On 13/11/11 13:31, Gabe Black wrote:
From: Gabe Black gabeblack@google.com
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@chromium.org
Applied to u-boot-x86/master
Thanks,
Graeme