Re: [PATCH v2 bpf-next 2/2] bpf: add selftest for stackmap with build_id in NMI context
From: Tobin C. Harding <hidden>
Date: 2018-05-03 07:19:07
On Wed, May 02, 2018 at 04:20:30PM -0700, Song Liu wrote:
This new test captures stackmap with build_id with hardware event PERF_COUNT_HW_CPU_CYCLES. Because we only support one ips-to-build_id lookup per cpu in NMI context, stack_amap will not be able to do the lookup in this test.
stack_map ?
quoted hunk ↗ jump to hunk
Therefore, we didn't do compare_stack_ips(), as it will alwasy fail. urandom_read.c is extended to run configurable cycles so that it can be caught by the perf event. Signed-off-by: Song Liu <redacted> --- tools/testing/selftests/bpf/test_progs.c | 137 +++++++++++++++++++++++++++++ tools/testing/selftests/bpf/urandom_read.c | 10 ++- 2 files changed, 145 insertions(+), 2 deletions(-)diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c index aa336f0..00bb08c 100644 --- a/tools/testing/selftests/bpf/test_progs.c +++ b/tools/testing/selftests/bpf/test_progs.c@@ -1272,6 +1272,142 @@ static void test_stacktrace_build_id(void) return; } +static void test_stacktrace_build_id_nmi(void) +{ + int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd; + const char *file = "./test_stacktrace_build_id.o"; + int err, pmu_fd, prog_fd; + struct perf_event_attr attr = { + .sample_freq = 5000, + .freq = 1, + .type = PERF_TYPE_HARDWARE, + .config = PERF_COUNT_HW_CPU_CYCLES, + }; + __u32 key, previous_key, val, duration = 0; + struct bpf_object *obj; + char buf[256]; + int i, j; + struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH]; + int build_id_matches = 0; + + err = bpf_prog_load(file, BPF_PROG_TYPE_PERF_EVENT, &obj, &prog_fd); + if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno)) + goto out;
perhaps: return;
+ pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
+ 0 /* cpu 0 */, -1 /* group id */,
+ 0 /* flags */);
+ if (CHECK(pmu_fd < 0, "perf_event_open",
+ "err %d errno %d. Does the test host support PERF_COUNT_HW_CPU_CYCLES?\n",
+ pmu_fd, errno))
+ goto close_prog;
+
+ err = ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
+ if (CHECK(err, "perf_event_ioc_enable", "err %d errno %d\n",
+ err, errno))
+ goto close_pmu;
+
+ err = ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
+ if (CHECK(err, "perf_event_ioc_set_bpf", "err %d errno %d\n",
+ err, errno))
+ goto disable_pmu;
+
+ /* find map fds */
+ control_map_fd = bpf_find_map(__func__, obj, "control_map");
+ if (CHECK(control_map_fd < 0, "bpf_find_map control_map",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ stackid_hmap_fd = bpf_find_map(__func__, obj, "stackid_hmap");
+ if (CHECK(stackid_hmap_fd < 0, "bpf_find_map stackid_hmap",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ stackmap_fd = bpf_find_map(__func__, obj, "stackmap");
+ if (CHECK(stackmap_fd < 0, "bpf_find_map stackmap", "err %d errno %d\n",
+ err, errno))
+ goto disable_pmu;
+
+ stack_amap_fd = bpf_find_map(__func__, obj, "stack_amap");
+ if (CHECK(stack_amap_fd < 0, "bpf_find_map stack_amap",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ assert(system("dd if=/dev/urandom of=/dev/zero count=4 2> /dev/null")
+ == 0);
+ assert(system("taskset 0x1 ./urandom_read 100000") == 0);
+ /* disable stack trace collection */
+ key = 0;
+ val = 1;
+ bpf_map_update_elem(control_map_fd, &key, &val, 0);
+
+ /* for every element in stackid_hmap, we can find a corresponding one
+ * in stackmap, and vise versa.
+ */
+ err = compare_map_keys(stackid_hmap_fd, stackmap_fd);
+ if (CHECK(err, "compare_map_keys stackid_hmap vs. stackmap",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ err = compare_map_keys(stackmap_fd, stackid_hmap_fd);
+ if (CHECK(err, "compare_map_keys stackmap vs. stackid_hmap",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ err = extract_build_id(buf, 256);
+
+ if (CHECK(err, "get build_id with readelf",
+ "err %d errno %d\n", err, errno))
+ goto disable_pmu;
+
+ err = bpf_map_get_next_key(stackmap_fd, NULL, &key);
+ if (CHECK(err, "get_next_key from stackmap",
+ "err %d, errno %d\n", err, errno))
+ goto disable_pmu;
+
+ do {
+ char build_id[64];
+
+ err = bpf_map_lookup_elem(stackmap_fd, &key, id_offs);
+ if (CHECK(err, "lookup_elem from stackmap",
+ "err %d, errno %d\n", err, errno))
+ goto disable_pmu;
+ for (i = 0; i < PERF_MAX_STACK_DEPTH; ++i)
+ if (id_offs[i].status == BPF_STACK_BUILD_ID_VALID &&
+ id_offs[i].offset != 0) {
+ for (j = 0; j < 20; ++j)
+ sprintf(build_id + 2 * j, "%02x",
+ id_offs[i].build_id[j] & 0xff);
+ if (strstr(buf, build_id) != NULL)
+ build_id_matches = 1;
+ }
+ previous_key = key;
+ } while (bpf_map_get_next_key(stackmap_fd, &previous_key, &key) == 0);
+
+ if (CHECK(build_id_matches < 1, "build id match",
+ "Didn't find expected build ID from the map\n"))
+ goto disable_pmu;
+
+ /*
+ * We intentionally skip compare_stack_ips(). This is because we
+ * only support one in_nmi() ips-to-build_id translation per cpu
+ * at any time, thus stack_amap here will always fallback to
+ * BPF_STACK_BUILD_ID_IP;
+ */
+
+disable_pmu:
+ ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
+
+close_pmu:
+ close(pmu_fd);
+
+close_prog:
+ bpf_object__close(obj);
+
+out:
+ return;
+}No real need for label 'out' right? We can just return directly and remove the last three lines of this function. Hope this helps, Tobin.