Re: [Qemu-devel] [PATCH v2] tests: set MALLOC_PERTURB_ to expose memory bugs

[Eric Blake]

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).

> @@ -180,7 +181,9 @@ $(patsubst %, check-qtest-%, $(QTEST_TARGETS)): 
> check-qtest-%: $(check-qtest-y)
>  .PHONY: $(patsubst %, check-%, $(check-unit-y))
>  $(patsubst %, check-%, $(check-unit-y)): check-%: %
>       $(if $(CONFIG_GCOV),@rm -f *.gcda */*.gcda */*/*.gcda */*/*/*.gcda,)
> -     $(call quiet-command,gtester $(GTESTER_OPTIONS) -m=$(SPEED) $*,"GTESTER 
> $*")
> +     $(call quiet-command, \
> +             MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(($RANDOM % 255 + 1))} \

More missing $$, and a case where RANDOM is better than $RANDOM for dash.

> +             gtester $(GTESTER_OPTIONS) -m=$(SPEED) $*,"GTESTER $*")
>       $(if $(CONFIG_GCOV),@for f in $(gcov-files-$(subst tests/,,$*)-y); do \
>         echo Gcov report for $$f:;\
>         $(GCOV) $(GCOV_OPTIONS) $$f -o `dirname $$f`; \
> diff --git a/tests/qemu-iotests/check b/tests/qemu-iotests/check
> index 432732c..74628ae 100755
> --- a/tests/qemu-iotests/check
> +++ b/tests/qemu-iotests/check
> @@ -214,7 +214,8 @@ do
>       start=`_wallclock`
>       $timestamp && echo -n " ["`date "+%T"`"]"
>       [ ! -x $seq ] && chmod u+x $seq # ensure we can run it
> -     ./$seq >$tmp.out 2>&1
> +     MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(($RANDOM % 255 + 1))} \
> +             ./$seq >$tmp.out 2>&1

THIS file requires /bin/bash, so using a bashism here is just fine.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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