Segmentation Fault While Unmapping Buffer glBindBuffer()

Question

There is a similar post at (Segmentation fault with glBufferData()), but it does not address my problem.

When I call glBingBuffer() below with the second parameter being 0 to unbind the buffer the program SEGFAULTS. If I uncomment out these lines then the program runs normally. Why is this?

QtRenderer::QtRenderer() :
  QGLWidget(){
}

QtRenderer::~QtRenderer() {
}

void QtRenderer::initializeGL() {
  makeCurrent();

  const char* vertexSource =
    "#version 150\n"
    "in vec2 position;"
    "void main() {"
    "   gl_Position = vec4( position, 0.0, 1.0 );"
    "}";
  const char* fragmentSource =
    "#version 150\n"
    "out vec4 outColor;"
    "void main() {"
    "   outColor = vec4( 1.0, 1.0, 1.0, 1.0 );"
    "}";

  glextensions_loader::load_gl_extensions();

  glGenBuffers( 1, &vbo );

  float vertices[] = {
    0.0f, 0.5f,
    0.5f, -0.5f,
    -0.5f, -0.5f
  };

  glBindBuffer( GL_ARRAY_BUFFER, vbo );
  glBufferData( GL_ARRAY_BUFFER, sizeof( vertices ), vertices, GL_STATIC_DRAW );
  glBindBuffer( GL_ARRAY_BUFFER, 0 ); // <-----------SEGFAULT

  // Create and compile the vertex shader
  GLuint vertexShader = glCreateShader( GL_VERTEX_SHADER );
  glShaderSource( vertexShader, 1, &vertexSource, NULL );
  glCompileShader( vertexShader );

  // Create and compile the fragment shader
  GLuint fragmentShader = glCreateShader( GL_FRAGMENT_SHADER );
  glShaderSource( fragmentShader, 1, &fragmentSource, NULL );
  glCompileShader( fragmentShader );

  // Link the vertex and fragment shader into a shader program
  GLuint shaderProgram = glCreateProgram();
  glAttachShader( shaderProgram, vertexShader );
  glAttachShader( shaderProgram, fragmentShader );
  //glBindFragDataLocation( shaderProgram, 0, "outColor" );
  glLinkProgram( shaderProgram );
  glUseProgram( shaderProgram );

  GLint posAttrib = glGetAttribLocation( shaderProgram, "position" );
  glEnableVertexAttribArray( posAttrib );
  glVertexAttribPointer( posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0 );
}

void QtRenderer::paintGL() {
  makeCurrent();

  // Clear the screen to black
  glClearColor( 0.0f, 0.0f, 0.0f, 1.0f );
  glClear( GL_COLOR_BUFFER_BIT );

  // Draw a triangle from the 3 vertices
  glBindBuffer( GL_ARRAY_BUFFER, vbo );
  glDrawArrays( GL_TRIANGLES, 0, 3 );
  glBindBuffer( GL_ARRAY_BUFFER, 0 );  // <-----------SEGFAULT
}

void QtRenderer::updateGL() {
  paintGL();
}

UPDATE

I dont know off hand where the core file is in RHEL 6.3 but I am looking for it. In the mean time the gdb info I have is:

[mehoggan@localhost online_samples_delete_later]$ gdb ./test
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-56.el6)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/mehoggan/Devel/GLExtensions/demos/online_samples_delete_later/test...done.
(gdb) r
Starting program: /home/mehoggan/Devel/GLExtensions/demos/online_samples_delete_later/test 
[Thread debugging using libthread_db enabled]

Program received signal SIGSEGV, Segmentation fault.
0x002eeef1 in ?? ()
Missing separate debuginfos, use: debuginfo-install GConf2-2.28.0-6.el6.i686 ORBit2-2.14.17-3.1.el6.i686 PackageKit-gtk-module-0.5.8-21.el6.i686 atk-1.28.0-2.el6.i686 avahi-glib-0.6.25-11.el6.i686 avahi-libs-0.6.25-11.el6.i686 cairo-1.8.8-3.1.el6.i686 dbus-glib-0.86-5.el6.i686 dbus-libs-1.2.24-5.el6_1.i686 expat-2.0.1-11.el6_2.i686 fontconfig-2.8.0-3.el6.i686 freetype-2.3.11-14.el6_3.1.i686 glib2-2.22.5-7.el6.i686 glibc-2.12-1.80.el6.i686 gnome-keyring-2.28.2-7.el6.i686 gnome-vfs2-2.24.2-6.el6.i686 gtk2-2.18.9-10.el6.i686 gtk2-engines-2.18.4-5.el6.i686 keyutils-libs-1.4-4.el6.i686 krb5-libs-1.10.3-10.el6.i686 libICE-1.0.6-1.el6.i686 libSM-1.2.1-2.el6.i686 libX11-1.5.0-4.el6.i686 libXau-1.0.5-1.el6.i686 libXcomposite-0.4.1-2.el6.i686 libXcursor-1.1.10-2.el6.i686 libXdamage-1.1.2-1.el6.i686 libXext-1.1-3.el6.i686 libXfixes-4.0.4-1.el6.i686 libXi-1.6.1-3.el6.i686 libXinerama-1.1-1.el6.i686 libXrandr-1.4.0-1.el6.i686 libXrender-0.9.7-2.el6.i686 libart_lgpl-2.3.20-5.1.el6.i686 libbonobo-2.24.2-5.el6.i686 libbonoboui-2.24.2-3.el6.i686 libcanberra-0.22-1.el6.i686 libcanberra-gtk2-0.22-1.el6.i686 libcom_err-1.41.12-12.el6.i686 libgcc-4.4.7-3.el6.i686 libgnome-2.28.0-11.el6.i686 libgnomecanvas-2.26.0-4.el6.i686 libgnomeui-2.24.1-4.el6.i686 libogg-1.1.4-2.1.el6.i686 libpng-1.2.49-1.el6_2.i686 libselinux-2.0.94-5.3.el6.i686 libstdc++-4.4.7-3.el6.i686 libtdb-1.2.10-1.el6.i686 libtool-ltdl-2.2.6-15.5.el6.i686 libuuid-2.17.2-12.7.el6.i686 libvorbis-1.2.3-4.el6_2.1.i686 libxcb-1.5-1.el6.i686 libxml2-2.7.6-4.el6_2.4.i686 mesa-libGLU-7.11-5.el6.i686 nss-softokn-freebl-3.12.9-11.el6.i686 openssl-1.0.0-20.el6_2.5.i686 pango-1.28.1-3.el6_0.5.i686 pixman-0.18.4-1.el6_0.1.i686 popt-1.13-7.el6.i686 qt-4.6.2-25.el6.i686 qt-x11-4.6.2-25.el6.i686 zlib-1.2.3-29.el6.i686
(gdb) where
#0  0x002eeef1 in ?? ()
#1  0x066422e7 in ?? () from /usr/lib/libnvidia-glcore.so.295.59
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Look at http://stackoverflow.com/questions/8806469/how-to-analyze-core-dump It would likely be useful to upload the stack trace to the question. — Rob Kielty, May 16 '13 at 18:45
compile the files with '-g' flag and then run the program under gdb. When the seg. fault happens, do a `bt` and post the back trace. That will help — A. K., May 16 '13 at 18:58
the backtrace is equivalent to the output from the 'where' command. It seems to be crashing in the driver that was installed from nvidia's website. — Matthew Hoggan, May 16 '13 at 19:07
This has little to do with Qt, unless you were using the Qt GL convenience wrappers (QOpenGLBuffer, QOpenGLShaderProgram, etc.) :-) — peppe, May 16 '13 at 20:31
I know Microsoft has been pushing their Bing search engine, and even trying to verb it like google, but has it really gained traction in OpenGL? — Ben Voigt, May 16 '13 at 20:48

score 1 · Accepted Answer · answered May 16 '13 at 19:49

The answer came from http://www.opengl.org/wiki/Buffer_Object:

While a buffer is mapped, you can freely unbind the buffer. However, you cannot call any function that would cause OpenGL to read, modify, or write to that buffer while it is mapped. Thus, calling glBufferData is out, as is using any function that would cause OpenGL to read from it (rendering with a VAO that uses it, etc).

Thus the necessary changes to the code would have to be.

void QtRenderer::initializeGL() {
  makeCurrent();

  const char* vertexSource =
    "#version 150\n"
    "in vec2 position;"
    "void main() {"
    "   gl_Position = vec4( position, 0.0, 1.0 );"
    "}";
  const char* fragmentSource =
    "#version 150\n"
    "out vec4 outColor;"
    "void main() {"
    "   outColor = vec4( 1.0, 1.0, 1.0, 1.0 );"
    "}";

  glextensions_loader::load_gl_extensions();

  glGenBuffers( 1, &vbo );

  float vertices[] = {
    0.0f, 0.5f,
    0.5f, -0.5f,
    -0.5f, -0.5f
  };

  glBindBuffer( GL_ARRAY_BUFFER, vbo );
  glBufferData( GL_ARRAY_BUFFER, sizeof( vertices ), vertices, GL_STATIC_DRAW );

  // Create and compile the vertex shader
  GLuint vertexShader = glCreateShader( GL_VERTEX_SHADER );
  glShaderSource( vertexShader, 1, &vertexSource, NULL );
  glCompileShader( vertexShader );

  // Create and compile the fragment shader
  GLuint fragmentShader = glCreateShader( GL_FRAGMENT_SHADER );
  glShaderSource( fragmentShader, 1, &fragmentSource, NULL );
  glCompileShader( fragmentShader );

  // Link the vertex and fragment shader into a shader program
  GLuint shaderProgram = glCreateProgram();
  glAttachShader( shaderProgram, vertexShader );
  glAttachShader( shaderProgram, fragmentShader );
  //glBindFragDataLocation( shaderProgram, 0, "outColor" );
  glLinkProgram( shaderProgram );
  glUseProgram( shaderProgram );

  GLint posAttrib = glGetAttribLocation( shaderProgram, "position" );
  glEnableVertexAttribArray( posAttrib );
  glVertexAttribPointer( posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0 );

  glBindBuffer( GL_ARRAY_BUFFER, 0 ); // <-----------NO SEGFAULT
}

void QtRenderer::paintGL() {
  makeCurrent();

  // Clear the screen to black
  glClearColor( 0.0f, 0.0f, 0.0f, 1.0f );
  glClear( GL_COLOR_BUFFER_BIT );

  // Draw a triangle from the 3 vertices
  glBindBuffer( GL_ARRAY_BUFFER, vbo );
  glDrawArrays( GL_TRIANGLES, 0, 3 );
  glBindBuffer( GL_ARRAY_BUFFER, 0 ); // <-----------NO SEGFAULT
}

Segmentation Fault While Unmapping Buffer glBindBuffer()

1 Answers1