U-Boot: Arm64: bootm gets stuck if RANDOMIZE_BASE is disabled

U-Boot: Arm64: bootm gets stuck if RANDOMIZE_BASE is disabled

[Ahsan Hussain]

Hello,

I'm dumbfounded by a seemingly unrelated early kernel hang/failing to 
boot when CONFIG_RANDOMIZE_BASE=n is set in kernel and we use FIT 
uImage. I've verified this behavior on a couple of i.MX8 SoCs (i.MX8M 
plus and i.MX8QXP) and the results remain consistent.

I'm able to boot kernel when I use booti command. However when I use 
bootm to boot a U-Boot fitImage (with kernel and fdt load 
addresses/entrypoint in .its file same as I used for booti command; also 
tried disabling relocation for fdt by setting fdt_high=~0UL), the boot 
gets stuck at "Starting kernel ...". On disabling RANDOMIZE_BASE kconfig 
in Linux the same fitImage is able to boot.

I've tried enabling earlycon and U-Boot debug messages in common/bootm.c 
and arch/arm/lib/bootm.c but found no helpful difference in both boot 
flows. Please let me know if I'm missing something obvious or where do I 
start looking to debug this issue.

Best regards,
Ehson


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: U-Boot: Arm64: bootm gets stuck if RANDOMIZE_BASE is disabled

[Mark Rutland]

On Tue, Jul 13, 2021 at 02:15:08PM +0500, Ahsan Hussain wrote:
> Hello,
> 
> I'm dumbfounded by a seemingly unrelated early kernel hang/failing to boot
> when CONFIG_RANDOMIZE_BASE=n is set in kernel and we use FIT uImage. I've
> verified this behavior on a couple of i.MX8 SoCs (i.MX8M plus and i.MX8QXP)
> and the results remain consistent.
> 
> I'm able to boot kernel when I use booti command. However when I use bootm
> to boot a U-Boot fitImage (with kernel and fdt load addresses/entrypoint in
> .its file same as I used for booti command; also tried disabling relocation
> for fdt by setting fdt_high=~0UL), the boot gets stuck at "Starting kernel
> ...". On disabling RANDOMIZE_BASE kconfig in Linux the same fitImage is able
> to boot.

Can you say which address you're trying to load the kernel to?

> I've tried enabling earlycon and U-Boot debug messages in common/bootm.c and
> arch/arm/lib/bootm.c but found no helpful difference in both boot flows.
> Please let me know if I'm missing something obvious or where do I start
> looking to debug this issue.

IIUC, the booti command respects the text_offset from the kernel header,
whereas bootm will not. If you have a hard-coded offset, it's possible
you're violating the offset the kernel expects, and where the kernel is
not relocatable, if can't fix itself up.

I suspect you have a hard-coded offset of 0x80000, whereas recent
kernels have a text offset of 0x00000. Your bootloader *should* read
this dynamially rather than hard-coding it.

For details, see:

https://www.kernel.org/doc/html/v5.4/arm64/booting.html#call-the-kernel-image

Thanks,
Mark.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: U-Boot: Arm64: bootm gets stuck if RANDOMIZE_BASE is disabled

[Ahsan Hussain]

On 7/13/21 2:25 PM, Mark Rutland wrote:
> On Tue, Jul 13, 2021 at 02:15:08PM +0500, Ahsan Hussain wrote:
>> Hello,
>>
>> I'm dumbfounded by a seemingly unrelated early kernel hang/failing to boot
>> when CONFIG_RANDOMIZE_BASE=n is set in kernel and we use FIT uImage. I've
>> verified this behavior on a couple of i.MX8 SoCs (i.MX8M plus and i.MX8QXP)
>> and the results remain consistent.
>>
>> I'm able to boot kernel when I use booti command. However when I use bootm
>> to boot a U-Boot fitImage (with kernel and fdt load addresses/entrypoint in
>> .its file same as I used for booti command; also tried disabling relocation
>> for fdt by setting fdt_high=~0UL), the boot gets stuck at "Starting kernel
>> ...". On disabling RANDOMIZE_BASE kconfig in Linux the same fitImage is able
>> to boot.
> Can you say which address you're trying to load the kernel to?
At 0xf0000000, towards the end of first DRAM bank which starts at 
0x40000000.
>> I've tried enabling earlycon and U-Boot debug messages in common/bootm.c and
>> arch/arm/lib/bootm.c but found no helpful difference in both boot flows.
>> Please let me know if I'm missing something obvious or where do I start
>> looking to debug this issue.
> IIUC, the booti command respects the text_offset from the kernel header,
> whereas bootm will not. If you have a hard-coded offset, it's possible
> you're violating the offset the kernel expects, and where the kernel is
> not relocatable, if can't fix itself up.

A minor correction is that when CONFIG_RANDOMIZE_BASE is _enabled_ the 
issue is gone. It is only observed when RANDOMIZE_BASE is _disabled_. 
Both booti and bootm calculate text_offset the same way based on arm64 
image header->image_size field, in booti_setup() routine from U-Boot 
arch/arm/lib/image.c.


Regards,
Ahsan

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: U-Boot: Arm64: bootm gets stuck if RANDOMIZE_BASE is disabled

[Ahsan Hussain]

Hello folks,

Any insight would be highly appreciated.

On 7/13/21 2:53 PM, Ahsan Hussain wrote:
>
> On 7/13/21 2:25 PM, Mark Rutland wrote:
>> On Tue, Jul 13, 2021 at 02:15:08PM +0500, Ahsan Hussain wrote:
>>> Hello,
>>>
>>> I'm dumbfounded by a seemingly unrelated early kernel hang/failing 
>>> to boot
>>> when CONFIG_RANDOMIZE_BASE=n is set in kernel and we use FIT uImage. 
>>> I've
>>> verified this behavior on a couple of i.MX8 SoCs (i.MX8M plus and 
>>> i.MX8QXP)
>>> and the results remain consistent.
>>>
>>> I'm able to boot kernel when I use booti command. However when I use 
>>> bootm
>>> to boot a U-Boot fitImage (with kernel and fdt load 
>>> addresses/entrypoint in
>>> .its file same as I used for booti command; also tried disabling 
>>> relocation
>>> for fdt by setting fdt_high=~0UL), the boot gets stuck at "Starting 
>>> kernel
>>> ...". On disabling RANDOMIZE_BASE kconfig in Linux the same fitImage 
>>> is able
>>> to boot.
>> Can you say which address you're trying to load the kernel to?
> At 0xf0000000, towards the end of first DRAM bank which starts at 
> 0x40000000.
>>> I've tried enabling earlycon and U-Boot debug messages in 
>>> common/bootm.c and
>>> arch/arm/lib/bootm.c but found no helpful difference in both boot 
>>> flows.
>>> Please let me know if I'm missing something obvious or where do I start
>>> looking to debug this issue.
>> IIUC, the booti command respects the text_offset from the kernel header,
>> whereas bootm will not. If you have a hard-coded offset, it's possible
>> you're violating the offset the kernel expects, and where the kernel is
>> not relocatable, if can't fix itself up.
>
> A minor correction is that when CONFIG_RANDOMIZE_BASE is _enabled_ the 
> issue is gone. It is only observed when RANDOMIZE_BASE is _disabled_. 
> Both booti and bootm calculate text_offset the same way based on arm64 
> image header->image_size field, in booti_setup() routine from U-Boot 
> arch/arm/lib/image.c.
>
>
> Regards,
> Ahsan
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel