Check if long mode is available

src/kernel/Link.ld

@@ -7,4 +7,9 @@ SECTIONS
     *(.multiboot)
     *(.text)
   }
+
+  .data :
+  {
+    *(.data)
+  }
 }

src/kernel/boot/boot.S

@@ -1,9 +1,58 @@
 .intel_syntax noprefix
 
+.section .data
+check_cpuid_stack_top:
+  .long 0
+  .long 0
+  .long 0
+check_cpuid_stack:
+  nop
+
 .section .text
-.global _start
+
 .code32
+error:
+  // Print "ERR!" in upper left corner
+  mov [0xb8000], dword ptr 0x4f524f45
+  mov [0xb8004], dword ptr 0x4f214f52
+  jmp $
+
+check_cpuid:
+  mov check_cpuid_stack, esp
+  pushfd
+  pushfd
+  xor dword ptr[esp], 1<<21
+  popfd
+  pushfd
+  pop eax
+  xor eax, [esp]
+  popfd
+  and eax, 1<<21
+  jz error
+  ret
+
+check_longmode:
+  // cpuid 0x8000 0000
+  mov eax, 0x80000000
+  cpuid
+  cmp eax, 0x80000001
+  jb error
+
+  // cpuid 0x8000 0001
+  mov eax, 0x80000001
+  cpuid
+
+  // Test for long mode flag
+  test edx, 1<<29
+  jz error
+  ret
+
+.global _start
 _start:
 cli
 
+call check_cpuid
+call check_longmode
+
+
 jmp $