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okay, here are some hints for debugging the lower-level parts of

linux/parisc.

1. Absolute addresses

A lot of the assembly code currently runs in real mode, which means

absolute addresses are used instead of virtual addresses as in the

rest of the kernel.  To translate an absolute address to a virtual

address you can lookup in System.map, add __PAGE_OFFSET (0xc0000000

currently).

2. HPMCs

When real-mode code tries to access non-existent memory, you'll get

an HPMC instead of a kernel oops.  To debug an HPMC, try to find

the System Responder/Requestor addresses.  The System Requestor

address should match (one of the) processor HPAs (high addresses in

the I/O range); the System Responder address is the address real-mode

code tried to access.

Typical values for the System Responder address are addresses larger

than __PAGE_OFFSET (0xc0000000) which mean a virtual address didn't

get translated to a physical address before real-mode code tried to

access it.

3. Q bit fun

Certain, very critical code has to clear the Q bit in the PSW.  What

happens when the Q bit is cleared is the CPU does not update the

registers interruption handlers read to find out where the machine

was interrupted - so if you get an interruption between the instruction

that clears the Q bit and the RFI that sets it again you don't know

where exactly it happened.  If you're lucky the IAOQ will point to the

instrucion that cleared the Q bit, if you're not it points anywhere

at all.  Usually Q bit problems will show themselves in unexplainable

system hangs or running off the end of physical memory.