Add an interrupt descriptor table.

Set up a very basic handler for divide by zero and
general protection faults.

zion/interrupt/interrupt_enter.s

@@ -0,0 +1,56 @@
+.macro interrupt_enter
+  push %rbp
+  push %r15
+  push %r14
+  push %r13
+  push %r12
+  push %r11
+  push %r10
+  push %r9
+  push %r8
+  push %rdi
+  push %rsi
+  push %rdx
+  push %rcx  # (Return Address)
+  push %rbx
+  push %rax
+.endm
+
+.macro interrupt_exit
+  pop %rax
+  pop %rbx
+  pop %rcx
+  pop %rdx
+  pop %rsi
+  pop %rdi
+  pop %r8
+  pop %r9
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %rbp
+
+  add $8, %rsp # Remove error code.
+.endm
+
+.macro isr_handler name error_code=0
+.global isr_\name
+isr_\name:
+  .if \error_code
+  .else
+  push $0 # if we don't have an error code, equalize the stack.
+  .endif
+  interrupt_enter
+  sti
+  mov %rsp, %rdi
+  call interrupt_\name
+  cli
+  interrupt_exit
+  iretq
+.endm
+
+isr_handler divide_by_zero
+isr_handler protection_fault,1