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Re: [Qemu-devel] [PATCH v2] tests: set MALLOC_PERTURB_ to expose memory
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2] tests: set MALLOC_PERTURB_ to expose memory bugs |
Date: |
Tue, 21 May 2013 17:17:15 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, May 21, 2013 at 06:56:07AM -0600, Eric Blake wrote:
> On 05/21/2013 06:43 AM, Stefan Hajnoczi wrote:
> > 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 pick a random
> > value from 1 to 255 to expose more bugs. If you need to reproduce a
> > crash use 'show environment' in gdb to extract the MALLOC_PERTURB_
> > value from a core dump.
> >
> > Both make check and qemu-iotests pass with MALLOC_PERTURB_ enabled.
> >
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> > tests/Makefile | 5 ++++-
> > tests/qemu-iotests/check | 3 ++-
> > 2 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/tests/Makefile b/tests/Makefile
> > index a307d5a..24880c6 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-$* \
> > + MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(($RANDOM % 255 + 1))} \
>
> This is a Makefile; don't you need to use $$ instead of $ (three instances)?
>
> $RANDOM is a bash-ism. If make is run with SHELL as /bin/sh on a
> platform where dash is the primary shell, it will fail:
>
> $ dash -c 'echo $(($RANDOM % 255))'
> dash: 1: arithmetic expression: expecting primary: " % 255"
>
> HOWEVER: you can exploit the fact that inside $(()), you don't need $ to
> use the value of a defined variable, and also the fact that unless set
> -u is in effect, an undefined variable name silently evaluates as 0:
>
> $ dash -c 'echo $((RANDOM % 255))'
> 0
>
> then you could write the shell code:
>
> MALLOC_PERTURB_=${MALLOC_PERTURB_:-$((RANDOM % 255 + 1))}
>
> or the Makefile code:
>
> MALLOC_PERTURB_=$${MALLOC_PERTURB_:-$$((RANDOM % 255 + 1))}
>
> and things will at least work on /bin/sh as dash (even though there will
> be no randomness and you are always testing with 1 in that case).
Silly me. I did test it but it silently "worked".
Will resend.
Stefan