[U-Boot] [PATCH 1/2] armv8: calculate __bss_size in u-boot-spl.lds

[Masahiro Yamada]

Hi.

(CCing Simon because he wrote the code addressed in this discussion.)


2017-01-17 18:27 GMT+09:00 Oded Gabbay <oded.gabbay at gmail.com>:
> Hi Mashiro,
> Could you please also take a look at the patch I sent to add the
> missing __bss_size ?
>
> Thanks,
> Oded
>
> On Mon, Dec 26, 2016 at 4:20 PM, Oded Gabbay <oded.gabbay at gmail.com> wrote:
>> This patch adds a missing __bss_size symbol to the default armv8
>> u-boot-spl.lds file.
>> Makefile.spl relies on __bss_size to be present when it creates the SPL
>> image. It uses that symbol to create a pad file that will be used to place
>> the dtb after the bss section.
>> In ARMv8 default u-boot-spl.lds, __bss_size was missing and therefore, the
>> pad file was always 0. As a result, the dtb was placed after
>> _image_binary_end, which caused a failure when loading it inside the SPL.
>>
>> Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
>> Cc: Albert Aribaud <albert.u.boot at aribaud.net>
>> ---
>>  arch/arm/cpu/armv8/u-boot-spl.lds | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm/cpu/armv8/u-boot-spl.lds b/arch/arm/cpu/armv8/u-boot-spl.lds
>> index cc427c3..e7799cc 100644
>> --- a/arch/arm/cpu/armv8/u-boot-spl.lds
>> +++ b/arch/arm/cpu/armv8/u-boot-spl.lds
>> @@ -70,6 +70,7 @@ SECTIONS
>>                 KEEP(*(.__bss_end));
>>         } >.sdram
>>
>> +       __bss_size = __bss_end - _image_binary_end;
>>         /DISCARD/ : { *(.dynsym) }
>>         /DISCARD/ : { *(.dynstr*) }
>>         /DISCARD/ : { *(.dynamic*) }



This patch seems wrong.


This linker script seems to support separate two memory regions.

MEMORY { .sram : ORIGIN = CONFIG_SPL_TEXT_BASE,
          LENGTH = CONFIG_SPL_MAX_SIZE }
MEMORY { .sdram : ORIGIN = CONFIG_SPL_BSS_START_ADDR,
          LENGTH = CONFIG_SPL_BSS_MAX_SIZE }


_image_binary_end is the end of the first region (.sram),
__bss_end is the end of the second region (.sdram).

So, with your patch,

   __bss_size = (gap between .sram and .sdram) + (size of .bss)

This will append really big padding there is a gap between the two regions.
(at least, it will break my boards.)


If you take a look at fdtdec_setup(),

    #  ifdef CONFIG_SPL_BUILD
    /* FDT is at end of BSS unless it is in a different memory region */
    if (IS_ENABLED(CONFIG_SPL_SEPARATE_BSS))
             gd->fdt_blob = (ulong *)&_image_binary_end;
    else
             gd->fdt_blob = (ulong *)&__bss_end;

I think you are supposed to enable CONFIG_SPL_SEPARATE_BSS
if you want to use SPL_OF_CONTROL on your arm64 boards.



Checking the following commit will help you.


commit 10172962479ddd6609101fdb83bde66c0719852c
Author: Simon Glass <sjg at chromium.org>
Date:   Sat Oct 17 19:41:19 2015 -0600

    dm: spl: Support device tree when BSS is in a different section

    At present in SPL we place the device tree immediately after BSS. This
    avoids needing to copy it out of the way before BSS can be used. However on
    some boards BSS is not placed with the image - e.g. it can be in RAM if
    available.

    Add an option to tell U-Boot that the device tree should be placed at the
    end of the image binary (_image_binary_end) instead of at the end of BSS.

    Note: A common reason to place BSS in RAM is to support the FAT filesystem.
    We should update the code so that it does not use so much BSS.

    Signed-off-by: Simon Glass <sjg at chromium.org>
    Signed-off-by: Michal Simek <michal.simek at xilinx.com>


-- 
Best Regards
Masahiro Yamada