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bpftool: Improve skeleton generation for data maps without DATASEC type

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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@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211021014404.2635234-7-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-10-20 18:44:00 -07:00 committed by Alexei Starovoitov
parent 8654b4d35e
commit ef9356d392
1 changed files with 46 additions and 7 deletions
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53
tools/bpf/bpftool/gen.c
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@ -213,22 +213,61 @@ 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);
if (!btf_is_datasec(t))
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;
err = codegen_datasec_def(obj, btf, d, t, obj_name);
if (err)
goto out;
if (!get_map_ident(map, map_ident, sizeof(map_ident)))
continue;
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;