Build error on Ubuntu 17.04

added Platform::GNU/Linux Severity::normal Type::bug Version::master git + 1 deleted label

changed milestone to %Bugs paradize

This is due to the mesa driver linking with libmir (or libmir-client, don't remember precisely), which in turns links to protobuf. mesa depending on libmir isn't the case on debian.

The crash can be reproduced with this sample https://hastebin.com/letonoxero.cpp (running it with full path to libmirclient.so as 1st parameter)

It's also what keeps our snapcraft build red.

That being said, I have no idea how to fix it properly. To my knowledge, it's not an issue of incompatible ABIs (for instance using protobuf-lite & protobuf in the same binary), but one might want to double check that statement.

How is that a VLC bug?

Not a VLC bug per-se, but definitely an impediment. And since I can't really figure out the precise root cause, I'm not so keen on closing and leaving ubuntu users to their misery.

It might be worth it to contact the ubuntu packagers

Stupid question: How do I subscribe to notifications for this bug?

Any interaction on this ticket will subscribe you. If you don't want to post a "blank" comment you can add your login in the CC field

https://github.com/google/protobuf/issues/206

Is there any sort of workaround? mv libmirclient.so libmirclient.goaway?

Currently the build fails because vlc-cache-gen segfaults when unloading libegl_wl_plugin.so

The modules depends on

linux-vdso.so.1 =>  (0x00007fff8c8fb000)
libvlccore.so.8 => /vlc/extras/package/snap/parts/vlc/build/src/.libs/libvlccore.so.8 (0x00007f4999d08000)
libEGL.so.1 => /usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1 (0x00007f4999aba000)
libwayland-egl.so.1 => /usr/lib/x86_64-linux-gnu/libwayland-egl.so.1 (0x00007f49998b8000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f49994f1000)
libidn.so.11 => /lib/x86_64-linux-gnu/libidn.so.11 (0x00007f49992be000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f499909e000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f4998e9a000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f4998b91000)
libanl.so.1 => /lib/x86_64-linux-gnu/libanl.so.1 (0x00007f499898d000)
libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007f4998741000)
/lib64/ld-linux-x86-64.so.2 (0x000055dc0cdc0000)
libX11-xcb.so.1 => /usr/lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f499853f000)
libxcb-dri2.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-dri2.so.0 (0x00007f4998338000)
libxcb-dri3.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-dri3.so.0 (0x00007f4998135000)
libxcb-present.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-present.so.0 (0x00007f4997f32000)
libxcb-xfixes.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007f4997d2a000)
libxcb-sync.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007f4997b23000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f4997901000)
libxshmfence.so.1 => /usr/lib/x86_64-linux-gnu/libxshmfence.so.1 (0x00007f49976fc000)
libwayland-client.so.0 => /usr/lib/x86_64-linux-gnu/libwayland-client.so.0 (0x00007f49974ed000)
libwayland-server.so.0 => /usr/lib/x86_64-linux-gnu/libwayland-server.so.0 (0x00007f49972db000)
libgbm.so.1 => /usr/lib/x86_64-linux-gnu/libgbm.so.1 (0x00007f49970ce000)
libmirclient.so.9 => /usr/lib/x86_64-linux-gnu/libmirclient.so.9 (0x00007f4996e26000)
libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f4996bfc000)
libdrm.so.2 => /usr/lib/x86_64-linux-gnu/libdrm.so.2 (0x00007f49969e9000)
libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f4996961000)
libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007f499675d000)
libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f4996557000)
libffi.so.6 => /usr/lib/x86_64-linux-gnu/libffi.so.6 (0x00007f499634f000)
librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f4996145000)
libxkbcommon.so.0 => /usr/lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007f4995f05000)
libmircommon.so.7 => /usr/lib/x86_64-linux-gnu/libmircommon.so.7 (0x00007f4995cbe000)
libmirprotobuf.so.3 => /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3 (0x00007f4995a3d000)
libcapnp-0.5.3.so => /usr/lib/x86_64-linux-gnu/libcapnp-0.5.3.so (0x00007f49957b8000)
libmircore.so.1 => /usr/lib/x86_64-linux-gnu/libmircore.so.1 (0x00007f49955af000)
libboost_system.so.1.62.0 => /usr/lib/x86_64-linux-gnu/libboost_system.so.1.62.0 (0x00007f49953a9000)
libprotobuf-lite.so.10 => /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.10 (0x00007f499515b000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f4994dd3000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f4994bbc000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f4994994000)
liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f499476e000)
liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f4994554000)
libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f4994245000)
libboost_filesystem.so.1.62.0 => /usr/lib/x86_64-linux-gnu/libboost_filesystem.so.1.62.0 (0x00007f499402c000)
libkj-0.5.3.so => /usr/lib/x86_64-linux-gnu/libkj-0.5.3.so (0x00007f4993e05000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f4993b92000)
libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f499397c000)

Crash stacktrace:

(gdb) back
[#0](https://code.videolan.org/videolan/vlc/-/issues/0)  0x00007fff9377ebb0 in  ()
[#1](https://code.videolan.org/videolan/vlc/-/issues/1)  0x00007fffdf7bffab in google::protobuf::ShutdownProtobufLibrary() () at /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.10
[#2](https://code.videolan.org/videolan/vlc/-/issues/2)  0x00007fffe00ae129 in  () at /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
[#3](https://code.videolan.org/videolan/vlc/-/issues/3)  0x00007ffff7ded689 in _dl_close_worker (map=map@entry=0x5555557d14a0, force=force@entry=false) at dl-close.c:286
[#4](https://code.videolan.org/videolan/vlc/-/issues/4)  0x00007ffff7dee47a in _dl_close_worker (force=false, map=0x5555557d14a0) at dl-close.c:125
[#5](https://code.videolan.org/videolan/vlc/-/issues/5)  0x00007ffff7dee47a in _dl_close (_map=0x5555557d14a0) at dl-close.c:840
[#6](https://code.videolan.org/videolan/vlc/-/issues/6)  0x00007ffff7de7874 in _dl_catch_error (objname=0x55555575fa70, errstring=0x55555575fa78, mallocedp=0x55555575fa68, operate=0x7ffff6e85fb0 <dlclose_doit>, args=0x5555557d14a0)
    at dl-error.c:187
[#7](https://code.videolan.org/videolan/vlc/-/issues/7)  0x00007ffff6e86581 in _dlerror_run (operate=operate@entry=0x7ffff6e85fb0 <dlclose_doit>, args=0x5555557d14a0) at dlerror.c:163
[#8](https://code.videolan.org/videolan/vlc/-/issues/8)  0x00007ffff6e85fdf in __dlclose (handle=<optimized out>) at dlclose.c:46
[#9](https://code.videolan.org/videolan/vlc/-/issues/9)  0x00007ffff758f775 in module_Unload (handle=<optimized out>) at posix/plugin.c:86
[#10](https://code.videolan.org/videolan/vlc/-/issues/10) 0x00007ffff750c854 in module_Unmap (plugin=0x5555557dc590) at modules/bank.c:557
[#11](https://code.videolan.org/videolan/vlc/-/issues/11) 0x00007ffff750c854 in module_EndBank (b_plugins=b_plugins@entry=true) at modules/bank.c:643
[#12](https://code.videolan.org/videolan/vlc/-/issues/12) 0x00007ffff74f37d1 in libvlc_InternalCleanup (p_libvlc=0x5555557572c0) at libvlc.c:427
[#13](https://code.videolan.org/videolan/vlc/-/issues/13) 0x00007ffff7bb9ee7 in libvlc_release (p_instance=0x555555757160) at core.c:104
[#14](https://code.videolan.org/videolan/vlc/-/issues/14) 0x0000555555554ab1 in main (argc=<optimized out>, argv=0x7fffffffe568) at cachegen.c:98
(gdb)    
[#0](https://code.videolan.org/videolan/vlc/-/issues/0)  0x00007fff9377ebb0 in  ()
[#1](https://code.videolan.org/videolan/vlc/-/issues/1)  0x00007fffdf7bffab in google::protobuf::ShutdownProtobufLibrary() () at /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.10
[#2](https://code.videolan.org/videolan/vlc/-/issues/2)  0x00007fffe00ae129 in  () at /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
[#3](https://code.videolan.org/videolan/vlc/-/issues/3)  0x00007ffff7ded689 in _dl_close_worker (map=map@entry=0x5555557d14a0, force=force@entry=false) at dl-close.c:286
[#4](https://code.videolan.org/videolan/vlc/-/issues/4)  0x00007ffff7dee47a in _dl_close_worker (force=false, map=0x5555557d14a0) at dl-close.c:125
[#5](https://code.videolan.org/videolan/vlc/-/issues/5)  0x00007ffff7dee47a in _dl_close (_map=0x5555557d14a0) at dl-close.c:840
[#6](https://code.videolan.org/videolan/vlc/-/issues/6)  0x00007ffff7de7874 in _dl_catch_error (objname=0x55555575fa70, errstring=0x55555575fa78, mallocedp=0x55555575fa68, operate=0x7ffff6e85fb0 <dlclose_doit>, args=0x5555557d14a0)
    at dl-error.c:187
[#7](https://code.videolan.org/videolan/vlc/-/issues/7)  0x00007ffff6e86581 in _dlerror_run (operate=operate@entry=0x7ffff6e85fb0 <dlclose_doit>, args=0x5555557d14a0) at dlerror.c:163
[#8](https://code.videolan.org/videolan/vlc/-/issues/8)  0x00007ffff6e85fdf in __dlclose (handle=<optimized out>) at dlclose.c:46
[#9](https://code.videolan.org/videolan/vlc/-/issues/9)  0x00007ffff758f775 in module_Unload (handle=<optimized out>) at posix/plugin.c:86
[#10](https://code.videolan.org/videolan/vlc/-/issues/10) 0x00007ffff750c854 in module_Unmap (plugin=0x5555557dc590) at modules/bank.c:557
[#11](https://code.videolan.org/videolan/vlc/-/issues/11) 0x00007ffff750c854 in module_EndBank (b_plugins=b_plugins@entry=true) at modules/bank.c:643
[#12](https://code.videolan.org/videolan/vlc/-/issues/12) 0x00007ffff74f37d1 in libvlc_InternalCleanup (p_libvlc=0x5555557572c0) at libvlc.c:427
[#13](https://code.videolan.org/videolan/vlc/-/issues/13) 0x00007ffff7bb9ee7 in libvlc_release (p_instance=0x555555757160) at core.c:104
[#14](https://code.videolan.org/videolan/vlc/-/issues/14) 0x0000555555554ab1 in main (argc=<optimized out>, argv=0x7fffffffe568) at cachegen.c:98

At least one other module is depending on libmirclient: libegl_x11_plugin.so

linux-vdso.so.1 =>  (0x00007ffeb93e7000)
libvlccore.so.8 => /vlc/extras/package/snap/parts/vlc/build/src/.libs/libvlccore.so.8 (0x00007fdec537c000)
libEGL.so.1 => /usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1 (0x00007fdec512e000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007fdec4df5000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fdec4a2e000)
libidn.so.11 => /lib/x86_64-linux-gnu/libidn.so.11 (0x00007fdec47fb000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fdec45db000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fdec43d7000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fdec40ce000)
libanl.so.1 => /lib/x86_64-linux-gnu/libanl.so.1 (0x00007fdec3eca000)
libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007fdec3c7e000)
/lib64/ld-linux-x86-64.so.2 (0x0000565236b88000)
libX11-xcb.so.1 => /usr/lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007fdec3a7c000)
libxcb-dri2.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-dri2.so.0 (0x00007fdec3875000)
libxcb-dri3.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-dri3.so.0 (0x00007fdec3672000)
libxcb-present.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-present.so.0 (0x00007fdec346f000)
libxcb-xfixes.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007fdec3267000)
libxcb-sync.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007fdec3060000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007fdec2e3e000)
libxshmfence.so.1 => /usr/lib/x86_64-linux-gnu/libxshmfence.so.1 (0x00007fdec2c39000)
libwayland-client.so.0 => /usr/lib/x86_64-linux-gnu/libwayland-client.so.0 (0x00007fdec2a2a000)
libwayland-server.so.0 => /usr/lib/x86_64-linux-gnu/libwayland-server.so.0 (0x00007fdec2818000)
libgbm.so.1 => /usr/lib/x86_64-linux-gnu/libgbm.so.1 (0x00007fdec260b000)
libmirclient.so.9 => /usr/lib/x86_64-linux-gnu/libmirclient.so.9 (0x00007fdec2363000)
libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007fdec2139000)
libdrm.so.2 => /usr/lib/x86_64-linux-gnu/libdrm.so.2 (0x00007fdec1f26000)
libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007fdec1e9e000)
libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007fdec1c9a000)
libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007fdec1a94000)
libffi.so.6 => /usr/lib/x86_64-linux-gnu/libffi.so.6 (0x00007fdec188c000)
librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fdec1682000)
libxkbcommon.so.0 => /usr/lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007fdec1442000)
libmircommon.so.7 => /usr/lib/x86_64-linux-gnu/libmircommon.so.7 (0x00007fdec11fb000)
libmirprotobuf.so.3 => /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3 (0x00007fdec0f7a000)
libcapnp-0.5.3.so => /usr/lib/x86_64-linux-gnu/libcapnp-0.5.3.so (0x00007fdec0cf5000)
libmircore.so.1 => /usr/lib/x86_64-linux-gnu/libmircore.so.1 (0x00007fdec0aec000)
libboost_system.so.1.62.0 => /usr/lib/x86_64-linux-gnu/libboost_system.so.1.62.0 (0x00007fdec08e6000)
libprotobuf-lite.so.10 => /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.10 (0x00007fdec0698000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fdec0310000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fdec00f9000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007fdebfed1000)
liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007fdebfcab000)
liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007fdebfa91000)
libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007fdebf782000)
libboost_filesystem.so.1.62.0 => /usr/lib/x86_64-linux-gnu/libboost_filesystem.so.1.62.0 (0x00007fdebf569000)
libkj-0.5.3.so => /usr/lib/x86_64-linux-gnu/libkj-0.5.3.so (0x00007fdebf342000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007fdebf0cf000)
libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007fdebeeb9000)

As noted by LocutusOfBorg on IRC, disabling chromecast is enough.

Indeed, providing --disable-chromecast does the trick.

For the time being, a patch has been proposed to prevent the chromecast, and therefor the protobuf library, to be unloaded.

I was worried that we would be required to do so for all module implicitely (or not) linking to libmirclient would need to do so, but this isn't the case since libmir has a workaround applied that voluntarily leaks a handle to their shared object, preventing it to be unloaded: http://bazaar.launchpad.net/~mir-team/mir/development-branch/revision/2701

Closing as this is not a VLC bug, or even something that VLC can work around.

The least disruptive work-around is to link protobuf statically in VLC. Alternatively, disable affected functionality.

assigned to @jbk and unassigned @MigrationBot

added Component::Build system: Contribs Status::not VLC labels and removed 1 deleted label

closed

I found the resolution for this segfault/crash - by using latest

protobuf v3.5.1(I built it from source using clang/LLVM and installed on my system)

instead of the default

protobuf v3.0.0

that's in Ubuntu 17.10 x86_64 repo. With that, I was able to build VLC 3.0.1 using clang/LLVM on my Ubuntu 17.10 x86_64.

I got the same reported stack-trace via gdb from the segfault via script setup only and not in isolation(this took time to figure out).

== Call stack during segfault/crash (Stack trace when the above segfault/crash was happening - obtained via gdb session during the make-command itself as the crash happened only via make-command run but not in isolated run of exec...)

Program received signal SIGSEGV, Segmentation fault.
0x00007fffc6887630 in ?? ()
(gdb) bt
[#0](https://code.videolan.org/videolan/vlc/-/issues/0)  0x00007fffc6887630 in  ()
[#1](https://code.videolan.org/videolan/vlc/-/issues/1)  0x00007fffd1006dc3 in google::protobuf::ShutdownProtobufLibrary() () at /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.10
[#2](https://code.videolan.org/videolan/vlc/-/issues/2)  0x00007fffd18fc0a9 in  () at /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
[#3](https://code.videolan.org/videolan/vlc/-/issues/3)  0x00007ffff7deb7b9 in _dl_close_worker (map=map@entry=0x6df150, force=force@entry=false) at dl-close.c:286
[#4](https://code.videolan.org/videolan/vlc/-/issues/4)  0x00007ffff7dec5aa in _dl_close_worker (force=false, map=0x6df150) at dl-close.c:125
[#5](https://code.videolan.org/videolan/vlc/-/issues/5)  0x00007ffff7dec5aa in _dl_close (_map=0x6df150) at dl-close.c:840
[#6](https://code.videolan.org/videolan/vlc/-/issues/6)  0x00007ffff792edb4 in _dl_catch_error () at /lib/x86_64-linux-gnu/libc.so.6
[#7](https://code.videolan.org/videolan/vlc/-/issues/7)  0x00007ffff6b44759 in _dlerror_run (operate=operate@entry=0x7ffff6b440d0 <dlclose_doit>, args=0x6df150) at dlerror.c:163
[#8](https://code.videolan.org/videolan/vlc/-/issues/8)  0x00007ffff6b440ff in __dlclose (handle=<optimized out>) at dlclose.c:46
[#9](https://code.videolan.org/videolan/vlc/-/issues/9)  0x00007ffff751d7db in module_Unmap (plugin=<optimized out>) at modules/bank.c:557
[#10](https://code.videolan.org/videolan/vlc/-/issues/10) 0x00007ffff751d7db in module_EndBank (b_plugins=<optimized out>) at modules/bank.c:643
[#11](https://code.videolan.org/videolan/vlc/-/issues/11) 0x00007ffff7508667 in libvlc_InternalCleanup (p_libvlc=0x602db0) at libvlc.c:427
[#12](https://code.videolan.org/videolan/vlc/-/issues/12) 0x00007ffff7bbed8f in libvlc_release (p_instance=0x602c50) at core.c:104
[#13](https://code.videolan.org/videolan/vlc/-/issues/13) 0x00000000004009dd in main (argc=<optimized out>, argv=0x7fffffffdad8) at cachegen.c:98
(gdb)

As the crashing code appeared to be within libprotobuf-lite library, I took the source code of protobuf to debug further and within it, from its github repo. This didn't change but instead there were some missing symbols(undefined references..) when linking the VLC. Then I went to the main github google protobuf repo/releases : https://github.com/google/protobuf/releases. From there took protobuf v3.5.1 source and built it using clang(itself and not gcc) and installed it to replace the earlier protobuf(from Ubuntu repo) and rebuilt VLC - I didn't see the segfault. In fact, the specific segfault issue was with dlclose() of libstream_out_chromecast_plugin.so - there appears to be race between the dlclose()/unloading and the destructors/cleanup code within libstream_out_chromecast_plugin.so which didn't work out with older version of protobuf but with protobuf v3.5.1. In fact, google::protobuf::ShutdownProtobufLibrary() mentions in its documentation that the caller should get a lock and guard the operation, etc. Anyway, either one can skip/disable chromecast plugin code before building VLC build or get the latest protobuf(v3.5.1 in my case) for the possible fixes therein. To arrive at the dlclose() point of crash within src/posix/plugin.c, I disabled all of the dlclose() to see if crash doesn't happen. There was no segfault. So, I started narrowing to down to the actual library for which dlclose() causes a crash - there I saw libstream_out_chromecast_plugin.so, disabled dlclose() only for that and debugged also within it. But, later on I decided to see if I upgrade protobuf to its latest available version, does the segfault vanish, and it worked. clang/VLC build completed successfully along with the lib dependencies fixed(mesa, SDL, xcb, Xau, Xdmcp) mentioned in the configure command's environment variable list. So, this was one case of annoying crash whose root cause was hard to find for quite a long period of time, and finally I figured out the way to fix it.

Next, I am on the way to bring this clang-built VLC up on the Ubuntu 17.10 x86_64 to see its proper working as it would be the case with gcc-built VLC. Will share the details soon.

== Crash case when using protobuf 3.0.0 (from default/Ubuntu-repo, specifically, libprotobuf-lite.so.10.0.0)

#### proto(c|buf) version #####

exp@exp:~$ 
exp@exp:~$ protoc --version
libprotoc 3.0.0
exp@exp:~$ 
exp@exp:~$ 

#### VLC make(with clang/LLVM) o/p -- last few lines showing crash happening around "vlc-cache-gen" ####

  CC       vlc_static-override.o
1 warning generated.
  CC       cachegen.o
  CCLD     vlc-wrapper
  CCLD     vlc
  CCLD     vlc-cache-gen
  CCLD     vlc-static
  GEN      ../modules/plugins.dat
/bin/sh: line 4:  8775 Segmentation fault      (core dumped) ./vlc-cache-gen `realpath ../modules`
Makefile:1786: recipe for target '../modules/plugins.dat' failed
make[2]: *** [../modules/plugins.dat] Error 139
make[2]: Leaving directory '.../vlc-clang/vlc-3.0.1/bin'
Makefile:1530: recipe for target 'all-recursive' failed
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory '.../vlc-clang/vlc-3.0.1'
Makefile:1415: recipe for target 'all' failed
make: *** [all] Error 2

== Final successful clang/VLC build (when using protobuf 3.5.1(specifically, libprotobuf-lite.so.15.0.1))

#### proto(c|buf) version #####

exp@exp:~$ 
exp@exp:~$ protoc --version
libprotoc 3.5.1
exp@exp:~$ 

#### google::protobuf::ShutdownProtobufLibrary() within libprotobuf-lite.so was the place of crash ####

exp@exp:~$ 
exp@exp:~$ nm /usr/local/lib/libprotobuf-lite.so.15.0.1 | grep ShutdownProtobufLibrary
000000000001cb00 T _ZN6google8protobuf23ShutdownProtobufLibraryEv
exp@exp:~$ 

#### VLC make(with clang/LLVM) o/p -- last few lines where crash used to happen around "vlc-cache-gen" ####
 .
 .
 .
 . 
    setuid (uid);
    ^~~~~~  ~~~
  CCLD     vlc-cache-gen
1 warning generated.
  CCLD     vlc-wrapper
  CCLD     vlc
  CCLD     vlc-static
  GEN      ../modules/plugins.dat
make[2]: Leaving directory '.../vlc-clang/vlc-3.0.1/bin'
Making all in test
make[2]: Entering directory '.../vlc-clang/vlc-3.0.1/test'
make[2]: Nothing to be done for 'all'.
make[2]: Leaving directory '.../vlc-clang/vlc-3.0.1/test'
make[2]: Entering directory '.../vlc-clang/vlc-3.0.1'
  GEN      cvlc
  GEN      qvlc
  GEN      rvlc
  GEN      svlc
  GEN      nvlc
  GEN      vlc
make[2]: Leaving directory '.../vlc-clang/vlc-3.0.1'
make[1]: Leaving directory '.../vlc-clang/vlc-3.0.1'
 .
 .
 .
 .

== Successful clang/VLC v3.0.1 build on Ubuntu 17.10 x86_64

exp@exp:~$ 
exp@exp:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 17.10
Release:	17.10
Codename:	artful
exp@exp:~$ 
exp@exp:~$ 

exp@exp:~$ 
exp@exp:~$ eclang /usr/local/bin/vlc-clang | head -1
++ strings -a /usr/local/bin/vlc-clang
++ grep 'clang version'
clang version 5.0.0-3 (tags/RELEASE_500/final)
exp@exp:~$ 
exp@exp:~$

exp@exp:~$ 
exp@exp:~$ /usr/local/bin/vlc-clang --version
VLC media player 3.0.1 Vetinari - Built from source using Clang/LLVM by Raghavan Santhanam on Ubuntu 17.10 x86_64 - With Qt5.10.1 (revision 3.0.1-0-gec0f700fcc)
VLC version 3.0.1 Vetinari - Built from source using Clang/LLVM by Raghavan Santhanam on Ubuntu 17.10 x86_64 - With Qt5.10.1 (3.0.1-0-gec0f700fcc)

Hello, two additional points:

there was in artful, a bug in gnutls-bin, preventing it from working correctly (during the build the binary was segfaulting).

I fixed this in bionic, by re-enabling chromecast, even if I can't know if it works or not, because I lack the hardware.

Since with bionic we will have chromecast enabled, can you please do the testing with that upcoming release and see if it is still an issue?

In case it is, we can backport a fix from new protobuf if we can isolate it, because I don't think updating protobuf at this point is possible due to regressions risk (and Debian didn't update yet too)

If I have time for that, I will get it a try and see if the issue still persists in the Debian repo and/or next Ubuntu release's repo. This project of mine was more of an independent research for me to see how clang/LLVM and VLC get along - it took quite a lot of time and effort to get this far.

"As protobuf has used some global variables, linking protobuf dynamically with dlopen across several modules are very problematic."

Yes, a library done for networking parsing of serialized data, cannot be loaded twice...

And not a library started in 1990s, a recent library...

Build error on Ubuntu 17.04

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