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Re: slapd-mtread crash on ppc64{,el} in stretch/sid

Hi Ryan,

On Mon, Jul 03, 2017 at 03:39:35PM -0700, Ryan Tandy wrote:
> Hi debian-powerpc,
> Would a ppc64(el) porter be able to help me look at #866122? I have
> requested a porterbox account but it's not gone through yet, and I am unable
> to reproduce the issue at all in a qemu VM.

You can also request a VM on the minicloud at
http://openpower.ic.unicamp.br/minicloud/ if you wish. They are usually
quick on creating accounts.

> The openldap test suite is failing on ppc64 and ppc64el in stretch and
> unstable: the slapd-mtread helper program segfaults (exit 139) in a certain
> test case.
> It looks like the builds tend to succeed on jessie's kernel and fail on
> stretch's kernel:

In fact, this problem seems to reproduce once in a while, thus, I would
not trust that it might be related to the kernel/gcc combination at this
very beginning. I am suspecting that it might be related to the amount
of threads created and the order, but I do not have a conclusion yet.
Still investigating.

>  apt-get build-dep openldap
>  apt-get source openldap
>  cd openldap-*/
>  DEB_BUILD_OPTIONS=nocheck dpkg-buildpackage -T build
>  cd debian/build/tests
>  ./run -b bdb test060-mt-hot

Nice. I was able to reproduce it and debug it further. The problem seems
to be related to a invalid branch/jump, the the next address is not
memory mapped, thus the segfault. The new address is completely random,
and definitely is wrong. The link register (LR), which is register that
shows the return of the branch (similar to call() on amd64) is always
constant when ALSR is disabled. Other than that, I also saw a stack
corruption, which caused the backtrace to be completely bogus.

Anyway, myself and a colleague are still investigating this problem. I will keep
you informed of the progress of this issue.


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