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[bpf-next,v2,2/6] docs/bpf: document the semantics of BTF tags with kind_flag

Message ID 20250127233955.2275804-3-ihor.solodrai@linux.dev (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series BTF: arbitrary __attribute__ encoding | expand

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Commit Message

Ihor Solodrai Jan. 27, 2025, 11:39 p.m. UTC 
Explain the meaning of kind_flag in BTF type_tags and decl_tags.
Update uapi btf.h kind_flag comment to reflect the changes.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 Documentation/bpf/btf.rst      | 25 +++++++++++++++++++++----
 include/uapi/linux/btf.h       |  3 ++-
 tools/include/uapi/linux/btf.h |  3 ++-
 3 files changed, 25 insertions(+), 6 deletions(-)

Comments

Andrii Nakryiko Jan. 30, 2025, 12:33 a.m. UTC | #1 
On Mon, Jan 27, 2025 at 3:40 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>
> Explain the meaning of kind_flag in BTF type_tags and decl_tags.
> Update uapi btf.h kind_flag comment to reflect the changes.
>
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
> ---
>  Documentation/bpf/btf.rst      | 25 +++++++++++++++++++++----
>  include/uapi/linux/btf.h       |  3 ++-
>  tools/include/uapi/linux/btf.h |  3 ++-
>  3 files changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
> index 2478cef758f8..48d9b33d59db 100644
> --- a/Documentation/bpf/btf.rst
> +++ b/Documentation/bpf/btf.rst
> @@ -102,7 +102,8 @@ Each type contains the following common data::
>           * bits 24-28: kind (e.g. int, ptr, array...etc)
>           * bits 29-30: unused
>           * bit     31: kind_flag, currently used by
> -         *             struct, union, fwd, enum and enum64.
> +        *             struct, union, enum, fwd, enum64,
> +        *             decl_tag and type_tag

tabs instead of spaces (docs seem to be using spaces)


>           */
>          __u32 info;
>          /* "size" is used by INT, ENUM, STRUCT, UNION and ENUM64.
> @@ -478,7 +479,7 @@ No additional type data follow ``btf_type``.
>
>  ``struct btf_type`` encoding requirement:
>   * ``name_off``: offset to a non-empty string
> - * ``info.kind_flag``: 0
> + * ``info.kind_flag``: 0 or 1
>   * ``info.kind``: BTF_KIND_DECL_TAG
>   * ``info.vlen``: 0
>   * ``type``: ``struct``, ``union``, ``func``, ``var`` or ``typedef``
> @@ -489,7 +490,6 @@ No additional type data follow ``btf_type``.
>          __u32   component_idx;
>      };
>
> -The ``name_off`` encodes btf_decl_tag attribute string.
>  The ``type`` should be ``struct``, ``union``, ``func``, ``var`` or ``typedef``.
>  For ``var`` or ``typedef`` type, ``btf_decl_tag.component_idx`` must be ``-1``.
>  For the other three types, if the btf_decl_tag attribute is
> @@ -499,12 +499,21 @@ the attribute is applied to a ``struct``/``union`` member or
>  a ``func`` argument, and ``btf_decl_tag.component_idx`` should be a
>  valid index (starting from 0) pointing to a member or an argument.
>
> +If ``info.kind_flag`` is 0, then this is a normal decl tag, and the
> +``name_off`` encodes btf_decl_tag attribute string.
> +
> +If ``info.kind_flag`` is 1, then the decl tag represents an arbitrary
> +__attribute__. In this case, ``name_off`` encodes a string
> +representing the attribute-list of the attribute specifier. For
> +example, for an ``__attribute__((aligned(4)))`` the string's contents
> +is ``aligned(4)``.
> +
>  2.2.18 BTF_KIND_TYPE_TAG
>  ~~~~~~~~~~~~~~~~~~~~~~~~
>
>  ``struct btf_type`` encoding requirement:
>   * ``name_off``: offset to a non-empty string
> - * ``info.kind_flag``: 0
> + * ``info.kind_flag``: 0 or 1
>   * ``info.kind``: BTF_KIND_TYPE_TAG
>   * ``info.vlen``: 0
>   * ``type``: the type with ``btf_type_tag`` attribute
> @@ -522,6 +531,14 @@ type_tag, then zero or more const/volatile/restrict/typedef
>  and finally the base type. The base type is one of
>  int, ptr, array, struct, union, enum, func_proto and float types.
>
> +Similarly to decl tags, if the ``info.kind_flag`` is 0, then this is a
> +normal type tag, and the ``name_off`` encodes btf_type_tag attribute
> +string.
> +
> +If ``info.kind_flag`` is 1, then the type tag represents an arbitrary
> +__attribute__, and the ``name_off`` encodes a string representing the
> +attribute-list of the attribute specifier.
> +
>  2.2.19 BTF_KIND_ENUM64
>  ~~~~~~~~~~~~~~~~~~~~~~
>
> diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
> index ec1798b6d3ff..266d4ffa6c07 100644
> --- a/include/uapi/linux/btf.h
> +++ b/include/uapi/linux/btf.h
> @@ -36,7 +36,8 @@ struct btf_type {
>          * bits 24-28: kind (e.g. int, ptr, array...etc)
>          * bits 29-30: unused
>          * bit     31: kind_flag, currently used by
> -        *             struct, union, enum, fwd and enum64
> +        *             struct, union, enum, fwd, enum64,
> +        *             decl_tag and type_tag
>          */
>         __u32 info;
>         /* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.
> diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
> index ec1798b6d3ff..266d4ffa6c07 100644
> --- a/tools/include/uapi/linux/btf.h
> +++ b/tools/include/uapi/linux/btf.h
> @@ -36,7 +36,8 @@ struct btf_type {
>          * bits 24-28: kind (e.g. int, ptr, array...etc)
>          * bits 29-30: unused
>          * bit     31: kind_flag, currently used by
> -        *             struct, union, enum, fwd and enum64
> +        *             struct, union, enum, fwd, enum64,
> +        *             decl_tag and type_tag
>          */
>         __u32 info;
>         /* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.
> --
> 2.48.1
>
diff mbox series

Patch

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 2478cef758f8..48d9b33d59db 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -102,7 +102,8 @@  Each type contains the following common data::
          * bits 24-28: kind (e.g. int, ptr, array...etc)
          * bits 29-30: unused
          * bit     31: kind_flag, currently used by
-         *             struct, union, fwd, enum and enum64.
+	 *             struct, union, enum, fwd, enum64,
+	 *             decl_tag and type_tag
          */
         __u32 info;
         /* "size" is used by INT, ENUM, STRUCT, UNION and ENUM64.
@@ -478,7 +479,7 @@  No additional type data follow ``btf_type``.
 
 ``struct btf_type`` encoding requirement:
  * ``name_off``: offset to a non-empty string
- * ``info.kind_flag``: 0
+ * ``info.kind_flag``: 0 or 1
  * ``info.kind``: BTF_KIND_DECL_TAG
  * ``info.vlen``: 0
  * ``type``: ``struct``, ``union``, ``func``, ``var`` or ``typedef``
@@ -489,7 +490,6 @@  No additional type data follow ``btf_type``.
         __u32   component_idx;
     };
 
-The ``name_off`` encodes btf_decl_tag attribute string.
 The ``type`` should be ``struct``, ``union``, ``func``, ``var`` or ``typedef``.
 For ``var`` or ``typedef`` type, ``btf_decl_tag.component_idx`` must be ``-1``.
 For the other three types, if the btf_decl_tag attribute is
@@ -499,12 +499,21 @@  the attribute is applied to a ``struct``/``union`` member or
 a ``func`` argument, and ``btf_decl_tag.component_idx`` should be a
 valid index (starting from 0) pointing to a member or an argument.
 
+If ``info.kind_flag`` is 0, then this is a normal decl tag, and the
+``name_off`` encodes btf_decl_tag attribute string.
+
+If ``info.kind_flag`` is 1, then the decl tag represents an arbitrary
+__attribute__. In this case, ``name_off`` encodes a string
+representing the attribute-list of the attribute specifier. For
+example, for an ``__attribute__((aligned(4)))`` the string's contents
+is ``aligned(4)``.
+
 2.2.18 BTF_KIND_TYPE_TAG
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
 ``struct btf_type`` encoding requirement:
  * ``name_off``: offset to a non-empty string
- * ``info.kind_flag``: 0
+ * ``info.kind_flag``: 0 or 1
  * ``info.kind``: BTF_KIND_TYPE_TAG
  * ``info.vlen``: 0
  * ``type``: the type with ``btf_type_tag`` attribute
@@ -522,6 +531,14 @@  type_tag, then zero or more const/volatile/restrict/typedef
 and finally the base type. The base type is one of
 int, ptr, array, struct, union, enum, func_proto and float types.
 
+Similarly to decl tags, if the ``info.kind_flag`` is 0, then this is a
+normal type tag, and the ``name_off`` encodes btf_type_tag attribute
+string.
+
+If ``info.kind_flag`` is 1, then the type tag represents an arbitrary
+__attribute__, and the ``name_off`` encodes a string representing the
+attribute-list of the attribute specifier.
+
 2.2.19 BTF_KIND_ENUM64
 ~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index ec1798b6d3ff..266d4ffa6c07 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -36,7 +36,8 @@  struct btf_type {
 	 * bits 24-28: kind (e.g. int, ptr, array...etc)
 	 * bits 29-30: unused
 	 * bit     31: kind_flag, currently used by
-	 *             struct, union, enum, fwd and enum64
+	 *             struct, union, enum, fwd, enum64,
+	 *             decl_tag and type_tag
 	 */
 	__u32 info;
 	/* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.
diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index ec1798b6d3ff..266d4ffa6c07 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -36,7 +36,8 @@  struct btf_type {
 	 * bits 24-28: kind (e.g. int, ptr, array...etc)
 	 * bits 29-30: unused
 	 * bit     31: kind_flag, currently used by
-	 *             struct, union, enum, fwd and enum64
+	 *             struct, union, enum, fwd, enum64,
+	 *             decl_tag and type_tag
 	 */
 	__u32 info;
 	/* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.