Using apitrace with Xvfb

Sat May 16 00:07:34 PDT 2015

Good idea. Here is the trace:

    0 glXQueryVersion(dpy = 0x1feb4f0, maj = &1, min = &4) = True
    1 glXQueryExtension(dpy = 0x1feb4f0, errorb = &153, event = &93) = True
    2 glXQueryExtensionsString(dpy = 0x1feb4f0, screen = 0) =
"GLX_ARB_get_proc_address GLX_ARB_multisample GLX_EXT_import_context
GLX_EXT_visual_info GLX_EXT_visual_rating GLX_MESA_copy_sub_buffer
GLX_MESA_multithread_makecurrent GLX_MESA_query_renderer
GLX_OML_swap_method GLX_SGI_make_current_read GLX_SGIS_multisample
GLX_SGIX_fbconfig GLX_SGIX_pbuffer GLX_EXT_texture_from_pixmap "
    3 glXChooseFBConfig(dpy = 0x1feb4f0, screen = 0, attribList =
{GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT, GLX_RENDER_TYPE, GLX_RGBA_BIT,
GLX_RED_SIZE, 1, GLX_GREEN_SIZE, 1, GLX_BLUE_SIZE, 1, GLX_ALPHA_SIZE, 1,
GLX_DOUBLEBUFFER, True, GLX_DEPTH_SIZE, 1, GLX_STENCIL_SIZE, 1, 0}, nitems
= &8) = {0x2028bc0, 0x2028da0, 0x202e070, 0x202e250, 0x2028cb0, 0x2028e90,
0x202e160, 0x202e340}
    4 glXGetVisualFromFBConfig(dpy = 0x1feb4f0, config = 0x2028bc0) =
&{visual = 0x1ff6700, visualid = 33, screen = 0, depth = 24, c_class = 4,
red_mask = 16711680, green_mask = 65280, blue_mask = 255, colormap_size =
256, bits_per_rgb = 8}

No call actually fails but the context fails to create because it can't
find the GLX_ARB_create_context extension (which is missing from the
extension string list). If glretrace gets a GLX version >= 1.4 and can't
find this extension and you request a core profile, the createContext
function returns NULL. This code is all in glws_glx.cpp in the
createContext function.

Further inspection using "DISPLAY=:99 glxinfo" does indicate that the GLX
server does not support GLX_ARB_create_context extension:

name of display: :99
display: :99  screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
    GLX_ARB_multisample, GLX_EXT_import_context,
GLX_EXT_texture_from_pixmap,
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer,
    GLX_OML_swap_method, GLX_SGIS_multisample, GLX_SGIX_fbconfig,
    GLX_SGIX_pbuffer, GLX_SGI_make_current_read
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
client glx extensions:
    GLX_ARB_create_context, GLX_ARB_create_context_profile,
    GLX_ARB_create_context_robustness, GLX_ARB_fbconfig_float,
    GLX_ARB_framebuffer_sRGB, GLX_ARB_get_proc_address,
GLX_ARB_multisample,
    GLX_EXT_buffer_age, GLX_EXT_create_context_es2_profile,
    GLX_EXT_fbconfig_packed_float, GLX_EXT_framebuffer_sRGB,
    GLX_EXT_import_context, GLX_EXT_texture_from_pixmap,
GLX_EXT_visual_info,
    GLX_EXT_visual_rating, GLX_INTEL_swap_event, GLX_MESA_copy_sub_buffer,
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer,
    GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control,
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer,
    GLX_SGIX_visual_select_group, GLX_SGI_make_current_read,
    GLX_SGI_swap_control, GLX_SGI_video_sync
GLX version: 1.4
GLX extensions:
    GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context,
    GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info,
GLX_EXT_visual_rating,
    GLX_MESA_copy_sub_buffer, GLX_MESA_multithread_makecurrent,
    GLX_MESA_query_renderer, GLX_OML_swap_method, GLX_SGIS_multisample,
    GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGI_make_current_read

The client supports the extension but not he server, thus it is not in the
GLX extensions list. So how does freeglut work in the first place? Looking
at the trace:

0 glXQueryExtension(dpy = 0xa444f0, errorb = NULL, event = NULL) = True
1 glXChooseFBConfig(dpy = 0xa444f0, screen = 0, attribList = {GLX_RED_SIZE,
1, GLX_GREEN_SIZE, 1, GLX_BLUE_SIZE, 1, GLX_DOUBLEBUFFER, True,
GLX_DEPTH_SIZE, 1, 0}, nitems = &64) = {0xa7e020, 0xa7e200, 0xa83480,
0xa83660, 0xa7d4e0, 0xa7d6c0, 0xa82940, 0xa82b20, 0xa7da80, 0xa7dc60,
0xa82ee0, 0xa830c0, 0xa7ce10, 0xa7d120, 0xa823a0, 0xa82580, 0xa7c2d0,
0xa7c4b0, 0xa81860, 0xa81a40, 0xa7b790, 0xa7b970, 0xa80d20, 0xa80f00,
0xa7bd30, 0xa7bf10, 0xa812c0, 0xa814a0, 0xa7b1f0, 0xa7b3d0, 0xa80780,
0xa80960, 0xa7e110, 0xa7e2f0, 0xa83570, 0xa83750, 0xa7d5d0, 0xa7d7b0,
0xa82a30, 0xa82c10, 0xa7db70, 0xa7dd50, 0xa82fd0, 0xa831b0, 0xa7cf00,
0xa7d210, 0xa82490, 0xa82670, 0xa7c3c0, 0xa7c5a0, 0xa81950, 0xa81b30,
0xa7b880, 0xa7ba60, 0xa80e10, 0xa80ff0, 0xa7be20, 0xa7c000, 0xa813b0,
0xa81590, 0xa7b2e0, 0xa7b4c0, 0xa80870, 0xa80a50}
2 glXGetVisualFromFBConfig(dpy = 0xa444f0, config = 0xa7e020) = &{visual =
0xa4f630, visualid = 297, screen = 0, depth = 24, c_class = 4, red_mask =
16711680, green_mask = 65280, blue_mask = 255, colormap_size = 256,
bits_per_rgb = 8}
3 glXGetProcAddressARB(procName = "glXCreateContextAttribsARB") =
0x7f49a8ac15f2
4 glXCreateContextAttribsARB(dpy = 0xa444f0, config = 0xa7e020,
share_context = NULL, direct = True, attrib_list =
{GLX_CONTEXT_MAJOR_VERSION_ARB, 3, GLX_CONTEXT_MINOR_VERSION_ARB, 3,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_DEBUG_BIT_ARB |
GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB, 0}) = 0xa55da0
5 glXIsDirect(dpy = 0xa444f0, ctx = 0xa55da0) = True

It seems it doesn't bother checking the extension string, preferring to
just call glXGetProcAddressARB("glXCreateContextAttribsARB") and using the
pointer returned. I don't know how valid this is. When I made a similar
change to apitrace, glreplay was able to replay the trace that was failing
before. If the context is direct, perhaps it doesn't matter than the glx
server doesn't support the GLX_ARB_create_context[_profile] extensions?

 -- Nick

On Fri, May 15, 2015 at 5:38 PM, Alexander Monakov <amonakov at ispras.ru>
wrote:

> To investigate this further, trace the replayer, i.e.:
>
>   DISPLAY=:99 apitrace trace -o rtrace apitrace replay trace
>
> This should show what GLX call is failing in the replayer.
>
> Alexander
>
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