Description of problem: The affected machine is an AMD Sempron with a VIA UniChrome integrated graphics chipset. This graphics chipset lacks support for the 3D capabilities required for Gnome Shell, so therefore it should be using llvmpipe as the software implementation. The AMD Sempron cpuinfo is as follows: [root@localhost ~]# cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 6 model : 8 model name : AMD Sempron(tm) 2400+ stepping : 1 cpu MHz : 1666.026 cache size : 256 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mp mmxext 3dnowext 3dnow bogomips : 3332.05 clflush size : 32 cache_alignment : 32 address sizes : 34 bits physical, 32 bits virtual power management: ts Note the lack of SSE2 support. When running Gnome Shell on this machine, the desktop runs in fallback mode instead of using llvmpipe. When investigating why, I found https://bugs.freedesktop.org/show_bug.cgi?id=27867 which mentions that llvm has a bug that makes it crash when SSE2 is not available. Therefore, a patch was added to mesa llvmpipe in order to disable it when SSE2 is not detected. I think this explains the fallback mode. However, this bug dates from 2010, and the affected llvm is 2.7. Fedora 18 uses llvm 3.1. Is this bug still relevant to the current version of llvm and mesa? Version-Release number of selected component (if applicable): mesa-dri-drivers-9.0.1-5.fc18.i686 llvm-libs-3.1-13.1.fc18.i686 How reproducible: Always (on affected machine) Steps to Reproduce: 1. Get non-SSE2 machine with old graphics card 2. Install Fedora 18 3. Start Gnome Shell Actual results: Fallback mode in desktop Expected results: Desktop should be running llvmpipe Additional info:
Apparently, with llvm-libs-3.2-2 and mesa-libGL-9.1-1, the patch is still present.
Fixed in Mesa 9.2: commit ca70de9bd20bc4a11b2d2d368e0cc1f49527a947 Author: Adam Jackson <ajax> Date: Thu Apr 4 17:16:22 2013 -0400 llvmpipe: Work without sse2 if llvm is new enough At least on llvm 3.2 this appears to work fine. Tested on an Athlon XP 2600+, which has sse and 3dnow but not sse2. Reviewed-by: Jose Fonseca <jfonseca> Signed-off-by: Adam Jackson <ajax>