This bug report was migrated from our old Bugzilla tracker.

These attachments are available in the static archive:

• gdb backtrace (file_1812.txt, text/plain, 2013-04-18 05:36:33 +0000, 1145 bytes)
• valgrind output (file_1812.txt, text/plain, 2013-04-18 05:37:03 +0000, 1298 bytes)
• minimal test program (file_1812.txt, text/plain, 2013-04-18 05:37:39 +0000, 905 bytes)
• patch to workaround this libXi bug (sdlpatch.txt, text/plain, 2013-07-15 15:31:48 +0000, 3058 bytes)

Reported in version: HG 2.0
Reported for operating system, platform: Linux, All

Comments on the original bug report:

On 2013-04-18 05:36:33 +0000, driedfruit wrote:

Created attachment 1116
gdb backtrace

On X11, sometimes, when you move your mouse and release the keyboard
key at the same time, you get a SIGSERV crash.

I've "tracked" it down to the X11_KeyRepeat function in
SDL_x11events.c. The function looks for next X11 event in the queue and
compares it to the current one, working around keyboard auto-repeat
feature of X11.

The culprit is XPeekEvent, which either crashes itself, either
corrupts something, so next XNextEvent call crashes.

To easier reproduce this, change "2" to "10" or a larger value here:

src/video/x11/SDL_x11events.c:113
((peekevent.xkey.time-event->xkey.time) < 2)) {

You're aiming to "inject" a MotionNotify event inbetween the
KeyRelease and the auto-repeated KeyPress. For me, it crashes reliably
when this happens.

I've tested this on different hardware (32 and 64 bit) and different libX11 versions, it doesn't seem to be an X bug, but an SDL2 bug :(

On 2013-04-18 05:37:03 +0000, driedfruit wrote:

Created attachment 1117
valgrind output

On 2013-04-18 05:37:39 +0000, driedfruit wrote:

Created attachment 1118
minimal test program

On 2013-04-18 19:08:30 +0000, Ondra Hošek wrote:

I can't reproduce this with the minimal program (and modification) you provided.

• Xlib 1.5.0
• X server 1.14.1
• awesome v3.5.1-1-g2d31033 (window manager)
• tip-of-the-trunk SDL2

What is your X server version? Which window manager are you using?

On 2013-04-19 02:38:42 +0000, driedfruit wrote:

• i686
• Xlib 1.4.1
• Xserver 1.9.4
• awesome 3.4.8 (wm)
• latest SDL hg

and

• amd64
• Xlib 1.3.3-4
• X server 1.7.7-14
• enlightenment wm (don't have info on the version right now)
• latest SDL hg

On 2013-04-30 11:10:05 +0000, driedfruit wrote:

After investigating more upon it, I've found that the reason for this crash has nothing to do with SDL2, but all with libXi:

http://cgit.freedesktop.org/xorg/lib/libXi/commit/?id=af65475b1f6b7209750220a74aaad9968d54aaf7

Applying this patch to 1.4.1 libXi fixes the issue. It's part of the more recent libXi releases. Sorry!

On 2013-07-15 15:31:48 +0000, Steve Soule wrote:

Created attachment 1236
patch to workaround this libXi bug

This patch is a workaround for the bug in libXi. It avoids calling X functions that trigger the bug. See the forum thread http://forums.libsdl.org/viewtopic.php?p=38071 for my explanation of what this workaround is intended to do.

On 2013-07-16 03:30:51 +0000, Sam Lantinga wrote:

Reopened to investigate Steve's patch.

On 2013-07-18 23:05:10 +0000, Ryan C. Gordon wrote:

That email thread has some really impressive research.

This patch looks good to me. Sam, you want to give this a looking at before I apply it?

Thanks,
--ryan.

On 2013-07-20 01:40:12 +0000, Sam Lantinga wrote:

It looks good to me. Go for it. Great work everyone!

On 2013-07-20 13:12:26 +0000, Ryan C. Gordon wrote:

This patch is now http://hg.libsdl.org/SDL/rev/c244bc85fb84, thanks!

--ryan.

On 2013-07-27 00:33:18 +0000, Ryan C. Gordon wrote:

*** Bug 1683 has been marked as a duplicate of this bug. ***