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IRQs cause exceptions?
https://forum.osdev.org/viewtopic.php?f=1&t=32646		 Page 1 of 1
Author:  thumble [ Fri Dec 22, 2017 11:14 pm ]
Post subject:  IRQs cause exceptions?
Once I enable interrupts with sti, I get an exception.
Before I enable IRQs, I first remap the PIC to offsets 0x20 on master and 0x28 on slave; here is the remapping code:

Code:
void irq_remap() {
   outb(0x20, 0x11);
   outb(0xA0, 0x11);
   outb(0x21, 0x20);
   outb(0xA1, 0x28);
   outb(0x21, 0x04);
   outb(0xA1, 0x02);
   outb(0x21, 0x01);
   outb(0xA1, 0x01);
   outb(0x21, 0x0);
   outb(0xA1, 0x0);
}


And this is my IRQ-installing code:
Code:
void install_irqs() {
   irq_remap();
   set_idt_gate(32, (unsigned)irq0, 0x08, 0x8E);
   set_idt_gate(33, (unsigned)irq1, 0x08, 0x8E);
   set_idt_gate(34, (unsigned)irq2, 0x08, 0x8E);
   set_idt_gate(35, (unsigned)irq3, 0x08, 0x8E);
   set_idt_gate(36, (unsigned)irq4, 0x08, 0x8E);
   set_idt_gate(37, (unsigned)irq5, 0x08, 0x8E);
   set_idt_gate(38, (unsigned)irq6, 0x08, 0x8E);
   set_idt_gate(39, (unsigned)irq7, 0x08, 0x8E);
   set_idt_gate(40, (unsigned)irq8, 0x08, 0x8E);
   set_idt_gate(41, (unsigned)irq9, 0x08, 0x8E);
   set_idt_gate(42, (unsigned)irq10, 0x08, 0x8E);
   set_idt_gate(43, (unsigned)irq11, 0x08, 0x8E);
   set_idt_gate(44, (unsigned)irq12, 0x08, 0x8E);
   set_idt_gate(45, (unsigned)irq13, 0x08, 0x8E);
   set_idt_gate(46, (unsigned)irq14, 0x08, 0x8E);
   set_idt_gate(47, (unsigned)irq15, 0x08, 0x8E);
}


Here is IRQ 0 in assembly:

Code:
irq0:
   cli
   push 0
   push 32
   jmp stub


This jumps to an assembly stub common to each IRQ:

Code:
stub:
   pushad
   mov eax, esp
   push eax
   mov eax, handle_irq
   call eax
   pop eax
   popad
   add esp, 8
   iret


Which then calls this C handler:

Code:
void handle_irq(struct regs *r) {
   void (*handler)(struct regs *r);
   handler = irq_routines[r->int_no - 32];
   if(handler) {
      handler(r);
   }
   if(r->int_no >= 40) {
      outb(0xA0, 0x20);
   }
   outb(0x20, 0x20);
}


I am somewhat suspicious that the issue is in my register frame, so here it is:

Code:
struct regs {   
   dword errcode, int_no, ebp, esp, ebx, edx, ecx, eax, esi, edi;
};


Does anyone know what may be the issue?
Thanks
Author:  thumble [ Fri Dec 22, 2017 11:22 pm ]
Post subject:  Re: IRQs cause exceptions?
Never mind. Really was a problem with my regs structure; forgot that the CPU pushes some things as well (plus my order was reversed)
Here it is:
Code:
struct regs {   
   dword edi, esi, ebp, esp, ebx, edx, ecx, eax, int_no, errcode, eip, cs, eflags, esp2, ss;
};
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