Interrupt Service Routines: Difference between revisions
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note that in long mode you need to use iretq rather than iret
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(note that in long mode you need to use iretq rather than iret) |
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For the system to know which interrupt service routine to call when a certain interrupt occurs, offsets to the ISRs are stored in the [[IDT|Interrupt Descriptor Table]] when you're in [[Protected mode]], or in the [[Interrupt Vector Table]] when you're in [[Real Mode]].
An ISR is called directly by the CPU, and the protocol for calling an ISR differs from calling e.g. a C function. Most importantly, an ISR has to end with the <tt>iret</tt> opcode (or <tt>iretq</tt> in long mode—yes, even when using intel syntax), whereas usual C functions end with <tt>ret</tt> or <tt>retf</tt>. The obvious but nevertheless wrong solution leads to one of the most "popular" triple-fault errors among OS programmers.
== The Problem ==
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