[v4,bpf-next,7/9] selftests/bpf: Add tailcall epilogue test

Commit Message

Martin KaFai Lau Aug. 27, 2024, 7:48 p.m. UTC

From: Martin KaFai Lau <[e-mail]>

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 <[e-mail]>
---
 .../selftests/bpf/prog_tests/pro_epilogue.c   | 38 ++++++++++++
 .../selftests/bpf/progs/epilogue_tailcall.c   | 58 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/epilogue_tailcall.c

Comments

Eduard Zingerman Aug. 29, 2024, 6:16 a.m. UTC | #1

On Tue, 2024-08-27 at 12:48 -0700, Martin KaFai Lau wrote:
> From: Martin KaFai Lau <[e-mail]>
> 
> 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 <[e-mail]>
> ---

Acked-by: Eduard Zingerman <[e-mail]>

[...]

> +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);
> +}

[...]

Martin KaFai Lau Aug. 29, 2024, 6:15 p.m. UTC | #2

On 8/28/24 11:16 PM, Eduard Zingerman wrote:
> On Tue, 2024-08-27 at 12:48 -0700, Martin KaFai Lau wrote:
>> From: Martin KaFai Lau <[e-mail]>
>>
>> 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 <[e-mail]>
>> ---
> 
> Acked-by: Eduard Zingerman <[e-mail]>
> 
> [...]
> 
>> +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?

Yes. and also the epilogue of the test_epilogue_subprog is executed.

> 
> 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.
>   */

Added. I massaged the wordings a little.

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c b/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
index 69e4a5a1756d..98de677c55a9 100644
--- a/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
+++ b/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
@@ -4,9 +4,47 @@ 
 #include <test_progs.h>
 #include "pro_epilogue_subprog.skel.h"
 #include "pro_epilogue_kfunc.skel.h"
+#include "epilogue_tailcall.skel.h"
+
+struct st_ops_args {
+	int a;
+};
+
+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;
+
+	/* 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);
+}
 
 void test_pro_epilogue(void)
 {
 	RUN_TESTS(pro_epilogue_subprog);
 	RUN_TESTS(pro_epilogue_kfunc);
+	if (test__start_subtest("tailcall"))
+		test_tailcall();
 }
diff --git a/tools/testing/selftests/bpf/progs/epilogue_tailcall.c b/tools/testing/selftests/bpf/progs/epilogue_tailcall.c
new file mode 100644
index 000000000000..7275dd594de0
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/epilogue_tailcall.c
@@ -0,0 +1,58 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "../bpf_testmod/bpf_testmod.h"
+#include "../bpf_testmod/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+static __noinline __used int subprog(struct st_ops_args *args)
+{
+	args->a += 1;
+	return args->a;
+}
+
+SEC("struct_ops/test_epilogue_subprog")
+int BPF_PROG(test_epilogue_subprog, struct st_ops_args *args)
+{
+	subprog(args);
+	return args->a;
+}
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+	__array(values, void (void));
+} epilogue_map SEC(".maps") = {
+	.values = {
+		[0] = (void *)&test_epilogue_subprog,
+	}
+};
+
+SEC("struct_ops/test_epilogue_tailcall")
+int test_epilogue_tailcall(unsigned long long *ctx)
+{
+	bpf_tail_call(ctx, &epilogue_map, 0);
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_st_ops epilogue_tailcall = {
+	.test_epilogue = (void *)test_epilogue_tailcall,
+};
+
+SEC(".struct_ops.link")
+struct bpf_testmod_st_ops epilogue_subprog = {
+	.test_epilogue = (void *)test_epilogue_subprog,
+};
+
+SEC("syscall")
+int syscall_epilogue_tailcall(struct st_ops_args *args)
+{
+	return bpf_kfunc_st_ops_test_epilogue(args);
+}