上一篇文章搭建了基于zImage的qemu环境，基本的环境配置已经可以使用，为了还原真正的嵌入式ARM启动场景，搭建基于u-boot的qemu环境。
1. u-boot下载及编译
1.1 下载地址 https://ftp.denx.de/pub/u-boot/，本文使用的版本为2019.10
1.2 下载后解压进行配置
# vim Makefile
CROSS_COMPILE = arm-linux-gnueabi-
# vim config.mk
ARCH = arm编译
sly@ubuntu:~/develop/u-boot-2019.10$ make vexpress_ca9x4_defconfig
sly@ubuntu:~/develop/u-boot-2019.10$ make -j20
1.3 qemu启动u-boot
sly@ubuntu:~/develop$ qemu-system-arm -M vexpress-a9 -m 512M -nographic -kernel u-boot-2019.10/u-boot
----省略部分打印，下面打印环境变量
=> print
arch=arm
baudrate=38400
board=vexpress
board_name=vexpress
bootargs=root=/dev/sda1 rw console=ttyAMA0,38400n8 mem=1024M mtdparts=armflash:1M@0x800000(uboot),7M@0x1000000(kernel),24M@0x2000000(initrd) mmci.fmax=190000 devtmpfs.mount=0 vmalloc=256M
console=ttyAMA0,38400n8
cpu=armv7
kernel_addr=0x44100000
kernel_addr_r=0x80008000
loadaddr=0x80008000
maxramdisk=0x1800000
mmc_boot=if mmc dev ${devnum}; then devtype=mmc; run scan_dev_for_boot_part; fi
mtd=armflash:1M@0x800000(uboot),7M@0x1000000(kernel),24M@0x2000000(initrd)
pxefile_addr_r=0x88000000
ramdisk_addr=0x44800000
ramdisk_addr_r=0x61000000
root=/dev/sda1 rw
scan_dev_for_boot=echo Scanning ${devtype} ${devnum}:${distro_bootpart}...; for prefix in ${boot_prefixes}; do run scan_dev_for_extlinux; run scan_dev_for_scripts; done;
scan_dev_for_boot_part=part list ${devtype} ${devnum} -bootable devplist; env exists devplist || setenv devplist 1; for distro_bootpart in ${devplist}; do if fstype ${devtype} ${devnum}:${distro_bootpart} bootfstype; then run scan_dev_for_boot; fi; done; setenv devplist
scan_dev_for_extlinux=if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${boot_syslinux_conf}; then echo Found ${prefix}${boot_syslinux_conf}; run boot_extlinux; echo SCRIPT FAILED: continuing...; fi
scan_dev_for_scripts=for script in ${boot_scripts}; do if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${script}; then echo Found U-Boot script ${prefix}${script}; run boot_a_script; echo SCRIPT FAILED: continuing...; fi; done
scriptaddr=0x88000000
stderr=serial
stdin=serial
stdout=serial
ubifs_boot=env exists bootubipart || env set bootubipart UBI; env exists bootubivol || env set bootubivol boot; if ubi part ${bootubipart} && ubifsmount ubi${devnum}:${bootubivol}; then devtype=ubi; run scan_dev_for_boot; fi
vendor=armltd
1.4 开始配置u-boot的内核启动参数，来启动Linux内核，并挂在根文件系统。