netdev - Re: [PATCH bpf-next 2/2] selftests/bpf: Test tail call counting with bpf2bpf and data on stack

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Date:   Thu, 16 Jun 2022 16:41:30 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Sitnicki <jakub@...udflare.com>, bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        kernel-team@...udflare.com
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Test tail call counting with
 bpf2bpf and data on stack

On 6/15/22 5:17 PM, Jakub Sitnicki wrote:
> Cover the case when tail call count needs to be passed from BPF function to
> BPF function, and the caller has data on stack. Specifically when the size
> of data allocated on BPF stack is not a multiple on 8.
> 
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
>   .../selftests/bpf/prog_tests/tailcalls.c      | 55 +++++++++++++++++++
>   .../selftests/bpf/progs/tailcall_bpf2bpf6.c   | 42 ++++++++++++++
>   2 files changed, 97 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> index c4da87ec3ba4..19c70880cfb3 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> @@ -831,6 +831,59 @@ static void test_tailcall_bpf2bpf_4(bool noise)
>   	bpf_object__close(obj);
>   }
>   
> +#include "tailcall_bpf2bpf6.skel.h"
> +
> +/* Tail call counting works even when there is data on stack which is
> + * not aligned to 8 bytes.
> + */
> +static void test_tailcall_bpf2bpf_6(void)
> +{
> +	struct tailcall_bpf2bpf6 *obj;
> +	int err, map_fd, prog_fd, main_fd, data_fd, i, val;
> +	LIBBPF_OPTS(bpf_test_run_opts, topts,
> +		.data_in = &pkt_v4,
> +		.data_size_in = sizeof(pkt_v4),
> +		.repeat = 1,
> +	);
> +
> +	obj = tailcall_bpf2bpf6__open_and_load();
> +	if (!ASSERT_OK_PTR(obj, "open and load"))
> +		return;
> +
> +	main_fd = bpf_program__fd(obj->progs.entry);
> +	if (!ASSERT_GE(main_fd, 0, "entry prog fd"))
> +		goto out;
> +
> +	map_fd = bpf_map__fd(obj->maps.jmp_table);
> +	if (!ASSERT_GE(map_fd, 0, "jmp_table map fd"))
> +		goto out;
> +
> +	prog_fd = bpf_program__fd(obj->progs.classifier_0);
> +	if (!ASSERT_GE(prog_fd, 0, "classifier_0 prog fd"))
> +		goto out;
> +
> +	i = 0;
> +	err = bpf_map_update_elem(map_fd, &i, &prog_fd, BPF_ANY);
> +	if (!ASSERT_OK(err, "jmp_table map update"))
> +		goto out;
> +
> +	err = bpf_prog_test_run_opts(main_fd, &topts);
> +	ASSERT_OK(err, "entry prog test run");
> +	ASSERT_EQ(topts.retval, 0, "tailcall retval");
> +
> +	data_fd = bpf_map__fd(obj->maps.bss);
> +	if (!ASSERT_GE(map_fd, 0, "bss map fd"))
> +		goto out;
> +
> +	i = 0;
> +	err = bpf_map_lookup_elem(data_fd, &i, &val);
> +	ASSERT_OK(err, "bss map lookup");
> +	ASSERT_EQ(val, 1, "done flag is set");
> +
> +out:
> +	tailcall_bpf2bpf6__destroy(obj);
> +}
> +
>   void test_tailcalls(void)
>   {
>   	if (test__start_subtest("tailcall_1"))
> @@ -855,4 +908,6 @@ void test_tailcalls(void)
>   		test_tailcall_bpf2bpf_4(false);
>   	if (test__start_subtest("tailcall_bpf2bpf_5"))
>   		test_tailcall_bpf2bpf_4(true);
> +	if (test__start_subtest("tailcall_bpf2bpf_6"))
> +		test_tailcall_bpf2bpf_6();
>   }
> diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> new file mode 100644
> index 000000000000..256de9bcc621
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#define __unused __attribute__((always_unused))
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u32));
> +} jmp_table SEC(".maps");
> +
> +int done = 0;
> +
> +SEC("tc")
> +int classifier_0(struct __sk_buff *skb __unused)
> +{
> +	done = 1;
> +	return 0;
> +}

Looks like this fails CI with:

   progs/tailcall_bpf2bpf6.c:17:40: error: unknown attribute 'always_unused' ignored [-Werror,-Wunknown-attributes]
   int classifier_0(struct __sk_buff *skb __unused)
                                          ^~~~~~~~
   progs/tailcall_bpf2bpf6.c:5:33: note: expanded from macro '__unused'
   #define __unused __attribute__((always_unused))
                                   ^~~~~~~~~~~~~
   1 error generated.
   make: *** [Makefile:509: /tmp/runner/work/bpf/bpf/tools/testing/selftests/bpf/tailcall_bpf2bpf6.o] Error 1
   make: *** Waiting for unfinished jobs....
   Error: Process completed with exit code 2.