blob: 3ab44afce7a0a930e1fd844fbbc0cfeb27368807 [file] [log] [blame]
#
# Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# Redistributions of source code must retain the above copyright notice, this
# list of conditions and the following disclaimer.
#
# Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# Neither the name of ARM nor the names of its contributors may be used
# to endorse or promote products derived from this software without specific
# prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
#
# Trusted Firmware Version
#
VERSION_MAJOR := 1
VERSION_MINOR := 2
# Default goal is build all images
.DEFAULT_GOAL := all
include make_helpers/build_macros.mk
################################################################################
# Default values for build configurations
################################################################################
# Build verbosity
V := 0
# Debug build
DEBUG := 0
# Build platform
DEFAULT_PLAT := fvp
PLAT := ${DEFAULT_PLAT}
# SPD choice
SPD := none
# Base commit to perform code check on
BASE_COMMIT := origin/master
# NS timer register save and restore
NS_TIMER_SWITCH := 0
# By default, BL1 acts as the reset handler, not BL31
RESET_TO_BL31 := 0
# Include FP registers in cpu context
CTX_INCLUDE_FPREGS := 0
# Determine the version of ARM GIC architecture to use for interrupt management
# in EL3. The platform port can change this value if needed.
ARM_GIC_ARCH := 2
# Determine the version of ARM CCI product used in the platform. The platform
# port can change this value if needed.
ARM_CCI_PRODUCT_ID := 400
# Flag used to indicate if ASM_ASSERTION should be enabled for the build.
# This defaults to being present in DEBUG builds only.
ASM_ASSERTION := ${DEBUG}
# Build option to choose whether Trusted firmware uses Coherent memory or not.
USE_COHERENT_MEM := 1
# Flag used to choose the power state format viz Extended State-ID or the Original
# format.
PSCI_EXTENDED_STATE_ID := 0
# Default FIP file name
FIP_NAME := fip.bin
# Default FWU_FIP file name
FWU_FIP_NAME := fwu_fip.bin
# By default, use the -pedantic option in the gcc command line
DISABLE_PEDANTIC := 0
# Flags to generate the Chain of Trust
GENERATE_COT := 0
CREATE_KEYS := 1
SAVE_KEYS := 0
# Flags to build TF with Trusted Boot support
TRUSTED_BOARD_BOOT := 0
# By default, consider that the platform's reset address is not programmable.
# The platform Makefile is free to override this value.
PROGRAMMABLE_RESET_ADDRESS := 0
# Build flag to treat usage of deprecated platform and framework APIs as error.
ERROR_DEPRECATED := 0
# By default, consider that the platform may release several CPUs out of reset.
# The platform Makefile is free to override this value.
COLD_BOOT_SINGLE_CPU := 0
# Flag to introduce an infinite loop in BL1 just before it exits into the next
# image. This is meant to help debugging the post-BL2 phase.
SPIN_ON_BL1_EXIT := 0
# Build PL011 UART driver in minimal generic UART mode
PL011_GENERIC_UART := 0
################################################################################
# Checkpatch script options
################################################################################
CHECK_IGNORE := --ignore COMPLEX_MACRO \
--ignore GERRIT_CHANGE_ID \
--ignore GIT_COMMIT_ID
CHECKPATCH_ARGS := --no-tree --no-signoff ${CHECK_IGNORE}
CHECKCODE_ARGS := --no-patch --no-tree --no-signoff ${CHECK_IGNORE}
# Do not check the coding style on C library files
CHECK_PATHS := $(shell ls -I include -I lib) \
$(addprefix include/,$(shell ls -I stdlib include)) \
$(addprefix lib/,$(shell ls -I stdlib lib))
################################################################################
# Process build options
################################################################################
# Verbose flag
ifeq (${V},0)
Q=@
CHECKCODE_ARGS += --no-summary --terse
else
Q=
endif
export Q
# Process Debug flag
$(eval $(call add_define,DEBUG))
ifneq (${DEBUG}, 0)
BUILD_TYPE := debug
CFLAGS += -g
ASFLAGS += -g -Wa,--gdwarf-2
# Use LOG_LEVEL_INFO by default for debug builds
LOG_LEVEL := 40
else
BUILD_TYPE := release
$(eval $(call add_define,NDEBUG))
# Use LOG_LEVEL_NOTICE by default for release builds
LOG_LEVEL := 20
endif
# Default build string (git branch and commit)
ifeq (${BUILD_STRING},)
BUILD_STRING := $(shell git log -n 1 --pretty=format:"%h")
endif
VERSION_STRING := v${VERSION_MAJOR}.${VERSION_MINOR}(${BUILD_TYPE}):${BUILD_STRING}
# The cert_create tool cannot generate certificates individually, so we use the
# target 'certificates' to create them all
ifneq (${GENERATE_COT},0)
FIP_DEPS += certificates
FWU_FIP_DEPS += fwu_certificates
endif
################################################################################
# Toolchain
################################################################################
CC := ${CROSS_COMPILE}gcc
CPP := ${CROSS_COMPILE}cpp
AS := ${CROSS_COMPILE}gcc
AR := ${CROSS_COMPILE}ar
LD := ${CROSS_COMPILE}ld
OC := ${CROSS_COMPILE}objcopy
OD := ${CROSS_COMPILE}objdump
NM := ${CROSS_COMPILE}nm
PP := ${CROSS_COMPILE}gcc -E
ASFLAGS += -nostdinc -ffreestanding -Wa,--fatal-warnings \
-Werror -Wmissing-include-dirs \
-mgeneral-regs-only -D__ASSEMBLY__ \
${DEFINES} ${INCLUDES}
CFLAGS += -nostdinc -ffreestanding -Wall \
-Werror -Wmissing-include-dirs \
-mgeneral-regs-only -mstrict-align \
-std=c99 -c -Os \
${DEFINES} ${INCLUDES}
CFLAGS += -ffunction-sections -fdata-sections
LDFLAGS += --fatal-warnings -O1
LDFLAGS += --gc-sections
################################################################################
# Common sources and include directories
################################################################################
BL_COMMON_SOURCES += common/bl_common.c \
common/tf_printf.c \
common/aarch64/debug.S \
lib/aarch64/cache_helpers.S \
lib/aarch64/misc_helpers.S \
lib/aarch64/xlat_helpers.c \
lib/stdlib/std.c \
plat/common/aarch64/platform_helpers.S
INCLUDES += -Iinclude/bl1 \
-Iinclude/bl31 \
-Iinclude/bl31/services \
-Iinclude/common \
-Iinclude/drivers \
-Iinclude/drivers/arm \
-Iinclude/drivers/auth \
-Iinclude/drivers/io \
-Iinclude/drivers/ti/uart \
-Iinclude/lib \
-Iinclude/lib/aarch64 \
-Iinclude/lib/cpus/aarch64 \
-Iinclude/plat/common \
-Iinclude/stdlib \
-Iinclude/stdlib/sys \
${PLAT_INCLUDES} \
${SPD_INCLUDES}
################################################################################
# Generic definitions
################################################################################
BUILD_BASE := ./build
BUILD_PLAT := ${BUILD_BASE}/${PLAT}/${BUILD_TYPE}
PLAT_MAKEFILE := platform.mk
# Generate the platforms list by recursively searching for all directories
# under /plat containing a PLAT_MAKEFILE. Append each platform with a `|`
# char and strip out the final '|'.
PLATFORMS := $(shell find plat/ -name '${PLAT_MAKEFILE}' -print0 | \
sed -r 's%[^\x00]*\/([^/]*)\/${PLAT_MAKEFILE}\x00%\1|%g' | \
sed -r 's/\|$$//')
SPDS := $(shell ls -I none services/spd)
# Platforms providing their own TBB makefile may override this value
INCLUDE_TBBR_MK := 1
################################################################################
# Include SPD Makefile if one has been specified
################################################################################
ifneq (${SPD},none)
ifdef EL3_PAYLOAD_BASE
$(warning "SPD and EL3_PAYLOAD_BASE are incompatible build options.")
$(warning "The SPD and its BL32 companion will be present but ignored.")
endif
# We expect to locate an spd.mk under the specified SPD directory
SPD_MAKE := $(shell m="services/spd/${SPD}/${SPD}.mk"; [ -f "$$m" ] && echo "$$m")
ifeq (${SPD_MAKE},)
$(error Error: No services/spd/${SPD}/${SPD}.mk located)
endif
$(info Including ${SPD_MAKE})
include ${SPD_MAKE}
# If there's BL32 companion for the chosen SPD, we expect that the SPD's
# Makefile would set NEED_BL32 to "yes". In this case, the build system
# supports two mutually exclusive options:
# * BL32 is built from source: then BL32_SOURCES must contain the list
# of source files to build BL32
# * BL32 is a prebuilt binary: then BL32 must point to the image file
# that will be included in the FIP
# If both BL32_SOURCES and BL32 are defined, the binary takes precedence
# over the sources.
endif
################################################################################
# Include the platform specific Makefile after the SPD Makefile (the platform
# makefile may use all previous definitions in this file)
################################################################################
ifeq (${PLAT},)
$(error "Error: Unknown platform. Please use PLAT=<platform name> to specify the platform")
endif
PLAT_MAKEFILE_FULL := $(shell find plat/ -wholename '*/${PLAT}/${PLAT_MAKEFILE}')
ifeq ($(PLAT_MAKEFILE_FULL),)
$(error "Error: Invalid platform. The following platforms are available: ${PLATFORMS}")
endif
include ${PLAT_MAKEFILE_FULL}
# If the platform has not defined ENABLE_PLAT_COMPAT, then enable it by default
ifndef ENABLE_PLAT_COMPAT
ENABLE_PLAT_COMPAT := 1
endif
# Include the platform compatibility helpers for PSCI
ifneq (${ENABLE_PLAT_COMPAT}, 0)
include plat/compat/plat_compat.mk
endif
# Include the CPU specific operations makefile, which provides default
# values for all CPU errata workarounds and CPU specific optimisations.
# This can be overridden by the platform.
include lib/cpus/cpu-ops.mk
################################################################################
# Check incompatible options
################################################################################
ifdef EL3_PAYLOAD_BASE
ifdef BL33_BASE
$(warning "BL33_BASE and EL3_PAYLOAD_BASE are incompatible \
build options. EL3_PAYLOAD_BASE has priority.")
endif
endif
ifeq (${NEED_BL33},yes)
ifdef EL3_PAYLOAD_BASE
$(warning "BL33 image is not needed when option \
BL33_PAYLOAD_BASE is used and won't be added to the FIP file.")
endif
ifdef BL33_BASE
$(warning "BL33 image is not needed when option BL33_BASE is \
used and won't be added to the FIP file.")
endif
endif
################################################################################
# Process platform overrideable behaviour
################################################################################
# Check if -pedantic option should be used
ifeq (${DISABLE_PEDANTIC},0)
CFLAGS += -pedantic
endif
# Using the ARM Trusted Firmware BL2 implies that a BL33 image also needs to be
# supplied for the FIP and Certificate generation tools. This flag can be
# overridden by the platform.
ifdef BL2_SOURCES
ifdef EL3_PAYLOAD_BASE
# If booting an EL3 payload there is no need for a BL33 image
# in the FIP file.
NEED_BL33 := no
else
ifdef BL33_BASE
# If booting a BL33 preloaded image there is no need of
# another one in the FIP file.
NEED_BL33 := no
else
NEED_BL33 ?= yes
endif
endif
endif
# Process TBB related flags
ifneq (${GENERATE_COT},0)
# Common cert_create options
ifneq (${CREATE_KEYS},0)
$(eval CRT_ARGS += -n)
$(eval FWU_CRT_ARGS += -n)
ifneq (${SAVE_KEYS},0)
$(eval CRT_ARGS += -k)
$(eval FWU_CRT_ARGS += -k)
endif
endif
# Include TBBR makefile (unless the platform indicates otherwise)
ifeq (${INCLUDE_TBBR_MK},1)
include make_helpers/tbbr/tbbr_tools.mk
endif
endif
################################################################################
# Auxiliary tools (fip_create, cert_create, etc)
################################################################################
# Variables for use with Certificate Generation Tool
CRTTOOLPATH ?= tools/cert_create
CRTTOOL ?= ${CRTTOOLPATH}/cert_create
# Variables for use with Firmware Image Package
FIPTOOLPATH ?= tools/fip_create
FIPTOOL ?= ${FIPTOOLPATH}/fip_create
################################################################################
# Build options checks
################################################################################
$(eval $(call assert_boolean,DEBUG))
$(eval $(call assert_boolean,NS_TIMER_SWITCH))
$(eval $(call assert_boolean,RESET_TO_BL31))
$(eval $(call assert_boolean,CTX_INCLUDE_FPREGS))
$(eval $(call assert_boolean,ASM_ASSERTION))
$(eval $(call assert_boolean,USE_COHERENT_MEM))
$(eval $(call assert_boolean,DISABLE_PEDANTIC))
$(eval $(call assert_boolean,GENERATE_COT))
$(eval $(call assert_boolean,CREATE_KEYS))
$(eval $(call assert_boolean,SAVE_KEYS))
$(eval $(call assert_boolean,TRUSTED_BOARD_BOOT))
$(eval $(call assert_boolean,PROGRAMMABLE_RESET_ADDRESS))
$(eval $(call assert_boolean,COLD_BOOT_SINGLE_CPU))
$(eval $(call assert_boolean,PSCI_EXTENDED_STATE_ID))
$(eval $(call assert_boolean,ERROR_DEPRECATED))
$(eval $(call assert_boolean,ENABLE_PLAT_COMPAT))
$(eval $(call assert_boolean,SPIN_ON_BL1_EXIT))
$(eval $(call assert_boolean,PL011_GENERIC_UART))
################################################################################
# Add definitions to the cpp preprocessor based on the current build options.
# This is done after including the platform specific makefile to allow the
# platform to overwrite the default options
################################################################################
$(eval $(call add_define,PLAT_${PLAT}))
$(eval $(call add_define,NS_TIMER_SWITCH))
$(eval $(call add_define,RESET_TO_BL31))
$(eval $(call add_define,CTX_INCLUDE_FPREGS))
$(eval $(call add_define,ARM_GIC_ARCH))
$(eval $(call add_define,ARM_CCI_PRODUCT_ID))
$(eval $(call add_define,ASM_ASSERTION))
$(eval $(call add_define,LOG_LEVEL))
$(eval $(call add_define,USE_COHERENT_MEM))
$(eval $(call add_define,TRUSTED_BOARD_BOOT))
$(eval $(call add_define,PROGRAMMABLE_RESET_ADDRESS))
$(eval $(call add_define,COLD_BOOT_SINGLE_CPU))
$(eval $(call add_define,PSCI_EXTENDED_STATE_ID))
$(eval $(call add_define,ERROR_DEPRECATED))
$(eval $(call add_define,ENABLE_PLAT_COMPAT))
$(eval $(call add_define,SPIN_ON_BL1_EXIT))
$(eval $(call add_define,PL011_GENERIC_UART))
# Define the EL3_PAYLOAD_BASE flag only if it is provided.
ifdef EL3_PAYLOAD_BASE
$(eval $(call add_define,EL3_PAYLOAD_BASE))
else
# Define the BL33_BASE flag only if it is provided and EL3_PAYLOAD_BASE
# is not defined, as it has priority.
ifdef BL33_BASE
$(eval $(call add_define,BL33_BASE))
endif
endif
################################################################################
# Include BL specific makefiles
################################################################################
ifdef BL1_SOURCES
NEED_BL1 := yes
include bl1/bl1.mk
endif
ifdef BL2_SOURCES
NEED_BL2 := yes
include bl2/bl2.mk
endif
ifdef BL2U_SOURCES
NEED_BL2U := yes
include bl2u/bl2u.mk
endif
ifdef BL31_SOURCES
# When booting an EL3 payload, there is no need to compile the BL31 image nor
# put it in the FIP.
ifndef EL3_PAYLOAD_BASE
NEED_BL31 := yes
include bl31/bl31.mk
endif
endif
################################################################################
# Build targets
################################################################################
.PHONY: all msg_start clean realclean distclean cscope locate-checkpatch checkcodebase checkpatch fiptool fip fwu_fip certtool
.SUFFIXES:
all: msg_start
msg_start:
@echo "Building ${PLAT}"
# Check if deprecated declarations should be treated as error or not.
ifeq (${ERROR_DEPRECATED},0)
CFLAGS += -Wno-error=deprecated-declarations
endif
# Expand build macros for the different images
ifeq (${NEED_BL1},yes)
$(eval $(call MAKE_BL,1))
endif
ifeq (${NEED_BL2},yes)
$(if ${BL2}, $(eval $(call MAKE_TOOL_ARGS,2,${BL2},tb-fw)),\
$(eval $(call MAKE_BL,2,tb-fw)))
endif
ifeq (${NEED_BL31},yes)
BL31_SOURCES += ${SPD_SOURCES}
$(if ${BL31}, $(eval $(call MAKE_TOOL_ARGS,31,${BL31},soc-fw)),\
$(eval $(call MAKE_BL,31,soc-fw)))
endif
# If a BL32 image is needed but neither BL32 nor BL32_SOURCES is defined, the
# build system will call FIP_ADD_IMG to print a warning message and abort the
# process. Note that the dependency on BL32 applies to the FIP only.
ifeq (${NEED_BL32},yes)
$(if ${BL32}, $(eval $(call MAKE_TOOL_ARGS,32,${BL32},tos-fw)),\
$(if ${BL32_SOURCES}, $(eval $(call MAKE_BL,32,tos-fw)),\
$(eval $(call FIP_ADD_IMG,BL32,--tos-fw))))
endif
# Add the BL33 image if required by the platform
ifeq (${NEED_BL33},yes)
$(eval $(call FIP_ADD_IMG,BL33,--nt-fw))
endif
ifeq (${NEED_BL2U},yes)
BL2U_PATH := $(if ${BL2U},${BL2U},$(call IMG_BIN,2u))
$(if ${BL2U}, ,$(eval $(call MAKE_BL,2u)))
$(eval $(call FWU_FIP_ADD_PAYLOAD,${BL2U_PATH},--ap-fwu-cfg))
endif
locate-checkpatch:
ifndef CHECKPATCH
$(error "Please set CHECKPATCH to point to the Linux checkpatch.pl file, eg: CHECKPATCH=../linux/script/checkpatch.pl")
else
ifeq (,$(wildcard ${CHECKPATCH}))
$(error "The file CHECKPATCH points to cannot be found, use eg: CHECKPATCH=../linux/script/checkpatch.pl")
endif
endif
clean:
@echo " CLEAN"
${Q}rm -rf ${BUILD_PLAT}
${Q}${MAKE} --no-print-directory -C ${FIPTOOLPATH} clean
${Q}${MAKE} PLAT=${PLAT} --no-print-directory -C ${CRTTOOLPATH} clean
realclean distclean:
@echo " REALCLEAN"
${Q}rm -rf ${BUILD_BASE}
${Q}rm -f ${CURDIR}/cscope.*
${Q}${MAKE} --no-print-directory -C ${FIPTOOLPATH} clean
${Q}${MAKE} PLAT=${PLAT} --no-print-directory -C ${CRTTOOLPATH} clean
checkcodebase: locate-checkpatch
@echo " CHECKING STYLE"
@if test -d .git ; then \
git ls-files | grep -v stdlib | while read GIT_FILE ; do ${CHECKPATCH} ${CHECKCODE_ARGS} -f $$GIT_FILE ; done ; \
else \
find . -type f -not -iwholename "*.git*" -not -iwholename "*build*" -not -iwholename "*stdlib*" -exec ${CHECKPATCH} ${CHECKCODE_ARGS} -f {} \; ; \
fi
checkpatch: locate-checkpatch
@echo " CHECKING STYLE"
${Q}git log -p ${BASE_COMMIT}..HEAD -- ${CHECK_PATHS} | ${CHECKPATCH} ${CHECKPATCH_ARGS} - || true
certtool: ${CRTTOOL}
.PHONY: ${CRTTOOL}
${CRTTOOL}:
${Q}${MAKE} PLAT=${PLAT} --no-print-directory -C ${CRTTOOLPATH}
@echo
@echo "Built $@ successfully"
@echo
ifneq (${GENERATE_COT},0)
certificates: ${CRT_DEPS} ${CRTTOOL}
${Q}${CRTTOOL} ${CRT_ARGS}
@echo
@echo "Built $@ successfully"
@echo "Certificates can be found in ${BUILD_PLAT}"
@echo
endif
${BUILD_PLAT}/${FIP_NAME}: ${FIP_DEPS} ${FIPTOOL}
${Q}${FIPTOOL} --dump ${FIP_ARGS} $@
@echo
@echo "Built $@ successfully"
@echo
ifneq (${GENERATE_COT},0)
fwu_certificates: ${FWU_CRT_DEPS} ${CRTTOOL}
${Q}${CRTTOOL} ${FWU_CRT_ARGS}
@echo
@echo "Built $@ successfully"
@echo "FWU certificates can be found in ${BUILD_PLAT}"
@echo
endif
${BUILD_PLAT}/${FWU_FIP_NAME}: ${FWU_FIP_DEPS} ${FIPTOOL}
${Q}${FIPTOOL} --dump ${FWU_FIP_ARGS} $@
@echo
@echo "Built $@ successfully"
@echo
fiptool: ${FIPTOOL}
fip: ${BUILD_PLAT}/${FIP_NAME}
fwu_fip: ${BUILD_PLAT}/${FWU_FIP_NAME}
.PHONY: ${FIPTOOL}
${FIPTOOL}:
${Q}${MAKE} --no-print-directory -C ${FIPTOOLPATH}
cscope:
@echo " CSCOPE"
${Q}find ${CURDIR} -name "*.[chsS]" > cscope.files
${Q}cscope -b -q -k
help:
@echo "usage: ${MAKE} PLAT=<${PLATFORMS}> [OPTIONS] [TARGET]"
@echo ""
@echo "PLAT is used to specify which platform you wish to build."
@echo "If no platform is specified, PLAT defaults to: ${DEFAULT_PLAT}"
@echo ""
@echo "Please refer to the User Guide for a list of all supported options."
@echo "Note that the build system doesn't track dependencies for build "
@echo "options. Therefore, if any of the build options are changed "
@echo "from a previous build, a clean build must be performed."
@echo ""
@echo "Supported Targets:"
@echo " all Build all individual bootloader binaries"
@echo " bl1 Build the BL1 binary"
@echo " bl2 Build the BL2 binary"
@echo " bl2u Build the BL2U binary"
@echo " bl31 Build the BL31 binary"
@echo " bl32 Build the BL32 binary"
@echo " certificates Build the certificates (requires 'GENERATE_COT=1')"
@echo " fip Build the Firmware Image Package (FIP)"
@echo " fwu_fip Build the FWU Firmware Image Package (FIP)"
@echo " checkcodebase Check the coding style of the entire source tree"
@echo " checkpatch Check the coding style on changes in the current"
@echo " branch against BASE_COMMIT (default origin/master)"
@echo " clean Clean the build for the selected platform"
@echo " cscope Generate cscope index"
@echo " distclean Remove all build artifacts for all platforms"
@echo " certtool Build the Certificate generation tool"
@echo " fiptool Build the Firmware Image Package(FIP) creation tool"
@echo ""
@echo "Note: most build targets require PLAT to be set to a specific platform."
@echo ""
@echo "example: build all targets for the FVP platform:"
@echo " CROSS_COMPILE=aarch64-none-elf- make PLAT=fvp all"