linux-kernel - Re: [PATCH] powerpc: remove meaningless KBUILD

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Message-ID: <20190717143811.GL20882@gate.crashing.org>
Date:   Wed, 17 Jul 2019 09:38:11 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc: remove meaningless KBUILD_ARFLAGS addition

On Tue, Jul 16, 2019 at 10:15:47PM +1000, Michael Ellerman wrote:
> Segher Boessenkool <segher@...nel.crashing.org> writes:
> And it's definitely calling ar with no flags, eg:
> 
>   rm -f init/built-in.a; powerpc-linux-ar rcSTPD init/built-in.a init/main.o init/version.o init/do_mounts.o init/do_mounts_rd.o init/do_mounts_initrd.o init/do_mounts_md.o init/initramfs.o init/init_task.o

This uses thin archives.  Those will work fine.

The failing case was empty files IIRC, stuff created from no inputs.

> So presumably at some point ar learnt to cope with objects that don't
> match its default? (how do I ask it what its default is?)

The first supported target in the --help list is the default, I think?

$ powerpc-linux-ar --help
 [...]
powerpc-linux-ar: supported targets: elf32-powerpc aixcoff-rs6000 elf32-powerpcle ppcboot elf64-powerpc elf64-powerpcle elf64-little elf64-big elf32-little elf32-big plugin srec symbolsrec verilog tekhex binary ihex

$ powerpc64-linux-ar --help
 [...]
powerpc64-linux-ar: supported targets: elf64-powerpc elf64-powerpcle elf32-powerpc elf32-powerpcle aixcoff-rs6000 aixcoff64-rs6000 aix5coff64-rs6000 elf64-little elf64-big elf32-little elf32-big plugin srec symbolsrec verilog tekhex binary ihex

$ powerpc64le-linux-ar --help
 [...]
powerpc64le-linux-ar: supported targets: elf64-powerpcle elf64-powerpc elf32-powerpcle elf32-powerpc aixcoff-rs6000 aixcoff64-rs6000 aix5coff64-rs6000 elf64-little elf64-big elf32-little elf32-big plugin srec symbolsrec verilog tekhex binary ihex

$ powerpcle-linux-ar --help
 [...]
powerpcle-linux-ar: supported targets: elf32-powerpcle aixcoff-rs6000 elf32-powerpc ppcboot elf64-powerpc elf64-powerpcle elf64-little elf64-big elf32-little elf32-big plugin srec symbolsrec verilog tekhex binary ihex

> > Then again, does that work at *all* nowadays?  Do we even consider that
> > important, *should* it work?
> 
> Yes and yes. There were a lot of bugs in the kernel makefiles after we
> added LE support which prevented a biarch/biendian compiler from working.
> But now it does work and we want it to keep working because it means you
> can have a single compiler for building 32-bit, 64-bit BE & 64-bit LE.

Good to hear :-)


Segher