When compiling userspace-rcu (commit 81dd913), I get a pair of warnings for
/userspace-rcu/doc/examples/hlist/cds_hlist_del_rcu.c at the
cds_hlist_for_each_entry_safe_2 call:
cds_hlist_for_each_entry_safe_2(node, n, &mylist, node) {
if (node->value > 0) {
cds_hlist_del_rcu(&node->node);
/*
* We can only reclaim memory after a grace
* period has passed after cds_hlist_del_rcu().
*/
call_rcu(&node->rcu_head, free_node_rcu);
}
}
The warnings are:
"attention: assignment makes pointer from integer without a cast"
"attention: left operand of comma operator has no effect"
The #define comes from userspace-rcu/urcu/hlist.h (here re-arranged a bit):
#define cds_hlist_for_each_entry_safe_2(entry, e, head, member) \
for (entry = ((head)->next == NULL ? NULL :
cds_hlist_entry((head)->next, __typeof__(*entry), member)); \
(entry != NULL) && \
(e = (entry->member.next == NULL ? NULL :
cds_hlist_entry(entry->member.next, __typeof__(*entry), member), 1)); \
entry = e)
The cds_hlist_del_rcu.c occurrence is the only use of
cds_hlist_for_each_entry_safe_2 and the problem seems to me to lie in this bit:
(e = (entry->member.next == NULL ? NULL : cds_hlist_entry(entry->member.next,
__typeof__(*entry), member), 1))
Because the comma operator has the lowest precedence of all operators, the
statement is equivalent to:
(e = ((entry->member.next == NULL ? NULL : cds_hlist_entry(entry->member.next,
__typeof__(*entry), member)), 1))
Which is in turn the same as:
(e = 1)
Now, if the macro is using the comma to make the second part of the && test
succeed regardless of the value fetched for e, then it should have been written:
#define cds_hlist_for_each_entry_safe_2(entry, e, head, member) \
for (entry = ((head)->next == NULL ? NULL :
cds_hlist_entry((head)->next, __typeof__(*entry), member)); \
(entry != NULL) && \
((e = (entry->member.next == NULL ? NULL :
cds_hlist_entry(entry->member.next, __typeof__(*entry), member))), 1); \
entry = e)
Which does compile without the warnings.
Daniel U. Thibault
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