On Tue, 2024-08-27 at 12:48 -0700, Martin KaFai Lau wrote:
> From: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
>
> This patch adds a gen_epilogue test to test a main prog
> using a bpf_tail_call.
>
> A non test_loader test is used. The tailcall target program,
> "test_epilogue_subprog", needs to be used in a struct_ops map
> before it can be loaded. Another struct_ops map is also needed
> to host the actual "test_epilogue_tailcall" struct_ops program
> that does the bpf_tail_call. The earlier test_loader patch
> will attach all struct_ops maps but the bpf_testmod.c does
> not support >1 attached struct_ops.
>
> The earlier patch used the test_loader which has already covered
> checking for the patched pro/epilogue instructions. This is done
> by the __xlated tag.
>
> This patch goes for the regular skel load and syscall test to do
> the tailcall test that can also allow to directly pass the
> the "struct st_ops_args *args" as ctx_in to the
> SEC("syscall") program.
>
> Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
> ---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
[...]
> +static void test_tailcall(void)
> +{
> + LIBBPF_OPTS(bpf_test_run_opts, topts);
> + struct epilogue_tailcall *skel;
> + struct st_ops_args args;
> + int err, prog_fd;
> +
> + skel = epilogue_tailcall__open_and_load();
> + if (!ASSERT_OK_PTR(skel, "epilogue_tailcall__open_and_load"))
> + return;
> +
> + topts.ctx_in = &args;
> + topts.ctx_size_in = sizeof(args);
> +
> + skel->links.epilogue_tailcall =
> + bpf_map__attach_struct_ops(skel->maps.epilogue_tailcall);
> + if (!ASSERT_OK_PTR(skel->links.epilogue_tailcall, "attach_struct_ops"))
> + goto done;
> +
Nitpick:
Both test_epilogue_tailcall and test_epilogue_subprog would be
augmented with epilogue, and we know that tail call run as expected
because only test_epilogue_subprog does +1, right?
If above is true, could you please update the comment a bit, e.g.:
/* Both test_epilogue_tailcall and test_epilogue_subprog are
* augmented with epilogue. When syscall_epilogue_tailcall()
* is run test_epilogue_tailcall() is triggered,
* it executes a tail call and control is transferred to
* test_epilogue_subprog(). Only test_epilogue_subprog()
* does args->a += 1, thus final args.a value of 10001
* guarantees that tail call was executed as expected.
*/
(For some reason it took me a while to understand what happens in this test)
> + /* tailcall prog + gen_epilogue */
> + memset(&args, 0, sizeof(args));
> + prog_fd = bpf_program__fd(skel->progs.syscall_epilogue_tailcall);
> + err = bpf_prog_test_run_opts(prog_fd, &topts);
> + ASSERT_OK(err, "bpf_prog_test_run_opts");
> + ASSERT_EQ(args.a, 10001, "args.a");
> + ASSERT_EQ(topts.retval, 10001 * 2, "topts.retval");
> +
> +done:
> + epilogue_tailcall__destroy(skel);
> +}
[...]
