From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, "Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Network Development" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v4 08/11] libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations
Date: Mon, 20 Sep 2021 17:57:16 -0700 [thread overview]
Message-ID: <CAADnVQKjoCLNYBwDvLjgG9cYxrZyhw1Bgvm0yzH0gUWQLNtZnw@mail.gmail.com> (raw)
In-Reply-To: <20210920141526.3940002-9-memxor@gmail.com>
On Mon, Sep 20, 2021 at 7:15 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> This change updates the BPF syscall loader to relocate BTF_KIND_FUNC
> relocations, with support for weak kfunc relocations. The next commit
> adds bpftool supports to set up the fd_array_sz parameter for light
> skeleton.
>
> A second map for keeping fds is used instead of adding fds to existing
> loader.map because of following reasons:
but it complicates signing bpf progs a lot.
> If reserving an area for map and BTF fds, we would waste the remaining
> of (MAX_USED_MAPS + MAX_KFUNC_DESCS) * sizeof(int), which in most cases
> will be unused by the program. Also, we must place some limit on the
> amount of map and BTF fds a program can possibly open.
That is just (256 + 64)*4 bytes of data. Really not much.
I wouldn't worry about reserving this space.
> If setting gen->fd_array to first map_fd offset, and then just finding
> the offset relative to this (for later BTF fds), such that they can be
> packed without wasting space, we run the risk of unnecessarily running
> out of valid offset for emit_relo stage (for kfuncs), because gen map
> creation and relocation stages are separated by other steps that can add
> lots of data (including bpf_object__populate_internal_map). It is also
> prone to break silently if features are added between map and BTF fd
> emits that possibly add more data (just ~128KB to break BTF fd, since
> insn->off allows for INT16_MAX (32767) * 4 bytes).
I don't follow this logic.
> Both of these issues are compounded by the fact that data map is shared
> by all programs, so it is easy to end up with invalid offset for BTF fd.
I don't follow this either. There is only one map and one program.
What sharing are you talking about?
next prev parent reply other threads:[~2021-09-21 1:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 14:15 [PATCH bpf-next v4 00/11] Support kernel module function calls from eBPF Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 01/11] bpf: Introduce BPF support for kernel module function calls Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 02/11] bpf: Be conservative while processing invalid kfunc calls Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 03/11] bpf: btf: Introduce helpers for dynamic BTF set registration Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 04/11] tools: Allow specifying base BTF file in resolve_btfids Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 05/11] bpf: Enable TCP congestion control kfunc from modules Kumar Kartikeya Dwivedi
2021-09-21 22:18 ` Andrii Nakryiko
2021-09-21 22:23 ` Kumar Kartikeya Dwivedi
2021-09-21 23:02 ` Andrii Nakryiko
2021-09-20 14:15 ` [PATCH bpf-next v4 06/11] libbpf: Support kernel module function calls Kumar Kartikeya Dwivedi
2021-09-21 22:41 ` Andrii Nakryiko
2021-09-24 23:54 ` Kumar Kartikeya Dwivedi
2021-09-25 0:30 ` Andrii Nakryiko
2021-09-20 14:15 ` [PATCH bpf-next v4 07/11] libbpf: Resolve invalid weak kfunc calls with imm = 0, off = 0 Kumar Kartikeya Dwivedi
2021-09-21 22:47 ` Andrii Nakryiko
2021-09-20 14:15 ` [PATCH bpf-next v4 08/11] libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations Kumar Kartikeya Dwivedi
2021-09-21 0:57 ` Alexei Starovoitov [this message]
2021-09-21 4:50 ` Kumar Kartikeya Dwivedi
2021-09-21 19:04 ` Alexei Starovoitov
2021-09-21 22:25 ` Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 09/11] tools: bpftool: Add separate fd_array map support for light skeleton Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 10/11] libbpf: Fix skel_internal.h to set errno on loader retval < 0 Kumar Kartikeya Dwivedi
2021-09-20 14:15 ` [PATCH bpf-next v4 11/11] bpf: selftests: Add selftests for module kfunc support Kumar Kartikeya Dwivedi
2021-09-21 23:00 ` Andrii Nakryiko
2021-09-21 23:13 ` Kumar Kartikeya Dwivedi
2021-09-21 23:28 ` Kumar Kartikeya Dwivedi
2021-09-22 0:03 ` Andrii Nakryiko
2021-09-22 6:06 ` Kumar Kartikeya Dwivedi
2021-09-22 18:24 ` Alexei Starovoitov
2021-09-21 0:29 ` [PATCH bpf-next v4 00/11] Support kernel module function calls from eBPF Andrii Nakryiko
2021-09-21 4:55 ` Kumar Kartikeya Dwivedi
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