x86_64: implement TSS initialisation and user/kernel stack pointer switching

arch/x86_64/tss.c

@@ -0,0 +1,48 @@
+#include "arch/msr.h"
+
+#include <arch/gdt.h>
+#include <arch/tss.h>
+#include <mango/libc/string.h>
+
+static void tss_flush(int index)
+{
+	index *= sizeof(struct gdt_entry);
+	index |= 3;
+	asm volatile("mov %0, %%eax; ltr %%ax" ::"r"(index));
+}
+
+void tss_init(struct tss *tss, struct tss_ptr *ptr)
+{
+	memset(tss, 0x0, sizeof *tss);
+
+	ptr->tss_base = (uint64_t)tss;
+	ptr->tss_limit = (uint16_t)sizeof *tss;
+}
+
+void tss_load(struct tss *tss)
+{
+	tss_flush(TSS_GDT_INDEX);
+
+	uintptr_t kernel_gs_base_reg = 0xC0000102;
+	wrmsr(kernel_gs_base_reg, (uintptr_t)tss);
+}
+
+virt_addr_t tss_get_kstack(struct tss *tss)
+{
+	return tss->rsp0;
+}
+
+virt_addr_t tss_get_ustack(struct tss *tss)
+{
+	return tss->rsp2;
+}
+
+void tss_set_kstack(struct tss *tss, virt_addr_t sp)
+{
+	tss->rsp0 = sp;
+}
+
+void tss_set_ustack(struct tss *tss, virt_addr_t sp)
+{
+	tss->rsp2 = sp;
+}