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

src/gdt.c

@@ -0,0 +1,55 @@
+#include "gdt.h"
+#include "types.h"
+
+typedef struct GdtPointer {
+    uint16 limit;
+    uint64 base;
+} __attribute__((packed)) GdtPointer;
+
+static uint64 gdtEntries[7];
+static GdtPointer gdtPointer;
+
+void gdtInit(void)
+{
+    gdtEntries[0] = 0x0000000000000000ull;
+    gdtEntries[1] = 0x00AF9A000000FFFFull;
+    gdtEntries[2] = 0x00CF92000000FFFFull;
+    gdtEntries[3] = 0x00AFFA000000FFFFull;
+    gdtEntries[4] = 0x00CFF2000000FFFFull;
+    gdtEntries[5] = 0x0000000000000000ull;
+    gdtEntries[6] = 0x0000000000000000ull;
+
+    gdtPointer.limit = (uint16)(sizeof(gdtEntries) - 1);
+    gdtPointer.base = (uint64)&gdtEntries;
+
+    __asm__ volatile(
+        "lgdt %0\n"
+        "pushq $0x08\n"
+        "leaq 1f(%%rip), %%rax\n"
+        "pushq %%rax\n"
+        "lretq\n"
+        "1:\n"
+        "movw $0x10, %%ax\n"
+        "movw %%ax, %%ds\n"
+        "movw %%ax, %%es\n"
+        "movw %%ax, %%ss\n"
+        "movw %%ax, %%fs\n"
+        "movw %%ax, %%gs\n"
+        :
+        : "m"(gdtPointer)
+        : "rax", "memory");
+}
+
+void gdtInstallTss(uint64 base, uint32 limit)
+{
+    uint64 low = 0;
+    low |= (uint64)(limit & 0xFFFF);
+    low |= (base & 0xFFFFull) << 16;
+    low |= ((base >> 16) & 0xFFull) << 32;
+    low |= (uint64)0x89 << 40;
+    low |= (uint64)((limit >> 16) & 0xF) << 48;
+    low |= ((base >> 24) & 0xFFull) << 56;
+
+    gdtEntries[5] = low;
+    gdtEntries[6] = (base >> 32) & 0xFFFFFFFFull;
+}