How to build and boot Linux aarch64 with U-Boot with Buildroot on QEMU?

Question

I tried:

git clone git://git.buildroot.net/buildroot
cd buildroot
git checkout 2019.08
make qemu_aarch64_virt_defconfig
make menuconfig

In menuconfig, I set:

• Bootloaders
  • U-Boot configuration (Using an in-tree board defconfig file)
    • qemu_arm64
• Kernel
  • Install kernel image to /boot in target

and finally:

make BR2_JLEVEL="$nproc"

Now, I can boot fine without U-Boot with the command line mentioned at: How to download the Torvalds Linux Kernel master, (re)compile it, and boot it with QEMU?

./output/host/usr/bin/qemu-system-aarch64 -M virt -cpu cortex-a57 -nographic -smp 1 -kernel output/images/Image -append "root=/dev/vda console=ttyAMA0" -netdev user,id=eth0 -device virtio-net-device,netdev=eth0 -drive file=output/images/rootfs.ext4,if=none,format=raw,id=hd0 -device virtio-blk-device,drive=hd0

but that is not using U-Boot.

When I do:

ls -l output/images/

it contains:

-rw-r--r-- 1 ciro ciro 6.5M 2019-09-20_13:36:23 Image
-rw-r--r-- 1 ciro ciro  60M 2019-09-20_13:39:02 rootfs.ext2
lrwxrwxrwx 1 ciro ciro   11 2019-09-20_13:36:25 rootfs.ext4 -> rootfs.ext2
-rw-r--r-- 1 ciro ciro 583K 2019-09-20_13:34:15 u-boot.bin

so there is a U-Boot binary there: u-boot.bin, but how do I use that with QEMU?

I tried as mentioned at: Can ARM qemu system emulator boot from card image without kernel param? to remove -kernel and -append and add -bios u-boot.bin:

./output/host/usr/bin/qemu-system-aarch64 -M virt -cpu cortex-a57 -nographic -smp 1 -bios output/images/u-boot.bin -netdev user,id=eth0 -device virtio-net-device,netdev=eth0 -drive file=output/images/rootfs.ext4,if=none,format=raw,id=hd0 -device virtio-blk-device,drive=hd0

Now I do get the U-Boot shell, but boot fails and leaves me no the U-Boot prompt:

U-Boot 2019.07 (Sep 20 2019 - 13:34:10 +0100)

DRAM:  128 MiB
Flash: 128 MiB
*** Warning - bad CRC, using default environment

In:    pl011@9000000
Out:   pl011@9000000
Err:   pl011@9000000
Net:   
Warning: virtio-net#31 using MAC address from ROM
eth0: virtio-net#31
Hit any key to stop autoboot:  0 
starting USB...
No working controllers found
USB is stopped. Please issue 'usb start' first.
scanning bus for devices...

Device 0: unknown device

Device 0: QEMU VirtIO Block Device
            Type: Hard Disk
            Capacity: 60.0 MB = 0.0 GB (122880 x 512)
... is now current device
** No partition table - virtio 0 **
starting USB...
No working controllers found
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (2 ms)
Using virtio-net#31 device
TFTP from server 10.0.2.2; our IP address is 10.0.2.15
Filename 'boot.scr.uimg'.
Load address: 0x40200000
Loading: *
TFTP error: 'Access violation' (2)
Not retrying...
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (0 ms)
Using virtio-net#31 device
TFTP from server 10.0.2.2; our IP address is 10.0.2.15
Filename 'boot.scr.uimg'.
Load address: 0x40400000
Loading: *
TFTP error: 'Access violation' (2)
Not retrying...
=> 

so it appears that U-Boot cannot handle the VirtIO device? Or according to Peter, I have to create a partition table. I couldn't find that automatically in Buildroot, but I could do it manually, here is one approach: https://unix.stackexchange.com/questions/209566/how-to-format-a-partition-inside-of-an-img-file/527132#527132

Another approach would be to keep -kernel -append and let QEMU put the kernel into memory as done without U-Boot, and then use the booti U-Boot command I've found on help:

booti     - boot Linux kernel 'Image' format from memory

so I just need to find out its address. But that is kind of cheating since I want U-boot to do the hard work rather than cheat with QEMU.

My goal is to reach a good setup to develop U-Boot and QEMU's early boot stuff.

Answer 1

Given that u-boot correctly detects the virtio block device, I think it is unlikely that it cannot handle it. The error printed is "** No partition table - virtio 0 **", which is correct, because you've set up the block device to contain just rootfs.ext4, which will be a filesystem image. That suggests that you'll have more luck if you create a disk image with a partition table and write the rootfs to a partition within the disk image.

Answer 2

I followed Peter's advice and put it into a partitioned image with the sfdisk-fs-to-img command from https://unix.stackexchange.com/questions/209566/how-to-format-a-partition-inside-of-an-img-file/527132#527132

I am now able to read the root filesystem with:

ls virtio 0 /boot

and that contains Image file.

Now I think there are only some U-Boot specifics to resolve, which I'm not very familiar with:

• load /boot/Image into memory with something like load virtio 0 0x100000 /boot/Image. TODO which address is valid? This arbitrary choice gave ** Reading file would overwrite reserved memory **
• find out how to load the DTB and kernel CLI arguments. The DTB would need to be auto-generated with QEMU with qemu-system-aarch64 -machine dumpdtb=dtb.dtb
• boot it with something like: booti 0x100000

I was hoping Buildroot would have automated things a bit more for me sadface.