[Crash-utility] [PATCH] netdump, diskdump: address the issue caused by no NT_PRSTATUS notes

Hello Dave, I have three patches today. The 1st and 2nd patches address the issue that vmcore has no NT_PRSTATUS notes. - The 1st patch makes crash consider the case where the number of NT_PRSTATUS notes is 0. Without this patch, crash leads to NULL pointer dereference when using bt command for active tasks. - The 2nd patch makes crash pass boot-time sanity check to nr_cpus memebr of diskdump header on x86 and x86_64 if it is 0. On both architectures, we can get cpu information from memory part. In fact, the value of nr_cpus member is not used except for the sanity check. I saw the situation where vmcore with no NT_PRSTATUS notes is generated, on Xen HVM, where the version of kexec not supporting Xen HVM. It determins if system is Xen Dom0 wrongly and uses interface for Dom0. As a result, vmcore doesn't contain any NT_PRSTATUS note. When converting this vmcore using makedumpfile, nr_cpus member of diskdump header of the resulted vmcore is 0. So the 2nd patch is needed. The 3rd patch is differnet from the above two, fixing potencial bug in panic task detection code, which I found during investigation for the above two patches. But sorry, I didn't test this yet. I made every patch on top of crash version 6.1.0. Thanks. HATAYAMA, Daisuke