build: Enable configuring with gcov

This allows generating code and test coverage reports using lcov &
genhtml.  Useful for understanding how much of the codebase is currently
covered by unit and autotests.

Makefile.am

@@ -749,12 +749,25 @@ if WIRED
 endif
 endif
 
-clean-local:
+gcov-clean:
+if GCOV
+	-$(LCOV) --quiet --directory $(builddir) -z
+	-rm -rf "$(builddir)/iwd-coverage.info" "$(builddir)/gcov"
+	-find . -name "*.gcda" -o -name "*.gcov" -o -name "*.gcno" -delete
+endif
+
+clean-local: gcov-clean
 	-rm -f unit/cert-*.pem unit/cert-*.csr unit/cert-*.srl unit/*-settings.8021x
 
 maintainer-clean-local:
 	-rm -rf build-aux ell
 
+gcov-report:
+if GCOV
+	$(LCOV) --quiet --directory $(builddir) --capture --output-file "iwd-coverage.info"
+	LANG=C $(GENHTML) --quiet --prefix $(builddir) --output-directory "$(builddir)/gcov" --title "iwd Code Coverage" --legend "$(builddir)/iwd-coverage.info"
+endif
+
 src/builtin.h: src/genbuiltin config.status
 	$(AM_V_at)$(MKDIR_P) $(@D)
 	$(AM_V_GEN)$(srcdir)/src/genbuiltin $(builtin_modules) > $@

acinclude.m4

@@ -46,6 +46,27 @@ AC_DEFUN([AC_PROG_CC_UBSAN], [
 	])
 ])
 
+AC_DEFUN([AC_PROG_CC_GCOV], [
+	AC_CACHE_CHECK([whether ${CC-cc} accepts -fprofile-arcs], ac_cv_prog_cc_profile_arcs, [
+		echo 'void f(){}' > conftest.c
+		if test -z "`${CC-cc} -fprofile-arcs -c conftest.c 2>&1`"; then
+			ac_cv_prog_cc_profile_arcs=yes
+		else
+			ac_cv_prog_cc_profile_arcs=no
+		fi
+		rm -rf conftest*
+	])
+	AC_CACHE_CHECK([whether ${CC-cc} accepts -ftest_coverage], ac_cv_prog_cc_test_coverage, [
+		echo 'void f(){}' > conftest.c
+		if test -z "`${CC-cc} -ftest-coverage -c conftest.c 2>&1`"; then
+			ac_cv_prog_cc_test_coverage=yes
+		else
+			ac_cv_prog_cc_test_coverage=no
+		fi
+		rm -rf conftest*
+	])
+])
+
 AC_DEFUN([COMPILER_FLAGS], [
 	if (test "${CFLAGS}" = ""); then
 		CFLAGS="-Wall -fsigned-char -fno-exceptions"

configure.ac

@@ -25,6 +25,7 @@ AC_PROG_CC_PIE
 AC_PROG_CC_ASAN
 AC_PROG_CC_LSAN
 AC_PROG_CC_UBSAN
+AC_PROG_CC_GCOV
 AC_PROG_INSTALL
 AC_PROG_MKDIR_P
 AC_PROG_LN_S
@@ -54,6 +55,28 @@ AC_ARG_ENABLE(debug, AS_HELP_STRING([--enable-debug],
 	fi
 ])
 
+AC_ARG_ENABLE(gcov, AS_HELP_STRING([--enable-gcov],
+			[enable compiling with code coverage information]), [
+	if (test "${enableval}" = "yes" &&
+			test "${ac_cv_prog_cc_profile_arcs}" = "yes" &&
+			test "${ac_cv_prog_cc_test_coverage}" = "yes"); then
+		CFLAGS="$CFLAGS -fprofile-arcs -ftest-coverage"
+	fi
+])
+
+if (test "${enable_gcov}" = "yes"); then
+	AC_CHECK_PROGS(LCOV, [lcov], "no")
+	AC_CHECK_PROGS(GENHTML, [genhtml], "no")
+	if (test "${LCOV}" == "no"); then
+		AC_MSG_ERROR([lcov is required])
+	fi
+	if (test "${GENHTML}" == "no"); then
+		AC_MSG_ERROR([genhtml is required])
+	fi
+fi
+
+AM_CONDITIONAL(GCOV, test "${enable_gcov}" != "no")
+
 AC_ARG_ENABLE(pie, AS_HELP_STRING([--enable-pie],
 			[enable position independent executables flag]), [
 	if (test "${enableval}" = "yes" &&