Re: Minor fix for H8 simulator

[Jeff Law via Gdb-patches <gdb-patches@sourceware.org>]

On 11/11/2021 10:55 AM, Mike Frysinger wrote:
> On 11 Nov 2021 09:50, Jeff Law via Gdb-patches wrote:
>> The upstream GCC tester has  showed spurious execution failures on the
>> H8 target for the H8/SX multilibs. I suspected memory corruption or an
>> uninitialized variable early as the same binary would sometimes work and
>> sometimes it got the wrong result. Worse yet, the point where the test
>> determined it was getting the wrong result would change.
>>
>> Because it only happened on the H8/SX variant I was able to zero in on
>> the "mova" support and the "short form" of those instructions in particular.
>>
>> As the code stands it checks if code->op3.type == 0 to try and identify
>> cases where op3 wasn't filled in and thus we've got the short form of
>> the mova instruction.
>>
>> But for the short-form of those instructions we never set any of the
>> "op3" data structure. We get whatever was lying around -- it's usually
>> zero and thus things usually work, but if the stale data was nonzero,
>> then we'd fail to recognize the instruction as a short-form and fail to
>> set up the various fields appropriately.
>>
>> I initially initialized the op3.type field to zero, but didn't like that
>> because it was inconsistent with how other operands were initialized.
>> Bringing consistency meant using -1 as the initializer value and
>> adjusting the check for short form mova appropriately.
>>
>> I've had this in the upstream GCC tester for perhaps a year at this
>> point and haven't seen any of the intermittent failures again.
> can you update the unittests too ?
IIRC it was dependent upon what instructions had recently executed as 
those impacted the state of code->op3.type -- my analysis is from over a 
year ago and had been sitting in my todo box for a while.  Even just 
reproducing was fairly painful.

>
> and while we have your eyes on H8, can you perhaps peek at the open reports ?
> https://sourceware.org/bugzilla/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&component=sim&&short_desc=h8300&short_desc_type=allwordssubstr
I can take a look at them as I'm familiar with the H8/S and earlier 
ISAs.  I've got virtually no experience with the SX variants.

Jeff