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






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