diff options
Diffstat (limited to 'kernel/l0/gdt.c')
| -rw-r--r-- | kernel/l0/gdt.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/kernel/l0/gdt.c b/kernel/l0/gdt.c new file mode 100644 index 0000000..9ed5210 --- /dev/null +++ b/kernel/l0/gdt.c @@ -0,0 +1,35 @@ +#include <gdt.h> +#include <string.h> + +#define GDT_ENTRIES 6 // The contents of each entry is defined in gdt_init. + +static gdt_entry_t gdt_entries[GDT_ENTRIES]; +static gdt_ptr_t gdt_ptr; + +/* For internal use only. Writes one entry of the GDT with given parameters. */ +static void gdt_setGate(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) { + gdt_entries[num].base_low = (base & 0xFFFF); + gdt_entries[num].base_middle = (base >> 16) & 0xFF; + gdt_entries[num].base_high = (base >> 24) & 0xFF; + + gdt_entries[num].limit_low = (limit & 0xFFFF); + gdt_entries[num].granularity = (limit >> 16) & 0x0F; + gdt_entries[num].granularity |= gran & 0xF0; + gdt_entries[num].access = access; +} + +/* Write data to the GDT and enable it. */ +void gdt_init() { + gdt_ptr.limit = (sizeof(gdt_entry_t) * GDT_ENTRIES) - 1; + gdt_ptr.base = (uint32_t)&gdt_entries; + + gdt_setGate(0, 0, 0, 0, 0); //Null segment + gdt_setGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); //Kernel code segment 0x08 + gdt_setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF); //Kernel data segment 0x10 + gdt_setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF); //User code segment 0x18 + gdt_setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF); //User data segment 0x20 + + asm volatile ("lgdt %0"::"m"(gdt_ptr):"memory"); +} + +/* vim: set ts=4 sw=4 tw=0 noet :*/ |