HLT

From Asmpedia

Halt the processor

Intel	AMD
+	+

Definition:

HLT

Causes the processor to stop executing instruction flow and wait for the following interrupts and signals to occur:

• Unmasked hardware interrupt (INTR)
• Non-maskable interrupt (NMI)
• System management interrupt (SMI)
• Debug exception
• BINIT#, INIT# and RESET# signals

Operation in pseudo code:

hlt()
{
   if (cpl) // current privilege level != 0
     throw #GP;

   enter_state(HALT);
}

Opcodes (x86/x64):

F4

-

HLT

-

EFLAGS

:31	:30	:29	:28	:27	:26	:25	:24	:23	:22	ID :21	VIP :20	VIF :19	AC :18	VM :17	RF :16	:15	NT :14	IOPL :13:12	OF :11	DF :10	IF :9	TF :8	SF :7	ZF :6	:5	AF :4	:3	PF :2	:1	CF :0
0	0	0	0	0	0	0	0	0	0	-	-	-	-	-	-	0	-	-	-	-	-	-	-	-	0	-	0	-	1	-

Annotated WinDbg disassembly (x86/x64):

f4              hlt