libbpf: Support layout section handling in BTF

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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 <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260326145444.2076244-3-alan.maguire@oracle.com

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Alan Maguire authored and Andrii Nakryiko committed 2026-04-09 15:12:21 -07:00

1 parent 462733ecb8

commit 87896082a7

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