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#include <kernel/arch/amd64/32/gdt.h>
#include <kernel/arch/generic.h>
#include <stdbool.h>
#include <stdint.h>
extern char _isr_mini_stack;
struct gdt_entry {
uint64_t limit_low : 16;
uint64_t base_low : 24;
uint64_t accessed : 1; // set by the processor
// CODE | DATA
uint64_t rw : 1; // readable? | writeable?
uint64_t conforming : 1; // conforming? | expands down?
uint64_t code : 1; // 1 | 0
uint64_t codeordata : 1; // 1 for everything other than TSS and LDT
uint64_t ring : 2;
uint64_t present : 1; // always 1
uint64_t limit_high : 4;
uint64_t available : 1; // ???
uint64_t long_mode : 1;
uint64_t x32 : 1;
uint64_t gran : 1; // 1 - 4kb, 0 - 1b
uint64_t base_high : 8;
} __attribute__((packed));
struct tss_entry {
uint32_t reserved0;
uint64_t rsp[3];
uint64_t ist[8];
uint64_t reserved2;
uint16_t reserved3;
uint16_t iopb;
} __attribute__((packed));
struct lgdt_arg {
uint16_t limit;
uint32_t base;
} __attribute__((packed));
__attribute__((section(".shared")))
struct gdt_entry GDT[SEG_end];
__attribute__((section(".shared")))
struct tss_entry TSS;
struct lgdt_arg lgdt_arg;
static void *memset32(void *s, int c, size_t n) {
uint8_t *s2 = s;
for (size_t i = 0; i < n; i++)
s2[i] = c;
return s;
}
static void gdt_fillout(struct gdt_entry* entry, uint8_t ring, bool code) {
*entry = (struct gdt_entry) {
// set up the identity mapping
.limit_low = 0xFFFF,
.limit_high = 0xF,
.gran = 1,
.base_low = 0,
.base_high = 0,
.ring = ring,
.code = code,
.accessed = 0,
.rw = 1,
.conforming = 0,
.codeordata = 1,
.present = 1,
.long_mode = 1,
.available = 1,
.x32 = 0,
};
}
void gdt_init(void) {
GDT[SEG_null].present = 0;
gdt_fillout(&GDT[SEG_r0code], 0, true);
gdt_fillout(&GDT[SEG_r0data], 0, false);
gdt_fillout(&GDT[SEG_r3code], 3, true);
gdt_fillout(&GDT[SEG_r3data], 3, false);
lgdt_arg.limit = sizeof(GDT) - 1;
lgdt_arg.base = (uint64_t) &GDT;
memset32(&TSS, 0, sizeof(TSS));
for (int i = 0; i < 3; i++)
TSS.rsp[i] = (uint64_t) &_isr_mini_stack;
TSS.ist[1] = (uint64_t) &_isr_mini_stack;
uint64_t tss_addr = (uint64_t) &TSS;
GDT[SEG_TSS] = (struct gdt_entry) {
.limit_low = sizeof(TSS),
.limit_high = sizeof(TSS) >> 16,
.gran = 0,
.base_low = tss_addr,
.base_high = tss_addr >> 24,
.accessed = 1,
.rw = 0,
.conforming = 0,
.code = 1,
.codeordata = 0,
.ring = 0, // was 3 pre-port
.present = 1,
.available = 1,
.long_mode = 0,
.x32 = 0,
};
*((uint64_t*)&GDT[SEG_TSS2]) = (tss_addr >> 32);
}
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