10.1-STABLE kern.vty=vt crashes PowerMac G5 extremely early in boot for 2560x1440 display...

[Mark Millard]

Basic context:

$ freebsd-version -ku; uname -a
10.1-STABLE
10.1-STABLE
FreeBSD FBSDG5S0 10.1-STABLE FreeBSD 10.1-STABLE #0 r279507M: Fri Mar  6 23:08:59 PST 2015     root at FBSDG5S0:/usr/obj/usr/src/sys/GENERIC64vtsc  powerpc


The crash details (X11 is not part of the context, just console use):

I tried using a 2560x1440 display with a PowerMac G5 but forgot to switch from kern.vty=vt to kern.vty=sc in /boot/loader.conf first.

But the result was new since the last time I'd done such a thing (long ago)...

It crashed so early that it returned to Apple's OpenFirmware.

That allowed me to use .registers in OpenFirmware to find where it had crashed at.

It turned out that the Interrupt Vector was 0x700 and SRR0 was 0x380. (Openfirmare does not put an exception handler at 0x380 (leaving zeros) so a 0x380 exception handler's attempted use leads to a double fault when OpenFirmware's handlers are all that are in place, the 2nd of the pair going to the 0x700 exception handler.)

Luckily LR is preserved in this sequence and it ended up pointing to:

vtbuf_init_early+0x78 (0x40787c was the address for the build)

and that was the instruction after a bl to .vtbuf_fill.

This was fully repeatable.


As conformation of the size dependency: Switching to a smaller display booted fine (again fully repeatable).


I'll note that kern.vty=sc handles the 2560x1440 display fine for that same PowerMac G5. sc uses most but not all of the width and it uses all of the height.


Other context details:

$ cd /usr/src
$ svnlite info
Path: .
Working Copy Root Path: /usr/src
URL: https://svn0.us-west.freebsd.org/base/stable/10
Relative URL: ^/stable/10
Repository Root: https://svn0.us-west.freebsd.org/base
Repository UUID: ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Revision: 279507
Node Kind: directory
Schedule: normal
Last Changed Author: ngie
Last Changed Rev: 279507
Last Changed Date: 2015-03-01 14:12:24 -0800 (Sun, 01 Mar 2015)

$ svnlite st --no-ignore
?       .snap
?       restoresymtable
M       sys/ddb/db_main.c
M       sys/ddb/db_script.c
I       sys/powerpc/conf/GENERIC64vtsc
I       sys/powerpc/conf/GENERICvtsc
M       sys/powerpc/ofw/ofw_machdep.c
M       sys/powerpc/ofw/ofwcall64.S
M       sys/powerpc/powerpc/dump_machdep.c

sys/powerpc/ofw/ofw_machdep.c has a PowerMac G5 specific change to avoid intermittent boot problems.

sys/ddb/... and sys/powerpc/ofw/ofwcall64.S are just to help me get evidence if I do end up with another early-boot failure. DDB and GDB are listed in sys/powerpc/conf/GENERIC64vtsc for the same reason.

sys/powerpc/powerpc/dump_machdep.c is from me forcing the DMA transfer size for dumps to be small enough not to be rejected as too large of a DMA request size.

sys/powerpc/conf/GENERIC64vtsc turns off ps3 in order to turn on both vt and sc. It includes the standard GENERIC64.

# more /etc/make.conf
#CPP=clang-cpp
#CC=clang
#CXX=clang++
WRKDIRPREFIX=/usr/obj/portswork
WITH_DEBUG=
MALLOC_PRODUCTION=

# more /etc/src.conf
#CPP=clang-cpp
#CC=clang
#CXX=clang++
#CFLAGS+=-DELF_VERBOSE
#WITH_DEBUG_FILES=
#WITHOUT_CLANG

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