bpf: btf: export btf types and name by offset from lib

This patch introduces btf__resolve_type() function and exports two
existing functions from libbpf. btf__resolve_type follows modifier
types like const and typedef until it hits a type which actually takes
up memory, and then returns it. This function follows similar pattern
to btf__resolve_size but instead of computing size, it just returns
the type.

These  functions will be used in the followig patch which parses
information inside array of `struct btf_type *`. btf_name_by_offset is
used for printing variable names.

Signed-off-by: Okash Khawaja <osk@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 45 insertions, 20 deletions

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 8c54a4b6f187..03161be094b4 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -17,6 +17,11 @@
 
 #define BTF_MAX_NR_TYPES 65535
 
+#define IS_MODIFIER(k) (((k) == BTF_KIND_TYPEDEF) || \
+                ((k) == BTF_KIND_VOLATILE) || \
+                ((k) == BTF_KIND_CONST) || \
+                ((k) == BTF_KIND_RESTRICT))
+
 static struct btf_type btf_void;
 
 struct btf {
@@ -33,14 +38,6 @@ struct btf {
         int fd;
 };
 
-static const char *btf_name_by_offset(const struct btf *btf, uint32_t offset)
-{
-        if (offset < btf->hdr->str_len)
-                return &btf->strings[offset];
-        else
-                return NULL;
-}
-
 static int btf_add_type(struct btf *btf, struct btf_type *t)
 {
         if (btf->types_size - btf->nr_types < 2) {
@@ -190,15 +187,6 @@ static int btf_parse_type_sec(struct btf *btf, btf_print_fn_t err_log)
         return 0;
 }
 
-static const struct btf_type *btf_type_by_id(const struct btf *btf,
-                                             uint32_t type_id)
-{
-        if (type_id > btf->nr_types)
-                return NULL;
-
-        return btf->types[type_id];
-}
-
 static bool btf_type_is_void(const struct btf_type *t)
 {
         return t == &btf_void || BTF_INFO_KIND(t->info) == BTF_KIND_FWD;
@@ -234,7 +222,7 @@ int64_t btf__resolve_size(const struct btf *btf, uint32_t type_id)
         int64_t size = -1;
         int i;
 
-        t = btf_type_by_id(btf, type_id);
+        t = btf__type_by_id(btf, type_id);
         for (i = 0; i < MAX_RESOLVE_DEPTH && !btf_type_is_void_or_null(t);
              i++) {
                 size = btf_type_size(t);
@@ -259,7 +247,7 @@ int64_t btf__resolve_size(const struct btf *btf, uint32_t type_id)
                         return -EINVAL;
                 }
 
-                t = btf_type_by_id(btf, type_id);
+                t = btf__type_by_id(btf, type_id);
         }
 
         if (size < 0)
@@ -271,6 +259,26 @@ int64_t btf__resolve_size(const struct btf *btf, uint32_t type_id)
         return nelems * size;
 }
 
+int btf__resolve_type(const struct btf *btf, __u32 type_id)
+{
+        const struct btf_type *t;
+        int depth = 0;
+
+        t = btf__type_by_id(btf, type_id);
+        while (depth < MAX_RESOLVE_DEPTH &&
+               !btf_type_is_void_or_null(t) &&
+               IS_MODIFIER(BTF_INFO_KIND(t->info))) {
+                type_id = t->type;
+                t = btf__type_by_id(btf, type_id);
+                depth++;
+        }
+
+        if (depth == MAX_RESOLVE_DEPTH || btf_type_is_void_or_null(t))
+                return -EINVAL;
+
+        return type_id;
+}
+
 int32_t btf__find_by_name(const struct btf *btf, const char *type_name)
 {
         uint32_t i;
@@ -280,7 +288,7 @@ int32_t btf__find_by_name(const struct btf *btf, const char *type_name)
 
         for (i = 1; i <= btf->nr_types; i++) {
                 const struct btf_type *t = btf->types[i];
-                const char *name = btf_name_by_offset(btf, t->name_off);
+                const char *name = btf__name_by_offset(btf, t->name_off);
 
                 if (name && !strcmp(type_name, name))
                         return i;
@@ -371,3 +379,20 @@ int btf__fd(const struct btf *btf)
 {
         return btf->fd;
 }
+
+const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
+{
+        if (offset < btf->hdr->str_len)
+                return &btf->strings[offset];
+        else
+                return NULL;
+}
+
+const struct btf_type *btf__type_by_id(const struct btf *btf,
+                                       __u32 type_id)
+{
+        if (type_id > btf->nr_types)
+                return NULL;
+
+        return btf->types[type_id];
+}