libbpf: Avoid joining .BTF.ext data with BPF programs by section name

Instead of using ELF section names as a joining key between .BTF.ext and
corresponding BPF programs, pre-build .BTF.ext section number to ELF
section index mapping during bpf_object__open() and use it later for
matching .BTF.ext information (func/line info or CO-RE relocations) to
their respective BPF programs and subprograms.

This simplifies corresponding joining logic and let's libbpf do
manipulations with BPF program's ELF sections like dropping leading '?'
character for non-autoloaded programs. Original joining logic in
bpf_object__relocate_core() (see relevant comment that's now removed)
was never elegant, so it's a good improvement regardless. But it also
avoids unnecessary internal assumptions about preserving original ELF
section name as BPF program's section name (which was broken when
SEC("?abc") support was added).

Fixes: a3820c481112 ("libbpf: Support opting out from autoloading BPF programs declaratively")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-5-andrii@kernel.org

1 files changed, 7 insertions, 2 deletions

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index d124e9e533f0..bb1e06eb1eca 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -2626,6 +2626,7 @@ static int btf_ext_setup_info(struct btf_ext *btf_ext,
 	const struct btf_ext_info_sec *sinfo;
 	struct btf_ext_info *ext_info;
 	__u32 info_left, record_size;
+	size_t sec_cnt = 0;
 	/* The start of the info sec (including the __u32 record_size). */
 	void *info;
 
@@ -2689,8 +2690,7 @@ static int btf_ext_setup_info(struct btf_ext *btf_ext,
 			return -EINVAL;
 		}
 
-		total_record_size = sec_hdrlen +
-				    (__u64)num_records * record_size;
+		total_record_size = sec_hdrlen + (__u64)num_records * record_size;
 		if (info_left < total_record_size) {
 			pr_debug("%s section has incorrect num_records in .BTF.ext\n",
 			     ext_sec->desc);
@@ -2699,12 +2699,14 @@ static int btf_ext_setup_info(struct btf_ext *btf_ext,
 
 		info_left -= total_record_size;
 		sinfo = (void *)sinfo + total_record_size;
+		sec_cnt++;
 	}
 
 	ext_info = ext_sec->ext_info;
 	ext_info->len = ext_sec->len - sizeof(__u32);
 	ext_info->rec_size = record_size;
 	ext_info->info = info + sizeof(__u32);
+	ext_info->sec_cnt = sec_cnt;
 
 	return 0;
 }
@@ -2788,6 +2790,9 @@ void btf_ext__free(struct btf_ext *btf_ext)
 {
 	if (IS_ERR_OR_NULL(btf_ext))
 		return;
+	free(btf_ext->func_info.sec_idxs);
+	free(btf_ext->line_info.sec_idxs);
+	free(btf_ext->core_relo_info.sec_idxs);
 	free(btf_ext->data);
 	free(btf_ext);
 }