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/*
* Copyright (C) 2017 Robin Krahl <robin.krahl@ireas.org>
*
* This program is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*/
#include <garmos/arch.h>
#include <garmos/gdt.h>
#include <garmos/kernel.h>
#include <garmos/types.h>
struct gdt_sgmt {
uint16_t limit_lo;
uint16_t base_lo;
uint8_t base_hi;
uint8_t access;
uint8_t flags_limit_h;
uint8_t base_vhi;
} __attribute__((packed));
enum gdt_sgmts {
GDT_SGMT_NULL,
GDT_SGMT_CODE,
GDT_SGMT_DATA,
GDT_SGMT_COUNT
};
struct gdt_sgmt gdt[GDT_SGMT_COUNT];
struct gdtp gdtp = {
.limit = GDT_SGMT_COUNT * sizeof(*gdt) - 1,
.pointer = gdt,
};
static void gdt_sgmt_set(uint32_t base, uint32_t limit, uint8_t access,
struct gdt_sgmt *s)
{
if (limit <= 0xFFFF) {
s->flags_limit_h = 0x40;
} else {
if ((limit & 0xFFF) != 0xFFF) {
limit = (limit >> 12) - 1;
} else {
limit >>= 12;
}
s->flags_limit_h = 0xC0;
}
s->limit_lo = limit & 0xFFFF;
s->flags_limit_h |= (limit >> 16) & 0xF;
s->base_lo = base & 0xFFFF;
s->base_hi = (base >> 16) & 0xFF;
s->base_vhi = (base >> 24) & 0xFF;
s->access = access;
}
void gdt_init(void)
{
ker_dbg("Initializing GDT ...");
gdt_sgmt_set(0, 0, 0, &gdt[GDT_SGMT_NULL]);
gdt_sgmt_set(0, 64 * 1024 * 1024, 0x9A, &gdt[GDT_SGMT_CODE]);
gdt_sgmt_set(0, 64 * 1024 * 1024, 0x92, &gdt[GDT_SGMT_NULL]);
gdtset(gdtp);
}
uint16_t gdt_get_code_offset(void)
{
return GDT_SGMT_CODE * sizeof(*gdt);
}
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