Hi!
After several days of debugging I would be grateful for a hint from one of
the experts, otherwise I have run out of ideas.
The situation:
My kernel is loaded with a custom bootloader, Michael van Elst's gobsd,
adapted for ELF and PPC by me and Gunther Nikl. The PPC's BATs and SRs may
be in undefined state. MSR is PSL_IP and HID0 is zero, when the bootloader
copies the kernel to its target address (0x08000000 in this case). It will
also flush the data- and instruction-cache for the kernel area, although the
caches should be off. Then jumps into locore.S (with rfi from reset vector).
locore.S clears the BATs and SRs, disables all interrupts and DMA,
calculates startsym/endsym and calls initppc() and main(). The usual
procedure. Caches will be invalidated and enabled before calling main().
Unfortunately the kernel sometimes hangs during initppc(). Often in
ksyms_init() or pmap_bootstrap(), but other locations were also observed. It
nearly hangs everytime when using kernel-symbols, but also rarely without.
I dumped all registers and important variables (like startsym, endsym,
endkernel, etc.) to memory for postmortem analysis, and everything looks
fine.
Frustrating is, that inserting debugging code sometimes moves the crash
location, or lets the kernel boot normally. And as the crashes are usually
before main(), I have no console, which doesn't make it easy.
I'm running with an adapted trap_subr.S, which works with exception vectors
at 0xfff00000 (PSL_IP). And I'm setting three IBATs and three DBATs at the
beginning of initppc() for128M at 0x08000000 (RAM), 512k at 0xfff00000
(exception area) and 16M at 0x00000000 (slow Amiga "Chip-RAM" for DMA and
memory-mapped I/O region). This is a 604e system.
As I'm quite new to kernel programming, do you have any ideas where I could
look for? Does this behaviour remind you on something you experienced
yourself?
Grateful for any hints...