Re: [Xen-users] Booting Xen on qemu-arm

[Julien Grall <julien.grall@xxxxxxx>]

On 02/06/2019 14:55, Denis Obrezkov wrote:
> Hello,
Hi Denis,

> I am trying to boot xen on qemu arm. I was able to boot Linux kernel
> with u-boot:
>
> ~/bin/qemu-3.1.0/arm-softmmu/qemu-system-arm -cpu cortex-a15 -machine
> virt -m 256M -bios u-boot.bin -device
> loader,file=zImage,force-raw=on,addr=0x41000000 -nographic -no-reboot
> -chardev
> socket,id=qemu-monitor,host=localhost,port=7777,server,nowait,telnet
> -mon qemu-monitor,mode=readline
>
> Then, in u-boot:
>
> setenv bootargs root=/dev/ram rw earlyprintk=serial,ttyAMA0 console=ttyAMA0
>
> bootz 0x41000000 - 0x40000000
>
> So, I use a device tree from this machine's default location - 0x40000000
>
> After that, I produced an image:
>
> mkimage -A arm -T kernel -a 0x46000000 -e 0x46000000 -C none -d
> "xen/xen" xen-uImage
You don't need to produce a uImage here. Xen is by default supporting the Linux 
boot protocol, so you could use bootz.
> And tried to launch it:
>
>   ~/bin/qemu-3.1.0/arm-softmmu/qemu-system-arm -cpu cortex-a15 -machine
> virt -m 512M -bios u-boot.bin -device
> loader,file=xen-uImage,force-raw=on,addr=0x41000000 -device
> loader,file=zImage,addr=0x45000000 -nographic -no-reboot -chardev
> socket,id=qemu-monitor,host=localhost,port=7777,server,nowait,telnet
> -mon qemu-monitor,mode=readline
>
> So, I put xen image to 0x41000000 and Linux zImage to 0x45000000. I want
> to use qemu's default device tree in 0x40000000.
>
> In u-boot:
>
> fdt addr 0x40000000
> fdt resize
>
> fdt set /chosen \#address-cells <1>
> fdt set /chosen \#size-cells <1>
>    
> fdt set /chosen xen,xen-bootargs "console=dtuart dtuart="/pl011@9000000""
> fdt mknod /chosen module@0
> fdt set /chosen/module@0 compatible "xen,linux-zimage"
> "xen,multiboot-module"
> fdt set /chosen/module@0 reg <0x45000000 0x853200 >
> fdt set /chosen/module@0 bootargs "earlyprintk=serial,ttyAMA0
> console=ttyAMA0,115200n8 earlycon=xenboot"
>
> bootm 0x41000000 - 0x40000000
>
> And I get the output:
>
> ## Booting kernel from Legacy Image at 41000000 ...
>     Image Name:
>     Created:      2019-06-02  10:16:13 UTC
>     Image Type:   ARM Linux Kernel Image (uncompressed)
>     Data Size:    753672 Bytes = 736 KiB
>     Load Address: 46000000
>     Entry Point:  46000000
>     Verifying Checksum ... OK
> ## Flattened Device Tree blob at 40000000
>     Booting using the fdt blob at 0x40000000
>     Loading Kernel Image ... OK
>     reserving fdt memory region: addr=40000000 size=2000
>     Using Device Tree in place at 40000000, end 40004fff
>
> Starting kernel ...
>
> And I have no output after that.
This maybe because Xen crashed before the console is setup. You can compile Xen 
with earlyprintk.
Can you provide the command line you use to build Xen?

> I don't understand several things:
>
> Where should I put xen-uImage, kernel and fdt? I assume they are loaded
> to ram to the specified addresses (ram is from 0x40000000).
You can put the blob wherever you want in the RAM as long as it does not clash 
with other things (e.g U-boot, DT).
> Can I use a
> default QEMU device tree in 0x40000000 or should I load the one
> generated by u-boot with the command:
fdt addr 0x40000000 will load the device tree and the subsequent one will 
directly modify it.
> ~/bin/qemu-3.1.0/arm-softmmu/qemu-system-arm -machine virt,gic_version=3 
> -machine virtualization=true -cpu cortex-a15 -machine type=virt -m 512 -display 
> none -machine dumpdtb=virt.dtb
>
> Also, we have created a node /chosen/module@0. Where can I find its 
> description? What is it?
You can read more about the description in [1]. In short, it used to to tell Xen 
where any modules (e.g Dom0 kernel, Dom0 Initramfs,...) are loaded in memory.
Cheers,

[1] https://xenbits.xen.org/docs/unstable/misc/arm/device-tree/booting.txt

--
Julien Grall

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