Hi Eliot, Unfortunately, I don't have a direct answer for you. However, I want to say that I appreciate you keeping the mailing list updated with your progress!
Cheers, Jason On Fri, Jan 6, 2023 at 10:07 AM Eliot Moss via gem5-users < gem5-users@gem5.org> wrote: > On 1/4/2023 11:51 PM, Eliot Moss via gem5-users wrote: > > So, what I have found is that the bad micro-op is coming from trying to > execute the micro-ops of an > > INT3 macro-instruction. The end of the sequence consists of the > micro-ops: > > > > andi t0, t5, 0x1 > > br 0x803d > > br 0x80b8 > > > > followed by a bunch of "panic" micro-ops. t5 holds an m5 register, > > where the low bit supposedly indicated whether we are in long mode. > > > > The br micro-ops branch into long sequences of micro-ops in the "ROM". > > I have found out some more things about this issue. > > - The macro instruction is INT_I (my mistake in saying INT3), but the > micro-ops are almost exactly the same. > > - My original though about a load instruction *is* connected somehow. > Here's > the big-picture sequence of events: > > 1) A garden flavor load from memory (mov reg <- offset(reg)) gets stuck > at > the head of the ROB. It was originally deferred because a page table > walk > was necessary to resolve the virtual address of the load. > > 2) The ROB fills (all 192) entries. > > 3) The panic happens. > > > So I tried adjusting the size of the ROB, just to see what would happen. > When > I increased it from 192 to 500, a panic still happened. I guess that if an > instruction remains stuck at the head of the ROB forever, the ROB fills and > then somehow causes the panic. > > When I *decreased* the ROB size from 192 to 64, the program worked. > > I am inclined to infer that there is (was) a bug in the O3 interactions > that > would make the load micro-op fully ready and not stuck at the head of the > ROB. > > What I wonder is whether any similar ROB lock-up behavior has been found > and > fixed since 21.0.0.0. There have been a lot of textual changes, but many > had > to do with names and such and did not really change what the code *does*. > I > am hoping someone out there can confirm one way or another whether this may > have been found and fixed already if I can manage to move the rest of my > changes forward to a newer release. > > Best - Eliot > _______________________________________________ > gem5-users mailing list -- gem5-users@gem5.org > To unsubscribe send an email to gem5-users-le...@gem5.org >
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