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

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, May 17, 2013 at 11:54 AM, Markus Armbruster <armbru@redhat.com> 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))

Covered in the commit description:
"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."

I didn't want to clutter output with "MALLOC_PERTURB_=123" on every
run.  AFAIK we have no log where this can be silently stashed.  I
guess we could write it to a file and add that to .gitignore.

Stefan