Add support for pkexec to elevate privileges

This seems to be a nice drop-in replacement for kdesu{,do} for
our purposes. And it's much more available compared to the other
helpers. Sadly, it doesn't support the `--attach` mode, but that's
not too bad either.

Fixes: #173

README.md

@@ -307,7 +307,7 @@ when using hotspot's record feature:
 
 To workaround this limitation, hotspot can temporarily elevate the perf privileges.
 This is achieved by applying [these steps](https://superuser.com/questions/980632/run-perf-without-root-right),
-bundled into [a script](scripts/elevate_perf_privileges.sh) that is run via `kdesudo` or `kdesu`.
+bundled into [a script](scripts/elevate_perf_privileges.sh) that is run via `pkexec`, `kdesudo` or `kdesu`.
 The resulting elevated privileges are also required for kernel tracing in general and Off-CPU profiling in particular.
 
 ## Qt Creator

src/perfrecord.cpp

@@ -86,7 +86,7 @@ void PerfRecord::startRecording(bool elevatePrivileges, const QStringList& perfO
         // once perf has started
         const auto sudoBinary = sudoUtil();
         if (sudoBinary.isEmpty()) {
-            emit recordingFailed(tr("No graphical sudo utility found. Please install kdesudo or kdesu."));
+            emit recordingFailed(tr("No sudo utility found. Please install pkexec, kdesudo or kdesu."));
             return;
         }
 
@@ -154,6 +154,10 @@ void PerfRecord::startRecording(bool elevatePrivileges, const QStringList& perfO
                     readSlot();
                     // then delete the process
                     m_elevatePrivilegesProcess->deleteLater();
+
+                    if (!m_perfRecordProcess) {
+                        emit recordingFailed(tr("Failed to elevate privileges."));
+                    }
                 });
 
         m_elevatePrivilegesProcess->start(sudoBinary, options);
@@ -308,7 +312,7 @@ void PerfRecord::sendInput(const QByteArray& input)
 QString PerfRecord::sudoUtil()
 {
     const auto commands = {
-        QStringLiteral("kdesudo"), QStringLiteral("kdesu"),
+        QStringLiteral("pkexec"), QStringLiteral("kdesudo"), QStringLiteral("kdesu"),
         // gksudo / gksu seem to close stdin and thus the elevate script doesn't wait on read
     };
     for (const auto& cmd : commands) {

src/recordpage.cpp

@@ -329,7 +329,7 @@ RecordPage::RecordPage(QWidget* parent)
         ui->elevatePrivilegesCheckBox->setChecked(false);
         ui->elevatePrivilegesCheckBox->setEnabled(false);
         ui->elevatePrivilegesCheckBox->setText(
-            tr("(Note: Install kdesudo or kdesu to temporarily elevate perf privileges.)"));
+            tr("(Note: Install pkexec, kdesudo or kdesu to temporarily elevate perf privileges.)"));
     }
 
     connect(ui->elevatePrivilegesCheckBox, &QCheckBox::toggled, this, &RecordPage::updateOffCpuCheckboxState);

src/recordpage.ui

@@ -223,7 +223,7 @@
       <item row="1" column="0">
        <widget class="QLabel" name="elevatePrivilegesLabel">
         <property name="toolTip">
-         <string>When enabled, hotspot will temporarily elevate the perf privileges via kdesudo or kdesu. This allows you to access advanced perf features such as kernel tracepoints required for Off-CPU profiling.</string>
+         <string>When enabled, hotspot will temporarily elevate the perf privileges via pkexec, kdesudo or kdesu. This allows you to access advanced perf features such as kernel tracepoints required for Off-CPU profiling.</string>
         </property>
         <property name="text">
          <string>Elevate Privileges:</string>
@@ -236,7 +236,7 @@
       <item row="1" column="1">
        <widget class="QCheckBox" name="elevatePrivilegesCheckBox">
         <property name="toolTip">
-         <string>When enabled, hotspot will temporarily elevate the perf privileges via kdesudo or kdesu. This allows you to access advanced perf features such as kernel tracepoints required for Off-CPU profiling.</string>
+         <string>When enabled, hotspot will temporarily elevate the perf privileges via pkexec, kdesudo or kdesu. This allows you to access advanced perf features such as kernel tracepoints required for Off-CPU profiling.</string>
         </property>
        </widget>
       </item>