Index: lib/libc/gen/getprogname.c
===================================================================
--- lib/libc/gen/getprogname.c
+++ lib/libc/gen/getprogname.c
@@ -7,6 +7,15 @@
 
 #include "libc_private.h"
 
+#ifdef PIC
+/*
+ * Note: __progname is defined in the main executable, but we add a weak
+ * definition to libc.so to allow linking other shared libraries with
+ * -Wl,--no-undefined/-Wl,--no-allow-shlib-undefined
+ */
+__weak_symbol const char *__progname = NULL;
+#endif
+
 __weak_reference(_getprogname, getprogname);
 
 const char *
Index: lib/libc/stdlib/Symbol.map
===================================================================
--- lib/libc/stdlib/Symbol.map
+++ lib/libc/stdlib/Symbol.map
@@ -134,4 +134,10 @@
 	__libc_system;
 	__cxa_thread_call_dtors;
 	__libc_atexit;
+	/*
+	 * These are provided by the csu code in the main executable, but need
+	 * to be defined in libc.so to allow linking with -Wl,--no-undefined:
+	 */
+	__progname;
+	environ;
 };
Index: lib/libc/stdlib/getenv.c
===================================================================
--- lib/libc/stdlib/getenv.c
+++ lib/libc/stdlib/getenv.c
@@ -57,6 +57,14 @@
  *			(re)builds of the environment.
  */
 extern char **environ;
+#if defined(PIC) && !defined(IN_RTLD)
+/*
+ * Note: environ is defined in the main executable, but we add a weak
+ * definition to libc.so to allow linking other shared libraries with
+ * -Wl,--no-undefined/-Wl,--no-allow-shlib-undefined
+ */
+__weak_symbol char **environ = NULL;
+#endif
 static char **origEnviron;
 static char **intEnviron = NULL;
 static int environSize = 0;