Re: [Qemu-devel] [PATCH] tests: set MALLOC_PERTURB_ to expose memory bugs

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, May 17, 2013 at 11:54:12AM +0200, Markus Armbruster wrote:
> Stefan Hajnoczi <stefanha@redhat.com> writes:
> 
> > glibc wipes malloc(3) memory when the MALLOC_PERTURB_ environment
> > variable is set.  The value of the environment variable determines the
> > bit pattern used to wipe memory.  For more information, see
> > http://udrepper.livejournal.com/11429.html.
> >
> > Set MALLOC_PERTURB_ for gtester and qemu-iotests.  Note we always set
> > the environment variable to 1 so the test is deterministic.  Setting a
> > random variable might expose more bugs but would be harder to reproduce.
> >
> > Both make check and qemu-iotests pass with MALLOC_PERTURB_ enabled.
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> > Lucas noticed KVM autotest failures when enabling MALLOC_PERTURB_.  By enabling
> > it for in-tree test suites we can detect memory management errors earlier.
> >
> >  tests/Makefile           | 4 +++-
> >  tests/qemu-iotests/check | 2 +-
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/tests/Makefile b/tests/Makefile
> > index a307d5a..25f6d28 100644
> > --- a/tests/Makefile
> > +++ b/tests/Makefile
> > @@ -171,6 +171,7 @@ GCOV_OPTIONS = -n $(if $(V),-f,)
> >  $(patsubst %, check-qtest-%, $(QTEST_TARGETS)): check-qtest-%: $(check-qtest-y)
> >  	$(if $(CONFIG_GCOV),@rm -f *.gcda */*.gcda */*/*.gcda */*/*/*.gcda,)
> >  	$(call quiet-command,QTEST_QEMU_BINARY=$*-softmmu/qemu-system-$* \
> > +		MALLOC_PERTURB_=1 \
> >  		gtester $(GTESTER_OPTIONS) -m=$(SPEED) $(check-qtest-$*-y),"GTESTER $@")
> >  	$(if $(CONFIG_GCOV),@for f in $(gcov-files-$*-y); do \
> >  	  echo Gcov report for $$f:;\
> 
> If you want punishment, why not go for extra punishment?
> 
> MALLOC_PERTURB_=$(($RANDOM % 255 + 1))

That could lead to non-reproducable failures though. I think it is better
to use a fixed value so that you're more likely to be able to reproduce
the issue every time you run the tests.

Rather than setting MALLOC_PERTURB_=1 unconditionally in the Makefile
though, it ought to honour any existing MALLOC_PERTURB_ env variable
the user has set. That could let automated test harness run repeatedly
with random MALLOC_PERTURB_, while still giving a deterministic value
for developers by default.


Daniel
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