Detect if an ELF binary was built with gprof instrumentation?

You could check for references to function mcount (or possibly _mcount or __mcount according to Implementation of Profiling). This function is necessary for profiling to work, and should be absent for non-profiled binaries.

Something like:

$ readelf -s someprog | egrep "\s(_+)?mcount\b" && echo "Profiling is on for someprog"

The above works on a quick test here.

The regular expression in the answer above doesn't always work...but the general idea of grepping for "mcount" in the output of 'readelf -s [binary]' is correct, I think