Message-ID: <CAEf4BzYf7+D_Jck6LH_tFTdsfNg+tWQvz-T2WccYYEefRHm3Vg@mail.gmail.com>
Date: Thu, 15 May 2025 09:03:39 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: bpf@...r.kernel.org, Quentin Monnet <qmo@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Daniel Xu <dxu@...uu.xyz>, Mykyta Yatsenko <yatsenko@...a.com>, 
	Tao Chen <chen.dylane@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2] bpftool: Add support for custom BTF path in
 prog load/loadall

On Wed, May 14, 2025 at 11:52 PM Jiayuan Chen <jiayuan.chen@...ux.dev> wrote:
>
> This patch exposes the btf_custom_path feature to bpftool, allowing users
> to specify a custom BTF file when loading BPF programs using prog load or
> prog loadall commands.
>
> The argument 'btf_custom_path' in libbpf is used for those kernes that
> don't have CONFIG_DEBUG_INFO_BTF enabled but still want to perform CO-RE
> relocations.
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@...ux.dev>
> ---
>  tools/bpf/bpftool/Documentation/bpftool-prog.rst |  7 ++++++-
>  tools/bpf/bpftool/bash-completion/bpftool        |  2 +-
>  tools/bpf/bpftool/prog.c                         | 12 +++++++++++-
>  3 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> index d6304e01afe0..e60a829ab8d0 100644
> --- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> +++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> @@ -127,7 +127,7 @@ bpftool prog pin *PROG* *FILE*
>      Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
>      character ('.'), which is reserved for future extensions of *bpffs*.
>
> -bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach]
> +bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach] [kernel_btf *BTF_DIR*]
>      Load bpf program(s) from binary *OBJ* and pin as *PATH*. **bpftool prog
>      load** pins only the first program from the *OBJ* as *PATH*. **bpftool prog
>      loadall** pins all programs from the *OBJ* under *PATH* directory. **type**
> @@ -153,6 +153,11 @@ bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | na
>      program does not support autoattach, bpftool falls back to regular pinning
>      for that program instead.
>
> +    The **kernel_btf** option allows specifying an external BTF file to replace
> +    the system's own vmlinux BTF file for CO-RE relocations. NOTE that any
> +    other feature (e.g., fentry/fexit programs, struct_ops, etc) will require
> +    actual kernel BTF like /sys/kernel/btf/vmlinux.
> +
>      Note: *PATH* must be located in *bpffs* mount. It must not contain a dot
>      character ('.'), which is reserved for future extensions of *bpffs*.
>
> diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
> index 1ce409a6cbd9..609938c287b7 100644
> --- a/tools/bpf/bpftool/bash-completion/bpftool
> +++ b/tools/bpf/bpftool/bash-completion/bpftool
> @@ -511,7 +511,7 @@ _bpftool()
>                              ;;
>                          *)
>                              COMPREPLY=( $( compgen -W "map" -- "$cur" ) )
> -                            _bpftool_once_attr 'type pinmaps autoattach'
> +                            _bpftool_once_attr 'type pinmaps autoattach kernel_btf'
>                              _bpftool_one_of_list 'offload_dev xdpmeta_dev'
>                              return 0
>                              ;;
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index f010295350be..3b6a361dd0f8 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1681,8 +1681,17 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>                 } else if (is_prefix(*argv, "autoattach")) {
>                         auto_attach = true;
>                         NEXT_ARG();
> +               } else if (is_prefix(*argv, "kernel_btf")) {
> +                       NEXT_ARG();
> +
> +                       if (!REQ_ARGS(1))
> +                               goto err_free_reuse_maps;
> +
> +                       open_opts.btf_custom_path = GET_ARG();
>                 } else {
> -                       p_err("expected no more arguments, 'type', 'map' or 'dev', got: '%s'?",
> +                       p_err("expected no more arguments, "
> +                             "'type', 'map', 'dev', 'offload_dev', 'xdpmeta_dev', 'pinmaps', "
> +                             "'autoattach', or 'kernel_btf', got: '%s'?",
>                               *argv);
>                         goto err_free_reuse_maps;
>                 }
> @@ -2474,6 +2483,7 @@ static int do_help(int argc, char **argv)
>                 "                         [map { idx IDX | name NAME } MAP]\\\n"
>                 "                         [pinmaps MAP_DIR]\n"
>                 "                         [autoattach]\n"
> +               "                         [kernel_btf BTF_DIR]\n"

Is it a DIR or a FILE/PATH?

>                 "       %1$s %2$s attach PROG ATTACH_TYPE [MAP]\n"
>                 "       %1$s %2$s detach PROG ATTACH_TYPE [MAP]\n"
>                 "       %1$s %2$s run PROG \\\n"
> --
> 2.47.1
>
>

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