Re: [PATCH bpf-next 1/3] selftests/bpf: Keep int return type for tailcall subprogs with maps

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Tue Jun 9, 2026 at 2:30 PM PDT, Yonghong Song wrote:
>
> const struct bpf_func_proto bpf_tail_call_proto = {         /* func is 
> unused for tail_call, we set it to pass the          * get_helper_proto 
> check          */         .func           = BPF_PTR_POISON,         
> .gpl_only       = false,         .ret_type       = RET_VOID,         
> .arg1_type      = ARG_PTR_TO_CTX,         .arg2_type      = 
> ARG_CONST_MAP_PTR,         .arg3_type      = ARG_ANYTHING, }; and for 
> RET_VOID, we have below in verifier.c:         switch 
> (base_type(ret_type)) {         case RET_INTEGER:                 /* 
> sets type to SCALAR_VALUE */                 mark_reg_unknown(env, regs, 
> BPF_REG_0);                 break;         case RET_VOID:               
>    regs[BPF_REG_0].type = NOT_INIT;                 break; so we cannot 
> return 'r0'.

Ahh, so bpf_tail_call() is a void return.
Then, I'll take it back. bpf_tail_call_static() is correct with void return.
I guess we have to teach the verifier to accept void subprogs asap.

In the meantime let's do shortest possible hack for tailcall_bpf2bpf_hierarchy1.c
to pass with llvm 23.