netdev - Re: [PATCH bpf 2/2] bpf: selftest to verify mixing bpf2bpf calls and tailcalls with insn patch

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Date:   Wed, 9 Jun 2021 17:57:04 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andriin@...com,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf 2/2] bpf: selftest to verify mixing bpf2bpf calls and
 tailcalls with insn patch

On Tue, Jun 08, 2021 at 12:30:33PM -0700, John Fastabend wrote:
> This adds some extra noise to the tailcall_bpf2bpf4 tests that will cause
> verifier to patch insns. This then moves around subprog start/end insn
> index and poke descriptor insn index to ensure that verify and JIT will
> continue to track these correctly.

This test is the most complicated one where I tried to document the scope
of it on the side of prog_tests/tailcalls.c. I feel that it would make it
more difficult to debug it if under any circumstances something would have
been broken with that logic.

Maybe a separate test scenario? Or is this an overkill? If so, I would
vote for moving it to tailcall_bpf2bpf1.c and have a little comment that
testing other bpf helpers mixed in is in scope of that test.

> 
> Reviewed-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
>  .../selftests/bpf/progs/tailcall_bpf2bpf4.c        |   17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> index 9a1b166b7fbe..0d70de5f97e2 100644
> --- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> @@ -2,6 +2,13 @@
>  #include <linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
>  
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u32));
> +} nop_table SEC(".maps");
> +
>  struct {
>  	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
>  	__uint(max_entries, 3);
> @@ -11,9 +18,19 @@ struct {
>  
>  static volatile int count;
>  
> +__noinline
> +int subprog_noise(struct __sk_buff *skb)
> +{
> +	__u32 key = 0;
> +
> +	bpf_map_lookup_elem(&nop_table, &key);
> +	return 0;
> +}
> +
>  __noinline
>  int subprog_tail_2(struct __sk_buff *skb)
>  {
> +	subprog_noise(skb);
>  	bpf_tail_call_static(skb, &jmp_table, 2);
>  	return skb->len * 3;
>  }
> 
>