Re: ARM memory layout

["Daniel Krüger" <daniel.krueger@systec-electronic.com>]

Hi Sascha,

thanks for the help. The patches work for my non-relocatable barebox. 
Malloc space is now below barebox.

Best regards,
   Daniel

Am 16.06.2016 um 15:22 schrieb Sascha Hauer:
> Hi Daniel,
>
> On Thu, Jun 16, 2016 at 12:11:10PM +0200, Daniel Krüger wrote:
>> Hello,
>>
>> during the porting of barebox to a new i.MX35 board I stumbled over some
>> crazy things with the memory layout. The comments in file
>> arch/arm/cpu/entry.c seem to be wrong or at least misleading.
>>
>> We configured barebox as non-relocatable image. So I think the configured
>> TEXT_BASE is very important.
>>
>> I use the following configuration with 128 MB RAM:
>> CONFIG_TEXT_BASE=0x87000000
>> CONFIG_STACK_SIZE=0x100000
>> CONFIG_MALLOC_SIZE=0xd00000
>>
>> The stack is configured very large in this project, because of other reason.
>>
>> I get the following memory layout:
>>      0x87ffffff top of RAM
>>       |           free-space (see arm_mem_stack() in
>>       |                       arch/arm/include/asm/barebox-arm.h)
>>      0x87ff0000 start of 64 kB free-space (vector table)
>>      0x87feffff top of stack
>>       |
>>      0x87ef0000 start of 1 MB reserved stack space
>>      0x87eeffff
>>       |         16 kB early translation table
>>      0x87eec000 early TTB (translation table base)
>>      0x87eebfff malloc end
>>       |          13 MB malloc space
>>      0x871ec000 malloc start
>>       |         some small free space
>>       |         barebox binary
>>      0x87000000 TEXT_BASE
>>
>> This does not comply to the comment in the above mentioned source file.
>> There the malloc space and the vector table are missing.
>>
>> I would expect some check in the source code, when TEXT_BASE is too high or
>> barebox binary is too large, so they collide with malloc space or stack. By
>> reverse engineering the detailed memory layout above, I discovered that in
>> another project the TEXT_BASE falls within the malloc space.
>>
>> How does is run on other ARM boards? Are they all running with
>> CONFIG_RELOCATABLE=Y?
>
> Most of them do, yes.
>
> It seems !CONFIG_RELOCATABLE became broken with:
>
> | commit 65071bd0910ef109c86b9645c570a6ceed7de534
> | Author: Markus Pargmann <mpa@pengutronix.de>
> | Date:   Tue Dec 8 10:39:29 2015 +0100
> |
> |   arm: Clarify memory layout calculation
>
> I just sent out a series from which the first patch should fix your
> issue. The malloc space should be below the barebox image, not above it.
> BTW you shouldn't have to specify the malloc size, barebox can pick a
> sensible default for you if you specify it to 0.
>
> Sascha
>

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