Add environment variable for configure maxJSStackSize and maxGCStackSize

QMLEngine by default allocates 4 MB for javascript stack and garbage
collection stack takes 2 MB. It is a lot of memory for platforms without
virtual memory.

Change-Id: I1575dd9584898dca33df66704f716c7b5a7c01c1
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

3 files changed, 33 insertions, 12 deletions

diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 5fa44ec1ef..0d3ae71b05 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -206,10 +206,19 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
 #endif
     , m_qmlEngine(nullptr)
 {
+    bool ok = false;
+    const int envMaxJSStackSize = qEnvironmentVariableIntValue("QV4_JS_MAX_STACK_SIZE", &ok);
+    if (ok && envMaxJSStackSize > 0)
+        m_maxJSStackSize = envMaxJSStackSize;
+
+    const int envMaxGCStackSize = qEnvironmentVariableIntValue("QV4_GC_MAX_STACK_SIZE", &ok);
+    if (ok && envMaxGCStackSize > 0)
+        m_maxGCStackSize = envMaxGCStackSize;
+
     memoryManager = new QV4::MemoryManager(this);
 
     if (maxCallDepth == -1) {
-        bool ok = false;
+        ok = false;
         maxCallDepth = qEnvironmentVariableIntValue("QV4_MAX_CALL_DEPTH", &ok);
         if (!ok || maxCallDepth <= 0) {
 #if defined(QT_NO_DEBUG) && !defined(__SANITIZE_ADDRESS__) && !QT_HAS_FEATURE(address_sanitizer)
@@ -223,24 +232,24 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
     Q_ASSERT(maxCallDepth > 0);
 
     // reserve space for the JS stack
-    // we allow it to grow to a bit more than JSStackLimit, as we can overshoot due to ScopedValues
+    // we allow it to grow to a bit more than m_maxJSStackSize, as we can overshoot due to ScopedValues
     // allocated outside of JIT'ed methods.
-    *jsStack = WTF::PageAllocation::allocate(JSStackLimit + 256*1024, WTF::OSAllocator::JSVMStackPages,
+    *jsStack = WTF::PageAllocation::allocate(m_maxJSStackSize + 256*1024, WTF::OSAllocator::JSVMStackPages,
                                              /* writable */ true, /* executable */ false,
                                              /* includesGuardPages */ true);
     jsStackBase = (Value *)jsStack->base();
 #ifdef V4_USE_VALGRIND
-    VALGRIND_MAKE_MEM_UNDEFINED(jsStackBase, JSStackLimit + 256*1024);
+    VALGRIND_MAKE_MEM_UNDEFINED(jsStackBase, m_maxJSStackSize + 256*1024);
 #endif
 
     jsStackTop = jsStackBase;
 
-    *gcStack = WTF::PageAllocation::allocate(GCStackLimit, WTF::OSAllocator::JSVMStackPages,
+    *gcStack = WTF::PageAllocation::allocate(m_maxGCStackSize, WTF::OSAllocator::JSVMStackPages,
                                              /* writable */ true, /* executable */ false,
                                              /* includesGuardPages */ true);
 
     {
-        bool ok = false;
+        ok = false;
         jitCallCountThreshold = qEnvironmentVariableIntValue("QV4_JIT_CALL_THRESHOLD", &ok);
         if (!ok)
             jitCallCountThreshold = 3;
@@ -258,7 +267,7 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
     jsSymbols = jsAlloca(NJSSymbols);
 
     // set up stack limits
-    jsStackLimit = jsStackBase + JSStackLimit/sizeof(Value);
+    jsStackLimit = jsStackBase + m_maxJSStackSize/sizeof(Value);
 
     identifierTable = new IdentifierTable(this);
 
@@ -1737,6 +1746,16 @@ QV4::ReturnedValue ExecutionEngine::metaTypeToJS(int type, const void *data)
     return fromVariant(variant);
 }
 
+int ExecutionEngine::maxJSStackSize() const
+{
+    return m_maxJSStackSize;
+}
+
+int ExecutionEngine::maxGCStackSize() const
+{
+    return m_maxGCStackSize;
+}
+
 ReturnedValue ExecutionEngine::global()
 {
     return globalObject->asReturnedValue();
diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index f8ac0e0268..ce25ab16b1 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -170,10 +170,6 @@ public:
 
     WTF::BumpPointerAllocator *bumperPointerAllocator; // Used by Yarr Regex engine.
 
-    enum {
-        JSStackLimit = 4*1024*1024,
-        GCStackLimit = 2*1024*1024
-    };
     WTF::PageAllocation *jsStack;
 
     WTF::PageAllocation *gcStack;
@@ -641,6 +637,9 @@ public:
     bool metaTypeFromJS(const Value *value, int type, void *data);
     QV4::ReturnedValue metaTypeToJS(int type, const void *data);
 
+    int maxJSStackSize() const;
+    int maxGCStackSize() const;
+
     bool checkStackLimits();
 
     bool canJIT(Function *f = nullptr)
@@ -734,6 +733,9 @@ private:
     QHash<QString, quint32> m_consoleCount;
 
     QVector<Deletable *> m_extensionData;
+
+    int m_maxJSStackSize = 4 * 1024 * 1024;
+    int m_maxGCStackSize = 2 * 1024 * 1024;
 };
 
 #define CHECK_STACK_LIMITS(v4) if ((v4)->checkStackLimits()) return Encode::undefined(); \
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index 9288d3e3b6..2c96d6fd3b 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -847,7 +847,7 @@ MarkStack::MarkStack(ExecutionEngine *engine)
 {
     base = (Heap::Base **)engine->gcStack->base();
     top = base;
-    limit = base + ExecutionEngine::GCStackLimit/sizeof(Heap::Base)*3/4;
+    limit = base + engine->maxGCStackSize()/sizeof(Heap::Base)*3/4;
 }
 
 void MarkStack::drain()