Re:[PATCH][Experimental] Debugging i386 using hardware task

[Chuck Ebbert]

  Buoyed by the success of silly usermode testing, I got brave and stuck
an int3 instruction right in the middle of arch/i386/kernel/irq.c:do_IRQ()
and captured this:

   *1 - EIP is at do_IRQ+0x38, with interrupts disabled
   *2 - 0x50 (80) bytes of kernel stack are in use
   *3 - ECX: last two interrupts were 199485 clocks apart
        (boot CPU speed is 199.491 MHz)
   *4 - ESI: int3 has been invoked 1653673 times since boot

This is with an SMP kernel on a 1-CPU machine.  The 1000 clocks of extra
overhead every interrupt don't seem to make much of a difference...

GDT entry #16: kernel TSS at c0393800, 236 bytes:

   CS:0060 <GDT#12,RPL0>   EIP:c010afa8   eflags:00000002 <IF:0>        *1
  SS0:0068 <GDT#13,RPL0>  ESP0:c2966000
  SS1:0060 <GDT#12,RPL0>  ESP1:c0393a00
  SS2:0000 <GDT#00,RPL0>  ESP2:00000000
   SS:0068 <GDT#13,RPL0>   ESP:c2965fb0                                 *2                                      
   DS:007b <GDT#15,RPL3>  ES:007b <GDT#15,RPL3>
   FS:0000 <GDT#00,RPL0>  GS:0000 <GDT#00,RPL0>
  EAX:c10a2020  EBX:00000000  ECX:00cb5f80  EDX:00000000
  ESI:c0393c00  EDI:00000000  EBP:bffffb78     BITMAP:8000
  LDT:0088 <GDT#17,RPL0>      CR3:035d1000   LINK:0000 <GDT#00,RPL0>

GDT entry #30: debugger TSS at c0395a00, 236 bytes:

   CS:0060 <GDT#12,RPL0>   EIP:c0110173   eflags:00000006 <IF:0>
  SS0:0068 <GDT#13,RPL0>  ESP0:c03f27a0
  SS1:0000 <GDT#00,RPL0>  ESP1:00000000
  SS2:0000 <GDT#00,RPL0>  ESP2:00000000
   SS:0068 <GDT#13,RPL0>   ESP:c03f27a0
   DS:007b <GDT#15,RPL3>  ES:007b <GDT#15,RPL3>
   FS:0000 <GDT#00,RPL0>  GS:0000 <GDT#00,RPL0>
  EAX:aa72bbf2  EBX:c0341a40  ECX:00030b3d  EDX:0000004e                *3
  ESI:00193ba9  EDI:00000010  EBP:c03f03a0     BITMAP:8000
  LDT:0088 <GDT#17,RPL0>      CR3:00101000   LINK:0080 <GDT#16,RPL0>    *4