diff --git a/.gitmodules b/.gitmodules
index 5ec6f60..0bb9f62 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -4,3 +4,6 @@
 [submodule "sys/ropkg"]
 	path = sys/ropkg
 	url = git@github.com:washh/ropkg.git
+[submodule "lib/libfx"]
+	path = lib/libfx
+	url = https://g.wash.red/wash/fx.git
diff --git a/lib/libc/core/stdio/printf.c b/lib/libc/core/stdio/printf.c
index e355825..988c085 100644
--- a/lib/libc/core/stdio/printf.c
+++ b/lib/libc/core/stdio/printf.c
@@ -1195,21 +1195,17 @@ int vsnprintf(char *buffer, size_t count, const char *format, va_list va)
 	return _vsnprintf(_out_buffer, buffer, count, format, va);
 }
 
-int fctprintf(
+int __libc_fctprintf(
 	void (*out)(char character, void *arg),
 	void *arg,
 	const char *format,
-	...)
+	va_list va)
 {
-	va_list va;
-	va_start(va, format);
 	const out_fct_wrap_type out_fct_wrap = {out, arg};
-	const int ret = _vsnprintf(
+	return _vsnprintf(
 		_out_fct,
 		(char *)(uintptr_t)&out_fct_wrap,
 		(size_t)-1,
 		format,
 		va);
-	va_end(va);
-	return ret;
 }
diff --git a/lib/libfx b/lib/libfx
new file mode 160000
index 0000000..6b04920
--- /dev/null
+++ b/lib/libfx
@@ -0,0 +1 @@
+Subproject commit 6b04920d29f6cc2feec24ad8dd8cf3edf2cf5297