[coreboot] C720 swapparoo

John Lewis jlewis at johnlewis.ie
Wed Jan 29 23:44:34 CET 2014

On 29/01/14 22:27, Aaron Durbin wrote:
> On Wed, Jan 29, 2014 at 4:25 PM, Aaron Durbin <adurbin at google.com> wrote:
>> On Wed, Jan 29, 2014 at 4:16 PM, John Lewis <jlewis at johnlewis.ie> wrote:
>>> 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
>>> and:
>>> ../coreboot/build/cbfstool c720-coreboot.bin print
>>> produces:
>>> c720-coreboot.bin:
>>> 1024 kB, bootblocksize 3144, romsize 8388608, offset 0x700000
>>> alignment: 64 bytes
>>> Name                           Offset     Type         Size
>>> zippo.
>> Try cherry-picking this one:
>> https://chrome-internal-review.googlesource.com/153037
> Ugh. If only my copy/past worked. Try this one instead:
> http://review.coreboot.org/#/c/4771/

Okay. I ran:

git fetch http://review.coreboot.org/coreboot refs/changes/71/4771/1 && 
git checkout FETCH_HEAD

then ran make, which updated the binary, but still no change in reading 
the file.

I also compiled and ran the cbfstool in ./util in case that was somehow 
different, but same result.


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