mk: add 'COVERAGE' option

'COVERAGE=yes' in 'target.mk' adds gcov-specific compiler flags and links the
program with libgcov.

Issue #3048

repos/base/mk/dep_prg.mk

@@ -16,6 +16,13 @@ include $(BASE_DIR)/mk/util.inc
 PRG_DIR := $(dir $(TARGET_MK))
 include $(TARGET_MK)
 
+#
+# Add libgcov if coverage is requested
+#
+ifeq ($(COVERAGE),yes)
+LIBS += libgcov
+endif
+
 #
 # Include lib-import description files
 #

repos/base/mk/generic.mk

@@ -55,6 +55,10 @@ endif
 %.o: %.cc
 	$(MSG_COMP)$@
 	$(VERBOSE)$(CXX) $(CXX_DEF) $(CC_CXX_OPT) $(INCLUDES) -c $< -o $@
+ifeq ($(COVERAGE),yes)
+	$(VERBOSE)mkdir -p $(INSTALL_DIR)/gcov_data/$(TARGET)/$(dir $@)
+	$(VERBOSE)ln -sf $(CURDIR)/$(@:.o=.gcno) $(INSTALL_DIR)/gcov_data/$(TARGET)/$(@:.o=.gcno)
+endif
 
 %.o: %.cpp
 	$(MSG_COMP)$@

repos/base/mk/global.mk

@@ -103,6 +103,32 @@ ifneq ($(STDLIB),yes)
 LD_OPT_NOSTDLIB := -nostdlib -Wl,-nostdlib
 endif
 
+#
+# Add coverage options
+#
+# The directory for the coverage data (generated at runtime) is derived from
+# the current build directory and is going to look like
+#
+# '/genodelabs/bin/test-log_gcov/2018-11-13/gcov_data/test-log_gcov'
+#
+# to match the path where the gcov note files (generated at build time) are
+# stored in the depot package of the test program.
+#
+# If depot packages are not used, the path is going to look like
+#
+# '/gcov_data/test-log_gcov'
+#
+ifeq ($(COVERAGE),yes)
+ifneq ($(findstring /depot/,$(CURDIR)),)
+PROFILE_DIR = $(shell echo $(CURDIR) | \
+                      sed -e 's/^.*\/depot\//\//' \
+                          -e 's/\.build\/.*//')/gcov_data/$(TARGET)
+else
+PROFILE_DIR = /gcov_data/$(TARGET)
+endif
+CC_OPT += -fprofile-arcs -ftest-coverage -fprofile-dir=$(PROFILE_DIR)
+endif
+
 #
 # Default optimization and warning levels
 #