Inconsistent ABIs depending on backend GLEW uses

[jengelh]

The ABI of libGLEW.so.2.2 changes between GLEW_EGL=ON and OFF:

22:04 a4:../glew/glew-2.2.0 $ cd build/cmake/
22:04 a4:../build/cmake $ cmake .
CMake Warning (dev) at CMakeLists.txt:5 (project):
  cmake_minimum_required() should be called prior to this top-level project()
  call.  Please see the cmake-commands(7) manual for usage documentation of
  both commands.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- The C compiler identification is GNU 15.0.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
CMake Deprecation Warning at CMakeLists.txt:7 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.


CMake Warning (dev) at /usr/share/cmake/Modules/FindOpenGL.cmake:415 (message):
  Policy CMP0072 is not set: FindOpenGL prefers GLVND by default when
  available.  Run "cmake --help-policy CMP0072" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  FindOpenGL found both a legacy GL library:

    OPENGL_gl_LIBRARY: /usr/lib64/libGL.so

  and GLVND libraries for OpenGL and GLX:

    OPENGL_opengl_LIBRARY: /usr/lib64/libOpenGL.so
    OPENGL_glx_LIBRARY: /usr/lib64/libGLX.so

  OpenGL_GL_PREFERENCE has not been set to "GLVND" or "LEGACY", so for
  compatibility with CMake 3.10 and below the legacy GL library will be used.
Call Stack (most recent call first):
  CMakeLists.txt:43 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Found OpenGL: /usr/lib64/libOpenGL.so
-- Found X11: /usr/include
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so - found
-- Looking for gethostbyname
-- Looking for gethostbyname - found
-- Looking for connect
-- Looking for connect - found
-- Looking for remove
-- Looking for remove - found
-- Looking for shmat
-- Looking for shmat - found
-- Looking for IceConnectionNumber in ICE
-- Looking for IceConnectionNumber in ICE - found
-- Configuring done (0.6s)
-- Generating done (0.0s)
-- Build files have been written to: ~/build/cmake
~ = for brevity

22:05 a4:../build/cmake $ make -j32
[ 12%] Building C object CMakeFiles/glew_s.dir~/src/glew.c.o
[ 25%] Building C object CMakeFiles/glew.dir~/src/glew.c.o
[ 37%] Linking C static library lib/libGLEW.a
[ 37%] Built target glew_s
[ 50%] Linking C shared library lib/libGLEW.so
[ 50%] Built target glew
[ 62%] Building C object CMakeFiles/glewinfo.dir~/src/glewinfo.c.o
[ 75%] Building C object CMakeFiles/visualinfo.dir~/src/visualinfo.c.o
[ 87%] Linking C executable bin/visualinfo
[ 87%] Built target visualinfo
[100%] Linking C executable bin/glewinfo
[100%] Built target glewinfo
22:05 a4:../build/cmake $ nm -D lib/libGLEW.so | grep SGIX_fbconfig
00000000000bf04d B __GLXEW_SGIX_fbconfig
22:05 a4:../build/cmake $ cmake . -DGLEW_EGL=ON
CMake Warning (dev) at CMakeLists.txt:5 (project):
  cmake_minimum_required() should be called prior to this top-level project()
  call.  Please see the cmake-commands(7) manual for usage documentation of
  both commands.
This warning is for project developers.  Use -Wno-dev to suppress it.

CMake Deprecation Warning at CMakeLists.txt:7 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.


CMake Warning (dev) at /usr/share/cmake/Modules/FindOpenGL.cmake:415 (message):
  Policy CMP0072 is not set: FindOpenGL prefers GLVND by default when
  available.  Run "cmake --help-policy CMP0072" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  FindOpenGL found both a legacy GL library:

    OPENGL_gl_LIBRARY: /usr/lib64/libGL.so

  and GLVND libraries for OpenGL and GLX:

    OPENGL_opengl_LIBRARY: /usr/lib64/libOpenGL.so
    OPENGL_glx_LIBRARY: /usr/lib64/libGLX.so

  OpenGL_GL_PREFERENCE has not been set to "GLVND" or "LEGACY", so for
  compatibility with CMake 3.10 and below the legacy GL library will be used.
Call Stack (most recent call first):
  CMakeLists.txt:43 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Configuring done (0.0s)
-- Generating done (0.0s)
-- Build files have been written to: ~/build/cmake
22:05 a4:../build/cmake $ make -j32
[ 12%] Building C object CMakeFiles/glew_s.dir~/src/glew.c.o
[ 25%] Building C object CMakeFiles/glew.dir~/src/glew.c.o
In file included from ~/src/glew.c:43:
~/build/cmake/../../include/GL/eglew.h:2649:80: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2649 | typedef EGLBoolean ( * PFNEGLBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                ^~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2650:80: warning: ‘struct wl_resource’ declared inside parameter list will not be visible outside of this definition or declaration
 2650 | typedef EGLBoolean ( * PFNEGLQUERYWAYLANDBUFFERWLPROC) (EGLDisplay dpy, struct wl_resource* buffer, EGLint attribute, EGLint* value);
      |                                                                                ^~~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2651:82: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2651 | typedef EGLBoolean ( * PFNEGLUNBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                  ^~~~~~~~~~
In file included from ~/src/glew.c:43:
~/build/cmake/../../include/GL/eglew.h:2649:80: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2649 | typedef EGLBoolean ( * PFNEGLBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                ^~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2650:80: warning: ‘struct wl_resource’ declared inside parameter list will not be visible outside of this definition or declaration
 2650 | typedef EGLBoolean ( * PFNEGLQUERYWAYLANDBUFFERWLPROC) (EGLDisplay dpy, struct wl_resource* buffer, EGLint attribute, EGLint* value);
      |                                                                                ^~~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2651:82: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2651 | typedef EGLBoolean ( * PFNEGLUNBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                  ^~~~~~~~~~
[ 37%] Linking C static library lib/libGLEW.a
[ 37%] Built target glew_s
[ 50%] Linking C shared library lib/libGLEW.so
[ 50%] Built target glew
[ 62%] Building C object CMakeFiles/glewinfo.dir~/src/glewinfo.c.o
[ 75%] Building C object CMakeFiles/visualinfo.dir~/src/visualinfo.c.o
In file included from ~/src/visualinfo.c:41:
~/build/cmake/../../include/GL/eglew.h:2649:80: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2649 | typedef EGLBoolean ( * PFNEGLBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                ^~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2650:80: warning: ‘struct wl_resource’ declared inside parameter list will not be visible outside of this definition or declaration
 2650 | typedef EGLBoolean ( * PFNEGLQUERYWAYLANDBUFFERWLPROC) (EGLDisplay dpy, struct wl_resource* buffer, EGLint attribute, EGLint* value);
      |                                                                                ^~~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2651:82: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2651 | typedef EGLBoolean ( * PFNEGLUNBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                  ^~~~~~~~~~
In file included from ~/src/glewinfo.c:38:
~/build/cmake/../../include/GL/eglew.h:2649:80: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2649 | typedef EGLBoolean ( * PFNEGLBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                ^~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2650:80: warning: ‘struct wl_resource’ declared inside parameter list will not be visible outside of this definition or declaration
 2650 | typedef EGLBoolean ( * PFNEGLQUERYWAYLANDBUFFERWLPROC) (EGLDisplay dpy, struct wl_resource* buffer, EGLint attribute, EGLint* value);
      |                                                                                ^~~~~~~~~~~
~/build/cmake/../../include/GL/eglew.h:2651:82: warning: ‘struct wl_display’ declared inside parameter list will not be visible outside of this definition or declaration
 2651 | typedef EGLBoolean ( * PFNEGLUNBINDWAYLANDDISPLAYWLPROC) (EGLDisplay dpy, struct wl_display* display);
      |                                                                                  ^~~~~~~~~~
[ 87%] Linking C executable bin/visualinfo
[ 87%] Built target visualinfo
[100%] Linking C executable bin/glewinfo
[100%] Built target glewinfo
22:05 a4:../build/cmake $ nm -D lib/libGLEW.so | grep SGIX_fbconfig

This is problematic because programs previously built no longer startup:

openscad: symbol lookup error: openscad: undefined symbol: __GLXEW_SGIX_fbconfig

Remedy: if it the ABI change is unavoidable, consider changing the filename produced by make/cmake to something else, e.g. libGLEW-egl.so.2.2.

[nigels-com]

That's as intended.

GLEW is a "wrangler", not a portable API.
It's available in three flavours: Windows WGL, GLX, or EGL.
These are not interchangeable.

[jengelh]

It's fine if it's not portable, but if two variants GLX , EGLare mutually non-interchangable, GLX and EGL cannot occupy the same library name if they are to be present in the system at the same time—which is desirable from a user stand point because programs P and Q may require different glew variants, and we don't want to deinstall P just to use Q and Q's desired variant of GLEW.

[amckinstry]

Hi,
I'm the Debian maintainer for glew. I've got requests to move to EGL, but others are currently using X11. I'm thinking of solving the problem by supplying both versions, with libglew-x11 (glx?) and libglew-egl variants, asking them to link accordingly.
What's you opinions?
Which should be the default?

[nigels-com]

Hello. Thanks for Debian, appreciate that and use it daily. I have thought that libGLEW ought to remain X11/GLX and we could add libEGLEW for EGL (no X11 or GLX). Similarly for Windows can have the two DLLs with glew32.dll remaining compatible. Since EGL is the new kid on the block, and doesn't seem to be going away (Wayland adoption) we do need an arrangement we can all agree on that serves both scenarios. It's long overdue, really.

[amckinstry]

Ok, I can go with that. New devel package libeglew-dev and library package libeglew2.3 ?
If they've different ABIs then would you also provide eglewinfo and evisualinfo ?

[nigels-com]

Yes, I think so.