diff options
| -rw-r--r-- | tools/lib/bpf/libbpf.c | 97 |
1 files changed, 78 insertions, 19 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8802e06c5569..027fd9565c16 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -1577,7 +1577,38 @@ static char *internal_map_name(struct bpf_object *obj, const char *real_name) } static int -bpf_map_find_btf_info(struct bpf_object *obj, struct bpf_map *map); +map_fill_btf_type_info(struct bpf_object *obj, struct bpf_map *map); + +/* Internal BPF map is mmap()'able only if at least one of corresponding + * DATASEC's VARs are to be exposed through BPF skeleton. I.e., it's a GLOBAL + * variable and it's not marked as __hidden (which turns it into, effectively, + * a STATIC variable). + */ +static bool map_is_mmapable(struct bpf_object *obj, struct bpf_map *map) +{ + const struct btf_type *t, *vt; + struct btf_var_secinfo *vsi; + int i, n; + + if (!map->btf_value_type_id) + return false; + + t = btf__type_by_id(obj->btf, map->btf_value_type_id); + if (!btf_is_datasec(t)) + return false; + + vsi = btf_var_secinfos(t); + for (i = 0, n = btf_vlen(t); i < n; i++, vsi++) { + vt = btf__type_by_id(obj->btf, vsi->type); + if (!btf_is_var(vt)) + continue; + + if (btf_var(vt)->linkage != BTF_VAR_STATIC) + return true; + } + + return false; +} static int bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type, @@ -1609,7 +1640,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type, def->max_entries = 1; def->map_flags = type == LIBBPF_MAP_RODATA || type == LIBBPF_MAP_KCONFIG ? BPF_F_RDONLY_PROG : 0; - def->map_flags |= BPF_F_MMAPABLE; + + /* failures are fine because of maps like .rodata.str1.1 */ + (void) map_fill_btf_type_info(obj, map); + + if (map_is_mmapable(obj, map)) + def->map_flags |= BPF_F_MMAPABLE; pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n", map->name, map->sec_idx, map->sec_offset, def->map_flags); @@ -1626,9 +1662,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type, return err; } - /* failures are fine because of maps like .rodata.str1.1 */ - (void) bpf_map_find_btf_info(obj, map); - if (data) memcpy(map->mmaped, data, data_sz); @@ -2540,7 +2573,7 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj, fill_map_from_def(map->inner_map, &inner_def); } - err = bpf_map_find_btf_info(obj, map); + err = map_fill_btf_type_info(obj, map); if (err) return err; @@ -2848,6 +2881,7 @@ static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf, __u32 size = 0, i, vars = btf_vlen(t); const char *sec_name = btf__name_by_offset(btf, t->name_off); struct btf_var_secinfo *vsi; + bool fixup_offsets = false; int err; if (!sec_name) { @@ -2855,21 +2889,34 @@ static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf, return -ENOENT; } - /* extern-backing datasecs (.ksyms, .kconfig) have their size and - * variable offsets set at the previous step, so we skip any fixups - * for such sections + /* Extern-backing datasecs (.ksyms, .kconfig) have their size and + * variable offsets set at the previous step. Further, not every + * extern BTF VAR has corresponding ELF symbol preserved, so we skip + * all fixups altogether for such sections and go straight to sorting + * VARs within their DATASEC. */ - if (t->size) + if (strcmp(sec_name, KCONFIG_SEC) == 0 || strcmp(sec_name, KSYMS_SEC) == 0) goto sort_vars; - err = find_elf_sec_sz(obj, sec_name, &size); - if (err || !size) { - pr_debug("sec '%s': failed to determine size from ELF: size %u, err %d\n", - sec_name, size, err); - return -ENOENT; - } + /* Clang leaves DATASEC size and VAR offsets as zeroes, so we need to + * fix this up. But BPF static linker already fixes this up and fills + * all the sizes and offsets during static linking. So this step has + * to be optional. But the STV_HIDDEN handling is non-optional for any + * non-extern DATASEC, so the variable fixup loop below handles both + * functions at the same time, paying the cost of BTF VAR <-> ELF + * symbol matching just once. + */ + if (t->size == 0) { + err = find_elf_sec_sz(obj, sec_name, &size); + if (err || !size) { + pr_debug("sec '%s': failed to determine size from ELF: size %u, err %d\n", + sec_name, size, err); + return -ENOENT; + } - t->size = size; + t->size = size; + fixup_offsets = true; + } for (i = 0, vsi = btf_var_secinfos(t); i < vars; i++, vsi++) { const struct btf_type *t_var; @@ -2901,7 +2948,19 @@ static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf, return -ENOENT; } - vsi->offset = sym->st_value; + if (fixup_offsets) + vsi->offset = sym->st_value; + + /* if variable is a global/weak symbol, but has restricted + * (STV_HIDDEN or STV_INTERNAL) visibility, mark its BTF VAR + * as static. This follows similar logic for functions (BPF + * subprogs) and influences libbpf's further decisions about + * whether to make global data BPF array maps as + * BPF_F_MMAPABLE. + */ + if (ELF64_ST_VISIBILITY(sym->st_other) == STV_HIDDEN + || ELF64_ST_VISIBILITY(sym->st_other) == STV_INTERNAL) + var->linkage = BTF_VAR_STATIC; } sort_vars: @@ -4223,7 +4282,7 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, Elf64_Shdr *shdr, Elf_Dat return 0; } -static int bpf_map_find_btf_info(struct bpf_object *obj, struct bpf_map *map) +static int map_fill_btf_type_info(struct bpf_object *obj, struct bpf_map *map) { int id; |