Interrupt Descriptor Table: Difference between revisions

An '''Interrupt Gate''' is used to specify an '''[[Interrupt Service Routines|Interrupt Service Routine]]'''. For example, when the assembly instruction '''INT 50''' is performed while running in protected mode, the CPU looks up the 50th entry (located at 50 * 8) in the '''IDT'''. Then the Interrupt Gate's '''Selector''' and '''Offset''' values are loaded. The '''Selector''' and '''Offset''' are used to call the '''Interrupt Service Routine'''. When the '''IRET''' instruction is performed, the CPU returns from the interrupt. If the CPU was running in 32-bit mode and the specified selector is a 16-bit gate, then the CPU will go in 16-bit '''[https://wiki.osdev.org/Protected_Mode Protected Mode'''] after calling the '''ISR'''. To return in this case, the '''O32 IRET''' instruction should be used, or else the CPU will not know that it should do a 32-bit return (reading 32-bit values off the [[stack]] instead of 16 bit).