From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/parisc/debugging | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 Documentation/parisc/debugging (limited to 'Documentation/parisc/debugging') diff --git a/Documentation/parisc/debugging b/Documentation/parisc/debugging new file mode 100644 index 00000000..d7285940 --- /dev/null +++ b/Documentation/parisc/debugging @@ -0,0 +1,39 @@ +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 (0x10000000 +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 (0x10000000) 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. -- cgit v1.2.3