diff --git a/.gitignore b/.gitignore
index b27256c..20aa13d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 tmp*
 a.out
 chibicc
+chibicc-gen*
diff --git a/Makefile b/Makefile
index 5c7dfaf..5b0986d 100644
--- a/Makefile
+++ b/Makefile
@@ -7,15 +7,23 @@ chibicc: $(OBJS)
 
 $(OBJS): chibi.h
 
-test: chibicc
+chibicc-gen2: chibicc $(SRCS) chibi.h
+	./self.sh
+
+extern.o: tests-extern
+	gcc -xc -c -o extern.o tests-extern
+
+test: chibicc extern.o
 	./chibicc tests > tmp.s
-	echo 'int ext1; int *ext2; int char_fn() { return 257; }' \
-          'int static_fn() { return 5; }' | \
-          gcc -xc -c -o tmp2.o -
-	gcc -static -o tmp tmp.s tmp2.o
+	gcc -static -o tmp tmp.s extern.o
+	./tmp
+
+test-gen2: chibicc-gen2 extern.o
+	./chibicc-gen2 tests > tmp.s
+	gcc -static -o tmp tmp.s extern.o
 	./tmp
 
 clean:
-	rm -f chibicc *.o *~ tmp*
+	rm -rf chibicc chibicc-gen* *.o *~ tmp*
 
 .PHONY: test clean
diff --git a/self.sh b/self.sh
new file mode 100755
index 0000000..a4608e2
--- /dev/null
+++ b/self.sh
@@ -0,0 +1,44 @@
+#!/bin/bash -x
+TMP=tmp-self
+
+mkdir -p $TMP
+
+expand() {
+    file=$1
+    cat <<EOF > $TMP/$1
+typedef struct FILE FILE;
+extern FILE *stdout;
+extern FILE *stderr;
+
+void *malloc(long size);
+void *calloc(long nmemb, long size);
+int *__errno_location();
+char *strerror(int errnum);
+FILE *fopen(char *pathname, char *mode);
+long fread(void *ptr, long size, long nmemb, FILE *stream);
+int feof(FILE *stream);
+static void assert() {}
+int strcmp(char *s1, char *s2);
+EOF
+
+    grep -v '^#' chibi.h >> $TMP/$1
+    grep -v '^#' $1 >> $TMP/$1
+    sed -i 's/\bbool\b/_Bool/g' $TMP/$1
+    sed -i 's/\berrno\b/*__errno_location()/g' $TMP/$1
+    sed -i 's/\btrue\b/1/g; s/\bfalse\b/0/g;' $TMP/$1
+    sed -i 's/\bNULL\b/0/g' $TMP/$1
+    sed -i 's/, \.\.\.//g' $TMP/$1
+
+    ./chibicc $TMP/$1 > $TMP/${1%.c}.s
+    gcc -c -o $TMP/${1%.c}.o $TMP/${1%.c}.s
+}
+
+cp *.c $TMP
+for i in $TMP/*.c; do
+  gcc -I. -c -o ${i%.c}.o $i
+done
+
+expand main.c
+expand type.c
+
+gcc -static -o chibicc-gen2 $TMP/*.o
diff --git a/tests-extern b/tests-extern
new file mode 100644
index 0000000..8b93f1f
--- /dev/null
+++ b/tests-extern
@@ -0,0 +1,5 @@
+// -*- c -*-
+int ext1;
+int *ext2;
+
+int static_fn() { return 5; }