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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Thu, 10 Jun 2021 11:14:01 -0700
Message-ID: <CAADnVQJu0gbKXLYQ_whsh0sENkxR7E3XOuVfAFrPkyXhQtdG1g@mail.gmail.com>
Subject: Re: Portability of bpf_tracing.h
To:     Lorenz Bauer <lmb@cloudflare.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        bpf <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
        Florent Revest <revest@chromium.org>
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On Thu, Jun 10, 2021 at 7:12 AM Lorenz Bauer <lmb@cloudflare.com> wrote:

> > > The idea of basing this on unique fields in types is neat, the
> > > downside I see is that we encode the logic in the BPF bitstream. If in
> > > the future struct pt_regs is changed, code breaks and we can't do much
> >
> > If pt_regs fields are renamed all PT_REGS-related stuff, provided by
> > libbpf in bpf_tracing.h will break as well and will require
> > re-compilation of BPF application.
>
> I'm thinking more along the lines of, if a PT_REGS definition changes
> so that the unique field isn't unique anymore. The BPF is still valid,
> but the logic that determines the platform isn't.

struct pt_regs is uapi on every arch.
They cannot change. New registers can be added :) but the chance is
close to zero.