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

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Message-ID: <20220829085451.upubyo5e7uop72lb@pali>
Date:   Mon, 29 Aug 2022 10:54:51 +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 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.