diff --git a/utils/cfg_builder/README.md b/utils/cfg_builder/README.md
new file mode 100644
index 0000000000..607a98eb67
--- /dev/null
+++ b/utils/cfg_builder/README.md
@@ -0,0 +1,8 @@
+# CFG Builder
+
+This script builds the control flow graph (CFG) of the whole program.
+
+To use this, first you have to setup libafl_cc with `LLVMPasses::DumpCfg` pass.
+Then, compile the program with env var `CFG_OUTPUT_PATH`. The llvm pass will dump the cfg of each module into `CFG_OUTPUT_PATH` directory.
+
+After that, you can run `CFG_OUTPUT_PATH=<directory> python3 build.py`, and then you'll get the control flow graph in cfg.xdot and call graph in cg.xdot
\ No newline at end of file
diff --git a/utils/cfg_builder/build.py b/utils/cfg_builder/build.py
index 0a39dd6db6..070f15e30b 100644
--- a/utils/cfg_builder/build.py
+++ b/utils/cfg_builder/build.py
@@ -3,23 +3,41 @@
 import json
 import os
 import networkx as nx
+import sys
+
 cfg = dict()
 
+if 'CFG_OUTPUT_PATH' not in os.environ:
+    sys.exit("CFG_OUTPUT_PATH not set")
+
 input_path = os.environ["CFG_OUTPUT_PATH"]
+
+
 for dirpath, _, files in os.walk(input_path):
     for x in files:
         if x.endswith(".cfg"):
             cfg[x] = json.load(open(os.path.join(dirpath, x)))
 
 G = nx.DiGraph()
+GG = nx.DiGraph()
+# First add all the edges
 
 node_ids = 0
+f_ids = 0
+
+fname2id = dict()
 
 for mname, module in cfg.items():
     fnname2SG = dict()
     # First, add all the intra-procedural edges
 
     for (fname, v) in module['edges'].items():
+
+        if fname not in fname2id:
+            GG.add_node(f_ids, label=fname)
+            fname2id[fname] = f_ids
+            f_ids += 1
+
         sz = len(v)
         for idx in range(node_ids, node_ids + sz):
             G.add_node(idx)
@@ -47,6 +65,7 @@ for mname, module in cfg.items():
 
                     # Now we have 2 index, build the edge
                     G.add_edge(src, dst)
+                    GG.add_edge(fname2id[fname], fname2id[target_fn])
 
-if "DOT_OUT" in os.environ:
-    nx.nx_agraph.write_dot(G, "cfg.xdot")
+nx.nx_agraph.write_dot(G, "cfg.xdot")
+nx.nx_agraph.write_dot(GG, "cg.xdot")