netdev - Re: [PATCH bpf-next 1/3] libbpf: capture value in BTF type info for BTF-defined map defs

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Date:   Thu, 27 Jun 2019 10:47:58 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Andrii Nakryiko <andriin@...com>, Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/3] libbpf: capture value in BTF type info for
 BTF-defined map defs

On Thu, Jun 27, 2019 at 10:27 AM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On Jun 26, 2019, at 4:21 PM, Andrii Nakryiko <andriin@...com> wrote:
> >
> > Change BTF-defined map definitions to capture compile-time integer
> > values as part of BTF type definition, to avoid split of key/value type
> > information and actual type/size/flags initialization for maps.
>
> If I have an old bpf program and compiled it with new llvm, will it
> work with new libbpf?

You mean BPF programs that used previous incarnation of BTF-defined
maps? No, they won't work. But we never released them, so I think it's
ok to change them. Nothing should be using that except for selftests,
which I fixed.

>
>
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---

<snip>

> > diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
> > index 1a5b1accf091..aa5ddf58c088 100644
> > --- a/tools/testing/selftests/bpf/bpf_helpers.h
> > +++ b/tools/testing/selftests/bpf/bpf_helpers.h
> > @@ -8,6 +8,9 @@
> >  */
> > #define SEC(NAME) __attribute__((section(NAME), used))
> >
> > +#define __int(name, val) int (*name)[val]
> > +#define __type(name, val) val *name
> > +
>
> I think we need these two in libbpf.

Yes, but it's another story for another set of patches. We'll need to
provide bpf_helpers as part of libbpf for inclusion into BPF programs,
but there are a bunch of problems right now with existing
bpf_heplers.h that prevents us from just copying it into libbpf. We'll
need to resolve those first.

But then again, there is no use of __int and __type for user-space
programs, so for now it's ok.

>
> Thanks,
> Song
>
> > /* helper macro to print out debug messages */
> > #define bpf_printk(fmt, ...)                          \
> > ({                                                    \
> > --
> > 2.17.1
> >
>