src/kernel/gdt_asm.s

/*
 * lgdt plus the mandatory segment-register reload. `lgdt` alone only
 * changes what the gdtr points at -- it does not refresh the hidden
 * descriptor-cache state already loaded into cs/ds/es/ss/fs/gs, so
 * every segment register has to be explicitly reloaded afterward or
 * the cpu keeps using the OLD table's cached descriptor for whatever
 * it doesn't reload. data segments reload with a plain mov; cs can't
 * be loaded with mov at all (no such instruction) -- the standard
 * trick is a far return: push the target selector and a return
 * address, then lretq pops both and does a real far jump into the new
 * cs.
 */
.section .text
 
.global load_gdt
.type load_gdt, @function
load_gdt:
	lgdt (%rdi)
 
	movw $0x10, %ax
	movw %ax, %ds
	movw %ax, %es
	movw %ax, %ss
	movw %ax, %fs
	movw %ax, %gs
 
	pushq $0x08
	leaq 1f(%rip), %rax
	pushq %rax
	lretq
1:
	ret