diff options
Diffstat (limited to 'src/kernel/mem/gdt.c')
| -rw-r--r-- | src/kernel/mem/gdt.c | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/src/kernel/mem/gdt.c b/src/kernel/mem/gdt.c index e9a1be5..8ee403a 100644 --- a/src/kernel/mem/gdt.c +++ b/src/kernel/mem/gdt.c @@ -2,19 +2,23 @@ #include <stdlib.h> #include <core/monitor.h> -extern void gdt_flush(uint32_t); //ASM (idt_.asm) +extern void gdt_flush(uint32_t); //ASM (imported from idt_.asm) extern void tss_flush(); -#define GDT_ENTRIES 6 +#define GDT_ENTRIES 6 // The contents of each entry is defined in gdt_init. static struct tss_entry tss_entry; static struct gdt_entry gdt_entries[GDT_ENTRIES]; static struct gdt_ptr gdt_ptr; +/* This function is called by the task_switch function on each context switch. + It updates the TSS so that an interrupt will be handled on the correct kernel stack + (one kernel stack is allocated to each thread). */ void gdt_setKernelStack(uint32_t esp0) { tss_entry.esp0 = esp0; } +/* 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; @@ -26,6 +30,7 @@ static void gdt_setGate(int num, uint32_t base, uint32_t limit, uint8_t access, gdt_entries[num].access = access; } +/* For internal use only. Writes one entry of the GDT, that entry being a pointer to the TSS. */ static void gdt_writeTss(int num, uint32_t ss0, uint32_t esp0) { uint32_t base = (uint32_t)&tss_entry; uint32_t limit = base + sizeof(struct tss_entry); @@ -40,15 +45,16 @@ static void gdt_writeTss(int num, uint32_t ss0, uint32_t esp0) { tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13; } +/* Write data to the GDT and enable it. */ void gdt_init() { gdt_ptr.limit = (sizeof(struct gdt_entry) * 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 - gdt_setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF); //Kernel data segment - gdt_setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF); //User code segment - gdt_setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF); //User data 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 gdt_writeTss(5, 0x10, 0); gdt_flush((uint32_t)&gdt_ptr); |