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gdt idt stuff

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slinky55
2026-06-12 23:03:00 -04:00
parent 5e823e570b
commit 00fb70c25b
7 changed files with 67 additions and 19 deletions
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41
kernel/gdt.c
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@@ -40,23 +40,44 @@
#define GDT_DATA_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(3) | SEG_DATA_RDWR
typedef struct __attribute__((packed)) {
uint16_t limit;
uint32_t base;
} gdt_ptr_t;
uint64_t gdt[5];
gdt_ptr_t gdtr;
extern void load_gdt();
uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
{
uint64_t descriptor;
// Create the high 32 bit segment
descriptor = limit & 0x000F0000; // set limit bits 19:16
descriptor |= (flag << 8) & 0x00F0FF00; // set type, p, dpl, s, g, d/b, l and avl fields
descriptor |= (base >> 16) & 0x000000FF; // set base bits 23:16
descriptor |= base & 0xFF000000; // set base bits 31:24
descriptor = limit & 0x000F0000;
descriptor |= (flag << 8) & 0x00F0FF00;
descriptor |= (base >> 16) & 0x000000FF;
descriptor |= base & 0xFF000000;
// Shift by 32 to allow for low part of segment
descriptor <<= 32;
// Create the low 32 bit segment
descriptor |= base << 16; // set base bits 15:0
descriptor |= limit & 0x0000FFFF; // set limit bits 15:0
descriptor |= base << 16;
descriptor |= limit & 0x0000FFFF;
return descriptor;
}
void init_gdt() {
gdt[0] = create_descriptor(0, 0, 0);
gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0));
gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0));
gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3));
gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3));
gdtr.limit = 5 * sizeof(uint64_t) - 1;
gdtr.base = (uint32_t)&gdt;
load_gdt();
}