[SeaBIOS] varlow/extrastack vs code

[Laszlo Ersek]

On 01/23/17 16:49, Kevin O'Connor wrote:
> On Mon, Jan 23, 2017 at 11:11:02AM +0100, Laszlo Ersek wrote:
>> On 01/20/17 20:39, Dr. David Alan Gilbert wrote:
>>> * Kevin O'Connor (kevin at koconnor.net) wrote:
>>>> On Fri, Jan 20, 2017 at 06:40:44PM +0000, Dr. David Alan Gilbert wrote:
>>>>> Hi,
>>>>>   I turned the debug level up to 4 on our smaller (128k) ROM downstream
>>>>> build and seem to have hit a case where it's been layed out so that the
>>>>> 'ExtraStack' is at the same location as some code (display_uuid) which
>>>>> was causing some very random behaviour;
> [...]
>> Would this be consistent with a stack overflow?
>>
>> See commit 46b82624c95b951e8825fab117d9352faeae0ec8. Perhaps
>> BUILD_EXTRA_STACK_SIZE (2KB) is too small now?
> 
> The ExtraStack isn't used at the point Dave reports the problem -
> display_uuid() is part of the init phase and that happens on the main
> "post" stack.
> 
> [...]
>> (This is based off 1.9.1)
> 
> I missed that earlier - there were some important fixes post 1.9.1 wrt
> reboots.  Commits b837e68d / a48f602c2 could explain the issue.  I'd
> make sure the issue is still present on the latest version.

That's a very promising hunch -- b837e68d explicitly mentions "reboot
loop" in the subject. It seems that Dave didn't mention any RHBZ numbers
in his email, but we have two somewhat similar bug reports (which I hope
share a root cause) and the second report triggers the issue with a
reboot loop specifically.

https://bugzilla.redhat.com/show_bug.cgi?id=1411275
https://bugzilla.redhat.com/show_bug.cgi?id=1382906

(Apologies that the 2nd RHBZ is not public; it's currently filed for the
RH kernel, and those BZs default to private. :/)

CC'ing DavidH too, for RHBZ#1382906.

Thank you!
Laszlo