The difference between "call gate" and "Software interrupt?

Question

These are safe, low-privilege ways to call kernel functions.

I don't know the difference between the two.

Answer 1

You can look through the intel manuals for all the gory bits; but in a nutshell:

1. Call Gate does not disable interrupts.
2. Call Gate can copy N arguments between the stacks on a privity switch.
3. Call Gate can be LDT private
4. Call Gate can be disguised as a normal function pointer, if your compiler happens to support intel medium,large compilations models.
5. Given 4, a normal "ret" instruction undoes a call gate entry.
6. Almost nobody every used Call Gates.

whereas:

1. Interrupt gates disable interrupts.
2. Interrupt gates don't care about arguments.
3. The IDT is a global resource.
4. The invocation sequence for interrupts is pretty unique from functions.