arch/x86/descriptor.c

/*
 * Copyright (c) 2009 Corey Tabaka
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include <compiler.h>
#include <arch/x86/descriptor.h>

/* not the best way to do this, but easy for now */
typedef struct {
	uint16_t limit_15_0;
	uint16_t base_15_0;
	uint8_t base_23_16;
	
	uint8_t type : 4;
	uint8_t s : 1;
	uint8_t dpl : 2;
	uint8_t p : 1;
	
	uint8_t limit_19_16 : 4;
	uint8_t avl : 1;
	uint8_t reserved_0 : 1;
	uint8_t d_b : 1;
	uint8_t g : 1;
	
	uint8_t base_31_24;
} __PACKED seg_desc_t;

extern seg_desc_t _gdt[];

void set_global_desc(seg_sel_t sel, void *base, uint32_t limit,
	uint8_t present, uint8_t ring, uint8_t sys, uint8_t type, uint8_t gran, uint8_t bits)
{
	// convert selector into index
	uint16_t index = sel >> 3;

	_gdt[index].limit_15_0 = limit & 0x0000ffff;
	_gdt[index].limit_19_16 = (limit & 0x000f0000) >> 16;

	_gdt[index].base_15_0 = ((uint32_t) base) & 0x0000ffff;
	_gdt[index].base_23_16 = (((uint32_t) base) & 0x00ff0000) >> 16;
	_gdt[index].base_31_24 = ((uint32_t) base) >> 24;

	_gdt[index].type = type & 0x0f;	// segment type
	_gdt[index].p = present != 0;	// present
	_gdt[index].dpl = ring & 0x03;	// descriptor privilege level
	_gdt[index].g = gran != 0;		// granularity
	_gdt[index].s = sys != 0;		// system / non-system
	_gdt[index].d_b = bits != 0;	// 16 / 32 bit
}