libbpf: capture value in BTF type info for BTF-defined map defs

Change BTF-defined map definitions to capture compile-time integer
values as part of BTF type definition, to avoid split of key/value type
information and actual type/size/flags initialization for maps.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 981fb5c..2a08eb1 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1029,40 +1029,40 @@ static const struct btf_type *skip_mods_and_typedefs(const struct btf *btf,
        }
 }
 
-static bool get_map_field_int(const char *map_name,
-                             const struct btf *btf,
+/*
+ * Fetch integer attribute of BTF map definition. Such attributes are
+ * represented using a pointer to an array, in which dimensionality of array
+ * encodes specified integer value. E.g., int (*type)[BPF_MAP_TYPE_ARRAY];
+ * encodes `type => BPF_MAP_TYPE_ARRAY` key/value pair completely using BTF
+ * type definition, while using only sizeof(void *) space in ELF data section.
+ */
+static bool get_map_field_int(const char *map_name, const struct btf *btf,
                              const struct btf_type *def,
-                             const struct btf_member *m,
-                             const void *data, __u32 *res) {
+                             const struct btf_member *m, __u32 *res) {
        const struct btf_type *t = skip_mods_and_typedefs(btf, m->type);
        const char *name = btf__name_by_offset(btf, m->name_off);
-       __u32 int_info = *(const __u32 *)(const void *)(t + 1);
+       const struct btf_array *arr_info;
+       const struct btf_type *arr_t;
 
-       if (BTF_INFO_KIND(t->info) != BTF_KIND_INT) {
-               pr_warning("map '%s': attr '%s': expected INT, got %u.\n",
+       if (BTF_INFO_KIND(t->info) != BTF_KIND_PTR) {
+               pr_warning("map '%s': attr '%s': expected PTR, got %u.\n",
                           map_name, name, BTF_INFO_KIND(t->info));
                return false;
        }
-       if (t->size != 4 || BTF_INT_BITS(int_info) != 32 ||
-           BTF_INT_OFFSET(int_info)) {
-               pr_warning("map '%s': attr '%s': expected 32-bit non-bitfield integer, "
-                          "got %u-byte (%d-bit) one with bit offset %d.\n",
-                          map_name, name, t->size, BTF_INT_BITS(int_info),
-                          BTF_INT_OFFSET(int_info));
-               return false;
-       }
-       if (BTF_INFO_KFLAG(def->info) && BTF_MEMBER_BITFIELD_SIZE(m->offset)) {
-               pr_warning("map '%s': attr '%s': bitfield is not supported.\n",
-                          map_name, name);
+
+       arr_t = btf__type_by_id(btf, t->type);
+       if (!arr_t) {
+               pr_warning("map '%s': attr '%s': type [%u] not found.\n",
+                          map_name, name, t->type);
                return false;
        }
-       if (m->offset % 32) {
-               pr_warning("map '%s': attr '%s': unaligned fields are not supported.\n",
-                          map_name, name);
+       if (BTF_INFO_KIND(arr_t->info) != BTF_KIND_ARRAY) {
+               pr_warning("map '%s': attr '%s': expected ARRAY, got %u.\n",
+                          map_name, name, BTF_INFO_KIND(arr_t->info));
                return false;
        }
-
-       *res = *(const __u32 *)(data + m->offset / 8);
+       arr_info = (const void *)(arr_t + 1);
+       *res = arr_info->nelems;
        return true;
 }
 
@@ -1075,7 +1075,6 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
        const struct btf_var_secinfo *vi;
        const struct btf_var *var_extra;
        const struct btf_member *m;
-       const void *def_data;
        const char *map_name;
        struct bpf_map *map;
        int vlen, i;
@@ -1132,7 +1131,6 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
        pr_debug("map '%s': at sec_idx %d, offset %zu.\n",
                 map_name, map->sec_idx, map->sec_offset);
 
-       def_data = data->d_buf + vi->offset;
        vlen = BTF_INFO_VLEN(def->info);
        m = (const void *)(def + 1);
        for (i = 0; i < vlen; i++, m++) {
@@ -1145,19 +1143,19 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
                }
                if (strcmp(name, "type") == 0) {
                        if (!get_map_field_int(map_name, obj->btf, def, m,
-                                              def_data, &map->def.type))
+                                              &map->def.type))
                                return -EINVAL;
                        pr_debug("map '%s': found type = %u.\n",
                                 map_name, map->def.type);
                } else if (strcmp(name, "max_entries") == 0) {
                        if (!get_map_field_int(map_name, obj->btf, def, m,
-                                              def_data, &map->def.max_entries))
+                                              &map->def.max_entries))
                                return -EINVAL;
                        pr_debug("map '%s': found max_entries = %u.\n",
                                 map_name, map->def.max_entries);
                } else if (strcmp(name, "map_flags") == 0) {
                        if (!get_map_field_int(map_name, obj->btf, def, m,
-                                              def_data, &map->def.map_flags))
+                                              &map->def.map_flags))
                                return -EINVAL;
                        pr_debug("map '%s': found map_flags = %u.\n",
                                 map_name, map->def.map_flags);
@@ -1165,7 +1163,7 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
                        __u32 sz;
 
                        if (!get_map_field_int(map_name, obj->btf, def, m,
-                                              def_data, &sz))
+                                              &sz))
                                return -EINVAL;
                        pr_debug("map '%s': found key_size = %u.\n",
                                 map_name, sz);
@@ -1208,7 +1206,7 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
                        __u32 sz;
 
                        if (!get_map_field_int(map_name, obj->btf, def, m,
-                                              def_data, &sz))
+                                              &sz))
                                return -EINVAL;
                        pr_debug("map '%s': found value_size = %u.\n",
                                 map_name, sz);