bpf: Fix subprog names in stack traces.

The commit 7337224f ("bpf: Improve the info.func_info and info.func_info_rec_size behavior")
accidently made bpf_prog_ksym_set_name() conservative for bpf subprograms.
Fixed it so instead of "bpf_prog_tag_F" the stack traces print "bpf_prog_tag_full_subprog_name".

Fixes: 7337224f ("bpf: Improve the info.func_info and info.func_info_rec_size behavior")
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220714211637.17150-1-alexei.starovoitov@gmail.com

kernel/bpf/verifier.c

@@ -13631,6 +13631,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 		/* Below members will be freed only at prog->aux */
 		func[i]->aux->btf = prog->aux->btf;
 		func[i]->aux->func_info = prog->aux->func_info;
+		func[i]->aux->func_info_cnt = prog->aux->func_info_cnt;
 		func[i]->aux->poke_tab = prog->aux->poke_tab;
 		func[i]->aux->size_poke_tab = prog->aux->size_poke_tab;
 
@@ -13643,9 +13644,6 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 				poke->aux = func[i]->aux;
 		}
 
-		/* Use bpf_prog_F_tag to indicate functions in stack traces.
-		 * Long term would need debug info to populate names
-		 */
 		func[i]->aux->name[0] = 'F';
 		func[i]->aux->stack_depth = env->subprog_info[i].stack_depth;
 		func[i]->jit_requested = 1;