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

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";