Re: [xdp-hints] Re: [PATCH bpf-next 00/11] xdp: hints via kfuncs

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Stanislav Fomichev <sdf@google.com> writes:

> On Tue, Nov 15, 2022 at 7:54 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>>
>> Stanislav Fomichev <sdf@google.com> writes:
>>
>> > - drop __randomize_layout
>> >
>> >   Not sure it's possible to sanely expose it via UAPI. Because every
>> >   .o potentially gets its own randomized layout, test_progs
>> >   refuses to link.
>>
>> So this won't work if the struct is in a kernel-supplied UAPI header
>> (which would include the __randomize_layout tag). But if it's *not* in a
>> UAPI header it should still be included in a stable form (i.e., without
>> the randomize tag) in vmlinux.h, right? Which would be the point:
>> consumers would be forced to read it from there and do CO-RE on it...
>
> So you're suggesting something like the following in the uapi header?
>
> #ifndef __KERNEL__
> #define __randomize_layout
> #endif
>
> ?

I actually just meant "don't put struct xdp_metadata in an UAPI header
file at all". However, I can see how that complicates having the
skb_metadata pointer in struct xdp_md, so if the above works, that's
fine with me as well :)

> Let me try to add some padding arguments to xdp_skb_metadata plus the
> above to see how it goes.

Cool!

-Toke