On Feb 13 16:01, Peter Maydell wrote:
> On Thu, 2 Feb 2023 at 21:13, Aaron Lindsay <aa...@os.amperecomputing.com>
> wrote:
> > +static inline bool isar_feature_aa64_pauth_epac(const ARMISARegisters *id)
> > +{
> > + return isar_feature_pauth_get_features(id) == 0b0010;
>
> This should ideally be ">= 0b0010", but it depends a bit on
> where we call it.
FYI - I did make this `>= 0b0010` after changing the logic around elsewhere to
be compatible as you suggested. I'm also planning to add a comment like this:
/*
* Note that unlike most AArch64 features, EPAC is treated (in the ARM
* psedocode, at least) as not being implemented by larger values of this
* field. Our usage of '>=' rather than '==' here causes our implementation
* of PAC logic to diverge slightly from ARM pseudocode.
*/
> This field, like most ID register fields, follows the "standard
> scheme", where the value increases and larger numbers always
> imply "all of the functionality from the lower values, plus
> some more". In QEMU we implement this by doing a >= type
> comparison on the field value.
>
> The PAC related ID fields are documented slightly confusingly,
> but they do work this way. The documentation suggests it might not
> be quite that way for FEAT_EPAC because it says that
> HaveEnhancedPAC() returns TRUE for 2 and FALSE for 3 and up.
> However this is more because the definition of the architectural
> features means that FEAT_EPAC is irrelevant, and it's an accident
> of the way the pseudocode was written that means that
> HaveEnhancedPAC() ever gets called when FEAT_PAuth2 is present.
>
> Other than EPAC, the rest of the values in these fields are
> straightforward and we can implement the isar_feature functions
> with a single >= comparison.
Thanks for your review!
I've made a number of your (simpler) suggested changes already, and will
target getting a new patchset out in the next couple weeks after I spend
more time withi the the remaining GETPC() changes that need a little
more thought/rework, and we sort out what the command-line options
should look like.
-Aaron
