Re: [Qemu-devel] Reporting Heisenbugs in qemu

[Aurelien Jarno <aurelien@aurel32.net>]

On Tue, May 07, 2013 at 01:38:57PM +0200, Torbjorn Granlund wrote:
> 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?
> 

Which version of QEMU are you using? This looks like a bug that has
appeared in version 1.3.0 and fixed in version 1.4.1. The corresponding
commit in master is 52ae646d4a3ebdcdcc973492c6a56f2c49b6578f

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net