diff --git a/adb/adb_utils_test.cpp b/adb/adb_utils_test.cpp
index aabc5d7..9daa397 100644
--- a/adb/adb_utils_test.cpp
+++ b/adb/adb_utils_test.cpp
@@ -111,7 +111,7 @@
   EXPECT_EQ("/system/bin", adb_dirname("/system/bin/sh/"));
 }
 
-void test_mkdirs(const std::string basepath) {
+void test_mkdirs(const std::string& basepath) {
   // Test creating a directory hierarchy.
   EXPECT_TRUE(mkdirs(basepath));
   // Test finding an existing directory hierarchy.
diff --git a/adb/commandline.cpp b/adb/commandline.cpp
index ab05b63..74a3451 100644
--- a/adb/commandline.cpp
+++ b/adb/commandline.cpp
@@ -1310,9 +1310,10 @@
         return hint;
     }
 
-    // If there are any slashes in it, assume it's a relative path;
+    // If any of the OS_PATH_SEPARATORS is found, assume it's a relative path;
     // make it absolute.
-    if (hint.find_first_of(OS_PATH_SEPARATORS) != std::string::npos) {
+    // NOLINT: Do not complain if OS_PATH_SEPARATORS has only one character.
+    if (hint.find_first_of(OS_PATH_SEPARATORS) != std::string::npos) {  // NOLINT
         std::string cwd;
         if (!getcwd(&cwd)) {
             fprintf(stderr, "adb: getcwd failed: %s\n", strerror(errno));
diff --git a/adb/file_sync_client.cpp b/adb/file_sync_client.cpp
index 651e8ca..6302eb7 100644
--- a/adb/file_sync_client.cpp
+++ b/adb/file_sync_client.cpp
@@ -433,7 +433,7 @@
 typedef void (sync_ls_cb)(unsigned mode, unsigned size, unsigned time, const char* name);
 
 static bool sync_ls(SyncConnection& sc, const char* path,
-                    std::function<sync_ls_cb> func) {
+                    const std::function<sync_ls_cb>& func) {
     if (!sc.SendRequest(ID_LIST, path)) return false;
 
     while (true) {
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 5dde490..314ed42 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -969,7 +969,7 @@
 }
 
 static void do_for_partition(Transport* transport, const std::string& part, const std::string& slot,
-                             std::function<void(const std::string&)> func, bool force_slot) {
+                             const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
     std::string current_slot;
 
@@ -1002,7 +1002,7 @@
  * partition does not support slots.
  */
 static void do_for_partitions(Transport* transport, const std::string& part, const std::string& slot,
-                              std::function<void(const std::string&)> func, bool force_slot) {
+                              const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
 
     if (slot == "all") {
diff --git a/fastboot/socket_test.cpp b/fastboot/socket_test.cpp
index affbdfd..373abc3 100644
--- a/fastboot/socket_test.cpp
+++ b/fastboot/socket_test.cpp
@@ -34,7 +34,7 @@
 // Creates connected sockets |server| and |client|. Returns true on success.
 bool MakeConnectedSockets(Socket::Protocol protocol, std::unique_ptr<Socket>* server,
                           std::unique_ptr<Socket>* client,
-                          const std::string hostname = "localhost") {
+                          const std::string& hostname = "localhost") {
     *server = Socket::NewServer(protocol, 0);
     if (*server == nullptr) {
         ADD_FAILURE() << "Failed to create server.";
diff --git a/init/service.cpp b/init/service.cpp
index f67af2d..44d9d8c 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -850,7 +850,7 @@
     return nullptr;
 }
 
-void ServiceManager::ForEachService(std::function<void(Service*)> callback) const {
+void ServiceManager::ForEachService(const std::function<void(Service*)>& callback) const {
     for (const auto& s : services_) {
         callback(s.get());
     }
diff --git a/init/service.h b/init/service.h
index aa73aaf..fb03a07 100644
--- a/init/service.h
+++ b/init/service.h
@@ -177,7 +177,7 @@
     Service* FindServiceByName(const std::string& name) const;
     Service* FindServiceByPid(pid_t pid) const;
     Service* FindServiceByKeychord(int keychord_id) const;
-    void ForEachService(std::function<void(Service*)> callback) const;
+    void ForEachService(const std::function<void(Service*)>& callback) const;
     void ForEachServiceInClass(const std::string& classname,
                                void (*func)(Service* svc)) const;
     void ForEachServiceWithFlags(unsigned matchflags,
diff --git a/init/util.cpp b/init/util.cpp
index 80b2325..c1750d2 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -317,7 +317,7 @@
 }
 
 void import_kernel_cmdline(bool in_qemu,
-                           std::function<void(const std::string&, const std::string&, bool)> fn) {
+                           const std::function<void(const std::string&, const std::string&, bool)>& fn) {
     std::string cmdline;
     android::base::ReadFileToString("/proc/cmdline", &cmdline);
 
diff --git a/init/util.h b/init/util.h
index 651e609..29d0497 100644
--- a/init/util.h
+++ b/init/util.h
@@ -55,7 +55,7 @@
 void remove_link(const char *oldpath, const char *newpath);
 int wait_for_file(const char *filename, int timeout);
 void import_kernel_cmdline(bool in_qemu,
-                           std::function<void(const std::string&, const std::string&, bool)>);
+                           const std::function<void(const std::string&, const std::string&, bool)>&);
 int make_dir(const char *path, mode_t mode);
 int restorecon(const char *pathname);
 int restorecon_recursive(const char *pathname);
diff --git a/libbacktrace/backtrace_offline_test.cpp b/libbacktrace/backtrace_offline_test.cpp
index 88a3533..d6dc2c9 100644
--- a/libbacktrace/backtrace_offline_test.cpp
+++ b/libbacktrace/backtrace_offline_test.cpp
@@ -73,7 +73,7 @@
   return ucontext;
 }
 
-static void OfflineBacktraceFunctionCall(std::function<int(void (*)(void*), void*)> function,
+static void OfflineBacktraceFunctionCall(const std::function<int(void (*)(void*), void*)>& function,
                                          std::vector<uintptr_t>* pc_values) {
   // Create a thread to generate the needed stack and registers information.
   g_exit_flag = false;