On Thu, Jan 4, 2024 at 2:39 PM <andrii@xxxxxxxxxx> wrote:
>
> From: Andrii Nakryiko <andrii@xxxxxxxxxx>
>
> Various tests specify extra testing prog_flags when loading BPF
> programs, like BPF_F_TEST_RND_HI32, and more recently also
> BPF_F_TEST_REG_INVARIANTS. While BPF_F_TEST_RND_HI32 is old enough to
> not cause much problem on older kernels, BPF_F_TEST_REG_INVARIANTS is
> very fresh and unconditionally specifying it causes selftests to fail on
> even slightly outdated kernels.
>
> This breaks libbpf CI test against 4.9 and 5.15 kernels, it can break
> some local development (done outside of VM), etc.
>
> To prevent this, and guard against similar problems in the future, do
> runtime detection of supported "testing flags", and only provide those
> that host kernel recognizes.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Song Liu <song@xxxxxxxxxx>
With one nit below.
[...]
> diff --git a/tools/testing/selftests/bpf/testing_helpers.c b/tools/testing/selftests/bpf/testing_helpers.c
> index d2458c1b1671..e1f797c5c501 100644
> --- a/tools/testing/selftests/bpf/testing_helpers.c
> +++ b/tools/testing/selftests/bpf/testing_helpers.c
> @@ -251,6 +251,34 @@ __u32 link_info_prog_id(const struct bpf_link *link, struct bpf_link_info *info)
> }
>
> int extra_prog_load_log_flags = 0;
> +static int prog_test_flags = -1;
nit: Move prog_test_flags to inside testing_prog_flags() as it is not
used by other
functions.
> +
> +int testing_prog_flags(void)
> +{
> + static int prog_flags[] = { BPF_F_TEST_RND_HI32, BPF_F_TEST_REG_INVARIANTS };
> + static struct bpf_insn insns[] = {
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + };
> + int insn_cnt = ARRAY_SIZE(insns), i, fd, flags = 0;
> + LIBBPF_OPTS(bpf_prog_load_opts, opts);
> +
> + if (prog_test_flags >= 0)
> + return prog_test_flags;
> +
> + for (i = 0; i < ARRAY_SIZE(prog_flags); i++) {
> + opts.prog_flags = prog_flags[i];
> + fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "flag-test", "GPL",
> + insns, insn_cnt, &opts);
> + if (fd >= 0) {
> + flags |= prog_flags[i];
> + close(fd);
> + }
> + }
> +
> + prog_test_flags = flags;
> + return prog_test_flags;
> +}
[...]
