From 31b4150dc3a789ffaf3f660151971127ac86510d Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Thu, 19 Sep 2024 16:57:32 -0700
Subject: [PATCH] QBenchmarkPerfEventsMeasurer: move the perf_event_attr data
 to the stack
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There's no need for it to be a global variable. It needed to be global
because we configured the event globally before start(), but in commit
4731baf6d3a18857e86cc16de000bc42e84bf6de (6.5.0) we instead introduced
the Q_GLOBAL_STATIC with a QList containing the globally-configured
events.

This is using designated initializers despite their being a C++20
feature, because GCC and Clang have supported them as an extension to C+
+ for a long time. This file has needed that extension since that commit
anyway.

Pick-to: 6.8
Change-Id: I1c9080d23df9f7ba3cbafffd7eae7bd57cd69b67
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
---
 src/testlib/qbenchmarkperfevents.cpp | 32 +++++++++++-----------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/src/testlib/qbenchmarkperfevents.cpp b/src/testlib/qbenchmarkperfevents.cpp
index 98224615f30..b42789ce590 100644
--- a/src/testlib/qbenchmarkperfevents.cpp
+++ b/src/testlib/qbenchmarkperfevents.cpp
@@ -53,26 +53,8 @@ struct PerfEvent
     quint32 type;
     quint64 config;
 };
-static perf_event_attr attr;
 Q_GLOBAL_STATIC(QList<PerfEvent>, eventTypes);
 
-static void initPerf()
-{
-    static bool done;
-    if (!done) {
-        memset(&attr, 0, sizeof attr);
-        attr.size = sizeof attr;
-        attr.read_format = PERF_FORMAT_TOTAL_TIME_ENABLED | PERF_FORMAT_TOTAL_TIME_RUNNING;
-        attr.disabled = true; // we'll enable later
-        attr.inherit = true; // let children processes inherit the monitoring
-        attr.pinned = true; // keep it running in the hardware
-        attr.inherit_stat = true; // aggregate all the info from child processes
-        attr.task = true; // trace fork/exits
-
-        done = true;
-    }
-}
-
 static QList<PerfEvent> defaultCounters()
 {
     return {
@@ -407,7 +389,6 @@ static QTest::QBenchmarkMetric metricForEvent(PerfEvent counter)
 
 void QBenchmarkPerfEventsMeasurer::setCounter(const char *name)
 {
-    initPerf();
     eventTypes->clear();
     std::string_view input = name;
     if (qsizetype idx = input.find(':'); idx >= 0)
@@ -473,7 +454,18 @@ void QBenchmarkPerfEventsMeasurer::init()
 
 void QBenchmarkPerfEventsMeasurer::start()
 {
-    initPerf();
+    QT_WARNING_DISABLE_GCC("-Wmissing-field-initializers")
+    QT_WARNING_DISABLE_CLANG("-Wmissing-field-initializers")
+    perf_event_attr attr = {
+        .size = sizeof attr,
+        .read_format = PERF_FORMAT_TOTAL_TIME_ENABLED | PERF_FORMAT_TOTAL_TIME_RUNNING,
+        .disabled = true,       // we'll enable later
+        .inherit = true,        // let children processes inherit the monitoring
+        .pinned = true,         // keep it running in the hardware
+        .inherit_stat = true,   // aggregate all the info from child processes
+        .task = true,           // trace fork/exits
+    };
+
     QList<PerfEvent> &counters = *eventTypes;
     if (counters.isEmpty())
         counters = defaultCounters();