Re: RFC: remove set_fs for m68k

[Michael Schmitz <schmitzmic@gmail.com>]

Thanks Linus (and Andreas),


On 24/08/21 09:49, Linus Torvalds wrote:
> On Mon, Aug 23, 2021 at 2:31 PM Michael Schmitz <schmitzmic@gmail.com> wrote:
>> Hi Linus,
>>
>>
>> On 24/08/21 05:59, Linus Torvalds wrote:
>>> On Sun, Aug 22, 2021 at 12:34 PM Michael Schmitz <schmitzmic@gmail.com> wrote:
>>>> Got this overnight:
>>>>
>>>>> [536154.200000] *** FORMAT ERROR ***   FORMAT=0
>>>>> [536154.210000] Current process id is 4656
>>>>> [536154.230000] BAD KERNEL TRAP: 00000000
>>>>> [536154.240000] Modules linked in: atari_scsi ne 8390p [last unloaded: atari_scsi]
>>>>> [536154.260000] PC: [<00002a8c>] resume_userspace+0x14/0x16
>>>>> [536154.270000] SR: 2208  SP: 977bd1be  a2: 8009b5e8
>>>>> [536154.290000] d0: 8009b5e8    d1: cfcfcfcf    d2: 00000000    d3: ffffffff
>>>>> [536154.300000] d4: 00000000    d5: 00000000    a0: 8008a108    a1: 8009b7df
>>>>> [536154.320000] Process savelog (pid: 4656, task=e49aa246)
>>>>> [536154.330000] Frame format=0
>>>>> [536154.340000] Stack from 00cc5fa4:
>>>>> [536154.340000]         02088004 3666b008 1c0eb209 007eb5e8 8006a2d0 efaec378 8004366c 61ff61ff
>>>>> [536154.340000]         8006a2d4 8006a2d2 00000000 030dfffb 0044fffa 0e000000 fffa1a00 fffa1c00
>>>>> [536154.340000]         fffa1e00 fffb0e40 fffb0e80 00049b66 00000040 005f5800 00000001
>>> Strange. If I read that stack frame correctly, that seems to be an
>>> exception frame of type 0xb ("Long Bus Cycle").
>> Not sure where you get the 0xb from - the frame format I see is 0.
> The "Frame format=0" is, afaik, the format of when the error happens.
>
> But I'm looking at what the stack contents are at the time of the
> exception, to see what actually *triggered* the error.
>
> And if I read it right, the RTE that took the format error fault had this stack:
>
>          02088004 3666b008 1c0eb209 ..
>
> and that means that it tried to return with status register 0208
> (which looks correct: supervisor bit clear), to PC 80043666 (which
> might be right - it's a similar address to the ones in A0/A1).
I see - found some information on the 030 exception stack frame format 
online now.

>
> And then the format/vector value is b008.
>
> That is, if I read it right, format 0xb, which is that "Long Bus Cycle" thing.
>
> NOTE! I may be misreading this entirely. My m68k knowledge is so
> out-of-date that it's not even funny, and it actually predates all
> this fancy format stuff. So I'm just pattern-matching with the manuals
> I found online.
I'll take your word for it (especially after Andreas confirmed it :-). 
The information in our show_registers ought to be enough for me to 
decode the various faults of this type I've seen, and spot any patterns.

Cheers,

     Michael