> 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 mode, > > regardless of the setting of CU0 bit". Does it mean that when in Kernel mode > > , the CU0 bit is always 1 and in User mode, the CU0 bit is 0? If the CU0 is > > 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 the > > interrupt priority is lowest,If an interrupt happens in a syscall exception > > handler, will it pause the syscall exception handler and run the interrupt > > handler? If not, why it enable the IE bit(STI) in the syscall exception > > handler?? The answer of this question? Thanks. machael thailer
