Issue when execute git diff command on a file and got :
diff --git a/your_file b/your_file old mode 100644 new mode 100755
If you see this, it is because the permissions of your_file has changed.
For information, the unix file permission mode(644=rw_r__r__ which means read and write for user, only read for group and only read for others, the same for 755=rwxrw_rw_, x for executable).
To disable the comparaison of file mode, the command to execute :
git config core.filemode false