Re: [Mesa3d-users] offscreen render segmentation fault with mesa 7.7

[Geng, X. (NIH/N. [C] <ge...@ni...>]

-----Original Message-----
From: Brian Paul [mailto:br...@vm...] 
Sent: Friday, December 04, 2009 10:14 AM
To: Geng, Xiujuan (NIH/NIDA) [C]
Cc: mes...@li...
Subject: Re: [Mesa3d-users] offscreen render segmentation fault with mesa 7.7

Geng, Xiujuan (NIH/NIDA) [C] wrote:
> Hi,
> 
> I'm new to mesa and openGL. I'm trying to do offscreen rendering on a 64bit Suse Linux machine. 
> 
> I started from a mesa demo code progs/osdemos/osdemo.c. I copied the main part below:
>  
>    /* Create an RGBA-mode context */
> #if OSMESA_MAJOR_VERSION * 100 + OSMESA_MINOR_VERSION >= 305
>    /* specify Z, stencil, accum sizes */
>    ctx = OSMesaCreateContextExt( OSMESA_RGBA, 16, 0, 0, NULL );
> #else
>    ctx = OSMesaCreateContext( OSMESA_RGBA, NULL );
> #endif
>    if (!ctx) {
>       printf("OSMesaCreateContext failed!\n");
>       return 0;
>    }
> 
>    /* Allocate the image buffer */
>    buffer = malloc( Width * Height * 4 * sizeof(GLubyte) );
>    if (!buffer) {
>       printf("Alloc image buffer failed!\n");
>       return 0;
>    }
> 
>    /* Bind the buffer to the context and make it current */
>    if (!OSMesaMakeCurrent( ctx, buffer, GL_UNSIGNED_BYTE, Width, Height )) {
>       printf("OSMesaMakeCurrent failed!\n");
>       return 0;
>    }  
> 
>    {
>       int z, s, a;
>       glGetIntegerv(GL_DEPTH_BITS, &z);
>       glGetIntegerv(GL_STENCIL_BITS, &s);
>       glGetIntegerv(GL_ACCUM_RED_BITS, &a);
>       printf("Depth=%d Stencil=%d Accum=%d\n", z, s, a);
>    }
>    render_image();
> 
> I compiled the code with no problem:
> gcc osdemo.c  -lglut -lGLU -lOSMesa -lm -o osdemo
> 
> But when I run it:
> ./osdemo output.ppm 400 400
> 
> It gave me a seg fault. I used gdb to debug it, and the error message is:
> 
> (gdb) run
> Starting program: /data/380/gengx/tools/Mesa-7.5.1/progs/osdemos/osdemo output.ppm 400 400
> [Thread debugging using libthread_db enabled]
> 
> Program received signal SIGSEGV, Segmentation fault.
> glGetIntegerv () at ../../../src/mesa/x86-64/glapi_x86-64.S:9444
> 9444            movq    2104(%rax), %r11
> Current language:  auto; currently asm
> 
> Our own offscreen code (also using " OSMesaCreateContextExt " and " OSMesaMakeCurrent ") faced the same segmentation problem. Basically it gave a segmentation at whatever gl routine first called in the code. 
> 
> We are currently using mesa7.7.
> 
> Any suggestion is appreciated! Thanks.

Can you run w/ valgrind and see if that finds anything?

Does the original osdemo.c work properly?

Maybe try disabling x86-64 optimizations or a debug build of Mesa.

-Brian

Brian,
Thanks for the suggestion.

I got the seg fault from the original osdemo.c. I ran it with valgrind, and didn't find anything particular. We also ran the same osdemo.c code using Mesa7.4 on Ubuntu 9.04, it gave the same segmentation fault. But if I modify the demo code to do on-screen rendering, e.g., using glutCreateWindow and render the image to the window instead of doing off-screen render with "OSMesaCreateContextExt" and "OSMesaMakeCurrent", it works without any segmentation fault.

We built mesa with a regular version and a debug version. The library is under /usr/lib/debug/usr/lib64/libOSMesa.so.7.7.0.debug
I assume I compiled the demo code using the debug build of mesa.
Here is the command I used to compile osdemo: 
gcc -g osdemo.c -lglut -lGLU -lOSMesa -lm -o osdemo

The gdb gave the following error message:
Program received signal SIGSEGV, Segmentation fault.
glGetIntegerv () at ../../../src/mesa/x86-64/glapi_x86-64.S:9444
9444            movq    2104(%rax), %r11

Is it possible that there's some bug in OSMesaCreateContextExt or OSMesaMakeCurrent? I really need off-screen rendering. Thanks again.

Xiujuan