Commit b7290384 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

docs/bpf: clarify how btf_type_tag gets encoded in the type chain 



Clarify where the BTF_KIND_TYPE_TAG gets encoded in the type chain,
so applications and kernel can properly parse them.

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220127154627.665163-1-yhs@fb.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 67ef7e1a

Documentation/bpf/btf.rst

+13 −0
Original line number Diff line number Diff line
@@ -503,6 +503,19 @@ valid index (starting from 0) pointing to a member or an argument. 
 * ``info.vlen``: 0

 * ``type``: the type with ``btf_type_tag`` attribute



Currently, ``BTF_KIND_TYPE_TAG`` is only emitted for pointer types.

It has the following btf type chain:

::



  ptr -> [type_tag]*

      -> [const | volatile | restrict | typedef]*

      -> base_type



Basically, a pointer type points to zero or more

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.



3. BTF Kernel API

=================