Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -727,9 +727,10 @@
 // filling this information.
 class ListOfModules {
  public:
-  ListOfModules() : modules_(kInitialCapacity) {}
+  ListOfModules() : initialized(false) {}
   ~ListOfModules() { clear(); }
   void init();
+  void fallbackInit();  // Uses fallback init if available, otherwise clears
   const LoadedModule *begin() const { return modules_.begin(); }
   LoadedModule *begin() { return modules_.begin(); }
   const LoadedModule *end() const { return modules_.end(); }
@@ -745,10 +746,15 @@
     for (auto &module : modules_) module.clear();
     modules_.clear();
   }
+  void clearOrInit() {
+    initialized ? clear() : modules_.Initialize(kInitialCapacity);
+    initialized = true;
+  }
 
-  InternalMmapVector<LoadedModule> modules_;
+  InternalMmapVectorNoCtor<LoadedModule> modules_;
   // We rarely have more than 16K loaded modules.
   static const uptr kInitialCapacity = 1 << 14;
+  bool initialized;
 };
 
 // Callback type for iterating over a set of memory ranges.
Index: lib/sanitizer_common/sanitizer_linux_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_linux_libcdep.cc
+++ lib/sanitizer_common/sanitizer_linux_libcdep.cc
@@ -424,7 +424,7 @@
 # endif
 
 struct DlIteratePhdrData {
-  InternalMmapVector<LoadedModule> *modules;
+  InternalMmapVectorNoCtor<LoadedModule> *modules;
   bool first;
 };
 
@@ -473,13 +473,13 @@
 #endif
 }
 
-static void procmapsInit(InternalMmapVector<LoadedModule> *modules) {
+static void procmapsInit(InternalMmapVectorNoCtor<LoadedModule> *modules) {
   MemoryMappingLayout memory_mapping(false);
   memory_mapping.DumpListOfModules(modules);
 }
 
 void ListOfModules::init() {
-  clear();
+  clearOrInit();
   if (requiresProcmaps()) {
     procmapsInit(&modules_);
   } else {
@@ -488,6 +488,13 @@
   }
 }
 
+// When a custom loader is used, dl_iterate_phdr may not contain the full
+// list of modules. Allow callers to fall back to using procmaps.
+void ListOfModules::fallbackInit() {
+  clearOrInit();
+  if (!requiresProcmaps()) procmapsInit(&modules_);
+}
+
 // getrusage does not give us the current RSS, only the max RSS.
 // Still, this is better than nothing if /proc/self/statm is not available
 // for some reason, e.g. due to a sandbox.
Index: lib/sanitizer_common/sanitizer_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_mac.cc
+++ lib/sanitizer_common/sanitizer_mac.cc
@@ -411,11 +411,13 @@
 }
 
 void ListOfModules::init() {
-  clear();
+  clearOrInit();
   MemoryMappingLayout memory_mapping(false);
   memory_mapping.DumpListOfModules(&modules_);
 }
 
+void ListOfModules::fallbackInit() { clear(); }
+
 static HandleSignalMode GetHandleSignalModeImpl(int signum) {
   switch (signum) {
     case SIGABRT:
Index: lib/sanitizer_common/sanitizer_procmaps.h
===================================================================
--- lib/sanitizer_common/sanitizer_procmaps.h
+++ lib/sanitizer_common/sanitizer_procmaps.h
@@ -76,7 +76,7 @@
   static void CacheMemoryMappings();
 
   // Adds all mapped objects into a vector.
-  void DumpListOfModules(InternalMmapVector<LoadedModule> *modules);
+  void DumpListOfModules(InternalMmapVectorNoCtor<LoadedModule> *modules);
 
  private:
   void LoadFromCache();
Index: lib/sanitizer_common/sanitizer_procmaps_common.cc
===================================================================
--- lib/sanitizer_common/sanitizer_procmaps_common.cc
+++ lib/sanitizer_common/sanitizer_procmaps_common.cc
@@ -120,7 +120,7 @@
 }
 
 void MemoryMappingLayout::DumpListOfModules(
-    InternalMmapVector<LoadedModule> *modules) {
+    InternalMmapVectorNoCtor<LoadedModule> *modules) {
   Reset();
   InternalScopedString module_name(kMaxPathLength);
   MemoryMappedSegment segment(module_name.data(), module_name.size());
Index: lib/sanitizer_common/sanitizer_procmaps_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_procmaps_mac.cc
+++ lib/sanitizer_common/sanitizer_procmaps_mac.cc
@@ -353,7 +353,7 @@
 }
 
 void MemoryMappingLayout::DumpListOfModules(
-    InternalMmapVector<LoadedModule> *modules) {
+    InternalMmapVectorNoCtor<LoadedModule> *modules) {
   Reset();
   InternalScopedString module_name(kMaxPathLength);
   MemoryMappedSegment segment(module_name.data(), kMaxPathLength);
Index: lib/sanitizer_common/sanitizer_symbolizer.h
===================================================================
--- lib/sanitizer_common/sanitizer_symbolizer.h
+++ lib/sanitizer_common/sanitizer_symbolizer.h
@@ -152,6 +152,7 @@
                                          uptr *module_offset,
                                          ModuleArch *module_arch);
   ListOfModules modules_;
+  ListOfModules fallback_modules_;
   // If stale, need to reload the modules before looking up addresses.
   bool modules_fresh_;
 
Index: lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
+++ lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
@@ -165,6 +165,7 @@
 
 void Symbolizer::RefreshModules() {
   modules_.init();
+  fallback_modules_.fallbackInit();
   RAW_CHECK(modules_.size() > 0);
   modules_fresh_ = true;
 }
@@ -198,6 +199,10 @@
     if (module) return module;
   }
 #endif
+
+  if (fallback_modules_.size()) {
+    module = SearchForModule(fallback_modules_, address);
+  }
   return module;
 }
 
Index: lib/sanitizer_common/sanitizer_win.cc
===================================================================
--- lib/sanitizer_common/sanitizer_win.cc
+++ lib/sanitizer_common/sanitizer_win.cc
@@ -524,7 +524,7 @@
 }
 
 void ListOfModules::init() {
-  clear();
+  clearOrInit();
   HANDLE cur_process = GetCurrentProcess();
 
   // Query the list of modules.  Start by assuming there are no more than 256
@@ -583,7 +583,9 @@
     modules_.push_back(cur_module);
   }
   UnmapOrDie(hmodules, modules_buffer_size);
-};
+}
+
+void ListOfModules::fallbackInit() { clear(); }
 
 // We can't use atexit() directly at __asan_init time as the CRT is not fully
 // initialized at this point.  Place the functions into a vector and use