Re: [PATCH] ARM: pxa: fix building with clang

Re: [PATCH] ARM: pxa: fix building with clang

[Robert Jarzmik]

Arnd Bergmann <arnd@kernel.org> writes:

> From: Arnd Bergmann <arnd@arndb.de>
>
> The integrated assembler in clang does not understand the xscale
> specific mra/mar instructions:
>
> arch/arm/mach-pxa/pxa27x.c:136:15: error: unsupported 
> architectural extension: xscale
>         asm volatile(".arch_extension xscale\n\t"
> arch/arm/mach-pxa/pxa27x.c:136:40: error: invalid instruction, 
> did you mean: mcr, mla, mrc, mrs, msr?
>         mra r2, r3, acc0
>
> Since these are coprocessor features, the same can be expressed 
> using
> mrrc/mcrr, so use that for builds with IAS.
Ok Arnd, but "mrrc" is an ARMv6 instruction if I'm not mistaken.
Yet PXA27X is an ARMv5 XScale instruction set IP.

Is that patch correct therefore, or is it just to make clang happy 
even if it's
not correct ?

Cheers.

--
Robert

Re: [PATCH] ARM: pxa: fix building with clang

[Arnd Bergmann]

On Sat, Dec 17, 2022, at 21:45, Robert Jarzmik wrote:
> Arnd Bergmann <arnd@kernel.org> writes:
>
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> The integrated assembler in clang does not understand the xscale
>> specific mra/mar instructions:
>>
>> arch/arm/mach-pxa/pxa27x.c:136:15: error: unsupported 
>> architectural extension: xscale
>>         asm volatile(".arch_extension xscale\n\t"
>> arch/arm/mach-pxa/pxa27x.c:136:40: error: invalid instruction, 
>> did you mean: mcr, mla, mrc, mrs, msr?
>>         mra r2, r3, acc0
>>
>> Since these are coprocessor features, the same can be expressed 
>> using
>> mrrc/mcrr, so use that for builds with IAS.
> Ok Arnd, but "mrrc" is an ARMv6 instruction if I'm not mistaken.
> Yet PXA27X is an ARMv5 XScale instruction set IP.
>
> Is that patch correct therefore, or is it just to make clang happy 
> even if it's not correct ?

According to

https://developer.arm.com/documentation/dui0231/b/arm-instruction-reference/coprocessor-instructions/mrrc-and-mrrc2?lang=en

"MRRC is available in ARMv6 and above, and E variants of ARMv5
excluding xP variants". I'm not entire sure what "xP variants"
means, but we do build for ARMv5E, so I think this is actually
correct.

    Arnd

Re: [PATCH] ARM: pxa: fix building with clang

[Robert Jarzmik]

"Arnd Bergmann" <arnd@arndb.de> writes:
> "MRRC is available in ARMv6 and above, and E variants of ARMv5
> excluding xP variants". I'm not entire sure what "xP variants"
> means, but we do build for ARMv5E, so I think this is actually
> correct.
Ah yes, and XScale is ARMv5TE.

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>

Cheers.

--
Robert