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

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Date:   Tue, 1 Nov 2022 23:12:55 +0100
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 Sunday 09 October 2022 13:06:52 Pali Rohár wrote:
> 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?

Christophe, any input from your side?