Re: [PATCH 2/2] powerpc/64: Use -mtune=pwr10/9/8 for clang

[Michael Ellerman <mpe@ellerman.id.au>]

Nathan Chancellor <nathan@kernel.org> writes:
> Hi Michael,
>
> Thanks for the workaround and sorry this has come to bite us :/
>
> On Fri, Mar 03, 2023 at 12:16:56AM +1100, Michael Ellerman wrote:
>> For the -mtune option clang doesn't accept power10/9/8, instead it
>> accepts pwr10/9/8. That will be fixed in future versions of clang, but
>> the kernel must support the clang versions in the wild.
>> 
>> So add support for the "pwr" spelling if clang is in use.
>> 
>> Reported-by: Nathan Chancellor <nathan@kernel.org>
>
> I think that should actually be
>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>

I guess yeah.

>> BugLink: https://github.com/ClangBuiltLinux/linux/issues/1799
>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Thanks.

>> ---
>>  arch/powerpc/platforms/Kconfig.cputype | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> Need to confirm the clang <= 16 statement is correct.
>
> Currently, this is indeed the case. It is possible that Nemanja's patch
> will get applied to release/16.x before 16.0.0 final but it might not.
>
> We can always update it later. I think we do want to push to get that
> patch applied because I forgot that it is only in 16.0.0 that '-mtune'
> starts to do something on PowerPC:
>
> https://github.com/llvm/llvm-project/commit/1dc26b80b872a94c581549a21943756a8c3448a3
>
> Prior to that change, '-mtune' was accepted but did nothing. It is only
> once it was hooked up to the backend that we got the spew of warnings. I
> think that warrants us trying to get Nemanja's patch into 16.0.0, which
> may allow us to drop this workaround altogether...

Aha OK, I missed that the warning was new in 16.

I'll sit on this for now then until we know if that change will make it
into clang 16.

cheers