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1=================2PA-RISC Debugging3=================4 5okay, here are some hints for debugging the lower-level parts of6linux/parisc.7 8 91. Absolute addresses10=====================11 12A lot of the assembly code currently runs in real mode, which means13absolute addresses are used instead of virtual addresses as in the14rest of the kernel. To translate an absolute address to a virtual15address you can lookup in System.map, add __PAGE_OFFSET (0x1000000016currently).17 18 192. HPMCs20========21 22When real-mode code tries to access non-existent memory, you'll get23an HPMC instead of a kernel oops. To debug an HPMC, try to find24the System Responder/Requestor addresses. The System Requestor25address should match (one of the) processor HPAs (high addresses in26the I/O range); the System Responder address is the address real-mode27code tried to access.28 29Typical values for the System Responder address are addresses larger30than __PAGE_OFFSET (0x10000000) which mean a virtual address didn't31get translated to a physical address before real-mode code tried to32access it.33 34 353. Q bit fun36============37 38Certain, very critical code has to clear the Q bit in the PSW. What39happens when the Q bit is cleared is the CPU does not update the40registers interruption handlers read to find out where the machine41was interrupted - so if you get an interruption between the instruction42that clears the Q bit and the RFI that sets it again you don't know43where exactly it happened. If you're lucky the IAOQ will point to the44instruction that cleared the Q bit, if you're not it points anywhere45at all. Usually Q bit problems will show themselves in unexplainable46system hangs or running off the end of physical memory.47