From 3bb3ee936f27e9749bf1a2c4bd5ded2f5167663f Mon Sep 17 00:00:00 2001
From: Max Staudt <mstaudt@suse.de>
Date: Mon, 12 Feb 2018 15:07:29 +0100
Subject: [PATCH] opengl: Bail if cached shader fails to load
References: boo#1080578, boo#1079465
Signed-off-by: Max Staudt <mstaudt@suse.de>

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.

Many thanks to Michal Srb and Fabian Vogt for hunting this down.
This was truly a joint effort.

Cc: Michal Srb <msrb@suse.com>
Cc: Fabian Vogt <fvogt@suse.de>
Signed-off-by: Max Staudt <mstaudt@suse.de>
---
 src/gui/opengl/qopenglprogrambinarycache.cpp | 11 ++++++++++-
 src/gui/opengl/qopenglshaderprogram.cpp      |  8 +-------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/gui/opengl/qopenglprogrambinarycache.cpp b/src/gui/opengl/qopenglprogrambinarycache.cpp
index 06373e1113..f50878ab5c 100644
--- a/src/gui/opengl/qopenglprogrambinarycache.cpp
+++ b/src/gui/opengl/qopenglprogrambinarycache.cpp
@@ -161,10 +161,19 @@ bool QOpenGLProgramBinaryCache::setProgramBinary(uint programId, uint blobFormat
     QOpenGLExtraFunctions *funcs = QOpenGLContext::currentContext()->extraFunctions();
     while (funcs->glGetError() != GL_NO_ERROR) { }
     funcs->glProgramBinary(programId, blobFormat, p, blobSize);
+
     int err = funcs->glGetError();
+    GLint link_status = 0;
+    funcs->glGetProgramiv(programId, GL_LINK_STATUS, &link_status);
+    if (link_status != GL_TRUE || err != GL_NO_ERROR) {
+        qCDebug(DBG_SHADER_CACHE, "Program binary failed to load for program %u, size %d, format 0x%x, link_status = 0x%x, err = 0x%x",
+                programId, blobSize, blobFormat, link_status, err);
+        return false;
+    }
+
     qCDebug(DBG_SHADER_CACHE, "Program binary set for program %u, size %d, format 0x%x, err = 0x%x",
             programId, blobSize, blobFormat, err);
-    return err == 0;
+    return true;
 }
 
 #ifdef Q_OS_UNIX
diff --git a/src/gui/opengl/qopenglshaderprogram.cpp b/src/gui/opengl/qopenglshaderprogram.cpp
index cc8af16bfe..3b82baccb3 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;
-- 
2.13.6