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Date: Wed, 12 Jan 2022 18:09:35 +0000
From: Quentin Monnet <quentin@...valent.com>
To: Mauricio Vásquez <mauricio@...volk.io>,
netdev@...r.kernel.org, bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Rafael David Tinoco <rafaeldtinoco@...il.com>,
Lorenzo Fontana <lorenzo.fontana@...stic.co>,
Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v4 7/8] bpftool: Implement relocations recording
for BTFGen
2022-01-12 09:27 UTC-0500 ~ Mauricio Vásquez <mauricio@...volk.io>
> This commit implements the logic to record the relocation information
> for the different kind of relocations.
>
> btfgen_record_field_relo() uses the target specification to save all the
> types that are involved in a field-based CO-RE relocation. In this case
> types resolved and added recursively (using btfgen_put_type()).
> Only the struct and union members and their types) involved in the
> relocation are added to optimize the size of the generated BTF file.
>
> On the other hand, btfgen_record_type_relo() saves the types involved in
> a type-based CO-RE relocation. In this case all the members for the
> struct and union types are added. This is not strictly required since
> libbpf doesn't use them while performing this kind of relocation,
> however that logic could change on the future. Additionally, we expect
> that the number of this kind of relocations in an BPF object to be very
> low, hence the impact on the size of the generated BTF should be
> negligible.
>
> Finally, btfgen_record_enumval_relo() saves the whole enum type for
> enum-based relocations.
>
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
> tools/bpf/bpftool/gen.c | 260 +++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 257 insertions(+), 3 deletions(-)
>
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index cef0ea99d4d9..8c13dde0b74d 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -1207,19 +1228,252 @@ btfgen_new_info(const char *targ_btf_path)
> +static struct btfgen_type *
> +_btfgen_put_type(struct btf *btf, struct btfgen_info *info, struct btf_type *btf_type,
> + unsigned int id, bool all_members)
> +{
> + struct btfgen_type *btfgen_type, *tmp;
> + struct btf_array *array;
> + unsigned int child_id;
> + struct btf_member *m;
> + int err, i, n;
> +
> + /* check if we already have this type */
> + if (hashmap__find(info->types, uint_as_hash_key(id), (void **) &btfgen_type)) {
> + if (!all_members || btfgen_type->all_members)
> + return btfgen_type;
> + } else {
> + btfgen_type = calloc(1, sizeof(*btfgen_type));
> + if (!btfgen_type)
> + return NULL;
> +
> + btfgen_type->type = btf_type;
> + btfgen_type->id = id;
> +
> + /* append this type to the types list before anything else */
> + err = hashmap__add(info->types, uint_as_hash_key(btfgen_type->id), btfgen_type);
> + if (err) {
> + free(btfgen_type);
> + return NULL;
> + }
> + }
> +
> + /* avoid infinite recursion and yet be able to add all
> + * fields/members for types also managed by this function
> + */
> + btfgen_type->all_members = all_members;
> +
> +
Nit: double blank line.
> + /* recursively add other types needed by it */
> + switch (btf_kind(btfgen_type->type)) {
> + case BTF_KIND_UNKN:
> + case BTF_KIND_INT:
> static int btfgen_record_field_relo(struct btfgen_info *info, struct bpf_core_spec *targ_spec)
> {
> - return -EOPNOTSUPP;
> + struct btf *btf = (struct btf *) info->src_btf;
> + struct btfgen_type *btfgen_type;
> + struct btf_member *btf_member;
> + struct btf_type *btf_type;
> + struct btf_array *array;
> + unsigned int id;
> + int idx, err;
> +
> + btf_type = (struct btf_type *) btf__type_by_id(btf, targ_spec->root_type_id);
> +
> + /* create btfgen_type for root type */
> + btfgen_type = btfgen_put_type(btf, info, btf_type, targ_spec->root_type_id);
> + if (!btfgen_type)
> + return -errno;
> +
> + /* add types for complex types (arrays, unions, structures) */
> + for (int i = 1; i < targ_spec->raw_len; i++) {
> + /* skip typedefs and mods */
> + while (btf_is_mod(btf_type) || btf_is_typedef(btf_type)) {
> + id = btf_type->type;
> + btfgen_type = btfgen_get_type(info, id);
> + if (!btfgen_type)
> + return -ENOENT;
> + btf_type = (struct btf_type *) btf__type_by_id(btf, id);
> + }
> +
> + switch (btf_kind(btf_type)) {
> + case BTF_KIND_STRUCT:
> + case BTF_KIND_UNION:
> + idx = targ_spec->raw_spec[i];
> + btf_member = btf_members(btf_type) + idx;
> + btf_type = (struct btf_type *) btf__type_by_id(btf, btf_member->type);
> +
> + /* add member to relocation type */
> + err = btfgen_add_member(btfgen_type, btf_member, idx);
> + if (err)
> + return err;
> + /* put btfgen type */
> + btfgen_type = btfgen_put_type(btf, info, btf_type, btf_member->type);
> + if (!btfgen_type)
> + return -errno;
> + break;
> + case BTF_KIND_ARRAY:
> + array = btf_array(btf_type);
> + btfgen_type = btfgen_get_type(info, array->type);
> + if (!btfgen_type)
> + return -ENOENT;
> + btf_type = (struct btf_type *) btf__type_by_id(btf, array->type);
> + break;
> + default:
> + p_err("spec type wasn't handled");
This message might benefit from a bit more context (step, type number?).
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> }
>
> static int btfgen_record_type_relo(struct btfgen_info *info, struct bpf_core_spec *targ_spec)
> {
> - return -EOPNOTSUPP;
> + struct btf *btf = (struct btf *) info->src_btf;
> + struct btfgen_type *btfgen_type;
> + struct btf_type *btf_type;
> +
> + btf_type = (struct btf_type *) btf__type_by_id(btf, targ_spec->root_type_id);
> +
> + btfgen_type = btfgen_put_type_all(btf, info, btf_type, targ_spec->root_type_id);
> + return btfgen_type ? 0 : -errno;
Nit: double space in "? 0".
> }
>
> static int btfgen_record_enumval_relo(struct btfgen_info *info, struct bpf_core_spec *targ_spec)
> {
> - return -EOPNOTSUPP;
> + struct btf *btf = (struct btf *) info->src_btf;
> + struct btfgen_type *btfgen_type;
> + struct btf_type *btf_type;
> +
> + btf_type = (struct btf_type *) btf__type_by_id(btf, targ_spec->root_type_id);
> +
> + btfgen_type = btfgen_put_type_all(btf, info, btf_type, targ_spec->root_type_id);
> + return btfgen_type ? 0 : -errno;
Nit: double space in "? 0".
> }
>
> static int btfgen_record_reloc(struct btfgen_info *info, struct bpf_core_spec *res)
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