1 okay, here are some hints for debugging the lower-level parts of
2 linux/parisc.
3
4
5 1. Absolute addresses
6
7 A lot of the assembly code currently runs in real mode, which means
8 absolute addresses are used instead of virtual addresses as in the
9 rest of the kernel. To translate an absolute address to a virtual
10 address you can lookup in System.map, add __PAGE_OFFSET (0x10000000
11 currently).
12
13
14 2. HPMCs
15
16 When real-mode code tries to access non-existent memory, you'll get
17 an HPMC instead of a kernel oops. To debug an HPMC, try to find
18 the System Responder/Requestor addresses. The System Requestor
19 address should match (one of the) processor HPAs (high addresses in
20 the I/O range); the System Responder address is the address real-mode
21 code tried to access.
22
23 Typical values for the System Responder address are addresses larger
24 than __PAGE_OFFSET (0x10000000) which mean a virtual address didn't
25 get translated to a physical address before real-mode code tried to
26 access it.
27
28
29 3. Q bit fun
30
31 Certain, very critical code has to clear the Q bit in the PSW. What
32 happens when the Q bit is cleared is the CPU does not update the
33 registers interruption handlers read to find out where the machine
34 was interrupted - so if you get an interruption between the instruction
35 that clears the Q bit and the RFI that sets it again you don't know
36 where exactly it happened. If you're lucky the IAOQ will point to the
37 instrucion that cleared the Q bit, if you're not it points anywhere
38 at all. Usually Q bit problems will show themselves in unexplainable
39 system hangs or running off the end of physical memory.
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