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bpf: Update .BTF_ids section in btf.rst with sets info 

Updating btf.rst doc with info about BTF_SET_START/END macros.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-12-jolsa@kernel.org
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Jiri Olsa 2020-08-25 21:21:21 +02:00 committed by Alexei Starovoitov
parent 6e22ab9da7
commit 68a26bc792
1 changed files with 25 additions and 0 deletions
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Documentation/bpf/btf.rst
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@ -724,6 +724,31 @@ want to define unused entry in BTF_ID_LIST, like::
BTF_ID_UNUSED
BTF_ID(struct, task_struct)
The ``BTF_SET_START/END`` macros pair defines sorted list of BTF ID values
and their count, with following syntax::
BTF_SET_START(set)
BTF_ID(type1, name1)
BTF_ID(type2, name2)
BTF_SET_END(set)
resulting in following layout in .BTF_ids section::
__BTF_ID__set__set:
.zero 4
__BTF_ID__type1__name1__3:
.zero 4
__BTF_ID__type2__name2__4:
.zero 4
The ``struct btf_id_set set;`` variable is defined to access the list.
The ``typeX`` name can be one of following::
struct, union, typedef, func
and is used as a filter when resolving the BTF ID value.
All the BTF ID lists and sets are compiled in the .BTF_ids section and
resolved during the linking phase of kernel build by ``resolve_btfids`` tool.