This could be either a Linux kernel or a Intel CPU errata, I'm not sure which. I have a box with two Xeon E5520 processors (Nehalem) running on an Intel S5520SC motherboard. I am trying to build the ATLAS BLAS library for this arch [http://math-atlas.sourceforge.net]. Running the configure statement shown below, and then "make", will crash the machine after a minute or two. The syslog shows the following message preceding the crash: # cat syslog | grep xprobe Jul 16 16:34:20 colossus kernel: [ 1358.179835] xprobe_gas_x863[11460]: segfault at d729778c ip 00000000004006b0 sp 00007fffd7297788 error 4 in xprobe_gas_x8632[400000+1000] Jul 16 16:34:20 colossus kernel: [ 1358.720744] xprobe_3dnow[11557] trap invalid opcode ip:40090a sp:7fff272686e8 error:0 in xprobe_3dnow[400000+1000] It appears that ATLAS is running a CPU check for 3dnow which causes the Xeon to die. This happens when building ATLAS 3.8.8 (stable) or 3.9.11 (unstable). I've tried both CentOS 5.3 [2.6.18-128.1.16] and Ubuntu Jaunty [2.6.28-13-generic] in 64-bit mode for my OS, with similar results. This error is *NOT* a thermal issue, as I have run both Distributed.net, John the Ripper, and cpuburn on all cores for days with no hiccups. ATLAS will consistently crash the machine within a minute or two. It is also *NOT* a memory issue, I have run memtest86+ on the box for two days with nary a burp. Please let me know if there is any other information I can offer. Atlas build options: ../configure -b 64 -Fa alg -fPIC -Si cputhrchk 0 Motherboard: Product Name: S5520SC Version: FRU Ver 0.05 CPU (x 2): Intel(R) Xeon(R) CPU E5520 ID: A5 06 01 00 FF FB EB BF Signature: Type 0, Family 6, Model 26, Stepping 5