[Stellarium-pubdevel] A couple patches to fix crash issues

[Greg A. <st...@ga...>]

Hi -

I checked out the bazaar repository, rev 5924, and built it and
discovered two separate issues that caused Stellarium to crash on startup
on my computer.  I'm new to Stellarium development (and to Bazaar) so I
hope I'm not doing this wrong...

First, the new solar system shadows are enabled by default, but if they
are initialized without StelRenderer::areFloatTexturesSupported() then
that triggers an assert failure in
StelRenderer::createTexture(void*,QSize,TextureDataFormat,TextureParams&).
I believe I saw this before other users because I am using unaccelerated
(software rendered) MesaGL.  My proposed remedy is to disable solar system
shadows (regardless of the config parameter) if float textures are
not supported.

Second, StelQGLGLSLShader.uniformStorage can be unaligned, both because
its start position may be unaligned and because it may contain members
(such as bool) which would introduce misalignment in subsequent members.
I believe I saw this before other users because I am running on ARM,
which gives a fatal SIGBUS for unaligned memory access.  My proposed
remedy is to enforce a minimum alignment in uniformStorage corresponding
to sizeof(void*), which should be harmless on most platforms, a slight
performance improvement on some, and the difference between
crashing-or-not on a few.  Note that I use the GCC
__attribute__((aligned(n))) extension.  I noticed that the similar GCC
extension __attribute__((packed)) was already used in Stellarium, so
hopefully that is not forbidden...

As an aside, I am working on the development branch of Stellarium because
I am attempting to improve the performance on my new laptop that does not
have accelerated GL drivers.  At first glance, the new build from Bazaar
appears to be about 400% slower than the 0.11.4 that I had been working
with, so that is where my focus will be if I have any future
contributions.

And thanks -- Stellarium is simply the best!!  Even at 1fps, I find I
can't live without it.

Patches below...

Cheers,
- Greg

=== modified file 'src/core/modules/SolarSystem.cpp'
--- src/core/modules/SolarSystem.cpp	2013-02-22 11:43:47 +0000
+++ src/core/modules/SolarSystem.cpp	2013-03-23 03:45:48 +0000
@@ -1035,7 +1035,7 @@
 
 	sharedPlanetGraphics.lazyInit(renderer);
 
-	if(StelApp::getInstance().getRenderSolarShadows() && sharedPlanetGraphics.shadowPlanetShader)
+	if(StelApp::getInstance().getRenderSolarShadows() && sharedPlanetGraphics.shadowPlanetShader && renderer->areFloatTexturesSupported())
 	{
 		StelTextureNew* shadowInfo = computeShadowInfo(renderer);
 

=== modified file 'src/core/renderer/StelQGLGLSLShader.cpp'
--- src/core/renderer/StelQGLGLSLShader.cpp	2012-09-17 18:12:57 +0000
+++ src/core/renderer/StelQGLGLSLShader.cpp	2013-03-23 04:31:25 +0000
@@ -22,9 +22,17 @@
 
 #include <stdint.h>
 
+#define ALIGN_UNIFORM_SIZE(x) (((x)+(UNIFORM_ALIGNMENT-1)) & ~(UNIFORM_ALIGNMENT-1))
+
 int StelQGLGLSLShader::UNIFORM_SIZES[UniformType_max] =
-	{0, sizeof(float), sizeof(Vec2f), sizeof(Vec3f),
-	 sizeof(Vec4f), sizeof(Mat4f), sizeof(bool), sizeof(int)};
+	{0,
+	ALIGN_UNIFORM_SIZE(sizeof(float)),
+	ALIGN_UNIFORM_SIZE(sizeof(Vec2f)),
+	ALIGN_UNIFORM_SIZE(sizeof(Vec3f)),
+	ALIGN_UNIFORM_SIZE(sizeof(Vec4f)),
+	ALIGN_UNIFORM_SIZE(sizeof(Mat4f)),
+	ALIGN_UNIFORM_SIZE(sizeof(bool)),
+	ALIGN_UNIFORM_SIZE(sizeof(int))};
 
 StelQGLGLSLShader::StelQGLGLSLShader(StelQGL2Renderer* renderer, bool internal) 
 	: StelGLSLShader()

=== modified file 'src/core/renderer/StelQGLGLSLShader.hpp'
--- src/core/renderer/StelQGLGLSLShader.hpp	2012-09-17 02:26:58 +0000
+++ src/core/renderer/StelQGLGLSLShader.hpp	2013-03-23 04:30:47 +0000
@@ -32,6 +32,11 @@
 //! Used to allow pointer casts to/from 2D float array for matrix uniform storage/upload.
 typedef float RAW_GL_MATRIX [4][4];
 
+// Minimum alignment for uniform members, both for efficiency and to
+// avoid SIGBUS on some platforms (like ARM).
+#define UNIFORM_ALIGNMENT sizeof(void*)
+
+
 //! QGL based StelGLSLShader implementation, used by the QGL2 renderer backend.
 //!
 //! @note This is an internal class of the Renderer subsystem and should not be used elsewhere.
@@ -394,7 +399,7 @@
 	//! The data is then uploaded by uploadUniforms().
 	//!
 	//! @see uploadUniforms, clearUniforms, pushUniformStorage
-	unsigned char uniformStorage [UNIFORM_STORAGE];
+	unsigned char uniformStorage [UNIFORM_STORAGE] __attribute__((aligned(UNIFORM_ALIGNMENT)));
 
 	//! Pointer to uniformStorage[uniformStorageUsed]. Avoids breaking strict aliasing.
 	void* uniformStoragePointer;