Re: [PATCH bpf-next v3 10/18] bpf: Search and add kfuncs in struct_ops prologue and epilogue

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2025-01-31 at 11:28 -0800, Amery Hung wrote:
> From: Amery Hung <amery.hung@bytedance.com>
> 
> Currently, add_kfunc_call() is only invoked once before the main
> verification loop. Therefore, the verifier could not find the
> bpf_kfunc_btf_tab of a new kfunc call which is not seen in user defined
> struct_ops operators but introduced in gen_prologue or gen_epilogue
> during do_misc_fixup(). Fix this by searching kfuncs in the patching
> instruction buffer and add them to prog->aux->kfunc_tab.
> 
> Signed-off-by: Amery Hung <amery.hung@bytedance.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

> @@ -20397,6 +20412,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
>  				return -ENOMEM;
>  			env->prog = new_prog;
>  			delta += cnt - 1;
> +
> +			ret = add_kfunc_in_insns(env, epilogue_buf, epilogue_cnt - 1);

Rant: the -1 here is a bit confusing, it is second time I forget that
      last instruction of the epilogue has to be some kind of control flow,
      and last instruction of the prologue has to be first instruction
      of the program.

> +			if (ret < 0)
> +				return ret;
>  		}
>  	}
>  

[...]