32-bit powerpc FreeBSD address 0x0-0xff content (physical addresses): What is the explanation?

[Mark Millard]

I've been trying to get evidence for periodic/random
panics in the likes of head -r317820 for 32-bit
powerpc FreeBSD used on an old PowerMac G5 so-called
"Quad Core".

One thing that I've noticed that looks odd is
that the vmcore.* files (debug.minidump=0) show
content that looks like the following for
physical address range 0x0..0xff (via a
hacked-to-work-a-little kgdb for physical
address access to such a vmcore.* file):

(kgdb) x/128wx 0x0
0x0:	0x00000000	0x00000000	0x00000000	0x00000000
0x10:	0x00000000	0xffa35e50	0xffa35ee8	0x00000000
0x20:	0x00000000	0x00000000	0x00000000	0x00000000
0x30:	0x00000000	0x00000000	0x00000000	0x00000000
0x40:	0x00000000	0x00000000	0x00000000	0x00000000
0x50:	0x00000000	0x00000000	0x00000000	0x00000000
0x60:	0x00000000	0x00000000	0x00000000	0x00000000
0x70:	0x00000000	0x00000000	0x00000000	0x00000000
0x80:	0x00000090	0x7ff7c080	0x7fc9e7c8	0x00000000
0x90:	0x3c007ff7	0x6000c100	0x7c0903a6	0x4e800421
0xa0:	0x00000000	0x00000000	0x00000000	0x00000000
0xb0:	0x00000000	0x00000000	0x00000000	0x00000000
0xc0:	0x00000000	0x00000000	0x00000000	0x00000000
0xd0:	0x00000000	0x00000000	0x00000000	0x00000000
0xe0:	0x00000000	0x00000000	0x00000000	0x00000000
0xf0:	0x00000000	0x00000000	0x00000000	0x00000000
. . .

Or viewed as instructions when the bit patterns
fit such (with added NOTE's):

(kgdb) x/128i 0x0
0x0:	.long 0x0
0x4:	.long 0x0
0x8:	.long 0x0
0xc:	.long 0x0
0x10:	.long 0x0
0x14:	.long 0xffa35e50
0x18:	.long 0xffa35ee8
0x1c:	.long 0x0
0x20:	.long 0x0
0x24:	.long 0x0
0x28:	.long 0x0
0x2c:	.long 0x0
0x30:	.long 0x0
0x34:	.long 0x0
0x38:	.long 0x0
0x3c:	.long 0x0
0x40:	.long 0x0
0x44:	.long 0x0
0x48:	.long 0x0
0x4c:	.long 0x0
0x50:	.long 0x0
0x54:	.long 0x0
0x58:	.long 0x0
0x5c:	.long 0x0
0x60:	.long 0x0
0x64:	.long 0x0
0x68:	.long 0x0
0x6c:	.long 0x0
0x70:	.long 0x0
0x74:	.long 0x0
0x78:	.long 0x0
0x7c:	.long 0x0
0x80:	.long 0x90
0x84:	.long 0x7ff7c080
0x88:	.long 0x7fc9e7c8
0x8c:	.long 0x0
0x90:	lis     r0,32759     (NOTE: 32759==0x7ff7)
0x94:	ori     r0,r0,49408  (NOTE: 49408==0xC100)
0x98:	mtctr   r0           (NOTE: So ctr==r0==0x7ff7C100)
0x9c:	bctrl                (NOTE: So to 0x7ff7C100 virtual address)
0xa0:	.long 0x0            (NOTE: lr would end up pointing here.)
0xa4:	.long 0x0
0xa8:	.long 0x0
0xac:	.long 0x0
0xb0:	.long 0x0
0xb4:	.long 0x0
0xb8:	.long 0x0
0xbc:	.long 0x0
0xc0:	.long 0x0
0xc4:	.long 0x0
0xc8:	.long 0x0
0xcc:	.long 0x0
0xd0:	.long 0x0
0xd4:	.long 0x0
0xd8:	.long 0x0
0xdc:	.long 0x0
0xe0:	.long 0x0
0xe4:	.long 0x0
0xe8:	.long 0x0
0xec:	.long 0x0
0xf0:	.long 0x0
0xf4:	.long 0x0
0xf8:	.long 0x0
0xfc:	.long 0x0
. . .

Is this deliberate? If yes: What is it for?
(I've not found what writes those bytes.)

I do not make the claim that the above is
tied to the periodic/random panics. It just
seems unusual.


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