in compile/remote-compile/lbc/libbpf/src/relo_core.c [1145:1295]
int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn,
int insn_idx,
const struct bpf_core_relo *relo,
int relo_idx,
const struct btf *local_btf,
struct bpf_core_cand_list *cands)
{
struct bpf_core_spec local_spec, cand_spec, targ_spec = {};
struct bpf_core_relo_res cand_res, targ_res;
const struct btf_type *local_type;
const char *local_name;
__u32 local_id;
const char *spec_str;
int i, j, err;
local_id = relo->type_id;
local_type = btf__type_by_id(local_btf, local_id);
if (!local_type)
return -EINVAL;
local_name = btf__name_by_offset(local_btf, local_type->name_off);
if (!local_name)
return -EINVAL;
spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
if (str_is_empty(spec_str))
return -EINVAL;
err = bpf_core_parse_spec(local_btf, local_id, spec_str, relo->kind, &local_spec);
if (err) {
pr_warn("prog '%s': relo #%d: parsing [%d] %s %s + %s failed: %d\n",
prog_name, relo_idx, local_id, btf_kind_str(local_type),
str_is_empty(local_name) ? "<anon>" : local_name,
spec_str, err);
return -EINVAL;
}
pr_debug("prog '%s': relo #%d: kind <%s> (%d), spec is ", prog_name,
relo_idx, core_relo_kind_str(relo->kind), relo->kind);
bpf_core_dump_spec(LIBBPF_DEBUG, &local_spec);
libbpf_print(LIBBPF_DEBUG, "\n");
/* TYPE_ID_LOCAL relo is special and doesn't need candidate search */
if (relo->kind == BPF_TYPE_ID_LOCAL) {
targ_res.validate = true;
targ_res.poison = false;
targ_res.orig_val = local_spec.root_type_id;
targ_res.new_val = local_spec.root_type_id;
goto patch_insn;
}
/* libbpf doesn't support candidate search for anonymous types */
if (str_is_empty(spec_str)) {
pr_warn("prog '%s': relo #%d: <%s> (%d) relocation doesn't support anonymous types\n",
prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind);
return -EOPNOTSUPP;
}
for (i = 0, j = 0; i < cands->len; i++) {
err = bpf_core_spec_match(&local_spec, cands->cands[i].btf,
cands->cands[i].id, &cand_spec);
if (err < 0) {
pr_warn("prog '%s': relo #%d: error matching candidate #%d ",
prog_name, relo_idx, i);
bpf_core_dump_spec(LIBBPF_WARN, &cand_spec);
libbpf_print(LIBBPF_WARN, ": %d\n", err);
return err;
}
pr_debug("prog '%s': relo #%d: %s candidate #%d ", prog_name,
relo_idx, err == 0 ? "non-matching" : "matching", i);
bpf_core_dump_spec(LIBBPF_DEBUG, &cand_spec);
libbpf_print(LIBBPF_DEBUG, "\n");
if (err == 0)
continue;
err = bpf_core_calc_relo(prog_name, relo, relo_idx, &local_spec, &cand_spec, &cand_res);
if (err)
return err;
if (j == 0) {
targ_res = cand_res;
targ_spec = cand_spec;
} else if (cand_spec.bit_offset != targ_spec.bit_offset) {
/* if there are many field relo candidates, they
* should all resolve to the same bit offset
*/
pr_warn("prog '%s': relo #%d: field offset ambiguity: %u != %u\n",
prog_name, relo_idx, cand_spec.bit_offset,
targ_spec.bit_offset);
return -EINVAL;
} else if (cand_res.poison != targ_res.poison || cand_res.new_val != targ_res.new_val) {
/* all candidates should result in the same relocation
* decision and value, otherwise it's dangerous to
* proceed due to ambiguity
*/
pr_warn("prog '%s': relo #%d: relocation decision ambiguity: %s %u != %s %u\n",
prog_name, relo_idx,
cand_res.poison ? "failure" : "success", cand_res.new_val,
targ_res.poison ? "failure" : "success", targ_res.new_val);
return -EINVAL;
}
cands->cands[j++] = cands->cands[i];
}
/*
* For BPF_FIELD_EXISTS relo or when used BPF program has field
* existence checks or kernel version/config checks, it's expected
* that we might not find any candidates. In this case, if field
* wasn't found in any candidate, the list of candidates shouldn't
* change at all, we'll just handle relocating appropriately,
* depending on relo's kind.
*/
if (j > 0)
cands->len = j;
/*
* If no candidates were found, it might be both a programmer error,
* as well as expected case, depending whether instruction w/
* relocation is guarded in some way that makes it unreachable (dead
* code) if relocation can't be resolved. This is handled in
* bpf_core_patch_insn() uniformly by replacing that instruction with
* BPF helper call insn (using invalid helper ID). If that instruction
* is indeed unreachable, then it will be ignored and eliminated by
* verifier. If it was an error, then verifier will complain and point
* to a specific instruction number in its log.
*/
if (j == 0) {
pr_debug("prog '%s': relo #%d: no matching targets found\n",
prog_name, relo_idx);
/* calculate single target relo result explicitly */
err = bpf_core_calc_relo(prog_name, relo, relo_idx, &local_spec, NULL, &targ_res);
if (err)
return err;
}
patch_insn:
/* bpf_core_patch_insn() should know how to handle missing targ_spec */
err = bpf_core_patch_insn(prog_name, insn, insn_idx, relo, relo_idx, &targ_res);
if (err) {
pr_warn("prog '%s': relo #%d: failed to patch insn #%u: %d\n",
prog_name, relo_idx, relo->insn_off / 8, err);
return -EINVAL;
}
return 0;
}