Contextbar crashes with alsa backend

[Chiitoo]

After bd512da [1], a segmentation fault will occur when adding an ALSA source.

Platform

Operating system and version: Gentoo Linux
OBS Studio version: git master

Expected Behavior

No segmentation fault occurs.

Current Behavior

Segmentation fault occurs.

Thread 1 "obs" received signal SIGSEGV, Segmentation fault.
0x00007ffff5f5d849 in obs_module_get_locale_string (mod=0x0, lookup_string=lookup_string@entry=0x55555575fa48 "Device", translated_string=translated_string@entry=0x7fffffff7fb0)
    at /[...]/libobs/obs-module.c:66
66      /[...]/libobs/obs-module.c: No such file or directory.
(gdb) bt
#0  0x00007ffff5f5d849 in obs_module_get_locale_string (mod=0x0, lookup_string=lookup_string@entry=0x55555575fa48 "Device", 
    translated_string=translated_string@entry=0x7fffffff7fb0) at /[...]/libobs/obs-module.c:66
#1  0x00007ffff5f5d894 in obs_module_get_locale_text (mod=<optimized out>, text=text@entry=0x55555575fa48 "Device")
    at /[...]/libobs/obs-module.c:77
#2  0x000055555570c4a9 in AudioCaptureToolbar::Init (this=0x555556c6d940)
    at /[...]/UI/context-bar-controls.cpp:201
#3  0x0000555555610ac0 in OBSBasic::UpdateContextBar (this=0x555555929450)
    at /[...]/UI/window-basic-main.cpp:2916
#4  0x00005555556ed393 in SourceTreeItem::Select (this=<optimized out>) at /[...]/UI/source-tree.cpp:531
#5  0x00005555555cb895 in SourceTreeItem::qt_static_metacall (_o=_o@entry=0x555556b3ee20, _id=_id@entry=7, _a=_a@entry=0x7fffffff8200, _c=QMetaObject::InvokeMetaMethod)
    at UI/obs_autogen/EWIEGA46WW/moc_source-tree.cpp:182
#6  0x00005555555cb932 in SourceTreeItem::qt_static_metacall (_o=_o@entry=0x555556b3ee20, _c=_c@entry=QMetaObject::InvokeMetaMethod, _id=_id@entry=7, _a=_a@entry=0x7fffffff8200)
    at UI/obs_autogen/EWIEGA46WW/moc_source-tree.cpp:171
#7  0x00007ffff56ac82b in QMetaMethod::invoke (this=<optimized out>, object=0x555556b3ee20, connectionType=Qt::DirectConnection, returnValue=..., val0=..., val1=..., val2=..., 
    val3=..., val4=..., val5=..., val6=..., val7=..., val8=..., val9=...)
    at /[...]/src/corelib/kernel/qmetaobject.cpp:2303
#8  0x00007ffff56ae148 in QMetaObject::invokeMethod (obj=obj@entry=0x555556b3ee20, member=member@entry=0x555555761606 "Select", type=type@entry=Qt::AutoConnection, ret=..., 
    val0=..., val1=..., val2=..., val3=..., val4=..., val5=..., val6=..., val7=..., val8=..., val9=...)
    at /[...]/src/corelib/kernel/qmetaobject.cpp:1515
#9  0x00005555556ead5e in QMetaObject::invokeMethod (val9=..., val8=..., val7=..., val6=..., val5=..., val4=..., val3=..., val2=..., val1=..., val0=..., 
    member=0x555555761606 "Select", obj=0x555556b3ee20) at /usr/include/qt5/QtCore/qobjectdefs.h:460
#10 operator() (__closure=0x0, cd=<optimized out>, data=0x555556b3ee20) at /[...]/UI/source-tree.cpp:223

Steps to Reproduce

1. Run OBS Studio.
2. Add 'Audio Capture Device (ALSA)'.
3. Select 'OK'.
4. Observe the segmentation fault doing its thing.

Additional information

This may or may not require a specific '.asoundrc' (I'll try to test it out soon (tm)).

[kkartaltepe]

Cannot replicate, given the crash it looks like a bad install.

[Programatic]

I also can not replicate

[Chiitoo]

Could you try with the following '.asoundrc' (edited for your hardware of course).

pcm.!default
{
        type asym
        playback.pcm "loopAndReal"
        capture.pcm "loopRecord"

        hint
        {
                show on
        }
}

pcm.loopRecord
{
        type hw
        card "Loopback"
        device 1
        subdevice 0
}

pcm.loopAndReal
{
        type plug
        slave.pcm "binder"
        route_policy "duplicate"
}

pcm.binder
{
        type multi
        slaves.a.pcm "generic"
        slaves.a.channels 2
        slaves.b.pcm "looper"
        slaves.b.channels 2

        bindings.0.slave a
        bindings.0.channel 0
        bindings.1.slave a
        bindings.1.channel 1
        bindings.2.slave b
        bindings.2.channel 0
        bindings.3.slave b
        bindings.3.channel 1
}

pcm.looper
{
        type dmix
        ipc_key 1024
        ipc_key_add_uid 0
        ipc_perm 0666

        slave
        {
                pcm "hw:Loopback,0,0"
                rate 48000
                period_size 2048
                buffer_size 8192
                format s32_le
        }
}

pcm.generic
{
        type dmix
        ipc_key 1028
        ipc_key_add_uid 0
        ipc_perm 0666

        slave
        {
                pcm "hw:0"
                rate 48000
                period_size 2048
                buffer_size 8192
                format s32_le
        }
}

[kkartaltepe]

This crash has nothing related to your configuration in it.

[Chiitoo]

What do you suggest it is related to then, aside from bad install?

I can reproduce this with the mentioned commig as much as I want to, and building with the commit before it, things just work.

Perhaps there is more to my set up that I haven't noticed yet. I'll try clearing all the configuration files and such, maybe even try a fresh user, but it may take a while for me to get to it.

Thanks so far!

[kkartaltepe]

It crashes in looking up translations for the UI

[kkartaltepe]

Closing this out since someone else could not replicate it either.

[Chiitoo]

For those who might stumble upon this: I changed 'linux-pulseaudio' to 'linux-alsa' in https://github.com/obsproject/obs-studio/blob/master/UI/context-bar-controls.cpp#L189 and things work again here.

(Obviously not an actual fix, but it works.)

[kkartaltepe]

if you compiled without PA support that might be the issue.

[Chiitoo]

Yes I do do that.

[Chiitoo]

Does this mean PulseAudio is now mandatory?

[kkartaltepe]

I think someone we have previously fixed issues to allow you to use alsa as the only backend. reopened for now.

[skinkie]

I have the same issue but I want to put something else forward. The crash is caused by the fact that mod = NULL when a non-existing backend is selected, and then crashes. So the least that should be done (even before fixing the pulseaudio vs alsa issue) is assuring that mod is actually set.

[Chiitoo]

I wonder if anyone enables both, ALSA and PulseAudio at the same time.

Not sure if it's a silly way to go about this, but I've been testing stuff like this now:

#if !defined(DISABLE_ALSA)
    obs_module_t *mod =
        get_os_module("win-wasapi", "mac-capture", "linux-alsa");
#else
    obs_module_t *mod =
        get_os_module("win-wasapi", "mac-capture", "linux-pulseaudio");
#endif

This of course only allows for one of them at a time, while I believe it's possible to build OBS Studio with both enabled.

Can't quite think of a way to add another back-end without larger changes right now.

It is also possible to build without either, but I guess in that case one will not have the sources to add and as such, won't be affected... except for when sources have been added in the past.

To prevent the crash in case mod is empty-like, I've been using this:

if (!mod)
    return;

Not sure if that's equally silly.

[skinkie]

@jp9000 this does not add alsa as option.

[kkartaltepe]

This bug is for the crash on the builds without pulseaudio support.

[Chiitoo]

Right, the toolbar will just be blank with ALSA only, but since I still don't quite have that part figured out better, it can be sorted later (or by someone else, should they get to it before I do).

At least the crash should no longer happen, which indeed is what this was mainly about.

[skinkie]

But be realistic. The actual bug was: there is no alsa backend, therefore it crashes. Not: the alsa backend returns a null pointer.