linux-kernel - Re: [PATCH v3 bpf-next 8/8] bpf/selftests: add tests for %pT format specifier

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Message-ID: <CAEf4BzZ8cbMBVNhxXRXapyZCm_b70y-85Xb5SpB0MWBixJ9h_w@mail.gmail.com>
Date:   Tue, 23 Jun 2020 11:16:43 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Joe Perches <joe@...ches.com>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        andriy.shevchenko@...ux.intel.com, corbet@....net,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 bpf-next 8/8] bpf/selftests: add tests for %pT format specifier

On Tue, Jun 23, 2020 at 5:12 AM Alan Maguire <alan.maguire@...cle.com> wrote:
>
> tests verify we get 0 return value from bpf_trace_print()
> using %pT format specifier with various modifiers/pointer
> values.
>
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  .../selftests/bpf/prog_tests/trace_printk_btf.c    | 45 +++++++++++++++++++++
>  .../selftests/bpf/progs/netif_receive_skb.c        | 47 ++++++++++++++++++++++
>  2 files changed, 92 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_printk_btf.c
>  create mode 100644 tools/testing/selftests/bpf/progs/netif_receive_skb.c
>

[...]

> diff --git a/tools/testing/selftests/bpf/progs/netif_receive_skb.c b/tools/testing/selftests/bpf/progs/netif_receive_skb.c
> new file mode 100644
> index 0000000..03ca1d8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/netif_receive_skb.c
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020, Oracle and/or its affiliates. */
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +int ret;
> +int num_subtests;
> +int ran_subtests;

oh, interesting, so Clang doesn't put these into the COM section
anymore? We used to need to explicitly zero-initialize these global
vars because of that.

> +
> +#define CHECK_PRINTK(_fmt, _p, res)                                    \
> +       do {                                                            \
> +               char fmt[] = _fmt;                                      \

pro tip: you can use `static const char fmt[] = _fmt` and it will just work.

> +               ++num_subtests;                                         \
> +               if (ret >= 0) {                                         \
> +                       ++ran_subtests;                                 \
> +                       ret = bpf_trace_printk(fmt, sizeof(fmt), (_p)); \
> +               }                                                       \
> +       } while (0)
> +
> +/* TRACE_EVENT(netif_receive_skb,
> + *     TP_PROTO(struct sk_buff *skb),
> + */
> +SEC("tp_btf/netif_receive_skb")
> +int BPF_PROG(trace_netif_receive_skb, struct sk_buff *skb)
> +{
> +       char skb_type[] = "struct sk_buff";

same, `static const char` will generate more optimal code (good to
have good examples in selftests for people to follow). But don't
bother re-spinning just for this.


> +       struct btf_ptr nullp = { .ptr = 0, .type = skb_type };
> +       struct btf_ptr p = { .ptr = skb, .type = skb_type };
> +
> +       CHECK_PRINTK("%pT\n", &p, &res);
> +       CHECK_PRINTK("%pTc\n", &p, &res);
> +       CHECK_PRINTK("%pTN\n", &p, &res);
> +       CHECK_PRINTK("%pTx\n", &p, &res);
> +       CHECK_PRINTK("%pT0\n", &p, &res);
> +       CHECK_PRINTK("%pTcNx0\n", &p, &res);
> +       CHECK_PRINTK("%pT\n", &nullp, &res);
> +       CHECK_PRINTK("%pTc\n", &nullp, &res);
> +       CHECK_PRINTK("%pTN\n", &nullp, &res);
> +       CHECK_PRINTK("%pTx\n", &nullp, &res);
> +       CHECK_PRINTK("%pT0\n", &nullp, &res);
> +       CHECK_PRINTK("%pTcNx0\n", &nullp, &res);
> +
> +       return 0;
> +}
> --
> 1.8.3.1
>