用QEMU模拟ARM开发板 搭建Linux kernel运行环境

前言

有的时候我们想调试linux kernel或者linux应用程序，但是又没有硬件环境，这个时候可以选择用模拟器的方法，模拟出一个硬件环境。

Android emulator

Android系统的模拟器叫Emulator，使用这个模拟器需要下载Android源代码，编译成功之后才能运行。由于编译Android源码还是需要一定的硬件配置，我尝试了没编译成功。

QEMU

QEMU是一个可以模拟ARM架构的开源软件，我们可以使用他来模拟vexpress-a9开发板，在上面搭建linux kernel运行环境。参考QEMU模拟vexpress-a9 搭建Linux kernel运行环境，成功的在ubuntu 16.04上模拟运行了linux kernel最小系统，这样就方便代码的调试学习了。

以下是kernel启动过程的打印：

neo@neo-virtual-machine:~/work/linux-4.14.7/arch/arm/boot/dts$ qemu-system-arm -M vexpress-a9 -m 512M -kernel ../zImage -dtb ./vexpress-v2p-ca9.dtb -nographic -append "root=/dev/mmcblk0 console=ttyAMA0 rw init=/linuxrc" -sd /home/neo/work/a9rootfs.ext3 WARNING: Image format was not specified for '/home/neo/work/a9rootfs.ext3' and probing guessed raw.Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.Specify the 'raw' format explicitly to remove the restrictions.pulseaudio: set_sink_input_volume() failedpulseaudio: Reason: Invalid argumentpulseaudio: set_sink_input_mute() failedpulseaudio: Reason: Invalid argumentBooting Linux on physical CPU 0x0Linux version 4.14.7 (neo@neo-virtual-machine) (gcc version 5.4.0 0609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.9)) #1 SMP Fri Jul 8 21:48:11 CST CPU: ARMv7 Processor [410fc090] revision 0 (ARMv7), cr=10c5387dCPU: PIPT / VIPT nonaliasing data cache, VIPT nonaliasing instruction cacheOF: fdt: Machine model: V2P-CA9Memory policy: Data cache writebackCPU: All CPU(s) started in SVC mode.percpu: Embedded 16 pages/cpu @9fbae000 s36428 r8192 d20916 u65536Built 1 zonelists, mobility grouping on. Total pages: 130048Kernel command line: root=/dev/mmcblk0 console=ttyAMA0 rw init=/linuxrclog_buf_len individual max cpu contribution: 4096 byteslog_buf_len total cpu_extra contributions: 12288 byteslog_buf_len min size: 16384 byteslog_buf_len: 32768 bytesearly log buf free: 14976(91%)PID hash table entries: 2048 (order: 1, 8192 bytes)Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)Memory: 509556K/524288K available (6144K kernel code, 402K rwdata, 1364K rodata, 1024K init, 169K bss, 14732K reserved, 0K cma-reserved)Virtual kernel memory layout:vector : 0xffff0000 - 0xffff1000 ( 4 kB)fixmap : 0xffc00000 - 0xfff00000 (3072 kB)vmalloc : 0xa0800000 - 0xff800000 (1520 MB)lowmem : 0x80000000 - 0xa0000000 ( 512 MB)modules : 0x7f000000 - 0x80000000 ( 16 MB).text : 0x80008000 - 0x80700000 (7136 kB).init : 0x80900000 - 0x80a00000 (1024 kB).data : 0x80a00000 - 0x80a649d8 ( 403 kB).bss : 0x80a6bcb8 - 0x80a96434 ( 170 kB)SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1Hierarchical RCU implementation.RCU event tracing is enabled.RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=4.RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=4NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16GIC CPU mask not found - kernel will fail to boot.GIC CPU mask not found - kernel will fail to boot.smp_twd: clock not found -2sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971nsclocksource: arm,sp804: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 nsFailed to initialize '/smb@4000000/motherboard/iofpga@7,00000000/timer@12000': -22Console: colour dummy device 80x30Calibrating local timer... 98.69MHz.Calibrating delay loop... 973.20 BogoMIPS (lpj=4866048)pid_max: default: 32768 minimum: 301Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)CPU: Testing write buffer coherency: okCPU0: thread -1, cpu 0, socket 0, mpidr 80000000Setting up static identity map for 0x60100000 - 0x60100060Hierarchical SRCU implementation.smp: Bringing up secondary CPUs ...smp: Brought up 1 node, 1 CPUSMP: Total of 1 processors activated (973.20 BogoMIPS).CPU: All CPU(s) started in SVC mode.devtmpfs: initializedrandom: get_random_u32 called from bucket_table_alloc+0xf0/0x240 with crng_init=0VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 0clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 nsfutex hash table entries: 1024 (order: 4, 65536 bytes)random: fast init doneNET: Registered protocol family 16DMA: preallocated 256 KiB pool for atomic coherent allocationscpuidle: using governor ladderhw-breakpoint: debug architecture 0x4 unsupported.Serial: AMBA PL011 UART driverOF: amba_device_add() failed (-19) for /memory-controller@100e0000OF: amba_device_add() failed (-19) for /memory-controller@100e1000OF: amba_device_add() failed (-19) for /watchdog@100e5000irq: type mismatch, failed to map hwirq-75 for /interrupt-controller@1e001000!10009000.uart: ttyAMA0 at MMIO 0x10009000 (irq = 38, base_baud = 0) is a PL011 rev1console [ttyAMA0] enabled1000a000.uart: ttyAMA1 at MMIO 0x1000a000 (irq = 39, base_baud = 0) is a PL011 rev11000b000.uart: ttyAMA2 at MMIO 0x1000b000 (irq = 40, base_baud = 0) is a PL011 rev11000c000.uart: ttyAMA3 at MMIO 0x1000c000 (irq = 41, base_baud = 0) is a PL011 rev1OF: amba_device_add() failed (-19) for /smb@4000000/motherboard/iofpga@7,00000000/wdt@f000SCSI subsystem initializedusbcore: registered new interface driver usbfsusbcore: registered new interface driver hubusbcore: registered new device driver usbAdvanced Linux Sound Architecture Driver Initialized.clocksource: Switched to clocksource arm,sp804NET: Registered protocol family 2TCP established hash table entries: 4096 (order: 2, 16384 bytes)TCP bind hash table entries: 4096 (order: 3, 32768 bytes)TCP: Hash tables configured (established 4096 bind 4096)UDP hash table entries: 256 (order: 1, 8192 bytes)UDP-Lite hash table entries: 256 (order: 1, 8192 bytes)NET: Registered protocol family 1RPC: Registered named UNIX socket transport module.RPC: Registered udp transport module.RPC: Registered tcp transport module.RPC: Registered tcp NFSv4.1 backchannel transport module.hw perfevents: enabled with armv7_cortex_a9 PMU driver, 1 counters availableworkingset: timestamp_bits=30 max_order=17 bucket_order=0squashfs: version 4.0 (/01/31) Phillip Lougherjffs2: version 2.2. (NAND) © 2001- Red Hat, Inc.9p: Installing v9fs 9p2000 file system supportio scheduler noop registered (default)io scheduler mq-deadline registeredio scheduler kyber registeredclcd-pl11x 10020000.clcd: PL111 designer 41 rev2 at 0x10020000clcd-pl11x 10020000.clcd: /clcd@10020000 hardware, 1024x768@59 displayConsole: switching to colour frame buffer device 128x48clcd-pl11x 1001f000.clcd: PL111 designer 41 rev2 at 0x1001f000clcd-pl11x 1001f000.clcd: /smb@4000000/motherboard/iofpga@7,00000000/clcd@1f000 hardware, 640x480@59 display40000000.flash: Found 2 x16 devices at 0x0 in 32-bit bank. Manufacturer ID 0x000000 Chip ID 0x000000Intel/Sharp Extended Query Table at 0x0031Using buffer write method40000000.flash: Found 2 x16 devices at 0x0 in 32-bit bank. Manufacturer ID 0x000000 Chip ID 0x000000Intel/Sharp Extended Query Table at 0x0031Using buffer write methodConcatenating MTD devices:(0): "40000000.flash"(1): "40000000.flash"into device "40000000.flash"libphy: Fixed MDIO Bus: probedlibphy: smsc911x-mdio: probedsmsc911x 4e000000.ethernet eth0: MAC Address: 52:54:00:12:34:56isp1760 4f000000.usb: bus width: 32, oc: digitalisp1760 4f000000.usb: NXP ISP1760 USB Host Controllerisp1760 4f000000.usb: new USB bus registered, assigned bus number 1isp1760 4f000000.usb: Scratch test failed.isp1760 4f000000.usb: can't setup: -19isp1760 4f000000.usb: USB bus 1 deregisteredusbcore: registered new interface driver usb-storagertc-pl031 10017000.rtc: rtc core: registered pl031 as rtc0IR NEC protocol handler initializedIR RC5(x/sz) protocol handler initializedIR RC6 protocol handler initializedIR JVC protocol handler initializedIR Sony protocol handler initializedIR SANYO protocol handler initializedIR Sharp protocol handler initializedIR MCE Keyboard/mouse protocol handler initializedIR XMP protocol handler initializedmmci-pl18x 10005000.mmci: Got CD GPIOmmci-pl18x 10005000.mmci: Got WP GPIOmmci-pl18x 10005000.mmci: mmc0: PL181 manf 41 rev0 at 0x10005000 irq 34,35 (pio)ledtrig-cpu: registered to indicate activity on CPUsusbcore: registered new interface driver usbhidusbhid: USB HID core drivermmc0: new SD card at address 4567mmcblk0: mmc0:4567 QEMU! 32.0 MiB input: AT Raw Set 2 keyboard as /devices/platform/smb@4000000/smb@4000000:motherboard/smb@4000000:motherboard:iofpga@7,00000000/10006000.kmi/serio0/input/input0aaci-pl041 10004000.aaci: ARM AC'97 Interface PL041 rev0 at 0x10004000, irq 33aaci-pl041 10004000.aaci: FIFO 512 entriesoprofile: using arm/armv7-ca9NET: Registered protocol family 179pnet: Installing 9P2000 supportRegistering SWP/SWPB emulation handlerrtc-pl031 10017000.rtc: setting system clock to -07-09 02:59:40 UTC (1657335580)ALSA device list:#0: ARM AC'97 Interface PL041 rev0 at 0x10004000, irq 33input: ImExPS/2 Generic Explorer Mouse as /devices/platform/smb@4000000/smb@4000000:motherboard/smb@4000000:motherboard:iofpga@7,00000000/10007000.kmi/serio1/input/input2EXT4-fs (mmcblk0): mounting ext3 file system using the ext4 subsystemEXT4-fs (mmcblk0): mounted filesystem with ordered data mode. Opts: (null)VFS: Mounted root (ext3 filesystem) on device 179:0.Freeing unused kernel memory: 1024Krandom: crng init donecan't run '/etc/init.d/rcS': No such file or directoryPlease press Enter to activate this console. / #

在启动的最后有这样一句打印，说明rootfs仍然不够完善：

can't run '/etc/init.d/rcS': No such file or directory

在进入控制台后发现只有根文件系统里的目录结构，而没有常用的/proc、/sys/等目录，/dev目录下也没有生成设备文件。

proc和sysfs虚拟文件系统需要手动挂载才会生成。分别mkdir创建/proc和、/sys/目录，然后执行以下指令：

mount -t proc proc /proc mount sysfs /sys -t sysfsmdev -s

就可以在目录下看到相应的文件。

/proc # ls1 28 768 execdomains partitions10 312 769 fb self11 313 770 filesystems slabinfo12 314 771 fs softirqs13 316 8 interruptsstat14 318 838 iomemswaps15 328 9 ioports sys16 4 asound irq sysrq-trigger17 444 buddyinfokallsyms sysvipc18 445 bus kmsg thread-self19 446 cgroups kpagecounttimer_list2 465 cmdline kpageflagstty20 5 config.gzloadavg uptime21 524 consoles locksversion22 6 cpu meminfo vmallocinfo23 678 cpuinfo misc vmstat24 7 crypto modules zoneinfo242 727 device-tree mounts25 764 devices mtd26 765 diskstatsnet27 766 driver pagetypeinfo

/sys # lsblockclassdevices fs modulebus dev firmware kernel power

/dev # lsconsole tty10tty55cpu_dma_latencytty11tty56fb0 tty12tty57fb1 tty13tty58fulltty14tty59gpiochip0 tty15tty6gpiochip1 tty16tty60gpiochip2 tty17tty61gpiochip3 tty18tty62hwrngtty19tty63inputtty2tty7kmsgtty20tty8

创建好了设备文件之后，应用程序才可以对设备驱动节点进行访问。

使用QEMU还可以用图形界面的方式启动linux kernel：

qemu-system-arm -M vexpress-a9 -m 512M -kernel ../zImage -dtb ./vexpress-v2p-ca9.dtb -append "root=/dev/mmcblk0 rw init=/linuxrc" -sd /home/neo/work/a9rootfs.ext3

效果就是模拟在显示器上显示控制台画面，因此可以调试写framebuffer刷屏的程序效果，下图执行程序向/dev/fb0写入，将屏幕刷成蓝色：