https://bugs.freedesktop.org/show_bug.cgi?id=83274
--- Comment #6 from Michel Dänzer michel@daenzer.net --- (In reply to nicolas from comment #5)
==5476== Command: /home/nicolas/.steam/steam/SteamApps/common/XCom-Enemy-Unknown/binaries/ linux/xcom.sh -arch=x86_64
Looks like valgrind was run with the xcom.sh script as its argument, so it probably only monitored execution of the shell interpreter. I think you need to hook it into the xcom.sh script itself so it monitors execution of the actual game executable.