Re: [TF-A] Getting BUILD_STRING from FIP file

Hi Daniele,

TBBR specification, from where fip format was introduced, is not very clear about usage of serial number and it can be used in IMP DEFINED manner "ToC Serial Number - 32 - The serial number of this ToC".

So, theoretically it's possible to use serial number for the purpose you described and it's a valid use of currently (un)used serial number. Currently, at boot time serial number is checked against a non-zero value, which certainly will hold true if you put a valid timstamp instead of "0x12345678".

IMO you can go ahead and implement a mechanism to feed Build timestamp to be used as serial number.

Thanks Manish P

________________________________ From: TF-A tf-a-bounces@lists.trustedfirmware.org on behalf of Manish Badarkhe via TF-A tf-a@lists.trustedfirmware.org Sent: 11 February 2021 11:39 To: Daniele Alessandrelli daniele.alessandrelli@linux.intel.com; tf-a@lists.trustedfirmware.org tf-a@lists.trustedfirmware.org Subject: Re: [TF-A] Getting BUILD_STRING from FIP file

Hi Daniele

Please see my replies inline.

Thanks

Manish Badarkhe

From: Daniele Alessandrelli daniele.alessandrelli@linux.intel.com Date: Thursday, 11 February 2021 at 11:22 To: Manish Badarkhe Manish.Badarkhe@arm.com, tf-a@lists.trustedfirmware.org tf-a@lists.trustedfirmware.org Subject: Re: [TF-A] Getting BUILD_STRING from FIP file

Hi Manish,

Thank you very much for the information.

16 bits are not enough to store an epoch, but I'll see if I can encode some other unique build information into 16 bits.

Just a question, from your answer I assume that I shouldn't use the 'serial_number' field for what I want to do; so I wonder: what is that field meant to be used for?

'serial_number' field is non-zero number provided by the fip creation tool. It is hardcoded value i.e. TOC_HEADER_SERIAL_NUMBER=0x12345678 as of now. Specifically used during the validation of the TOC header in the code.

Regards, Daniele

On Thu, 2021-02-11 at 10:14 +0000, Manish Badarkhe wrote:

Hi Daniele

You can use the ‘flag’ field to mention the platform-specific data(in your case, a build number). Usage of the ‘flag’ field(64 bit) in the toc_header are as below: Bits 0-31 -> reserved Bits 32-47 -> platform defined data Bits 48-63 -> reserved You can make use of the flag[32:47] to put build information. I am not sure if you can accommodate epoch (converted timestamp) into this field but, you can encode any data to fit into this 16bit flag field to identify the FIP build.

You can use a build command: fiptool update/create --plat-toc-flags <platform defined data> <your fip bin path> to put the platform defined data in the FIP image.

Thanks Manish Badarkhe From: TF-A tf-a-bounces@lists.trustedfirmware.org on behalf of Daniele Alessandrelli via TF-A tf-a@lists.trustedfirmware.org Date: Wednesday, 10 February 2021 at 17:04 To: tf-a@lists.trustedfirmware.org tf-a@lists.trustedfirmware.org Subject: [TF-A] Getting BUILD_STRING from FIP file

Hi,

Is there a way to get BUILD_STRING (or a similar string / number that uniquely identifies the TF-A build, e.g., BUILD_MESSAGE_TIMESTAMP) from the FIP file?

Basically, I'm trying to find a way to know the build number of a FIP without flashing it.

I've seen that the FIP TOC header has a 32-bit field named 'serial_number'. Can it be used to this end? I'm considering converting BUILD_MESSAGE_TIMESTAMP into an epoch and adding it as 'serial number', but I'm worried that might be an unintended usage of the 'serial_number' field.

Regards, Daniele