head -r354701 seems to be why/when 32-bit powerpc FreeBSD stopped being able to boot PowerMac G5s (2 socket ones, anyway)

(NOTE: I only have access to 2-socket G5's, so I do not
know the behavior for other kinds. I've access to both
2-cores-each and 1-core-each contexts.)

This analysis is based on installing
artifact.ci.freebsd.org materials and testing
if they boot the G5's or not. Other than
a little /etc/fstab and /boot/loader.conf
material, the artifact materials are unchanged.
My builds are not involved.

-r354702 fails to boot. (Details later, below.)

-r354700 (the closest prior 32-bit powerpc
artifcact) boots fine.


-r354701 and -r354702 are:



Author: bdragon
Date: Thu Nov 14 04:34:17 2019
New Revision: 354701
URL: 
https://svnweb.freebsd.org/changeset/base/354701


Log:
  powerpc: Kernel fixes for ppc32 and powerpcspe w/ lld
  
  Fix wrong section ordering that was causing a ".got is not contiguous with
  other relro sections" lld error. This also brings ldscript.powerpc and
  ldscript.powerpcspe closer to ldscript.powerpc64.
  
  Also, remove unnecessary text relocs from the ppc32 AIM trap code.



Author: mav
Date: Thu Nov 14 04:34:58 2019
New Revision: 354702
URL: 
https://svnweb.freebsd.org/changeset/base/354702


Log:
  Make ntb(4) send bus_get_dma_tag() requests to parent buses passing real
  bus' child pointers instead of grandchilds.
  
  DMAR does not like requests from devices not parented directly by PCI.



At this point I'm guessing -r354701 since it
is powerpc specific.


The following is based on typing from
screen images . . .

Failure style #1:

. . .
Trying to mount root from ufs:/dev/ada0s3 [rw,noatime]...
SMP: 2 CPUs found; 2 CPUs usable; 1 CPUs woken
WARNING: WITNESS option enabled, expect reduced performance.

(And that is all.)

Failure style #2:

. . .
Trying to mount root from ufs:/dev/ada0s3 [rw,noatime]...
SMP: 2 CPUs found; 2 CPUs usable; 1 CPUs woken
WARNING: WITNESS option enabled, expect reduced performance.
[ thread pid 1 tid 100002 ]
Stopped at dsmisssize+0x68c: illegal instruction 0
db> 

(So just 3 more lines showing up.)



NOTE: I do not claim that there are not more
problems later in head's history that fail
even earlier in the boot, thus hiding what is
reported here. There is one that I've not yet
isolated the first artifact version for. Thus,
testing for what I'm reporting here may require
using older vintages of FreeBSD, unless other
problems are dealt with first.


===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)