The last part of the BTFGen algorithm is to create a new BTF object with
all the types that were recorded in the previous steps.
This function performs two different steps:
1. Add the types to the new BTF object by using btf__add_type(). Some
special logic around struct and unions is implemented to only add the
members that are really used in the field-based relocations. The type
ID on the new and old BTF objects is stored on a map.
2. Fix all the type IDs on the new BTF object by using the IDs saved in
the previous step.
Signed-off-by: Mauricio Vásquez <mauricio@xxxxxxxxxx>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@xxxxxxxxxxx>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@xxxxxxxxxx>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@xxxxxxxxxx>
---
tools/bpf/bpftool/gen.c | 100 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 99 insertions(+), 1 deletion(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 806001020841..25a336846d9f 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1505,10 +1505,108 @@ static int btfgen_record_obj(struct btfgen_info *info, const char *obj_path)
return err;
}
+static int btfgen_remap_id(__u32 *type_id, void *ctx)
+{
+ unsigned int *ids = ctx;
+
+ *type_id = ids[*type_id];
+
+ return 0;
+}
+
/* Generate BTF from relocation information previously recorded */
static struct btf *btfgen_get_btf(struct btfgen_info *info)
{
- return ERR_PTR(-EOPNOTSUPP);
+ struct btf *btf_new = NULL;
+ unsigned int *ids = NULL;
+ unsigned int i, n = btf__type_cnt(info->marked_btf);
+ int err = 0;
+
+ btf_new = btf__new_empty();
+ if (!btf_new) {
+ err = -errno;
+ goto err_out;
+ }
+
+ ids = calloc(n, sizeof(*ids));
+ if (!ids) {
+ err = -errno;
+ goto err_out;
+ }
+
+ /* first pass: add all marked types to btf_new and add their new ids to the ids map */
+ for (i = 1; i < n; i++) {
+ const struct btf_type *cloned_type, *type;
+ const char *name;
+ int new_id;
+
+ cloned_type = btf__type_by_id(info->marked_btf, i);
+
+ if (cloned_type->name_off != MARKED)
+ continue;
+
+ type = btf__type_by_id(info->src_btf, i);
+
+ /* add members for struct and union */
+ if (btf_is_composite(type)) {
+ struct btf_member *cloned_m, *m;
+ unsigned short vlen;
+ int idx_src;
+
+ name = btf__str_by_offset(info->src_btf, type->name_off);
+
+ if (btf_is_struct(type))
+ err = btf__add_struct(btf_new, name, type->size);
+ else
+ err = btf__add_union(btf_new, name, type->size);
+
+ if (err < 0)
+ goto err_out;
+ new_id = err;
+
+ cloned_m = btf_members(cloned_type);
+ m = btf_members(type);
+ vlen = btf_vlen(cloned_type);
+ for (idx_src = 0; idx_src < vlen; idx_src++, cloned_m++, m++) {
+ /* add only members that are marked as used */
+ if (cloned_m->name_off != MARKED)
+ continue;
+
+ name = btf__str_by_offset(info->src_btf, m->name_off);
+ err = btf__add_field(btf_new, name, m->type,
+ BTF_MEMBER_BIT_OFFSET(m->offset),
+ BTF_MEMBER_BITFIELD_SIZE(m->offset));
+ if (err < 0)
+ goto err_out;
+ }
+ } else {
+ err = btf__add_type(btf_new, info->src_btf, type);
+ if (err < 0)
+ goto err_out;
+ new_id = err;
+ }
+
+ /* add ID mapping */
+ ids[i] = new_id;
+ }
+
+ /* second pass: fix up type ids */
+ for (i = 1; i < btf__type_cnt(btf_new); i++) {
+ struct btf_type *btf_type = (struct btf_type *) btf__type_by_id(btf_new, i);
+
+ err = btf_type_visit_type_ids(btf_type, btfgen_remap_id, ids);
+ if (err)
+ goto err_out;
+ }
+
+ free(ids);
+ return btf_new;
+
+err_out:
+ btf__free(btf_new);
+ free(ids);
+ errno = -err;
+ return NULL;
}
/* Create minimized BTF file for a set of BPF objects.
--
2.25.1
