https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114217
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC actually doesn't diagnose on mere pointer assignment, but what triggers the
alignment check is
&entry->offset
even when the code later on just takes its address, entry must be sufficiently
aligned, otherwise entry->offset is invalid.
Under standard C rules, already forming the pointer would be UB, so somewhere
in the caller when you prepare what to pass to the f function.
If you want something that will still be invalid C,
but will not trigger UBSAN errors, then e.g.
unsigned long long h(struct dir_entry *entry)
{
return get_unaligned((unsigned long long *) (((char *) entry) + offsetof
(struct dir_entry, offset)));
}
will do.
If you want something that will be valid even in C, don't pass struct dir_entry
*entry
argument, but void *entry instead, and use e.g.
__get_unaligned_t(__typeof(((struct dir_entry *)0)->offset), ((char
*)entry)+offsetof(struct dir_entry, offset)))
You can surely hide that all under some macro.
