1. Coverage analysis using gcc (or g++) source code source code executable run results coverage gcc –ftest-coverage –fprofile-arcs myprogram.exe myprogram.cpp myprogram.exe myprogram.gcno myprogram.gcda myprogram.gcov text report gcov –c –f –b myprogram 1.Compile the program with additional options -creates the control flow graph (static analysis) -instruments the code to save statistics on executed statements 2.Run the program with your desired (test) input -saves the covered statements and other statistics 3.Analyze the results of the run for coverage -merges the control flow graph with collected statistics -saves results in human-readable form

2. Example Actual code (ispow3.cpp) Control flow graphs (ispow3.gcno) Covered statements (ispow3.gcda) A simple program to compute if a number is a power of 3

3. gcov – First impression gcov ispow3 Simplest output: shows, per file number of lines executed out of total number of executable lines Example (for ispow3 run with the input ‘100’) File '/opt/local/include/gcc44/c++/bits/ios_base.h' Lines executed:0.00% of 2 /opt/local/include/gcc44/c++/bits/ios_base.h:creating 'ios_base.h.gcov' File '/opt/local/include/gcc44/c++/ostream' Lines executed:0.00% of 13 /opt/local/include/gcc44/c++/ostream:creating 'ostream.gcov' File '/opt/local/include/gcc44/c++/bits/basic_ios.h' Lines executed:0.00% of 10 /opt/local/include/gcc44/c++/bits/basic_ios.h:creating 'basic_ios.h.gcov' File 'ispow3.cpp' Lines executed:90.91% of 11 ispow3.cpp:creating 'ispow3.cpp.gcov' File '/opt/local/include/gcc44/c++/iostream' Lines executed:100.00% of 1 /opt/local/include/gcc44/c++/iostream:creating 'iostream.gcov' File '/opt/local/include/gcc44/c++/bits/char_traits.h' Lines executed:0.00% of 2 /opt/local/include/gcc44/c++/bits/char_traits.h:creating 'char_traits.h.gcov' File '/opt/local/include/gcc44/c++/bits/locale_facets.h' Lines executed:0.00% of 5 /opt/local/include/gcc44/c++/bits/locale_facets.h:creating 'locale_facets.h.gcov’ Comments the program covers one source file and 6 headers for each file, a.gcov detailed report is generated (we’ll examine these next) Read this as: 90.91% of 11 executable lines in ispow3.cpp were covered

4. gcov – Simple per-file report File 'ispow3.cpp' Lines executed:90.91% of 11 ispow3.cpp:creating 'ispow3.cpp.gcov' Column 1: line execution status ‘-’ not an executable line ‘3’ line execution count #### line not covered, i.e. not executed Column 2: line nr. in source file Column 3: source code Indeed, this line is not executed for input x == 100 So which are these ‘11 executable lines’ in ispow3.cpp? Why is the closing brace marked as ‘executable’??

5. gcov – Detailed per-file report Generate with gcov –c ispow3 We now also see function call reports function name (mangled, use c++filt to demangle) number of times the function is called number of times the function returned whether all the control-flow-graph blocks in the function were executed after each line containing branches (e.g. the for loop) how many times each branch was taken after each line containing function calls (e.g. << operator) how many times each call returned Indeed, for the run x==100, we take only branch x>=0 (hence, the else block below is never executed) There are 2 function calls counted for the ‘closing brace’ line these are part of the finalization code (execution of global cleanup operations) this is the ‘missing’ 11 th executable line…

6. Typical gcov usage build your code base with the gcov options (-ftest-coverage –fprofile-arcs) run all your testsuite as usual collect all *.gcov files and gcov text output compute statistics from this output to assess the effectiveness of your testuite (how much was covered) improve the testsuite see what was not covered (enough) design new tests to cover those cases Strong points of gcov works out of the box for any program compilable with gcc/g++ no complex set-up or configuration files needed can embed analysis output easily in any build/test process you can (in theory) read the *.gcno and *.gcda files to add your own analyses several other options, not explained here (see man page) more statistics (per-block, per-function, unconditional branches, …) it is free and supported on many platforms

7. Weak(er) points of gcov output needs some postprocessing to be easily read file-based output is not always easy to read OK for source files can be confusing for header files (think e.g. of multiple inclusion) must be aware of low(er) level details hidden code (e.g. initialization and destruction) name mangling optimization (best to switch it off completely) control-flow-graph statistics do not always map well to line-oriented statistics not every line is a graph node (or block of nodes) problems with multiple instructions per line macros gcov does only statement coverage function coverage function call coverage branch coverage gcov does not do loop coverage, (multiple) condition coverage, path coverage