Better fix for setenv (..., NULL, ...)

* stdlib/setenv.c (__add_to_environ):
Dump core quickly if setenv (..., NULL, ...) is called.
This time, do it the right way, and pacify GCC with a pragma.

ChangeLog

@@ -1,3 +1,9 @@
+2015-04-19  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* stdlib/setenv.c (__add_to_environ):
+	Dump core quickly if setenv (..., NULL, ...) is called.
+	This time, do it the right way, and pacify GCC with a pragma.
+
 2015-04-17  Roland McGrath  <roland@hack.frob.com>
 
 	* elf/dl-close.c (_dl_close_worker) [DL_NNS == 1]: Just assert that

stdlib/setenv.c

@@ -19,6 +19,13 @@
 # include <config.h>
 #endif
 
+/* Pacify GCC; see the commentary about VALLEN below.  This is needed
+   at least through GCC 4.9.2.  Pacify GCC for the entire file, as
+   there seems to be no way to pacify GCC selectively, only for the
+   place where it's needed.  Do not use DIAG_IGNORE_NEEDS_COMMENT
+   here, as it's not defined yet.  */
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+
 #include <errno.h>
 #if !_LIBC
 # if !defined errno && !defined HAVE_ERRNO_DECL
@@ -114,8 +121,17 @@ __add_to_environ (name, value, combined, replace)
 {
   char **ep;
   size_t size;
+
+  /* Compute lengths before locking, so that the critical section is
+     less of a performance bottleneck.  VALLEN is needed only if
+     COMBINED is null (unfortunately GCC is not smart enough to deduce
+     this; see the #pragma at the start of this file).  Testing
+     COMBINED instead of VALUE causes setenv (..., NULL, ...)  to dump
+     core now instead of corrupting memory later.  */
   const size_t namelen = strlen (name);
-  const size_t vallen = value != NULL ? strlen (value) + 1 : 0;
+  size_t vallen;
+  if (combined == NULL)
+    vallen = strlen (value) + 1;
 
   LOCK;