[U-Boot] [PATCH] arm: Allow u-boot to run from offset base address

[Steve Rae]

On 14-06-10 11:45 PM, Albert ARIBAUD wrote:
> Hi Wolfgang,
>
> On Wed, 11 Jun 2014 06:49:28 +0200, Wolfgang Denk <wd at denx.de> wrote:
>
>> Dear Steve,
>>
>> In message <53979199.5010100 at broadcom.com> you wrote:
>>>
>>> OK - I think that one of the alternate proposals would be to
>>> conditionally reserve a "32 byte block" prior to the _start symbol (in
>>> "arch/arm/cpu/armv8/start.S") which would then be filled in by a
>>> post-processing step... This could be implemented by:
>>
>> Yes, that illustrates the idea.  However, this implementation suffers
>> from the use of an #ifdef where none is actually needed.  Instead, you
>> can create your own source file which defines the header; this could
>> be then even in it's own segment, say:
>>
>> your_header.c:
>>
>> struct your_header {
>> 	u_int32[8];
>> } your_header __attribute__ ((__section__ (".your_hdr")));
>>
>> All that is needed then is to make the linker place this segment in
>> front of the text segment.
>>
>> This avoids an ugly #ifdef, and also modifications in the common code.
>
> Agreed and seconded.
>
> Plus, using a dedicated 'header' section and a separate C source file
> for the header makes it automatic that if no input 'header' section
> were provided then no output 'header' section would be emitted; IOW,
> we would not need two different linker scripts, a single one would be
> useable for both 'headerless' and 'headerful' image types.
>
> Also, the alignment constraint should be configurable.
>
>> Best regards,
>>
>> Wolfgang Denk
>
> Amicalement,
>

Albert, Wolfgang, et al.

I didn't know about the automatic handling of "conditional" sections in 
the linker script file - Thanks!!!

So if I add a "your_header.c" as above, then

(1) I need to modify "arch/arm/cpu/armv8/u-boot.lds":
  	. = 0x00000000;

+ 	. = ALIGN(8);
+	.your_hdr : {
+		KEEP(*(.your_hdr*));
+	}
+
	. = ALIGN(8);
  	.text :
  	{

(2) then (I believe) I need to modify the "Makefile" to define the start 
address of this new section:
+LDFLAGS_u-boot += --section-start=".your_hdr"=CONFIG_YOUR_HEADER_ADDR

(3) and (I believe) I need to modify the OBJCOPYFLAGS (somewhere) in 
order to include this new section in the u-boot.bin:
+OBJCOPYFLAGS += -j .your_hdr

(... I don't actually have this working yet; so I suspect more changes 
are required ...)

And in the end, (I believe) I am just going to have a block (likely 4096 
bytes) prepended to the "original" u-boot.bin; which I can do today with 
no code changes at all....

Remember that original design request was effectively a two line change:
+	gd->mon_len += CONFIG_SYS_TEXT_BASE % 4096;
and
+	gd->relocaddr += CONFIG_SYS_TEXT_BASE % 4096;

Regrettably, since this is not going to be accepted, I am abandoning 
this change.
Thanks, Steve