Disable Hardware & Software Interrupts

Question

Hello!

Is it possible to disable all interrupts with a ASM/C/C++ program to get full control about the processor?

If yes -> how?

If not -> how do "atomic" operation system calls work (for example entering a critical section)?

Sorry for my English! Thanks for your help!

Answer 1

on x86 and most other modern processors you can get atomic instructions. Ones that are GURANTEED not to be finished executing before another thread/processor can access that memory.

Under Win32 you have the Interlocked* functions that abstract that from you on supported platforms.

On a MIPS a lot of instruction can have a .I added to the end of the instruction to guarantee interlocking.

Answer 2

In x86 assembly the the commands are

• sti set interrupt disable bit
• cli clear interrupt disable bit

These commands set and clear the IF Flag. They don't work in unprivileged mode (usually everything higher than ring 0, depending on IOPL) though.