Example of using USDT

examples/cpp/CMakeLists.txt

@@ -26,3 +26,7 @@ install (TARGETS RandomRead DESTINATION share/bcc/examples/cpp)
 add_executable(LLCStat LLCStat.cc)
 target_link_libraries(LLCStat bcc-static)
 install (TARGETS LLCStat DESTINATION share/bcc/examples/cpp)
+
+add_executable(FollyRequestContextSwitch FollyRequestContextSwitch.cc)
+target_link_libraries(FollyRequestContextSwitch bcc-static)
+install (TARGETS FollyRequestContextSwitch DESTINATION share/bcc/examples/cpp)

examples/cpp/FollyRequestContextSwitch.cc

+/*
+ * FollyRequestContextSwitch Monitor RequestContext switch events for any binary
+ *                           uses the class from [folly](http://bit.ly/2h6S1yx).
+ *                           For Linux, uses BCC, eBPF. Embedded C.
+ *
+ * Basic example of using USDT with BCC.
+ *
+ * USAGE: FollyRequestContextSwitch PATH_TO_BINARY
+ *
+ * Copyright (c) Facebook, Inc.
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+
+#include <signal.h>
+#include <iostream>
+#include <vector>
+
+#include "BPF.h"
+
+const std::string BPF_PROGRAM = R"(
+#include <linux/sched.h>
+#include <uapi/linux/ptrace.h>
+
+struct event_t {
+  int pid;
+  char name[16];
+  uint64_t old_addr;
+  uint64_t new_addr;
+};
+
+BPF_PERF_OUTPUT(events);
+
+int on_context_switch(struct pt_regs *ctx) {
+  struct event_t event = {};
+
+  event.pid = bpf_get_current_pid_tgid();
+  bpf_get_current_comm(&event.name, sizeof(event.name));
+  
+  bpf_usdt_readarg(1, ctx, &event.old_addr);
+  bpf_usdt_readarg(2, ctx, &event.new_addr);
+
+  events.perf_submit(ctx, &event, sizeof(event));
+  return 0;
+}
+)";
+
+// Define the same struct to use in user space.
+struct event_t {
+  int pid;
+  char name[16];
+  uint64_t old_addr;
+  uint64_t new_addr;
+};
+
+void handle_output(void* cb_cookie, void* data, int data_size) {
+  auto event = static_cast<event_t*>(data);
+  std::cout << "PID " << event->pid << " (" << event->name << ") ";
+  std::cout << "folly::RequestContext switch from " << event->old_addr << " to "
+            << event->new_addr << std::endl;
+}
+
+ebpf::BPF* bpf;
+
+void signal_handler(int s) {
+  std::cerr << "Terminating..." << std::endl;
+  delete bpf;
+  exit(0);
+}
+
+int main(int argc, char** argv) {
+  if (argc != 2) {
+    std::cout << "USAGE: FollyRequestContextSwitch PATH_TO_BINARY" << std::endl;
+    exit(1);
+  }
+  std::string binary_path(argv[1]);
+
+  bpf = new ebpf::BPF();
+  std::vector<ebpf::USDT> u;
+  u.emplace_back(binary_path, "folly", "request_context_switch_before",
+                 "on_context_switch");
+  auto init_res = bpf->init(BPF_PROGRAM, {}, u);
+  if (init_res.code() != 0) {
+    std::cerr << init_res.msg() << std::endl;
+    return 1;
+  }
+
+  auto attach_res = bpf->attach_usdt(u[0]);
+  if (attach_res.code() != 0) {
+    std::cerr << attach_res.msg() << std::endl;
+    return 1;
+  }
+
+  auto open_res = bpf->open_perf_buffer("events", &handle_output);
+  if (open_res.code() != 0) {
+    std::cerr << open_res.msg() << std::endl;
+    return 1;
+  }
+
+  signal(SIGINT, signal_handler);
+  std::cout << "Started tracing, hit Ctrl-C to terminate." << std::endl;
+  while (true)
+    bpf->poll_perf_buffer("events");
+
+  return 0;
+}