netdev - Re: [PATCH bpf-next] libbpf: fix call relocation offset calculation bug

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Date:   Tue, 19 Nov 2019 14:16:41 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH bpf-next] libbpf: fix call relocation offset calculation
 bug

On Mon, Nov 18, 2019 at 10:21:51PM -0800, Andrii Nakryiko wrote:
>  
> -static __attribute__ ((noinline))
> -int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
> +__attribute__ ((noinline))
> +int test_pkt_access_subprog2(int val, struct __sk_buff *skb)
>  {
>  	return skb->len * val;
>  }

Did you run test_progs -n 8?

Above breaks it with:
10: (61) r1 = *(u32 *)(r6 +40)
func 'test_pkt_access_subprog2' doesn't have 6-th argument
invalid bpf_context access off=40 size=4

The point of the subprog2 is to test the scenario where BTF disagress with llvm
optimizations.