Bug#775235: Repeatable failure to start on i386 running under kvm

[Bernhard Übelacker]

Hello,
first a question about this merging with bug #770130 and #776911.
These bugs seem to happen on real hardware with some intel
graphics card and giving an error:
    "*ERROR* pipe A underrun".

But bug #775235 was explicitly opened by Steve McIntyre to be
run inside a i386 KVM and gives an error:
    "LLVM ERROR: Do not know how to split the result of this operator!"

Therefore I wonder if these should really be merged?

----------------

Second I searched a little bit further and came across
this patch discussion: https://freedesktop.org/patch/34445/

This is the start of the patch description by Maarten Lankhorst:
    This fixes a crash when llvmpipe tries to use sse instructions,
    but llvm detects a cpu that doesn't support them.
    
    Fixes for example piglit/bin/amd_seamless_cubemap_per_texture -fbo -auto
    on i386 when run inside "qemu -cpu qemu32", which would otherwise error with:
    "LLVM ERROR: Do not know how to split the result of this operator!"

Looks very similiar to our issue here.
Therefore I build a own local build of libgl1-mesa-dri and that was
successfully solving the issue inside the i386 KVM.

Unfortunately I cannot find this patch ever applied upstream.
The discussion reads (as far as I could follow) that there are
probably better ways to detect CPU features.
Also cannot say which impact it would have on every other systems.

----------------

Did some additional starts of the VM (with debian built packages) to verify:
    qemu-system-i386 -cpu core2duo               works 
    qemu-system-i386 -cpu pentium2               works
    qemu-system-i386 --enable-kvm -cpu host      works
    qemu-system-i386 --enable-kvm -cpu kvm32     works
    qemu-system-i386 --enable-kvm -cpu qemu32    fails
    qemu-system-i386 --enable-kvm                fails
    qemu-system-x86_64 --enable-kvm              fails

Unfortunately "qemu32" seems to be the default.



Kind regards,
Bernhard



These steps should make a local build of libgl1-mesa-dri with the mentioned patch applied:
    mkdir mesa; cd mesa
    apt-get source libgl1-mesa-dri
    cd mesa-10.3.2/
    wget "https://freedesktop.org/patch/34445/raw/" -O debian/patches/08_gallivm_force_sse_instructions_for_llvm_3.5+.patch
    echo 08_gallivm_force_sse_instructions_for_llvm_3.5+.patch >> debian/patches/series
    # install build dependencies
    dpkg-buildpackage -b
    cd ..
    su
        dpkg -i libgl1-mesa-dri_10.3.2-1_i386.deb libgl1-mesa-dri-dbg_10.3.2-1_i386.deb