93 lines
2.2 KiB
C
93 lines
2.2 KiB
C
#include <stdint.h>
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#include <stddef.h>
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#include "compiler/attr.h"
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#include "hal/hal.h"
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#include "gdt.h"
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#define GDT_PRESENT 0x80
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#define GDT_TSS 0x89
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#define KSTACK 8192
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ALIGNED(16) static uint8_t kernelstack[KSTACK];
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typedef struct {
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uint16_t limitlow;
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uint16_t baselow;
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uint8_t basemid;
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uint8_t access;
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uint8_t gran;
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uint8_t basehigh;
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} PACKED GdtEntry;
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typedef struct {
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uint16_t limit;
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uint64_t base;
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} PACKED GdtPtr;
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typedef struct {
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GdtEntry old[5];
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GdtEntry tsslow;
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GdtEntry tsshigh;
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} PACKED ExtendedGdt;
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ALIGNED(16) Tss tss = {0};
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ALIGNED(16) static ExtendedGdt gdt = {0};
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void gdt_setentry(GdtEntry *ent, uint32_t base, uint32_t limit, uint8_t acc, uint8_t gran) {
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ent->baselow = base & 0xffff;
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ent->basemid = (base >> 16) & 0xff;
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ent->basehigh = (base >> 24) & 0xff;
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ent->limitlow = limit & 0xffff;
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ent->gran = ((limit >> 16) & 0x0f) | (gran & 0xf0);
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ent->access = acc;
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}
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void gdt_init(void) {
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hal_memset(&tss, 0, sizeof(tss));
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tss.iopb_off = sizeof(tss);
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tss.rsp0 = (uint64_t)(kernelstack + sizeof(kernelstack));
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uint64_t tss_base = (uint64_t)&tss;
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uint32_t tss_limit = sizeof(tss) - 1;
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gdt_setentry(&gdt.old[0], 0, 0, 0, 0);
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gdt_setentry(&gdt.old[1], 0, 0xFFFFF, 0x9a, 0xA0);
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gdt_setentry(&gdt.old[2], 0, 0xFFFFF, 0x92, 0xC0);
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gdt_setentry(&gdt.old[3], 0, 0xFFFFF, 0xfa, 0xA0);
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gdt_setentry(&gdt.old[4], 0, 0xFFFFF, 0xf2, 0xC0);
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gdt_setentry(&gdt.tsslow, tss_base & 0xFFFFFFFF, tss_limit, GDT_PRESENT | GDT_TSS, 0x0);
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uint32_t tssbasehi = tss_base >> 32;
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gdt.tsshigh.limitlow = tssbasehi & 0xffff;
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gdt.tsshigh.baselow = (tssbasehi >> 16) & 0xffff;
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gdt.tsshigh.basemid = 0;
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gdt.tsshigh.basehigh = 0;
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gdt.tsshigh.access = 0;
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gdt.tsshigh.gran = 0;
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GdtPtr gdtr;
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gdtr.limit = sizeof(gdt) - 1;
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gdtr.base = (uint64_t)&gdt;
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asm volatile("lgdt %0" :: "m"(gdtr));
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asm volatile(
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"pushq %[kcode]\n"
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"lea 1f(%%rip), %%rax\n"
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"pushq %%rax\n"
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"lretq\n"
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"1:\n"
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"movw %[kdata], %%ax\n"
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"movw %%ax, %%ds\n"
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"movw %%ax, %%es\n"
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"movw %%ax, %%ss\n"
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:
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: [kcode] "i"(KCODE), [kdata] "i"(KDATA)
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: "rax", "memory"
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);
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asm volatile("ltr %0" :: "r"((uint16_t)TSS));
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}
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