#289 frequent crashes on exit

[Anonymous]

When syncterm exits, a crash occurs more often than not. This appears to be caused by the fact that the blinker thread is not stopped on exit, causing an UAF.

#0  0x0000000000000000 in ??? ()
#1  0x00007fd4120b0cbc in SDL_PeepEvents_REAL () at /lib64/libSDL2.so
#2  0x0000000000625e21 in sdl_user_func (func=0) at sdl_con.c:252
#3  0x00000000006264d3 in sdl_flush () at sdl_con.c:350
#4  0x000000000062f21d in cb_flush () at bitmap_con.c:1051
#5  0x000000000062fa46 in blinker_thread (data=0x0) at bitmap_con.c:1226
#6  0x00007fd41297ac19 in start_thread () at /lib64/libc.so.6
#7  0x00007fd4129fe5cc in __clone3 () at /lib64/libc.so.6

[Stephen James Hurd]

Try using the native output mode instead of SDL.

[Anonymous]

I am using the SDL backend because the Wayland backend has issues (keyboard shortcuts don't work and there are no window decorations). I don't have time to fix this myself but the fix would be along these lines:

• in blinker_thread(), replace SLEEP(10) by a call to pthread_cond_timedwait()
• when exiting, before destroying any object (SDL handles and so on), set a quit_requested bool to true, signal the blinker condition variable then join the blinker thread
• in blinker_thread(), when pthread_cond_timedwait() returns, if quit_requested is true, return from the function to let the quit thread return from pthread_join(); it is then safe to destroy global objects and exit

Hope this helps.

[Stephen James Hurd]

The no window decorations in Wayland are because your desktop of choice refuses to provide them (SyncTERM requests them), but there are keyboard shortcuts for everything except minimizing. I'll take a look at the "keyboard shortcuts don't work" issue and see if I can reproduce that. The XWayland backend should work properly.

It's really too bad these two issues weren't reported until after the release, there's not likely to be another release for quite a while.

[Stephen James Hurd]

All of these reported issues (except your desktop not supporting window decorations) should be fixed in tomorrows v1.10a nightly.

[Anonymous]

I'm using GNOME so the Wayland compositor is mutter. I'm not really worried about Wayland decorations nor shortcuts because the SDL backend (which also uses Wayland under the hood via SDL) works fine, except for the minor annoyance of the exit crash that I've explained above.

For reference, the two shortcuts I've tested which don't work on pure Wayland but work on SDL are Alt-Z and Alt-Enter. I've had similar shortcut issues with other apps (IIRC dosbox and/or qemu) so they're probably caused by bugs and/or "security" limitations of mutter/gnome-shell.

I'll be testing the new version when I find some time, thanks for your great work and responsiveness!

[Stephen James Hurd]

Yeah, Alt+Z was layout-specific, so it was really Alt+<key to right of left shift> and it looks like Alt+Enter was just plain broken.