linux-kernel - Re: [PATCH v2] powerpc/boot: Don't always pass -mcpu=powerpc when building 32-bit uImage

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Message-ID: <20220827190013.c3odakqxqnqgkzxm@pali>
Date:   Sat, 27 Aug 2022 21:00:13 +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 v2] powerpc/boot: Don't always pass -mcpu=powerpc when
 building 32-bit uImage

On Saturday 27 August 2022 20:36:08 Pali Rohár wrote:
> On Saturday 27 August 2022 18:32:42 Christophe Leroy wrote:
> > Le 27/08/2022 à 19:36, Pali Rohár a écrit :
> > > On Saturday 27 August 2022 17:31:10 Christophe Leroy wrote:
> > >> Le 27/08/2022 à 15:39, Pali Rohár a écrit :
> > >>> For 32-bit uImage try to use CONFIG_TARGET_CPU option for -mcpu. This fixes
> > >>> following compiler 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
> > >>>
> > >>> For 64-bit uImage and 64-bit kernels with 32-bit uImage wrapper there is no
> > >>> change.
> > >>>
> > >>> Similar change was already introduced for the main powerpc Makefile in
> > >>> commit 446cda1b21d9 ("powerpc/32: Don't always pass -mcpu=powerpc to the
> > >>> compiler").
> > >>>
> > >>> Fixes: 40a75584e526 ("powerpc/boot: Build wrapper for an appropriate CPU")
> > >>> Cc: stable@...r.kernel.org
> > >>> Signed-off-by: Pali Rohár <pali@...nel.org>
> > >>> ---
> > >>>    arch/powerpc/boot/Makefile | 8 ++++++++
> > >>>    1 file changed, 8 insertions(+)
> > >>>
> > >>> diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
> > >>> index a9cd2ea4a861..f56a5f90a5d8 100644
> > >>> --- a/arch/powerpc/boot/Makefile
> > >>> +++ b/arch/powerpc/boot/Makefile
> > >>> @@ -44,8 +44,16 @@ else
> > >>>    BOOTCFLAGS	+= -m64 -mcpu=powerpc64
> > >>>    endif
> > >>>    else
> > >>> +ifdef CONFIG_PPC32
> > >>> +ifdef CONFIG_TARGET_CPU_BOOL
> > >>> +BOOTCFLAGS	+= -m32 -mcpu=$(CONFIG_TARGET_CPU)
> > >>> +else
> > >>> +BOOTCFLAGS	+= -m32 -mcpu=powerpc
> > >>
> > >> You can't do that. You get here only if user has selected
> > >> TOOLCHAIN_DEFAULT_CPU, in which case you don't want to for -mcpu=powerpc.
> > > 
> > > So do I understand it correctly that in this branch I should omit -mcpu=powerpc?
> > 
> > Correct.
> 
> Ok, I will fix it in v3.
> 
> > > 
> > >> -mcpu=powerpc is set when user selects CONFIG_POWERPC_CPU, in which case
> > >> CONFIG_TARGET_CPU_BOOL is set as well.
> > >>
> > >>> +endif
> > >>> +else
> > >>>    BOOTCFLAGS	+= -m32 -mcpu=powerpc
> > >>
> > >> Same, for PPC64 I think you don't want that either, unless the
> > >> CONFIG_GENERIC_CPU has been selected in which case
> > >> CONFIG_TARGET_CPU_BOOL is not set.
> > >>
> > >> When CONFIG_TARGET_CPU_BOOL is set for PPC64 you also want
> > >> -mcpu=$(CONFIG_TARGET_CPU)
> > > 
> > > I understand that this branch is called for PPC64 build with 32-bit
> > > uImage wrapper. So in this case should not be used TARGET_CPU as it
> > > would be 64-bit and not 32-bit as requited for 32-bit uImage wrapper.
> > 
> > Why ?
> > 
> > -mcpu=e6500 -m32 works as far as I can see.
> 
> Hm... I did not know that. Ok, if you want I will put it into
> -m32 -mcpu=$(CONFIG_TARGET_CPU) branch too.

And when CONFIG_TARGET_CPU_BOOL is not set but CONFIG_PPC64_BOOT_WRAPPER
is, should be -mcpu=powerpc64le or -mcpu=powerpc64 still passed?

> > > 
> > > Anyway, in this change I'm touching only PPC32 build, so all PPC64 stay
> > > as it was before.
> > > 
> > >>>    endif
> > >>> +endif
> > >>>    
> > >>>    BOOTCFLAGS	+= -isystem $(shell $(BOOTCC) -print-file-name=include)
> > >>>