ARM64 kernel Image size limitations?

[Florian Fainelli]

On 08/29/2017 01:15 AM, Ard Biesheuvel wrote:
> On 28 August 2017 at 22:24, Florian Fainelli <f.fainelli at gmail.com> wrote:
>> (fixed Will's address, apologies)
>>
>> On 08/28/2017 01:01 PM, Ard Biesheuvel wrote:
>>> Hi,
>>>
>>> On 28 August 2017 at 20:55, Florian Fainelli <f.fainelli at gmail.com> wrote:
>>>> Hi,
>>>>
>>>> I have been fighting with a reasonably large kernel Image: 46MB and
>>>> found unable to boot it. This is on v4.13-rc6, but I could go back as
>>>> far as v4.9~ish. It is so big, because it's got some debugging enabled,
>>>> and the initramfs compression is disabled, but still that ought to be
>>>> possible.
>>>>
>>>> After some experimentation I found that the breaking size is somewhere
>>>> around 33MB total for arch/arm64/boot/Image and when that happens, I get
>>>> the following backtrace which suggests that there is some memory
>>>> corruption of some kind (or so it seems to me), other experiments
>>>> indicated that the backtrace may point back to where the bootloader had
>>>> set up its exception vector. I am fairly confident that the bootloader
>>>> is not responsible for corrupting the Image that is loaded.
>>>>
>>>> Is there such a size limitation or am I possibly tripping over something
>>>> else?
>>>>
>>>
>>> What boot environment are you using? Is it possible the DTB is copied
>>> on top of the kernel by the boot loader?
>>
>> Bootloader is BOLT (Broadcom's own implementation, has PSCI and is
>> capable of doing FDT live patching), and yes the DTB is provided by the
>> bootloader at an address higher than the kernel.
>>
>> Physical offset of the RAM on this platform is 0, so the load is going
>> to be at PA 0x80000, 0x80000 + size (35MB) = 0x2280000, DTB is placed at
>> 0x771f000 and is 0x90ef bytes.
>>
> 
> Could you try to dump __log_buf from gdb?

Silly me, this is a bootloader limitation, unlike what I thought the
load address is not at PA 0, it is at PA 0x06FFC000 and there is only
~34MB worth of space available, mayhem ensues.

Thanks!
-- 
Florian