Re: [PATCH v13 bpf-next 2/8] libbpf: Support layout section handling in BTF

On Fri, Mar 6, 2026 at 3:37 AM Alan Maguire <[email protected]> wrote:
>
> 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
>
> Signed-off-by: Alan Maguire <[email protected]>
> ---
>  tools/lib/bpf/btf.c | 309 ++++++++++++++++++++++++++++----------------
>  1 file changed, 200 insertions(+), 109 deletions(-)
>

[...]

>
> -       memcpy(p, hdr, hdr->hdr_len);
> +       memcpy(p, hdr, min((__u32)sizeof(struct btf_header), hdr->hdr_len));

in all these cases where we have sizeof(struct btf_header), this
smells like a potential issue, tbh. We are silently truncating the
original header here, potentially. Which is ok for read-only case, but
do we error out if someone is trying to modify/write such BTF where we
don't really understand all of it? Should we?

>         if (swap_endian)
> -               btf_bswap_hdr(p);
> +               btf_bswap_hdr(p, hdr->hdr_len);
>         p += hdr->hdr_len;
>
>         memcpy(p, btf->types_data, hdr->type_len);

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