Re: [PATCH v3] arm: rust: Enable Rust support for ARMv7

["Arnd Bergmann" <arnd@arndb.de>]

On Fri, Jan 31, 2025, at 16:34, Christian Schrefl wrote:
202397be76d8037b531b34dee16c7dfcfd0124ef..3375c91e698c024f95a85682f5a91d9815c355e5 
>>> 100644
>>> --- a/arch/arm/Kconfig
>>> +++ b/arch/arm/Kconfig
>>> @@ -130,6 +130,7 @@ config ARM
>>>  	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
>>>  	select HAVE_REGS_AND_STACK_ACCESS_API
>>>  	select HAVE_RSEQ
>>> +	select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7
>> 
>> The ARMv7 dependency makes sense, but I think it needs
>> be disabled on combined v6/v7 kernels, like (CPU_V7 && !CPU_V6 && !CPU_V6K).
>
> That might be correct, I don't know much about the build
> system for the kernel. I've tried it and it still builds
> with this change.
>
> Also it should probably be relatively easy to support 
> armv6 as well.

ARMv6K should be trivial to support, as it contains the same
set of barriers and atomics as ARMv7, the main difference
being the lack of Thumb2 mode. The plain ARMv6 may be
a little harder to get right since that needs special barriers
and can only do 32-bit atomics but not 8/16/64.

As there is only really one relevant machine left with the
original ARMv6 (Nokia N8x0), we already plan to drop that
in a year, and I wouldn't put too much work into supporting
it. ARMv5 and earlier will stay around for a while longer,
but are getting rare enough that you probably don't need to
worry about those either.

     Arnd