Bug #664

Segmentation fault on video playback

Added by Robin Nehls over 9 years ago. Updated over 8 years ago.

Status:FixedStart date:08/29/2011
Priority:NormalDue date:
Assignee:Andreas Smas% Done:


Target version:4.0
Found in version:3.1.210.g26900 Platform:


I tried to confirm another bug i have on the ps3 and ran into this issue on my laptop. When i try to play a video (it doesn't mater what kind of video) showtime segfaults. Maybe this is an issue of my crapy intel graphics card. To build showtime on my machine i changed the configure script to exept an older version of ffmpeg. By looking at the stacktrace and some debugger output I don't think this is related, but you never know.
I use Gentoo Linux amd64.
I will monitor this bug in case more feedback is needed.

Before submit i did some additional debuging. The Segfault rises in this line in glw_opengl.c

544: glUniform4f(gbr->gbr_current->gp_uniform_color, r, g, b, a);

The problem is, that in my case gbr_current is 0. The compiler translates this part of the code to

MOV RAX, QWORD PTR [RDI+8] <- at RDI+8 is a 0 were should be the pointer to gbr_current
MOV RDI, DWORD PTR [RAX+28] <- this trys to get gp_uniform_color but RAX is 0 so it trys to load a value from 001c with is not mapped and causes a segfault.

I tried to find the cause for this, but it seems that opengl code is even harder to read than assemly.

segfault.txt Magnifier - A dump of stderr when running showtime -d (11.8 KB) Robin Nehls, 08/30/2011 12:55 AM

Related issues

Duplicated by Bug #792: Crash when trying to playback Fixed 11/26/2011
Duplicated by Bug #380: When in non-shader mode on X11 Showtime GLW can not play ... Fixed 02/14/2011

Associated revisions

Revision 5ca9af92
Added by Andreas Smas over 8 years ago

glw/opengl: Never use the fixed function pipeline as it cannot play video

fixes #792
fixes #664
fixes #380

Change included in version 3.99.449


#1 Updated by Andreas Smas over 9 years ago

This is a known issue. :/

#2 Updated by Robin Nehls over 9 years ago

I'm sorry i could not find an existing issue for this. Could you post a link so i can participate in case i find something usefull?

#3 Updated by Andreas Smas over 9 years ago

Ok sorry I meant that this is a known "problem". I'm not sure if there is a filed issue for it.

#4 Updated by Andreas Smas over 9 years ago

  • Status changed from New to Accepted
  • Target version set to 33

#5 Updated by Robin Nehls over 9 years ago

I did some more diging in the code. Looks like the code were the segfault happens is highly dependant on shader stuff, with is disabeld in glw_opengl_init_context for Mesa OpenGL drivers. Removing the Mesa check worked for me only once. Videos played, but had smal blue dots in them. After closing showtime I could not make it work again. Strange.
So the problem seems to be an missing implementation for shaderless playback, witch leeds me to the conclusion that you already know what i just wrote. Sorry for the nagging.

#6 Updated by Henrik Andersson almost 9 years ago

I just stumble upon this bug and as mentioned before shaders are disabled if Mesa driver
is used and down the rendering code path shaders a expected to work even if disabled as
stated in earlier comments.

With about zero knowledge about shaders and Mesa compatibility i just removed the check
and got glw ui to work ?!

GLW [INFO]: OpenGL Renderer: 'Mesa DRI Intel(R) G45/G43 ' by 'Tungsten Graphics, Inc'

If the non-shader codepath is "broken" / "uncomplete" it should not take that road
especially if there is a possibility the Mesa driver + shaders works, my suggestion is to
remove the Mesa check and add some log output that the user is on a experimental road..

diff --git a/src/ui/glw/glw_opengl_ogl.c b/src/ui/glw/glw_opengl_ogl.c
index 0b7875b..33409d1 100644
--- a/src/ui/glw/glw_opengl_ogl.c
+++ b/src/ui/glw/glw_opengl_ogl.c
@@ -175,9 +175,6 @@ glw_opengl_init_context(glw_root_t *gr)

   int use_shaders = 1;

-  if(strstr(renderer, "Mesa"))
-      use_shaders = 0;
   if(use_shaders) {
     return glw_opengl_shaders_init(gr);
   } else {

#7 Updated by Andreas Smas over 8 years ago

  • Status changed from Accepted to Fixed
  • % Done changed from 0 to 100

#8 Updated by Andreas Smas over 8 years ago

  • Target version changed from 33 to 4.0

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