On Mon, Jul 02, 2012 at 10:04:13AM -0500, W. Michael Petullo wrote:
> >> I am attempting to run Xen on an AMD FX-4170 Quad-Core Processor.
> >> I have installed Fedora 17 to serve as Dom0.
> >> 
> >> I am finding that Python does not run well on this
> >> configuration. Specifically, "import random" causes the Python interpreter
> >> to terminate with "Illegal instruction". This means that xend and yum will
> >> not run.
> >> 
> >> I filed a bug under yum [1], but just realized that things work if I
> >> boot Fedora 17 on bare metal.
> >> 
> >> Under Xen, /proc/cpuinfo reports the following flags:
> >> 
> >> fpu de tsc msr pae cx8 apic cmov pat clflush mmx fxsr sse sse2 ht syscall
> >> nx mmxext fxsr_opt lm constant_tsc rep_good nopl nonstop_tsc extd_apicid
> >> aperfmperf pni pclmulqdq ssse3 cx16 sse4_1 sse4_2 popcnt aes hypervisor
> >> lahf_lm cmp_legacy extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch
> >> xop fma4 perfctr_core arat cpb hw_pstate
> >> 
> >> Has anyone had similar trouble?
>  
> > No. But it sounds like the AVX disaster.
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=801650
> 
> It seems to be.
> 
> I booted bare metal and used yum to install gdb and the debug symbols
> for Python and glibc.
> 
> Then I rebooted in Xen. I found that gdb itself crashed when the debug
> symbols were installed, so I removed them. I ran gdb again and obtained
> a partial backtrace on "import random":
> 
> (gdb) ba
> #0  0x00007ffff71474ec in __ieee754_exp_fma4 () from /lib64/libm.so.6
> #1  0x00007ffff009e415 in ?? () from /usr/lib64/python2.7/lib-dynload/math.so
> #2  0x00007ffff7b00053 in PyEval_EvalFrameEx () from 
> /lib64/libpython2.7.so.1.0
> #3  0x00007ffff7b00b2f in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
> #4  0x00007ffff7b00c02 in PyEval_EvalCode () from /lib64/libpython2.7.so.1.0
> #5  0x00007ffff7b1017d in PyImport_ExecCodeModuleEx () from 
> /lib64/libpython2.7.so.1.0
> [...]
> 
> After looking a little closer, it seems that __ieee754_exp_fma4 is
> executing "vmovsd %xmm0,-0x20(%rsp)".
> 
> I thought booting Xen with xsave=1 might help, but this causes Xen to
> crash on this hardware. As mentioned above, it looks like there has been

Right. That is b/c of Fedora's incorrect extra patch that neuters xsave.

> work in glibc to properly detect AVX (my understanding is that you have
> to check that both the processor and OS supports it). Is it possible
> that this glibc work missed something?

Very likely. There was another fix to it that got added in Debian (or Ubuntu)
that checked for FMA4 on AMD (which had a different CPUID).

Can you open a Red Hat bugzilla please? And CC me on it: ketuzs...@darnok.org

> 
> -- 
> Mike
> 
> :wq
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