arch_selector.c

newos is new operation system

/*
** Copyright 2002, Michael Noisternig. All rights reserved.
** Distributed under the terms of the NewOS License.
*/
#include <boot/arch/i386/stage2.h>
#include <kernel/arch/cpu.h>
#include <kernel/smp.h>
#include <kernel/int.h>

#include <kernel/arch/i386/selector.h>

#define MAX_SELECTORS (GDT_LIMIT/8)
#define ENTRIES (MAX_SELECTORS/(sizeof(uint32)*8))

static uint32 selector_bitmap[ENTRIES]
	= { 0x000000ff };  // first 8 selectors reserved

static selector_type *gdt_table;
static struct gdt_idt_descr descr = { GDT_LIMIT - 1, NULL };

void i386_selector_init( void *gdt )
{
	gdt_table = (selector_type *)gdt;
	descr.b = (unsigned int *)gdt_table;
}

// creates a new selector in the gdt of given type (use SELECTOR macro)
// IN:	selector type
// RET:	selector that can be directly used for segment registers
//		0 on error
selector_id i386_selector_add( selector_type type )
{
	static int spinlock;
	uint32 mask;
	selector_id id = 0;
	unsigned i;

	int_disable_interrupts();
	acquire_spinlock( &spinlock );

	for ( i = 0; i < ENTRIES; i++ )
		if ( selector_bitmap[i] != 0xffffffff ) {  // found free place in there
			id = i*sizeof(uint32)*8;
			mask = 1;
			while ( selector_bitmap[i] & mask ) {
				mask <<= 1;
				id++;
			}
			selector_bitmap[i] |= mask;
			gdt_table[id] = type;
			break;
		}

	release_spinlock( &spinlock );
	int_restore_interrupts();

	if ( id ) {
		asm("lgdt	%0;"
			: : "m" (descr));
	}

	return id*8;
}

// removes a selector with given id from the gdt
void i386_selector_remove( selector_id id )
{
	if ( id < 8*8 || id >= MAX_SELECTORS*8 )
		return;

	id /= 8;
	gdt_table[id] = 0;

	atomic_and( &selector_bitmap[id/32], ~(1<<(id&31)) );

	asm("lgdt	%0;"
		: : "m" (descr));
}

// returns the selector type of a given id
selector_type i386_selector_get( selector_id id )
{
	return gdt_table[id/8];
}