Wikipedia
Gcov
Gcov is a source code coverage analysis and statement-by-statement profiling tool. Gcov generates exact counts of the number of times each statement in a program is executed and annotates source code to add instrumentation. Gcov comes as a standard utility with the GNU Compiler Collection (GCC) suite.
The gcov utility gives information on how often a program executes segments of code. It produces a copy of the source file, annotated with execution frequencies. The gcov utility does not produce any time-based data and works only on code compiled with the GCC suite. The manual claims it is not compatible with any other profiling or test coverage mechanism, but it works with llvm-generated files, too.