--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2009-01-14  Bruno Haible  <bruno@clisp.org>
+
+	* lib/progname.c (set_program_name): Add more comments.
+	Reported by Sergey Poznyakoff <gray@gnu.org.ua>.
+
 2009-01-14  Simon Josefsson  <simon@josefsson.org>
 
 	* lib/sys_stat.in.h: Include sys/types.h for nlink_t on systems

--- a/lib/progname.c
+++ b/lib/progname.c
@@ -1,5 +1,5 @@
 /* Program name management.
-   Copyright (C) 2001-2003, 2005-2008 Free Software Foundation, Inc.
+   Copyright (C) 2001-2003, 2005-2009 Free Software Foundation, Inc.
    Written by Bruno Haible <haible@clisp.cons.org>, 2001.
 
    This program is free software: you can redistribute it and/or modify
@@ -35,6 +35,8 @@
 {
   /* libtool creates a temporary executable whose name is sometimes prefixed
      with "lt-" (depends on the platform).  It also makes argv[0] absolute.
+     But the name of the temporary executable is a detail that should not be
+     visible to the end user and to the test suite.
      Remove this "<dirname>/.libs/" or "<dirname>/.libs/lt-" prefix here.  */
   const char *slash;
   const char *base;
@@ -47,5 +49,15 @@
       if (strncmp (base, "lt-", 3) == 0)
 	argv0 = base + 3;
     }
+
+  /* But don't strip off a leading <dirname>/ in general, because when the user
+     runs
+         /some/hidden/place/bin/cp foo foo
+     he should get the error message
+         /some/hidden/place/bin/cp: `foo' and `foo' are the same file
+     not
+         cp: `foo' and `foo' are the same file
+   */
+
   program_name = argv0;
 }