Make maximum number of frames configurable via a CLI argument

The default stays at 64, but it is now possible to unwind more
frames if desired.

Change-Id: I8da2ea340bf97678b2bbbd495b4864da0cf0fddc
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

3 files changed, 25 insertions, 6 deletions

diff --git a/app/main.cpp b/app/main.cpp
index 41be9ab..fee9055 100644
--- a/app/main.cpp
+++ b/app/main.cpp
@@ -168,6 +168,15 @@ int main(int argc, char *argv[])
                                    QLatin1String("buffer-size"), QLatin1String("10240"));
     parser.addOption(bufferSize);
 
+    QCommandLineOption maxFrames(QLatin1String("max-frames"),
+                                  QCoreApplication::translate(
+                                   "main", "Maximum number of frames that will be unwound."
+                                   " Set the value to -1 to unwind as many frames as possible."
+                                   " Beware that this can then potentially lead to infinite loops "
+                                   " when the stack got corrupted. Default value is 64."),
+                                   QLatin1String("max-frames"), QLatin1String("64"));
+    parser.addOption(maxFrames);
+
     parser.process(app);
 
     QScopedPointer<QFile> outfile;
@@ -203,12 +212,19 @@ int main(int argc, char *argv[])
         return InvalidOption;
     }
 
+    int maxFramesValue = parser.value(maxFrames).toInt(&ok);
+    if (!ok) {
+        qWarning() << "Failed to parse max-frames argument. Expected integer, got:"
+                   << parser.value(maxFrames);
+        return InvalidOption;
+    }
+
     PerfUnwind unwind(outfile.data(), parser.value(sysroot), parser.isSet(debug) ?
                           parser.value(debug) : parser.value(sysroot) + parser.value(debug),
                       parser.value(extra), parser.value(appPath), parser.isSet(kallsymsPath)
                         ? parser.value(kallsymsPath)
                         : parser.value(sysroot) + parser.value(kallsymsPath),
-                      parser.isSet(printStats), maxEventBufferSize);
+                      parser.isSet(printStats), maxEventBufferSize, maxFramesValue);
 
     PerfHeader header(infile.data());
     PerfAttributes attributes;
diff --git a/app/perfunwind.cpp b/app/perfunwind.cpp
index 5975968..37e418c 100644
--- a/app/perfunwind.cpp
+++ b/app/perfunwind.cpp
@@ -76,13 +76,15 @@ void PerfUnwind::Stats::finishedRound()
 
 PerfUnwind::PerfUnwind(QIODevice *output, const QString &systemRoot, const QString &debugPath,
                        const QString &extraLibsPath, const QString &appPath,
-                       const QString &kallsymsPath, bool printStats, uint maxEventBufferSize) :
+                       const QString &kallsymsPath, bool printStats, uint maxEventBufferSize,
+                       int maxFrames) :
     m_output(output), m_architecture(PerfRegisterInfo::ARCH_INVALID), m_systemRoot(systemRoot),
     m_extraLibsPath(extraLibsPath), m_appPath(appPath), m_debugPath(debugPath), m_kallsyms(kallsymsPath),
     m_maxEventBufferSize(maxEventBufferSize), m_eventBufferSize(0), m_lastFlushMaxTime(0)
 {
     m_stats.enabled = printStats;
     m_currentUnwind.unwind = this;
+    m_currentUnwind.maxFrames = maxFrames;
     m_offlineCallbacks.find_elf = dwfl_build_id_find_elf;
     m_offlineCallbacks.find_debuginfo =  dwfl_standard_find_debuginfo;
     m_offlineCallbacks.section_address = dwfl_offline_section_address;
@@ -288,7 +290,7 @@ static int frameCallback(Dwfl_Frame *state, void *arg)
 
     bool isactivation;
     if (!dwfl_frame_pc(state, &pc, &isactivation)
-            || ui->frames.length() > PerfUnwind::s_maxFrames
+            || (ui->maxFrames != -1 && ui->frames.length() > ui->maxFrames)
             || pc == 0) {
         ui->firstGuessedFrame = ui->frames.length();
         qWarning() << dwfl_errmsg(dwfl_errno()) << ui->firstGuessedFrame;
diff --git a/app/perfunwind.h b/app/perfunwind.h
index c80fb47..ffff2f2 100644
--- a/app/perfunwind.h
+++ b/app/perfunwind.h
@@ -89,23 +89,24 @@ public:
     };
 
     struct UnwindInfo {
-        UnwindInfo() : frames(0), unwind(0), sample(0),
+        UnwindInfo() : frames(0), unwind(0), sample(0), maxFrames(64),
             firstGuessedFrame(-1), isInterworking(false) {}
 
         QHash<quint32, QHash<quint64, Dwarf_Word>> stackValues;
         QVector<qint32> frames;
         PerfUnwind *unwind;
         const PerfRecordSample *sample;
+        int maxFrames;
         int firstGuessedFrame;
         bool isInterworking;
     };
 
     static const quint32 s_kernelPid = std::numeric_limits<quint32>::max();
-    static const int s_maxFrames = 64;
 
     PerfUnwind(QIODevice *output, const QString &systemRoot, const QString &debugInfo,
                const QString &extraLibs, const QString &appPath,
-               const QString &kallsymsPath, bool printStats, uint maxEventBufferSize);
+               const QString &kallsymsPath, bool printStats, uint maxEventBufferSize,
+               int maxFrames);
     ~PerfUnwind();
 
     PerfRegisterInfo::Architecture architecture() const { return m_architecture; }