+ REPLACE_MEMCHR=1
+ fi
+
+ if test $ac_cv_func_memchr = yes; then
+ # Detect platform-specific bugs in some versions of glibc:
+ # memchr should not dereference anything with length 0
+ # http://bugzilla.redhat.com/499689
+ # memchr should not dereference overestimated length after a match
+ # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
+ # http://sourceware.org/bugzilla/show_bug.cgi?id=10162
+ # Assume that memchr works on platforms that lack mprotect.
+ AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
+ [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <string.h>
+#if HAVE_SYS_MMAN_H
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+# ifndef MAP_FILE
+# define MAP_FILE 0
+# endif
+#endif
+]], [[
+ char *fence = NULL;
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# if HAVE_MAP_ANONYMOUS
+ const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+ const int fd = -1;
+# else /* !HAVE_MAP_ANONYMOUS */
+ const int flags = MAP_FILE | MAP_PRIVATE;
+ int fd = open ("/dev/zero", O_RDONLY, 0666);
+ if (fd >= 0)
+# endif
+ {
+ int pagesize = getpagesize ();
+ char *two_pages =
+ (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+ flags, fd, 0);
+ if (two_pages != (char *)(-1)
+ && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+ fence = two_pages + pagesize;
+ }
+#endif
+ if (fence)
+ {
+ if (memchr (fence, 0, 0))
+ return 1;
+ strcpy (fence - 9, "12345678");
+ if (memchr (fence - 9, 0, 79) != fence - 1)
+ return 2;
+ }
+ return 0;
+]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
+ [dnl Be pessimistic for now.
+ gl_cv_func_memchr_works="guessing no"])])
+ if test "$gl_cv_func_memchr_works" != yes; then
+ gl_PREREQ_MEMCHR
+ REPLACE_MEMCHR=1
+ AC_LIBOBJ([memchr])
+ fi