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[v10,bpf-next,11/14] bpf: Update .BTF_ids section in btf.rst with sets info

Message ID 20200807094559.571260-12-jolsa@kernel.org
State New
Headers show
Series bpf: Add d_path helper | expand

Commit Message

Jiri Olsa Aug. 7, 2020, 9:45 a.m. UTC 
Updating btf.rst doc with info about BTF_SET_START/END macros.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 Documentation/bpf/btf.rst | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
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Patch

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index b5361b8621c9..44dc789de2b4 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -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.