From 11d5daa89254ba2233d422777d52dbf24666b280 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 25 Apr 2022 17:45:05 -0700 Subject: 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 Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220426004511.2691730-5-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(-) (limited to 'tools/lib') 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 946b4590c4d3..81f2b987fd77 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) \ -- cgit v1.2.3