linux-kernel - Re: [PATCH v1 4/5] powerpc: Remove cpu-as-y completely

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Date:   Mon, 20 Feb 2023 17:00:47 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>, jbglaw@...-owl.de
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 4/5] powerpc: Remove cpu-as-y completely

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> cpu-as-y is there to force assembler building options.
> But there is no need for that. Gcc is passed the necessary
> options and it automatically pass the appropriate option to
> GAS.
>
> GCC is given -maltivec when relevant, so no need
> for -Wa,-maltivec in addition
>
> And -Wa,-many is wrong as it will hide innapropriate
> instructions. Better to detect them and handle them on a
> case by case basis.
> -Wa,-many was added by commit 960e30029863 ("powerpc/Makefile:
> Fix PPC_BOOK3S_64 ASFLAGS") in order to fix an issue with
> clang and the passed -Wa,-mpower4 option. But we have now
> removed it expecting the compiler to automatically pass the
> proper options and instructions based on -mcpu=power4

I wanted to apply this one, but it caused a lot of breakage for big
endian Book3S-64 builds - where we build for power4 but have lots of
code that uses >= power5 instructions.

I'll try and get those all fixed and pick this up for the next merge
window.

cheers