QML: Encode "missing" line number as negated address of stack frame

This way we can identify which entry in a stack frame to amend when
processing an exception in generated code. However, negative line
numbers are also used to signal the position of "Ret" instructions.
Since you cannot throw an exception from a "Ret" instruction, those
cannot collide, but we cannot qAbs() the line number anymore when saving
it in the stack trace. We have to qAbs() it in all the places where it's
read.

Pick-to: 6.5
Fixes: QTBUG-112946
Change-Id: I24dc4008fb7eab38e4d24e70211c22e46f1b72a7
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

7 files changed, 40 insertions, 18 deletions

diff --git a/src/qml/jsapi/qjsengine.cpp b/src/qml/jsapi/qjsengine.cpp
index eda1c4c931..eca6562b90 100644
--- a/src/qml/jsapi/qjsengine.cpp
+++ b/src/qml/jsapi/qjsengine.cpp
@@ -530,7 +530,7 @@ QJSValue QJSEngine::evaluate(const QString& program, const QString& fileName, in
             for (auto &&frame: trace)
                 exceptionStackTrace->push_back(QString::fromLatin1("%1:%2:%3:%4").arg(
                                           frame.function,
-                                          QString::number(frame.line),
+                                          QString::number(qAbs(frame.line)),
                                           QString::number(frame.column),
                                           frame.source)
                                       );
diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index d1ddde7089..f1a2bc0947 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -1234,7 +1234,7 @@ StackTrace ExecutionEngine::stackTrace(int frameLimit) const
         QV4::StackFrame frame;
         frame.source = f->source();
         frame.function = f->function();
-        frame.line = qAbs(f->lineNumber());
+        frame.line = f->lineNumber();
         frame.column = -1;
         stack.append(frame);
         if (f->isJSTypesFrame()) {
@@ -1272,7 +1272,7 @@ static inline char *v4StackTrace(const ExecutionContext *context)
             const QString fileName = url.isLocalFile() ? url.toLocalFile() : url.toString();
             str << "frame={level=\"" << i << "\",func=\"" << stackTrace.at(i).function
                 << "\",file=\"" << fileName << "\",fullname=\"" << fileName
-                << "\",line=\"" << stackTrace.at(i).line << "\",language=\"js\"}";
+                << "\",line=\"" << qAbs(stackTrace.at(i).line) << "\",language=\"js\"}";
         }
     }
     str << ']';
@@ -1467,7 +1467,7 @@ QQmlError ExecutionEngine::catchExceptionAsQmlError()
     if (!trace.isEmpty()) {
         QV4::StackFrame frame = trace.constFirst();
         error.setUrl(QUrl(frame.source));
-        error.setLine(frame.line);
+        error.setLine(qAbs(frame.line));
         error.setColumn(frame.column);
     }
     QV4::Scoped<QV4::ErrorObject> errorObj(scope, exception);
diff --git a/src/qml/jsruntime/qv4errorobject.cpp b/src/qml/jsruntime/qv4errorobject.cpp
index 516c81864f..35b5952d38 100644
--- a/src/qml/jsruntime/qv4errorobject.cpp
+++ b/src/qml/jsruntime/qv4errorobject.cpp
@@ -56,7 +56,7 @@ void Heap::ErrorObject::init(const Value &message, ErrorType t)
     e->d()->stackTrace = new StackTrace(scope.engine->stackTrace());
     if (!e->d()->stackTrace->isEmpty()) {
         setProperty(scope.engine, QV4::ErrorObject::Index_FileName, scope.engine->newString(e->d()->stackTrace->at(0).source));
-        setProperty(scope.engine, QV4::ErrorObject::Index_LineNumber, Value::fromInt32(e->d()->stackTrace->at(0).line));
+        setProperty(scope.engine, QV4::ErrorObject::Index_LineNumber, Value::fromInt32(qAbs(e->d()->stackTrace->at(0).line)));
     }
 
     if (!message.isUndefined())
@@ -84,7 +84,7 @@ void Heap::ErrorObject::init(const Value &message, const QString &fileName, int
 
     Q_ASSERT(!e->d()->stackTrace->isEmpty());
     setProperty(scope.engine, QV4::ErrorObject::Index_FileName, scope.engine->newString(e->d()->stackTrace->at(0).source));
-    setProperty(scope.engine, QV4::ErrorObject::Index_LineNumber, Value::fromInt32(e->d()->stackTrace->at(0).line));
+    setProperty(scope.engine, QV4::ErrorObject::Index_LineNumber, Value::fromInt32(qAbs(e->d()->stackTrace->at(0).line)));
 
     if (!message.isUndefined())
         setProperty(scope.engine, QV4::ErrorObject::Index_Message, message);
diff --git a/src/qml/jsruntime/qv4stackframe.cpp b/src/qml/jsruntime/qv4stackframe.cpp
index e8ff9a89bc..5117e745a0 100644
--- a/src/qml/jsruntime/qv4stackframe.cpp
+++ b/src/qml/jsruntime/qv4stackframe.cpp
@@ -40,7 +40,7 @@ int CppStackFrame::lineNumber() const
 {
     if (auto *line = lineAndStatement(this))
         return line->line;
-    return -1;
+    return missingLineNumber();
 }
 
 int CppStackFrame::statementNumber() const
@@ -50,6 +50,15 @@ int CppStackFrame::statementNumber() const
     return -1;
 }
 
+int CppStackFrame::missingLineNumber() const
+{
+    // Remove the first bit so that we can cast to positive int and negate.
+    // Remove the last bit so that it can't be -1.
+    const int result = -int(quintptr(this) & 0x7ffffffe);
+    Q_ASSERT(result < -1);
+    return result;
+}
+
 ReturnedValue QV4::CppStackFrame::thisObject() const
 {
     if (isJSTypesFrame())
diff --git a/src/qml/jsruntime/qv4stackframe_p.h b/src/qml/jsruntime/qv4stackframe_p.h
index 2777d79c31..9c3e3700ce 100644
--- a/src/qml/jsruntime/qv4stackframe_p.h
+++ b/src/qml/jsruntime/qv4stackframe_p.h
@@ -83,6 +83,8 @@ struct Q_QML_PRIVATE_EXPORT CppStackFrame : protected CppStackFrameBase
     int lineNumber() const;
     int statementNumber() const;
 
+    int missingLineNumber() const;
+
     CppStackFrame *parentFrame() const { return parent; }
     void setParentFrame(CppStackFrame *parentFrame) { parent = parentFrame; }
 
diff --git a/src/qml/qml/qqml.cpp b/src/qml/qml/qqml.cpp
index 4304934019..ca9c1d8e52 100644
--- a/src/qml/qml/qqml.cpp
+++ b/src/qml/qml/qqml.cpp
@@ -1234,13 +1234,25 @@ static bool initValueLookup(QV4::Lookup *l, QV4::ExecutableCompilationUnit *comp
 
 static void amendException(QV4::ExecutionEngine *engine)
 {
+    const int missingLineNumber = engine->currentStackFrame->missingLineNumber();
     const int lineNumber = engine->currentStackFrame->lineNumber();
-    engine->exceptionStackTrace.front().line = lineNumber;
+    Q_ASSERT(missingLineNumber != lineNumber);
+
+    auto amendStackTrace = [&](QV4::StackTrace *stackTrace) {
+        for (auto it = stackTrace->begin(), end = stackTrace->end(); it != end; ++it) {
+            if (it->line == missingLineNumber) {
+                it->line = lineNumber;
+                break;
+            }
+        }
+    };
+
+    amendStackTrace(&engine->exceptionStackTrace);
 
     QV4::Scope scope(engine);
     QV4::Scoped<QV4::ErrorObject> error(scope, *engine->exceptionValue);
     if (error) // else some other value was thrown
-        error->d()->stackTrace->front().line = lineNumber;
+        amendStackTrace(error->d()->stackTrace);
 }
 
 
diff --git a/src/qml/qml/qqmlbuiltinfunctions.cpp b/src/qml/qml/qqmlbuiltinfunctions.cpp
index 9d75073e84..ebb5c301db 100644
--- a/src/qml/qml/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/qqmlbuiltinfunctions.cpp
@@ -1755,15 +1755,14 @@ static QString jsStack(QV4::ExecutionEngine *engine) {
         const QV4::StackFrame &frame = stackTrace.at(i);
 
         QString stackFrame;
-        if (frame.column >= 0)
-            stackFrame = QStringLiteral("%1 (%2:%3:%4)").arg(frame.function,
-                                                             frame.source,
-                                                             QString::number(frame.line),
-                                                             QString::number(frame.column));
-        else
-            stackFrame = QStringLiteral("%1 (%2:%3)").arg(frame.function,
-                                                             frame.source,
-                                                             QString::number(frame.line));
+        if (frame.column >= 0) {
+            stackFrame = QStringLiteral("%1 (%2:%3:%4)").arg(
+                frame.function, frame.source,
+                QString::number(qAbs(frame.line)), QString::number(frame.column));
+        } else {
+            stackFrame = QStringLiteral("%1 (%2:%3)").arg(
+                frame.function, frame.source, QString::number(qAbs(frame.line)));
+        }
 
         if (i)
             stack += QLatin1Char('\n');