usdt: permit to enable probes from a pid and a particular binary

Currently, for usdt, the commands where both a pid and a binary path are specified are not well supported. For example, ``` funccount -p <pid> 'u:<binary_path>:probe' ``` will count `probe` occurances for all binary paths in `pid`, not just `<binary_path>`. The command ``` argdist -p <pid> 'u:<binary_path>:probe():s64:arg1' ``` will also count `probe` occurances for all binary paths in `pid` with my previous patch. Furthermore, suppose user want to trace linker `setjmp` probe point with command ``` trace.py -p <pid> 'u:/usr/lib64/ld-2.17.so:setjmp' ``` Without my previous patch, user will have incorrect results as both `libc:setjmp` and `rtld:setjmp` exists and the bcc just picks the first one which is `libc:setjmp`. My last patch will cause `enable_probe` failures if in the same usdt context, two probes have the same probe_name but different provider name. To fix all these issues, this patch passes additional binary path to the pid-based usdt context, so that only probes from that particular binary will be added to the context. This solved all the above mentioned issues. Signed-off-by: Yonghong Song <yhs@fb.com>
andyfangdz · Jan 12, 2018 · fead16a · fead16a
1 parent 2489457
commit fead16a
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Showing 6 changed files with 31 additions and 6 deletions.
diff --git a/src/cc/bcc_usdt.h b/src/cc/bcc_usdt.h
@@ -22,7 +22,7 @@ extern "C" {
 
 #include <stdint.h>
 
-void *bcc_usdt_new_frompid(int pid);
+void *bcc_usdt_new_frompid(int pid, const char *path);
 void *bcc_usdt_new_frompath(const char *path);
 void bcc_usdt_close(void *usdt);
 

diff --git a/src/cc/link_all.cc b/src/cc/link_all.cc
@@ -13,7 +13,7 @@ namespace {
       if (::getenv("bar") != (char *)-1)
         return;
 
-      (void)bcc_usdt_new_frompid(-1);
+      (void)bcc_usdt_new_frompid(-1, nullptr);
       (void)bcc_usdt_new_frompath(nullptr);
       (void)bcc_usdt_close(nullptr);
     }

diff --git a/src/cc/usdt.h b/src/cc/usdt.h
@@ -249,6 +249,7 @@ class Context {
 public:
   Context(const std::string &bin_path);
   Context(int pid);
+  Context(int pid, const std::string &bin_path);
   ~Context();
 
   optional<int> pid() const { return pid_; }

diff --git a/src/cc/usdt/usdt.cc b/src/cc/usdt/usdt.cc
@@ -365,6 +365,22 @@ Context::Context(int pid) : pid_(pid), pid_stat_(pid),
     probe->finalize_locations();
 }
 
+Context::Context(int pid, const std::string &bin_path)
+    : pid_(pid), pid_stat_(pid),
+      mount_ns_instance_(new ProcMountNS(pid)), loaded_(false) {
+  std::string full_path = resolve_bin_path(bin_path);
+  if (!full_path.empty()) {
+    if (bcc_elf_foreach_usdt(full_path.c_str(), _each_probe, this) == 0) {
+      cmd_bin_path_ = ebpf::get_pid_exe(pid);
+      if (cmd_bin_path_.empty())
+        return;
+      loaded_ = true;
+    }
+  }
+  for (const auto &probe : probes_)
+    probe->finalize_locations();
+}
+
 Context::~Context() {
   if (pid_stat_ && !pid_stat_->is_stale()) {
     for (auto &p : probes_) p->disable();
@@ -374,8 +390,13 @@ Context::~Context() {
 
 extern "C" {
 
-void *bcc_usdt_new_frompid(int pid) {
-  USDT::Context *ctx = new USDT::Context(pid);
+void *bcc_usdt_new_frompid(int pid, const char *path) {
+  USDT::Context *ctx;
+
+  if (!path)
+    ctx = new USDT::Context(pid);
+  else
+    ctx = new USDT::Context(pid, path);
   if (!ctx->loaded()) {
     delete ctx;
     return nullptr;

diff --git a/src/python/bcc/libbcc.py b/src/python/bcc/libbcc.py
@@ -179,7 +179,7 @@ class bcc_symbol_option(ct.Structure):
 lib.bcc_symcache_refresh.argtypes = [ct.c_void_p]
 
 lib.bcc_usdt_new_frompid.restype = ct.c_void_p
-lib.bcc_usdt_new_frompid.argtypes = [ct.c_int]
+lib.bcc_usdt_new_frompid.argtypes = [ct.c_int, ct.c_char_p]
 
 lib.bcc_usdt_new_frompath.restype = ct.c_void_p
 lib.bcc_usdt_new_frompath.argtypes = [ct.c_char_p]

diff --git a/src/python/bcc/usdt.py b/src/python/bcc/usdt.py
@@ -127,7 +127,10 @@ class USDT(object):
     def __init__(self, pid=None, path=None):
         if pid and pid != -1:
             self.pid = pid
-            self.context = lib.bcc_usdt_new_frompid(pid)
+            if path:
+                self.context = lib.bcc_usdt_new_frompid(pid, path.encode('ascii'))
+            else:
+                self.context = lib.bcc_usdt_new_frompid(pid, ct.c_char_p(0))
             if self.context == None:
                 raise USDTException("USDT failed to instrument PID %d" % pid)
         elif path: