[PATCH v2 1/8] Support coverage testing with GCC/gcov

With gcc's --coverage option, we can perform automatic coverage data collection for the test suite.

Add a new Makefile target 'coverage' that scraps all previous coverage results, recompiles git with the required compiler/linker flags (in addition to any flags you specify manually), then runs the test suite and compiles a report.

The compilation must be done with all optimizations disabled, since inlined functions (and for line-by-line coverage, also optimized branches/loops) break coverage tracking.

The tests are run serially (with -j1). The coverage code should theoretically allow concurrent access to its data files, but the author saw random test failures. Obviously this could be improved.

The report currently consists of a list of functions that were never executed during the tests, which is written to 'coverage-untested-functions'. Once this list becomes reasonably short, we would also want to look at branches that were never taken.

Currently only toplevel *.c files are considered. It would be nice to at least include xdiff, but --coverage did not save data to subdirectories on the system used to write this (gcc 4.3.2).

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

Let the 'all' sub-build of 'coverage' run with the caller's -j setting so that it can parallelize.

Interdiff:

   --- a/Makefile
   +++ b/Makefile
  @@ -21,8 +21,9 @@
   +COVERAGE_LDFLAGS = $(CFLAGS)  -O0 -lgcov
   +
   +coverage-build: coverage-clean
  ++      $(MAKE) CFLAGS="$(COVERAGE_CFLAGS)" LDFLAGS="$(COVERAGE_LDFLAGS)" all
   +      $(MAKE) CFLAGS="$(COVERAGE_CFLAGS)" LDFLAGS="$(COVERAGE_LDFLAGS)" \
  -+              -j1 all test
  ++              -j1 test
   +
   +coverage-report:
   +      gcov -b *.c

 Makefile |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)