libbpf: Split bpf_core_apply_relo()

BTFGen needs to run the core relocation logic in order to understand
what are the types involved in a given relocation.

Currently bpf_core_apply_relo() calculates and **applies** a relocation
to an instruction. Having both operations in the same function makes it
difficult to only calculate the relocation without patching the
instruction. This commit splits that logic in two different phases: (1)
calculate the relocation and (2) patch the instruction.

For the first phase bpf_core_apply_relo() is renamed to
bpf_core_calc_relo_insn() who is now only on charge of calculating the
relocation, the second phase uses the already existing
bpf_core_patch_insn(). bpf_object__relocate_core() uses both of them and
the BTFGen will use only bpf_core_calc_relo_insn().

Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220215225856.671072-2-mauricio@kinvolk.io

1 files changed, 40 insertions, 31 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2262bcdfee92..d3c457fb045e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5530,11 +5530,12 @@ static int record_relo_core(struct bpf_program *prog,
 	return 0;
 }
 
-static int bpf_core_apply_relo(struct bpf_program *prog,
-			       const struct bpf_core_relo *relo,
-			       int relo_idx,
-			       const struct btf *local_btf,
-			       struct hashmap *cand_cache)
+static int bpf_core_resolve_relo(struct bpf_program *prog,
+				 const struct bpf_core_relo *relo,
+				 int relo_idx,
+				 const struct btf *local_btf,
+				 struct hashmap *cand_cache,
+				 struct bpf_core_relo_res *targ_res)
 {
 	struct bpf_core_spec specs_scratch[3] = {};
 	const void *type_key = u32_as_hash_key(relo->type_id);
@@ -5543,20 +5544,7 @@ static int bpf_core_apply_relo(struct bpf_program *prog,
 	const struct btf_type *local_type;
 	const char *local_name;
 	__u32 local_id = relo->type_id;
-	struct bpf_insn *insn;
-	int insn_idx, err;
-
-	if (relo->insn_off % BPF_INSN_SZ)
-		return -EINVAL;
-	insn_idx = relo->insn_off / BPF_INSN_SZ;
-	/* adjust insn_idx from section frame of reference to the local
-	 * program's frame of reference; (sub-)program code is not yet
-	 * relocated, so it's enough to just subtract in-section offset
-	 */
-	insn_idx = insn_idx - prog->sec_insn_off;
-	if (insn_idx >= prog->insns_cnt)
-		return -EINVAL;
-	insn = &prog->insns[insn_idx];
+	int err;
 
 	local_type = btf__type_by_id(local_btf, local_id);
 	if (!local_type)
@@ -5566,15 +5554,6 @@ static int bpf_core_apply_relo(struct bpf_program *prog,
 	if (!local_name)
 		return -EINVAL;
 
-	if (prog->obj->gen_loader) {
-		const char *spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
-
-		pr_debug("record_relo_core: prog %td insn[%d] %s %s %s final insn_idx %d\n",
-			prog - prog->obj->programs, relo->insn_off / 8,
-			btf_kind_str(local_type), local_name, spec_str, insn_idx);
-		return record_relo_core(prog, relo, insn_idx);
-	}
-
 	if (relo->kind != BPF_CORE_TYPE_ID_LOCAL &&
 	    !hashmap__find(cand_cache, type_key, (void **)&cands)) {
 		cands = bpf_core_find_cands(prog->obj, local_btf, local_id);
@@ -5591,19 +5570,21 @@ static int bpf_core_apply_relo(struct bpf_program *prog,
 		}
 	}
 
-	return bpf_core_apply_relo_insn(prog_name, insn, insn_idx, relo,
-					relo_idx, local_btf, cands, specs_scratch);
+	return bpf_core_calc_relo_insn(prog_name, relo, relo_idx, local_btf, cands, specs_scratch,
+				       targ_res);
 }
 
 static int
 bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
 {
 	const struct btf_ext_info_sec *sec;
+	struct bpf_core_relo_res targ_res;
 	const struct bpf_core_relo *rec;
 	const struct btf_ext_info *seg;
 	struct hashmap_entry *entry;
 	struct hashmap *cand_cache = NULL;
 	struct bpf_program *prog;
+	struct bpf_insn *insn;
 	const char *sec_name;
 	int i, err = 0, insn_idx, sec_idx;
 
@@ -5654,6 +5635,8 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
 			 sec_name, sec->num_info);
 
 		for_each_btf_ext_rec(seg, sec, i, rec) {
+			if (rec->insn_off % BPF_INSN_SZ)
+				return -EINVAL;
 			insn_idx = rec->insn_off / BPF_INSN_SZ;
 			prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx);
 			if (!prog) {
@@ -5668,12 +5651,38 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
 			if (!prog->load)
 				continue;
 
-			err = bpf_core_apply_relo(prog, rec, i, obj->btf, cand_cache);
+			/* adjust insn_idx from section frame of reference to the local
+			 * program's frame of reference; (sub-)program code is not yet
+			 * relocated, so it's enough to just subtract in-section offset
+			 */
+			insn_idx = insn_idx - prog->sec_insn_off;
+			if (insn_idx >= prog->insns_cnt)
+				return -EINVAL;
+			insn = &prog->insns[insn_idx];
+
+			if (prog->obj->gen_loader) {
+				err = record_relo_core(prog, rec, insn_idx);
+				if (err) {
+					pr_warn("prog '%s': relo #%d: failed to record relocation: %d\n",
+						prog->name, i, err);
+					goto out;
+				}
+				continue;
+			}
+
+			err = bpf_core_resolve_relo(prog, rec, i, obj->btf, cand_cache, &targ_res);
 			if (err) {
 				pr_warn("prog '%s': relo #%d: failed to relocate: %d\n",
 					prog->name, i, err);
 				goto out;
 			}
+
+			err = bpf_core_patch_insn(prog->name, insn, insn_idx, rec, i, &targ_res);
+			if (err) {
+				pr_warn("prog '%s': relo #%d: failed to patch insn #%u: %d\n",
+					prog->name, i, insn_idx, err);
+				goto out;
+			}
 		}
 	}