Bug#1030336: ... Darktable does not work well under OpenCL.

[Ole Streicher]

Dear maintainer,

I tried to debug this a bit with

$ strace -f darktable-cltest -d opencl

and found that the reason is that the library "libnvidia-nvvm.so.4" was 
not found for the compilation. Darktable searches

/usr/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/tls/haswell/x86_64/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/tls/haswell/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/tls/x86_64/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/tls/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/haswell/x86_64/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/haswell/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/x86_64/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/libnvidia-nvvm.so.525.85.12

(and also on more places outside of /usr/lib/x86_64-linux-gnu/).

The installed driver libnvidia-nvvm4 however puts them under

/usr/lib/x86_64-linux-gnu/nvidia/current/libnvidia-nvvm.so.4
/usr/lib/x86_64-linux-gnu/nvidia/current/libnvidia-nvvm.so.525.85.12

which is *not* searched. Pragmatically creating a symlink

libnvidia-nvvm.so.4 -> nvidia/current/libnvidia-nvvm.so.4

in /usr/lib/x86_64-linux-gnu/ resolves this; the darktable-cltest 
succeeds and darktable runs with OpenCL support.

I have no idea whether this syslink was forgotten in the libnvidia-nvvm4 
package or darktable should be adjusted to search in the new places. 
However, with this hint the problem should be resolvable in one of the 
packages.

Cheers

Ole