netdev - Re: [PATCH bpf v1] bpf: fix libelf endian handling in resolv

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Date:   Thu, 17 Jun 2021 12:44:42 +0200
From:   Mark Wielaard <mark@...mp.org>
To:     Jiri Olsa <jolsa@...hat.com>,
        Tony Ambardar <tony.ambardar@...il.com>
Cc:     Yonghong Song <yhs@...com>, Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Stable <stable@...r.kernel.org>, Jiri Olsa <jolsa@...nel.org>,
        Frank Eigler <fche@...hat.com>
Subject: Re: [PATCH bpf v1] bpf: fix libelf endian handling in resolv_btfids

On Thu, 2021-06-17 at 11:10 +0200, Jiri Olsa wrote:
> On Wed, Jun 16, 2021 at 03:09:13PM -0700, Tony Ambardar wrote:
> > On Wed, 16 Jun 2021 at 09:38, Jiri Olsa <jolsa@...hat.com> wrote:
> > > I have no idea how is this handled in libelf (perhaps it's ok),
> > > but just that comment above suggests it could be also 64 bits,
> > > cc-ing Frank and Mark for more insight
> > > 
> > 
> > One other area I'd like to confirm is with section compression. Is
> > it safe
> > to ignore this for .BTF_ids? I've done so because
> > include/linux/btf_ids.h
> > appears to define the section with SHF_ALLOC flag set, which is
> > incompatible with compression based on "libelf.h" comments.
> 
> not sure what you mean.. where it wouldn't be safe?
> what workflow/processing

I haven't looked at the code/patch, but Tony is correct that if a
section has SHF_ALLOC set it cannot be a compressed section.
SHF_COMPRESSED is incompatbile with SHF_ALLOC (or SHF_NOBITS) sections,
because it would be unclear what a loader would need to do with them
(uncompress the data first, then map it, or map the compressed data as
is into memory).

So ignoring whether or not a section is compressed for SHF_ALLOC
sections is fine.

Cheers,

Mark