[PATCH dwarves v4 0/2] pahole: Inject kfunc decl tags into BTF

[Daniel Xu <dxu@dxuuu.xyz>]

This patchset teaches pahole to parse symbols in .BTF_ids section in
vmlinux and discover exported kfuncs. Pahole then takes the list of
kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc.

Example of encoding:

        $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l
        121

        $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337
        [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static
        [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1

This enables downstream users and tools to dynamically discover which
kfuncs are available on a system by parsing vmlinux or module BTF, both
available in /sys/kernel/btf.

=== Changelog ===

Changes from v3:
* Guard kfunc tagging behind feature flag
* Use struct btf_id_set8 definition
* Remove unnecessary member from btf_encoder
* Fix code styling

Changes from v2:
* More reliably detect kfunc membership in set8 by tracking set addr ranges
* Rename some variables/functions to be more clear about kfunc vs func

Changes from v1:
* Fix resource leaks
* Fix callee -> caller typo
* Rename btf_decl_tag from kfunc -> bpf_kfunc
* Only grab btf_id_set funcs tagged kfunc
* Presort btf func list

Daniel Xu (2):
  pahole: Add --btf_feature=decl_tag_kfuncs feature
  pahole: Inject kfunc decl tags into BTF

 btf_encoder.c | 361 ++++++++++++++++++++++++++++++++++++++++++++++++++
 dwarves.h     |   1 +
 pahole.c      |   1 +
 3 files changed, 363 insertions(+)

-- 
2.42.1