Re: [PATCH bpf-next 2/2] libbpf: fix BPF skeleton forward/backward compat handling

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2024-07-03 at 17:15 -0700, 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
                                                  ^^
                                          nit: "struct"
> 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")
> Co-developed-by: Mykyta Yatsenko <yatsenko@meta.com>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---

I double-checked all uses of bpf_object_skeleton->{maps,progs},
all seems in order.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

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