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Subject: Re: [PATCH v2 4/5] bpf ppc32: add support for BPF_ATOMIC bitwise
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To: Christophe Leroy <christophe.leroy@csgroup.eu>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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From: Hari Bathini <hbathini@linux.ibm.com>
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On 11/06/22 10:44 pm, Christophe Leroy wrote:
> 
> 
> Le 10/06/2022 à 17:55, Hari Bathini a écrit :
>> Adding instructions for ppc32 for
>>
>> atomic_and
>> atomic_or
>> atomic_xor
>> atomic_fetch_add
>> atomic_fetch_and
>> atomic_fetch_or
>> atomic_fetch_xor
>>
>> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
>> ---
>>
>> Changes in v2:
>> * Used an additional register (BPF_REG_AX)
>>       - to avoid clobbering src_reg.
>>       - to keep the lwarx reservation as intended.
>>       - to avoid the odd switch/goto construct.
> 
> Might be a stupid question as I don't know the internals of BPF: Are we
> sure BPF_REG_AX cannot be the src reg or the dst reg ?
> 

AFAICS, BPF_REG_AX wouldn't be used as src_reg or dst_reg unless this
code is reused internally, by arch-specific code, for JIT'ing some other
instruction(s) using BPF_REG_AX as either src or dst reg..

Thanks
Hari