/usr/share/systemtap/tapset/choose_defined.stpm is in systemtap-common 2.3-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | // Use the first parameter if it's @defined, otherwise use the second parameter
@define choose_defined(value_if_defined, alternate) %(
( @defined(@value_if_defined) ? (@value_if_defined) : (@alternate) )
%)
|