Pahole fails to encode BTF for some Go projects (e.g. Kubernetes and
Podman) due to recursive type definitions that create reference loops
not representable in C. These recursive typedefs trigger a failure in
the BTF deduplication algorithm.

This patch extends btf_dedup_struct_types() to properly handle potential
recursion for BTF_KIND_TYPEDEF, similar to how recursion is already
handled for BTF_KIND_STRUCT. This allows pahole to successfully
generate BTF for Go binaries using recursive types without impacting
existing C-based workflows.

Changes in v3:
  1. Patch 1: Adjusted the comment of btf_dedup_ref_type() to refer to
  typedef as well.
  2. Patch 2: Update of the "dedup: recursive typedef" test to include a
  duplicated version of the types to make sure deduplication still happens
  in this case.

Changes in v2:
  1. Patch 1: Refactored code to prevent copying existing logic. Instead of
  adding a new function we modify the existing btf_dedup_struct_type()
  function to handle the BTF_KIND_TYPEDEF case. Calls to btf_hash_struct()
  and btf_shallow_equal_struct() are replaced with calls to functions that
  select btf_hash_struct() / btf_hash_typedef() based on the type.
  2. Patch 2: Added tests

v2: https://lore.kernel.org/lkml/cover.1762956564.git.paul.houssel@orange.com/

v1: https://lore.kernel.org/lkml/20251107153408.159342-1-paulhoussel2@gmail.com/

Paul Houssel (2):
  libbpf: fix BTF dedup to support recursive typedef definitions
  selftests/bpf: add BTF dedup tests for recursive typedef definitions

 tools/lib/bpf/btf.c                          | 73 +++++++++++++++-----
 tools/testing/selftests/bpf/prog_tests/btf.c | 65 +++++++++++++++++
 2 files changed, 121 insertions(+), 17 deletions(-)

-- 
2.51.0