Question

I am writing a cuda code available in the
http://code.google.com/p/snp-gpgpu/source/browse/trunk/cuda_by_example_codes/chapter08/basic_interop.cu?r=4

I replaced the headers by mentioning headers explicitly and I mentioned them as follows :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/gl.h>
#include <GL/glut.h>
#include <cuda.h>
#include <cuda_runtime.h>
#include "cutil.h"
#include <cuda_gl_interop.h>

I am compiling the code issuing the command
nvcc -o test_cuda basic_prog_num_1.cu -lGL -lGLU -lglut
The program is getting compiled without any error and test_cuda executable gets created. But when I am trying to run the executable issuing
./test_cuda
then it is giving me segmentation fault. One thing I would like to mention, previously when I was compiling with “cutil.h” an error was occurring that there is no such file or directory as cutil.h. So I explicitly downloaded “cutil.h” and included in the same folder as the program. The program is getting compiled without any error but while running it is returning a segmentation fault.

The code is given below :

PFNGLBINDBUFFERARBPROC    glBindBuffer     = NULL;
PFNGLDELETEBUFFERSARBPROC glDeleteBuffers  = NULL;
PFNGLGENBUFFERSARBPROC    glGenBuffers     = NULL;
PFNGLBUFFERDATAARBPROC    glBufferData     = NULL;

#define     DIM    512

GLuint  bufferObj;
cudaGraphicsResource *resource;

__global__ void kernel( uchar4 *ptr ) {
    // map from threadIdx/BlockIdx to pixel position
    int x = threadIdx.x + blockIdx.x * blockDim.x;
    int y = threadIdx.y + blockIdx.y * blockDim.y;
    int offset = x + y * blockDim.x * gridDim.x;

    // now calculate the value at that position
    float fx = x/(float)DIM - 0.5f;
    float fy = y/(float)DIM - 0.5f;
    unsigned char   green = 128 + 127 *
                            sin( abs(fx*100) - abs(fy*100) );

    // accessing uchar4 vs unsigned char*
    ptr[offset].x = 0;
    ptr[offset].y = green;
    ptr[offset].z = 0;
    ptr[offset].w = 255;
}

static void key_func( unsigned char key, int x, int y ) {
    switch (key) {
        case 27:

            HANDLE_ERROR( cudaGraphicsUnregisterResource( resource ) );
            glBindBuffer( GL_PIXEL_UNPACK_BUFFER_ARB, 0 );
            glDeleteBuffers( 1, &bufferObj );
            exit(0);
    }
}

static void draw_func( void ) {

    glDrawPixels( DIM, DIM, GL_RGBA, GL_UNSIGNED_BYTE, 0 );
    glutSwapBuffers();
}


int main( int argc, char **argv ) {
    cudaDeviceProp  prop;
    int dev;

    memset( &prop, 0, sizeof( cudaDeviceProp ) );
    prop.major = 1;
    prop.minor = 0;
    HANDLE_ERROR( cudaChooseDevice( &dev, &prop ) );

    cudaGLSetGLDevice( dev );


    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_DOU@harrism : BLE | GLUT_RGBA );
    glutInitWindowSize( DIM, DIM );
    glutCreateWindow( "bitmap" );

    /*glBindBuffer    = (PFNGLBINDBUFFERARBPROC)GET_PROC_ADDRESS("glBindBuffer");
    glDeleteBuffers = (PFNGLDELETEBUFFERSARBPROC)GET_PROC_ADDRESS("glDeleteBuffers");
    glGenBuffers    = (PFNGLGENBUFFERSARBPROC)GET_PROC_ADDRESS("glGenBuffers");
    glBufferData    = (PFNGLBUFFERDATAARBPROC)GET_PROC_ADDRESS("glBufferData");*/


    glGenBuffers( 1, &bufferObj );
    glBindBuffer( GL_PIXEL_UNPACK_BUFFER_ARB, bufferObj );
    glBufferData( GL_PIXEL_UNPACK_BUFFER_ARB, DIM * DIM * 4,
                  NULL, GL_DYNAMIC_DRAW_ARB );


        cudaGraphicsGLRegisterBuf@harrism : fer( &resource, 
                                      bufferObj, 
                                      cudaGraphicsMapFlagsNone );


   cudaGraphicsMapResources( 1, &resource, NULL );
    uchar4* devPtr;
    size_t  size;

        cudaGraphicsResourceGetMappedPointer( (void**)&devPtr, 
                                              &size, 
                                              resource);

    dim3    grids(DIM/16,DIM/16);
    dim3    threads(16,16);
    kernel<<<grids,threads>>>( devPtr );
  cudaGraphicsUnmapResources( 1, &resource, NULL );

    // set up GLUT and kick off main loop
    glutKeyboardFunc( key_func );
    glutDisplayFunc( draw_func );
    glutMainLoop();
}

Answer 1

You had several critical lines from the original book example commented out in your code. Why you did this, I don’t know, but the net effect is that you were trying certain OGL calls (glGenBuffers was where the seg fault was coming from) before an openGL rendering context had been properly created.

Uncommenting these 4 lines resulted in showing that “GET_PROC_ADDRESS” macro was missing from your code and headers. This led me to discover that you didn’t include the original book headers properly. Your code also contains some garbage in it, such as @harrism in various places.

Anyway I took your code and added some things to it, the following works for me:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/gl.h>
#include <GL/glut.h>
#include <cuda.h>
#include <cuda_runtime.h>
// #include "cutil.h"
#include <cuda_gl_interop.h>

#include <GL/glext.h>
#include <GL/glx.h>
#define GET_PROC_ADDRESS( str ) glXGetProcAddress( (const GLubyte *)str )

static void HandleError( cudaError_t err, const char *file,  int line ) {
    if (err != cudaSuccess) {
            printf( "%s in %s at line %d\n", cudaGetErrorString( err ),  file, line );
            exit( EXIT_FAILURE );
    }
}
#define HANDLE_ERROR( err ) (HandleError( err, __FILE__, __LINE__ ))



PFNGLBINDBUFFERARBPROC    glBindBuffer     = NULL;
PFNGLDELETEBUFFERSARBPROC glDeleteBuffers  = NULL;
PFNGLGENBUFFERSARBPROC    glGenBuffers     = NULL;
PFNGLBUFFERDATAARBPROC    glBufferData     = NULL;

#define     DIM    512

GLuint  bufferObj;
cudaGraphicsResource *resource;

__global__ void kernel( uchar4 *ptr ) {
// map from threadIdx/BlockIdx to pixel position
int x = threadIdx.x + blockIdx.x * blockDim.x;
int y = threadIdx.y + blockIdx.y * blockDim.y;
int offset = x + y * blockDim.x * gridDim.x;

// now calculate the value at that position
float fx = x/(float)DIM - 0.5f;
float fy = y/(float)DIM - 0.5f;
unsigned char   green = 128 + 127 *
                        sin( abs(fx*100) - abs(fy*100) );

// accessing uchar4 vs unsigned char*
ptr[offset].x = 0;
ptr[offset].y = green;
ptr[offset].z = 0;
ptr[offset].w = 255;
}

static void key_func( unsigned char key, int x, int y ) {
  switch (key) {
    case 27:

        HANDLE_ERROR( cudaGraphicsUnregisterResource( resource ) );
        glBindBuffer( GL_PIXEL_UNPACK_BUFFER_ARB, 0 );
        glDeleteBuffers( 1, &bufferObj );
        exit(0);
  }
}

static void draw_func( void ) {

glDrawPixels( DIM, DIM, GL_RGBA, GL_UNSIGNED_BYTE, 0 );
glutSwapBuffers();
}


int main( int argc, char **argv ) {
cudaDeviceProp  prop;
int dev;

memset( &prop, 0, sizeof( cudaDeviceProp ) );
prop.major = 1;
prop.minor = 0;
HANDLE_ERROR( cudaChooseDevice( &dev, &prop ) );

cudaGLSetGLDevice( dev );

glutInit( &argc, argv );
glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGBA );
glutInitWindowSize( DIM, DIM );
glutCreateWindow( "bitmap" );

glBindBuffer    = (PFNGLBINDBUFFERARBPROC)GET_PROC_ADDRESS("glBindBuffer");
glDeleteBuffers = (PFNGLDELETEBUFFERSARBPROC)GET_PROC_ADDRESS("glDeleteBuffers");
glGenBuffers    = (PFNGLGENBUFFERSARBPROC)GET_PROC_ADDRESS("glGenBuffers");
glBufferData    = (PFNGLBUFFERDATAARBPROC)GET_PROC_ADDRESS("glBufferData");


glGenBuffers( 1, &bufferObj );
glBindBuffer( GL_PIXEL_UNPACK_BUFFER_ARB, bufferObj );
glBufferData( GL_PIXEL_UNPACK_BUFFER_ARB, DIM * DIM * 4,
              NULL, GL_DYNAMIC_DRAW_ARB );


cudaGraphicsGLRegisterBuffer( &resource,
                                  bufferObj,
                                  cudaGraphicsMapFlagsNone );


cudaGraphicsMapResources( 1, &resource, NULL );
uchar4* devPtr;
size_t  size;

cudaGraphicsResourceGetMappedPointer( (void**)&devPtr,
                                          &size,
                                          resource);

dim3    grids(DIM/16,DIM/16);
dim3    threads(16,16);
kernel<<<grids,threads>>>( devPtr );
cudaGraphicsUnmapResources( 1, &resource, NULL );

// set up GLUT and kick off main loop
glutKeyboardFunc( key_func );
glutDisplayFunc( draw_func );
glutMainLoop();
}