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#include "cpu.h"
#include <stdint.h>
#define GDT_ENTRIES 16
#define IDT_ENTRIES 256
#define CODE_SEG_INDEX 1
#define DATA_SEG_INDEX 2
struct dtr64
{
uint16_t limit;
uint64_t base;
} __attribute__((packed));
struct segment_descriptor
{
uint16_t limit0;
uint16_t base0;
uint8_t base16;
uint8_t access;
uint8_t flags_limit16;
uint8_t base24;
} __attribute__((packed));
enum segment_descriptor_type
{
CODE64_SEG,
DATA_SEG,
};
struct gate_descriptor
{
uint16_t offset0;
uint16_t selector;
uint8_t ist;
uint8_t access;
uint16_t offset16;
uint64_t offset32;
} __attribute__((packed));
enum gate_descriptor_type
{
INT64_GATE,
TRAP64_GATE,
};
// TODO: is 16 enough?
static struct segment_descriptor gdt[GDT_ENTRIES];
static struct gate_descriptor idt[IDT_ENTRIES];
static void set_gdt(int index,
uint64_t base,
uint64_t limit,
enum segment_descriptor_type type)
{
gdt[index].limit0 = limit & 0xffff;
gdt[index].base0 = base & 0xffff;
gdt[index].base16 = (base >> 16) & 0xff;
gdt[index].flags_limit16 = (limit >> 16) & 0xf;
gdt[index].base24 = (base >> 24) & 0xff;
switch (type)
{
case CODE64_SEG:
gdt[index].access = 0x9a;
gdt[index].flags_limit16 |= 0xa0;
break;
case DATA_SEG:
gdt[index].access = 0x92;
gdt[index].flags_limit16 |= 0xc0;
break;
};
}
static void set_idt(int index,
uint16_t selector,
uint64_t offset,
enum gate_descriptor_type type)
{
idt[index].offset0 = offset & 0xffff;
idt[index].selector = selector;
idt[index].offset16 = (offset >> 16) & 0xffff;
idt[index].offset32 = (offset >> 32) & 0xffffffff;
switch (type)
{
case INT64_GATE:
idt[index].access = 0x8e;
break;
case TRAP64_GATE:
idt[index].access = 0x8f;
break;
}
}
static void gdt_init(void)
{
set_gdt(CODE_SEG_INDEX, 0, (uint64_t)-1, CODE64_SEG);
set_gdt(DATA_SEG_INDEX, 0, (uint64_t)-1, DATA_SEG);
struct dtr64 gdtr = {sizeof(gdt) - 1, (uint64_t)&gdt};
__asm__ volatile
(
// can't have interrupts during GDT reload
// but don't re-enable interrupts if they were already disabled
"pushf\n"
"cli\n"
"lgdt %0\n"
"mov %w2, %%ds\n"
"mov %w2, %%es\n"
"mov %w2, %%fs\n"
"mov %w2, %%gs\n"
// make a far return frame on the stack
// [ss] @rsp+8
// [rip] @rsp
"pushq %1\n"
"lea .flush(%%rip), %%rax\n"
"push %%rax\n"
// far return, now we're in the code segment
// defined here.
"lretq\n"
".flush:\n"
"popf\n"
// dependency on pre-boot GDT is now gone
:: "m"(gdtr), "i"(CODE_SEG_INDEX << 3), "r"(DATA_SEG_INDEX << 3)
);
}
static void idt_init(void)
{
struct dtr64 idtr = {sizeof(idt) - 1, (uint64_t)&idt};
__asm__ volatile
(
// can't have interrupts enabled during IDT reload--obviously.
// as with GDT don't re-enable interrupts if they were already
// disabled.
"pushf\n"
"cli\n"
"lidt %0\n"
"popf\n"
// much more straightforward than the gdt code.
:: "m"(idtr)
);
}
void cpu_init(void)
{
gdt_init();
idt_init();
}
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