1 files changed, 99 insertions, 0 deletions
diff --git a/gl/m4/memchr.m4 b/gl/m4/memchr.m4
new file mode 100644
index 0000000..db227e7
--- /dev/null
+++ b/gl/m4/memchr.m4
@@ -0,0 +1,99 @@
+# memchr.m4 serial 13
+dnl Copyright (C) 2002-2004, 2009-2019 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN_ONCE([gl_FUNC_MEMCHR],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+
+  dnl Check for prerequisites for memory fence checks.
+  gl_FUNC_MMAP_ANON
+  AC_CHECK_HEADERS_ONCE([sys/mman.h])
+  AC_CHECK_FUNCS_ONCE([mprotect])
+
+  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
+  m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [
+    dnl These days, we assume memchr is present.  But if support for old
+    dnl platforms is desired:
+    AC_CHECK_FUNCS_ONCE([memchr])
+    if test $ac_cv_func_memchr = no; then
+      HAVE_MEMCHR=0
+    fi
+  ])
+  if test $HAVE_MEMCHR = 1; then
+    # Detect platform-specific bugs in some versions of glibc:
+    # memchr should not dereference anything with length 0
+    #   https://bugzilla.redhat.com/show_bug.cgi?id=499689
+    # memchr should not dereference overestimated length after a match
+    #   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
+    #   https://sourceware.org/bugzilla/show_bug.cgi?id=10162
+    # Assume that memchr works on platforms that lack mprotect.
+    AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
+      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <string.h>
+#if HAVE_SYS_MMAN_H
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+# ifndef MAP_FILE
+#  define MAP_FILE 0
+# endif
+#endif
+]], [[
+  int result = 0;
+  char *fence = NULL;
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# if HAVE_MAP_ANONYMOUS
+  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+  const int fd = -1;
+# else /* !HAVE_MAP_ANONYMOUS */
+  const int flags = MAP_FILE | MAP_PRIVATE;
+  int fd = open ("/dev/zero", O_RDONLY, 0666);
+  if (fd >= 0)
+# endif
+    {
+      int pagesize = getpagesize ();
+      char *two_pages =
+        (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+                       flags, fd, 0);
+      if (two_pages != (char *)(-1)
+          && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+        fence = two_pages + pagesize;
+    }
+#endif
+  if (fence)
+    {
+      if (memchr (fence, 0, 0))
+        result |= 1;
+      strcpy (fence - 9, "12345678");
+      if (memchr (fence - 9, 0, 79) != fence - 1)
+        result |= 2;
+      if (memchr (fence - 1, 0, 3) != fence - 1)
+        result |= 4;
+    }
+  return result;
+]])],
+         [gl_cv_func_memchr_works=yes],
+         [gl_cv_func_memchr_works=no],
+         [case "$host_os" in
+                    # Guess yes on native Windows.
+            mingw*) gl_cv_func_memchr_works="guessing yes" ;;
+                    # Be pessimistic for now.
+            *)      gl_cv_func_memchr_works="guessing no" ;;
+          esac
+         ])
+      ])
+    case "$gl_cv_func_memchr_works" in
+      *yes) ;;
+      *) REPLACE_MEMCHR=1 ;;
+    esac
+  fi
+])
+
+# Prerequisites of lib/memchr.c.
+AC_DEFUN([gl_PREREQ_MEMCHR], [
+  AC_CHECK_HEADERS([bp-sym.h])
+])