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> --- tools/bpf/bpftool/gen.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index 6f2e20be0c62..e7f11899437a 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -205,6 +205,29 @@ static int codegen_datasec_def(struct bpf_object *obj, off = sec_var->offset + sec_var->size; } printf(" } *%s;\n", sec_ident); + + /* Walk through the section again to emit size asserts */ + sec_var = btf_var_secinfos(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); + + /* 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("\tBPF_STATIC_ASSERT("); + printf("sizeof(((struct %s__%s*)0)->%s) == %lld, ", + obj_name, sec_ident, var_ident, var_size); + printf("\"unexpected size of field %s\");\n", var_ident); + } + return 0; } @@ -756,6 +779,12 @@ static int do_skeleton(int argc, char **argv) \n\ #include <bpf/skel_internal.h> \n\ \n\ + #ifdef __cplusplus \n\ + #define BPF_STATIC_ASSERT static_assert \n\ + #else \n\ + #define BPF_STATIC_ASSERT _Static_assert \n\ + #endif \n\ + \n\ struct %1$s { \n\ struct bpf_loader_ctx ctx; \n\ ", @@ -774,6 +803,12 @@ static int do_skeleton(int argc, char **argv) #include <stdlib.h> \n\ #include <bpf/libbpf.h> \n\ \n\ + #ifdef __cplusplus \n\ + #define BPF_STATIC_ASSERT static_assert \n\ + #else \n\ + #define BPF_STATIC_ASSERT _Static_assert \n\ + #endif \n\ + \n\ struct %1$s { \n\ struct bpf_object_skeleton *skeleton; \n\ struct bpf_object *obj; \n\ -- 2.34.1
