On 11/7/23 9:15 PM, Yonghong Song wrote:
Martin reported that there is a libbpf complaining of non-zero-value tail padding with LIBBPF_OPTS_RESET macro if struct bpf_netkit_opts is modified to have a 4-byte tail padding. This only happens to clang compiler. The commend line is: ./test_progs -t tc_netkit_multi_links Martin and I did some investigation and found this indeed the case and the following are the investigation details.
[...] Too bad we need this detour, but fix lgtm, thanks!
diff --git a/tools/lib/bpf/libbpf_common.h b/tools/lib/bpf/libbpf_common.h index b7060f254486..8fe248e14eb6 100644 --- a/tools/lib/bpf/libbpf_common.h +++ b/tools/lib/bpf/libbpf_common.h @@ -79,11 +79,14 @@ */ #define LIBBPF_OPTS_RESET(NAME, ...) \ do { \ - memset(&NAME, 0, sizeof(NAME)); \ - NAME = (typeof(NAME)) { \ - .sz = sizeof(NAME), \ - __VA_ARGS__ \ - }; \ + typeof(NAME) ___##NAME = ({ \ + memset(&___##NAME, 0, sizeof(NAME)); \ + (typeof(NAME)) { \ + .sz = sizeof(NAME), \ + __VA_ARGS__ \ + }; \ + }); \ + memcpy(&NAME, &___##NAME, sizeof(NAME)); \ } while (0)#endif /* __LIBBPF_LIBBPF_COMMON_H */
