[RF] Fix dangling stack normSet after xRooNode::BuildHistogram

roofit/roofitcore/inc/RooAbsArg.h

@@ -492,6 +492,7 @@ class RooAbsArg : public TNamed, public RooPrintable {
 
    RooAbsProxy *getProxy(Int_t index) const;
    Int_t numProxies() const;
+   void setProxyNormSet(const RooArgSet *nset);
 
    /// De-duplicated pointer to this object's name.
    /// This can be used for fast name comparisons.
@@ -582,7 +583,6 @@ class RooAbsArg : public TNamed, public RooPrintable {
    void unRegisterProxy(RooArgProxy &proxy);
    void unRegisterProxy(RooSetProxy &proxy);
    void unRegisterProxy(RooListProxy &proxy);
-   void setProxyNormSet(const RooArgSet *nset);
 
    // Attribute list
    std::set<std::string> _boolAttrib;                // Boolean attributes

roofit/roofitcore/src/RooAbsArg.cxx

@@ -1284,7 +1284,10 @@ Int_t RooAbsArg::numProxies() const
 }
 
 /// Forward a change in the cached normalization argset
-/// to all the registered proxies.
+/// to all the registered proxies. Passing `nullptr` makes this object forget
+/// any normalization set previously passed to `getVal()`, which is required if
+/// that set may not outlive this object (e.g. it lived on the caller's stack),
+/// as the proxies only keep a bare pointer to it.
 
 void RooAbsArg::setProxyNormSet(const RooArgSet *nset)
 {

roofit/xroofit/src/xRooNode.cxx

@@ -9355,6 +9355,25 @@ TH1 *xRooNode::BuildHistogram(RooAbsLValue *v, bool empty, bool errors, int binS
       }
    }
 
+   // We evaluated the above with `normSet`, which lives on this function's stack.
+   // RooFit proxies only cache a bare pointer to the last normSet and re-use it
+   // later (e.g. RooProduct::evaluate reads back _compRSet.nset()), so before it
+   // goes out of scope we must clear it everywhere it could have been cached,
+   // otherwise a later evaluation dereferences freed stack ("use of uninitialised
+   // value" in valgrind). sterilize() only walks clients, but getVal() propagates
+   // the normSet to the servers of the evaluated function, so reset those here.
+   {
+      RooArgSet evaluatedNodes;
+      for (RooAbsArg *treeRoot : {static_cast<RooAbsArg *>(rar), static_cast<RooAbsArg *>(p),
+                                  static_cast<RooAbsArg *>(oldrar), _coefs.get<RooAbsArg>()}) {
+         if (treeRoot)
+            treeRoot->treeNodeServerList(&evaluatedNodes);
+      }
+      for (RooAbsArg *node : evaluatedNodes) {
+         node->setProxyNormSet(nullptr);
+      }
+   }
+
    if (oldrar) {
       std::vector<RooAbsArg *> extra;
       if (auto s = dynamic_cast<RooSimultaneous *>(rar)) {