Buildroot and QEMU – the quickest recipe for your own Linux

I will show the quickest way of running your own-built Linux system in QEMU emulator. Did I say quickest? Let’s start then:

$ git clone git://
$ cd buildroot/
$ make qemu_arm_versatile_defconfig

Where qemu_arm_versatile_defconfig is file & defconfig name from buildroot/configs directory. Next:

$ make menuconfig

And menu similar to Linux kernel menuconfig shows up. Since we preconfigured it with the defconfig file, there is almost nothing to change here. Be sure to have all tools from Build options —> Commands menu installed in your host system.

In Build options check Enable compiler cache which will save compiler output files and make consequent compilations faster. It is not necessary though.

Now type this and get some coffee:

$ make

We have now the time to chat a bit. So, what we have just done is we run a massive process of downloading core packages and compiling them into toolchain, kernel and root filesystem that will became our own, small Linux OS. Ever heard that making Linux for embedded devices is hard? Well, it is. But we have taken three huge shortcuts.

First, by using Buildroot which is a big set of Makefiles that configures and compiles GCC, C library and whole OS ecosystem (BusyBox). What it produces in the end are the Linux kernel and the image of root filesystem.

Second shortcut is configuring Buildroot with qemu_arm_versatile_defconfig. There is nothing to change within the kernel thanks to this. This configuration file along with buildroot/board/qemu/arm-versatile/linux-4.9.config tells Buildroot to set kernel configuration to suit ARM Versatile boards template. This is one of the development platforms supported both by Linux and QEMU out of the box.

The last one is the use of QEMU. Because of that, we do not have to configure any bootloader (like U-Boot for instance). All we need to do is to run one command right after the compilation ends:

$ qemu-system-arm -M versatilepb -kernel output/images/zImage -dtb output/images/versatile-pb.dtb -drive file=output/images/rootfs.ext2,if=scsi -append "root=/dev/sda console=ttyAMA0,115200" -nographic

This was inspired by buildroot/board/qemu/arm-versatile/readme.txt.

And there it is!

pulseaudio: set_sink_input_volume() failed
pulseaudio: Reason: Invalid argument
pulseaudio: set_sink_input_mute() failed
pulseaudio: Reason: Invalid argument
vpb_sic_write: Bad register offset 0x2c
Booting Linux on physical CPU 0x0
Linux version 4.9.6 (pillot@pillot) (gcc version 5.4.0 (Buildroot 2017.05-rc2-00013-g4d1c2c82e) ) #1 Sat May 20 00:42:18 CEST 2017
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00093177
CPU: VIVT data cache, VIVT instruction cache
OF: fdt:Machine model: ARM Versatile PB
Memory policy: Data cache writeback
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: 125088K/131072K available (3390K kernel code, 131K rwdata, 756K rodata, 132K init, 207K bss, 5984K 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 - 0xc0357e80   (3392 kB)
      .init : 0xc042f000 - 0xc0450000   ( 132 kB)
      .data : 0xc0450000 - 0xc0470de0   ( 132 kB)
       .bss : 0xc0470de0 - 0xc04a49f8   ( 208 kB)
SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
NR_IRQS:16 nr_irqs:16 16
VIC @c8800000: id 0x00041190, vendor 0x41
FPGA IRQ chip 0 "intc" @ c8802000, 20 irqs, parent IRQ: 47
clocksource: arm,sp804: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns
sched_clock: 32 bits at 1000kHz, resolution 1000ns, wraps every 2147483647500ns
Failed to initialize '/amba/timer@101e3000': -22
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
Console: colour dummy device 80x30
Calibrating delay loop... 464.48 BogoMIPS (lpj=2322432)
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
OF: amba_device_add() failed (-19) for /amba/smc@10100000
OF: amba_device_add() failed (-19) for /amba/mpmc@10110000
OF: amba_device_add() failed (-19) for /amba/sctl@101e0000
OF: amba_device_add() failed (-19) for /amba/watchdog@101e1000
OF: amba_device_add() failed (-19) for /amba/sci@101f0000
OF: amba_device_add() failed (-19) for /amba/ssp@101f4000
OF: amba_device_add() failed (-19) for /amba/fpga/sci@a000
Serial: AMBA PL011 UART driver
101f1000.uart: ttyAMA0 at MMIO 0x101f1000 (irq = 28, base_baud = 0) is a PL011 rev1
console [ttyAMA0] enabled
101f2000.uart: ttyAMA1 at MMIO 0x101f2000 (irq = 29, base_baud = 0) is a PL011 rev1
101f3000.uart: ttyAMA2 at MMIO 0x101f3000 (irq = 30, base_baud = 0) is a PL011 rev1
uart-pl011 10009000.uart: aliased and non-aliased serial devices found in device tree. Serial port enumeration may be unpredictable.
10009000.uart: ttyAMA3 at MMIO 0x10009000 (irq = 54, base_baud = 0) is a PL011 rev1
vgaarb: loaded
SCSI subsystem initialized
clocksource: Switched to clocksource arm,sp804
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)
workingset: timestamp_bits=30 max_order=15 bucket_order=0
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)
OF: PCI: host bridge /amba/pci-controller@10001000 ranges:
OF: PCI:    IO 0x43000000..0x4300ffff -> 0x00000000
OF: PCI:   MEM 0x50000000..0x5fffffff -> 0x50000000
OF: PCI:   MEM 0x60000000..0x6fffffff -> 0x60000000
versatile-pci 10001000.pci-controller: PCI core found (slot 11)
versatile-pci 10001000.pci-controller: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [bus 00-ff]
pci_bus 0000:00: root bus resource [io  0x0000-0xffff]
pci_bus 0000:00: root bus resource [mem 0x50000000-0x5fffffff]
pci_bus 0000:00: root bus resource [mem 0x60000000-0x6fffffff pref]
PCI: bus0: Fast back to back transfers disabled
pci 0000:00:0c.0: BAR 2: assigned [mem 0x50000000-0x50001fff]
pci 0000:00:0c.0: BAR 1: assigned [mem 0x50002000-0x500023ff]
pci 0000:00:0c.0: BAR 0: assigned [io  0x1000-0x10ff]
clcd-pl11x dev:20: PL110 designer 41 rev0 at 0x10120000
clcd-pl11x dev:20: Versatile hardware, VGA display
Console: switching to colour frame buffer device 80x30
sym53c8xx 0000:00:0c.0: enabling device (0100 -> 0103)
sym0: <895a> rev 0x0 at pci 0000:00:0c.0 irq 66
sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
sym0: SCSI BUS has been reset.
scsi host0: sym-2.2.3
random: fast init done
scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.5+ 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      2.5+ 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
libphy: Fixed MDIO Bus: probed
sd 0:0:0:0: [sda] 122880 512-byte logical blocks: (62.9 MB/60.0 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
versatile reboot driver registered
NET: Registered protocol family 10
sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
NET: Registered protocol family 17
sd 0:0:0:0: [sda] Attached SCSI disk
input: AT Raw Set 2 keyboard as /devices/platform/amba/amba:fpga/10006000.kmi/serio0/input/input0
input: ImExPS/2 Generic Explorer Mouse as /devices/platform/amba/amba:fpga/10007000.kmi/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: 132K (c042f000 - c0450000)
This architecture does not have kernel memory protection.
EXT4-fs (sda): warning: mounting unchecked fs, 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... done.
Starting network: Waiting for interface eth0 to appear............... timeout!
run-parts: /etc/network/if-pre-up.d/wait_iface: exit status 1

Welcome to Buildroot
buildroot login: root
# cat /proc/cpuinfo 
processor       : 0
model name      : ARM926EJ-S rev 5 (v5l)
BogoMIPS        : 464.48
Features        : swp half thumb fastmult edsp java 
CPU implementer : 0x41
CPU architecture: 5TEJ
CPU variant     : 0x0
CPU part        : 0x926
CPU revision    : 5

Hardware        : ARM-Versatile (Device Tree Support)
Revision        : 0000
Serial          : 0000000000000000

As in every shortcut there is not much to understand here. Please go further:

13. September 2013 by resset
Categories: Software | Tags: , , , , , , , , , | 6 comments

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