On 26/05/2021 19:23, Joel Sherrill wrote:
On Wed, May 26, 2021 at 6:02 AM Sebastian Huber
<sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>> wrote:
On 25/05/2021 20:33, Christian Mauderer wrote:
>
>>
>> I thought Sebastian added a "malloc" for the BSP to use before the
>> heap was initialized. But I don't remember the name. Am I
remembering
>> correctly?
>
> I don't really know that malloc. But I doubt that it works that
early.
> Again: Copying the FDT is one of the first things that these BSPs
do. If
> you want to know the exact location: For ARM it's here:
>
>
https://git.rtems.org/rtems/tree/bsps/arm/shared/start/start.S#n325
<https://git.rtems.org/rtems/tree/bsps/arm/shared/start/start.S#n325>
>
> So it's really basic setup before that. It's interrupt stack,
switching
> modes, setup stack pointer and then it's already copy FDT.
Yes, there is an early "malloc". This is _Memory_Allocate() using
_Memory_Get(). However, for the device tree copy this is not early
enough. We don't know the device tree location provided by the boot
loader. It could be somewhere in the memory area used by the
application. So, it is important to copy this very early into a fixed
location. Also, the device tree may be used to get the size of the
memory provided by _Memory_Get().
I assume read-only is only from the perspective of higher level
language code. Is it possible that being read-only it could be
mapped to Flash?
If the code is mapped to flash, the BSP is broken. I think there are
options for such a case so that the FDT is placed in another section.
Not sure whether any BSP is using them.
This kind of copy should be only done on BSPs that run out of RAM. Like
I said earlier: Normally that's the case for BSPs that are loaded by U-Boot.
For the purposes of minimum size analysis, I will subtract the
size of the FDT block from the minimum .text size and if it
is still over 64, flag it.
Sounds reasonable.
Best regards
Christian
--joel
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