linux-kernel - Re: [PATCH v3] powerpc/boot: Don't always pass -mcpu=powerpc when building 32-bit uImage

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Message-ID: <20221009110652.h7senqesk7nabxmn@pali>
Date:   Sun, 9 Oct 2022 13:06:52 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Joel Stanley <joel@....id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] powerpc/boot: Don't always pass -mcpu=powerpc when
 building 32-bit uImage

On Monday 29 August 2022 10:54:51 Pali Rohár wrote:
> On Sunday 28 August 2022 17:43:53 Christophe Leroy wrote:
> > Le 28/08/2022 à 19:41, Pali Rohár a écrit :
> > > On Sunday 28 August 2022 17:39:25 Christophe Leroy wrote:
> > >> Le 28/08/2022 à 19:33, Christophe Leroy a écrit :
> > >>>
> > >>>
> > >>> Le 28/08/2022 à 11:56, Pali Rohár a écrit :
> > >>>> When CONFIG_TARGET_CPU is specified then pass its value to the compiler
> > >>>> -mcpu option. This fixes following build error when building kernel with
> > >>>> powerpc e500 SPE capable cross compilers:
> > >>>>
> > >>>>       BOOTAS  arch/powerpc/boot/crt0.o
> > >>>>     powerpc-linux-gnuspe-gcc: error: unrecognized argument in option
> > >>>> ‘-mcpu=powerpc’
> > >>>>     powerpc-linux-gnuspe-gcc: note: valid arguments to ‘-mcpu=’ are:
> > >>>> 8540 8548 native
> > >>>>     make[1]: *** [arch/powerpc/boot/Makefile:231:
> > >>>> arch/powerpc/boot/crt0.o] Error 1
> > >>>
> > >>> corenet64_smp_defconfig :
> > >>>
> > >>>     BOOTAS  arch/powerpc/boot/crt0.o
> > >>> powerpc64-linux-gcc: error: missing argument to '-mcpu='
> > >>> make[1]: *** [arch/powerpc/boot/Makefile:237 : arch/powerpc/boot/crt0.o]
> > >>> Erreur 1
> > >>> make: *** [arch/powerpc/Makefile:253 : uImage] Erreur 2
> > >>>
> > >>>
> > >>
> > >> Seems like in fact, E5500_CPU and E6500_CPU are not taken into account
> > >> in CONFIG_TARGET_CPU, and get special treatment directly in
> > >> arch/powerpc/Makefile.
> > >>
> > >> This goes unnoticed because of CFLAGS-$(CONFIG_TARGET_CPU_BOOL) +=
> > >> $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
> > >>
> > >> I think we need to fix that prior to your patch.
> > > 
> > > It looks like that CONFIG_TARGET_CPU is broken.
> > > 
> > >    $ make ARCH=powerpc corenet64_smp_defconfig CROSS_COMPILE=powerpc64-linux-gnu-
> > >    ...
> > >    # configuration written to .config
> > > 
> > >    $ grep CONFIG_TARGET_CPU .config
> > >    CONFIG_TARGET_CPU_BOOL=y
> > > 
> > > CONFIG_TARGET_CPU_BOOL is set but CONFIG_TARGET_CPU not!
> > 
> > Yes, because there is no default value for E5500_CPU and E6500_CPU. We 
> > need to add one for each.
> 
> I see... Will you prepare this fixup for your previous patch?
> 
> And I think that following construct
> 
>   $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
> 
> should be changed just to
> 
>   -mcpu=$(CONFIG_TARGET_CPU)
> 
> Because if user specified that want build for specific target CPU, it
> should not be silently ignored.

Christophe, should I do something in this area?