On Tue, May 28, 2024 at 5:26 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Map distilled base BTF type ids referenced in split BTF and their
> references to the base BTF passed in, and if the mapping succeeds,
> reparent the split BTF to the base BTF.
>
> Relocation is done by first verifying that distilled base BTF
> only consists of named INT, FLOAT, ENUM, FWD, STRUCT and
> UNION kinds; then we sort these to speed lookups. Once sorted,
> the base BTF is iterated, and for each relevant kind we check
> for an equivalent in distilled base BTF. When found, the
> mapping from distilled -> base BTF id and string offset is recorded.
> In establishing mappings, we need to ensure we check STRUCT/UNION
> size when the STRUCT/UNION is embedded in a split BTF STRUCT/UNION,
> and when duplicate names exist for the same STRUCT/UNION. Otherwise
> size is ignored in matching STRUCT/UNIONs.
>
> Once all mappings are established, we can update type ids
> and string offsets in split BTF and reparent it to the new base.
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/lib/bpf/Build | 2 +-
> tools/lib/bpf/btf.c | 17 ++
> tools/lib/bpf/btf.h | 14 ++
> tools/lib/bpf/btf_relocate.c | 430 ++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.map | 1 +
> tools/lib/bpf/libbpf_internal.h | 3 +
> 6 files changed, 466 insertions(+), 1 deletion(-)
> create mode 100644 tools/lib/bpf/btf_relocate.c
>
[...]
> +/* Set temporarily in relocation id_map if distilled base struct/union is
> + * embedded in a split BTF struct/union; in such a case, size information must
> + * match between distilled base BTF and base BTF representation of type.
> + */
> +#define BTF_IS_EMBEDDED ((__u32)-1)
> +
> +/* <name, size, id> triple used in sorting/searching distilled base BTF. */
> +struct btf_name_info {
> + const char *name;
> + int size:31;
> + /* set when search requires a size match */
> + bool needs_size;
this was meant to be a 1-bit field, right? `: 1` is missing?
> + __u32 id;
> +};
> +
[...]
> + case BTF_KIND_INT:
> + if (dist_kind != base_kind ||
> + btf_int_encoding(base_t) != btf_int_encoding(dist_t))
> + continue;
> + break;
> + case BTF_KIND_FLOAT:
> + if (dist_kind != base_kind)
> + continue;
> + break;
> + case BTF_KIND_ENUM:
> + /* ENUM and ENUM64 are encoded as sized ENUM in
> + * distilled base BTF.
> + */
> + if (dist_kind != base_kind && base_kind != BTF_KIND_ENUM64)
> + continue;
probably unnecessarily strict, I'd check something like
if (!btf_is_enum_any(dist_t) || !btf_is_enum_any(base_t) ||
dist_t->size != base_t->size)
continue;
it's minor, unlikely to matter in practice
> + break;
> + case BTF_KIND_STRUCT:
> + case BTF_KIND_UNION:
> + /* size verification is required for embedded
> + * struct/unions.
> + */
> + if (r->id_map[dist_name_info->id] == BTF_IS_EMBEDDED &&
> + base_t->size != dist_t->size)
> + continue;
> + break;
> + default:
> + continue;
> + }
> + /* map id and name */
> + r->id_map[dist_name_info->id] = id;
> + r->str_map[dist_t->name_off] = base_t->name_off;
> + }
[...]
