[PATCH] board_f: Relocate fdt if SKIP_RELOC and fdt is in bss

[Kunihiko Hayashi]

Hi Simon,

Thank you for your comment.

On 2023/06/13 6:17, Simon Glass wrote:
> Hi Kunihiko,
> 
> On Thu, 8 Jun 2023 at 07:53, Kunihiko Hayashi
> <hayashi.kunihiko at socionext.com> wrote:
>>
>> There are cases that the devicetree blob is placed after _end, such as
>> fdt_find_separate() returns _end. This is in bss area cleared before
>> relocation.
>>
>> When GD_FLG_SKIP_RELOC is set, the blob is still in bss, but will be
>> cleared. As a result, the devicetree become invalid.
>>
>> To avoid this issue, should relocate it to the new fdt area using the
>> latter condition in reloc_fdt().
>>
>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko at socionext.com>
>> ---
>>   common/board_f.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/common/board_f.c b/common/board_f.c
>> index 51d2f3c365e9..9a245872d190 100644
>> --- a/common/board_f.c
>> +++ b/common/board_f.c
>> @@ -622,7 +622,8 @@ static int init_post(void)
>>   static int reloc_fdt(void)
>>   {
>>          if (!IS_ENABLED(CONFIG_OF_EMBED)) {
>> -               if (gd->flags & GD_FLG_SKIP_RELOC)
>> +               if (gd->flags & GD_FLG_SKIP_RELOC &&
>> +                   gd->fdt_blob != &_end)
> 
> !IS_ENABLED(CONFIG_OF_EMBED)  == IS_ENABLED(CONFIG_OF_SEPARATE)
> 
> reloc_fdt() is only called by U-Boot (not SP)
> 
> So the FDT was found by fdt_find_separate() and gd->fdt_blob == &_end
> 
> So, is there any case where:
> 
> gd->flags & GD_FLG_SKIP_RELO is true
> gd->fdt_blob != &_end is true
> 
> ?

Yes. But in fact,
if (gd->flags & GD_FLG_SKIP_RELOC is true) and (gd->fdt_blob overlaps .bss section),
the fdt should be relocated because clear_bss() will clear the fdt after that.

> I can't think of one.
> 
> If that is the case, then you could add a comment to this effect and
> unconditionally relocate if !CONFIG_OF_EMBED.

I'm not sure if it is possible to unconditionally relocate the fdt,
I think we need to know if the fdt overlaps .bss section.

> Of course the down size is that you would probably rather relocate it
> to just after BSS (rather than to the top of memory) but it doesn't
> much matter, I suspect.
Thank you,

---
Best Regards
Kunihiko Hayashi