Re: RFC: remove set_fs for m68k

Linus Torvalds
2021-08-23T21:50:12Z

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).

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out-of-date that it's not even funny, and it actually predates all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.

Linus