From 0aac3074b607898d988aab6138eedfc0b94bccf2 Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Wed, 12 Mar 2025 17:57:02 -0400
Subject: [PATCH] Fix recursive error on virtual interfaces (#5854).

---
 Changes                                   |  1 +
 src/V3LinkCells.cpp                       |  6 +--
 test_regress/t/t_virtual_interface_pkg.py | 18 +++++++
 test_regress/t/t_virtual_interface_pkg.v  | 64 +++++++++++++++++++++++
 4 files changed, 86 insertions(+), 3 deletions(-)
 create mode 100755 test_regress/t/t_virtual_interface_pkg.py
 create mode 100644 test_regress/t/t_virtual_interface_pkg.v

diff --git a/Changes b/Changes
index 33c252fda..80261cb9c 100644
--- a/Changes
+++ b/Changes
@@ -42,6 +42,7 @@ Verilator 5.035 devel
 * Fix NBA shared flag reuse (#5848). [Geza Lore]
 * Fix removal of callbacks no longer in current list (#5851) (#5852). [Gilberto Abram]
 * Fix segmentation fault on member compare (#5853).
+* Fix recursive error on virtual interfaces (#5854). [Yilou Wang]
 
 
 Verilator 5.034 2025-02-24
diff --git a/src/V3LinkCells.cpp b/src/V3LinkCells.cpp
index 6e3d13fe3..21bec741b 100644
--- a/src/V3LinkCells.cpp
+++ b/src/V3LinkCells.cpp
@@ -125,8 +125,8 @@ class LinkCellsVisitor final : public VNVisitor {
         return nodep->user1u().toGraphVertex();
     }
     void newEdge(V3GraphVertex* fromp, V3GraphVertex* top, int weight, bool cuttable) {
-        UINFO(9, "newEdge " << fromp->name() << " -> " << top->name() << endl);
-        new V3GraphEdge{&m_graph, fromp, top, weight, cuttable};
+        V3GraphEdge* const edgep = new V3GraphEdge{&m_graph, fromp, top, weight, cuttable};
+        UINFO(9, "    newEdge " << edgep << " " << fromp->name() << " -> " << top->name() << endl);
     }
 
     AstNodeModule* findModuleSym(const string& modName) {
@@ -237,7 +237,7 @@ class LinkCellsVisitor final : public VNVisitor {
         if (modp) {
             if (VN_IS(modp, Iface)) {
                 // Track module depths, so can sort list from parent down to children
-                newEdge(vertex(m_modp), vertex(modp), 1, false);
+                if (!nodep->isVirtual()) { newEdge(vertex(m_modp), vertex(modp), 1, false); }
                 if (!nodep->cellp()) nodep->ifacep(VN_AS(modp, Iface));
             } else if (VN_IS(modp, NotFoundModule)) {  // Will error out later
             } else {
diff --git a/test_regress/t/t_virtual_interface_pkg.py b/test_regress/t/t_virtual_interface_pkg.py
new file mode 100755
index 000000000..bd059b0f2
--- /dev/null
+++ b/test_regress/t/t_virtual_interface_pkg.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=['--binary'])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_virtual_interface_pkg.v b/test_regress/t/t_virtual_interface_pkg.v
new file mode 100644
index 000000000..0167863c1
--- /dev/null
+++ b/test_regress/t/t_virtual_interface_pkg.v
@@ -0,0 +1,64 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Yilou Wang.
+// SPDX-License-Identifier: CC0-1.0
+
+package my_pkg;
+
+   virtual class CallBackBase;
+      pure virtual function void add(int a, int b);
+   endclass
+
+   class my_class extends CallBackBase;
+      virtual my_interface vif;
+
+      function new(virtual my_interface vif);
+         this.vif = vif;
+         $display("my_class::new");
+         vif.register_callback(this);
+      endfunction
+
+      function void add(int a, int b);
+         // $display("a + b = %0d", a + b);
+      endfunction
+   endclass
+
+endpackage
+
+interface my_interface;
+   import my_pkg::*;
+   CallBackBase callback_obj;
+
+   function void register_callback(CallBackBase obj);
+      callback_obj = obj;
+   endfunction
+
+   logic clk;
+   always @(posedge clk) begin
+      if (callback_obj != null)
+        callback_obj.add(1, 2);
+      else $display("callback_obj is null");
+   end
+endinterface
+
+module t;
+   import my_pkg::*;
+   logic clk = 0;
+   my_interface vif();
+   my_class cl;
+
+   assign vif.clk = clk;
+
+   initial begin
+      forever #5 clk = ~clk;
+   end
+
+   initial begin
+      #10;
+      cl = new(vif);
+      #100;
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule