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#include "aplos.h"
#define DESCRIPTOR_SIZE 8
#define IDT_ENTRIES 256
enum {
GDT_START,
NULL_SEGMENT = GDT_START,
KERNEL_CODE_SEGMENT,
KERNEL_DATA_SEGMENT,
TASK_STATE_SEGMENT,
TASK_STATE_SEGMENT_CONT,
GDT_END = TASK_STATE_SEGMENT_CONT,
IDT_START,
IDT_END = IDT_START + (2*IDT_ENTRIES) - 1,
TOTAL_ENTRY_COUNT
};
enum {
TYPE_NULL_SEGMENT = 0x10,
TYPE_DATA_SEGMENT = 0x12,
TYPE_CODE_SEGMENT = 0x18,
TYPE_TSS_SEGMENT = 0x09,
TYPE_IDT = 0x0E,
USER_TYPE_MASK = 0x10
};
struct descriptor
{
int type;
/* TASK_STATE_SEGMENT */
struct encoded_tss_entry *tss;
/* IDT */
void (*isr)(void);
};
struct encoded_descriptor
{
alignas(DESCRIPTOR_SIZE) uint8_t data[DESCRIPTOR_SIZE];
};
static_assert(sizeof(struct encoded_descriptor) == DESCRIPTOR_SIZE);
struct encoded_tss_entry
{
uint8_t data[104]; /* Not part of this is used yet... */
};
struct table_reg
{
uint8_t data[10];
};
static_assert(sizeof(struct table_reg) == 10);
static struct encoded_tss_entry tss;
static struct descriptor entries[TOTAL_ENTRY_COUNT] = {
[NULL_SEGMENT] = {
.type = TYPE_NULL_SEGMENT
},
[KERNEL_CODE_SEGMENT] = {
.type = TYPE_CODE_SEGMENT
},
[KERNEL_DATA_SEGMENT] = {
.type = TYPE_DATA_SEGMENT
},
[TASK_STATE_SEGMENT] = {
.type = TYPE_TSS_SEGMENT,
.tss = &tss,
},
};
static struct encoded_descriptor encoded[nelem(entries)];
static void encode_descriptors(struct table_reg *, uint64_t, uint64_t);
static void encode_descriptor(struct descriptor *, struct encoded_descriptor *);
void
setup_descriptors(void)
{
struct table_reg reg;
print(u8"Setting up GDT and IDT\n");
disable_interrupts();
encode_descriptors(®, GDT_START, GDT_END);
set_gdt(®, DESCRIPTOR_SIZE*KERNEL_CODE_SEGMENT, DESCRIPTOR_SIZE*KERNEL_DATA_SEGMENT, DESCRIPTOR_SIZE*TASK_STATE_SEGMENT);
for(uint64_t i = IDT_START; i < IDT_END; i += 2)
entries[i].type = TYPE_IDT;
for(uint64_t i = 0; i < nelem(isr_stubs); i++)
entries[IDT_START+i*2].isr = isr_stubs[i];
encode_descriptors(®, IDT_START, IDT_END);
set_idt(®);
enable_interrupts();
}
static void
encode_descriptors(struct table_reg *reg, uint64_t start, uint64_t end)
{
uint64_t count = 1 + end - start;
struct descriptor *d = entries + start;
struct encoded_descriptor *e = encoded + start;
memset(e, 0, sizeof(*e) * count);
for(uint64_t i = 0; i < count; i++){
encode_descriptor(d+i, e+i);
if(!(d[i].type & USER_TYPE_MASK))
i++; /* System types are twice as big */
}
write_uint16_le(reg->data, count*DESCRIPTOR_SIZE - 1);
write_uint64_le(reg->data+2, (uint64_t)e);
}
static void
encode_descriptor(struct descriptor *d, struct encoded_descriptor *e)
{
e->data[5] |= d->type&0x1F; /* Type */
e->data[5] |= 1<<7; /* Present */
e->data[6] |= 1<<5; /* Long mode */
uint64_t v;
switch(d->type){
case TYPE_TSS_SEGMENT:
write_uint16_le(e->data, sizeof(*d->tss));
v = (uint64_t)d->tss;
write_uint16_le(e->data+2, v & 0xFFFF);
e->data[4] = (v >> 16) & 0xFF;
e->data[7] = (v >> 24) & 0xFF;
write_uint32_le((uint8_t *)(e+1), (v >> 32) & 0xFFFFFFFF);
break;
case TYPE_IDT:
v = (uint64_t)d->isr;
write_uint16_le(e->data, v & 0xFFFF);
write_uint16_le(e->data+6, (v >> 16) & 0xFFFF);
write_uint32_le(e->data+8, (v >> 32) & 0xFFFFFFFF);
write_uint16_le(e->data+2, DESCRIPTOR_SIZE*KERNEL_CODE_SEGMENT);
}
}
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