Re: [Qemu-arm] [Qemu-devel] [PATCH v2 05/14] target/arm/helper: zcr: Add build bug next to value range assumption

[Dave Martin]

On Mon, Jun 24, 2019 at 12:30:37PM +0100, Andrew Jones wrote:
> On Mon, Jun 24, 2019 at 12:05:07PM +0100, Dave Martin wrote:
> > On Fri, Jun 21, 2019 at 05:34:13PM +0100, Andrew Jones wrote:
> > 
> > The purpose of this check should probably at least be described in a
> > comment -- i.e., what actually depends on this?
> 
> I was thinking the already present "Bits other than [3:0] are RAZ/WI."
> explained that, but how about this for an improvement?
> 
> /*
>  * Only the lowest 4 bits of ZCR_ELx may be used to constrain the vector
>  * length, the rest of the bits are RAZ/WI. Since the vector length of
>  * 128-bits (1 in quadwords) is represented as zero in ZCR_ELx, and all
>  * vector lengths are represented as their length in quadwords minus 1,
>  * then four bits allow up to quadword 16 to be selected.
>  */

No, maybe the existing comment is enough.

I thought there might be more code elsewhere that assumes that checks
sve_max_vq <= ARM_MAX_VQ then then assumes that sve_max_vq <= 16.  But
if not, we probably don't need an additional comment here.

I haven't tried to understand all the code in the series beyond the
user/kernel interactions, so maybe I was just paranoid.

[...]

Cheers
---Dave