qemu machine settings and root fs for armv8?

On 08/09/2018 07:15 PM, Nick Desaulniers wrote:

On Thu, Aug 9, 2018 at 12:36 AM Laura Abbott [off-list ref] wrote:

quoted

I usually use a buildroot environment and just boot as an initramfs:

I need to play around more with buildroot, but I'll bet that's an
option to make a ramdisk instead of a full disk image?

quoted

qemu-system-aarch64 \
         -s \
         -smp 8 \
         -machine virt \
         -cpu cortex-a57 \
         -machine type=virt \
         -nographic \
         -m 1024 \
         -kernel /path/to/kernel \
         --append "nokaslr slub_debug=- console=ttyAMA0 debug_pagealloc=on
earlycon=pl011,0x9000000" \

Very cool, thank you for sharing!

I'm guessing that kaslr makes it difficult to keep track of addresses
in between reboots?  There's a parameter "panic=-1" that will reboot
the kernel on panic that probably works well with this >

Yes, I just disable nokaslr for most testing to make looking
at the addresses easier since I'm often staring at kernel panics
and dumps.

quoted

         -initrd /path/to/arm64_rootfs.cpio \
         -fsdev local,security_model=passthrough,id=fsdev0,path=/tmp/share \
         -device virtio-9p-pci,id=fs0,fsdev=fsdev0,mount_tag=hostshare

I'll note that this setup makes using kernel modules a big pain but

How come?

I build the buildroot initrd separately from the kernel. This means that
to include modules in the initrd I have to rebuild the initrd which is
yet another step.

quoted

it's useful for certain types of testing.
The virtio settings are from https://www.linux-kvm.org/page/9p_virtio
for sharing files.

Wow, that's super cool!  That probably helps so that you don't need to
keep rebuilding your ramdisk.  For binaries I'd guess that any
dynamically linked dependencies would have to be in that dir, too,
otherwise the VM wouldn't be able to load them.  But maybe nice for
statically linked cross compiled binaries.

Yes, binaries are a bit of a pain. buildroot has a good selection of
libraries available to include so I can rebuild the ramdisk to include
those. It's still a lot of trial and error so if I can get away with
it I prefer to have everything statically linked.

Thanks again.

Thanks,
Laura