How Other People Use QEMU

Viller

qemu-system-arm \
-M vexpress-a15 \
-kernel buildroot/output/images/zImage \
-dtb buildroot/output/images/vexpress-v2p-ca15_a7.dtb \
-drive file=buildroot/output/images/rootfs.ext2,if=sd \
-smp 2 \
-s \
-serial stdio \
-append "root=/dev/mmcblk0 console=ttyAMA0,115200n8" \
-net nic,vlan=1 -net user,vlan=1,hostfwd=udp:127.0.0.1:6669-:69

利用 buildroot 與 Qemu 建構簡易 Embedded Linux 環境

Embedded Linux development

Building Embedded Linux Full Tutorial for ARM

Components

cross toolchain
- libc: glibc / uclibc / musl
bootloader
- uboot / barebox
kernel
rootfs
- busybox
- applications
- development toolkits

Some limitations

Different sources download path
- url
- local
- ... and so on, one for each package
Different download tools
- tar ball / zip
- git/svn/mercurial
- copy (for local)
Some patches might required for embedded environment
- non-glibc
- busybox
- rootfs path
- and so on
Package dependency

builtroot

(wiki) A set of Makefiles and patches that simplifies and automates the process of building a complete and bootable Linux environment for an embedded system
menuconfig to select alternatives and versions of
- board
- bootloaders
- compiler, binutils and libc
- kernel version
- supported packages
How to support one package, e.g. foo
- foo.mk (Makefile DSL). Commands for
  - download
  - configure
  - build
  - install
- Config.in (menuconfig selection)
  - Example mk for customized package, e.g. bpftest.mk ~~~ BPFTEST_VERSION = 1.0 BPFTEST_SITE = $(TOPDIR)/../bpftest BPFTEST_SOURCE = "apps modules" BPFTEST_SITE_METHOD = local BPFTEST_LICENSE = GPLv3+ BPFTEST_LICENSE_FILES = COPYING
  BPFTEST_MODULE_SUBDIRS = modules BPF_MODULE_MAKE_OPTS = KVERSION=$(LINUX_VERSION_PROBED) KERNEL_DIR=$(LINUX_DIR)
  
  define BPFTEST_EXTRACT_CMDS cp -a $(TOPDIR)/$(BPFTEST_SOURCE) $(@D) endef
  
  define BPFTEST_BUILD_CMDS $(MAKE) CC="$(TARGET_CC)" LD="$(TARGET_LD)" -C $(@D)/apps all endef
  
  define BPFTEST_INSTALL_TARGET_CMDS $(INSTALL) -D -m 0755 $(@D)/apps/hello $(TARGET_DIR)/usr/bin endef
  
  $(eval $(kernel-module)) $(eval $(generic-package)) ~~~

Qemu

My target: arm vexpress
- Supported by vanilla kernel
- Supported by Qemu

Steps

Build

$ configure --prefix=/path/to/install --target-list=arm-softmmu
$ make
$ make install

Run
- https://wiki.linaro.org/PeterMaydell/QemuVersatileExpress
  - target: -M vexpress-a15 (Feedback) Can try virtio (?)
  - images:
    - kernel: -kernel /path/to/zImage
    - dtb: -dtb /path/to/dtb
    - disk: -drive ...
  - serial output to tty: -serial stdio
  - virtual NAT and port forwarding:-net nic,vlan=1 -net user,vlan=1,hostfwd=udp:127.0.0.1:6669-:69 (Feedback) Can try tap
  - boot args: -append "root=/dev/mmcblk0 console=ttyAMA0,115200n8"
  - debug:-s or -gdb tcp::1234 / -S
  - CPU logging: -d op -D /path/to/qemu.log
- example command
```
$ /path/to/install/bin/qemu-system-arm \
-M vexpress-a15 \
-kernel buildroot/output/images/zImage \
-dtb buildroot/output/images/vexpress-v2p-ca15_a7.dtb \
-drive file=buildroot/output/images/rootfs.ext2,if=sd \
-smp 2 \
-s \
-serial stdio \
-append "root=/dev/mmcblk0 console=ttyAMA0,115200n8" \
-net nic,vlan=1 -net user,vlan=1,hostfwd=udp:127.0.0.1:6669-:69
```

Wen

qemu-system-arm \
-M versatilepb \
-kernel /tmp/kernel/linux-stable/arch/arm/boot/zImage \
-drive file=output/images/rootfs.ext2,if=scsi,format=raw \
-append "root=/dev/sda console=ttyAMA0,115200" \
-serial stdio \
-net nic,model=rtl8139 \
-net user

Linux Kernel Pratice 0: Buildroot (1/2)

理論上不應該要邊移動邊開火，延長戰線。不過計劃趕不上變化，既來之則安之。

最近因為特別因素開始學習Linux kernel，看能不能Linux kernel和STM32兩邊都不要漏掉。不管怎樣，學習和實習絕對分不開，所以還是從環境架設開始吧。這次的實習環境架設的目標是：

可以使用ARM 平臺。一方面追求流行，一方面我不想再開x86這個副本
可以方便地建立ARM平臺的Linux Rootfs和kernel版本
可以方便地更改指定要編譯的Kernel版本
透過Qemu ，使用2的Rootfs和kernel開機
透過Qemu和搭配的工具可以分析Linux kernel的run time 行為

今天只有辦到1, 2和4而已，剩下的還要繼續努力。

測試環境

因為我已經裝過開發相關的套件，因此如果您是新手可能要自行摸索也許有需要另外安裝的套件如git。嘛，練習解讀錯誤訊息也是一種學習。

$ lsb_release -a
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 14.04.5 LTS
Release:    14.04
Codename:    trusty

安裝Buildroot

主要分成下面三個步驟

下載Buildroot
設定ARM 環境
編譯及輸出

下載Buildroot

直接看例子，剪下貼上就好

mkdir buildroot
cd buildroot
git clone git://git.buildroot.net/buildroot

設定ARM 環境

網路上查到大部分都是從make menuconfig開始。不過我是很明確地要用Qemu跑ARM的系統。所以就找了一下發現有下面的指令

make qemu_x86_defconfig

想說既然有x86_defconfig，那應該有arm_defconfig吧? 錯！那我就去buildroot/board/qemu目錄下找，有看到arm-versatile。印象中以前有用過Qemu跑的Debian系統也是versatile。所以就很高興地下了

make qemu_arm-versatile_defconfig

結果一樣GG，估狗查才知道正確的用法是：

make qemu_arm_versatile_defconfig

更新: 後來看手冊才知道有make list-defconfigs可以查詢有哪些default config，果然前輩說要RTFM是對的，唉。

接下來就用make menuconfig做細項調整，我主要是改成

使用glibc
使用gcc 4.8
- 預設5.x，因為我想要編Linux kernel 4.4.2。以前PC經驗使用gcc 5.x極端痛苦，後來還是換回gcc 4.8
一些除錯設定

另外本來想要嘗試設定更動Kernel版本，但是發現需要更進一步的瞭解buildroot才能夠達成。當作下次目標吧。

編譯及輸出

編譯只要下make就會幫你下載和編譯開機需要的

套件和一些常用工具，並封裝到output/image/roofs.ext2
Kernel(預設4.7)，編譯成zImage，放在output/image/zImage

測試

接下來也不難，可以參考board/qemu/arm-versatile/readme.txt 簡單來說就是執行下面指令，開機完使用root登入不用密碼，使用poweroff後再手動離開qemu。

qemu-system-arm -M versatilepb -kernel output/images/zImage -dtb output/images/versatile-pb.dtb -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net user

執行畫面如下

$ qemu-system-arm -M versatilepb -kernel output/images/zImage -dtb output/images/versatile-pb.dtb -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net user
...
Booting Linux on physical CPU 0x0
Linux version 4.7.0 (user@host) (gcc version 4.8.5 (Buildroot 2016.11-git-00439-g14b2472) ) #1 Mon Sep 26 22:36:42 CST 2016
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00093177
CPU: VIVT data cache, VIVT instruction cache
Machine model: ARM Versatile PB
....
EXT4-fs (sda): re-mounted. Opts: block_validity,barrier,user_xattr,errors=remount-ro
Starting logging: OK
Initializing random number generator... random: dd urandom read with 46 bits of entropy available
done.
Starting network: 8139cp 0000:00:0c.0 eth0: link up, 100Mbps, full-duplex, lpa 0x05E1
...
adding dns 10.0.2.3
OK

Welcome to Buildroot
buildroot login: root
#

參考資料

The Buildroot user manual
- 只有看部份，不過官方文件本來就是應該放在第一位
Buildroot and QEMU – the quickest receipe for your own Linux
- 東西弄完才看到的文章，入門好文

下次準備看的資料

Qemu and the Kernel
- 使用Qemu debug kernel的資料
Stackoverflow: Can virtfs/9p be used as root file system?
- Qemu和Host主機共享資料，甚至直接把rootfs放host讓qemu去讀取的方式

Linux Kernel Pratice 0: Buildroot (2/2) - 自行編譯kernel

前情提要

上一篇提到，設定實習環境的目標有：

可以使用ARM 平臺。一方面追求流行，一方面我不想再開x86這個副本
可以方便地建立ARM平臺的Linux Rootfs和kernel版本
可以方便地更改指定要編譯的Kernel版本
透過Qemu ，使用2的Rootfs和kernel開機
透過Qemu和搭配的工具可以分析Linux kernel的run time 行為

今天就是來解決3 的項目。更細分的話，這次目標是

使用官方Linux kernel 編譯Versatile
編譯出來的kernel binary可以在Qemu上順利載入
編譯出來的kernel binary可以順利的載入buildroot產生的rootfs，以及網路介面和相關設備

測試環境

做組裝的最重要的原則之一就是要能夠reproduce，所以交代測試環境是一定要的

$ lsb_release -a
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 14.04.5 LTS
Release:    14.04
Codename:    trusty

$ git --version
git version 2.10.0

buildroot 版本
- commit hash: 14b24726a81b719b35fee70c8ba8be2d682a7313

下載Linux Kernel Source

沒啥好講的，就剪貼指令吧

git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

設定和編譯

東西下載完不是就閉著眼睛開幹，因為我們在開始編譯前需要

切換到你想要研究的版本
如果不是x86，你需要指定平臺
細項Kernel config設定

那麼就來見招拆招吧

切換版本

非常簡單，先git tag，切過去就好。我要切到4.4.2就是

git tag                 # 找你要的版本
git checkout v4.4.2     # 切到tag
git checkout -b v4.4.2  # 理論上會這邊改東改西，就先開branch吧

設定ARM Versatile預設config

先講結論

make ARCH=arm versatile_defconfig

開始~~沒人要看~~的解釋吧。基本上也亂看找出來的，簡單講一下當初的「脈絡」

我知道我們平臺是versatile，所以就find | grep versatile。從一堆檔案中我看到有趣的檔案./arch/arm/configs/versatile_defconfig。
接下來就是要找make 的時候怎麼和這個檔案勾起來。網路上找一下會發現一個變數ARCH，剩下就試看看make ARCH=arm versatile_defconfig，能不能動，可以動所以打完收工。

然後你就知道

Linux kernel source中有些平臺會提供default config
透過ARCH可以讓make時自動參考這些檔案產生config

設定Qemu VM支援的硬體

**建議不要把buildroot compile cache打開。我花了很多時間在kernel 編譯後Qemu還是沒有使用編譯後的kernel的問題，最後發現關閉buildroot compile cache問題就消失了。**

如果閉著眼睛開始編譯，你會很高興地發現可以開機了，但是接下來就會很失望的發現kernel panic，原因是認不出開機的disk。

之所以會發生這樣的原因是因為Linux kernel 提供的default config選項和buildroot 給Qemu的kernel 選項不同(參考)，比對buildroot 開機畫面，會發現他們有偵測到兩個硬體，分別是

SCSI 控制器，用來辨認rootfs
Realtek 8139 網路卡，不用我解釋吧

那麼我們這邊直接把這兩個加上去就收工沒錯吧？答案是對也不對，因為這兩個東西會和其他的部份有關。

以下是我用笨方式一個一個試出來需要開啟的東西，不一定最簡潔甚至正確，但是他可以開機就是了。要注意不要編成module，編譯的細節我假設讀者都知道，如果完全不懂可能要找一下新手入門資訊了。另外我列出的選項是Kernel 4.4.2下的選項，請自行斟酌。

記得請用make ARCH=arm menuconfig更改設定

PCI bus，原因是SCSI控制器和網路卡是PCI bus介面，不開就沒有不會看到這些選項。
SCSI 包括
- SSCI device
- Disk
- 我有開Generic，懶得關掉看會不會出問題了
- SCSI low-level drivers -> SYM53C8XX Version 2 SCSI support
Network device support
- Ethernet driver suppor -> Realtek devices
  - RealTek RTL-8139 C+ PCI Fast Ethernet Adapter support
要支援buildroot預設的device node管理方式。有興趣的可以看這邊
- Device Drivers -> Generic Driver Options ->
  - Maintain a devtmpfs filesystem to mount at /dev
  - Automount devtmpfs at /dev, after the kernel mounted the rootfs
File system 要支援ext2，原因是buildroot產生的是ext2檔案格式
tmpfs要開啟
- File systems -> Pseudo filesystems
  - Tmpfs virtual memory file system support (former shm fs)

建議順便巡一下其他kernel選項，用不到的可以關一下。比如說MTD，一堆有的沒的網卡，音效支援之類的。

編譯

Buildroot

make menuconfig
- Toolchain -> Custom kernel headers series
  - 改成你現在Linux 版本
make

Linux kernel

指令如下

make CROSS_COMPILE=/tmp/buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi- ARCH=arm V=1 bzImage

這其實就是make bzImage的囉唆版，多了

ARCH=arm
- 指定ARM平臺
CROSS_COMPILE=..
- Cross compile prefix，既然我們使用buildroot內建toolchain，就用他們來編譯kernel
V=1
- 身為組裝工，沒看到編譯指令訊息跳出來就會沒安全感

測試

這邊卡關的原因是預設的buildroot (Linux kernel 4.7)使用qemu載入的時候需要指定device tree檔案。但是在Linux 4.4.2下面指定device tree檔案反而無法順利開機。我怎麼知道到的？撈git commit log去看的。

剩下就剪貼了

我在buildroot top目錄執行的，你要嘛就切到buildroot目錄下，要嘛就指定-drive file到你自己rootfs的路徑

qemu-system-arm -M versatilepb -kernel /tmp/kernel/linux-stable/arch/arm/boot/zImage -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net use

單純提出來一個參數表示這是我編譯出來的kernel而不是buildroot的

-kernel /tmp/kernel/linux-stable/arch/arm/boot/zImage

開機節錄畫面如下

Uncompressing Linux... done, booting the kernel.
Booting Linux on physical CPU 0x0
Linux version 4.4.2 (user@host) (gcc version 4.8.5 (Buildroot 2016.11-git-00439-g14b2472) ) #2 Fri Sep 30 22:46:53 CST 2016
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00093177
CPU: VIVT data cache, VIVT instruction cache
Machine: ARM-Versatile PB
Memory policy: Data cache writeback
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 32512
Kernel command line: root=/dev/sda console=ttyAMA0,115200
PID hash table entries: 512 (order: -1, 2048 bytes)
Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
Memory: 125956K/131072K available (2780K kernel code, 148K rwdata, 776K rodata, 128K init, 79K bss, 5116K reserved, 0K cma-reserved)
Virtual kernel memory layout:
    vector  : 0xffff0000 - 0xffff1000   (   4 kB)
    fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
    vmalloc : 0xc8800000 - 0xff800000   ( 880 MB)
    lowmem  : 0xc0000000 - 0xc8000000   ( 128 MB)
    modules : 0xbf000000 - 0xc0000000   (  16 MB)
      .text : 0xc0008000 - 0xc038158c   (3558 kB)
      .init : 0xc0382000 - 0xc03a2000   ( 128 kB)
      .data : 0xc03a2000 - 0xc03c7300   ( 149 kB)
       .bss : 0xc03c7300 - 0xc03daf2c   (  80 kB)
NR_IRQS:224
VIC @f1140000: id 0x00041190, vendor 0x41
FPGA IRQ chip 0 "SIC" @ f1003000, 13 irqs, parent IRQ: 63
clocksource: timer3: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns
Console: colour dummy device 80x30
Calibrating delay loop... 641.43 BogoMIPS (lpj=3207168)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
CPU: Testing write buffer coherency: ok
Setting up static identity map for 0x8400 - 0x8458
devtmpfs: initialized
VFP support v0.3: implementor 41 architecture 1 part 10 variant 9 rev 0
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
NET: Registered protocol family 16
DMA: preallocated 256 KiB pool for atomic coherent allocations
Serial: AMBA PL011 UART driver
dev:f1: ttyAMA0 at MMIO 0x101f1000 (irq = 44, base_baud = 0) is a PL011 rev1
console [ttyAMA0] enabled
dev:f2: ttyAMA1 at MMIO 0x101f2000 (irq = 45, base_baud = 0) is a PL011 rev1
dev:f3: ttyAMA2 at MMIO 0x101f3000 (irq = 46, base_baud = 0) is a PL011 rev1
fpga:09: ttyAMA3 at MMIO 0x10009000 (irq = 70, base_baud = 0) is a PL011 rev1
PCI core found (slot 11)
PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [mem 0x50000000-0x5fffffff]
pci_bus 0000:00: root bus resource [mem 0x60000000-0x6fffffff pref]
pci_bus 0000:00: root bus resource [io  0x1000-0xffff]
pci_bus 0000:00: No busn resource found for root bus, will use [bus 00-ff]
PCI: bus0: Fast back to back transfers disabled
pci 0000:00:0c.0: BAR 6: assigned [mem 0x60000000-0x6003ffff pref]
pci 0000:00:0d.0: BAR 2: assigned [mem 0x50000000-0x50001fff]
pci 0000:00:0d.0: BAR 1: assigned [mem 0x50002000-0x500023ff]
pci 0000:00:0c.0: BAR 0: assigned [io  0x1000-0x10ff]
pci 0000:00:0c.0: BAR 1: assigned [mem 0x50002400-0x500024ff]
pci 0000:00:0d.0: BAR 0: assigned [io  0x1400-0x14ff]
vgaarb: loaded
SCSI subsystem initialized
clocksource: Switched to clocksource timer3
NET: Registered protocol family 2
TCP established hash table entries: 1024 (order: 0, 4096 bytes)
TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
TCP: Hash tables configured (established 1024 bind 1024)
UDP hash table entries: 256 (order: 0, 4096 bytes)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
NET: Registered protocol family 1
NetWinder Floating Point Emulator V0.97 (double precision)
futex hash table entries: 256 (order: -1, 3072 bytes)
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254)
io scheduler noop registered
io scheduler deadline registered
io scheduler cfq registered (default)
pl061_gpio dev:e4: PL061 GPIO chip @0x101e4000 registered
pl061_gpio dev:e5: PL061 GPIO chip @0x101e5000 registered
pl061_gpio dev:e6: PL061 GPIO chip @0x101e6000 registered
pl061_gpio dev:e7: PL061 GPIO chip @0x101e7000 registered
clcd-pl11x dev:20: PL110 rev0 at 0x10120000
clcd-pl11x dev:20: Versatile hardware, VGA display
Console: switching to colour frame buffer device 80x60
sym53c8xx 0000:00:0d.0: enabling device (0100 -> 0103)
sym0: <895a> rev 0x0 at pci 0000:00:0d.0 irq 94
sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
sym0: SCSI BUS has been reset.
scsi host0: sym-2.2.3
sym0: unknown interrupt(s) ignored, ISTAT=0x5 DSTAT=0x80 SIST=0x0
scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.0. PQ: 0 ANSI: 5
scsi target0:0:0: tagged command queuing enabled, command queue depth 16.
scsi target0:0:0: Beginning Domain Validation
scsi target0:0:0: Domain Validation skipping write tests
scsi target0:0:0: Ending Domain Validation
scsi 0:0:2:0: CD-ROM            QEMU     QEMU CD-ROM      2.0. PQ: 0 ANSI: 5
scsi target0:0:2: tagged command queuing enabled, command queue depth 16.
scsi target0:0:2: Beginning Domain Validation
scsi target0:0:2: Domain Validation skipping write tests
scsi target0:0:2: Ending Domain Validation
sd 0:0:0:0: Attached scsi generic sg0 type 0
scsi 0:0:2:0: Attached scsi generic sg1 type 5
8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
8139cp 0000:00:0c.0: enabling device (0100 -> 0103)
8139cp 0000:00:0c.0 eth0: RTL-8139C+ at 0xc8974400, 52:54:00:12:34:56, IRQ 93
sd 0:0:0:0: [sda] 12666 512-byte logical blocks: (6.48 MB/6.18 MiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sd 0:0:0:0: [sda] Attached SCSI disk
mousedev: PS/2 mouse device common for all mice
NET: Registered protocol family 17
input: AT Raw Set 2 keyboard as /devices/fpga:06/serio0/input/input0
input: ImExPS/2 Generic Explorer Mouse as /devices/fpga:07/serio1/input/input2
VFS: Mounted root (ext2 filesystem) readonly on device 8:0.
devtmpfs: mounted
Freeing unused kernel memory: 128K (c0382000 - c03a2000)
EXT2-fs (sda): warning: mounting unchecked fs, running e2fsck is recommended
Starting logging: OK
Initializing random number generator... random: dd urandom read with 48 bits of entropy available
done.
Starting network: 8139cp 0000:00:0c.0 eth0: link up, 100Mbps, full-duplex, lpa 0x05E1
udhcpc: started, v1.25.0
udhcpc: sending discover
udhcpc: sending select for 10.0.2.15
udhcpc: lease of 10.0.2.15 obtained, lease time 86400
deleting routers
adding dns 10.0.2.3
OK

Welcome to Buildroot
buildroot login: root
# 
random: nonblocking pool is initialized

參考資料

Buildroot 官方手冊

附錄

使用Buildroot 內建套件指定編譯Linux kernel 4.2.2

當初會去做這個主要是因為開始編譯獨立的Linux kernel前要先驗證buildroot自己編的Linux 4.4.2是否可以用qemu開機。另外的好處的就是buildroot編譯出來的kernel config (在output/build/linux-4.4.2/.config) 可以和你自己的kernel config比對。

步驟如下

找出buildroot 4.4.x的kernel config
更改buildroot config指定使用Linux 4.4.2
測試驗證

找出buildroot 4.4.x的kernel config

前篇有提到make qemu_arm_versatile_defconfig這個指令和buildroot/board/qemu/arm-versatile這個目錄。我們進一步去看一下這個目錄

$ ls -gG board/qemu/arm-versatile
total 8
-rw-rw-r-- 1 890 Sep 30 21:32 linux-4.7.config
-rw-rw-r-- 1 404 Sep 30 21:32 readme.txt

直接破梗

readme.txt 告訴你怎麼用qemu 開機
linux-4.7.config 是Linux kernel config

所以我會去git log .，撈看看有沒有Linux kernel 4.4.x的資料。果然給我看到一個commit

commit 93c640f00537d40fd25280c4c2c60f3b30808256
Author: Gustavo Zacarias 
Date:   Sun Feb 7 18:19:13 2016 -0300

    configs/qemu: bump to the latest linux versions
...
    arm_versatile           4.4.1           2.3.0   YES     OK

剩下就是使用git切到該commit，撈出資料，另存新檔。我把他存在 /tmp/linux-4.4.config

更改buildroot config指定使用Linux 4.4.2

make menuconfig
- Kernel -> Kernel version -> Custom version
- Kernel -> Kernel version: 填 4.4.2
- Kernel -> Kernel configuration -> Using a custom (def)config file
- Kernel -> Configuration file path: 填/tmp/linux-4.4.config
make

測試驗證

根據buildroot/board/qemu/arm-versatile中4.4.2版時的readme.txt，qemu指令執行如下，基本上就是不去載入device tree檔案。

qemu-system-arm -M versatilepb -kernel output/images/zImage -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net user

以下是開機畫面

Uncompressing Linux... done, booting the kernel.
Booting Linux on physical CPU 0x0
Linux version 4.4.2 (user@host) (gcc version 4.8.5 (Buildroot 2016.11-git-00439-g14b2472) ) #1 Fri Sep 30 22:36:58 CST 2016
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00093177
CPU: VIVT data cache, VIVT instruction cache
Machine: ARM-Versatile PB
Memory policy: Data cache writeback
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 32512
Kernel command line: root=/dev/sda console=ttyAMA0,115200
PID hash table entries: 512 (order: -1, 2048 bytes)
Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
Memory: 125264K/131072K available (3246K kernel code, 158K rwdata, 880K rodata, 120K init, 198K bss, 5808K reserved, 0K cma-reserved)
Virtual kernel memory layout:
    vector  : 0xffff0000 - 0xffff1000   (   4 kB)
    fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
    vmalloc : 0xc8800000 - 0xff800000   ( 880 MB)
    lowmem  : 0xc0000000 - 0xc8000000   ( 128 MB)
    modules : 0xbf000000 - 0xc0000000   (  16 MB)
      .text : 0xc0008000 - 0xc040fdcc   (4128 kB)
      .init : 0xc0410000 - 0xc042e000   ( 120 kB)
      .data : 0xc042e000 - 0xc04559e0   ( 159 kB)
       .bss : 0xc04559e0 - 0xc04873a8   ( 199 kB)
SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
NR_IRQS:224
VIC @f1140000: id 0x00041190, vendor 0x41
FPGA IRQ chip 0 "SIC" @ f1003000, 13 irqs, parent IRQ: 63
clocksource: timer3: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns
Console: colour dummy device 80x30
Calibrating delay loop... 637.74 BogoMIPS (lpj=3188736)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
CPU: Testing write buffer coherency: ok
Setting up static identity map for 0x8400 - 0x8458
devtmpfs: initialized
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
NET: Registered protocol family 16
DMA: preallocated 256 KiB pool for atomic coherent allocations
Serial: AMBA PL011 UART driver
dev:f1: ttyAMA0 at MMIO 0x101f1000 (irq = 44, base_baud = 0) is a PL011 rev1
console [ttyAMA0] enabled
dev:f2: ttyAMA1 at MMIO 0x101f2000 (irq = 45, base_baud = 0) is a PL011 rev1
dev:f3: ttyAMA2 at MMIO 0x101f3000 (irq = 46, base_baud = 0) is a PL011 rev1
fpga:09: ttyAMA3 at MMIO 0x10009000 (irq = 70, base_baud = 0) is a PL011 rev1
PCI core found (slot 11)
PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [mem 0x50000000-0x5fffffff]
pci_bus 0000:00: root bus resource [mem 0x60000000-0x6fffffff pref]
pci_bus 0000:00: root bus resource [io  0x1000-0xffff]
pci_bus 0000:00: No busn resource found for root bus, will use [bus 00-ff]
PCI: bus0: Fast back to back transfers disabled
pci 0000:00:0c.0: BAR 6: assigned [mem 0x60000000-0x6003ffff pref]
pci 0000:00:0d.0: BAR 2: assigned [mem 0x50000000-0x50001fff]
pci 0000:00:0d.0: BAR 1: assigned [mem 0x50002000-0x500023ff]
pci 0000:00:0c.0: BAR 0: assigned [io  0x1000-0x10ff]
pci 0000:00:0c.0: BAR 1: assigned [mem 0x50002400-0x500024ff]
pci 0000:00:0d.0: BAR 0: assigned [io  0x1400-0x14ff]
vgaarb: loaded
SCSI subsystem initialized
clocksource: Switched to clocksource timer3
NET: Registered protocol family 2
TCP established hash table entries: 1024 (order: 0, 4096 bytes)
TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
TCP: Hash tables configured (established 1024 bind 1024)
UDP hash table entries: 256 (order: 0, 4096 bytes)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
NET: Registered protocol family 1
futex hash table entries: 256 (order: -1, 3072 bytes)
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254)
io scheduler noop registered
io scheduler deadline registered
io scheduler cfq registered (default)
clcd-pl11x dev:20: PL110 rev0 at 0x10120000
clcd-pl11x dev:20: Versatile hardware, VGA display
Console: switching to colour frame buffer device 80x30
sym53c8xx 0000:00:0d.0: enabling device (0100 -> 0103)
sym0: <895a> rev 0x0 at pci 0000:00:0d.0 irq 94
sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
sym0: SCSI BUS has been reset.
scsi host0: sym-2.2.3
sym0: unknown interrupt(s) ignored, ISTAT=0x5 DSTAT=0x80 SIST=0x0
scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.0. PQ: 0 ANSI: 5
scsi target0:0:0: tagged command queuing enabled, command queue depth 16.
scsi target0:0:0: Beginning Domain Validation
scsi target0:0:0: Domain Validation skipping write tests
scsi target0:0:0: Ending Domain Validation
scsi 0:0:2:0: CD-ROM            QEMU     QEMU CD-ROM      2.0. PQ: 0 ANSI: 5
scsi target0:0:2: tagged command queuing enabled, command queue depth 16.
scsi target0:0:2: Beginning Domain Validation
scsi target0:0:2: Domain Validation skipping write tests
scsi target0:0:2: Ending Domain Validation
8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
8139cp 0000:00:0c.0: enabling device (0100 -> 0103)
8139cp 0000:00:0c.0 eth0: RTL-8139C+ at 0xc8978400, 52:54:00:12:34:56, IRQ 93
sd 0:0:0:0: [sda] 12666 512-byte logical blocks: (6.48 MB/6.18 MiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
mousedev: PS/2 mouse device common for all mice
sd 0:0:0:0: [sda] Attached SCSI disk
NET: Registered protocol family 10
sit: IPv6 over IPv4 tunneling driver
NET: Registered protocol family 17
input: AT Raw Set 2 keyboard as /devices/fpga:06/serio0/input/input0
input: ImExPS/2 Generic Explorer Mouse as /devices/fpga:07/serio1/input/input2
EXT4-fs (sda): couldn't mount as ext3 due to feature incompatibilities
EXT4-fs (sda): mounting ext2 file system using the ext4 subsystem
EXT4-fs (sda): mounted filesystem without journal. Opts: (null)
VFS: Mounted root (ext2 filesystem) readonly on device 8:0.
devtmpfs: mounted
Freeing unused kernel memory: 120K (c0410000 - c042e000)
EXT4-fs (sda): warning: mounting unchecked fs, running e2fsck is recommended
EXT4-fs warning (device sda): ext4_update_dynamic_rev:717: updating to rev 1 because of new feature flag, running e2fsck is recommended
EXT4-fs (sda): re-mounted. Opts: block_validity,barrier,user_xattr,errors=remount-ro
Starting logging: OK
Initializing random number generator... random: dd urandom read with 43 bits of entropy available
done.
Starting network: 8139cp 0000:00:0c.0 eth0: link up, 100Mbps, full-duplex, lpa 0x05E1
udhcpc: started, v1.25.0
udhcpc: sending discover
udhcpc: sending select for 10.0.2.15
udhcpc: lease of 10.0.2.15 obtained, lease time 86400
deleting routers
adding dns 10.0.2.3
OK

Welcome to Buildroot
buildroot login: root
#

Virt-2.7

qemu-system-arm \
-M virt-2.7 \
-S \
-m 1024 \
-cpu cortex-a15 \
-nographic \
-device virtio-9p-device,fsdev=host_fs,mount_tag=/dev/root \
-fsdev local,id=host_fs,security_model=none,path=$(pwd)/../sysroot \
-kernel ./arch/arm/boot/zImage \
-append 'root=/dev/root rootfstype=9p rootflags=trans=virtio rw \
-netdev user,id=unet -device virtio-net-device,netdev=unet

How Other People Use QEMU

Viller

﻿利用 buildroot 與 Qemu 建構簡易 Embedded Linux 環境

Embedded Linux development

Components

Some limitations

builtroot

Qemu

Steps

Wen

Linux Kernel Pratice 0: Buildroot (1/2)

目錄

測試環境

安裝Buildroot

下載Buildroot

設定ARM 環境

編譯及輸出

測試

參考資料

下次準備看的資料

Linux Kernel Pratice 0: Buildroot (2/2) - 自行編譯kernel

前情提要

目錄

測試環境

下載Linux Kernel Source

設定和編譯

切換版本

設定ARM Versatile預設config

設定Qemu VM支援的硬體

編譯

Buildroot

Linux kernel

測試

參考資料

附錄

使用Buildroot 內建套件指定編譯Linux kernel 4.2.2

找出buildroot 4.4.x的kernel config

更改buildroot config指定使用Linux 4.4.2

測試驗證

Virt-2.7

利用 buildroot 與 Qemu 建構簡易 Embedded Linux 環境