Hi Raef,

It's look like GCC create a separate instance for each fih_int variable and keep it even out of scope of visibility. So, each FIH_CALL produces own set of variables in function stack even for a release build.

> That is interesting - I was under the impression that having the structure marked as volatile was semantically the same as having all of its member volatile. Do you notice a considerable stack usage change with this fix?

For example there is difference about 500 bytes for tfm_hal_set_up_static_boundaries in our platform.

Best regards,

Roman.

-----Original Message-----

From: Raef Coles <Raef.Coles@arm.com>

Sent: Monday, December 11, 2023 11:09

To: tf-m@lists.trustedfirmware.org; Mazurak Roman (CSS ICW SW FW 3) <Roman.Mazurak@infineon.com>

Subject: Re: FIH volatile structure and stack usage

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Hey Roman

That is interesting - I was under the impression that having the structure marked as volatile was semantically the same as having all of its member volatile. Do you notice a considerable stack usage change with this fix?

I think if you do notice one, we'd be happy to have that change upstream. There's always some performance/size penalty to the FIH code but we should definitely try to minimize it if we can.

Raef

________________________________________

From: Roman.Mazurak--- via TF-M <tf-m@lists.trustedfirmware.org>

Sent: 08 December 2023 19:58

To: tf-m@lists.trustedfirmware.org

Subject: [TF-M] FIH volatile structure and stack usage

Hi all,

I found that using FIH medium/high profile with gcc  generates code that uses stack extensively. It happens because fih_int structure is marked as volatile.

Is there any reason why structure itself is marked as volatile? Why it’s not enough to make val and msk volatile members of fih_int structure?

Best regards,

Roman.