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

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

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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@gmail.com>
>>>> ---
>>>> 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

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