Re: [PATCH v4 1/1] RISC-V: Add platform property/capability extensions

[Jin Ma]

> >> [Implications]
> >>
> >> (Due to reservation set size constraints)
> >> -   'Za64rs' -> 'Za128rs'
> >
> > Hi, Tsukasa
> >
> > Since I am not very clear about this extension, I have some confusion
> > about this
> > implication. Are we upside down this? In my opinion, shouldn't we
> > 'Za128rs' -> 'Za64rs'?
> 
> Hi Jin,
> 
> I am busy so that I cannot return to GNU Binutils development for a
> while but luckily I found your email now so I'll explain this.
> 
> <https://github.com/riscv/riscv-profiles/blob/f2e15b5d66988a7165e9167b50ef10d2fd03b402/src/profiles.adoc>
> 
> You can see the definitions of 'Za64rs' and 'Za128rs' above.
> I'll quote them here, too:
> 
> > Za128rs: Reservation sets must be contiguous, naturally aligned, and at most 128 bytes in size.
> > Za64rs: Reservation sets are contiguous, naturally aligned, and a maximum of 64 bytes.
> 
> The keywords here are "at most" / "maximum".  Smaller reservation set
> means stricter constraint (more fine grained control of atomic ops).
> 
> So, we can imply bigger reservation set constraint extension from the
> smaller one.  Of course, satisfying the condition of the 'Za64rs'
> extension is a superset of the 'Za128rs' extension, even if we account
> other conditions.
> 
> Sorry for a rushed response.
> Tsukasa

I see. Thank you very much for your quick and professional reply :)

BR
Jin