debugging.rst (1694B)
1================= 2PA-RISC Debugging 3================= 4 5okay, here are some hints for debugging the lower-level parts of 6linux/parisc. 7 8 91. Absolute addresses 10===================== 11 12A lot of the assembly code currently runs in real mode, which means 13absolute addresses are used instead of virtual addresses as in the 14rest of the kernel. To translate an absolute address to a virtual 15address you can lookup in System.map, add __PAGE_OFFSET (0x10000000 16currently). 17 18 192. HPMCs 20======== 21 22When real-mode code tries to access non-existent memory, you'll get 23an HPMC instead of a kernel oops. To debug an HPMC, try to find 24the System Responder/Requestor addresses. The System Requestor 25address should match (one of the) processor HPAs (high addresses in 26the I/O range); the System Responder address is the address real-mode 27code tried to access. 28 29Typical values for the System Responder address are addresses larger 30than __PAGE_OFFSET (0x10000000) which mean a virtual address didn't 31get translated to a physical address before real-mode code tried to 32access it. 33 34 353. Q bit fun 36============ 37 38Certain, very critical code has to clear the Q bit in the PSW. What 39happens when the Q bit is cleared is the CPU does not update the 40registers interruption handlers read to find out where the machine 41was interrupted - so if you get an interruption between the instruction 42that clears the Q bit and the RFI that sets it again you don't know 43where exactly it happened. If you're lucky the IAOQ will point to the 44instruction that cleared the Q bit, if you're not it points anywhere 45at all. Usually Q bit problems will show themselves in unexplainable 46system hangs or running off the end of physical memory.