快速链接:
.
???????????? 个人博客笔记导读目录(全部) ????????????

根据BLx_SOURCE是否定义，来选择编译的镜像. BLx_SOURCE的第一次定义一般在plat/xxx/platform.mk

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

这里是平台的定义，选择哪一个SPD(secure payload dispatcher)
即当敲击make -C $DIRPATH RESET_TO_BL31=1 PLAT=xxx all，传过来的PLAT值

ifeq (${PLAT},xxx)
SPD                             := opteed
endif

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

给NEED_BL31宏赋值

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

调用MAKE_BL(31,in_fip)编译BL31

(Makefile)
ifeq (${NEED_BL31},yes)
BL31_SOURCES += ${SPD_SOURCES}
$(if ${BL31}, $(eval $(call MAKE_TOOL_ARGS,31,${BL31},in_fip)),\
        $(eval $(call MAKE_BL,31,in_fip)))
endif

MAKE_BL函数的实现：

(make_helpers/build_macros.mk)
# MAKE_BL macro defines the targets and options to build each BL image.
# Arguments:
#   $(1) = BL stage (2, 2u, 30, 31, 32, 33)
#   $(2) = In FIP (false if empty)
define MAKE_BL
        $(eval BUILD_DIR  := ${BUILD_PLAT}/bl$(1))
        $(eval BL_SOURCES := $(BL$(call uppercase,$(1))_SOURCES))
        $(eval SOURCES    := $(BL_SOURCES) $(BL_COMMON_SOURCES) $(PLAT_BL_COMMON_SOURCES))
        $(eval OBJS       := $(addprefix $(BUILD_DIR)/,$(call SOURCES_TO_OBJS,$(SOURCES))))
        $(eval LINKERFILE := $(call IMG_LINKERFILE,$(1)))
        $(eval MAPFILE    := $(call IMG_MAPFILE,$(1)))
        $(eval ELF        := $(call IMG_ELF,$(1)))
        $(eval DUMP       := $(call IMG_DUMP,$(1)))
        $(eval BIN        := $(call IMG_BIN,$(1)))
        $(eval BL_LINKERFILE := $(BL$(call uppercase,$(1))_LINKERFILE))

        $(eval $(call MAKE_OBJS,$(BUILD_DIR),$(SOURCES),$(1)))
        $(eval $(call MAKE_LD,$(LINKERFILE),$(BL_LINKERFILE)))

$(BUILD_DIR):
        $$(Q)mkdir -p "$$@"

$(ELF): $(OBJS) $(LINKERFILE)
        @echo "  LD      $$@"
        @echo 'const char build_message[] = "Built : "__TIME__", "__DATE__; \
               const char version_string[] = "${VERSION_STRING}";' | \
                $$(CC) $$(CFLAGS) -xc - -o $(BUILD_DIR)/build_message.o
        $$(Q)$$(LD) -o $$@ $$(LDFLAGS) -Map=$(MAPFILE) --script $(LINKERFILE) \
                                        $(BUILD_DIR)/build_message.o $(OBJS)

$(DUMP): $(ELF)
        @echo "  OD      $$@"
        $${Q}$${OD} -dx $$< > $$@

$(BIN): $(ELF)
        @echo "  BIN     $$@"
        $$(Q)$$(OC) -O binary $$< $$@
        @echo
        @echo "Built $$@ successfully"
        @echo
ifeq ($(1),31)
        cp $$@ $(BUILD_PLAT)/sloader.img
endif

.PHONY: bl$(1)
bl$(1): $(BUILD_DIR) $(BIN) $(DUMP)

all: bl$(1)

$(eval $(call MAKE_TOOL_ARGS,$(1),$(BIN),$(2)))

endef

ELF的生成使用到了LINKERFILE，而LINKERFILE就等于bl31.ld.S

$(eval BL_LINKERFILE := $(BL$(call uppercase,$(1))_LINKERFILE))
$(eval $(call MAKE_LD,$(LINKERFILE),$(BL_LINKERFILE)))
BL31_LINKERFILE         :=      bl31/bl31.ld.S