Re: [PATCH bpf-next 4/8] arm32, bpf: add support for unconditional bswap instruction

[Puranjay Mohan]

On Tue, Sep 05 2023, Russell King (Oracle) wrote:

> On Tue, Sep 05, 2023 at 09:06:17PM +0000, Puranjay Mohan wrote:
>> The cpuv4 added a new unconditional bswap instruction with following
>> behaviour:
>> 
>> BPF_ALU64 | BPF_TO_LE | BPF_END with imm = 16/32/64 means:
>> dst = bswap16(dst)
>> dst = bswap32(dst)
>> dst = bswap64(dst)
>> 
>> As we already support converting to big-endian from little-endian we can
>> use the same for unconditional bswap.
>> Since ARM32 is always little-endian, just treat the unconditional scenario
>
> This is not true. Arm32 BPF is disabled for BE32 but not for BE8. It's
> entirely possible to build a kernel using BE8 for ARMv7 and have the
> BPF JIT enabled:
>
>         select HAVE_EBPF_JIT if !CPU_ENDIAN_BE32
>
> So it's not true to say "Since ARM32 is always little-endian".

Sure, I will change the commit message in next version.

Thanks,
Puranjay