> On Tue, Aug 21, 2001 at 09:34:00AM +0800, machael thailer wrote:
> > I am confused about CU0 and UM(ERL EXL) bit of STATUS register.
> > The user manual says that " CP0 is always usable when in Kernel
> > regardless of the setting of CU0 bit". Does it mean that when in Kernel
> > , the CU0 bit is always 1 and in User mode, the CU0 bit is 0? If the CU0
> > 0, can we be sure that it is in User mode?
> In the Linux kernel CU0 is used to indicate that we're running on the
> kernel stack.
Yes, when CU0 is 1, we can see we are running on the kernel stack.
But when CU0 is 0, can we say it is in User mode?
> > Another question about exception priority:
> > In entry.S, some exception handlers enables global interrupt bit(IE) but
> > others disables it.
> We have to avoid infinite recursion of exceptions; in same cases it's
> just paranoia or minor performance issue.
> > Also syscall exception handler enables global interrupt bit(IE). Since
> > interrupt priority is lowest,If an interrupt happens in a syscall
> > handler, will it pause the syscall exception handler and run the
> > handler? If not, why it enable the IE bit(STI) in the syscall exception
> > handler??
The answer of this question? Thanks.