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

[Wolfgang Denk]

Dear Steve,

In message <5398A640.3050105 at broadcom.com> you wrote:
> 
> 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 :
>   	{

ALIGN(8) looks pretty much bogus to me?

Quoting the "ld" docs:

'ALIGN(ALIGN)'
'ALIGN(EXP,ALIGN)'
     Return the location counter ('.') or arbitrary expression aligned
     to the next ALIGN boundary.  The single operand 'ALIGN' doesn't
     change the value of the location counter--it just does arithmetic
     on it.  The two operand 'ALIGN' allows an arbitrary expression to
     be aligned upwards ('ALIGN(ALIGN)' is equivalent to 'ALIGN(.,
     ALIGN)').

     Here is an example which aligns the output '.data' section to the
     next '0x2000' byte boundary after the preceding section and sets a
     variable within the section to the next '0x8000' boundary after the
     input sections:
          SECTIONS { ...
            .data ALIGN(0x2000): {
              *(.data)
              variable = ALIGN(0x8000);
            }
          ... }
     The first use of 'ALIGN' in this example specifies the location of
     a section because it is used as the optional ADDRESS attribute of a
     section definition (*note Output Section Address::).  The second
     use of 'ALIGN' is used to defines the value of a symbol.


Are you sure you do not ant to hae an ALIGN(4096) there?

> (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

Why?

> (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

Why?

> 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....

Well, we don't chaneg any code here, right? Just the linker script.
It's this, or some other script.  But the linker is the standard way
to create a linked image with the correct memory map, so this is the
right place...

> Remember that original design request was effectively a two line change:

Yes, indeed  But a pretty much bogus one.

Best regards,

Wolfgang Denk

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