netdev - Re: [PATCH 03/11] bpf: Add btf

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Date:   Thu, 18 Jun 2020 18:02:48 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andriin@...com>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 03/11] bpf: Add btf_ids object

On Tue, Jun 16, 2020 at 3:05 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Adding support to generate .BTF_ids section that would
> hold various BTF IDs list for verifier.
>
> Adding macros help to define lists of BTF IDs placed in
> .BTF_ids section. They are initially filled with zeros
> (during compilation) and resolved later during the
> linking phase by btfid tool.
>
> Following defines list of one BTF ID that is accessible
> within kernel code as bpf_skb_output_btf_ids array.
>
>   extern int bpf_skb_output_btf_ids[];
>
>   BTF_ID_LIST(bpf_skb_output_btf_ids)
>   BTF_ID(struct, sk_buff)
>
> Suggested-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/asm-generic/vmlinux.lds.h |  4 ++
>  kernel/bpf/Makefile               |  2 +-
>  kernel/bpf/btf_ids.c              |  3 ++
>  kernel/bpf/btf_ids.h              | 70 +++++++++++++++++++++++++++++++
>  4 files changed, 78 insertions(+), 1 deletion(-)
>  create mode 100644 kernel/bpf/btf_ids.c
>  create mode 100644 kernel/bpf/btf_ids.h
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index db600ef218d7..0be2ee265931 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -641,6 +641,10 @@
>                 __start_BTF = .;                                        \
>                 *(.BTF)                                                 \
>                 __stop_BTF = .;                                         \
> +       }                                                               \
> +       . = ALIGN(4);                                                   \
> +       .BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {                   \
> +               *(.BTF_ids)                                             \
>         }
>  #else
>  #define BTF
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 1131a921e1a6..21e4fc7c25ab 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -7,7 +7,7 @@ obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list
>  obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o
>  obj-$(CONFIG_BPF_SYSCALL) += disasm.o
>  obj-$(CONFIG_BPF_JIT) += trampoline.o
> -obj-$(CONFIG_BPF_SYSCALL) += btf.o
> +obj-$(CONFIG_BPF_SYSCALL) += btf.o btf_ids.o
>  obj-$(CONFIG_BPF_JIT) += dispatcher.o
>  ifeq ($(CONFIG_NET),y)
>  obj-$(CONFIG_BPF_SYSCALL) += devmap.o
> diff --git a/kernel/bpf/btf_ids.c b/kernel/bpf/btf_ids.c
> new file mode 100644
> index 000000000000..e7f9d94ad293
> --- /dev/null
> +++ b/kernel/bpf/btf_ids.c
> @@ -0,0 +1,3 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include "btf_ids.h"

hm... what's the purpose of this btf_ids.c file?

> diff --git a/kernel/bpf/btf_ids.h b/kernel/bpf/btf_ids.h
> new file mode 100644
> index 000000000000..68aa5c38a37f
> --- /dev/null
> +++ b/kernel/bpf/btf_ids.h

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