--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2010-09-14  Eric Blake  <eblake@redhat.com>
+
+	memchr: detect glibc Alpha bug
+	Avoids http://sourceware.org/bugzilla/show_bug.cgi?id=12019.
+	* m4/memchr.m4 (gl_FUNC_MEMCHR): Detect glibc 2.11.2 failure on
+	Alpha.
+	* doc/posix-functions/memchr.texi (memchr): Tweak wording.
+	* tests/test-memchr.c (main): Enhance test.
+	Reported by Nelson H. F. Beebe.
+
 2010-09-13  Paul Eggert  <eggert@cs.ucla.edu>
 
 	fts, getcwd, glob: audit for dirfd returning -1

--- a/doc/posix-functions/memchr.texi
+++ b/doc/posix-functions/memchr.texi
@@ -13,7 +13,7 @@
 
 @item
 This function dereferences too much memory on some platforms:
-glibc 2.10 on x86_64, IA-64, Alpha.
+glibc 2.10 on x86_64, IA-64; glibc 2.11 on Alpha.
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/m4/memchr.m4
+++ b/m4/memchr.m4
@@ -1,4 +1,4 @@
-# memchr.m4 serial 8
+# memchr.m4 serial 9
 dnl Copyright (C) 2002-2004, 2009-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -62,6 +62,8 @@
       strcpy (fence - 9, "12345678");
       if (memchr (fence - 9, 0, 79) != fence - 1)
         return 2;
+      if (memchr (fence - 1, 0, 3) != fence - 1)
+        return 3;
     }
   return 0;
 ]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],

--- a/tests/test-memchr.c
+++ b/tests/test-memchr.c
@@ -87,25 +87,37 @@
 
   /* Check that memchr() does not read past the first occurrence of the
      byte being searched.  See the Austin Group's clarification
-     <http://www.opengroup.org/austin/docs/austin_454.txt>.  */
+     <http://www.opengroup.org/austin/docs/austin_454.txt>.
+     Test both '\0' and something else, since some implementations
+     special-case searching for NUL.
+  */
   {
     char *page_boundary = (char *) zerosize_ptr ();
+    /* Too small, and we miss cache line boundary tests; too large,
+       and the test takes cubically longer to complete.  */
+    int limit = 257;
 
     if (page_boundary != NULL)
       {
-        for (n = 1; n <= 500; n++)
+        for (n = 1; n <= limit; n++)
           {
             char *mem = page_boundary - n;
             memset (mem, 'X', n);
             ASSERT (MEMCHR (mem, 'U', n) == NULL);
+            ASSERT (MEMCHR (mem, 0, n) == NULL);
 
             {
               size_t i;
+              size_t k;
 
               for (i = 0; i < n; i++)
                 {
                   mem[i] = 'U';
-                  ASSERT (MEMCHR (mem, 'U', 4000) == mem + i);
+                  for (k = i + 1; k < n + limit; k++)
+                    ASSERT (MEMCHR (mem, 'U', k) == mem + i);
+                  mem[i] = 0;
+                  for (k = i + 1; k < n + limit; k++)
+                    ASSERT (MEMCHR (mem, 0, k) == mem + i);
                   mem[i] = 'X';
                 }
             }