Add probe result verification for usdt unit test

Signed-off-by: Yonghong Song <yhs@fb.com>

tests/python/test_usdt.py

@@ -10,6 +10,7 @@ from bcc import BPF, USDT
 from unittest import main, TestCase
 from subprocess import Popen, PIPE
 from tempfile import NamedTemporaryFile
+import ctypes as ct
 import os
 import signal
 
@@ -22,16 +23,15 @@ class TestUDST(TestCase):
 
 int main() {
   char s[100];
-  int i, a = 20, b = 40;
+  int i, a = 200, b = 40;
   for (i = 0; i < 100; i++) s[i] = (i & 7) + (i & 6);
   while (1) {
     FOLLY_SDT(test, probe_point_1, s[7], b);
     FOLLY_SDT(test, probe_point_3, a, b);
-    sleep(3);
-    a++; b++;
     FOLLY_SDT(test, probe_point_1, s[4], a);
     FOLLY_SDT(test, probe_point_2, 5, s[10]);
     FOLLY_SDT(test, probe_point_3, s[4], s[7]);
+    sleep(1);
   }
   return 1;
 }
@@ -39,13 +39,44 @@ int main() {
         # BPF program
         self.bpf_text = """
 #include <uapi/linux/ptrace.h>
+
+struct probe_result_t1 {
+  char v1;
+  int  v2;
+};
+
+struct probe_result_t2 {
+  int  v1;
+  char v2;
+};
+
+struct probe_result_t3 {
+  int v1;
+  int v2;
+};
+
+BPF_PERF_OUTPUT(event1);
+BPF_PERF_OUTPUT(event2);
+BPF_PERF_OUTPUT(event3);
 int do_trace(struct pt_regs *ctx) {
+    struct probe_result_t1 result = {};
+    bpf_usdt_readarg(1, ctx, &result.v1);
+    bpf_usdt_readarg(2, ctx, &result.v2);
+    event1.perf_submit(ctx, &result, sizeof(result));
     return 0;
 };
 int do_trace2(struct pt_regs *ctx) {
+    struct probe_result_t2 result = {};
+    bpf_usdt_readarg(1, ctx, &result.v1);
+    bpf_usdt_readarg(2, ctx, &result.v2);
+    event2.perf_submit(ctx, &result, sizeof(result));
     return 0;
 }
 int do_trace3(struct pt_regs *ctx) {
+    struct probe_result_t3 result = {};
+    bpf_usdt_readarg(1, ctx, &result.v1);
+    bpf_usdt_readarg(2, ctx, &result.v2);
+    event3.perf_submit(ctx, &result, sizeof(result));
     return 0;
 }
 """
@@ -69,6 +100,55 @@ int do_trace3(struct pt_regs *ctx) {
         u.enable_probe(probe="probe_point_3", fn_name="do_trace3")
         b = BPF(text=self.bpf_text, usdt_contexts=[u])
 
+        # Event states for each event:
+        # 0 - probe not caught, 1 - probe caught with correct value,
+        # 2 - probe caught with incorrect value
+        self.evt_st_1 = 0
+        self.evt_st_2 = 0
+        self.evt_st_3 = 0
+
+        # define output data structure in Python
+        class Data1(ct.Structure):
+            _fields_ = [("v1", ct.c_char),
+                        ("v2", ct.c_int)]
+
+        class Data2(ct.Structure):
+            _fields_ = [("v1", ct.c_int),
+                        ("v2", ct.c_char)]
+
+        class Data3(ct.Structure):
+            _fields_ = [("v1", ct.c_int),
+                        ("v2", ct.c_int)]
+
+        def check_event_val(event, event_state, v1, v2, v3, v4):
+            if ((event.v1 == v1 and event.v2 == v2) or (event.v1 == v3 and event.v2 == v4)):
+                if (event_state == 0 or event_state == 1):
+                    return 1
+            return 2
+
+        def print_event1(cpu, data, size):
+            event = ct.cast(data, ct.POINTER(Data1)).contents
+            self.evt_st_1 = check_event_val(event, self.evt_st_1, b'\x0d', 40, b'\x08', 200)
+
+        def print_event2(cpu, data, size):
+            event = ct.cast(data, ct.POINTER(Data2)).contents
+            # pretend we have two identical probe points to simplify the code
+            self.evt_st_2 = check_event_val(event, self.evt_st_2, 5, b'\x04', 5, b'\x04')
+
+        def print_event3(cpu, data, size):
+            event = ct.cast(data, ct.POINTER(Data3)).contents
+            self.evt_st_3 = check_event_val(event, self.evt_st_3, 200, 40, 8, 13)
+
+        # loop with callback to print_event
+        b["event1"].open_perf_buffer(print_event1)
+        b["event2"].open_perf_buffer(print_event2)
+        b["event3"].open_perf_buffer(print_event3)
+
+        # three iterations to make sure we get some probes and have time to process them
+        for i in range(3):
+            b.kprobe_poll()
+        self.assertTrue(self.evt_st_1 == 1 and self.evt_st_2 == 1 and self.evt_st_3 == 1)
+
     def tearDown(self):
         # kill the subprocess, clean the environment
         self.app.kill()