linux-kernel - Re: [PATCH v2] powerpc: Pass correct CPU reference to assembler

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Date:   Fri, 16 Dec 2022 17:57:46 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Segher Boessenkool <segher@...nel.crashing.org>
CC:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jan-Benedict Glaw <jbglaw@...-owl.de>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH v2] powerpc: Pass correct CPU reference to assembler

CC Joel for the -many subject.

Le 16/12/2022 à 18:18, Segher Boessenkool a écrit :
> Hi!
> 
> On Fri, Dec 16, 2022 at 09:35:50AM +0100, Christophe Leroy wrote:
>> The problem comes from the fact that CONFIG_PPC_E500MC is selected for
>> both the e500mc (32 bits) and the e5500 (64 bits), and therefore the
>> following makefile rule is wrong:
>>
>>    cpu-as-$(CONFIG_PPC_E500MC)    += $(call as-option,-Wa$(comma)-me500mc)
> 
> Yes.
> 
>> Today we have CONFIG_TARGET_CPU which provides the identification of the
>> expected CPU, it is used for GCC. Use it as well for the assembler.
> 
> Why do you use -Wa, at all for this?  The compiler should already pass
> proper options always!

That's historical I guess. Comes from commit 14cf11af6cf6 ("powerpc: 
Merge enough to start building in arch/powerpc.")

> 
>> +cpu-as-$(CONFIG_PPC_BOOK3S_64)	+= $(call as-option,-Wa$(comma)-many)
> 
> What is this for?  Using -many is a huge step back, it hides many
> problems :-(

The only thing I did is removed the -Wa,-mpower4 from the line, leaving 
the remaining part. Initialy it was:

cpu-as-$(CONFIG_PPC_BOOK3S_64) += $(call as-option,-Wa$(comma)-mpower4) 
$(call as-option,-Wa$(comma)-many)

It was added in 2018 by commit 960e30029863 ("powerpc/Makefile: Fix 
PPC_BOOK3S_64 ASFLAGS"). There is a long explanation it the commit.

Should we remove it ?

Christophe