bpf: Show precise rejected function when attaching fexit/fmod_ret to __noreturn functions

JIRA: https://issues.redhat.com/browse/RHEL-78204

commit a5a6b29
Author: KaFai Wan <[email protected]>
Date:   Thu Jul 24 23:14:51 2025 +0800

    bpf: Show precise rejected function when attaching fexit/fmod_ret to __noreturn functions
    
    With this change, we know the precise rejected function name when
    attaching fexit/fmod_ret to __noreturn functions from log.
    
    $ ./fexit
    libbpf: prog 'fexit': BPF program load failed: -EINVAL
    libbpf: prog 'fexit': -- BEGIN PROG LOAD LOG --
    Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.
    
    Suggested-by: Leon Hwang <[email protected]>
    Signed-off-by: KaFai Wan <[email protected]>
    Acked-by: Yafang Shao <[email protected]>
    Acked-by: Yonghong Song <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Alexei Starovoitov <[email protected]>

Signed-off-by: Jerome Marchand <[email protected]>

Author: jeromemarchand

kernel/bpf/verifier.c

@@ -23989,7 +23989,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 	} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
 		   prog->expected_attach_type == BPF_MODIFY_RETURN) &&
 		   btf_id_set_contains(&noreturn_deny, btf_id)) {
-		verbose(env, "Attaching fexit/fmod_ret to __noreturn functions is rejected.\n");
+		verbose(env, "Attaching fexit/fmod_ret to __noreturn function '%s' is rejected.\n",
+			tgt_info.tgt_name);
 		return -EINVAL;
 	}
 

tools/testing/selftests/bpf/progs/fexit_noreturns.c

@@ -8,7 +8,7 @@
 char _license[] SEC("license") = "GPL";
 
 SEC("fexit/do_exit")
-__failure __msg("Attaching fexit/fmod_ret to __noreturn functions is rejected.")
+__failure __msg("Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.")
 int BPF_PROG(noreturns)
 {
 	return 0;