Add a clarification to gcov instructions

diff --git a/doc/HACKING b/doc/HACKING
index b4d258612ee7b494bf78b519543f0d7781820812..9f9e6447b7febdeb1df745ddf53c81256daea2ec 100644 (file)
--- a/doc/HACKING
+++ b/doc/HACKING
@@ -133,6 +133,7 @@ line was never reached.  Lines with numbers were called that number of times.
 
 If that doesn't work:
    * Try configuring Tor with --disable-gcc-hardening
+   * You might need to run 'make clean' after you run './configure'.
 
 Profiling Tor with oprofile
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~