[bug#37725] [PATCH] gnu: lxqt-config: Add libkscreen as propagated-inputs.

["Reza Alizadeh Majd" <r.majd@pantherx.org>]

Hi Ludo, 

Sure, here is a minimal operating system configuration that we used for a
minimal LXQt desktop on Guix:

```
(use-modules (gnu) (gnu system nss) (gnu packages kde-plasma))
(use-service-modules desktop networking ssh sddm dbus)
(use-package-modules ssh certs tls lxqt xorg)

(operating-system
  (host-name "panther")
  (timezone "Asia/Tehran")
  (locale "en_US.utf8")

  ;; Boot in "legacy" BIOS mode
  (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (target "/dev/sda")))
  (file-systems (cons (file-system
                        (device (file-system-label "my-root"))
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))
  (users (cons (user-account
                (name "user")
                (password "1234")
                (group "users")
                (supplementary-groups '("wheel" "audio" "video"))
                (home-directory "/home/user"))
               %base-user-accounts))
  (packages (cons* openssh nss-certs gnutls 
                   lxqt lxqt-globalkeys
                   
                   ;; commented in order to re-produce the issue
                   ; libkscreen   
                   %base-packages))
  (services (cons*
	      (sddm-service
		    (sddm-configuration
		      (minimum-uid 1000)
		      (theme "elarun")))
	      (elogind-service)
	      (udisks-service)
	      (dbus-service)
	      (colord-service)
	      (service polkit-service-type)
	      (service upower-service-type)
	      (service dhcp-client-service-type)
	      ;; network configuration
	      (service openssh-service-type
		       (openssh-configuration
			 (port-number 22)
			 (permit-root-login #t)
			 (authorized-keys
			   `(("panther" ,(local-file "/etc/vagrant.pub"))
			     ("root" ,(local-file "/etc/vagrant.pub"))))))
	      (service wpa-supplicant-service-type)
	      %base-services))
  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))
```  
  
the issue occurs when I try to execute `lxqt-config-monitor`.


here is also the GDB backtrace log that I received during application crash:

```
root@panther /home/panther# cat monitor.txt 
Starting program: /gnu/store/k09wlkkmllwyr5d41bzn2mn9kvylgszr-profile/bin/lxqt-config-monitor 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/gnu/store/h90vnqw0nwd0hhm1l5dgxsdrigddfmq4-glibc-2.28/lib/libthread_db.so.1".
[New Thread 0x7ffff3bfb700 (LWP 860)]
[New Thread 0x7ffff32d4700 (LWP 861)]
[Detaching after fork from child process 862]
[New Thread 0x7fffea615700 (LWP 863)]
[New Thread 0x7fffe9e14700 (LWP 864)]
[New Thread 0x7fffe9613700 (LWP 865)]
[New Thread 0x7fffe8e12700 (LWP 866)]

Thread 1 "lxqt-config-mon" received signal SIGSEGV, Segmentation fault.
0x00007ffff7fa1b01 in KScreen::GetConfigOperation::start() ()
   from /gnu/store/ds7ib4ndgy48ac0hxrrsgc6xc4lsccva-libkscreen-5.15.1/lib/libKF5Screen.so.7
#0  0x00007ffff7fa1b01 in KScreen::GetConfigOperation::start() ()
   from /gnu/store/ds7ib4ndgy48ac0hxrrsgc6xc4lsccva-libkscreen-5.15.1/lib/libKF5Screen.so.7
#1  0x00007ffff7fbe48d in KScreen::ConfigOperation::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) ()
   from /gnu/store/ds7ib4ndgy48ac0hxrrsgc6xc4lsccva-libkscreen-5.15.1/lib/libKF5Screen.so.7
#2  0x00007ffff6f28ad1 in QObject::event(QEvent*) () from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#3  0x00007ffff788214c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Widgets.so.5
#4  0x00007ffff7889280 in QApplication::notify(QObject*, QEvent*) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Widgets.so.5
#5  0x00007ffff6efd4f8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#6  0x00007ffff6efff2b in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#7  0x00007ffff6f51643 in ?? () from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#8  0x00007ffff43ddb57 in g_main_context_dispatch () from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#9  0x00007ffff43ddd98 in g_main_context_iterate.isra () from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#10 0x00007ffff43dde3c in g_main_context_iteration () from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#11 0x00007ffff6f50caf in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#12 0x00007ffff3deb3c1 in ?? ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/qt5/plugins/platforms/../../../libQt5XcbQpa.so.5
#13 0x00007ffff6efbe4a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#14 0x00007ffff6f04740 in QCoreApplication::exec() () from /gnu/store/ahyi57vlk48cmzsvxjwhxlxg2fdhxl9w-qtbase-5.11.3/lib/libQt5Core.so.5
#15 0x000000000040f92c in main ()
Quit
quit

```

Best, 
Reza



On Fri, Oct 18, 2019, at 1:24 PM, Ludovic Courtès wrote:
> Hi Reza,
> 
> "Reza Alizadeh Majd" <r.majd@pantherx.org> skribis:
> 
> > maybe I could describe better about this patch file.
> >
> > `libkscreen`  is used by `lxqt-config-monitor` to modify
> > the desktop resolution in LXQt desktop. 
> >
> > the problem is that, during execution of `lxqt-config-monitor` 
> > application crashes with "segmentation fault". 
> >
> > we had a review over `lxqt-config-monitor` source code, 
> > but didn't find any unusual usage of `ksceen` library. just 
> > a normal link during build process and binaries were made 
> > successfully. 
> >
> > this issue might because of crash inside `libkscreen`, but we
> > didn't  review that yet. 
> >
> > so as a quick workaround we find that adding the `libkscreen`
> > as a propagated input could fix this issue.
> 
> Thanks for explaining, I understand better now.
> 
> I think that it’s not satisfying to apply a workaround that we don’t
> understand.  That is, intuitively, I see now reason why propagating
> libkscreen would “fix” a segfault.
> 
> Could you either (1) provide an ‘operating-system’ config and
> instructions to reproduce the problem, or (2) grab a backtrace of the
> segfaulted program with GDB?
> 
> Let us know if you need guidance.
> 
> Thanks,
> Ludo’.
>