Add basic support for PERF_FORMAT_LOST in PerfRecordSample parsing

Without this, we incorrectly interpreted the binary data stream
leading to totally bogus failures. Most notably, we ended up using
the id of the PERF_FORMAT_LOST as the number of callchain samples
which was really bad as that number is often very large, leading to
excessive memory consumption.

We do not actually read the lost values anywhere, this can come
in a follow-up patch next.

Fixes: KDAB/hotspot#578
Change-Id: I3f73a5f02507fd31e21577585dd89679312782d9

app/perfattributes.h

@@ -58,8 +58,9 @@ class PerfEventAttributes {
         FORMAT_TOTAL_TIME_RUNNING = 1U << 1,
         FORMAT_ID                 = 1U << 2,
         FORMAT_GROUP              = 1U << 3,
+        FORMAT_LOST               = 1U << 4,
 
-        FORMAT_MAX                = 1U << 4
+        FORMAT_MAX                = 1U << 5
     };
 
     /*

app/perfdata.cpp

@@ -646,6 +646,7 @@ QDataStream &operator>>(QDataStream &stream, PerfRecordSample &record)
     quint32 waste32;
 
     const quint64 sampleType = record.m_sampleId.sampleType();
+    const auto withLostFormat = record.m_readFormat & PerfEventAttributes::FORMAT_LOST;
 
     if (sampleType & PerfEventAttributes::SAMPLE_IDENTIFIER)
         stream >> record.m_sampleId.m_id;
@@ -682,10 +683,14 @@ QDataStream &operator>>(QDataStream &stream, PerfRecordSample &record)
         if (record.m_readFormat & PerfEventAttributes::FORMAT_GROUP) {
             while (numFormats-- > 0) {
                 stream >> format.value >> format.id;
+                if (withLostFormat)
+                    stream  >> format.lost;
                 record.m_readFormats << format;
             }
         } else {
             stream >> format.id;
+            if (withLostFormat)
+                stream >> format.lost;
             record.m_readFormats << format;
         }
     }

app/perfdata.h

@@ -505,6 +505,7 @@ class PerfRecordSample : public PerfRecord {
     struct ReadFormat {
         quint64 value;
         quint64 id;
+        quint64 lost;
     };
 
     QList<ReadFormat> readFormats() const { return m_readFormats; }