[coreboot] C720 swapparoo

John Lewis jlewis at johnlewis.ie
Wed Jan 29 23:16:36 CET 2014

On 29/01/14 22:03, Aaron Durbin wrote:
>> This is where we reach the crux of the matter - In the stock/shellball
>> firmware, extracting BOOT_STUB doesn't yield a file which cbfstool in
>> upstream coreboot or CrOS coreboot can decipher. Looking at the file in
>> hexedit it appears to be almost identical to a CBFS that is recognised, but
>> that's it. I have managed to extract the SVGA binary from the CBFS in the
>> RW_LEGACY slot, and I've made an educated guess as to where the system-agent
>> begins and ends in the unrecognised CBFS (section beginning "LARCHIVE
>> mrc.bin" or similar with the binary itself following, surrounded by FF's)
>> copying and pasting it to a file. I would like to know if I am correct in my
>> assumptions about extracting that file manually and what size it should be,
>> in bytes?
> That's interesting. It is just a regular 'ol cbfs. The images that
> shipped with your device is an 8MiB SPI. First 2MiB Duncan covered.
> The next 5 have nothing to do w/ coreboot proper -- all the extra
> vboot firmware bits. The last 1MiB is the cbfs.

Okay, well I extracted the attached file using:

eval `./fmap_decode bios.bin | grep BOOT_STUB`
dd if=c720.rom ibs=$((area_offset)) skip=1 | dd bs=$((area_size)) 
iflag=fullblock of=c720-coreboot.bin


../coreboot/build/cbfstool c720-coreboot.bin print


1024 kB, bootblocksize 3144, romsize 8388608, offset 0x700000
alignment: 64 bytes

Name                           Offset     Type         Size


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