diff --git a/.gitignore b/.gitignore
index 29ee3de9..7ad7f3bd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,6 @@
 *.a
 *.so
 getarch
-getos
\ No newline at end of file
+getos
+sems
+sems-stats
\ No newline at end of file
diff --git a/core/lib/.placeholder b/core/lib/.placeholder
new file mode 100644
index 00000000..b6cff41c
--- /dev/null
+++ b/core/lib/.placeholder
@@ -0,0 +1 @@
+Please do not delete this file (Git does not like empty directories).
\ No newline at end of file