Bug#726733: av_register_all() segfaults on s390x in some cases (regression, causes FTBFS)

[Moritz Muehlenhoff]

Package: libavformat-dev
Version: 6:9.10-1
Severity: serious
File: /usr/include/libavformat/avformat.h
Hi,
https://buildd.debian.org/status/package.php?p=yorick-av
It used to build fine previously.
After investigation, I can build a minimal example which still fails and only contains a call to av_register_all() and segfaults precisely on this line.
This is in the context of a plug-in which is dlopen'ed from an interpreter (yorick). The plug-in works fine on all other architectures. I also tried calling av_register_all() directly from main() in a C program, it doesn't fail there. There may be something odd happening with the dlopening or the link flags that this requires (-fPIC -shared).

Adding ***@l.d.o to CC.

Thibaut, can you post your minimal test case?

Cheers,
Moritz

[Thibaut Paumard]

Post by Moritz Muehlenhoff

After investigation, I can build a minimal example which still fails and only contains a call to av_register_all() and segfaults precisely on this line.

Thibaut, can you post your minimal test case?
Cheers,
Moritz

Oops, I forgot, thanks for mentioning.

I've attached it to the bug report know, to avoid flooding e-mail addresses:

http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=15;filename=buggy.tgz;att=1;bug=726733

Kind regards, Thibaut.

[Adam D. Barratt]

can you perhaps also provide a backtrace? It seems that there are no
public s390x porter machines where I could get that myself.

***@zelenka:~$ schroot --list | grep s390x
chroot:experimental_s390x-dchroot
chroot:jessie_s390x-dchroot
chroot:sid_s390x-dchroot
chroot:wheezy-backports_s390x-dchroot
chroot:wheezy_s390x-dchroot
source:experimental_s390x-dchroot
source:jessie_s390x-dchroot
source:sid_s390x-dchroot
source:wheezy-backports_s390x-dchroot
source:wheezy_s390x-dchroot

Regards,

Adam

[Thibaut Paumard]

Dear Reinhard,

Hi Thibaut,
can you perhaps also provide a backtrace? It seems that there are no
public s390x porter machines where I could get that myself.

Unfortunately, I can't: gdb seems to be broken on s390x. Reporting bug
as we speak:

(sid_s390x-dchroot)***@zelenka:~/buggy$ gdb --args yorick -i check.i
GNU gdb (GDB) 7.6.1 (Debian 7.6.1-1)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "s390x-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/lib/yorick/bin/yorick...Reading symbols from
/usr/lib/debug/usr/lib/yorick/bin/yorick...done.
done.
(gdb) r
Starting program: /usr/bin/yorick -i check.i
Couldn't write registers: Invalid argument.
(gdb)

Also, I wonder why s390x would require -DPIC -fPIC in compilation
flags, but s390 would not.

Where did you get that impression? As far as I can tell, the required
flags are -fPIC -shared, on all platforms.

In the meantime, I checked that my minimal example compiles and runs
fine on wheezy s390x. I can't check sid s390 as it has been retired.

Kind regards, Thibaut.