Re: [PATCH v13 09/10] xen/riscv: introduce ANDN_INSN

[oleksii.kurochko@xxxxxxxxx]

On Wed, 2024-06-26 at 09:53 +0200, Jan Beulich wrote:
> On 25.06.2024 23:10, Andrew Cooper wrote:
> > On 25/06/2024 3:49 pm, Jan Beulich wrote:
> > > On 25.06.2024 15:51, Oleksii Kurochko wrote:
> > > > --- a/xen/arch/riscv/include/asm/cmpxchg.h
> > > > +++ b/xen/arch/riscv/include/asm/cmpxchg.h
> > > > @@ -18,6 +18,20 @@
> > > >          : "r" (new) \
> > > >          : "memory" );
> > > >  
> > > > +/*
> > > > + * Binutils < 2.37 doesn't understand ANDN.  If the toolchain
> > > > is too
> > > > +ld, form
> > > Same question: Why's 2.37 suddenly of interest?
> > 
> > You deleted the commit message which explains why:
> 
> Not really. My whole point is that while the intention of the change
> looks
> okay, description and comment describe things insufficiently, to say
> the
> least.
> 
> > > RISC-V does a conditional toolchain test for the Zbb extension
> > > (xen/arch/riscv/rules.mk), but unconditionally uses the ANDN
> > > instruction in emulate_xchg_1_2().
> > 
> > Either Zbb needs to be mandatory (both in the toolchain and the
> > board
> > running Xen), or emulate_xchg_1_2() needs to not use the ANDN
> > instruction.
> > 
> > I opted for the latter.
> 
> And I agree with that.
Okay, then I'll update that in the next patch version.

~ Oleksii