Re: How to start an armv8 machine in EL3?

[Alex Bennée]

ckim@etri.re.kr writes:

> 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

Hold on you've just switched from -M virt to -M ab21q? I don't even
recognise that model.

> 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.

Is it the instruction you expect? Try single stepping with gdbstub while
using -d int,exec,in_asm on your command line for more details.

>
> 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


-- 
Alex Bennée