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docs/bpf: Add documentation for BTF_KIND_TAG

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Add BTF_KIND_TAG documentation in btf.rst.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210914223103.249100-1-yhs@fb.com
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Yonghong Song 2021-09-14 15:31:03 -07:00 committed by Alexei Starovoitov
parent c240ba2878
commit 48f5a6c416
1 changed files with 28 additions and 1 deletions
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Documentation/bpf/btf.rst
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@ -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
*****************