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

From: Lucas Meneghel Rodrigues
Subject: Re: [Qemu-devel] [PATCH] tests: set MALLOC_PERTURB_ to expose memory bugs
Date: Fri, 17 May 2013 09:52:18 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4

On 17/05/13 07:58 AM, Markus Armbruster wrote:
"Daniel P. Berrange" <address@hidden> writes:

On Fri, May 17, 2013 at 11:54:12AM +0200, Markus Armbruster wrote:
Stefan Hajnoczi <address@hidden> 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

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 <address@hidden>
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-%: 
        $(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.

A fixed value misses failures.

A random value is just as reproducible as a fixed one, simply use the
same value.  Requires the value to be logged, of course.

That's a pretty great idea, Markus. I'm going to implement it in virt-test, thanks!

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