eduOS/arch/x86/kernel/gdt.c
2014-01-22 12:12:39 +01:00

137 lines
4.9 KiB
C

/*
* Copyright (c) 2010, Stefan Lankes, RWTH Aachen University
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <eduos/stdio.h>
#include <eduos/string.h>
#include <eduos/stdlib.h>
#include <eduos/tasks.h>
#include <eduos/errno.h>
#include <eduos/processor.h>
#include <eduos/time.h>
#include <asm/gdt.h>
#include <asm/tss.h>
gdt_ptr_t gp;
static tss_t task_state_segment __attribute__ ((aligned (PAGE_SIZE)));
// currently, our kernel has full access to the ioports
static gdt_entry_t gdt[GDT_ENTRIES] = {[0 ... GDT_ENTRIES-1] = {0, 0, 0, 0, 0, 0}};
/*
* This is defined in entry.asm. We use this to properly reload
* the new segment registers
*/
extern void gdt_flush(void);
/* Setup a descriptor in the Global Descriptor Table */
void gdt_set_gate(int num, unsigned long base, unsigned long limit,
unsigned char access, unsigned char gran)
{
configure_gdt_entry(&gdt[num], base, limit, access, gran);
}
void configure_gdt_entry(gdt_entry_t *dest_entry, unsigned long base, unsigned long limit,
unsigned char access, unsigned char gran)
{
/* Setup the descriptor base address */
dest_entry->base_low = (base & 0xFFFF);
dest_entry->base_middle = (base >> 16) & 0xFF;
dest_entry->base_high = (base >> 24) & 0xFF;
/* Setup the descriptor limits */
dest_entry->limit_low = (limit & 0xFFFF);
dest_entry->granularity = ((limit >> 16) & 0x0F);
/* Finally, set up the granularity and access flags */
dest_entry->granularity |= (gran & 0xF0);
dest_entry->access = access;
}
/*
* This will setup the special GDT
* pointer, set up the entries in our GDT, and then
* finally call gdt_flush() in our assembler file in order
* to tell the processor where the new GDT is and update the
* new segment registers
*/
void gdt_install(void)
{
unsigned long mode, limit;
memset(&task_state_segment, 0x00, sizeof(tss_t));
mode = GDT_FLAG_32_BIT;
limit = 0xFFFFFFFF;
/* Setup the GDT pointer and limit */
gp.limit = (sizeof(gdt_entry_t) * GDT_ENTRIES) - 1;
gp.base = (size_t) &gdt;
/* Our NULL descriptor */
gdt_set_gate(0, 0, 0, 0, 0);
/*
* The second entry is our Code Segment. The base address
* is 0, the limit is 4 GByte, it uses 4KByte granularity,
* uses 32-bit opcodes, and is a Code Segment descriptor.
*/
gdt_set_gate(1, 0, limit,
GDT_FLAG_RING0 | GDT_FLAG_SEGMENT | GDT_FLAG_CODESEG | GDT_FLAG_PRESENT,
GDT_FLAG_4K_GRAN | mode);
/*
* The third entry is our Data Segment. It's EXACTLY the
* same as our code segment, but the descriptor type in
* this entry's access byte says it's a Data Segment
*/
gdt_set_gate(2, 0, limit,
GDT_FLAG_RING0 | GDT_FLAG_SEGMENT | GDT_FLAG_DATASEG | GDT_FLAG_PRESENT,
GDT_FLAG_4K_GRAN | mode);
/*
* Create code segement for userspace applications (ring 3)
*/
gdt_set_gate(3, 0, limit,
GDT_FLAG_RING3 | GDT_FLAG_SEGMENT | GDT_FLAG_CODESEG | GDT_FLAG_PRESENT,
GDT_FLAG_4K_GRAN | mode);
/*
* Create data segement for userspace applications (ring 3)
*/
gdt_set_gate(4, 0, limit,
GDT_FLAG_RING3 | GDT_FLAG_SEGMENT | GDT_FLAG_DATASEG | GDT_FLAG_PRESENT,
GDT_FLAG_4K_GRAN | mode);
/* set default values */
task_state_segment.eflags = 0x1202;
task_state_segment.ss0 = 0x10; // data segment
task_state_segment.esp0 = 0xDEADBEEF; // invalid pseudo address
gdt_set_gate(5, (unsigned long) (&task_state_segment), sizeof(tss_t)-1,
GDT_FLAG_PRESENT | GDT_FLAG_TSS | GDT_FLAG_RING0, mode);
/* Flush out the old GDT and install the new changes! */
gdt_flush();
}