Avoid stack overflows during GC runs

When marking very large objects, the old code could overflow
the GC stack, as it would push all it's children onto the GC
stack.

Be more careful about this and drain the mark stack from time
to time if required.

Change-Id: If11ca521f405ce63b894d4e43a83b68d33a844af
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 15 insertions, 3 deletions

diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index c025dd09a4..f117bbc10f 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -885,9 +885,21 @@ void MemoryManager::drainMarkStack(Value *markBase)
                     ValueArray<0> *a = reinterpret_cast<ValueArray<0> *>(mem);
                     Value *v = a->values;
                     const Value *end = v + a->alloc;
-                    while (v < end) {
-                        v->mark(engine);
-                        ++v;
+                    if (a->alloc > 32*1024) {
+                        // drain from time to time to avoid overflows in the js stack
+                        Value *currentBase = engine->jsStackTop;
+                        while (v < end) {
+                            v->mark(engine);
+                            ++v;
+                            if (engine->jsStackTop >= currentBase + 32*1024)
+                                drainMarkStack(currentBase);
+                        }
+
+                    } else {
+                        while (v < end) {
+                            v->mark(engine);
+                            ++v;
+                        }
                     }
                     break;
                 }