opengl: Bail if cached shader fails to load

QOpenGLProgramBinaryCache::setProgramBinary() should check
GL_LINK_STATUS after glProgramBinary(), but doesn't.

In practice, this means that SDDM is a white screen, and KDE is just
a gray task bar.

So far, Qt tries to check this using its internal ::link() function.
But in case the cached binary fails to load, Qt currently attempts to
link the inexistent program, resulting in a zero-length, fixed
pipeline shader.

Checking this already in ::setProgramBinary() makes the call to
::link() superfluous, so we remove that as well.

Done-with: Max Staudt <mstaudt@suse.com>
Done-with: Michal Srb <msrb@suse.com>
Done-with: Fabian Vogt <fvogt@suse.de>
Task-number: QTBUG-66420
Change-Id: Iabb51d0eb2c0c16bde696efff623e57d15f28d82
Reviewed-by: Jesus Fernandez <Jesus.Fernandez@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 1 insertions, 7 deletions

diff --git a/src/gui/opengl/qopenglshaderprogram.cpp b/src/gui/opengl/qopenglshaderprogram.cpp
index b044397f8e..1fe30f7e0e 100644
--- a/src/gui/opengl/qopenglshaderprogram.cpp
+++ b/src/gui/opengl/qopenglshaderprogram.cpp
@@ -3824,13 +3824,7 @@ bool QOpenGLShaderProgramPrivate::linkBinary()
     bool needsCompile = true;
     if (binCache.load(cacheKey, q->programId())) {
         qCDebug(DBG_SHADER_CACHE, "Program binary received from cache");
-        linkBinaryRecursion = true;
-        bool ok = q->link();
-        linkBinaryRecursion = false;
-        if (ok)
-            needsCompile = false;
-        else
-            qCDebug(DBG_SHADER_CACHE, "Link failed after glProgramBinary");
+        needsCompile = false;
     }
 
     bool needsSave = false;