[Android6.0][RK3399] Uboot 代码分析

前一篇文章中我们了解到了make rk3399_defconfig 的原理，在 uboot 根目录会生成 .config 文件。
然后我们执行 make 命令，下面是他的流程：
Makefile 中默认执行 make all

1	815 all: $(ALL-y)

ALL-y 需要生成四个目标文件

1 2	757 # Always append ALL so that arch config.mk's can add custom ones 758 ALL-y += u-boot.srec u-boot.bin System.map binary_size_check

目标文件1 u-boot.srec

1 2	844 u-boot.hex u-boot.srec: u-boot FORCE 845 $(call if_changed,objcopy)

目标文件2 u-boot.bin

863 u-boot.bin: u-boot FORCE
864         $(call if_changed,objcopy)
865         $(call DO_STATIC_RELA,$<,$@,$(CONFIG_SYS_TEXT_BASE))
866         $(BOARD_SIZE_CHECK)

目标文件3 System.map

1 2	1280 System.map: u-boot 1281 @$(call SYSTEM_MAP,$<) > $@

目标文件4 binary_size_check

849 binary_size_check: u-boot.bin FORCE
850         @file_size=$(shell wc -c u-boot.bin | awk '{print $$1}') ; \
851         map_size=$(shell cat u-boot.map | \
852                 awk '/_image_copy_start/ {start = $$1} /_image_binary_end/ {end = $$1} END {if (start      != "" && end != "") print "ibase=16; " toupper(end) " - " toupper(start)}' \
853                 | sed 's/0X//g' \
854                 | bc); \
855         if [ "" != "$$map_size" ]; then \
856                 if test $$map_size -ne $$file_size; then \
857                         echo "u-boot.map shows a binary size of $$map_size" >&2 ; \
858                         echo "  but u-boot.bin shows $$file_size" >&2 ; \
859                         exit 1; \
860                 fi \
861         fi

所以可以看到，他们首先都需要 u-boot 这个 elf 文件。

1128 u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds
1129         $(call if_changed,u-boot__)
1130 ifeq ($(CONFIG_KALLSYMS),y)
1131         $(call cmd,smap)
1132         $(call cmd,u-boot__) common/system_map.o
1133 endif

进一步分析 u-boot 依赖于三个参数 u-boot-init u-boot-main u-boot.lds
第一个参数 u-boot-init 定义为

1 2	701 u-boot-init := $(head-y) 630 head-y := $(CPUDIR)/start.o

第二个参数 u-boot-main定义为

702 u-boot-main := $(libs-y)
# libs-y 为各种库和驱动，暂列一些比较关键的
 636 libs-y += lib/
 637 libs-$(HAVE_VENDOR_COMMON_LIB) += board/$(VENDOR)/common/
 638 libs-y += $(CPUDIR)/
 639 ifdef SOC
 640 libs-y += $(CPUDIR)/$(SOC)/
 641 endif
 642 libs-$(CONFIG_OF_EMBED) += dts/
 643 libs-y += arch/$(ARCH)/lib/
 644 libs-y += fs/
 645 libs-y += net/
 646 libs-y += disk/
 647 libs-y += drivers/
 648 libs-y += drivers/dma/
 649 libs-y += drivers/gpio/
 650 libs-y += drivers/i2c/
 651 libs-y += drivers/mmc/
 652 libs-y += drivers/mtd/
 653 libs-$(CONFIG_CMD_NAND) += drivers/mtd/nand/
 654 libs-y += drivers/mtd/onenand/
 655 libs-$(CONFIG_CMD_UBI) += drivers/mtd/ubi/
 656 libs-y += drivers/mtd/spi/
 657 libs-y += drivers/net/
 658 libs-y += drivers/net/phy/
 659 libs-y += drivers/pci/
 660 libs-y += drivers/power/ \
 661         drivers/power/fuel_gauge/ \
 662         drivers/power/mfd/ \
 663         drivers/power/pmic/ \
 664         drivers/power/charge/ \
 665         drivers/power/battery/
 666 libs-y += drivers/spi/
 667 libs-$(CONFIG_FMAN_ENET) += drivers/net/fm/
 668 libs-$(CONFIG_SYS_FSL_DDR) += drivers/ddr/fsl/
 669 libs-y += drivers/serial/
 670 libs-y += drivers/usb/eth/
 671 libs-y += drivers/usb/gadget/
 672 libs-y += drivers/usb/host/
 673 libs-y += drivers/usb/musb/
 674 libs-y += drivers/usb/musb-new/
 675 libs-y += drivers/usb/phy/
 676 libs-y += drivers/usb/ulpi/
 677 libs-y += common/
 678 libs-y += lib/libfdt/
 679 libs-$(CONFIG_API) += api/
 680 libs-$(CONFIG_HAS_POST) += post/
 681 libs-y += test/
 682 libs-y += test/dm/
 683 
 684 ifneq (,$(filter $(SOC), mx25 mx27 mx5 mx6 mx31 mx35 mxs vf610))
 685 libs-y += arch/$(ARCH)/imx-common/
 686 endif

值得注意的是，其中的 VENDOR、CPU、SOC、DIR、ARCH 宏是定义在 config.mk 。

第三个参数 u-boot.lds 定义为

1 2	1245 u-boot.lds: $(LDSCRIPT) prepare FORCE 1246 $(call if_changed_dep,cpp_lds)

546 # If there is no specified link script, we look in a number of places for it
547 ifndef LDSCRIPT
548         ifeq ($(wildcard $(LDSCRIPT)),)
549                 LDSCRIPT := $(srctree)/board/$(BOARDDIR)/u-boot.lds
550         endif
551         ifeq ($(wildcard $(LDSCRIPT)),)
552                 LDSCRIPT := $(srctree)/$(CPUDIR)/u-boot.lds
553         endif
554         ifeq ($(wildcard $(LDSCRIPT)),)
555                 LDSCRIPT := $(srctree)/arch/$(ARCH)/cpu/u-boot.lds
556         endif
557 endif

对于上面三个 lds，优先级从前到后依次增加。

prepare 定义：