Re: [PATCH 2/2] selftest/bpf: Test returning zero from a perf bpf program suppresses SIGIO.

[Yonghong Song <yonghong.song@linux.dev>]

On 12/4/23 3:14 PM, Kyle Huey wrote:
> The test sets a hardware breakpoint and uses a bpf program to suppress the
> I/O availability signal if the ip matches the expected value.
>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> ---
>   .../selftests/bpf/prog_tests/perf_skip.c      | 95 +++++++++++++++++++
>   .../selftests/bpf/progs/test_perf_skip.c      | 23 +++++
>   2 files changed, 118 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..b269a31669b7
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +#include <test_progs.h>
> +#include "test_perf_skip.skel.h"
> +#include <linux/hw_breakpoint.h>
> +#include <sys/mman.h>
> +
> +#define BPF_OBJECT            "test_perf_skip.bpf.o"
> +
> +static void handle_sig(int)

I hit a warning here:
home/yhs/work/bpf-next/tools/testing/selftests/bpf/prog_tests/perf_skip.c:10:27: error: omitting the parameter name in a function definition is a C23 extension [-Werror,-Wc23-extensions]
    10 | static void handle_sig(int)
       |

Add a parameter and marked as unused can resolve the issue.

#define __always_unused         __attribute__((__unused__))

static void handle_sig(int unused __always_unused)
{
         ASSERT_OK(1, "perf event not skipped");
}


> +{
> +	ASSERT_OK(1, "perf event not skipped");
> +}
> +
> +static noinline int test_function(void)
> +{
> +	return 0;
> +}
> +
> +void serial_test_perf_skip(void)
> +{
> +	sighandler_t previous;
> +	int duration = 0;
> +	struct test_perf_skip *skel = NULL;
> +	int map_fd = -1;
> +	long page_size = sysconf(_SC_PAGE_SIZE);
> +	uintptr_t *ip = NULL;
> +	int prog_fd = -1;
> +	struct perf_event_attr attr = {0};
> +	int perf_fd = -1;
> +	struct f_owner_ex owner;
> +	int err;
> +
> +	previous = signal(SIGIO, handle_sig);
> +
> +	skel = test_perf_skip__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel_load"))
> +		goto cleanup;
> +
> +	prog_fd = bpf_program__fd(skel->progs.handler);
> +	if (!ASSERT_OK(prog_fd < 0, "bpf_program__fd"))
> +		goto cleanup;
> +
> +	map_fd = bpf_map__fd(skel->maps.ip);
> +	if (!ASSERT_OK(map_fd < 0, "bpf_map__fd"))
> +		goto cleanup;
> +
> +	ip = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, map_fd, 0);
> +	if (!ASSERT_OK_PTR(ip, "mmap bpf map"))
> +		goto cleanup;
> +
> +	*ip = (uintptr_t)test_function;
> +
> +	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;
> +
> +	perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> +	if (CHECK(perf_fd < 0, "perf_event_open", "err %d\n", perf_fd))
> +		goto cleanup;
> +
> +	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 = gettid();

I hit a compilation failure here:

/home/yhs/work/bpf-next/tools/testing/selftests/bpf/prog_tests/perf_skip.c:75:14: error: call to undeclared function 'gettid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    75 |         owner.pid = gettid();
       |                     ^

If you looked at some other examples, the common usage is do 'syscall(SYS_gettid)'.
So the following patch should fix the compilation error:

#include <sys/syscall.h>
...
         owner.pid = syscall(SYS_gettid);
...

> +	err = fcntl(perf_fd, F_SETOWN_EX, &owner);
> +	if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> +		goto cleanup;
> +
> +	err = ioctl(perf_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
> +	if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_SET_BPF)"))
> +		goto cleanup;
> +
> +	test_function();

As Andrii has mentioned in previous comments, we will have
issue is RELEASE version of selftest is built
   RELEASE=1 make ...

See https://lore.kernel.org/bpf/20231127050342.1945270-1-yonghong.song@linux.dev

> +
> +cleanup:
> +	if (perf_fd >= 0)
> +		close(perf_fd);
> +	if (ip)
> +		munmap(ip, page_size);
> +	if (skel)
> +		test_perf_skip__destroy(skel);
> +
> +	signal(SIGIO, previous);
> +}
> 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..ef01a9161afe
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> @@ -0,0 +1,23 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(map_flags, BPF_F_MMAPABLE);
> +	__type(key, uint32_t);
> +	__type(value, uintptr_t);
> +} ip SEC(".maps");
> +
> +SEC("perf_event")
> +int handler(struct bpf_perf_event_data *data)
> +{
> +	const uint32_t index = 0;
> +	uintptr_t *v = bpf_map_lookup_elem(&ip, &index);
> +
> +	return !(v && *v == PT_REGS_IP(&data->regs));
> +}
> +
> +char _license[] SEC("license") = "GPL";