Xenix Watchpoints

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1 total messages Started by Ron Kuris Tue, 10 Apr 1990 13:21

#355

Author: Ron Kuris
Date: Tue, 10 Apr 1990 13:21

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I'm considering trying to get watchpoints working for SCO Xenix.
I understand this was done on an Interactive machine.  Does anyone
with Interactive have a knowledge of what the OS does with the
debug registers when it does a task switch?  Does it push them on
the kernel stack?

Alternatively, perhaps someone with an excellent 386 understanding
could explain to me how a program with a CPL>0 can use the local
bits of the debug registers.  According to the Intel documentation,
you can't do anything with the debug registers unless your CPL is
zero.  Also, I think your CPL changes when you task switch.  Can
someone explain this better?

I looked at the interrupt handler code in SCO xenix (isn't the
'disassemble' option of gdb nice?) and saw that it just pushed the
general purpose registers (i also noticed that there is a kernel
stack pointer which isn't used when the program restores -- hmmm...
maybe I can use this to store ONE debug register :-).
-- 
--
...!pyramid!unify!rdk386!ron -or- ...!ames!pacbell!sactoh0!siva!rdk386!ron
It's not how many mistakes you make, its how quickly you recover from them.

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