kumquat-buildroot/toolchain/helpers.mk

# This Makefile fragment declares toolchain related helper functions.

# The copy_toolchain_lib_root function copies a toolchain library and
# its symbolic links from the sysroot directory to the target
# directory. Note that this function is used both by the external
# toolchain logic, and the glibc package, so care must be taken when
# changing this function.
#
# $1: library name pattern (can include glob wildcards)
#
copy_toolchain_lib_root = \
	LIBPATTERN="$(strip $1)"; \
	LIBPATHS=`find $(STAGING_DIR)/ -name "$${LIBPATTERN}" 2>/dev/null` ; \
	for LIBPATH in $${LIBPATHS} ; do \
		while true ; do \
			LIBNAME=`basename $${LIBPATH}`; \
			DESTDIR=`echo $${LIBPATH} | sed "s,^$(STAGING_DIR)/,," | xargs dirname` ; \
			mkdir -p $(TARGET_DIR)/$${DESTDIR}; \
			rm -fr $(TARGET_DIR)/$${DESTDIR}/$${LIBNAME}; \
			if test -h $${LIBPATH} ; then \
				cp -d $${LIBPATH} $(TARGET_DIR)/$${DESTDIR}/$${LIBNAME}; \
				LIBPATH="`readlink -f $${LIBPATH}`"; \
			elif test -f $${LIBPATH}; then \
				$(INSTALL) -D -m0755 $${LIBPATH} $(TARGET_DIR)/$${DESTDIR}/$${LIBNAME}; \
				break ; \
			else \
				exit -1; \
			fi; \
		done; \
	done

#
# Copy the full external toolchain sysroot directory to the staging
# dir. The operation of this function is rendered a little bit
# complicated by the support for multilib toolchains.
#
# We start by copying etc, 'lib', sbin, usr and usr/'lib' from the
# sysroot of the selected architecture variant (as pointed to by
# ARCH_SYSROOT_DIR). This allows to import into the staging directory
# the C library and companion libraries for the correct architecture
# variant. 'lib' may not be literally 'lib' but could be something else,
# e.g. lib32-fp (as determined by ARCH_LIB_DIR) and we only want to copy
# that lib directory and no other. When copying usr, we therefore need
# to be extra careful not to include usr/lib* but we _do_ want to
# include usr/libexec.
# We are selective in the directories we copy since other directories
# might exist for other architecture variants (on Codesourcery
# toolchain, the sysroot for the default architecture variant contains
# the armv4t and thumb2 subdirectories, which are the sysroot for the
# corresponding architecture variants), and we don't want to import
# them.
#
# If ARCH_LIB_DIR is not a singular directory component, e.g.
# 'lib32/octeon2', then symbolic links in ARCH_LIB_DIR and
# usr/ARCH_LIB_DIR may be broken because Buildroot will flatten the
# directory structure (e.g. lib32/octeon2/foo is actually stored in
# lib/foo). This is only relevant for links that contain one or more ../
# components, as links to the current directory are always fine.
# We need to fix the broken links by removing the right amount of ../
# dots from the link destination.
# Once the link destination is valid again, it can be simplified to
# remove the dependency on intermediate directory symlinks.
#
# It is possible that ARCH_LIB_DIR does not contain the dynamic loader
# (ld*.so or similar) because it (or the main symlink to it) normally
# resides in /lib while ARCH_LIB_DIR may be something else (e.g. lib64,
# lib/<tuple>, ...). Therefore, copy the dynamic loader separately.
#
# Then, if the selected architecture variant is not the default one
# (i.e, if SYSROOT_DIR != ARCH_SYSROOT_DIR), then we :
#
#  * Import the header files from the default architecture
#    variant. Header files are typically shared between the sysroots
#    for the different architecture variants. If we use the
#    non-default one, header files were not copied by the previous
#    step, so we copy them here from the sysroot of the default
#    architecture variant.
#
#  * Create a symbolic link that matches the name of the subdirectory
#    for the architecture variant in the original sysroot. This is
#    required as the compiler will by default look in
#    sysroot_dir/arch_variant/ for libraries and headers, when the
#    non-default architecture variant is used. Without this, the
#    compiler fails to find libraries and headers.
#
# Some toolchains (i.e Linaro binary toolchains) store support
# libraries (libstdc++, libgcc_s) outside of the sysroot, so we simply
# copy all the libraries from the "support lib directory" into our
# sysroot.
#
# Note that the 'locale' directories are not copied. They are huge
# (400+MB) in CodeSourcery toolchains, and they are not really useful.
#
# $1: main sysroot directory of the toolchain
# $2: arch specific sysroot directory of the toolchain
# $3: arch specific subdirectory in the sysroot
# $4: directory of libraries ('lib', 'lib32' or 'lib64')
# $5: support lib directories (for toolchains storing libgcc_s,
#     libstdc++ and other gcc support libraries outside of the
#     sysroot)
copy_toolchain_sysroot = \
	SYSROOT_DIR="$(strip $1)"; \
	ARCH_SYSROOT_DIR="$(strip $2)"; \
	ARCH_SUBDIR="$(strip $3)"; \
	ARCH_LIB_DIR="$(strip $4)" ; \
	SUPPORT_LIB_DIR="$(strip $5)" ; \
	for i in etc $${ARCH_LIB_DIR} sbin usr usr/$${ARCH_LIB_DIR}; do \
		if [ ! -d $${ARCH_SYSROOT_DIR}/$$i ] ; then \
			continue ; \
		fi ; \
		if [ "$$i" = "usr" ]; then \
			rsync -au --chmod=u=rwX,go=rX --exclude 'locale/' \
				--include '/libexec*/' --exclude '/lib*/' \
				$${ARCH_SYSROOT_DIR}/$$i/ $(STAGING_DIR)/$$i/ ; \
		else \
			rsync -au --chmod=u=rwX,go=rX --exclude 'locale/' \
				$${ARCH_SYSROOT_DIR}/$$i/ $(STAGING_DIR)/$$i/ ; \
		fi ; \
	done ; \
	for link in $$(find $(STAGING_DIR) -type l); do \
		target=$$(readlink $${link}) ; \
		if [ "$${target}" == "$${target$(SHARP_SIGN)/}" ] ; then \
			continue ; \
		fi ; \
		relpath="$(call relpath_prefix,$${target$(SHARP_SIGN)/})" ; \
		echo "Fixing symlink $${link} from $${target} to $${relpath}$${target$(SHARP_SIGN)/}" ; \
		ln -sf $${relpath}$${target$(SHARP_SIGN)/} $${link} ; \
	done ; \
	relpath="$(call relpath_prefix,$${ARCH_LIB_DIR})" ; \
	if [ "$${relpath}" != "" ]; then \
		for i in $$(find -H $(STAGING_DIR)/$${ARCH_LIB_DIR} $(STAGING_DIR)/usr/$${ARCH_LIB_DIR} -type l -xtype l); do \
			LINKTARGET=`readlink $$i` ; \
			NEWLINKTARGET=$${LINKTARGET\#$$relpath} ; \
			ln -sf $${NEWLINKTARGET} $$i ; \
			$(call simplify_symlink,$$i,$(STAGING_DIR)) ; \
		done ; \
	fi ; \
	if [ ! -e $(STAGING_DIR)/lib/ld*.so.* ]; then \
		if [ -e $${ARCH_SYSROOT_DIR}/lib/ld*.so.* ]; then \
			cp -a $${ARCH_SYSROOT_DIR}/lib/ld*.so.* $(STAGING_DIR)/lib/ ; \
		fi ; \
	fi ; \
	if [ `readlink -f $${SYSROOT_DIR}` != `readlink -f $${ARCH_SYSROOT_DIR}` ] ; then \
		if [ ! -d $${ARCH_SYSROOT_DIR}/usr/include ] ; then \
			cp -a $${SYSROOT_DIR}/usr/include $(STAGING_DIR)/usr ; \
		fi ; \
		mkdir -p `dirname $(STAGING_DIR)/$${ARCH_SUBDIR}` ; \
		relpath="$(call relpath_prefix,$${ARCH_SUBDIR})./" ; \
		ln -s $${relpath} $(STAGING_DIR)/$${ARCH_SUBDIR} ; \
		echo "Symlinking $(STAGING_DIR)/$${ARCH_SUBDIR} -> $${relpath}" ; \
	fi ; \
	if test -n "$${SUPPORT_LIB_DIR}" ; then \
		cp -a $${SUPPORT_LIB_DIR}/* $(STAGING_DIR)/lib/ ; \
	fi ; \
	find $(STAGING_DIR) -type d | xargs chmod 755

#
# Check the specified kernel headers version actually matches the
# version in the toolchain.
#
# $1: build directory
# $2: sysroot directory
# $3: kernel version string, in the form: X.Y
# $4: test to do for the latest kernel version, 'strict' or 'loose'
#     always 'strict' if this is not the latest version.
#
check_kernel_headers_version = \
	if ! support/scripts/check-kernel-headers.sh $(1) $(2) $(3) \
		$(if $(BR2_TOOLCHAIN_HEADERS_LATEST),$(4),strict); \
	then \
		exit 1; \
	fi

#
# Check the specific gcc version actually matches the version in the
# toolchain
#
# $1: path to gcc
# $2: expected gcc version
#
check_gcc_version = \
	expected_version="$(strip $2)" ; \
	if [ -z "$${expected_version}" ]; then \
		exit 0 ; \
	fi; \
	real_version=`$(1) -dumpversion` ; \
	if [[ ! "$${real_version}." =~ ^$${expected_version}\. ]] ; then \
		printf "Incorrect selection of gcc version: expected %s.x, got %s\n" \
			"$${expected_version}" "$${real_version}" ; \
		exit 1 ; \
	fi

#
# Check the availability of a particular glibc feature. This function
# is used to check toolchain options that are always supported by
# glibc, so we simply check that the corresponding option is properly
# enabled.
#
# $1: Buildroot option name
# $2: feature description
#
check_glibc_feature = \
	if [ "$($(1))" != "y" ] ; then \
		echo "$(2) available in C library, please enable $(1)" ; \
		exit 1 ; \
	fi

#
# Check the availability of RPC support in a glibc toolchain
#
# $1: sysroot directory
#
check_glibc_rpc_feature = \
	IS_IN_LIBC=`test -f $(1)/usr/include/rpc/rpc.h && echo y` ; \
	if [ "$(BR2_TOOLCHAIN_HAS_NATIVE_RPC)" != "y" -a "$${IS_IN_LIBC}" = "y" ] ; then \
		echo "RPC support available in C library, please enable BR2_TOOLCHAIN_EXTERNAL_INET_RPC" ; \
		exit 1 ; \
	fi ; \
	if [ "$(BR2_TOOLCHAIN_HAS_NATIVE_RPC)" = "y" -a "$${IS_IN_LIBC}" != "y" ] ; then \
		echo "RPC support not available in C library, please disable BR2_TOOLCHAIN_EXTERNAL_INET_RPC" ; \
		exit 1 ; \
	fi

#
# Check the correctness of a glibc external toolchain configuration.
#  1. Check that the C library selected in Buildroot matches the one
#     of the external toolchain
#  2. Check that all the C library-related features are enabled in the
#     config, since glibc always supports all of them
#
# $1: sysroot directory
#
check_glibc = \
	SYSROOT_DIR="$(strip $1)"; \
	if test `find -L $${SYSROOT_DIR}/ -maxdepth 2 -name 'ld-linux*.so.*' -o -name 'ld.so.*' -o -name 'ld64.so.*' | wc -l` -eq 0 ; then \
		echo "Incorrect selection of the C library"; \
		exit -1; \
	fi; \
	$(call check_glibc_feature,BR2_USE_MMU,MMU support) ;\
	$(call check_glibc_rpc_feature,$${SYSROOT_DIR})

#
# Check that the selected C library really is musl
#
# $1: cross-gcc path
# $2: cross-readelf path
check_musl = \
	__CROSS_CC=$(strip $1) ; \
	libc_a_path=`$${__CROSS_CC} -print-file-name=libc.a` ; \
	if ! strings $${libc_a_path} | grep -q MUSL_LOCPATH ; then \
		echo "Incorrect selection of the C library" ; \
		exit -1; \
	fi

#
# Check the conformity of Buildroot configuration with regard to the
# uClibc configuration of the external toolchain, for a particular
# feature.
#
# If 'Buildroot option name' ($2) is empty it means the uClibc option
# is mandatory.
#
# $1: uClibc macro name
# $2: Buildroot option name
# $3: uClibc config file
# $4: feature description
#
check_uclibc_feature = \
	IS_IN_LIBC=`grep -q "\#define $(1) 1" $(3) && echo y` ; \
	if [ -z "$(2)" ] ; then \
		if [ "$${IS_IN_LIBC}" != "y" ] ; then \
			echo "$(4) not available in C library, toolchain unsuitable for Buildroot" ; \
			exit 1 ; \
		fi ; \
	else \
		if [ "$($(2))" != "y" -a "$${IS_IN_LIBC}" = "y" ] ; then \
			echo "$(4) available in C library, please enable $(2)" ; \
			exit 1 ; \
		fi ; \
		if [ "$($(2))" = "y" -a "$${IS_IN_LIBC}" != "y" ] ; then \
			echo "$(4) not available in C library, please disable $(2)" ; \
			exit 1 ; \
		fi ; \
	fi

#
# Check the correctness of a uclibc external toolchain configuration
#  1. Check that the C library selected in Buildroot matches the one
#     of the external toolchain
#  2. Check that the features enabled in the Buildroot configuration
#     match the features available in the uClibc of the external
#     toolchain
#
# $1: sysroot directory
#
check_uclibc = \
	SYSROOT_DIR="$(strip $1)"; \
	if ! test -f $${SYSROOT_DIR}/usr/include/bits/uClibc_config.h ; then \
		echo "Incorrect selection of the C library"; \
		exit -1; \
	fi; \
	UCLIBC_CONFIG_FILE=$${SYSROOT_DIR}/usr/include/bits/uClibc_config.h ; \
	$(call check_uclibc_feature,__ARCH_USE_MMU__,BR2_USE_MMU,$${UCLIBC_CONFIG_FILE},MMU support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_LFS__,,$${UCLIBC_CONFIG_FILE},Large file support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_IPV6__,,$${UCLIBC_CONFIG_FILE},IPv6 support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_RPC__,BR2_TOOLCHAIN_HAS_NATIVE_RPC,$${UCLIBC_CONFIG_FILE},RPC support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_LOCALE__,BR2_ENABLE_LOCALE,$${UCLIBC_CONFIG_FILE},Locale support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_WCHAR__,BR2_USE_WCHAR,$${UCLIBC_CONFIG_FILE},Wide char support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_THREADS__,BR2_TOOLCHAIN_HAS_THREADS,$${UCLIBC_CONFIG_FILE},Thread support) ;\
	$(call check_uclibc_feature,__PTHREADS_DEBUG_SUPPORT__,BR2_TOOLCHAIN_HAS_THREADS_DEBUG,$${UCLIBC_CONFIG_FILE},Thread debugging support) ;\
	$(call check_uclibc_feature,__UCLIBC_HAS_THREADS_NATIVE__,BR2_TOOLCHAIN_HAS_THREADS_NPTL,$${UCLIBC_CONFIG_FILE},NPTL thread support)

#
# Check that the Buildroot configuration of the ABI matches the
# configuration of the external toolchain.
#
# $1: cross-gcc path
# $2: cross-readelf path
#
check_arm_abi = \
	__CROSS_CC=$(strip $1) ; \
	EXT_TOOLCHAIN_TARGET=`LANG=C $${__CROSS_CC} -v 2>&1 | grep ^Target | cut -f2 -d ' '` ; \
	if ! echo $${EXT_TOOLCHAIN_TARGET} | grep -qE 'eabi(hf)?$$' ; then \
		echo "External toolchain uses the unsuported OABI" ; \
		exit 1 ; \
	fi ; \
	if ! echo 'int main(void) {}' | $${__CROSS_CC} -x c -o $(BUILD_DIR)/.br-toolchain-test.tmp - ; then \
		rm -f $(BUILD_DIR)/.br-toolchain-test.tmp*; \
		abistr_$(BR2_ARM_EABI)='EABI'; \
		abistr_$(BR2_ARM_EABIHF)='EABIhf'; \
		echo "Incorrect ABI setting: $${abistr_y} selected, but toolchain is incompatible"; \
		exit 1 ; \
	fi ; \
	rm -f $(BUILD_DIR)/.br-toolchain-test.tmp*

#
# Check that the external toolchain supports C++
#
# $1: cross-g++ path
#
check_cplusplus = \
	__CROSS_CXX=$(strip $1) ; \
	$${__CROSS_CXX} -v > /dev/null 2>&1 ; \
	if test $$? -ne 0 ; then \
		echo "C++ support is selected but is not available in external toolchain" ; \
		exit 1 ; \
	fi

#
#
# Check that the external toolchain supports D language
#
# $1: cross-gdc path
#
check_dlang = \
	__CROSS_GDC=$(strip $1) ; \
	__o=$(BUILD_DIR)/.br-toolchain-test-dlang.tmp ; \
	printf 'import std.stdio;\nvoid main() { writeln("Hello World!"); }\n' | \
	$${__CROSS_GDC} -x d -o $${__o} - ; \
	if test $$? -ne 0 ; then \
		rm -f $${__o}* ; \
		echo "D language support is selected but is not available in external toolchain" ; \
		exit 1 ; \
	fi ; \
	rm -f $${__o}* \

#
#
# Check that the external toolchain supports Fortran
#
# $1: cross-gfortran path
#
check_fortran = \
	__CROSS_FC=$(strip $1) ; \
	__o=$(BUILD_DIR)/.br-toolchain-test-fortran.tmp ; \
	printf 'program hello\n\tprint *, "Hello Fortran!\\n"\nend program hello\n' | \
	$${__CROSS_FC} -x f95 -o $${__o} - ; \
	if test $$? -ne 0 ; then \
		rm -f $${__o}* ; \
		echo "Fortran support is selected but is not available in external toolchain" ; \
		exit 1 ; \
	fi ; \
	rm -f $${__o}* \

#
#
# Check that the external toolchain supports OpenMP
#
# $1: cross-gcc path
#
check_openmp = \
	__CROSS_CC=$(strip $1) ; \
	__o=$(BUILD_DIR)/.br-toolchain-test-openmp.tmp ; \
	printf '\#include <omp.h>\nint main(void) { return omp_get_thread_num(); }' | \
	$${__CROSS_CC} -fopenmp -x c -o $${__o} - ; \
	if test $$? -ne 0 ; then \
		rm -f $${__o}* ; \
		echo "OpenMP support is selected but is not available in external toolchain"; \
		exit 1 ; \
	fi ; \
	rm -f $${__o}* \

#
# Check that the cross-compiler given in the configuration exists
#
# $1: cross-gcc path
#
check_cross_compiler_exists = \
	__CROSS_CC=$(strip $1) ; \
	$${__CROSS_CC} -v > /dev/null 2>&1 ; \
	if test $$? -ne 0 ; then \
		echo "Cannot execute cross-compiler '$${__CROSS_CC}'" ; \
		exit 1 ; \
	fi

#
# Check for toolchains known not to work with Buildroot.
# - For the Angstrom toolchains, we check by looking at the vendor part of
#   the host tuple.
# - Exclude distro-class toolchains which are not relocatable.
# - Exclude broken toolchains which return "libc.a" with -print-file-name.
# - Exclude toolchains which doesn't support --sysroot option.
#
# $1: cross-gcc path
#
check_unusable_toolchain = \
	__CROSS_CC=$(strip $1) ; \
	vendor=`$${__CROSS_CC} -dumpmachine | cut -f2 -d'-'` ; \
	if test "$${vendor}" = "angstrom" ; then \
		echo "Angstrom toolchains are not pure toolchains: they contain" ; \
		echo "many other libraries than just the C library, which makes" ; \
		echo "them unsuitable as external toolchains for build systems" ; \
		echo "such as Buildroot." ; \
		exit 1 ; \
	fi; \
	with_sysroot=`$${__CROSS_CC} -v 2>&1 |sed -r -e '/.* --with-sysroot=([^[:space:]]+)[[:space:]].*/!d; s//\1/'`; \
	if test "$${with_sysroot}"  = "/" ; then \
		echo "Distribution toolchains are unsuitable for use by Buildroot," ; \
		echo "as they were configured in a way that makes them non-relocatable,"; \
		echo "and contain a lot of pre-built libraries that would conflict with"; \
		echo "the ones Buildroot wants to build."; \
		exit 1; \
	fi; \
	libc_a_path=`$${__CROSS_CC} -print-file-name=libc.a` ; \
	if test "$${libc_a_path}" = "libc.a" ; then \
		echo "Unable to detect the toolchain sysroot, Buildroot cannot use this toolchain." ; \
		exit 1 ; \
	fi ; \
	sysroot_dir="$(call toolchain_find_sysroot,$${__CROSS_CC})" ; \
	if test -z "$${sysroot_dir}" ; then \
		echo "External toolchain doesn't support --sysroot. Cannot use." ; \
		exit 1 ; \
	fi

#
# Check if the toolchain has SSP (stack smashing protector) support
#
# $1: cross-gcc path
# $2: gcc ssp option
#
check_toolchain_ssp = \
	__CROSS_CC=$(strip $1) ; \
	__HAS_SSP=`echo 'void main(){}' | $${__CROSS_CC} -Werror -fstack-protector -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 && echo y` ; \
	if [ "$(BR2_TOOLCHAIN_HAS_SSP)" != "y" -a "$${__HAS_SSP}" = "y" ] ; then \
		echo "SSP support available in this toolchain, please enable BR2_TOOLCHAIN_EXTERNAL_HAS_SSP" ; \
		exit 1 ; \
	fi ; \
	if [ "$(BR2_TOOLCHAIN_HAS_SSP)" = "y" -a "$${__HAS_SSP}" != "y" ] ; then \
		echo "SSP support not available in this toolchain, please disable BR2_TOOLCHAIN_EXTERNAL_HAS_SSP" ; \
		exit 1 ; \
	fi ; \
	__SSP_OPTION=$(2); \
	if [ -n "$${__SSP_OPTION}" ] ; then \
		if ! echo 'void main(){}' | $${__CROSS_CC} -Werror $${__SSP_OPTION} -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 ; then \
			echo "SSP option $${__SSP_OPTION} not available in this toolchain, please select another SSP level" ; \
			exit 1 ; \
		fi; \
	fi; \
	rm -f $(BUILD_DIR)/.br-toolchain-test.tmp*

#
# Generate gdbinit file for use with Buildroot
#
gen_gdbinit_file = \
	mkdir -p $(STAGING_DIR)/usr/share/buildroot/ ; \
	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit ; \
	echo "add-auto-load-safe-path $(STAGING_DIR)" >> $(STAGING_DIR)/usr/share/buildroot/gdbinit

# Given a path, determine the relative prefix (../) needed to return to the
# root level. Note that the last component is treated as a file component; use a
# trailing slash to force treating it as a directory. Examples:
#     relpath_prefix(lib32) = ""
#     relpath_prefix(lib32/octeon2) = "../"
#     relpath_prefix(lib32/octeon2/) = "../../"
#
# $1: input path
define relpath_prefix
$$( \
	prefix="" ; \
	nbslashs=`printf $1 | sed 's%[^/]%%g' | wc -c` ; \
	for slash in `seq 1 $${nbslashs}` ; do \
		prefix=$${prefix}"../" ; \
	done ; \
	printf "$$prefix" ; \
)
endef

# Replace the destination of a symbolic link with a simpler version
# For example,
#     usr/lib/libfoo.so -> ../../lib32/libfoo.so.1
# becomes
#     usr/lib/libfoo.so -> ../../lib/libfoo.so.1
# since 'lib32' is a symlink to 'lib'.
#
# Likewise,
#     usr/lib/octeon2/libbar.so -> ../../../lib32/octeon2/libbar.so.1
# becomes
#     usr/lib/octeon2/libbar.so -> ../../lib/libbar.so.1
# assuming lib32->lib and lib/octeon2->lib.
#
# $1: symlink
# $2: base path
define simplify_symlink
( \
	FULL_SRC="$$(readlink -f $$(dirname $1))/$$(basename $1)" ; \
	FULL_DEST="$$(readlink -f $1)" ; \
	FULL_BASE="$$(readlink -f $2)" ; \
	REL_SRC="$${FULL_SRC#$${FULL_BASE}/}" ; \
	REL_DEST="$${FULL_DEST#$${FULL_BASE}/}" ; \
	DOTS="$(call relpath_prefix,$${REL_SRC})" ; \
	ln -sf "$${DOTS}$${REL_DEST}" "$${FULL_SRC}" ; \
)
endef