Newer Xen versions (at least 4.2) clear cpu_online_map during crash. In this case it is not possible to check which CPUs were available. cpu_present_map contains such information but it has different meaning. However, we do not have a choice and we must use cpu_present_map instead of cpu_online_map. Signed-off-by: Daniel Kiper <daniel.kiper(a)oracle.com&gt; diff -Npru crash-6.1.0.orig/xen_hyper.c crash-6.1.0/xen_hyper.c --- crash-6.1.0.orig/xen_hyper.c 2012-11-13 15:08:41.000000000 +0100 +++ crash-6.1.0/xen_hyper.c 2012-11-13 15:09:03.000000000 +0100 @@ -1912,11 +1912,10 @@ xen_hyper_get_cpu_info(void) if((xht->cpumask = malloc(XEN_HYPER_SIZE(cpumask_t))) == NULL) { error(FATAL, "cannot malloc cpumask space.\n"); } - /* kakuma: It may be better to use cpu_present_map. */ - addr = symbol_value("cpu_online_map"); + addr = symbol_value("cpu_present_map"); if (!readmem(addr, KVADDR, xht->cpumask, - XEN_HYPER_SIZE(cpumask_t), "cpu_online_map", RETURN_ON_ERROR)) { - error(FATAL, "cannot read cpu_online_map.\n"); + XEN_HYPER_SIZE(cpumask_t), "cpu_present_map", RETURN_ON_ERROR)) { + error(FATAL, "cannot read cpu_present_map.\n"); } if (xht->cpu_idxs) { free(xht->cpu_idxs);