Re: [PATCH for 4.21 v7 3/4] xen/riscv: make zbb as mandatory

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 2/26/25 3:49 PM, Jan Beulich wrote:

> On 26.02.2025 15:38, Oleksii Kurochko wrote:
> > On 2/26/25 1:58 PM, Jan Beulich wrote:
> > > On 20.02.2025 18:44, Oleksii Kurochko wrote:
> > > > According to riscv/booting.txt, it is expected that Zbb should be supported.
> > > >
> > > > Signed-off-by: Oleksii Kurochko<oleksii.kurochko@xxxxxxxxx>
> > > > ---
> > > > Changes in v7:
> > > >   - new patch.
> > > > ---
> > > >   xen/arch/riscv/arch.mk | 7 ++-----
> > > >   1 file changed, 2 insertions(+), 5 deletions(-)
> > > >           
> > > Please can you also tidy asm/cmpxchg.h of ANDN_INSN() then?
> > >         
> > Sure, I can leave only:
> > /*
> >   * To not face an issue that gas doesn't understand ANDN instruction
> >   * it is encoded using .insn directive.
> >   */
> > #define ANDN_INSN(rd, rs1, rs2)                 \
> >      ".insn r OP, 0x7, 0x20, " rd ", " rs1 ", " rs2 "\n"
> >       
> Wait, no - why would you? Patch 0.5 is supposed to be setting a baseline
> where Zbb is known by the tool chain. With that proper "andn" can be used
> wherever we like.
>     
I thought that Zbb in binutils (part of whic is gas) was added later then
I mentioned in Patch 0.5 but Zbb was added starting from 2.37, so we can
just really use `andn` instruction instead of `.insn` .

Thanks for clarification.

~ Oleksii