powerpc: 32BIT vs. 64BIT (PPC32 vs. PPC64)

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:

> On Fri, 6 Jul 2018 21:58:29 -0700
> Randy Dunlap <rdunlap at infradead.org> wrote:
>
>> On 07/06/2018 06:45 PM, Benjamin Herrenschmidt wrote:
>> > On Thu, 2018-07-05 at 14:30 -0700, Randy Dunlap wrote:  
>> >> Hi,
>> >>
>> >> Is there a good way (or a shortcut) to do something like:
>> >>
>> >> $ make ARCH=powerpc O=PPC32 [other_options] allmodconfig
>> >>   to get a PPC32/32BIT allmodconfig
>> >>
>> >> and also be able to do:
>> >>
>> >> $make ARCH=powerpc O=PPC64 [other_options] allmodconfig
>> >>   to get a PPC64/64BIT allmodconfig?  
>> > 
>> > Hrm... O= is for the separate build dir, so there much be something
>> > else.
>> > 
>> > You mean having ARCH= aliases like ppc/ppc32 and ppc64 ?  
>> 
>> Yes.
>> 
>> > That would be a matter of overriding some .config defaults I suppose, I
>> > don't know how this is done on other archs.
>> > 
>> > I see the aliasing trick in the Makefile but that's about it.
>> >   
>> >> Note that arch/x86, arch/sh, and arch/sparc have ways to do
>> >> some flavor(s) of this (from Documentation/kbuild/kbuild.txt;
>> >> sh and sparc based on a recent "fix" patch from me):  
>> > 
>> > I fail to see what you are actually talking about here ... sorry. Do
>> > you have concrete examples on x86 or sparc ? From what I can tell the
>> > "i386" or "sparc32/sparc64" aliases just change SRCARCH in Makefile and
>> > 32 vs 64-bit is just a Kconfig option...  
>> 
>> Yes, your summary is mostly correct.
>> 
>> I'm just looking for a way to do cross-compile builds that are close to
>> ppc32 allmodconfig and ppc64 allmodconfig.
>
> Would there a problem with adding ARCH=ppc32 / ppc64 matching? This
> seems to work...

It's a cute trick but I'd rather avoid it.

It overloads ARCH which can be confusing to people and tools. For
example I'd have to special case it in kisskb.

I think we can achieve a similar result by having more PHONY defconfig
targets.

eg, we can do ppc32_allmodconfig like below. And if there's interest we
could do a 4xx_allmodconfig etc.

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 2ea575cb3401..2556c2182789 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -354,6 +354,11 @@ mpc86xx_smp_defconfig:
 	$(call merge_into_defconfig,mpc86xx_basic_defconfig,\
 		86xx-smp 86xx-hw fsl-emb-nonhw)
 
+PHONY += ppc32_allmodconfig
+ppc32_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/book3s_32.config \
+		-f $(srctree)/Makefile allmodconfig
+
 define archhelp
   @echo '* zImage          - Build default images selected by kernel config'
   @echo '  zImage.*        - Compressed kernel image (arch/$(ARCH)/boot/zImage.*)'
diff --git a/arch/powerpc/configs/book3s_32.config b/arch/powerpc/configs/book3s_32.config
new file mode 100644
index 000000000000..8721eb7b1294
--- /dev/null
+++ b/arch/powerpc/configs/book3s_32.config
@@ -0,0 +1,2 @@
+CONFIG_PPC64=n
+CONFIG_PPC_BOOK3S_32=y


cheers