feat(cpu): add GDT and TSS for ring 0 and ring 3 segments

src/tss.c

@@ -0,0 +1,38 @@
+#include "tss.h"
+#include "gdt.h"
+#include "string.h"
+
+typedef struct Tss {
+    uint32 reserved0;
+    uint64 rsp0;
+    uint64 rsp1;
+    uint64 rsp2;
+    uint64 reserved1;
+    uint64 ist1;
+    uint64 ist2;
+    uint64 ist3;
+    uint64 ist4;
+    uint64 ist5;
+    uint64 ist6;
+    uint64 ist7;
+    uint64 reserved2;
+    uint16 reserved3;
+    uint16 iomapBase;
+} __attribute__((packed)) Tss;
+
+static Tss tss;
+
+void tssInit(uint64 rsp0)
+{
+    memset(&tss, 0, sizeof(tss));
+    tss.rsp0 = rsp0;
+    tss.iomapBase = sizeof(Tss);
+
+    gdtInstallTss((uint64)&tss, sizeof(Tss) - 1);
+    __asm__ volatile("ltr %w0" : : "r"((uint16)tssSelector));
+}
+
+void tssSetRsp0(uint64 rsp0)
+{
+    tss.rsp0 = rsp0;
+}