When emitting type declarations in skeletons, bpftool will now also emit static assertions on the size of the data/bss/rodata/etc fields. This ensures that in situations where userspace and kernel types have the same name but differ in size we do not silently produce incorrect results but instead break the build. This was reported in [1] and as expected the repro in [2] fails to build on the new size assert after this change. [1]: Closes: https://github.com/libbpf/libbpf/issues/433 [2]: https://github.com/fuweid/iovisor-bcc-pr-3777 Signed-off-by: Delyan Kratunov <delyank@xxxxxx> Acked-by: Hengqi Chen <hengqi.chen@xxxxxxxxx> Tested-by: Hengqi Chen <hengqi.chen@xxxxxxxxx> --- v3 -> v4: - rebase - style fixes v2 -> v3: - group all static asserts in one function at the end of the file - only use macros in C++ mode v1 -> v2: - drop the stdint approach in favor of static asserts right after the structs tools/bpf/bpftool/gen.c | 133 +++++++++++++++++++++++++++++++++------- 1 file changed, 111 insertions(+), 22 deletions(-) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index f8c1413523a3..a42545bcb12d 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -209,15 +209,38 @@ static int codegen_datasec_def(struct bpf_object *obj, return 0; } +static const struct btf_type *find_type_for_map(struct bpf_object *obj, + const char *map_ident) +{ + struct btf *btf = bpf_object__btf(obj); + int n = btf__type_cnt(btf), i; + char sec_ident[256]; + + 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) + return t; + } + return NULL; +} + static int codegen_datasecs(struct bpf_object *obj, const char *obj_name) { struct btf *btf = bpf_object__btf(obj); - int n = btf__type_cnt(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; + char map_ident[256]; + int err = 0; d = btf_dump__new(btf, codegen_btf_dump_printf, NULL, NULL); err = libbpf_get_error(d); @@ -234,23 +257,7 @@ static int codegen_datasecs(struct bpf_object *obj, const char *obj_name) 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; - } - } + sec = find_type_for_map(obj, map_ident); /* In some cases (e.g., sections like .rodata.cst16 containing * compiler allocated string constants only) there will be @@ -363,6 +370,78 @@ static size_t bpf_map_mmap_sz(const struct bpf_map *map) return map_sz; } +/* Emit type size asserts for all top-level fields in memory-mapped internal maps. + */ +static void codegen_asserts(struct bpf_object *obj, const char *obj_name) +{ + struct btf *btf = bpf_object__btf(obj); + struct bpf_map *map; + struct btf_var_secinfo *sec_var; + int i, vlen; + const struct btf_type *sec; + char map_ident[256], var_ident[256]; + + codegen("\ + \n\ + \n\ + #ifdef __cplusplus \n\ + #define _Static_assert static_assert \n\ + #endif \n\ + \n\ + __attribute__((unused)) static void \n\ + %1$s__type_asserts(struct %1$s *s) \n\ + { \n\ + ", obj_name); + + bpf_object__for_each_map(map, obj) { + if (!bpf_map__is_internal(map)) + continue; + if (!(bpf_map__map_flags(map) & BPF_F_MMAPABLE)) + continue; + if (!get_map_ident(map, map_ident, sizeof(map_ident))) + continue; + + sec = find_type_for_map(obj, map_ident); + if (!sec) { + /* best effort, couldn't find the type for this map */ + continue; + } + + sec_var = btf_var_secinfos(sec); + vlen = btf_vlen(sec); + + for (i = 0; i < vlen; i++, sec_var++) { + const struct btf_type *var = btf__type_by_id(btf, sec_var->type); + const char *var_name = btf__name_by_offset(btf, var->name_off); + __u32 var_type_id = var->type; + __s64 var_size = btf__resolve_size(btf, var_type_id); + + if (var_size < 0) + continue; + + /* static variables are not exposed through BPF skeleton */ + if (btf_var(var)->linkage == BTF_VAR_STATIC) + continue; + + var_ident[0] = '\0'; + strncat(var_ident, var_name, sizeof(var_ident) - 1); + sanitize_identifier(var_ident); + + printf("\t_Static_assert(sizeof(s->%1$s->%2$s) == %3$lld, \"unexpected size of '%2$s'\");\n", + map_ident, var_ident, var_size); + } + } + codegen("\ + \n\ + } \n\ + \n\ + #ifdef __cplusplus \n\ + #undef _Static_assert \n\ + #endif \n\ + "); +} + + static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name) { struct bpf_program *prog; @@ -641,6 +720,8 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h } \n\ ", obj_name); + codegen_asserts(obj, obj_name); + codegen("\ \n\ \n\ @@ -1046,9 +1127,17 @@ static int do_skeleton(int argc, char **argv) const void *%1$s::elf_bytes(size_t *sz) { return %1$s__elf_bytes(sz); } \n\ #endif /* __cplusplus */ \n\ \n\ - #endif /* %2$s */ \n\ ", - obj_name, header_guard); + obj_name); + + codegen_asserts(obj, obj_name); + + codegen("\ + \n\ + \n\ + #endif /* %1$s */ \n\ + ", + header_guard); err = 0; out: bpf_object__close(obj); -- 2.34.1
