Turns out I wasn't building the syscall libraries. Do so.

plat/linux/libsys/open.c

@@ -0,0 +1,25 @@
+/* $Source: /cvsroot/tack/Ack/plat/linux386/libsys/open.c,v $
+ * $State: Exp $
+ * $Revision: 1.1 $
+ */
+
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include "libsys.h"
+
+int open(const char* path, int access, ...)
+{
+	int mode = 0;
+	
+	if (access & O_CREAT)
+	{
+		va_list ap;
+		va_start(ap, access);
+		mode = va_arg(ap, int);
+		va_end(ap);
+	}
+	
+	return _syscall(__NR_open, (quad) path, access, mode);
+}