From: Andrii Nakryiko <andrii@xxxxxxxxxx>
It can happen that some data sections (e.g., .rodata.cst16, containing
compiler populated string constants) won't have a corresponding BTF
DATASEC type. Now that libbpf supports .rodata.* and .data.* sections,
situation like that will cause invalid BPF skeleton to be generated that
won't compile successfully, as some parts of skeleton would assume
memory-mapped struct definitions for each special data section.
Fix this by generating empty struct definitions for such data sections.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/bpf/bpftool/gen.c | 51 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 45 insertions(+), 6 deletions(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 5fbd90bb0c09..889a5b1542c9 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -214,22 +214,61 @@ static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
struct btf *btf = bpf_object__btf(obj);
int n = btf__get_nr_types(btf);
struct btf_dump *d;
+ struct bpf_map *map;
+ const struct btf_type *sec;
+ char sec_ident[256], map_ident[256];
int i, err = 0;
d = btf_dump__new(btf, NULL, NULL, codegen_btf_dump_printf);
if (IS_ERR(d))
return PTR_ERR(d);
- for (i = 1; i <= n; i++) {
- const struct btf_type *t = btf__type_by_id(btf, i);
+ bpf_object__for_each_map(map, obj) {
+ /* only generate definitions for memory-mapped internal maps */
+ if (!bpf_map__is_internal(map))
+ continue;
+ if (!(bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))
+ continue;
- if (!btf_is_datasec(t))
+ if (!get_map_ident(map, map_ident, sizeof(map_ident)))
continue;
- err = codegen_datasec_def(obj, btf, d, t, obj_name);
- if (err)
- goto out;
+ sec = NULL;
+ for (i = 1; i <= n; i++) {
+ const struct btf_type *t = btf__type_by_id(btf, i);
+ const char *name;
+
+ if (!btf_is_datasec(t))
+ continue;
+
+ name = btf__str_by_offset(btf, t->name_off);
+ if (!get_datasec_ident(name, sec_ident, sizeof(sec_ident)))
+ continue;
+
+ if (strcmp(sec_ident, map_ident) == 0) {
+ sec = t;
+ break;
+ }
+ }
+
+ /* In some cases (e.g., sections like .rodata.cst16 containing
+ * compiler allocated string constants only) there will be
+ * special internal maps with no corresponding DATASEC BTF
+ * type. In such case, generate empty structs for each such
+ * map. It will still be memory-mapped and its contents
+ * accessible from user-space through BPF skeleton.
+ */
+ if (!sec) {
+ printf(" struct %s__%s {\n", obj_name, map_ident);
+ printf(" } *%s;\n", map_ident);
+ } else {
+ err = codegen_datasec_def(obj, btf, d, sec, obj_name);
+ if (err)
+ goto out;
+ }
}
+
+
out:
btf_dump__free(d);
return err;
--
2.30.2
