fix: correct 64-bit IDT gate descriptor layout to prevent triple fault on keypress

Co-authored-by: aider (openrouter/anthropic/claude-sonnet-4.6) <aider@aider.chat>

platform_kernel.c

@@ -50,16 +50,37 @@ static void serial_init(void) {
     outb(0x3F8 + 4, 0x0B);
 }
 
-static uint64_t idt_entries[256][2];
+/* Each 64-bit IDT entry is 16 bytes = two uint64_t words.
+ *
+ * Word 0 layout:
+ *   [15: 0] offset[15:0]
+ *   [31:16] segment selector
+ *   [34:32] IST (0 = no IST)
+ *   [39:35] reserved (0)
+ *   [47:40] type+attr  (0x8E = present, DPL=0, 64-bit interrupt gate)
+ *   [63:48] offset[31:16]
+ *
+ * Word 1 layout:
+ *   [31: 0] offset[63:32]
+ *   [63:32] reserved (0)
+ */
+typedef struct {
+    uint64_t low;
+    uint64_t high;
+} __attribute__((packed)) IdtEntry;
+
+static IdtEntry idt_entries[256];
 
 static void idt_set_gate(int vector, uint64_t offset, uint16_t selector, uint8_t type_attr) {
-    uint64_t low = (offset & 0xFFFFULL) |
+    uint64_t low =
-                   ((uint64_t)selector << 16) |
+        (offset & 0x000000000000FFFFULL)          |   /* offset[15:0]  */
-                   ((uint64_t)(type_attr & 0xFF) << 40) |
+        ((uint64_t)selector          << 16)        |   /* selector      */
-                   ((offset & 0xFFFF0000ULL) << 32);
+        /* bits 34:32 = IST=0, bits 39:35 = 0 */
-    uint64_t high = offset >> 32;
+        ((uint64_t)type_attr         << 40)        |   /* type+attr     */
-    idt_entries[vector][0] = low;
+        ((offset  & 0x00000000FFFF0000ULL) << 32); /* offset[31:16] */
-    idt_entries[vector][1] = high;
+    uint64_t high = offset >> 32;                      /* offset[63:32] */
+    idt_entries[vector].low  = low;
+    idt_entries[vector].high = high;
 }
 
 static struct {
@@ -224,8 +245,8 @@ void kernel_main(void) {
     serial_init();
 
     idt_set_gate(0x21, (uint64_t)isr_keyboard, 0x08, 0x8E);
-    idt_ptr.limit = sizeof(idt_entries) - 1;
+    idt_ptr.limit = (uint16_t)(sizeof(idt_entries) - 1);
-    idt_ptr.base = (uint64_t)idt_entries;
+    idt_ptr.base  = (uint64_t)(uintptr_t)idt_entries;
     __asm__ volatile ("lidt %0" : : "m"(idt_ptr));
 
     pic_remap();