Based on kernel version 4.2. Page generated on 2015-09-09 12:14 EST.
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 instruction 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.