RE: How to start an armv8 machine in EL3?

[ckim]

Hello Alex Bennée,

Thank you for the help!
I didn't know "-kernel xxx.elf" method makes it start at EL1 by the loader stub,
and doing "--machine virtualization=on" makes it start at EL2. I checked these 
using gdb.

And then I tested your suggestion : 
${QEMU_DIR}/qemu-system-aarch64 -M ab21q -cpu cortex-a72 -nographic -smp 1 -m 
2048 -drive if=pflash,file=${KER_DIR}/ab21s_test.bin,format=raw,readonly=on -s 
-S
And it gave me :
qemu-system-aarch64: device requires 67108864 bytes, block backend provides 
776704 bytes

Looks like the pflash device size is 64MB and my .bin file (which I made with 
objcopy from .elf file) is not big enough to fill the device.
I made the .bin file inside the pflash.img file by doing 
(https://xnand.netlify.app/2019/10/03/armv8-qemu-efi-aarch64.html )

    cp ${KER_DIR}/ab21s_test.bin pflash.img
    dd if=/dev/zero of=pflash.img bs=1c count=1 seek=67108863

and tried 
${QEMU_DIR}/qemu-system-aarch64 -M virt -cpu cortex-a72 -nographic -smp 1 -m 
2048 -drive if=pflash,file=pflash.img,format=raw,readonly=on -s -S
To see how the code works, but it traps from the first instruction.

Can you tell me what's wrong with my command? (BTW I made .bin file by 
aarch64-elf-objcopy -O binary test.elf test.bin )

Again thanks for the kind explanation!
Best regards,

Chan Kim

> -----Original Message-----
> From: Alex Bennée <alex.bennee@linaro.org>
> Sent: Wednesday, March 3, 2021 7:05 PM
> To: ckim@etri.re.kr
> Cc: qemu-discuss@nongnu.org
> Subject: Re: How to start an armv8 machine in EL3?
> 
> 
> ckim@etri.re.kr writes:
> 
> > Hello all,
> >
> > I found out in a baremetal program I run for qemu aarch64 'virt'
> > machine (cpu is cortex-a72),
> >
> > the "msr sp_el1, x0" instruction causes trap making PC jump to 0x200
> > which is the vector address for synchronous exception, from current EL
> > while using SP_ELx (if the vector base address was 0, which is the case).
> >
> > (Ref :
> > https://developer.arm.com/documentation/102412/0100/The-vector-tables
> > )
> >
> > When I read the 'EL' value by 'msr x8, currentel', x8 became '0x4' so
> > it is
> > EL1
> > (https://community.arm.com/developer/ip-products/processors/f/cortex-a
> > -forum
> > /10303/armv8-a-currentel-register-definition)
> >
> > How come cortex-a72 machines started at EL1?
> 
> Are you booting a kernel directly? In this case the kernel will boot into
> EL1 unless you specify -machine type=virt,virtualization=on in which case
> it will boot into EL2 and allow the kernel to utilise the virtualisation
> extensions.
> 
> > And if I want to make the virtual machine start at EL3 (this baremetal
> > code assumes it should be in EL3 after reset, and it runs ok in rtl
> > sim.), what should I do?
> 
> Generally as only firmware deals with EL3 you would have it running on
> some sort of flash device which the model would boot to directly in EL3
> rather than running the stub loader we have for the kernel. For example to
> load the EDK firmware you would have:
> 
>    -drive
> if=pflash,file=/usr/share/AAVMF/AAVMF_CODE.fd,format=raw,readonly=on \
>    -drive if=pflash,file=/home/alex/models/qemu-arm64-efivars,format=raw
> 
> as part of your command line. You also need to enable secure mode in the
> machine options (-machine type=virt,secure=on).
> 
> >
> > Thank you very much for reading.
> >
> > Chan Kim
> >
> >
> 
> 
> --
> Alex Bennée