gem5 full system Linux boot fails with "Kernel panic - not syncing: VFS: Unable to mount root fs" - arm

Question

I want to run arm's linux system in gem5's fs mode,I download related files from this address:
http://www.gem5.org/documentation/general_docs/fullsystem/guest_binaries
I was able to configure the correct file path, but finally got this output in the terminal2:
[ 0.661620] No filesystem could mount root, tried:
[ 0.661621] ext3
[ 0.661650] ext4`enter code here`
[ 0.661663] ext2
[ 0.661676] vfat
[ 0.661690] fuseblk
[ 0.661703]
[ 0.661728] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(254,0)
And got this terrible output in the terminal1:
warn: Tried to read RealView I/O at offset 0x60 that doesn't exist
warn: Tried to write RVIO at offset 0xa8 (data 0) that doesn't exist
warn: Kernel panic in simulated kernel
I can provide my command line input, but simply adjusting the configuration inside will only lead to the same result:
./build/ARM/gem5.opt configs/example/arm/starter_fs.py --cpu="minor" --num-cores=4 --disk-image=/home/ad/GEM5/ARM_GEM5/gem5/my_image/disks/aarch64-ubuntu-trusty-headless.img --dtb=/home/ad/GEM5/ARM_GEM5/gem5/my_image/binaries/armv7_gem5_v1_4cpu.dtb --kernel=/home/ad/GEM5/ARM_GEM5/gem5/my_image/binaries/vmlinux
How can I solve this?
Regards,

Answer 1

Here is a full diagnostic procedure for this kind of problem: https://askubuntu.com/questions/41930/kernel-panic-not-syncing-vfs-unable-to-mount-root-fs-on-unknown-block0-0/1048477#1048477
In summary, you have to ensure that:
the kernel has the config to read the disk type, for emulation usually:
CONFIG_VIRTIO_PCI=y
CONFIG_VIRTIO_BLK=y
This seems to be the problem since there was no list of partitions given above? Please confirm. If not, the kernel can't read bytes from the disk it seems.
the kernel has the config to read the filesystem type. You kernel mentions ext2,3,4 though, so likely that's not the problem.
you are pointing the root= kernel CLI to the right partition
See also: https://cirosantilli.com/linux-kernel-module-cheat/#not-syncing That also contains a Buildroot setup that just works.
I also highly recommend that you first get it working on QEMU which boots much faster.

Answer 2

I had a similar problem. Trying to run a full-system emulation of both Ubuntu and Linaro minimal (from the gem5 website) under a 64-bit kernel, with the original starter_fs.py script, gives me this kernel panic:
[ 0.224367] List of all partitions:
[ 0.224394] fe00 1048320 vda
[ 0.224397] driver: virtio_blk
[ 0.224440] fe01 1048288 vda1 00000000-01
[ 0.224441]
[ 0.224480] No filesystem could mount root, tried:
[ 0.224481] ext3
[ 0.224510] ext4
[ 0.224524] ext2
[ 0.224537] squashfs
[ 0.224551] vfat
[ 0.224566] fuseblk
[ 0.224579]
[ 0.224606] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(254,0)
[ 0.224656] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0+ #1
[ 0.224692] Hardware name: V2P-CA15 (DT)
[ 0.224717] Call trace:
[ 0.224741] dump_backtrace+0x0/0x1c0
[ 0.224765] show_stack+0x14/0x20
[ 0.224790] dump_stack+0x8c/0xac
[ 0.224812] panic+0x130/0x288
[ 0.224836] mount_block_root+0x22c/0x294
[ 0.224861] mount_root+0x140/0x174
[ 0.224884] prepare_namespace+0x138/0x180
[ 0.224910] kernel_init_freeable+0x1c0/0x1e0
[ 0.224939] kernel_init+0x10/0x108
[ 0.224961] ret_from_fork+0x10/0x18
[ 0.224987] Kernel Offset: disabled
[ 0.225009] CPU features: 0x21c06492
[ 0.225032] Memory Limit: 2048 MB
[ 0.225056] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(254,0) ]---
Weird thing is that, few weeks ago, it worked like a charm. The problem lying into the specification of the root partition, on the kernel command line. In the starter_fs.py, change this line:
"root=/dev/vda",
By this:
"root=/dev/vda1",
You can see that before, the VirtIO block device was specified. The kernel wants a partition, not a block device. Then, you can run gem5:
build/ARM/gem5.opt -configs/example/arm/starter_fs.py --cpu="hpi" --num-cores=1 --disk-image="linaro-minimal-aarch64.img" --kernel="vmlinux.arm64"
And for me, the kernel panic is gone and I am able to boot my system again:
[ 0.228847] EXT4-fs (vda1): mounted filesystem without journal. Opts: (null)
[ 0.228906] VFS: Mounted root (ext4 filesystem) on device 254:1.
[ 0.229539] devtmpfs: mounted
[ 0.229792] Freeing unused kernel memory: 448K
INIT: version 2.88 booting
[ 0.234168] random: fast init done
Starting udev
[ 0.277039] udevd[715]: starting version 182
[ 0.411534] EXT4-fs (vda1): re-mounted. Opts: block_validity,delalloc,barrier,user_xattr
Starting Bootlog daemon: bootlogd.
[ 0.426573] random: dd: uninitialized urandom read (512 bytes read)
Populating dev cache
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
hwclock: can't open '/dev/misc/rtc': No such file or directory
Mon Jan 27 08:00:00 UTC 2014
hwclock: can't open '/dev/misc/rtc': No such file or directory
INIT: Entering runlevel: 5
Configuring network interfaces... ifconfig: SIOCGIFFLAGS: No such device
Starting rpcbind daemon...rpcbind: cannot create socket for udp6
rpcbind: cannot create socket for tcp6
done.
rpcbind: cannot get uid of '': Success
creating NFS state directory: done
starting statd: done
Starting auto-serial-console: done
Stopping Bootlog daemon:
bootlogd.
Last login: Mon Jan 27 08:00:00 UTC 2014 on tty1
INIT: no more processes left in this runlevel
root#genericarmv8:~# id
id
uid=0(root) gid=0(root) groups=0(root)
root#genericarmv8:~#