[OpenBIOS] Solaris 8 - fun with CPUs :)

[Mark Cave-Ayland]

On 08/04/11 11:08, Mark Cave-Ayland wrote:

> Talking of kadb, if I try and invoke it at the moment, I get this:
>
> Configuration device id QEMU version 1 machine id 32
> CPUs: 1 x FMI,MB86904
> UUID: 00000000-0000-0000-0000-000000000000
> Welcome to OpenBIOS v1.0 built on Apr 5 2011 08:40
> Type 'help' for detailed information
>
> 0 > boot cdrom:d kadb -kdv Not a bootable ELF image
> Loading a.out image...
> Loaded 7680 bytes
> entry point is 0x4000
> bootpath: /iommu/sbus/espdma/esp/sd at 2,0:d
>
> Jumping to entry point 00004000 for type 00000005...
> switching to new context:
> Size: 119204+222573+28987 Bytes
> kadb:
> kadb: kernel/unix
> Size: 259040+54154+47486 Bytes
> /platform/SUNW,SPARCstation-5/kernel/unix loaded - 0x95000 bytes used
> kadb[0]: :c
> Begin traceback... sp = 12f9e0
> Called from fbd01700, fp=12fa50, args=9 f0086444 f0086438 0 f0258f2c 0
> Called from f00859e0, fp=12fad8, args=f0258fc0 44 12fbf8 0 f0258f2c
> f0258f70
> Called from f0082518, fp=12fb38, args=f0258fc0 0 44 0 0 fbd039e4
> Called from f0081c48, fp=12fb98, args=12fbf8 f0258de8 12fbf8 fbd58800
> f0040000 f0240000
> Called from f00819c0, fp=12fff8, args=130168 f0258f70 f0258ed8 f0258ed0
> 2 130168
> Called from f007ff0c, fp=130058, args=f0258c00 f0258c00 fbd54860 130168
> f0258d08 f
> End traceback...
> fault and calling cmd: trap 9 sp 12f9e0 pc f0086444 npc f0086438
> stopped at:
> kadb[0]:
>
>
> I think trap #9 is "data access error" but it only occurs when booting
> the kernel with kadb. Looks like this will need a bit more investigation.

As an aside, I managed to spend a few hours over the weekend trying to 
work out why kadb doesn't want to start the kernel. Fortunately enough, 
kadb is non-stripped which always makes debugging these kinds of things 
easier :)

It was fairly easy to isolate the call to obp_dumb_memalloc() for the 
region of memory in question, so I started tracing through the parent 
function, readfile, in kadb. Stepping through the code here showed a 
very interesting section whereby additional memory is added to the 
amount to be allocated for the kernel (and possibly modules) depending 
upon whether the variable use_align is set.

A quick watchpoint later showed that this is in fact controlled by the 
presence of a zero-length attribute called "aligned-allocator" under 
/openprom. Since this property appears in the sample prtconf output, 
then it suggests that this code path is triggered by OBP. Rather 
bizarrely, if I add this property to OpenBIOS then kadb crashes further 
down the line - BUT if I simply use gdb to make kadb think the property 
is present by changing the relevant register within gdb then I am able 
to load kadb?!

I think I'm probably about 90% there when it comes to getting kadb up 
and running under OpenBIOS, but I still need to figure out why just 
adding the missing property isn't enough here.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: +44 870 608 0063

Sirius Labs: http://www.siriusit.co.uk/labs