Add MSR_EFER and rdmsr()

src/hulk/cpu.d

@@ -5,6 +5,8 @@ module hulk.cpu;
 
 import ldc.llvmasm;
 
+enum uint MSR_EFER = 0xC000_0080u;
+
 void cli()
 {
     __asm("cli", "");
@@ -45,6 +47,14 @@ ulong read_cr4()
     return __asm!ulong("mov %cr4, %rax", "={rax}");
 }
 
+ulong rdmsr(uint msr)
+{
+    return __asm!ulong(`
+            rdmsr
+            shl $$32, %rdx
+            or %rdx, %rax`, "={rax},{ecx},~{rdx}", msr);
+}
+
 ubyte in8(ushort ioaddr)
 {
     return __asm!ubyte("inb %dx, %al", "={al},{dx}", ioaddr);