Add BTF_KIND_TAG documentation in btf.rst.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
Documentation/bpf/btf.rst | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 846354cd2d69..1bfe4072f5fc 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -85,6 +85,7 @@ sequentially and type id is assigned to each recognized type starting from id
#define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */
#define BTF_KIND_FLOAT 16 /* Floating point */
+ #define BTF_KIND_TAG 17 /* Tag */
Note that the type section encodes debug info, not just pure types.
``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
@@ -106,7 +107,7 @@ Each type contains the following common data::
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
- * FUNC and FUNC_PROTO.
+ * FUNC, FUNC_PROTO and TAG.
* "type" is a type_id referring to another type.
*/
union {
@@ -465,6 +466,32 @@ map definition.
No additional type data follow ``btf_type``.
+2.2.17 BTF_KIND_TAG
+~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+ * ``name_off``: offset to a non-empty string
+ * ``info.kind_flag``: 0
+ * ``info.kind``: BTF_KIND_TAG
+ * ``info.vlen``: 0
+ * ``type``: ``struct``, ``union``, ``func`` or ``var``
+
+``btf_type`` is followed by ``struct btf_tag``.::
+
+ struct btf_tag {
+ __u32 component_idx;
+ };
+
+The ``name_off`` encodes btf_tag attribute string.
+The ``type`` should be ``struct``, ``union``, ``func`` or ``var``.
+For ``var`` type, ``btf_tag.component_idx`` must be ``-1``.
+For the other three types, if the btf_tag attribute is
+applied to the ``struct``, ``union`` or ``func`` itself,
+``btf_tag.component_idx`` must be ``-1``. Otherwise,
+the attribute is applied to a ``struct``/``union`` member or
+a ``func`` argument, and ``btf_tag.component_idx`` should be a
+valid index (starting from 0) pointing to a member or an argument.
+
3. BTF Kernel API
*****************
--
2.30.2
