Link with `-z relro' when available.

* acinclude.m4 (GUILE_GNU_LD_RELRO): New macro.

* configure.in: Use `GUILE_GNU_LD_RELRO'.

acinclude.m4

@@ -1,3 +1,5 @@
+dnl -*- Autoconf -*-
+
 dnl  On the NeXT, #including <utime.h> doesn't give you a definition for
 dnl  struct utime, unless you #define _POSIX_SOURCE.
 
@@ -308,3 +310,20 @@ else
 fi
 AC_LANG_RESTORE
 ])dnl ACX_PTHREAD
+
+
+dnl Check whether GNU ld's read-only relocations (the `PT_GNU_RELRO'
+dnl ELF segment header) are supported.  This allows things like
+dnl statically allocated cells (1) to eventually be remapped read-only
+dnl by the loader, and (2) to be identified as pointerless by the
+dnl garbage collector.
+AC_DEFUN([GUILE_GNU_LD_RELRO], [
+  AC_MSG_CHECKING([whether the linker understands `-z relro'])
+
+  save_LDFLAGS="$LDFLAGS"
+  LDFLAGS="$LDFLAGS -Wl,-z -Wl,relro"
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])],
+    [AC_MSG_RESULT([yes])],
+    [AC_MSG_RESULT([no])
+     LDFLAGS="$save_LDFLAGS"])
+])

configure.in

@@ -4,7 +4,7 @@ dnl
 
 define(GUILE_CONFIGURE_COPYRIGHT,[[
 
-Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
+Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
 
 This file is part of GUILE
 
@@ -1448,6 +1448,10 @@ esac
 
 AC_SUBST(GCC_CFLAGS)
 
+# Check for GNU ld's "-z relro".
+GUILE_GNU_LD_RELRO
+
+
 ## If we're creating a shared library (using libtool!), then we'll
 ## need to generate a list of .lo files corresponding to the .o files
 ## given in LIBOBJS.  We'll call it LIBLOBJS.