On 04/07/2024 01:15, Andrii Nakryiko wrote:
> BPF skeleton was designed from day one to be extensible. Generated BPF
> skeleton code specifies actual sizes of map/prog/variable skeletons for
> that reason and libbpf is supposed to work with newer/older versions
> correctly.
>
> Unfortunately, it was missed that we implicitly embed hard-coded most
> up-to-date (according to libbpf's version of libbpf.h header used to
> compile BPF skeleton header) sizes of those strucs, which can differ
> from the actual sizes at runtime when libbpf is used as a shared
> library.
>
> We have a few places were we just index array of maps/progs/vars, which
> implicitly uses these potentially invalid sizes of structs.
>
> This patch aims to fix this problem going forward. Once this lands,
> we'll backport these changes in Github repo to create patched releases
> for older libbpfs.
>
> Fixes: d66562fba1ce ("libbpf: Add BPF object skeleton support")
> Fixes: 430025e5dca5 ("libbpf: Add subskeleton scaffolding")
Great catch! I suppose it also sort of
Fixes: 08ac454e258 ("libbpf: Auto-attach struct_ops BPF maps in BPF
skeleton")
...since that introduced the new bpf_map_skeleton field. Not a big deal
since it's new and not a stable backport candidate.
> Co-developed-by: Mykyta Yatsenko <yatsenko@xxxxxxxx>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
I'm guessing that you found this when auto-attach silently didn't happen?
Nit: would it be worth dropping a debug logging message here
/* Skeleton is created with earlier version of bpftool
* which does not support auto-attachment
*/
- if (s->map_skel_sz < sizeof(struct bpf_map_skeleton))
+ if (s->map_skel_sz < sizeof(struct bpf_map_skeleton)) {
+ pr_debug("libbpf version mismatch, cannot auto-attach\n");
return 0;
+ }
...as it's a hard issue to spot?
For the series:
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
