diff mbox series

[v3,4/4] selftest/bpf: Test a perf bpf program that suppresses side effects.

Message ID 20231211045543.31741-5-khuey@kylehuey.com (mailing list archive)
State New, archived
Delegated to: BPF
Headers show
Series Combine perf and bpf for fast eval of hw breakpoint conditions | expand

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Commit Message

Kyle Huey Dec. 11, 2023, 4:55 a.m. UTC 
The test sets a hardware breakpoint and uses a bpf program to suppress the
side effects of a perf event sample, including I/O availability signals,
SIGTRAPs, and decrementing the event counter limit, if the ip matches the
expected value. Then the function with the breakpoint is executed multiple
times to test that all effects behave as expected.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
---
 .../selftests/bpf/prog_tests/perf_skip.c      | 140 ++++++++++++++++++
 .../selftests/bpf/progs/test_perf_skip.c      |  15 ++
 2 files changed, 155 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_skip.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_perf_skip.c

Comments

Song Liu Jan. 2, 2024, 10:49 p.m. UTC | #1 
On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@kylehuey.com> wrote:
>
> The test sets a hardware breakpoint and uses a bpf program to suppress the
> side effects of a perf event sample, including I/O availability signals,
> SIGTRAPs, and decrementing the event counter limit, if the ip matches the
> expected value. Then the function with the breakpoint is executed multiple
> times to test that all effects behave as expected.
>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> ---
>  .../selftests/bpf/prog_tests/perf_skip.c      | 140 ++++++++++++++++++
>  .../selftests/bpf/progs/test_perf_skip.c      |  15 ++
>  2 files changed, 155 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_skip.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_perf_skip.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/perf_skip.c b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> new file mode 100644
> index 000000000000..0200736a8baf
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> @@ -0,0 +1,140 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +
> +#include <test_progs.h>
> +#include "test_perf_skip.skel.h"
> +#include <linux/compiler.h>
> +#include <linux/hw_breakpoint.h>
> +#include <sys/mman.h>
> +
> +#ifndef TRAP_PERF
> +#define TRAP_PERF 6
> +#endif
> +
> +int signals_unexpected = 1;
> +int sigio_count, sigtrap_count;
> +
> +static void handle_sigio(int sig __always_unused)
> +{
> +       ASSERT_OK(signals_unexpected, "perf event not skipped");

ASSERT_OK is a little confusing. Maybe do something like:

static int signals_expected;
static void handle_sigio(int sig __always_unused)
{
    ASSERT_EQ(signals_expected, 1, "expected sig_io");
}
serial_test_perf_skip()
{
...
signals_expected = 1;
}

> +       ++sigio_count;
> +}
> +
> +static void handle_sigtrap(int signum __always_unused,
> +                          siginfo_t *info,
> +                          void *ucontext __always_unused)
> +{
> +       ASSERT_OK(signals_unexpected, "perf event not skipped");
ditto

> +       ASSERT_EQ(info->si_code, TRAP_PERF, "wrong si_code");
> +       ++sigtrap_count;
> +}
> +
> +static noinline int test_function(void)
> +{
> +       asm volatile ("");
> +       return 0;
> +}
> +
> +void serial_test_perf_skip(void)
> +{
> +       struct sigaction action = {};
> +       struct sigaction previous_sigtrap;
> +       sighandler_t previous_sigio;
> +       struct test_perf_skip *skel = NULL;
> +       struct perf_event_attr attr = {};
> +       int perf_fd = -1;
> +       int err;
> +       struct f_owner_ex owner;
> +       struct bpf_link *prog_link = NULL;
> +
> +       action.sa_flags = SA_SIGINFO | SA_NODEFER;
> +       action.sa_sigaction = handle_sigtrap;
> +       sigemptyset(&action.sa_mask);
> +       if (!ASSERT_OK(sigaction(SIGTRAP, &action, &previous_sigtrap), "sigaction"))
> +               return;
> +
> +       previous_sigio = signal(SIGIO, handle_sigio);

handle signal() errors here?

> +
> +       skel = test_perf_skip__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_load"))
> +               goto cleanup;
> +
> +       attr.type = PERF_TYPE_BREAKPOINT;
> +       attr.size = sizeof(attr);
> +       attr.bp_type = HW_BREAKPOINT_X;
> +       attr.bp_addr = (uintptr_t)test_function;
> +       attr.bp_len = sizeof(long);
> +       attr.sample_period = 1;
> +       attr.sample_type = PERF_SAMPLE_IP;
> +       attr.pinned = 1;
> +       attr.exclude_kernel = 1;
> +       attr.exclude_hv = 1;
> +       attr.precise_ip = 3;
> +       attr.sigtrap = 1;
> +       attr.remove_on_exec = 1;
> +
> +       perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> +       if (perf_fd < 0 && (errno == ENOENT || errno == EOPNOTSUPP)) {
> +               printf("SKIP:no PERF_TYPE_BREAKPOINT/HW_BREAKPOINT_X\n");
> +               test__skip();
> +               goto cleanup;
> +       }
> +       if (!ASSERT_OK(perf_fd < 0, "perf_event_open"))
> +               goto cleanup;
> +
> +       /* Configure the perf event to signal on sample. */
> +       err = fcntl(perf_fd, F_SETFL, O_ASYNC);
> +       if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
> +               goto cleanup;
> +
> +       owner.type = F_OWNER_TID;
> +       owner.pid = syscall(__NR_gettid);
> +       err = fcntl(perf_fd, F_SETOWN_EX, &owner);
> +       if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> +               goto cleanup;
> +
> +       /*
> +        * Allow at most one sample. A sample rejected by bpf should
> +        * not count against this.
> +        */

Multi-line comment style should be like

        /* Allow at most one sample. A sample rejected by bpf should
        * not count against this.
        */

> +       err = ioctl(perf_fd, PERF_EVENT_IOC_REFRESH, 1);
> +       if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_REFRESH)"))
> +               goto cleanup;
> +
> +       prog_link = bpf_program__attach_perf_event(skel->progs.handler, perf_fd);
> +       if (!ASSERT_OK_PTR(prog_link, "bpf_program__attach_perf_event"))
> +               goto cleanup;
> +
> +       /* Configure the bpf program to suppress the sample. */
> +       skel->bss->ip = (uintptr_t)test_function;
> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 0, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 0, "sigtrap_count");
> +
> +       /* Configure the bpf program to allow the sample. */
> +       skel->bss->ip = 0;
> +       signals_unexpected = 0;
> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> +
> +       /*
> +        * Test that the sample above is the only one allowed (by perf, not
> +        * by bpf)
> +        */

ditto.

> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> +
> +cleanup:
> +       bpf_link__destroy(prog_link);
> +       if (perf_fd >= 0)
> +               close(perf_fd);
> +       test_perf_skip__destroy(skel);
> +
> +       signal(SIGIO, previous_sigio);
> +       sigaction(SIGTRAP, &previous_sigtrap, NULL);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_perf_skip.c b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> new file mode 100644
> index 000000000000..7eb8b6de7a57
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> @@ -0,0 +1,15 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +uintptr_t ip;
> +
> +SEC("perf_event")
> +int handler(struct bpf_perf_event_data *data)
> +{
> +       /* Skip events that have the correct ip. */
> +       return ip != PT_REGS_IP(&data->regs);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.34.1
>
Kyle Huey Jan. 19, 2024, 12:08 a.m. UTC | #2 
On Tue, Jan 2, 2024 at 2:49 PM Song Liu <song@kernel.org> wrote:
>
> On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@kylehuey.com> wrote:
> >
> > The test sets a hardware breakpoint and uses a bpf program to suppress the
> > side effects of a perf event sample, including I/O availability signals,
> > SIGTRAPs, and decrementing the event counter limit, if the ip matches the
> > expected value. Then the function with the breakpoint is executed multiple
> > times to test that all effects behave as expected.
> >
> > Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> > ---
> >  .../selftests/bpf/prog_tests/perf_skip.c      | 140 ++++++++++++++++++
> >  .../selftests/bpf/progs/test_perf_skip.c      |  15 ++
> >  2 files changed, 155 insertions(+)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_skip.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/test_perf_skip.c
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/perf_skip.c b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> > new file mode 100644
> > index 000000000000..0200736a8baf
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> > @@ -0,0 +1,140 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#define _GNU_SOURCE
> > +
> > +#include <test_progs.h>
> > +#include "test_perf_skip.skel.h"
> > +#include <linux/compiler.h>
> > +#include <linux/hw_breakpoint.h>
> > +#include <sys/mman.h>
> > +
> > +#ifndef TRAP_PERF
> > +#define TRAP_PERF 6
> > +#endif
> > +
> > +int signals_unexpected = 1;
> > +int sigio_count, sigtrap_count;
> > +
> > +static void handle_sigio(int sig __always_unused)
> > +{
> > +       ASSERT_OK(signals_unexpected, "perf event not skipped");
>
> ASSERT_OK is a little confusing. Maybe do something like:
>
> static int signals_expected;
> static void handle_sigio(int sig __always_unused)
> {
>     ASSERT_EQ(signals_expected, 1, "expected sig_io");
> }
> serial_test_perf_skip()
> {
> ...
> signals_expected = 1;
> }
>

I'll just drop signals_expected. Now that I'm counting the exact
number of signals it's redundant.

> > +       ++sigio_count;
> > +}
> > +
> > +static void handle_sigtrap(int signum __always_unused,
> > +                          siginfo_t *info,
> > +                          void *ucontext __always_unused)
> > +{
> > +       ASSERT_OK(signals_unexpected, "perf event not skipped");
> ditto
>
> > +       ASSERT_EQ(info->si_code, TRAP_PERF, "wrong si_code");
> > +       ++sigtrap_count;
> > +}
> > +
> > +static noinline int test_function(void)
> > +{
> > +       asm volatile ("");
> > +       return 0;
> > +}
> > +
> > +void serial_test_perf_skip(void)
> > +{
> > +       struct sigaction action = {};
> > +       struct sigaction previous_sigtrap;
> > +       sighandler_t previous_sigio;
> > +       struct test_perf_skip *skel = NULL;
> > +       struct perf_event_attr attr = {};
> > +       int perf_fd = -1;
> > +       int err;
> > +       struct f_owner_ex owner;
> > +       struct bpf_link *prog_link = NULL;
> > +
> > +       action.sa_flags = SA_SIGINFO | SA_NODEFER;
> > +       action.sa_sigaction = handle_sigtrap;
> > +       sigemptyset(&action.sa_mask);
> > +       if (!ASSERT_OK(sigaction(SIGTRAP, &action, &previous_sigtrap), "sigaction"))
> > +               return;
> > +
> > +       previous_sigio = signal(SIGIO, handle_sigio);
>
> handle signal() errors here?

Addressed in v4.

> > +
> > +       skel = test_perf_skip__open_and_load();
> > +       if (!ASSERT_OK_PTR(skel, "skel_load"))
> > +               goto cleanup;
> > +
> > +       attr.type = PERF_TYPE_BREAKPOINT;
> > +       attr.size = sizeof(attr);
> > +       attr.bp_type = HW_BREAKPOINT_X;
> > +       attr.bp_addr = (uintptr_t)test_function;
> > +       attr.bp_len = sizeof(long);
> > +       attr.sample_period = 1;
> > +       attr.sample_type = PERF_SAMPLE_IP;
> > +       attr.pinned = 1;
> > +       attr.exclude_kernel = 1;
> > +       attr.exclude_hv = 1;
> > +       attr.precise_ip = 3;
> > +       attr.sigtrap = 1;
> > +       attr.remove_on_exec = 1;
> > +
> > +       perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> > +       if (perf_fd < 0 && (errno == ENOENT || errno == EOPNOTSUPP)) {
> > +               printf("SKIP:no PERF_TYPE_BREAKPOINT/HW_BREAKPOINT_X\n");
> > +               test__skip();
> > +               goto cleanup;
> > +       }
> > +       if (!ASSERT_OK(perf_fd < 0, "perf_event_open"))
> > +               goto cleanup;
> > +
> > +       /* Configure the perf event to signal on sample. */
> > +       err = fcntl(perf_fd, F_SETFL, O_ASYNC);
> > +       if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
> > +               goto cleanup;
> > +
> > +       owner.type = F_OWNER_TID;
> > +       owner.pid = syscall(__NR_gettid);
> > +       err = fcntl(perf_fd, F_SETOWN_EX, &owner);
> > +       if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> > +               goto cleanup;
> > +
> > +       /*
> > +        * Allow at most one sample. A sample rejected by bpf should
> > +        * not count against this.
> > +        */
>
> Multi-line comment style should be like

Addressed in v4.

>         /* Allow at most one sample. A sample rejected by bpf should
>         * not count against this.
>         */
>
> > +       err = ioctl(perf_fd, PERF_EVENT_IOC_REFRESH, 1);
> > +       if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_REFRESH)"))
> > +               goto cleanup;
> > +
> > +       prog_link = bpf_program__attach_perf_event(skel->progs.handler, perf_fd);
> > +       if (!ASSERT_OK_PTR(prog_link, "bpf_program__attach_perf_event"))
> > +               goto cleanup;
> > +
> > +       /* Configure the bpf program to suppress the sample. */
> > +       skel->bss->ip = (uintptr_t)test_function;
> > +       test_function();
> > +
> > +       ASSERT_EQ(sigio_count, 0, "sigio_count");
> > +       ASSERT_EQ(sigtrap_count, 0, "sigtrap_count");
> > +
> > +       /* Configure the bpf program to allow the sample. */
> > +       skel->bss->ip = 0;
> > +       signals_unexpected = 0;
> > +       test_function();
> > +
> > +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> > +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> > +
> > +       /*
> > +        * Test that the sample above is the only one allowed (by perf, not
> > +        * by bpf)
> > +        */
>
> ditto.
>
> > +       test_function();
> > +
> > +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> > +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> > +
> > +cleanup:
> > +       bpf_link__destroy(prog_link);
> > +       if (perf_fd >= 0)
> > +               close(perf_fd);
> > +       test_perf_skip__destroy(skel);
> > +
> > +       signal(SIGIO, previous_sigio);
> > +       sigaction(SIGTRAP, &previous_sigtrap, NULL);
> > +}
> > diff --git a/tools/testing/selftests/bpf/progs/test_perf_skip.c b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> > new file mode 100644
> > index 000000000000..7eb8b6de7a57
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> > @@ -0,0 +1,15 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "vmlinux.h"
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +uintptr_t ip;
> > +
> > +SEC("perf_event")
> > +int handler(struct bpf_perf_event_data *data)
> > +{
> > +       /* Skip events that have the correct ip. */
> > +       return ip != PT_REGS_IP(&data->regs);
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> > --
> > 2.34.1
> >

- Kyle
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/perf_skip.c b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
new file mode 100644
index 000000000000..0200736a8baf
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
@@ -0,0 +1,140 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <test_progs.h>
+#include "test_perf_skip.skel.h"
+#include <linux/compiler.h>
+#include <linux/hw_breakpoint.h>
+#include <sys/mman.h>
+
+#ifndef TRAP_PERF
+#define TRAP_PERF 6
+#endif
+
+int signals_unexpected = 1;
+int sigio_count, sigtrap_count;
+
+static void handle_sigio(int sig __always_unused)
+{
+	ASSERT_OK(signals_unexpected, "perf event not skipped");
+	++sigio_count;
+}
+
+static void handle_sigtrap(int signum __always_unused,
+			   siginfo_t *info,
+			   void *ucontext __always_unused)
+{
+	ASSERT_OK(signals_unexpected, "perf event not skipped");
+	ASSERT_EQ(info->si_code, TRAP_PERF, "wrong si_code");
+	++sigtrap_count;
+}
+
+static noinline int test_function(void)
+{
+	asm volatile ("");
+	return 0;
+}
+
+void serial_test_perf_skip(void)
+{
+	struct sigaction action = {};
+	struct sigaction previous_sigtrap;
+	sighandler_t previous_sigio;
+	struct test_perf_skip *skel = NULL;
+	struct perf_event_attr attr = {};
+	int perf_fd = -1;
+	int err;
+	struct f_owner_ex owner;
+	struct bpf_link *prog_link = NULL;
+
+	action.sa_flags = SA_SIGINFO | SA_NODEFER;
+	action.sa_sigaction = handle_sigtrap;
+	sigemptyset(&action.sa_mask);
+	if (!ASSERT_OK(sigaction(SIGTRAP, &action, &previous_sigtrap), "sigaction"))
+		return;
+
+	previous_sigio = signal(SIGIO, handle_sigio);
+
+	skel = test_perf_skip__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_load"))
+		goto cleanup;
+
+	attr.type = PERF_TYPE_BREAKPOINT;
+	attr.size = sizeof(attr);
+	attr.bp_type = HW_BREAKPOINT_X;
+	attr.bp_addr = (uintptr_t)test_function;
+	attr.bp_len = sizeof(long);
+	attr.sample_period = 1;
+	attr.sample_type = PERF_SAMPLE_IP;
+	attr.pinned = 1;
+	attr.exclude_kernel = 1;
+	attr.exclude_hv = 1;
+	attr.precise_ip = 3;
+	attr.sigtrap = 1;
+	attr.remove_on_exec = 1;
+
+	perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
+	if (perf_fd < 0 && (errno == ENOENT || errno == EOPNOTSUPP)) {
+		printf("SKIP:no PERF_TYPE_BREAKPOINT/HW_BREAKPOINT_X\n");
+		test__skip();
+		goto cleanup;
+	}
+	if (!ASSERT_OK(perf_fd < 0, "perf_event_open"))
+		goto cleanup;
+
+	/* Configure the perf event to signal on sample. */
+	err = fcntl(perf_fd, F_SETFL, O_ASYNC);
+	if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
+		goto cleanup;
+
+	owner.type = F_OWNER_TID;
+	owner.pid = syscall(__NR_gettid);
+	err = fcntl(perf_fd, F_SETOWN_EX, &owner);
+	if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
+		goto cleanup;
+
+	/*
+	 * Allow at most one sample. A sample rejected by bpf should
+	 * not count against this.
+	 */
+	err = ioctl(perf_fd, PERF_EVENT_IOC_REFRESH, 1);
+	if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_REFRESH)"))
+		goto cleanup;
+
+	prog_link = bpf_program__attach_perf_event(skel->progs.handler, perf_fd);
+	if (!ASSERT_OK_PTR(prog_link, "bpf_program__attach_perf_event"))
+		goto cleanup;
+
+	/* Configure the bpf program to suppress the sample. */
+	skel->bss->ip = (uintptr_t)test_function;
+	test_function();
+
+	ASSERT_EQ(sigio_count, 0, "sigio_count");
+	ASSERT_EQ(sigtrap_count, 0, "sigtrap_count");
+
+	/* Configure the bpf program to allow the sample. */
+	skel->bss->ip = 0;
+	signals_unexpected = 0;
+	test_function();
+
+	ASSERT_EQ(sigio_count, 1, "sigio_count");
+	ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
+
+	/*
+	 * Test that the sample above is the only one allowed (by perf, not
+	 * by bpf)
+	 */
+	test_function();
+
+	ASSERT_EQ(sigio_count, 1, "sigio_count");
+	ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
+
+cleanup:
+	bpf_link__destroy(prog_link);
+	if (perf_fd >= 0)
+		close(perf_fd);
+	test_perf_skip__destroy(skel);
+
+	signal(SIGIO, previous_sigio);
+	sigaction(SIGTRAP, &previous_sigtrap, NULL);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_perf_skip.c b/tools/testing/selftests/bpf/progs/test_perf_skip.c
new file mode 100644
index 000000000000..7eb8b6de7a57
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
@@ -0,0 +1,15 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+uintptr_t ip;
+
+SEC("perf_event")
+int handler(struct bpf_perf_event_data *data)
+{
+	/* Skip events that have the correct ip. */
+	return ip != PT_REGS_IP(&data->regs);
+}
+
+char _license[] SEC("license") = "GPL";