On Mon, Jun 30, 2025 at 6:06 PM Marat Khalili <[email protected]> wrote: > > > -----Original Message----- > > From: David Marchand <[email protected]> > > Sent: Monday 23 June 2025 14:53 > > To: [email protected] > > Cc: [email protected]; Bruce Richardson <[email protected]>; Tyler > > Retzlaff <[email protected]>; Neil Horman > > <[email protected]> > > Subject: [PATCH v2 07/10] tailq: fix cast macro for null pointer > > > > Doing arithmetics with the NULL pointer is undefined. > > > > Caught by UBSan: > > > > ../app/test/test_tailq.c:111:9: runtime error: > > member access within null pointer of type 'struct rte_tailq_head' > > > > Fixes: f6b4f6c9c123 ("tailq: use a single cast macro") > > Cc: [email protected] > > > > Signed-off-by: David Marchand <[email protected]> > > Acked-by: Bruce Richardson <[email protected]> > > --- > > lib/eal/include/rte_tailq.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/lib/eal/include/rte_tailq.h b/lib/eal/include/rte_tailq.h > > index 89f7ef2134..c23df77d96 100644 > > --- a/lib/eal/include/rte_tailq.h > > +++ b/lib/eal/include/rte_tailq.h > > @@ -54,7 +54,7 @@ struct rte_tailq_elem { > > * Return the first tailq entry cast to the right struct. > > */ > > #define RTE_TAILQ_CAST(tailq_entry, struct_name) \ > > - (struct struct_name *)&(tailq_entry)->tailq_head > > + (tailq_entry == NULL ? NULL : (struct struct_name *)&(tailq_entry)- > > >tailq_head) > > > > /** > > * Utility macro to make looking up a tailqueue for a particular struct > > easier. > > First tailq_entry is missing parentheses. Also, it is worrying that we now > use macro argument twice. E.g. RTE_TAILQ_LOOKUP may become twice slower as a > result. > > Could we perhaps simplify the macro to `(struct struct_name *)(tailq_entry)`. > I tried to find or understand the reasons behind the original construction, > but could not.
Thanks for the comment, it made me relookup at this code. I realise this macro should be called with a correct object in the first place. Instead the lookup macro itself is the part that is undefined behavior (wrt comment in case of an error). -- David Marchand
