[Qemu-devel] Reporting Heisenbugs in qemu

[Torbjorn Granlund <tg@gmplib.org>]

I am trying to use qemu to

1. cover more of the assembly code in GMP
2. check configuration logic of GMP

but I am not as successful as I would like to be.

The 2nd table of http://gmplib.org/devel/testsystems.html shows all
emulated systems I am using, most of which are qemu-based.

Unfortunately, several of the qemu-based systems experience intermittent
but common segfaults:

1. Linux mips64eb 2.6.32-5-5kc-malta #1 Sun Sep 23 12:29:36 UTC 2012 mips64 GNU/Linux
2. Linux mips64el 2.6.32-5-5kc-malta #1 Fri Feb 15 21:38:11 UTC 2013 mips64 GNU/Linux
3. Linux kick.gmplib.org 2.6.18-6-sparc32 #1 Sat Dec 27 09:13:12 UTC 2008 sparc GNU/Linux

An example of a failure is:

gmp/tests/cxx/t-ops2.cc: In function 'void checkz()':
gmp/tests/cxx/t-ops2.cc:86: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
For Debian GNU/Linux specific bug reporting instructions,
see <URL:file:///usr/share/doc/gcc-4.1/README.Bugs>.
The bug is not reproducible, so it is likely a hardware or OS problem.

(This was from the sparc32 system.)

rootrem.c: In function 'mpn_rootrem_internal':
rootrem.c:120:1: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-4.6/README.Bugs> for instructions.
The bug is not reproducible, so it is likely a hardware or OS problem.

(From the mips64eb system.)

I am aware of that these systems don't exactly use the
kernel-of-the-week.  Newer kernels I have tried cause non-boot.  (I
don't think I've tried any newer sparc kernel, as building that would
require a stable sparc system...)

I realise that linux might have been debugged until it works on real
hardware, but that qemu might trigger untested linux execution paths.

Yesterday, I disabled GMP testing on these qemu systems, as I got tired
of the many false alarms, and since GMP looked bad.  Is there any hope
that these qemu systems will become stable?  Or aren't these problems
qemu's fault?

-- 
Torbjörn