Re: [PATCH v6 bpf-next 01/10] btf: add kind layout encoding to UAPI

Mykyta Yatsenko
2025-12-13T02:52:31Z

On 12/10/25 20:32, Alan Maguire wrote:
> BTF kind layouts provide information to parse BTF kinds. By separating
> parsing BTF from using all the information it provides, we allow BTF
> to encode new features even if they cannot be used by readers. This
> will be helpful in particular for cases where older tools are used
> to parse newer BTF with kinds the older tools do not recognize;
> the BTF can still be parsed in such cases using kind layout.
>
> The intent is to support encoding of kind layouts optionally so that
> tools like pahole can add this information. For each kind, we record
>
> - length of singular element following struct btf_type
> - length of each of the btf_vlen() elements following
>
> The ideas here were discussed at [1], [2]; hence
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>
> [1] https://lore.kernel.org/bpf/CAEf4BzYjWHRdNNw4B=eOXOs_ONrDwrgX4bn=Nuc1g8JPFC34MA@mail.gmail.com/
> [2] https://lore.kernel.org/bpf/20230531201936.1992188-1-alan.maguire@oracle.com/
> ---
> include/uapi/linux/btf.h | 10 ++++++++++
> tools/include/uapi/linux/btf.h | 10 ++++++++++
> 2 files changed, 20 insertions(+)
>
> diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
> index 266d4ffa6c07..64dd681274f4 100644
> --- a/include/uapi/linux/btf.h
> +++ b/include/uapi/linux/btf.h
> @@ -8,6 +8,14 @@
> #define BTF_MAGIC 0xeB9F
> #define BTF_VERSION 1
>
> +/* kind layout section consists of a struct btf_kind_layout for each known
> + * kind at BTF encoding time.
> + */
We switched to kernel style comments in the new code:
/*
* comment
*/

instead of
/* comment
*/
> +struct btf_kind_layout {
> + __u8 info_sz; /* size of singular element after btf_type */
> + __u8 elem_sz; /* size of each of btf_vlen(t) elements */
> +};
> +
> struct btf_header {
> __u16 magic;
> __u8 version;
> @@ -19,6 +27,8 @@ struct btf_header {
> __u32 type_len; /* length of type section */
> __u32 str_off; /* offset of string section */
> __u32 str_len; /* length of string section */
> + __u32 kind_layout_off;/* offset of kind layout section */
> + __u32 kind_layout_len;/* length of kind layout section */
> };
>
> /* Max # of type identifier */
> diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
> index 266d4ffa6c07..64dd681274f4 100644
> --- a/tools/include/uapi/linux/btf.h
> +++ b/tools/include/uapi/linux/btf.h
> @@ -8,6 +8,14 @@
> #define BTF_MAGIC 0xeB9F
> #define BTF_VERSION 1
>
> +/* kind layout section consists of a struct btf_kind_layout for each known
> + * kind at BTF encoding time.
> + */
> +struct btf_kind_layout {
> + __u8 info_sz; /* size of singular element after btf_type */
> + __u8 elem_sz; /* size of each of btf_vlen(t) elements */
> +};
> +
> struct btf_header {
> __u16 magic;
> __u8 version;
> @@ -19,6 +27,8 @@ struct btf_header {
> __u32 type_len; /* length of type section */
> __u32 str_off; /* offset of string section */
> __u32 str_len; /* length of string section */
> + __u32 kind_layout_off;/* offset of kind layout section */
> + __u32 kind_layout_len;/* length of kind layout section */
> };
>
> /* Max # of type identifier */