kernel/linux.git/tools/lib/bpf/btf.c, branch v7.1

libbpf: BTF validation can use layout for unknown kinds

2026-03-26T20:53:56+00:00

BTF parsing can use layout to navigate unknown kinds, so btf_validate_type() should take layout information into account to avoid failure when an unrecognized kind is met. Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260326145444.2076244-6-alan.maguire@oracle.com

libbpf: Add layout encoding support

2026-03-26T20:53:56+00:00

Support encoding of BTF layout data via btf__new_empty_opts(). Current supported opts are base_btf and add_layout. Layout information is maintained in btf.c in the layouts[] array; when BTF is created with the add_layout option it represents the current view of supported BTF kinds. Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260326145444.2076244-5-alan.maguire@oracle.com

libbpf: Use layout to compute an unknown kind size

2026-03-26T20:53:56+00:00

This allows BTF parsing to proceed even if we do not know the kind. Fall back to base BTF layout if layout information is not in split BTF. Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260326145444.2076244-4-alan.maguire@oracle.com

libbpf: Support layout section handling in BTF

2026-03-26T20:53:56+00:00

Support reading in layout fixing endian issues on reading; also support writing layout section to raw BTF object. There is not yet an API to populate the layout with meaningful information. As part of this, we need to consider multiple valid BTF header sizes; the original or the layout-extended headers. So to support this, the "struct btf" representation is modified to contain a "struct btf_header" and we copy the valid portion from the raw data to it; this means we can always safely check fields like btf->hdr.layout_len . Note if parsed-in BTF has extra header information beyond sizeof(struct btf_header) - if so we make that BTF ineligible for modification by setting btf->has_hdr_extra . Ensure that we handle endianness issues for BTF layout section, though currently only field that needs this (flags) is unused. Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260326145444.2076244-3-alan.maguire@oracle.com

libbpf: Support appending split BTF in btf__add_btf()

2026-03-05T22:57:58+00:00

btf__add_btf() currently rejects split BTF sources with -ENOTSUP. This prevents merging types from multiple kernel module BTFs that are all split against the same vmlinux base. Extend btf__add_btf() to handle split BTF sources by: - Replacing the blanket -ENOTSUP with a validation that src and dst share the same base BTF pointer when both are split, returning -EOPNOTSUPP on mismatch. - Computing src_start_id from the source's base to distinguish base type ID references (which must remain unchanged) from split type IDs (which must be remapped to new positions in the destination). - Using src_btf->nr_types instead of btf__type_cnt()-1 for the type count, which is correct for both split and non-split sources. - Skipping base string offsets (< start_str_off) during the string rewrite loop, mirroring the type ID skip pattern. Since src and dst share the same base BTF, base string offsets are already valid and need no remapping. For non-split sources the behavior is identical: src_start_id is 1, the type_id < 1 guard is never true (VOID is already skipped), and the remapping formula reduces to the original. start_str_off is 0 so no string offsets are skipped. Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Josef Bacik Signed-off-by: Andrii Nakryiko Reviewed-by: Alan Maguire Link: https://lore.kernel.org/bpf/c00216ed48cf7897078d9645679059d5ebf42738.1772657690.git.josef@toxicpanda.com

btf: Refactor the code by calling str_is_empty

2026-01-14T00:21:56+00:00

Calling the str_is_empty function to clarify the code and no functional changes are introduced. Signed-off-by: Donglin Peng Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260109130003.3313716-12-dolinux.peng@gmail.com

libbpf: Verify BTF sorting

2026-01-14T00:16:59+00:00

This patch checks whether the BTF is sorted by name in ascending order. If sorted, binary search will be used when looking up types. Signed-off-by: Donglin Peng Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260109130003.3313716-6-dolinux.peng@gmail.com

libbpf: Optimize type lookup with binary search for sorted BTF

2026-01-14T00:16:58+00:00

This patch introduces binary search optimization for BTF type lookups when the BTF instance contains sorted types. The optimization significantly improves performance when searching for types in large BTF instances with sorted types. For unsorted BTF, the implementation falls back to the original linear search. Signed-off-by: Donglin Peng Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260109130003.3313716-5-dolinux.peng@gmail.com

libbpf: Add BTF permutation support for type reordering

2026-01-14T00:10:39+00:00

Introduce btf__permute() API to allow in-place rearrangement of BTF types. This function reorganizes BTF type order according to a provided array of type IDs, updating all type references to maintain consistency. Signed-off-by: Donglin Peng Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260109130003.3313716-2-dolinux.peng@gmail.com

libbpf: Add debug messaging in dedup equivalence/identity matching

2025-12-05T23:55:54+00:00

We have seen a number of issues like [1]; failures to deduplicate key kernel data structures like task_struct. These are often hard to debug from pahole even with verbose output, especially when identity/equivalence checks fail deep in a nested struct comparison. Here we add debug messages of the form libbpf: STRUCT 'task_struct' size=2560 vlen=194 cand_id[54222] canon_id[102820] shallow-equal but not equiv for field#23 'sched_class': 0 These will be emitted during dedup from pahole when --verbose/-V is specified. This greatly helps identify exactly where dedup failures are experienced. [1] https://lore.kernel.org/bpf/b8e8b560-bce5-414b-846d-0da6d22a9983@oracle.com/ Changes since v1: - updated debug messages to refer to shallow-equal, added ids (Andrii) Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20251203191507.55565-1-alan.maguire@oracle.com