Downstream-only patch to deal more gracefully with upgrades on
live systems.  Without it, a newer libc.so will fail to load
if the process was started with an older ld.so.

diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index f2d62fa2ccbb479d..5512c83d536874cb 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1303,8 +1303,26 @@ extern void _dl_show_scope (struct link_map *new, int from)
 extern struct link_map *_dl_find_dso_for_object (const ElfW(Addr) addr);
 rtld_hidden_proto (_dl_find_dso_for_object)
 
+#if !IS_IN (libc) || !defined SHARED
 extern enum dl_readonly_area_error_type _dl_readonly_area (const void *ptr,
 							   size_t size);
+#else
+/* In libc, only use _dl_readonly_area if it is available, so that
+   loadling libc does not fail with an undefined symbol reference to
+   _dl_readonly_area.  */
+static inline enum dl_readonly_area_error_type
+_dl_readonly_area (const void *ptr, size_t size)
+{
+  extern __typeof (_dl_readonly_area) _dl_readonly_area_real
+    __asm__ ("_dl_readonly_area") __attribute__ ((weak));
+  if (_dl_readonly_area_real != NULL)
+    return _dl_readonly_area_real (ptr, size);
+  else
+    /* This triggers the fallback to __readonly_area_fallback (using
+       /proc/self/maps).  */
+    return dl_readonly_area_not_found;
+}
+#endif
 
 /* Initialization which is normally done by the dynamic linker.  */
 extern void _dl_non_dynamic_init (void)