diff --git a/GNUmakefile.in b/GNUmakefile.in
index a1ef990a1e..a050d13ff1 100644
--- a/GNUmakefile.in
+++ b/GNUmakefile.in
@@ -44,16 +44,20 @@ DEFS = @DEFS@
 LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@
 
-GMP_USE_BUILTIN = @GMP_USE_BUILTIN@
+BUILD_GMP = @BUILD_GMP@
 GMP_CPPFLAGS = @GMP_CPPFLAGS@
 GMP_LDFLAGS = @GMP_LDFLAGS@
 
 READLINE_LDFLAGS = @READLINE_LDFLAGS@
 
-BOEHM_CPPFLAGS = @BOEHM_CPPFLAGS@
+BUILD_BOEHM_GC = @BUILD_BOEHM_GC@
+BOEHM_GC_CPPFLAGS = @BOEHM_GC_CPPFLAGS@
 BOEHM_LDFLAGS = @BOEHM_LDFLAGS@
+
+BUILD_LIBATOMIC_OPS = @BUILD_LIBATOMIC_OPS@
 LIBATOMIC_OPS_CPPFLAGS = @LIBATOMIC_OPS_CPPFLAGS@
 LIBATOMIC_OPS_LDFLAGS = @LIBATOMIC_OPS_LDFLAGS@
+
 PTHREAD_CFLAGS = @PTHREAD_CFLAGS@
 PTHREAD_LIBS = @PTHREAD_LIBS@
 
diff --git a/Makefile.rules b/Makefile.rules
index 80432d7434..7c2e48262b 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -12,9 +12,11 @@
 # Default rule: build gap
 ########################################################################
 all: gap$(EXEEXT) gac
+.PHONY: all
 
 # Backwards compatibility: add "default" target as alias for "all"
 default: all
+.PHONY: default
 
 
 ########################################################################
@@ -142,7 +144,7 @@ GAP_CPPFLAGS += $(GMP_CPPFLAGS)
 
 # Add HPC-GAP specific flacks if necessary
 ifeq ($(HPCGAP),yes)
-GAP_CPPFLAGS += $(BOEHM_CPPFLAGS) $(LIBATOMIC_OPS_CPPFLAGS)
+GAP_CPPFLAGS += $(BOEHM_GC_CPPFLAGS) $(LIBATOMIC_OPS_CPPFLAGS)
 endif
 
 # HACK: teach GAP how to "find itself". For a proper solution,
@@ -378,6 +380,7 @@ docomp: #gap$(EXEEXT)
 	  "$(abs_top_srcdir)"/cnf/GAP-C-GEN $(DOCOMP_PREFIX) $$file ./gap$(EXEEXT) ; \
 	done
 
+.PHONY: docomp
 
 ########################################################################
 # Rules for 'make clean'
@@ -391,32 +394,126 @@ clean:
 	rm -rf obj
 	rm -f gap$(EXEEXT) gac
 
+.PHONY: clean distclean
+
 
 ########################################################################
 # Building subprojects
 ########################################################################
 
-ifeq ($(GMP_USE_BUILTIN),yes)
-gap$(EXEEXT): gmp
+
+# master target for external dependencies / subprojects
+EXTERN_FILES =
+
+
+#
+# GMP
+#
+ifeq ($(BUILD_GMP),yes)
+
+GMP_BUILDDIR := extern/build/gmp
+GMP_PREFIX := extern/install/gmp
+# GMP_PREREQ := $(GMP_BUILDDIR)/config.status
+GMP_FILES := $(GMP_PREFIX)/lib/libgmp.la
+
+EXTERN_FILES += $(GMP_FILES)
+
+gmp: $(GMP_FILES)
+$(GMP_FILES):
+	MAKE=$(MAKE) $(srcdir)/cnf/build-extern.sh gmp "$(abs_top_srcdir)/extern/gmp" ABI=$(ABI)
+
+.PHONY: gmp
+
+# TODO: add clean, distclean, check targets?
+# TODO: pass on cachfile?
+# TODO: pass on certain *FLAGS ?
+
+
+else
+
 gmp:
-	$(MAKE) -C extern/gmp -s
+	echo "Using external GMP, nothing to do be done"
+
+endif # BUILD_GMP
+
+
+#
+# libatomic_ops
+#
+ifeq ($(BUILD_LIBATOMIC_OPS),yes)
 
-$(OBJS): extern/gmp/gmp.h
-extern/gmp/gmp.h:
-	$(MAKE) -C extern/gmp -s gmp.h
+LIBATOMIC_OPS_BUILDDIR := extern/build/libatomic_ops
+LIBATOMIC_OPS_PREFIX := extern/install/libatomic_ops
+#LIBATOMIC_OPS_PREREQ := $(LIBATOMIC_OPS_BUILDDIR)/config.status
+LIBATOMIC_OPS_FILES := $(LIBATOMIC_OPS_PREFIX)/lib/libatomic_ops.la
 
-clean: clean-gmp
-clean-gmp:
-	$(MAKE) -C extern/gmp -s clean
+EXTERN_FILES += $(LIBATOMIC_OPS_FILES)
 
-check: check-gmp
-check-gmp:
-	$(MAKE) -C extern/gmp -s check
+libatomic_ops: $(LIBATOMIC_OPS_FILES)
+$(LIBATOMIC_OPS_FILES):
+	MAKE=$(MAKE) $(srcdir)/cnf/build-extern.sh libatomic_ops "$(abs_top_srcdir)/hpcgap/extern/libatomic_ops" ABI=$(ABI)
 
-.PHONY: gmp clean-gmp check-gmp
+# TODO: MAKEFLAGS=-j1
+
+.PHONY: libatomic_ops
+
+endif # BUILD_LIBATOMIC_OPS
+
+
+#
+# Boehm GC
+#
+ifeq ($(BUILD_BOEHM_GC),yes)
 
+# TODO: ensure Boehm GC is built *after* libatomic_ops, at least if
+# we are building or own libatomic_ops.
+# Also, ensure that it uses the right version of libatomic_ops,
+# by passing --with-libatomic-ops=...
+
+# TODO: also pass
+
+# TODO: refactor code which handles dependencies like GMP, Boehm, libatomic,
+# to reduce code duplication.
+
+# TODO: pass on more things to configure, e.g. the build / host system type...
+# 
+
+BOEHM_GC_BUILDDIR := extern/build/gc
+BOEHM_GC_PREFIX := extern/install/gc
+#BOEHM_GC_PREREQ := $(BOEHM_GC_BUILDDIR)/config.status
+BOEHM_GC_FILES := $(BOEHM_GC_PREFIX)/lib/libgc.la
+
+EXTERN_FILES += $(BOEHM_GC_FILES)
+
+boehm: gc # alias
+gc: $(BOEHM_GC_FILES)
+$(BOEHM_GC_FILES):
+	MAKE=$(MAKE) $(srcdir)/cnf/build-extern.sh gc "$(abs_top_srcdir)/hpcgap/extern/gc" ABI=$(ABI)
+
+ifeq ($(BUILD_LIBATOMIC_OPS),yes)
+$(BOEHM_GC_FILES): $(LIBATOMIC_OPS_FILES)
+endif
+
+.PHONY: boehm gc
+
+endif # BUILD_BOEHM_GC
+
+
+foobar:
+	echo FOOBAR: $(EXTERN_FILES) QUUX
+
+# ensure subprojects are built and "installed" before compiling and linking GAP
+gap$(EXEEXT): $(EXTERN_FILES)
+$(OBJS): $(EXTERN_FILES)
+ifeq ($(HPCGAP),yes)
+$(SOURCES): $(EXTERN_FILES)
 endif
 
+distclean: distclean-extern
+distclean-extern:
+	rm -rf extern/build
+	rm -rf extern/install
+
 
 ########################################################################
 # Compatibility mode
@@ -547,6 +644,8 @@ gen/gap_version.c: $(top_srcdir)/src/gap_version.c.in $(GVF)
 	@$(MKDIR_P) $(@D)
 	$(QUIET_SED)sed -e "s/@GAP_VERSION@/$(GAP_VERSION)/" < $< > $@
 
+.PHONY: FORCE
+
 
 ########################################################################
 # Regenerate parts of the build system as needed.
@@ -586,16 +685,3 @@ GNUmakefile: $(srcdir)/GNUmakefile.in config.status
 
 gac: $(srcdir)/cnf/gac.in config.status
 	$(SHELL) ./config.status $@
-
-
-########################################################################
-# All .PHONY targets
-########################################################################
-
-.PHONY: all clean distclean check docomp
-
-# The following is needed for the rules handling the GAP version
-.PHONY: FORCE
-
-# Backwards compatibility rules
-.PHONY: default
diff --git a/cnf/build-extern.sh b/cnf/build-extern.sh
new file mode 100755
index 0000000000..83219fe19c
--- /dev/null
+++ b/cnf/build-extern.sh
@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+#
+# This script is used by the build system to build external dependencies
+# such as GMP and Boehm GC in a controlled and uniform way
+
+set -e
+
+echo "=== START building $pkg ==="
+
+# read arguments (TODO: error handling)
+pkg=$1; shift
+src=$1; shift # directory with package sources -- must be an absolute path
+
+builddir=extern/build/$pkg
+prefix=$PWD/extern/install/$pkg
+
+mkdir -p "$builddir"
+
+if [[ ! "$builddir/config.status" -nt "$src/configure" ]] ; then
+  pushd "$builddir"
+  "$src/configure" --prefix=$prefix "$@"
+  popd
+fi
+
+$MAKE -C "$builddir"
+$MAKE -C "$builddir" install
+
+# TODO: insert command to check whether make needs to be called at all?
+echo "=== DONE building $pkg ==="
diff --git a/configure.ac b/configure.ac
index a51db841c6..5a44991c24 100644
--- a/configure.ac
+++ b/configure.ac
@@ -252,7 +252,7 @@ dnl External dependencies
 dnl
 
 dnl Find GMP
-GMP_USE_BUILTIN=no
+BUILD_GMP=no
 AC_ARG_WITH([gmp],
   [AS_HELP_STRING([--with-gmp[=DIR]],  
                   [prefix of GMP installation. e.g. /usr/local or /usr])],
@@ -268,7 +268,7 @@ AC_ARG_WITH([gmp],
 
 AS_IF([test x$with_gmp = xbuiltin],
   # user explicitly requested to use builtin GMP?
-  [GMP_USE_BUILTIN=yes
+  [BUILD_GMP=yes
    AC_MSG_NOTICE([Using bundled GMP])
   ],
   # otherwise try to link against GMP
@@ -280,7 +280,7 @@ AS_IF([test x$with_gmp = xbuiltin],
     AC_CHECK_LIB([gmp], [__gmpz_init],
     [], # all is good
     [AS_IF([test x$with_gmp = xcheck],
-      [GMP_USE_BUILTIN=yes
+      [BUILD_GMP=yes
        AC_MSG_NOTICE([No usable GMP found, switching to included GMP])
       ],
       [AC_MSG_ERROR([GMP not found at prefix $with_gmp])]
@@ -290,14 +290,13 @@ AS_IF([test x$with_gmp = xbuiltin],
     LDFLAGS="$tmp_LDFLAGS"
   ])
 
-AS_IF([test x$GMP_USE_BUILTIN = xyes],[
-  AC_CONFIG_SUBDIRS([extern/gmp])
-  GMP_USE_BUILTIN=yes
-  GMP_CPPFLAGS=' -I${builddir}/extern/gmp'
-  GMP_LDFLAGS=' ${builddir}/extern/gmp/libgmp.la'
+AS_IF([test x$BUILD_GMP = xyes],[
+  BUILD_GMP=yes
+  GMP_CPPFLAGS='-I${builddir}/extern/install/gmp/include'
+  GMP_LDFLAGS='${builddir}/extern/install/gmp/lib/libgmp.la'
 ])
 
-AC_SUBST([GMP_USE_BUILTIN])
+AC_SUBST([BUILD_GMP])
 AC_SUBST([GMP_CPPFLAGS])
 AC_SUBST([GMP_LDFLAGS])
 
@@ -363,36 +362,41 @@ AS_IF([test "x$enable_hpcgap" = xyes],
   AS_IF([test "x$ADDGUARDS2" = x], AC_MSG_ERROR([could not locate addguards2]))
 
 
-# TODO: there are further hpcgap specific external dependencies:
-#  gc - the Boehm garbage collector, see http://www.hboehm.info/gc/
-#  libatomic_ops - part of gc, but see also https://github.com/ivmai/libatomic_ops
-#  ...
-
-# HACK
-AC_DEFINE([BOEHM_GC], [1], [Use Boehm garbage collector])
-
-# TODO: detect BOEHM GC and set flags suitably
-#  -> may want to build the one shipped with HPC-GAP,
-#  as that has special improvements for HPC-GAP
-AS_IF([test "x$enable_hpcgap" = xyes],[BOEHM_LDFLAGS="-lgc"])
-AC_SUBST([BOEHM_CPPFLAGS])
-AC_SUBST([BOEHM_LDFLAGS])
-
-# TODO: detected libatomic and set flags suitably
-#  -> may want to build the one shipped with HPC-GAP,
-#  as that has special improvements for HPC-GAP
-AC_SUBST([LIBATOMIC_OPS_CPPFLAGS])
-AC_SUBST([LIBATOMIC_OPS_LDFLAGS])
-
-# FIXME: what about these defines which HPC-GAP seems to "know"?
-# - DISABLE_GC
-# - NUM_CPUS
-# - VERBOSE_GUARDS
-
+  # We bundle two libraries we need for HPC-GAP:
+  # Boehm garbage collector, see http://www.hboehm.info/gc/
+  # libatomic_ops - part of Boehm GC, but see also https://github.com/ivmai/libatomic_ops
+  #
+  # We bundle them because we need a few patches to Boehm GC which are
+  # not upstream (and it is unclear whether they ever will be).
+  # And we bundle libatomic_ops because its version must match that
+  # of Boehm GC; the easiest way to ensure that is to include that, too.
+  #
+  # As a side benefit, users do not have to worry about installing dependencies.
+
+  BUILD_LIBATOMIC_OPS=yes
+  LIBATOMIC_OPS_CPPFLAGS='-I${builddir}/extern/install/libatomic_ops/include'
+  LIBATOMIC_OPS_LDFLAGS='${builddir}/extern/install/libatomic_ops/lib/libatomic_ops.la'
+  AC_SUBST([BUILD_LIBATOMIC_OPS])
+  AC_SUBST([LIBATOMIC_OPS_CPPFLAGS])
+  AC_SUBST([LIBATOMIC_OPS_LDFLAGS])
+
+  ATOMIC_OPS_CFLAGS=$LIBATOMIC_OPS_CPPFLAGS
+  ATOMIC_OPS_LIBS=$LIBATOMIC_OPS_LDFLAGS
+
+  AC_DEFINE([BOEHM_GC], [1], [Use Boehm garbage collector])
+  BUILD_BOEHM_GC=yes
+  BOEHM_GC_CPPFLAGS='-I${builddir}/extern/install/gc/include'
+  BOEHM_LDFLAGS='${builddir}/extern/install/gc/lib/libgc.la'
+  AC_SUBST([BUILD_BOEHM_GC])
+  AC_SUBST([BOEHM_GC_CPPFLAGS])
+  AC_SUBST([BOEHM_LDFLAGS])
   ]
 )
 
 
+# HACK to see if a cache file is set, and what it is
+AS_BOX([cache_file = $cache_file.])
+
 
 dnl
 dnl Detect host specific setting