FreeRADIUS 2 not listening on right port

Alan DeKok aland at
Thu May 29 08:07:02 CEST 2008

Phil Mayers wrote:
> For those not following the Fedora bug, it (or rather, it's dependency)
> has been closed by Ulrich Drepper. He seems to be saying that the
> FreeRadius code is incorrect and specifically that an invalid typecast
> is triggering the compiler to generate bad code:

  Interesting.  So GCC doesn't complain, and it generates bad assembly
for C code that it thinks is perfectly valid.

> Summary (as far as I can make out): Because the code looks like this:
> ...the compiler can't detect that the "i" value is "used", and optimises
> the code touching it away.

  i.e.  GCC doesn't properly analyze the code that it optimizes, so it
generates the wrong optimizations.  GCC has a history of doing this...

> I'm not expert enough in the C99 standard to judge whether the comments
> at the above URL are correct or not; I suspect it's a matter of some
> controversy, and will back slowly away now... ;o)

  I think your comments about the underlying cause are correct.
Ulrich's comments about Posix are interesting:

>>> The invalid casts are forbidden by ISO C.  POSIX
>>> does not and cannot guarantee anything about this type of use of
>>> sockaddr_storage.

  To quote the Opengroup page:

The <sys/socket.h> header shall define the sockaddr_storage structure.
This structure shall be:

    * Large enough to accommodate all supported protocol-specific
address structures

    * Aligned at an appropriate boundary so that pointers to it can be
cast as pointers to protocol-specific address structures and used to
access the fields of those structures without alignment problems

  i.e. the code in FreeRADIUS is correct.  It uses sockaddr_stoage as a
generic container for protocol-specific address structures.  It casts a
pointer to sockaddr_storage to a pointer to protocol-specific address
structures.  The recommendation to use a union to hold both
sockaddr_storage && sockaddr_in is... interesting.  If you have to do
that, WTF is the use of sockaddr_storage?

  Looking on the net, I also found a fair amount of code using
sockaddr_storage in the recommended Posix way.  It appears that
FreeRADIUS is OK, and just got hit by a GCC bug.

  i.e. for ANY code like this:

	foo = (type_t *) bar;
	switch (x) {
	case 1:
		foo->a = 1;

  GCC will "optimize away" the line doing "foo->a = 1;".  Nice.

  Alan DeKok.

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