--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2009-06-12  Eric Blake  <ebb9@byu.net>
+
+	memchr: detect broken x86_64 and alpha implementations
+	* modules/memchr-tests (Depends-on): Move mmap detection...
+	* modules/memchr (Depends-on): ...here.
+	(configure.ac): Set indicator.
+	* lib/string.in.h (memchr): Declare replacement.
+	* modules/string (Makefile.am): Trigger replacement.
+	* m4/string_h.m4 (gl_HEADER_STRING_H_DEFAULTS): Likewise.
+	* m4/memchr.m4 (gl_FUNC_MEMCHR): Use mmap to detect platform
+	bugs.
+	* doc/posix-functions/memchr.texi (memchr): Document the bug.
+	* modules/getpagesize (License): Relax license.
+
 2009-06-11  Bruno Haible  <bruno@clisp.org>
 
 	* lib/idpriv.h: Add more references.

--- a/doc/posix-functions/memchr.texi
+++ b/doc/posix-functions/memchr.texi
@@ -10,6 +10,10 @@
 @itemize
 @item
 This function is missing on some older platforms.
+
+@item
+This function dereferences too much memory on some platforms:
+glibc 2.10 on x86_64 or Alpha
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -1,6 +1,6 @@
 /* A GNU-like <string.h>.
 
-   Copyright (C) 1995-1996, 2001-2008 Free Software Foundation, Inc.
+   Copyright (C) 1995-1996, 2001-2009 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -49,6 +49,23 @@
 #endif
 
 
+/* Return the first instance of C within N bytes of S, or NULL.  */
+#if @GNULIB_MEMCHR@
+# if @REPLACE_MEMCHR@
+#  define memchr rpl_memchr
+# endif
+# if @REPLACE_MEMCHR@
+extern void *memchr (void const *__s, int __c, size_t __n)
+  __attribute__ ((__pure__));
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef memchr
+# define memchr(s,c,n) \
+    (GL_LINK_WARNING ("memchr has platform-specific bugs - " \
+                      "use gnulib module memchr for portability" ), \
+     memchr (s, c, n))
+#endif
+
 /* Return the first occurrence of NEEDLE in HAYSTACK.  */
 #if @GNULIB_MEMMEM@
 # if @REPLACE_MEMMEM@

--- a/m4/memchr.m4
+++ b/m4/memchr.m4
@@ -1,4 +1,4 @@
-# memchr.m4 serial 5
+# memchr.m4 serial 6
 dnl Copyright (C) 2002, 2003, 2004, 2009 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,9 +6,76 @@
 
 AC_DEFUN([gl_FUNC_MEMCHR],
 [
+  dnl Check for prerequisites for memory fence checks.
+  gl_FUNC_MMAP_ANON
+  AC_CHECK_HEADERS_ONCE([sys/mman.h])
+  AC_CHECK_FUNCS_ONCE([mprotect])
+
+  dnl These days, we assume memchr is present.  But just in case...
+  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
   AC_REPLACE_FUNCS([memchr])
   if test $ac_cv_func_memchr = no; then
     gl_PREREQ_MEMCHR
+    REPLACE_MEMCHR=1
+  fi
+
+  if test $ac_cv_func_memchr = yes; then
+    # Detect platform-specific bugs in some versions of glibc:
+    # memchr should not dereference anything with length 0
+    #   http://bugzilla.redhat.com/499689
+    # memchr should not dereference overestimated length after a match
+    #   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
+    # Assume that memchr works on platforms that lack mprotect.
+    AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
+      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <string.h>
+#if HAVE_SYS_MMAN_H
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+# ifndef MAP_FILE
+#  define MAP_FILE 0
+# endif
+#endif
+]], [[
+  char *fence = NULL;
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# if HAVE_MAP_ANONYMOUS
+  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+  const int fd = -1;
+# else /* !HAVE_MAP_ANONYMOUS */
+  const int flags = MAP_FILE | MAP_PRIVATE;
+  int fd = open ("/dev/zero", O_RDONLY, 0666);
+  if (fd >= 0)
+# endif
+    {
+      int pagesize = getpagesize ();
+      char *two_pages =
+	(char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+		       flags, fd, 0);
+      if (two_pages != (char *)(-1)
+	  && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+	fence = two_pages + pagesize;
+    }
+#endif
+  if (fence)
+    {
+      if (memchr (fence, 0, 0))
+        return 1;
+      strcpy (fence - 9, "12345678");
+      if (memchr (fence - 9, 0, 79) != fence - 1)
+        return 2;
+    }
+  return 0;
+]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
+      [dnl Be pessimistic for now.
+       gl_cv_func_memchr_works="guessing no"])])
+    if test "$gl_cv_func_memchr_works" != yes; then
+      gl_PREREQ_MEMCHR
+      REPLACE_MEMCHR=1
+      AC_LIBOBJ([memchr])
+    fi
   fi
 ])
 

--- a/m4/string_h.m4
+++ b/m4/string_h.m4
@@ -1,11 +1,11 @@
 # Configure a GNU-like replacement for <string.h>.
 
-# Copyright (C) 2007, 2008 Free Software Foundation, Inc.
+# Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
 # with or without modifications, as long as this notice is preserved.
 
-# serial 6
+# serial 7
 
 # Written by Paul Eggert.
 
@@ -32,6 +32,7 @@
 
 AC_DEFUN([gl_HEADER_STRING_H_DEFAULTS],
 [
+  GNULIB_MEMCHR=0;      AC_SUBST([GNULIB_MEMCHR])
   GNULIB_MEMMEM=0;      AC_SUBST([GNULIB_MEMMEM])
   GNULIB_MEMPCPY=0;     AC_SUBST([GNULIB_MEMPCPY])
   GNULIB_MEMRCHR=0;     AC_SUBST([GNULIB_MEMRCHR])
@@ -83,6 +84,7 @@
   HAVE_DECL_STRERROR=1;		AC_SUBST([HAVE_DECL_STRERROR])
   HAVE_DECL_STRSIGNAL=1;	AC_SUBST([HAVE_DECL_STRSIGNAL])
   HAVE_STRVERSCMP=1;		AC_SUBST([HAVE_STRVERSCMP])
+  REPLACE_MEMCHR=0;		AC_SUBST([REPLACE_MEMCHR])
   REPLACE_MEMMEM=0;		AC_SUBST([REPLACE_MEMMEM])
   REPLACE_STRDUP=0;		AC_SUBST([REPLACE_STRDUP])
   REPLACE_STRSTR=0;		AC_SUBST([REPLACE_STRSTR])

--- a/modules/getpagesize
+++ b/modules/getpagesize
@@ -18,7 +18,7 @@
 <unistd.h>
 
 License:
-LGPL
+LGPLv2+
 
 Maintainer:
 Jim Meyering

--- a/modules/memchr
+++ b/modules/memchr
@@ -4,11 +4,16 @@
 Files:
 lib/memchr.c
 m4/memchr.m4
+m4/mmap-anon.m4
 
 Depends-on:
+extensions
+getpagesize
+string
 
 configure.ac:
 gl_FUNC_MEMCHR
+gl_STRING_MODULE_INDICATOR([memchr])
 
 Makefile.am:
 

--- a/modules/memchr-tests
+++ b/modules/memchr-tests
@@ -1,16 +1,10 @@
 Files:
 tests/test-memchr.c
 tests/zerosize-ptr.h
-m4/mmap-anon.m4
 
 Depends-on:
-extensions
-getpagesize
 
 configure.ac:
-gl_FUNC_MMAP_ANON
-AC_CHECK_HEADERS_ONCE([sys/mman.h])
-AC_CHECK_FUNCS_ONCE([mprotect])
 
 Makefile.am:
 TESTS += test-memchr

--- a/modules/string
+++ b/modules/string
@@ -38,6 +38,7 @@
 	      -e 's|@''GNULIB_MBSSPN''@|$(GNULIB_MBSSPN)|g' \
 	      -e 's|@''GNULIB_MBSSEP''@|$(GNULIB_MBSSEP)|g' \
 	      -e 's|@''GNULIB_MBSTOK_R''@|$(GNULIB_MBSTOK_R)|g' \
+	      -e 's|@''GNULIB_MEMCHR''@|$(GNULIB_MEMCHR)|g' \
 	      -e 's|@''GNULIB_MEMMEM''@|$(GNULIB_MEMMEM)|g' \
 	      -e 's|@''GNULIB_MEMPCPY''@|$(GNULIB_MEMPCPY)|g' \
 	      -e 's|@''GNULIB_MEMRCHR''@|$(GNULIB_MEMRCHR)|g' \
@@ -74,6 +75,7 @@
 	      -e 's|@''HAVE_DECL_STRERROR''@|$(HAVE_DECL_STRERROR)|g' \
 	      -e 's|@''HAVE_DECL_STRSIGNAL''@|$(HAVE_DECL_STRSIGNAL)|g' \
 	      -e 's|@''HAVE_STRVERSCMP''@|$(HAVE_STRVERSCMP)|g' \
+	      -e 's|@''REPLACE_MEMCHR''@|$(REPLACE_MEMCHR)|g' \
 	      -e 's|@''REPLACE_MEMMEM''@|$(REPLACE_MEMMEM)|g' \
 	      -e 's|@''REPLACE_STRCASESTR''@|$(REPLACE_STRCASESTR)|g' \
 	      -e 's|@''REPLACE_STRDUP''@|$(REPLACE_STRDUP)|g' \