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

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Tue, 2024-06-25 at 22:10 +0100, 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:
> 
> > 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.
But we can't go without Zbb there are some things in <xen/bitops.h>
which now requires this extension. At the current state of development
it is mandatory.

~ Oleksii

> 
> I opted for the latter.
> 
> ~Andrew