lcov --diff usage

# Pathnames in the diff file need to be absolute (note
# to self: document)
diff -u $(PWD)/hello_old.c $(PWD)/hello_new.c > difffile

# Without --convert-filenames, the data from RUN1 will
# still be associated with hello_old.c
lcov --diff RUN1.INFO difffile --convert-filenames -o RUN1_CONVERTED.INFO

然后修改RUN1_CONVERTED.INFO的TN和SF，与RUN2.INFO一致

# Add data from both runs
lcov -a RUN1_CONVERTED.INFO -a RUN2.INFO -o RUN_ALL.INFO

oldfile

newfile

merge old coverage to newfile

merge all coverage result