[PATCH bpf-next v2 0/3] libbpf: btf_decl_tag attribute for btf dump in C format

[Eduard Zingerman <eddyz87@gmail.com>]

Support for clang's __attribute__((btf_decl_tag("..."))) by
btf_dump__dump_type and btf_dump__dump_type_data functions.
Decl tag attributes are restored for:
- structs and unions
- struct and union fields
- typedefs
- global variables
- function prototype parameters

The attribute is restored using __btf_decl_tag macro that is printed
upon first call to btf_dump__dump_type function:

 #if __has_attribute(btf_decl_tag)
 #define __btf_decl_tag(x) __attribute__((btf_decl_tag(x)))
 #else
 #define __btf_decl_tag(x)
 #endif

To simplify testing of the btf_dump__dump_type_data the
prog_tests/btf_dump.c:test_btf_dump_case is extended to invoke
btf_dump__dump_type_data for each DATASEC object in the test case
binary file.

Changelog:
v1 -> v2:
- prog_tests/btf_dump.c:test_btf_dump_case modified to print DATASECs
  using btf_dump__dump_type_data;
- support for decl tags applied to global variables and function
  prototype parameters;
- update to support interleaved calls to btf_dump__dump_type and
  btf__add_decl_tag (incremental dump);
- fix for potential double free error in btf_dump_assign_decl_tags;
- styling fixes suggested by Andrii.

RFC -> v1:
- support for decl tags applied to struct / union fields and typedefs;
- __btf_decl_tag macro;
- btf_dump->decl_tags hash and equal functions updated to use integer
  key instead of a pointer;
- realloc_decl_tags function removed;
- update for allocation logic in btf_dump_assign_decl_tags.

[v1]  https://lore.kernel.org/bpf/20221103134522.2764601-1-eddyz87@gmail.com/
[RFC] https://lore.kernel.org/bpf/20221025222802.2295103-4-eddyz87@gmail.com/

Eduard Zingerman (3):
  libbpf: __attribute__((btf_decl_tag("..."))) for btf dump in C format
  selftests/bpf: Dump data sections as part of btf_dump_test_case tests
  selftests/bpf: Tests for BTF_KIND_DECL_TAG dump in C format

 tools/lib/bpf/btf_dump.c                      | 186 +++++++++++++++-
 .../selftests/bpf/prog_tests/btf_dump.c       | 198 ++++++++++++++++--
 .../bpf/progs/btf_dump_test_case_decl_tag.c   |  65 ++++++
 3 files changed, 427 insertions(+), 22 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/btf_dump_test_case_decl_tag.c

-- 
2.34.1