https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116983
qinzhao at gcc dot gnu.org changed:
What |Removed |Added
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CC| |qinzhao at gcc dot gnu.org
--- Comment #1 from qinzhao at gcc dot gnu.org ---
(In reply to Kees Cook from comment #0)
> When counted_by is present in a structure, it means that the object must be
> a singleton.
>
> For example:
>
> struct counted {
> int counter;
> int array[] __attribute__((counted_by(counter)));
> };
>
> struct notcounted {
> int counter;
> int array[];
> };
>
> void __attribute__((noinline)) emit_length(size_t length)
> {
> printf("%zu\n", length);
> }
>
> // This correctly cannot know size of p object, and returns SIZE_MAX
> void objsize_notcounted(struct notcounted *p)
> {
> emit_length(__builtin_dynamic_object_size(p, 1));
> }
>
> // This must be operating on a singleton, therefor the
> // return must be:
> // max(sizeof(*p),
> // sizeof(*p) + offsetof(typeof(*p), array) * p->counter)
> void objsize_counted(struct counted *p)
> {
> emit_length(__builtin_dynamic_object_size(p, 1));
> }
could you explicitly explain what's wrong in the current implementation?
