On Thu, Oct 27, 2022 at 5:26 PM Rong Tao rtoax@foxmail.com wrote:
Thanks for your reply, `enable[0] = '\0';` at the beginning and then strncat() still has the same compile warning
--- a/tools/testing/selftests/bpf/cgroup_helpers.c +++ b/tools/testing/selftests/bpf/cgroup_helpers.c @@ -77,7 +77,8 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers enable[len] = 0; close(fd); } else {
strncpy(enable, controllers, sizeof(enable));
enable[0] = '\0';strncat(enable, controllers, sizeof(enable)); }In function ‘__enable_controllers’: tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-truncation] 81 | strncat(enable, controllers, sizeof(enable)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-overflow=]
So, i think just add '-1' for strncpy() is a good way.
no, it's not, see my previous email about ending up with non-zero-terminated C string.
check strncat() API, it leaves the dst string zero terminated, and yes, you need -1 for strncat as well, your compiler is right