configure: Implement --enable-host-pie

[ This is my third attempt to add this configure option.  The first
version was approved but it came too late in the development cycle.
The second version was also approved, but I had to revert it:
<https://gcc.gnu.org/pipermail/gcc-patches/2022-November/607082.html>.
I've fixed the problem (by moving $(PICFLAG) from INTERNAL_CFLAGS to
ALL_COMPILERFLAGS).  Another change is that since r13-4536 I no longer
need to touch Makefile.def, so this patch is simplified. ]

This patch implements the --enable-host-pie configure option which
makes the compiler executables PIE.  This can be used to enhance
protection against ROP attacks, and can be viewed as part of a wider
trend to harden binaries.

It is similar to the option --enable-host-shared, except that --e-h-s
won't add -shared to the linker flags whereas --e-h-p will add -pie.
It is different from --enable-default-pie because that option just
adds an implicit -fPIE/-pie when the compiler is invoked, but the
compiler itself isn't PIE.

Since r12-5768-gfe7c3ecf, PCH works well with PIE, so there are no PCH
regressions.

When building the compiler, the build process may use various in-tree
libraries; these need to be built with -fPIE so that it's possible to
use them when building a PIE.  For instance, when --with-included-gettext
is in effect, intl object files must be compiled with -fPIE.  Similarly,
when building in-tree gmp, isl, mpfr and mpc, they must be compiled with
-fPIE.

With this patch and --enable-host-pie used to configure gcc:

$ file gcc/cc1{,plus,obj,gm2} gcc/f951 gcc/lto1 gcc/cpp gcc/go1 gcc/rust1 gcc/gnat1
gcc/cc1:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=98e22cde129d304aa6f33e61b1c39e144aeb135e, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1plus: ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=859d1ea37e43dfe50c18fd4e3dd9a34bb1db8f77, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1obj:  ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=1964f8ecee6163182bc26134e2ac1f324816e434, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1gm2:  ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=a396672c7ff913d21855829202e7b02ecf42ff4c, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/f951:    ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=59c523db893186547ac75c7a71f48be0a461c06b, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/lto1:    ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=084a7b77df7be2d63c2d4c655b5bbc3fcdb6038d, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cpp:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=3503bf8390d219a10d6653b8560aa21158132168, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/go1:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=988cc673af4fba5dcb482f4b34957b99050a68c5, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/rust1:   ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=b6a5d3d514446c4dcdee0707f086ab9b274a8a3c, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/gnat1:   ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=bb11ccdc2c366fe3fe0980476bcd8ca19b67f9dc, for GNU/Linux 3.2.0, with debug_info, not stripped

I plan to add an option to link with -Wl,-z,now.

Bootstrapped on x86_64-pc-linux-gnu with --with-included-gettext
--enable-host-pie as well as without --enable-host-pie.  Also tested
on a Debian system where the system gcc was configured with
--enable-default-pie.

Co-Authored by: Iain Sandoe  <iain@sandoe.co.uk>

ChangeLog:

	* configure.ac (--enable-host-pie): New check.  Set PICFLAG after this
	check.
	* configure: Regenerate.

c++tools/ChangeLog:

	* Makefile.in: Rename PIEFLAG to PICFLAG.  Set LD_PICFLAG.  Use it.
	Use pic/libiberty.a if PICFLAG is set.
	* configure.ac (--enable-default-pie): Set PICFLAG instead of PIEFLAG.
	(--enable-host-pie): New check.
	* configure: Regenerate.

fixincludes/ChangeLog:

	* Makefile.in: Set and use PICFLAG and LD_PICFLAG.  Use the "pic"
	build of libiberty if PICFLAG is set.
	* configure.ac:
	* configure: Regenerate.

gcc/ChangeLog:

	* Makefile.in: Set LD_PICFLAG.  Use it.  Set enable_host_pie.
	Remove NO_PIE_CFLAGS and NO_PIE_FLAG.  Pass LD_PICFLAG to
	ALL_LINKERFLAGS.  Use the "pic" build of libiberty if --enable-host-pie.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-pie.

gcc/ada/ChangeLog:

	* gcc-interface/Make-lang.in (ALL_ADAFLAGS): Remove NO_PIE_CFLAGS.  Add
	PICFLAG.  Use PICFLAG when building ada/b_gnat1.o and ada/b_gnatb.o.
	* gcc-interface/Makefile.in: Use pic/libiberty.a if PICFLAG is set.
	Remove NO_PIE_FLAG.

gcc/m2/ChangeLog:

	* Make-lang.in: New var, GM2_PICFLAGS.  Use it.

gcc/d/ChangeLog:

	* Make-lang.in: Remove NO_PIE_CFLAGS.

intl/ChangeLog:

	* Makefile.in: Use @PICFLAG@ in COMPILE as well.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libcody/ChangeLog:

	* Makefile.in: Pass LD_PICFLAG to LDFLAGS.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.

libcpp/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libdecnumber/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libiberty/ChangeLog:

	* configure.ac: Also set shared when enable_host_pie.
	* configure: Regenerate.

zlib/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

8 files changed, 130 insertions, 70 deletions

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 4be82e8..669a2a0 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -158,6 +158,9 @@ LDFLAGS = @LDFLAGS@
 # Should we build position-independent host code?
 PICFLAG = @PICFLAG@
 
+# The linker flag for the above.
+LD_PICFLAG = @LD_PICFLAG@
+
 # Flags to determine code coverage. When coverage is disabled, this will
 # contain the optimization flags, as you normally want code coverage
 # without optimization.
@@ -283,19 +286,19 @@ LINKER = $(CC)
 LINKER_FLAGS = $(CFLAGS)
 endif
 
+enable_host_pie = @enable_host_pie@
+
 # Enable Intel CET on Intel CET enabled host if needed.
 CET_HOST_FLAGS = @CET_HOST_FLAGS@
 COMPILER += $(CET_HOST_FLAGS)
 
-NO_PIE_CFLAGS = @NO_PIE_CFLAGS@
-NO_PIE_FLAG = @NO_PIE_FLAG@
 DO_LINK_MUTEX = @DO_LINK_MUTEX@
 
-# We don't want to compile the compilers with -fPIE, it make PCH fail.
-COMPILER += $(NO_PIE_CFLAGS)
+# Maybe compile the compilers with -fPIE or -fPIC.
+COMPILER += $(PICFLAG)
 
-# Link with -no-pie since we compile the compiler with -fno-PIE.
-LINKER += $(NO_PIE_FLAG)
+# Link with -pie, or -no-pie, depending on the above.
+LINKER += $(LD_PICFLAG)
 
 # Like LINKER, but use a mutex for serializing front end links.
 ifeq (@DO_LINK_MUTEX@,true)
@@ -1067,7 +1070,7 @@ RTL_SSA_H = $(PRETTY_PRINT_H) insn-config.h splay-tree-utils.h \
 # programs built during a bootstrap.
 # autoconf inserts -DCROSS_DIRECTORY_STRUCTURE if we are building a
 # cross compiler which does not use the native headers and libraries.
-INTERNAL_CFLAGS = -DIN_GCC $(PICFLAG) @CROSS@
+INTERNAL_CFLAGS = -DIN_GCC @CROSS@
 
 # This is the variable actually used when we compile. If you change this,
 # you probably want to update BUILD_CFLAGS in configure.ac
@@ -1085,21 +1088,24 @@ ALL_CXXFLAGS = $(T_CFLAGS) $(CFLAGS-$@) $(CXXFLAGS) $(INTERNAL_CFLAGS) \
 ALL_CPPFLAGS = $(INCLUDES) $(CPPFLAGS)
 
 # This is the variable to use when using $(COMPILER).
-ALL_COMPILERFLAGS = $(ALL_CXXFLAGS)
+ALL_COMPILERFLAGS = $(ALL_CXXFLAGS) $(PICFLAG)
 
 # This is the variable to use when using $(LINKER).
-ALL_LINKERFLAGS = $(ALL_CXXFLAGS)
+ALL_LINKERFLAGS = $(ALL_CXXFLAGS) $(LD_PICFLAG)
 
 # Build and host support libraries.
 
-# Use the "pic" build of libiberty if --enable-host-shared, unless we are
-# building for mingw.
+# Use the "pic" build of libiberty if --enable-host-shared or --enable-host-pie,
+# unless we are building for mingw.
 LIBIBERTY_PICDIR=$(if $(findstring mingw,$(target)),,pic)
-ifeq ($(enable_host_shared),yes)
+ifneq ($(enable_host_shared)$(enable_host_pie),)
 LIBIBERTY = ../libiberty/$(LIBIBERTY_PICDIR)/libiberty.a
-BUILD_LIBIBERTY = $(build_libobjdir)/libiberty/$(LIBIBERTY_PICDIR)/libiberty.a
 else
 LIBIBERTY = ../libiberty/libiberty.a
+endif
+ifeq ($(enable_host_shared),yes)
+BUILD_LIBIBERTY = $(build_libobjdir)/libiberty/$(LIBIBERTY_PICDIR)/libiberty.a
+else
 BUILD_LIBIBERTY = $(build_libobjdir)/libiberty/libiberty.a
 endif
 
diff --git a/gcc/ada/gcc-interface/Make-lang.in b/gcc/ada/gcc-interface/Make-lang.in
index d7bab7d..364dea6 100644
--- a/gcc/ada/gcc-interface/Make-lang.in
+++ b/gcc/ada/gcc-interface/Make-lang.in
@@ -73,8 +73,8 @@ endif
 
 ADA_CFLAGS =
 ALL_ADAFLAGS = \
-  $(CFLAGS) $(NO_PIE_CFLAGS) $(ADA_CFLAGS) \
-  $(ADAFLAGS) $(CHECKING_ADAFLAGS) $(WARN_ADAFLAGS)
+  $(CFLAGS) $(ADA_CFLAGS) $(ADAFLAGS) $(CHECKING_ADAFLAGS) \
+  $(WARN_ADAFLAGS) $(PICFLAG)
 FORCE_DEBUG_ADAFLAGS = -g
 COMMON_ADA_INCLUDES = -I- -I. -Iada/generated -Iada -I$(srcdir)/ada
 
@@ -1112,7 +1112,7 @@ ada/b_gnat1.adb : $(GNAT1_ADA_OBJS)
 ada/b_gnat1.o : ada/b_gnat1.adb
         # Do not use ADAFLAGS to get rid of -gnatg which generates a lot
         # of style messages.
-	$(CC) -c $(CFLAGS) $(ADA_CFLAGS) -gnatp -gnatws $(ADA_INCLUDES) \
+	$(CC) -c $(CFLAGS) $(ADA_CFLAGS) $(PICFLAG) -gnatp -gnatws $(ADA_INCLUDES) \
 	    $< $(ADA_OUTPUT_OPTION)
 
 ada/b_gnatb.adb : $(GNATBIND_OBJS) ada/gnatbind.o
@@ -1121,7 +1121,7 @@ ada/b_gnatb.adb : $(GNATBIND_OBJS) ada/gnatbind.o
 	$(MV) b_gnatb.adb b_gnatb.ads ada/
 
 ada/b_gnatb.o : ada/b_gnatb.adb
-	$(CC) -c $(CFLAGS) $(ADA_CFLAGS) -gnatp -gnatws $(ADA_INCLUDES) \
+	$(CC) -c $(CFLAGS) $(ADA_CFLAGS) $(PICFLAG) -gnatp -gnatws $(ADA_INCLUDES) \
 	    $< $(ADA_OUTPUT_OPTION)
 
 include $(srcdir)/ada/Make-generated.in
diff --git a/gcc/ada/gcc-interface/Makefile.in b/gcc/ada/gcc-interface/Makefile.in
index da6a56f..dc0e54f 100644
--- a/gcc/ada/gcc-interface/Makefile.in
+++ b/gcc/ada/gcc-interface/Makefile.in
@@ -91,6 +91,7 @@ LS = ls
 RANLIB = @RANLIB@
 RANLIB_FLAGS = @ranlib_flags@
 AWK = @AWK@
+PICFLAG = @PICFLAG@
 
 COMPILER = $(CC)
 COMPILER_FLAGS = $(CFLAGS)
@@ -239,7 +240,11 @@ ALL_CPPFLAGS = $(CPPFLAGS)
 ALL_COMPILERFLAGS = $(ALL_CFLAGS)
 
 # This is where we get libiberty.a from.
+ifeq ($(PICFLAG),)
 LIBIBERTY = ../../libiberty/libiberty.a
+else
+LIBIBERTY = ../../libiberty/pic/libiberty.a
+endif
 
 # We need to link against libbacktrace because diagnostic.c in
 # libcommon.a uses it.
@@ -256,9 +261,6 @@ TOOLS_LIBS = ../version.o ../link.o ../targext.o ../../ggc-none.o \
   $(LIBGNAT) $(LIBINTL) $(LIBICONV) ../$(LIBBACKTRACE) ../$(LIBIBERTY) \
   $(SYSLIBS) $(TGT_LIB)
 
-# Add -no-pie to TOOLS_LIBS since some of them are compiled with -fno-PIE.
-TOOLS_LIBS += @NO_PIE_FLAG@
-
 # Specify the directories to be searched for header files.
 # Both . and srcdir are used, in that order,
 # so that tm.h and config.h will be found in the compilation
diff --git a/gcc/configure b/gcc/configure
index 3aa2534..a4563a9 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -632,10 +632,10 @@ ac_includes_default="\
 ac_subst_vars='LTLIBOBJS
 LIBOBJS
 CET_HOST_FLAGS
-NO_PIE_FLAG
-NO_PIE_CFLAGS
-enable_default_pie
+LD_PICFLAG
 PICFLAG
+enable_default_pie
+enable_host_pie
 enable_host_shared
 enable_plugin
 pluginlibs
@@ -1030,6 +1030,7 @@ enable_link_serialization
 enable_version_specific_runtime_libs
 enable_plugin
 enable_host_shared
+enable_host_pie
 enable_libquadmath_support
 with_linker_hash_style
 with_diagnostics_color
@@ -1792,6 +1793,7 @@ Optional Features:
                           in a compiler-specific directory
   --enable-plugin         enable plugin support
   --enable-host-shared    build host code as shared libraries
+  --enable-host-pie       build host code as PIE
   --disable-libquadmath-support
                           disable libquadmath support for Fortran
   --enable-default-pie    enable Position Independent Executable as default
@@ -32085,13 +32087,17 @@ fi
 # Enable --enable-host-shared
 # Check whether --enable-host-shared was given.
 if test "${enable_host_shared+set}" = set; then :
-  enableval=$enable_host_shared; PICFLAG=-fPIC
-else
-  PICFLAG=
+  enableval=$enable_host_shared;
 fi
 
 
 
+# Enable --enable-host-pie
+# Check whether --enable-host-pie was given.
+if test "${enable_host_pie+set}" = set; then :
+  enableval=$enable_host_pie;
+fi
+
 
 
 # Check whether --enable-libquadmath-support was given.
@@ -32245,10 +32251,6 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_c_no_fpie" >&5
 $as_echo "$gcc_cv_c_no_fpie" >&6; }
-if test "$gcc_cv_c_no_fpie" = "yes"; then
-  NO_PIE_CFLAGS="-fno-PIE"
-fi
-
 
 # Check if -no-pie works.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for -no-pie option" >&5
@@ -32273,11 +32275,28 @@ rm -f core conftest.err conftest.$ac_objext \
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_no_pie" >&5
 $as_echo "$gcc_cv_no_pie" >&6; }
-if test "$gcc_cv_no_pie" = "yes"; then
-  NO_PIE_FLAG="-no-pie"
+
+if test x$enable_host_shared = xyes; then
+  PICFLAG=-fPIC
+elif test x$enable_host_pie = xyes; then
+  PICFLAG=-fPIE
+elif test x$gcc_cv_c_no_fpie = xyes; then
+  PICFLAG=-fno-PIE
+else
+  PICFLAG=
+fi
+
+if test x$enable_host_pie = xyes; then
+  LD_PICFLAG=-pie
+elif test x$gcc_cv_no_pie = xyes; then
+  LD_PICFLAG=-no-pie
+else
+  LD_PICFLAG=
 fi
 
 
+
+
 # Enable Intel CET on Intel CET enabled host if jit is enabled.
  # Check whether --enable-cet was given.
 if test "${enable_cet+set}" = set; then :
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 524ef76..9c680ec 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -7416,11 +7416,14 @@ fi
 # Enable --enable-host-shared
 AC_ARG_ENABLE(host-shared,
 [AS_HELP_STRING([--enable-host-shared],
-		[build host code as shared libraries])],
-[PICFLAG=-fPIC], [PICFLAG=])
+		[build host code as shared libraries])])
 AC_SUBST(enable_host_shared)
-AC_SUBST(PICFLAG)
 
+# Enable --enable-host-pie
+AC_ARG_ENABLE(host-pie,
+[AS_HELP_STRING([--enable-host-pie],
+		[build host code as PIE])])
+AC_SUBST(enable_host_pie)
 
 AC_ARG_ENABLE(libquadmath-support,
 [AS_HELP_STRING([--disable-libquadmath-support],
@@ -7542,10 +7545,6 @@ AC_CACHE_CHECK([for -fno-PIE option],
      [gcc_cv_c_no_fpie=yes],
      [gcc_cv_c_no_fpie=no])
    CXXFLAGS="$saved_CXXFLAGS"])
-if test "$gcc_cv_c_no_fpie" = "yes"; then
-  NO_PIE_CFLAGS="-fno-PIE"
-fi
-AC_SUBST([NO_PIE_CFLAGS])
 
 # Check if -no-pie works.
 AC_CACHE_CHECK([for -no-pie option],
@@ -7556,10 +7555,27 @@ AC_CACHE_CHECK([for -no-pie option],
      [gcc_cv_no_pie=yes],
      [gcc_cv_no_pie=no])
    LDFLAGS="$saved_LDFLAGS"])
-if test "$gcc_cv_no_pie" = "yes"; then
-  NO_PIE_FLAG="-no-pie"
+
+if test x$enable_host_shared = xyes; then
+  PICFLAG=-fPIC
+elif test x$enable_host_pie = xyes; then
+  PICFLAG=-fPIE
+elif test x$gcc_cv_c_no_fpie = xyes; then
+  PICFLAG=-fno-PIE
+else
+  PICFLAG=
 fi
-AC_SUBST([NO_PIE_FLAG])
+
+if test x$enable_host_pie = xyes; then
+  LD_PICFLAG=-pie
+elif test x$gcc_cv_no_pie = xyes; then
+  LD_PICFLAG=-no-pie
+else
+  LD_PICFLAG=
+fi
+
+AC_SUBST([PICFLAG])
+AC_SUBST([LD_PICFLAG])
 
 # Enable Intel CET on Intel CET enabled host if jit is enabled.
 GCC_CET_HOST_FLAGS(CET_HOST_FLAGS)
diff --git a/gcc/d/Make-lang.in b/gcc/d/Make-lang.in
index 1679fb8..4fbf209 100644
--- a/gcc/d/Make-lang.in
+++ b/gcc/d/Make-lang.in
@@ -64,7 +64,7 @@ ALL_DFLAGS = $(DFLAGS-$@) $(GDCFLAGS) -fversion=IN_GCC $(CHECKING_DFLAGS) \
 	$(PICFLAG) $(ALIASING_FLAGS) $(NOEXCEPTION_DFLAGS) $(COVERAGE_FLAGS) \
 	$(WARN_DFLAGS)
 
-DCOMPILE.base = $(GDC) $(NO_PIE_CFLAGS) -c $(ALL_DFLAGS) -o $@
+DCOMPILE.base = $(GDC) -c $(ALL_DFLAGS) -o $@
 DCOMPILE = $(DCOMPILE.base) -MT $@ -MMD -MP -MF $(@D)/$(DEPDIR)/$(*F).TPo
 DPOSTCOMPILE = @mv $(@D)/$(DEPDIR)/$(*F).TPo $(@D)/$(DEPDIR)/$(*F).Po
 DLINKER = $(GDC) $(NO_PIE_FLAG) -lstdc++
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 7bcf978..a38d293 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1075,14 +1075,26 @@ code.
 
 @item --enable-host-shared
 Specify that the @emph{host} code should be built into position-independent
-machine code (with -fPIC), allowing it to be used within shared libraries,
-but yielding a slightly slower compiler.
+machine code (with @option{-fPIC}), allowing it to be used within shared
+libraries, but yielding a slightly slower compiler.
 
 This option is required when building the libgccjit.so library.
 
 Contrast with @option{--enable-shared}, which affects @emph{target}
 libraries.
 
+@item --enable-host-pie
+Specify that the @emph{host} executables should be built into
+position-independent executables (with @option{-fPIE} and @option{-pie}),
+yielding a slightly slower compiler (but faster than
+@option{--enable-host-shared}).  Position-independent executables are loaded
+at random addresses each time they are executed, therefore provide additional
+protection against Return Oriented Programming (ROP) attacks.
+
+@option{--enable-host-pie}) may be used with @option{--enable-host-shared}),
+in which case @option{-fPIC} is used when compiling, and @option{-pie} when
+linking.
+
 @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
diff --git a/gcc/m2/Make-lang.in b/gcc/m2/Make-lang.in
index 252b48a..15da74a 100644
--- a/gcc/m2/Make-lang.in
+++ b/gcc/m2/Make-lang.in
@@ -478,6 +478,11 @@ GM2_MIN_FLAGS=$(GM2_G) $(GM2_OS) \
  -Wpedantic-cast -Wpedantic-param-names -fno-exceptions \
  -ffunction-sections -fdata-sections $(GM2_CPP)
 
+# ALL_LINKERFLAGS may include -pie (when GCC is configured with
+# --enable-host-pie), so use -fPIE if needed.  (It would not be
+# a good idea to override CFLAGS.)
+GM2_PICFLAGS = $(PICFLAG)
+
 O2=-O2 -g
 SO_O2=-O2 -g -fPIC
 SO=-O0 -g -fPIC
@@ -1362,23 +1367,23 @@ m2/boot-bin/mc$(exeext): $(BUILD-MC-BOOT-O) $(BUILD-MC-INTERFACE-O) \
 
 m2/mc-boot/$(SRC_PREFIX)%.o: m2/mc-boot/$(SRC_PREFIX)%.cc m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) $(CXXFLAGS) -g -c -I. -I$(srcdir)/m2/mc-boot-ch -I$(srcdir)/m2/mc-boot -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) $< -o $@
+	$(CXX) $(CXXFLAGS) $(GM2_PICFLAGS) -g -c -I. -I$(srcdir)/m2/mc-boot-ch -I$(srcdir)/m2/mc-boot -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) $< -o $@
 
 m2/mc-boot-ch/$(SRC_PREFIX)%.o: m2/mc-boot-ch/$(SRC_PREFIX)%.c m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) $(CXXFLAGS) -DHAVE_CONFIG_H -g -c -I. -Im2/gm2-libs -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) -Im2/gm2-libs $< -o $@
+	$(CXX) $(CXXFLAGS) $(GM2_PICFLAGS) -DHAVE_CONFIG_H -g -c -I. -Im2/gm2-libs -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) -Im2/gm2-libs $< -o $@
 
 m2/mc-boot-ch/$(SRC_PREFIX)%.o: m2/mc-boot-ch/$(SRC_PREFIX)%.cc m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) $(CXXFLAGS) -DHAVE_CONFIG_H -g -c -I. -Im2/gm2-libs -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) -Im2/gm2-libs $< -o $@
+	$(CXX) $(CXXFLAGS) $(GM2_PICFLAGS) -DHAVE_CONFIG_H -g -c -I. -Im2/gm2-libs -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) -Im2/gm2-libs $< -o $@
 
 m2/mc-boot/main.o: $(M2LINK) $(srcdir)/m2/init/mcinit
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
 	unset CC ; $(M2LINK) -s --langc++ --exit --name m2/mc-boot/main.cc $(srcdir)/m2/init/mcinit
-	$(CXX) $(CXXFLAGS) -g -c -I. -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) m2/mc-boot/main.cc -o $@
+	$(CXX) $(CXXFLAGS) $(GM2_PICFLAGS) -g -c -I. -I$(srcdir)/../include -I$(srcdir) $(INCLUDES) m2/mc-boot/main.cc -o $@
 
 mcflex.o: mcflex.c m2/gm2-libs/gm2-libs-host.h
-	$(CC) $(CFLAGS) -I$(srcdir)/m2/mc -g -c $< -o $@   # remember that mcReserved.h is copied into m2/mc
+	$(CC) $(CFLAGS) $(GM2_PICFLAGS) -I$(srcdir)/m2/mc -g -c $< -o $@   # remember that mcReserved.h is copied into m2/mc
 
 mcflex.c: $(srcdir)/m2/mc/mc.flex
 	flex -t $< > $@
@@ -1386,17 +1391,17 @@ mcflex.c: $(srcdir)/m2/mc/mc.flex
 m2/gm2-libs-boot/M2RTS.o: $(srcdir)/m2/gm2-libs/M2RTS.mod $(MCDEPS) $(BUILD-BOOT-H)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
 	$(MC) --suppress-noreturn -o=m2/gm2-libs-boot/M2RTS.c $(srcdir)/m2/gm2-libs/M2RTS.mod
-	$(COMPILER) -c -DIN_GCC $(CFLAGS) -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(MCINCLUDES) $(INCLUDES) m2/gm2-libs-boot/M2RTS.c -o $@
+	$(COMPILER) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(MCINCLUDES) $(INCLUDES) m2/gm2-libs-boot/M2RTS.c -o $@
 
 m2/gm2-libs-boot/%.o: $(srcdir)/m2/gm2-libs-boot/%.mod $(MCDEPS) $(BUILD-BOOT-H)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
 	$(MC) -o=m2/gm2-libs-boot/$*.c $(srcdir)/m2/gm2-libs-boot/$*.mod
-	$(COMPILER) -c -DIN_GCC $(CFLAGS) $(MCINCLUDES) m2/gm2-libs-boot/$*.c -o $@
+	$(COMPILER) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) $(MCINCLUDES) m2/gm2-libs-boot/$*.c -o $@
 
 m2/gm2-libs-boot/%.o: $(srcdir)/m2/gm2-libs/%.mod $(MCDEPS) $(BUILD-BOOT-H)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
 	$(MC) -o=m2/gm2-libs-boot/$*.c $(srcdir)/m2/gm2-libs/$*.mod
-	$(COMPILER) -c -DIN_GCC $(CFLAGS) -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(MCINCLUDES) $(INCLUDES) m2/gm2-libs-boot/$*.c -o $@
+	$(COMPILER) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(MCINCLUDES) $(INCLUDES) m2/gm2-libs-boot/$*.c -o $@
 
 m2/gm2-libs-boot/$(SRC_PREFIX)%.h: $(srcdir)/m2/gm2-libs/%.def $(MCDEPS)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
@@ -1404,49 +1409,49 @@ m2/gm2-libs-boot/$(SRC_PREFIX)%.h: $(srcdir)/m2/gm2-libs/%.def $(MCDEPS)
 
 m2/gm2-libs-boot/RTcodummy.o: $(srcdir)/m2/gm2-libs-ch/RTcodummy.c m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c -DIN_GCC $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/RTintdummy.o: $(srcdir)/m2/gm2-libs-ch/RTintdummy.c m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c -DIN_GCC $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/wrapc.o: $(srcdir)/m2/gm2-libs-ch/wrapc.c m2/gm2-libs-boot/$(SRC_PREFIX)wrapc.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c -DHAVE_CONFIG_H $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libs $(INCLUDES) $< -o $@
+	$(CXX) -c -DHAVE_CONFIG_H $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libs $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/UnixArgs.o: $(srcdir)/m2/gm2-libs-ch/UnixArgs.cc m2/gm2-libs-boot/$(SRC_PREFIX)UnixArgs.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c -DIN_GCC $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c -DIN_GCC $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/choosetemp.o: m2/gm2-libs-ch/choosetemp.c m2/gm2-libiberty/Gchoosetemp.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libiberty -I$(srcdir)/m2/gm2-libiberty/ $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libiberty -I$(srcdir)/m2/gm2-libiberty/ $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/errno.o: $(srcdir)/m2/gm2-libs-ch/errno.c m2/gm2-libs-boot/$(SRC_PREFIX)errno.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/dtoa.o: $(srcdir)/m2/gm2-libs-ch/dtoa.cc m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/ldtoa.o: $(srcdir)/m2/gm2-libs-ch/ldtoa.cc m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/termios.o: $(srcdir)/m2/gm2-libs-ch/termios.c $(BUILD-LIBS-BOOT-H) m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/SysExceptions.o: $(srcdir)/m2/gm2-libs-ch/SysExceptions.c \
                                   m2/gm2-libs-boot/$(SRC_PREFIX)SysExceptions.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/SysStorage.o: $(srcdir)/m2/gm2-libs/SysStorage.mod $(MCDEPS) $(BUILD-BOOT-H)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
 	$(MC) -o=m2/gm2-libs-boot/SysStorage.c $(srcdir)/m2/gm2-libs/SysStorage.mod
-	$(COMPILER) -DIN_GCC -c $(CFLAGS) \
+	$(COMPILER) -DIN_GCC -c $(CFLAGS) $(GM2_PICFLAGS) \
           -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(MCINCLUDES) $(INCLUDES) \
           m2/gm2-libs-boot/SysStorage.c -o m2/gm2-libs-boot/SysStorage.o
 
@@ -1519,7 +1524,7 @@ m2/gm2-compiler/%.o: m2/gm2-compiler/%.mod
 
 m2/gm2-libs-iso/%.o: $(srcdir)/m2/gm2-libs-iso/%.c m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -DBUILD_GM2_LIBS_TARGET -DBUILD_GM2_LIBS -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -DBUILD_GM2_LIBS_TARGET -DBUILD_GM2_LIBS -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs-iso/%.o: $(srcdir)/m2/gm2-libs-iso/%.mod
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
@@ -1621,15 +1626,15 @@ m2/gm2-libs/%.o: $(srcdir)/m2/gm2-libs/%.mod $(MCDEPS) $(BUILD-BOOT-H)
 
 m2/gm2-libs/%.o: $(srcdir)/m2/gm2-libs-ch/%.c m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -DBUILD_GM2_LIBS -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -DBUILD_GM2_LIBS -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs/%.o: $(srcdir)/m2/gm2-libs-ch/%.cc m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot $(INCLUDES) $< -o $@
 
 m2/gm2-libs/choosetemp.o: m2/gm2-libs-ch/choosetemp.c m2/gm2-libiberty/Gchoosetemp.h m2/gm2-libs/gm2-libs-host.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) -c $(CFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libiberty -I$(srcdir)/m2/gm2-libiberty/ $(INCLUDES) $< -o $@
+	$(CXX) -c $(CFLAGS) $(GM2_PICFLAGS) -Im2/gm2-libs -I$(srcdir)/m2 -Im2 -I. -Im2/gm2-libs-boot -Im2/gm2-libiberty -I$(srcdir)/m2/gm2-libiberty/ $(INCLUDES) $< -o $@
 
 m2/gm2-libs-boot/libgm2.a: m2/boot-bin/mc$(exeext) $(BUILD-LIBS-BOOT)
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
@@ -1729,11 +1734,11 @@ include m2/Make-maintainer
 else
 m2/pge-boot/%.o: m2/pge-boot/%.c m2/gm2-libs/gm2-libs-host.h m2/gm2config.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) $(CFLAGS) $(INCLUDES) -I$(srcdir)/m2/pge-boot -Im2/gm2-libs -g -c $< -o $@
+	$(CXX) $(CFLAGS) $(GM2_PICFLAGS) $(INCLUDES) -I$(srcdir)/m2/pge-boot -Im2/gm2-libs -g -c $< -o $@
 
 m2/pge-boot/%.o: m2/pge-boot/%.cc m2/gm2-libs/gm2-libs-host.h m2/gm2config.h
 	-test -d $(@D) || $(mkinstalldirs) $(@D)
-	$(CXX) $(CXXFLAGS) $(INCLUDES) -I$(srcdir)/m2/pge-boot -Im2/gm2-libs -g -c $< -o $@
+	$(CXX) $(CXXFLAGS) $(GM2_PICFLAGS) $(INCLUDES) -I$(srcdir)/m2/pge-boot -Im2/gm2-libs -g -c $< -o $@
 
 $(PGE): $(BUILD-PGE-O)
 	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ $(BUILD-PGE-O) -lm