After reading decoder.cc, it seems that in case of execution being inside
microcode rom, you can get some dummy value (defined in x86_traits.hh) for
machInst. Otherwise you should get correct value for machInst.
--
Nilay
On Thu, 12 Apr 2012, Steve Reinhardt wrote:
I'm running into some problems where I'm tracediffing two x86 runs and
getting some seemingly spurious differences in the decode output.
The key question I have is: what is the meaning of the machInst field of a
micro op?
The problem seems to be in the code below (from
http://repo.gem5.org/gem5/file/d062cc7a8bdf/src/cpu/simple/base.cc#l403).
Note that if we're executing a macroop, then curMacroStaticInst has the
correct machInst, but the DPRINTF at the bottom is printing the machInst
from the microop (via curStaticInst), which appears in at least some cases
to be garbage.
Am I diagnosing this properly? Any ideas on a fix?
Steve
//If we decoded an instruction and it's microcoded, start pulling
//out micro ops
if (instPtr && instPtr->isMacroop()) {
curMacroStaticInst = instPtr;
curStaticInst =
curMacroStaticInst->fetchMicroop(pcState.microPC());
} else {
curStaticInst = instPtr;
}
} else {
//Read the next micro op from the macro op
curStaticInst = curMacroStaticInst->fetchMicroop(pcState.microPC());
}
//If we decoded an instruction this "tick", record information about it.
if(curStaticInst)
{
#if TRACING_ON
traceData = tracer->getInstRecord(curTick(), tc,
curStaticInst, thread->pcState(), curMacroStaticInst);
DPRINTF(Decode,"Decode: Decoded %s instruction: 0x%x\n",
curStaticInst->getName(), curStaticInst->machInst);
#endif // TRACING_ON
}
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