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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>, Kernel Team <kernel-team@fb.com>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH v3 bpf-next 1/3] bpf: switch BPF UAPI #define constants used from BPF program side to enums
Date: Wed, 04 Mar 2020 10:37:27 +0100	[thread overview]
Message-ID: <87blpc4g14.fsf@toke.dk> (raw)
In-Reply-To: <CAEf4BzZWXRX_TrFSPb=ORcfun8B+GdGOAF6C29B-3xB=NaJO7A@mail.gmail.com>

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Tue, Mar 3, 2020 at 3:01 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> On 3/3/20 1:32 AM, Andrii Nakryiko wrote:
>> > Switch BPF UAPI constants, previously defined as #define macro, to anonymous
>> > enum values. This preserves constants values and behavior in expressions, but
>> > has added advantaged of being captured as part of DWARF and, subsequently, BTF
>> > type info. Which, in turn, greatly improves usefulness of generated vmlinux.h
>> > for BPF applications, as it will not require BPF users to copy/paste various
>> > flags and constants, which are frequently used with BPF helpers. Only those
>> > constants that are used/useful from BPF program side are converted.
>> >
>> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>>
>> Just thinking out loud, is there some way this could be resolved generically
>> either from compiler side or via additional tooling where this ends up as BTF
>> data and thus inside vmlinux.h as anon enum eventually? bpf.h is one single
>> header and worst case libbpf could also ship a copy of it (?), but what about
>> all the other things one would need to redefine e.g. for tracing? Small example
>> that comes to mind are all these TASK_* defines in sched.h etc, and there's
>> probably dozens of other similar stuff needed too depending on the particular
>> case; would be nice to have some generic catch-all, hmm.
>
> Enum convertion seems to be the simplest and cleanest way,
> unfortunately (as far as I know). DWARF has some extensions capturing
> #defines, but values are strings (and need to be parsed, which is pain
> already for "1 << 1ULL"), and it's some obscure extension, not a
> standard thing. I agree would be nice not to have and change all UAPI
> headers for this, but I'm not aware of the solution like that.

Since this is a UAPI header, are we sure that no userspace programs are
using these defines in #ifdefs or something like that?

-Toke


  reply	other threads:[~2020-03-04  9:37 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-03  0:32 [PATCH v3 bpf-next 0/3] Convert BPF UAPI constants into enum values Andrii Nakryiko
2020-03-03  0:32 ` [PATCH v3 bpf-next 1/3] bpf: switch BPF UAPI #define constants used from BPF program side to enums Andrii Nakryiko
2020-03-03 23:01   ` Daniel Borkmann
2020-03-03 23:24     ` Andrii Nakryiko
2020-03-04  9:37       ` Toke Høiland-Jørgensen [this message]
2020-03-04 15:38         ` Daniel Borkmann
2020-03-04 15:50           ` Alexei Starovoitov
2020-03-04 16:03             ` Daniel Borkmann
2020-03-04 15:57           ` Daniel Borkmann
2020-03-04 16:02             ` Andrii Nakryiko
2020-03-04 16:07             ` Alexei Starovoitov
2020-03-05 10:50             ` Toke Høiland-Jørgensen
2020-06-02  5:31           ` Michael Forney
2020-06-02 19:17             ` Alexei Starovoitov
2020-06-02 21:40               ` Michael Forney
2020-06-02 23:07                 ` Alexei Starovoitov
2020-06-02 23:21                   ` Michael Forney
2020-06-02 23:36                     ` Alexei Starovoitov
2020-06-03 21:22                       ` Michael Forney
2020-03-03  0:32 ` [PATCH v3 bpf-next 2/3] libbpf: assume unsigned values for BTF_KIND_ENUM Andrii Nakryiko
2020-03-03  0:32 ` [PATCH v3 bpf-next 3/3] tools/runqslower: drop copy/pasted BPF_F_CURRENT_CPU definiton Andrii Nakryiko
2020-03-04 15:21 ` [PATCH v3 bpf-next 0/3] Convert BPF UAPI constants into enum values Daniel Borkmann
2020-03-04 15:34   ` Andrii Nakryiko

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