https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107952
--- Comment #12 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
(In reply to qinzhao from comment #7)
> (In reply to Richard Biener from comment #1)
> > GCC considered this as a flex-array.
>
> do you mean for the following example:
>
> typedef struct {
> char pad;
> char data[];
> } F2;
>
> typedef struct {
> unsigned pad;
> F2 flex;
> } S2;
>
> although C standard disallow the above, GCC extension treats S2.flex.data as
> a flex-array?
>
> How about:
>
> typedef struct {
> char pad;
> char data[];
> } F2;
>
> typedef struct {
> F2 flex;
> unsigned pad;
> } S2;
>
> do we have any documentation on this Gcc extension?
There's an open bug to document these semantics:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77650(In reply to
rguent...@suse.de from comment #11)
> On Tue, 24 Jan 2023, qing.zhao at oracle dot com wrote:
>
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107952
> >
> > --- Comment #10 from Qing Zhao <qing.zhao at oracle dot com> ---
> > > --- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
> > >
> > > GCC handles for example
> > >
> > > struct A { char data[1]; };
> > > struct B { int n; struct A a; };
> > >
> > > as if the a.data[] array is a flex-array.
> >
> > Okay. Then the maximum size of __builtin_object_size for it should be -1,
> > right?
>
> I think so.
Why? If the a B object is allocated with a visible allocator call, we can
return the correct size here too.
