On Thu, 18 Nov 2004 10:27:49 +0530, Mandeep Sandhu <mandeep_sandhu@xxxxxxxxxxx> wrote: > a basic question. How does the kernel handle NULL pointer > dereferencing inside kernel space. Indeed. Since everyone else jumped on to a fantastic discussion of NULL vs. 0 and other pointerisms but failed to answer your original question concisely, I'll pipe up now. This varies by architecture, but the kernel essentially contains a deliberately bad NULL page which is mapped at zero so that any dereferences to that virtual address will result in a processor exception calling the page_fault_handler, and having an oops error result. It's just a simple case of throwing away a single page to try to handle bad code. > I think on PowerPC 0 is a valid address On some processors, zero is not a valid address, on PowerPC processors which substantially follow the specification then it is valid to have a mapping at that location in virtual memory and zero is certainly a valid physical memory address (as it usually is on most processors Linux supports). So it's valid but deliberately triggers a page fault. Jon. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
