Ubuntu
mediascanner2 package

Mediascanner2 test failure on yakkety/{armhf,arm64,ppc64el} with latest dbus-cpp

Bug #1621002 reported by James Henstridge
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
dbus-cpp (Ubuntu)
New
Undecided
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mediascanner2 (Ubuntu)
Fix Released
Undecided
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Bug Description

When trying to build a new mediascanner2 release, tests failed on a number of architectures when building under Yakkety. Some relevant logs:

https://launchpadlibrarian.net/281862518/buildlog_ubuntu-yakkety-armhf.mediascanner2_0.112+16.10.20160831-0ubuntu1_BUILDING.txt.gz
https://launchpadlibrarian.net/282074929/buildlog_ubuntu-yakkety-arm64.mediascanner2_0.112+16.10.20160831-0ubuntu1_BUILDING.txt.gz
https://launchpadlibrarian.net/281862178/buildlog_ubuntu-yakkety-ppc64el.mediascanner2_0.112+16.10.20160831-0ubuntu1_BUILDING.txt.gz

The failure is occurring in code not touched by the changes in the silo, and I suspect that this is related to dbus-cpp or possibly GCC 6.

The segfault doesn't occur on x86, but I was able to reproduce it on my Chromebook. Attached is a stacktrace from the test_dbus test program.

Related branches

lp:~jamesh/mediascanner2/bug-1621002
Michi Henning (community): Approve
unity-api-1-bot: Approve (continuous-integration)
Diff: 37 lines (+13/-2)
2 files modified
debian/rules (+7/-1)
src/ms-dbus/CMakeLists.txt (+6/-1)
Revision history for this message
James Henstridge (jamesh) wrote :
Revision history for this message
James Henstridge (jamesh) wrote :

This is looking like a case of the code being miscompiled under optimisation. To reproduce, build mediascanner2 using the "RelWithDebInfo" build type and then run:

    ./test/test_dbus --gtest_filter=*filter_codec

The test program segfaults when calling Variant::as<std::string>() on a variant that should have been initialised by reading out of a Message::Reader.

When compiling with the "Debug" build type, the test program completes without error.

I can probably solve the immediate problem in mediascanner2 by disabling optimisation for the affected file.

Revision history for this message
Michi Henning (michihenning) wrote :

Good catch!

I've seen this in the past due to uninitialised variables. With optimisation, the compiler gets more aggressive about register re-use, so a bug can manifest under optimisation when the uninitialised variable ends up in a register that had a previous value in it. (In debug mode, the variable often picks up a zero value instead.)

Not sure if there is an easy way to track down whether this is the case or if this is a genuine code generation problem.

Revision history for this message
Michi Henning (michihenning) wrote :

+1!

Revision history for this message
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package mediascanner2 - 0.112+16.10.20160909-0ubuntu1

---------------
mediascanner2 (0.112+16.10.20160909-0ubuntu1) yakkety; urgency=medium

  [ James Henstridge ]
  * When multiple volumes are mounted in quick succession, scan them
    serially to avoid reentrancy problems in the initial scan. (LP:
    #1489656)
  * Add apparmor-easyprof hardware directories to package so AppArmor
    profile can compile when apparmor-easyprof-ubuntu isn't installed.
    (LP: #1443693)
  * Disable optimisation when compiling dbus-codec.cc to avoid gcc 6
    compilation bug. (LP: #1621002)
  * Replace deprecated use of GetConnectionAppArmorSecurityContext
    method with GetConnectionCredentials. (LP: #1489489)

  [ You-Sheng Yang ]
  * Update mediascanner-extractor apparmor profile to cover Android
    library locations on 64-bit systems.

 -- James Henstridge <email address hidden> Fri, 09 Sep 2016 13:46:43 +0000

Changed in mediascanner2 (Ubuntu):
status: New → Fix Released
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