configure: Implement --enable-host-bind-now

As promised in the --enable-host-pie patch, this patch adds another
configure option, --enable-host-bind-now, which adds -z now when linking
the compiler executables in order to extend hardening.  BIND_NOW with RELRO
allows the GOT to be marked RO; this prevents GOT modification attacks.

This option does not affect linking of target libraries; you can use
LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now to enable RELRO/BIND_NOW.

With this patch:
$ readelf -Wd cc1{,plus,obj,gm2} f951 lto1 cpp  rust1 gnat1 | grep FLAGS
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE

c++tools/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.
	* configure: Regenerate.

gcc/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Add
	-Wl,-z,now to LD_PICFLAG if --enable-host-bind-now.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-bind-now.

lto-plugin/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Link with
	-z,now.
	* configure: Regenerate.

3 files changed, 36 insertions, 3 deletions

diff --git a/gcc/configure b/gcc/configure
index c99105f..496da71 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -635,6 +635,7 @@ CET_HOST_FLAGS
 LD_PICFLAG
 PICFLAG
 enable_default_pie
+enable_host_bind_now
 enable_host_pie
 enable_host_shared
 enable_plugin
@@ -1031,6 +1032,7 @@ enable_version_specific_runtime_libs
 enable_plugin
 enable_host_shared
 enable_host_pie
+enable_host_bind_now
 enable_libquadmath_support
 with_linker_hash_style
 with_diagnostics_color
@@ -1794,6 +1796,7 @@ Optional Features:
   --enable-plugin         enable plugin support
   --enable-host-shared    build host code as shared libraries
   --enable-host-pie       build host code as PIE
+  --enable-host-bind-now  link host code as BIND_NOW
   --disable-libquadmath-support
                           disable libquadmath support for Fortran
   --enable-default-pie    enable Position Independent Executable as default
@@ -19847,7 +19850,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19850 "configure"
+#line 19853 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -19953,7 +19956,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19956 "configure"
+#line 19959 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -32100,6 +32103,14 @@ fi
 
 
 
+# Enable --enable-host-bind-now
+# Check whether --enable-host-bind-now was given.
+if test "${enable_host_bind_now+set}" = set; then :
+  enableval=$enable_host_bind_now;
+fi
+
+
+
 # Check whether --enable-libquadmath-support was given.
 if test "${enable_libquadmath_support+set}" = set; then :
   enableval=$enable_libquadmath_support; ENABLE_LIBQUADMATH_SUPPORT=$enableval
@@ -32286,6 +32297,8 @@ else
   PICFLAG=
 fi
 
+
+
 if test x$enable_host_pie = xyes; then
   LD_PICFLAG=-pie
 elif test x$gcc_cv_no_pie = xyes; then
@@ -32294,6 +32307,9 @@ else
   LD_PICFLAG=
 fi
 
+if test x$enable_host_bind_now = xyes; then
+  LD_PICFLAG="$LD_PICFLAG -Wl,-z,now"
+fi
 
 
 
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 0428ee4..e91073b 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -7425,6 +7425,12 @@ AC_ARG_ENABLE(host-pie,
 		[build host code as PIE])])
 AC_SUBST(enable_host_pie)
 
+# Enable --enable-host-bind-now
+AC_ARG_ENABLE(host-bind-now,
+[AS_HELP_STRING([--enable-host-bind-now],
+		[link host code as BIND_NOW])])
+AC_SUBST(enable_host_bind_now)
+
 AC_ARG_ENABLE(libquadmath-support,
 [AS_HELP_STRING([--disable-libquadmath-support],
   [disable libquadmath support for Fortran])],
@@ -7566,6 +7572,8 @@ else
   PICFLAG=
 fi
 
+AC_SUBST([PICFLAG])
+
 if test x$enable_host_pie = xyes; then
   LD_PICFLAG=-pie
 elif test x$gcc_cv_no_pie = xyes; then
@@ -7574,7 +7582,10 @@ else
   LD_PICFLAG=
 fi
 
-AC_SUBST([PICFLAG])
+if test x$enable_host_bind_now = xyes; then
+  LD_PICFLAG="$LD_PICFLAG -Wl,-z,now"
+fi
+
 AC_SUBST([LD_PICFLAG])
 
 # Enable Intel CET on Intel CET enabled host if jit is enabled.
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index a38d293..e099cd0 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1095,6 +1095,12 @@ protection against Return Oriented Programming (ROP) attacks.
 in which case @option{-fPIC} is used when compiling, and @option{-pie} when
 linking.
 
+@item --enable-host-bind-now
+Specify that the @emph{host} executables should be linked with the option
+@option{-Wl,-z,now}, which means that the dynamic linker will resolve all
+symbols when the executables are started, and that in turn allows RELRO to
+mark the GOT read-only, resulting in better security.
+
 @item @anchor{with-gnu-as}--with-gnu-as
 Specify that the compiler should assume that the
 assembler it finds is the GNU assembler.  However, this does not modify