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Subject[PATCH bpf-next v5 1/3] bpf: btf: export btf types and name by offset from lib
Date
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>

---
tools/lib/bpf/btf.c | 65 ++++++++++++++++++++++++++++++++++++----------------
tools/lib/bpf/btf.h | 3 ++
2 files changed, 48 insertions(+), 20 deletions(-)

--- 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
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 b
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 b
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 b
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 b

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];
+}
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -17,6 +17,9 @@ void btf__free(struct btf *btf);
struct btf *btf__new(uint8_t *data, uint32_t size, btf_print_fn_t err_log);
int32_t btf__find_by_name(const struct btf *btf, const char *type_name);
int64_t btf__resolve_size(const struct btf *btf, uint32_t type_id);
+int btf__resolve_type(const struct btf *btf, __u32 type_id);
int btf__fd(const struct btf *btf);
+const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
+const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id);

#endif
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