[U-Boot] [PATCH v2] x86: Fix how the location of the realmode and bios blobs are calculated

[Graeme Russ]

On 09/11/11 09:19, Gabe Black wrote:
> There are two blobs embedded into the u-boot image which are linked to run
> at an address which is different from where they actually end up in the
> ROM, one called "realmode" and one called "bios". There are realmode_setup
> and bios_setup functions which prepare those blobs by copying them into the
> location they're supposed to run from, among other things.
> 
> During u-boot relocation from ROM to RAM, the text and a few data segments
> are copied over. The realmode and bios sections are not copied, and so the
> only place they can be read from is their original location in the ROM.
> Looking specifically at the bios blob, there are symbols defined in the
> linker script called __bios_start and __bios_size which are defined to be
> the start and size of the blob in the ROM.
> 
> In the bios_setup function, there seem to be two mistakes happening. First,
> the offset from ROM to RAM is being added to __bios_start which implies that
> this code expects to use the copy moved to RAM. No such copy is made, so
> that's wrong. More subtly, when u-boot relocates itself, it goes through
> all of the relocations stored in .rel.dyn and fixes them up. This has the
> effect of transforming the __bios_start reference in bios_setup so that it
> refers to the version in RAM (if one existed) instead of the one in ROM. To
> correct for that, the offset actually needs to be subtracted out again to
> translate the address back into the ROM.
> 
> The net effect is that for both blobs, a + needs to be changed to a -.
> 
> Signed-off-by: Gabe Black <gabeblack at chromium.org>

Fixes breakage introduced by commit 5fed8211... 'x86: Fix incorrect usage
of relocation offset'

Acked-by: Graeme Russ <graeme.russ at gmail.com>