[Swan-dev] pointer initialization and fcfcde7422a4805a56a3a4a175271c56fbbbab12

[D. Hugh Redelmeier]

This commit is technically wrong.  I admit that the problem will not show 
up on most machines.

The C standard does not require that the binary representation of a NULL 
pointer be 0.  Initializing a struct by zeroing bytes does not guarantee 
that pointer fields are initialized to NULL.

On the other hand, the C standard requires a static object be
initialized by default in such a way that pointers are initialized to
NULL.  (The rule gets more intricate for unions: the first alternative is 
initialized.)

That's why the original code was written the way it was.

That's why many calls the zero() note the issue of NULL.

commit fcfcde7422a4805a56a3a4a175271c56fbbbab12
Author: Andrew Cagney <cagney at gnu.org>
Date:   Thu Feb 11 20:05:00 2016 -0500

    pluto: allocate empty "struct state" using alloc_thing()

diff --git a/programs/pluto/state.c b/programs/pluto/state.c
index 1b8b538..ee3884d 100644
--- a/programs/pluto/state.c
+++ b/programs/pluto/state.c
@@ -460,13 +460,10 @@ static struct state_hash_table statetable = {
  */
 struct state *new_state(void)
 {
-	/* initialized all to zero & NULL */
-	static const struct state blank_state;
-
 	static so_serial_t next_so = SOS_FIRST;
 	struct state *st;
 
-	st = clone_thing(blank_state, "struct state in new_state()");
+	st = alloc_thing(struct state, "struct state in new_state()");
 	st->st_serialno = next_so++;
 	passert(next_so > SOS_FIRST);   /* overflow can't happen! */
 	st->st_whack_sock = NULL_FD;