Ring 3 multitasking

src/kernel/gdt_asm.asm

@@ -0,0 +1,28 @@
+global gdt_flush
+global tss_flush
+
+section .text
+
+gdt_flush:
+    lgdt [rdi]      ; Load GDT from the pointer passed in RDI
+
+    mov ax, 0x10    ; 0x10 is our offset in the GDT to our data segment
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+
+    ; Far jump to update CS
+    push 0x08       ; 0x08 is our offset to the code segment
+    lea rax, [rel .flush]
+    push rax
+    retfq
+
+.flush:
+    ret
+
+tss_flush:
+    mov ax, 0x28    ; 0x28 is our offset in the GDT to the TSS
+    ltr ax
+    ret