base_low = (base & 0xFFFF);
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ENTRY(num).base_middle = (base >> 16) & 0xFF;
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ENTRY(num).base_high = (base >> 24) & 0xFF;
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/* Limits */
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ENTRY(num).limit_low = (limit & 0xFFFF);
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ENTRY(num).granularity = (limit >> 16) & 0X0F;
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/* Granularity */
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ENTRY(num).granularity |= (gran & 0xF0);
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/* Access flags */
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ENTRY(num).access = access;
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}
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static void write_tss(int32_t num, uint16_t ss0, uint32_t esp0);
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void gdt_install(void) {
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gdt_pointer_t *gdtp = &gdt.pointer;
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gdtp->limit = sizeof gdt.entries - 1;
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gdtp->base = (uintptr_t)&ENTRY(0);
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gdt_set_gate(0, 0, 0, 0, 0); /* NULL segment */
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gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); /* Code segment */
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gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF); /* Data segment */
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gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF); /* User code */
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gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF); /* User data */
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write_tss(5, 0x10, 0x0);
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/* Go go go */
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gdt_flush((uintptr_t)gdtp);
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tss_flush();
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}
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static void write_tss(int32_t num, uint16_t ss0, uint32_t esp0) {
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tss_entry_t * tss = &gdt.tss;
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uintptr_t base = (uintptr_t)tss;
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uintptr_t limit = base + sizeof *tss;
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/* Add the TSS descriptor to the GDT */
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gdt_set_gate(num, base, limit, 0xE9, 0x00);
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memset(tss, 0x0, sizeof *tss);
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tss->ss0 = ss0;
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tss->esp0 = esp0;
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tss->cs = 0x0b;
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tss->ss = 0x13;
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tss->ds = 0x13;
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tss->es = 0x13;
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tss->fs = 0x13;
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tss->gs = 0x13;
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tss->iomap_base = sizeof *tss;
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}
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void set_kernel_stack(uintptr_t stack) {
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/* Set the kernel stack */
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gdt.tss.esp0 = stack;
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}
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