btrfs-progs: build: add support for gcov

With 'make D=gcov' the files are built with gcov support. After running
the workload, the results can be viewed by 'gcov file.c' or by
lcov+genhtml.

Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

Makefile

@@ -30,6 +30,7 @@
 #                  tsan    - enable thread sanitizer compiler feature
 #                  ubsan   - undefined behaviour sanitizer compiler feature
 #                  bcheck  - extended build checks
+#                  gcov    - enable GCOV support during build
 #   W=123          build with warnings (default: off)
 #   DEBUG_CFLAGS   additional compiler flags for debugging build
 #   EXTRA_CFLAGS   additional compiler flags
@@ -284,6 +285,11 @@ ifeq ("$(origin D)", "command line")
   DEBUG_LDFLAGS_INTERNAL = $(DEBUG_LDFLAGS_DEFAULT) $(DEBUG_LDFLAGS)
 endif
 
+ifneq (,$(findstring gcov,$(D)))
+  DEBUG_CFLAGS_INTERNAL += -fprofile-arcs -ftest-coverage --coverage
+  DEBUG_LDFLAGS_INTERNAL += -fprofile-generate --coverage
+endif
+
 ifneq (,$(findstring verbose,$(D)))
   DEBUG_CFLAGS_INTERNAL += -DDEBUG_VERBOSE_ERROR=1
 endif
@@ -841,6 +847,7 @@ clean: $(CLEANDIRS)
 		crypto/*.o crypto/.deps/*.o.d \
 		tune/*.o tune/.deps/*.o.d \
 		libbtrfs/*.o libbtrfs/.deps/*.o.d \
+		*.gcno *.gcda *.gcov */*.gcno */*.gcda */*/.gcov \
 	      ioctl-test quick-test library-test library-test-static \
               mktables btrfs.static mkfs.btrfs.static fssum \
 	      btrfs.box btrfs.box.static json-formatter-test \