Thanks Gabe. Good catch about the actual value -- I just saw a negative number and assumed -1, whoops. Based on what Nirmit is seeing, it seems like HINT_NOP or MOV_R_I must be the instruction causing the fault, but yeah a backtrace will probably help confirm.
Nirmit, can you please try running stable with a debug build (to get a backtrace) and develop with a release build and let us know what you see? Matt On Wed, Dec 1, 2021 at 10:47 PM Gabe Black <gabe.bl...@gmail.com> wrote: > I realize this is probably a hard question to answer with Exec being > broken, but do you know what instruction is causing the problem? HINT_NOP? > Probably the first thing that someone should do (if they haven't already) > is to run this under gdb and see what the backtrace looks like, since that > would give us a lot more info to work with. > > Looking at the info we have here, I see that the return from classValue() > is -854770912 (not -1?) which to me looks like junk. I think probably > what's happening is that the RegId being passed to the instruction's > printReg function is from a bad pointer of some sort which is why it > doesn't know how to print the register name. The RegId in this case refers > to a particular register/operand, not the instruction as a whole. For > instance, when the previous instruction prints out eax, that would be a > RegId with classValue() (member regClass) set to IntRegClass, and regIdx > set to INTREG_RAX. > > This works a little differently now and is in the process of being > significantly reworked, although the gist is largely the same, particularly > in the details involved here. The RegId structure tells you what type of > register you're dealing with, aka its class, and also which particular > register within that space you're referring to. The printReg method is > trying to figure out what the name of that register is so it can be printed > as part of the disassembly. > > I think the real bug is going to be that the RegId itself is bogus, and so > when it's operated on, it's random junk will lead to random behavior or > errors. It could be, for instance, that the instruction is trying to print > a register name in its disassembly, but it doesn't actually *have* a > register value set up in that slot and so is using uninitialized values. > Typically the instructions would try to print out, say, destination > register 0 when forming the disassembly string. Alternatively, O3 could > have done something whacky and could be trying to do something with a > nonsense instruction. I would personally lean towards the first option, but > without more info it's hard to tell. > > I would also suggest trying this with develop. I don't think that's a > *solution* to the problem, but it would possibly help isolate a cause. Like > I said, how things work in develop are a little bit different, so we might > get more info by also seeing what happens in those slightly different > circumstances. > > Gabe > > On Wed, Dec 1, 2021 at 8:30 PM Matt Sinclair <mattdsinclair.w...@gmail.com> > wrote: > >> Hi Gabe, >> >> I was trying to dig through the RegClass code earlier to figure out why >> the value is -1 for this instruction, and the only thing that I can think >> of is HINT_NOP needs a RegClass value set for it, but it isn't set for some >> reason (which is not 100% clear to me). You know this code much better >> than I do though, hence I was hoping you might see something I'm not seeing. >> >> Since this error is happening on a clean checkout of gem5 on stable, it >> seems like a bug that anyone could face if they use the Exec debug flag. >> >> Thanks, >> Matt >> >> ---------- Forwarded message --------- >> From: Nirmit Jallawar via gem5-users <gem5-users@gem5.org> >> Date: Wed, Dec 1, 2021 at 10:25 PM >> Subject: [gem5-users] Unrecognized register class when using the "Exec" >> debug flag >> To: gem5-users@gem5.org <gem5-users@gem5.org> >> Cc: Nirmit Jallawar <jalla...@wisc.edu> >> >> >> Hi all, >> >> >> >> I was trying to run a gem5 simulation using the O3CPU but encountered >> problems with gem5 “panic” when running with the “Exec” debug flags >> enabled. I have built gem5 for the x86 ISA, and am using the stable branch. >> >> The full log can be found in the zip linked below (crash_debug_log). >> >> The error in the log seems to be related to this: >> >> build/X86/arch/x86/insts/static_inst.cc:253: panic: Unrecognized register >> class. >> >> >> >> On further debugging, it seems that the register class value is being set >> to -1: >> >> …. >> >> 7335000: system.cpu: T0 : 0x7ffff801bbdd @_end+140737354234813. 2 : >> CALL_NEAR_I : stis t7, SS:[rsp + 0xfffffffffffffff8] : MemWrite : >> D=0x00007ffff801bbe2 A=0x7fffffffed48 >> >> 7335000: system.cpu: T0 : 0x7ffff801bbdd @_end+140737354234813. 3 : >> CALL_NEAR_I : subi rsp, rsp, 0x8 : IntAlu : D=0x00007fffffffed48 >> >> 7335000: system.cpu: T0 : 0x7ffff801bbdd @_end+140737354234813. 4 : >> CALL_NEAR_I : wrip t7, t1 : IntAlu : >> >> 7447000: system.cpu: T0 : 0x7ffff801d080 @_end+140737354240096 : hint >> >> 7447000: system.cpu: T0 : 0x7ffff801d080 @_end+140737354240096. 0 : >> HINT_NOP : fault NoFault : No_OpClass : >> >> 7447000: system.cpu: T0 : 0x7ffff801d084 @_end+140737354240100 : mov >> eax, 0xc >> >> 7447000: system.cpu: T0 : 0x7ffff801d084 @_end+140737354240100. 0 : >> MOV_R_I : limm eax, 0xc : IntAlu : D=0x000000000000000c >> >> build/X86/arch/x86/insts/static_inst.cc:254: panic: Unknown register >> class: -854770912 (reg.classValue()) >> >> Memory Usage: 632228 KBytes >> >> Program aborted at tick 7455000 >> >> --- BEGIN LIBC BACKTRACE --- >> >> …. >> >> The error does not appear when using no debug flags or using flags like >> 'IEW'. >> >> The command used to run the simulation is: >> >> ../build/X86/gem5.opt --debug-flags=Exec DAXPY-newCPU.py daxpy --cpu O3CPU >> >> If needed, you can find the related files here: >> https://drive.google.com/file/d/1Sxg-c9Gy0NU2r3_nd88A_le18C5RkuR_/view?usp=sharing >> >> I would appreciate any help on this. >> >> >> >> Best, >> >> Nirmit >> >> >> >> >> >> >> _______________________________________________ >> gem5-users mailing list -- gem5-users@gem5.org >> To unsubscribe send an email to gem5-users-le...@gem5.org >> %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s >> >
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