[Piglit] [PATCH] dispatch: Fix lookup for core OpenGL symbols

[Chad Versace]

The following commit regressed lookup of some new OpenGL symbols:

    commit cb334db3f2bb7ddf9b2f43641f898896f99c69b1
    Author: Daniel Kurtz <djkurtz at chromium.org>
    Date:   Thu Oct 16 21:36:01 2014 +0800
    Subject: dispatch: Use dlsym to lookup core symbols for EGL (v2)

It regressed these Piglit tests on i965:
    spec at arb_pipeline_statistics_query@arb_pipeline_statistics_query-vert_adj
    spec at arb_pipeline_statistics_query@arb_pipeline_statistics_query-geom

Fix the tests by consistently using egl/glXGetProcAddress to lookup core
OpenGL symbols instead of dlsym(), and add a lengthy comment explaining
why. (For core OpenGL ES symbols, continue using dlsym() as in
cb334db3).

Cc: Marek Olšák <marek.olsak at amd.com>
Cc: Mark Janes <mark.a.janes at intel.com>
Cc: Daniel Kurtz <djkurtz at chromium.org>
---
 tests/util/piglit-dispatch-init.c | 42 +++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/tests/util/piglit-dispatch-init.c b/tests/util/piglit-dispatch-init.c
index a47d4cc..ead6d2f 100644
--- a/tests/util/piglit-dispatch-init.c
+++ b/tests/util/piglit-dispatch-init.c
@@ -157,13 +157,9 @@ get_core_proc_address(const char *function_name, int gl_10x_version)
 #else /* Linux */
 
 #if defined(PIGLIT_HAS_EGL)
-#define GLX_LIB "libGL.so.1"
 #define GLES1_LIB "libGLESv1_CM.so.1"
 #define GLES2_LIB "libGLESv2.so.2"
 
-/** dlopen() return value for libGL.so.1 */
-static void *glx_handle;
-
 /** dlopen() return value for libGLESv1_CM.so.1 */
 static void *gles1_handle;
 
@@ -213,11 +209,32 @@ get_ext_proc_address(const char *function_name)
  * This function is used to retrieve the address of core GL functions
  * on Linux.
  *
- * eglGetProcAddress supports querying core functions only if EGL >= 1.5
- * or if EGL_KHR_get_all_proc_addresses or
- * EGL_KHR_client_get_all_proc_addresses is supported. Rather than worry
- * about such details, when using EGL we consistently use dlsym() on the
- * client library to lookup core functions.
+ * eglGetProcAddress supports querying core functions only if EGL >= 1.5 or if
+ * EGL_KHR_get_all_proc_addresses or EGL_KHR_client_get_all_proc_addresses is
+ * supported. Rather than worry about such details, we consistently use dlysm()
+ * to lookup core *OpenGL ES* functions on systems where EGL is available.
+ *
+ * Lookup for core *OpenGL* functions is more complicated because the EGL 1.4
+ * specification, the antiquated OpenGL ABI for Linux [1] from year 2000, and
+ * various libGL.so implementations all disagree on the set of symbols that
+ * libGL.so should statically expose and which are queryable with
+ * eglGetProcAddress.  The EGL 1.4 spec (as explained above) does not require
+ * eglGetProcAddress to work for core functions.  The OpenGL ABI spec requires
+ * that libGL.so expose *no* symbols statically except those contained in GL
+ * 1.2 and select extensions. Actual driver vendors tend to expose most, if not
+ *   all, symbols statically from libGL.so.
+ *
+ * Considering how messy this situation is, the best way to query a core OpenGL
+ * function on EGL is eglGetProcAddress (or even glXGetProcAddress!). Sometimes
+ * Mesa's libGL doesn't statically expose all OpenGL functions supported by the
+ * driver, but Mesa's eglGetProcAddress does work for all GL functions, core
+ * and extension.  Some other vendors of desktop OpenGL drivers, such as
+ * Nvidia, do the same. (By coincidence, Mesa's glXGetProcAddress also returns
+ * the same addresses as eglGetProcAddress). We don't need to worry about
+ * platforms on which eglGetProcAddress does not work for core functions, such
+ * as Mali, because those platforms support only OpenGL ES.
+ *
+ * [1] https://www.opengl.org/registry/ABI/
  */
 static piglit_dispatch_function_ptr
 get_core_proc_address(const char *function_name, int gl_10x_version)
@@ -230,8 +247,11 @@ get_core_proc_address(const char *function_name, int gl_10x_version)
 		return do_dlsym(&gles2_handle, GLES2_LIB, function_name);
 	case 10:
 	default:
-		/* GL does not have its own library, so use GLX */
-		return do_dlsym(&glx_handle, GLX_LIB, function_name);
+		/* We query the address of core OpenGL functions as if they
+		 * were extension functions. Read about the gory details
+		 * above. */
+		(void) gl_10x_version;
+		return get_ext_proc_address(function_name);
 	}
 #else
 	/* We don't need to worry about the GL version, since when using GLX
-- 
2.3.6