PowerMac G5 boot hangups before Copyright notice: "Stopped at 0: illegal instruction 0" [10.1-BETA1 example]

[Mark Millard]

In part I sent directly to you because of a past exchange (July-27) where you had written:

> Nathan and I both speculate that it's
> dropping into Open Firmware (we make extensive use of OFW), and then
> messing something up, taking a page fault or something.

The specific text that I report and its uniformity when it is produced seems to add a little information beyond a speculated "page fault or something" and so might eventually help a little. As I understand the text it is reporting execution reaching address zero without any prior un-handled exceptions or other such that would stop it. A corrupted stack (pointer) so a bad return address or some such? I'd guess there are no explicit jumps to address zero so I expect that indirection is likely involved, with the content for the indirection messed up.

I really wish that I had a logic analyzer configuration for this. I've not found a way to make the failing context visible so far and the extra way of looking at things might have helped.




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Mark Millard
markmi at dsl-only.net

On Sep 16, 2014, at 8:28 PM, Justin Hibbits <chmeeedalf at gmail.com> wrote:

Hi mark,

I see this on my G5, and I think it's due to the amount of RAM in the machine. More than 4gb seems to confuse open firmware when called by FreeBSD. There is some effort to remove the need of the callbacks but thus far it's not far along. The good news is that after it boots it's solid except when switching vtys, buy earlier this year or last year I added a sysctl hack to disable the call into open firmware on vty switch (don't recall offhand and not at my computer right now, but if you grep the sysctl output for reset and ofw you can find it).

-Justin

On Sep 16, 2014 8:01 PM, "Mark Millard" <markmi at dsl-only.net> wrote:
I've now spent time with rebooting and power-off/power-on for all 3 PowerMac G5's (one PowerMac7,2 and two PowerMac11,2's) and all 3 get the

> GDB: no debug ports present
> KDB: debugger backends: DDB
> KDB: current backend: DDB
> [ thread pid -1 tid 1006665719 ]
> Stopped at 0: illegal instruction 0
> db>

when they fail just before the Copyright notice would normally be displayed. None fail any earlier. At that spot none have failed any other way. It is the same SSD in all 3. (Happens with other SSD's as well.) Overall there is a mix of Radeon and NVIDIA display boards. Besides the SSD use and RAM upgrades the rest is stock equipment. scons used, not vt. (I've yet to try vt.)

Seeing a failure after the Copyright notice as been fairly rare in all my experiments from when I started last April or so. The ones that I've noted had Data Storage Interrupt reported. So far no examples of the above have been reported after the Copyright notice. So I'd guess that they are separate issues. Of course it seems that only in the last few days would I have seen the above sort of thing if it did happen after the Copyright notice: The prior history does not count for judgements about that.

===
Mark Millard
markmi at dsl-only.net

On Sep 16, 2014, at 8:15 AM, Mark Millard <markmi at dsl-only.net> wrote:

Using 10.1-BETA1 I added "options DDB" and "options GDB" to powerpc64's GENERIC64. (I also used WITH_DEBUG_FILES=, WITHOUT_CLANG=, and WITH_DEBUG= in /etc/make.conf.) So buildworld, kernel was basically just set up to have more of a debugging context around (including for any ports builds).

The result was new information about the PowerMac G5 boot hangups: The screen is no longer blank when the G5 is hung up without there being a Copyright notice yet. It says...

> GDB: no debug ports present
> KDB: debugger backends: DDB
> KDB: current backend: DDB
> [ thread pid -1 tid 1006665719 ]
> Stopped at 0: illegal instruction 0
> db>

(I had no ability to input at that point.) Normally the Copyright notice would have displayed instead of "[...]" and what follows. (I do not claim to have all the spacing, capitalization, and such correct above.)

That text is constant from hang to hang when it hangs just before it would normally output the Copyright notice: The numbers do not vary, much less the other text. It has never failed until after the two KDB messages are present. So far I've only tested one PowerMac G5, booting over and over for a few hours.



(I do not claim to be set up for remote kernel debugging. I just decided to let GDB go along for the ride when I added DDB.)

===
Mark Millard
markmi at dsl-only.net