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SubjectRe: AMD K6 "Bug"
Date
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From the K6 errata:

-----------------------------------------------------------------
2.3 Interrupts and Exceptions.

Products affected: A (*) stepping.

Normal Specified operation. An attempt to access memory with a segment
register that contains a null selector causes a general protection
fault to occur.

Non-Confomance. On enteringe System Mamagement Mode (SMM), the
processor saves its state into the SMM state-save area. The processor
returns from SMM when it executes the RSM (resume) instruction from
within the SMM service routine. If any of the segment registers
contains a null selector on entering the SMM, then after executing the
RSM instruction, the internal state bit associated with the
corresponding segment descriptor is erroneously set to indicate that
this segment is readable. In this case the processor does not
generate a general protection fault when attempting to read memory
using a null selector, but instead allows the memory read cycle to
occur without generating an exception.

Potential effect on System. Unless an application is errant, an
application generally does not access segements using null
selectors. However, an application that depends on the processor to
generate a general protection fault if a null selector is used will
not execute successfully.

This erratum has not been observed to adversely affect a system. It
was detected by design inspection.

Suggested workaround. None.

Resolution status. This erratum will be corrected in a future stepping
of the AMD-K6 processor.

------------------------ Typo's are mine -------------------------

(*) And B and C stepping which are K6-MMX.


This is a serious problem for Linux right?

Assuming SMM has something to do with system calls or interrupts, Or
would Linux never allow me to load a NULL segment register? In 32bit
mode, I don't expect to be able to load segment registers but WINE and
DOSEMU would have to be able to do this right?


Roger.

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If it's there and you can't see it, it's TRANSPARENT | Tel: +31-15-2137555 |
If it's not there and you can see it, it's VIRTUAL |__FAX:_+31-15-2138217 |
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