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@xxxxxxxxx>
---
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
*/
__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
