From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>
Cc: <andrii@kernel.org>, <kernel-team@fb.com>
Subject: [PATCH bpf-next 04/10] libbpf: avoid joining .BTF.ext data with BPF programs by section name
Date: Mon, 25 Apr 2022 17:45:05 -0700 [thread overview]
Message-ID: <20220426004511.2691730-5-andrii@kernel.org> (raw)
In-Reply-To: <20220426004511.2691730-1-andrii@kernel.org>
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>
---
tools/lib/bpf/btf.c | 9 +++-
tools/lib/bpf/libbpf.c | 78 +++++++++++++++++++++------------
tools/lib/bpf/libbpf_internal.h | 7 +++
3 files changed, 65 insertions(+), 29 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);
}
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 840a26428937..efc1ea91e12e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2765,6 +2765,9 @@ static int bpf_object__init_btf(struct bpf_object *obj,
btf__set_pointer_size(obj->btf, 8);
}
if (btf_ext_data) {
+ struct btf_ext_info *ext_segs[3];
+ int seg_num, sec_num;
+
if (!obj->btf) {
pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
BTF_EXT_ELF_SEC, BTF_ELF_SEC);
@@ -2778,6 +2781,43 @@ static int bpf_object__init_btf(struct bpf_object *obj,
obj->btf_ext = NULL;
goto out;
}
+
+ /* setup .BTF.ext to ELF section mapping */
+ ext_segs[0] = &obj->btf_ext->func_info;
+ ext_segs[1] = &obj->btf_ext->line_info;
+ ext_segs[2] = &obj->btf_ext->core_relo_info;
+ for (seg_num = 0; seg_num < ARRAY_SIZE(ext_segs); seg_num++) {
+ struct btf_ext_info *seg = ext_segs[seg_num];
+ const struct btf_ext_info_sec *sec;
+ const char *sec_name;
+ Elf_Scn *scn;
+
+ if (seg->sec_cnt == 0)
+ continue;
+
+ seg->sec_idxs = calloc(seg->sec_cnt, sizeof(*seg->sec_idxs));
+ if (!seg->sec_idxs) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ sec_num = 0;
+ for_each_btf_ext_sec(seg, sec) {
+ /* preventively increment index to avoid doing
+ * this before every continue below
+ */
+ sec_num++;
+
+ sec_name = btf__name_by_offset(obj->btf, sec->sec_name_off);
+ if (str_is_empty(sec_name))
+ continue;
+ scn = elf_sec_by_name(obj, sec_name);
+ if (!scn)
+ continue;
+
+ seg->sec_idxs[sec_num - 1] = elf_ndxscn(scn);
+ }
+ }
}
out:
if (err && libbpf_needs_btf(obj)) {
@@ -5642,7 +5682,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
struct bpf_program *prog;
struct bpf_insn *insn;
const char *sec_name;
- int i, err = 0, insn_idx, sec_idx;
+ int i, err = 0, insn_idx, sec_idx, sec_num;
if (obj->btf_ext->core_relo_info.len == 0)
return 0;
@@ -5663,33 +5703,18 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
}
seg = &obj->btf_ext->core_relo_info;
+ sec_num = 0;
for_each_btf_ext_sec(seg, sec) {
+ sec_idx = seg->sec_idxs[sec_num];
+ sec_num++;
+
sec_name = btf__name_by_offset(obj->btf, sec->sec_name_off);
if (str_is_empty(sec_name)) {
err = -EINVAL;
goto out;
}
- /* bpf_object's ELF is gone by now so it's not easy to find
- * section index by section name, but we can find *any*
- * bpf_program within desired section name and use it's
- * prog->sec_idx to do a proper search by section index and
- * instruction offset
- */
- prog = NULL;
- for (i = 0; i < obj->nr_programs; i++) {
- if (strcmp(obj->programs[i].sec_name, sec_name) == 0) {
- prog = &obj->programs[i];
- break;
- }
- }
- if (!prog) {
- pr_warn("sec '%s': failed to find a BPF program\n", sec_name);
- return -ENOENT;
- }
- sec_idx = prog->sec_idx;
- pr_debug("sec '%s': found %d CO-RE relocations\n",
- sec_name, sec->num_info);
+ pr_debug("sec '%s': found %d CO-RE relocations\n", sec_name, sec->num_info);
for_each_btf_ext_rec(seg, sec, i, rec) {
if (rec->insn_off % BPF_INSN_SZ)
@@ -5873,14 +5898,13 @@ static int adjust_prog_btf_ext_info(const struct bpf_object *obj,
void *rec, *rec_end, *new_prog_info;
const struct btf_ext_info_sec *sec;
size_t old_sz, new_sz;
- const char *sec_name;
- int i, off_adj;
+ int i, sec_num, sec_idx, off_adj;
+ sec_num = 0;
for_each_btf_ext_sec(ext_info, sec) {
- sec_name = btf__name_by_offset(obj->btf, sec->sec_name_off);
- if (!sec_name)
- return -EINVAL;
- if (strcmp(sec_name, prog->sec_name) != 0)
+ sec_idx = ext_info->sec_idxs[sec_num];
+ sec_num++;
+ if (prog->sec_idx != sec_idx)
continue;
for_each_btf_ext_rec(ext_info, sec, i, rec) {
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 054cd8e93d7c..4abdbe2fea9d 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -376,6 +376,13 @@ struct btf_ext_info {
void *info;
__u32 rec_size;
__u32 len;
+ /* optional (maintained internally by libbpf) mapping between .BTF.ext
+ * section and corresponding ELF section. This is used to join
+ * information like CO-RE relocation records with corresponding BPF
+ * programs defined in ELF sections
+ */
+ __u32 *sec_idxs;
+ int sec_cnt;
};
#define for_each_btf_ext_sec(seg, sec) \
--
2.30.2
next prev parent reply other threads:[~2022-04-26 0:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-26 0:45 [PATCH bpf-next 00/10] Teach libbpf to "fix up" BPF verifier log Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 01/10] libbpf: fix anonymous type check in CO-RE logic Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 02/10] libbpf: drop unhelpful "program too large" guess Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 03/10] libbpf: fix logic for finding matching program for CO-RE relocation Andrii Nakryiko
2022-04-26 0:45 ` Andrii Nakryiko [this message]
2022-04-26 0:45 ` [PATCH bpf-next 05/10] selftests/bpf: add CO-RE relos and SEC("?...") to linked_funcs selftests Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 06/10] libbpf: record subprog-resolved CO-RE relocations unconditionally Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 07/10] libbpf: refactor CO-RE relo human description formatting routine Andrii Nakryiko
2022-04-26 18:52 ` Alexei Starovoitov
2022-04-26 22:20 ` Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 08/10] libbpf: simplify bpf_core_parse_spec() signature Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 09/10] libbpf: fix up verifier log for unguarded failed CO-RE relos Andrii Nakryiko
2022-04-26 18:59 ` Alexei Starovoitov
2022-04-26 22:16 ` Andrii Nakryiko
2022-04-26 0:45 ` [PATCH bpf-next 10/10] selftests/bpf: add libbpf's log fixup logic selftests Andrii Nakryiko
2022-04-26 22:50 ` [PATCH bpf-next 00/10] Teach libbpf to "fix up" BPF verifier log patchwork-bot+netdevbpf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220426004511.2691730-5-andrii@kernel.org \
--to=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=kernel-team@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.