Following up on this, it seems that Brad is correct about where the
uninitialized values originate. Specifically, this code snippet in
src/arch/alpha/tlb.cc is the culprit:
> mode_type mode =
>
> (mode_type)DTB_CM_CM(tc->readMiscRegNoEffect(IPR_DTB_CM));
That uninitialized value eventually trickles down to these conditions:
"if (!(entry->xwe & MODE2MASK(mode))) {"
and
"if (!(entry->xre & MODE2MASK(mode))) {"
For SE mode, I'm wondering where/if the IPR registers are ever
initialized? The indexing to the IPR registers get set in
"initializeIprTable" but the actual registers themselves do not to my
knowledge . Since SE is primarily just user_mode execution, I would
guess typically the IPR registers dont matter for execution except for
a case like this where TLB faults need to acquire a IPR value.
If I set the IPR_DTB_CM register to an arbitrary value in the ISA
constructor (arch/alpha/isa.cc), then the valgrind "uninitialized"
error goes away. However, I'm not exactly sure what that value should
be set to for a SE workload (i'm assuming in FS, the kernel sets that
appropriately), and its not exactly the cleanest solution to hardcode
that in the constructor even if I were sure of the right value.
It's possible, that the uninitialized values causes the # of TLB
faults in SE mode to change, allowing the actual simulation output to
the stay the same but slightly changing the execution time and other
"small" stats. That's just my theory though.
Anyone have additional thoughts on this?
--
- Korey
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