Why does kcov add two sh files

I'm using kcov to do the code coverage test.
For example, saying that I have a bash script named 1.sh:

#!/bin/sh
echo NOTHING

Then I execute kcov report 1.sh to generate the directory report which contains the result of kcov.

I thought that the code covered should be 100% whereas it gave me 25%.

I found that it was because there were two new sh files coming out: bash-helper.sh and bash-helper-debug-trap.sh.

Where do they come from? Can I avoid generating them to get a 100% for the 1.sh?