Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -692,6 +692,7 @@
   ListOfModules() : modules_(kInitialCapacity) {}
   ~ListOfModules() { clear(); }
   void init();
+  bool enableFallbackInit();
   const LoadedModule *begin() const { return modules_.begin(); }
   LoadedModule *begin() { return modules_.begin(); }
   const LoadedModule *end() const { return modules_.end(); }
@@ -711,6 +712,8 @@
   InternalMmapVector<LoadedModule> modules_;
   // We rarely have more than 16K loaded modules.
   static const uptr kInitialCapacity = 1 << 14;
+
+  bool use_fallback_init_ = false;
 };
 
 // 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
@@ -26,6 +26,7 @@
 #include "sanitizer_placement_new.h"
 #include "sanitizer_procmaps.h"
 #include "sanitizer_stacktrace.h"
+#include "sanitizer_symbolizer.h"
 
 #include <dlfcn.h>  // for dlsym()
 #include <link.h>
@@ -457,6 +458,18 @@
   return 0;
 }
 
+// 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.
+// Returns false if the fallback init is already enabled to allow callers
+// to prevent unnecessary reloads.
+bool ListOfModules::enableFallbackInit() {
+  if (use_fallback_init_) {
+    return false;
+  }
+  use_fallback_init_ = true;
+  return true;
+}
+
 #if SANITIZER_ANDROID && __ANDROID_API__ < 21
 extern "C" __attribute__((weak)) int dl_iterate_phdr(
     int (*)(struct dl_phdr_info *, size_t, void *), void *);
@@ -470,11 +483,16 @@
   // The runtime check allows the same library to work with
   // both K and L (and future) Android releases.
   if (api_level <= ANDROID_LOLLIPOP_MR1) { // L or earlier
+    enableFallbackInit();
+  }
+#endif
+
+  if (use_fallback_init_) {
     MemoryMappingLayout memory_mapping(false);
     memory_mapping.DumpListOfModules(&modules_);
     return;
   }
-#endif
+
   DlIteratePhdrData data = {&modules_, true};
   dl_iterate_phdr(dl_iterate_phdr_cb, &data);
 }
Index: lib/sanitizer_common/sanitizer_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_mac.cc
+++ lib/sanitizer_common/sanitizer_mac.cc
@@ -410,6 +410,8 @@
 #endif
 }
 
+bool ListOfModules::enableFallbackInit() { return false; }
+
 void ListOfModules::init() {
   clear();
   MemoryMappingLayout memory_mapping(false);
Index: lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
+++ lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc
@@ -176,6 +176,7 @@
       return &modules_[i];
     }
   }
+
   // dlopen/dlclose interceptors invalidate the module list, but when
   // interception is disabled, we need to retry if the lookup fails in
   // case the module list changed.
@@ -185,7 +186,11 @@
     return FindModuleForAddress(address);
   }
 #endif
-  return 0;
+
+  if (modules_.enableFallbackInit()) {
+    return FindModuleForAddress(address);
+  }
+  return nullptr;
 }
 
 // For now we assume the following protocol:
Index: lib/sanitizer_common/sanitizer_win.cc
===================================================================
--- lib/sanitizer_common/sanitizer_win.cc
+++ lib/sanitizer_common/sanitizer_win.cc
@@ -524,6 +524,8 @@
   return (uptr)pe_header->ImageBase;
 }
 
+bool ListOfModules::enableFallbackInit() { return false; }
+
 void ListOfModules::init() {
   clear();
   HANDLE cur_process = GetCurrentProcess();