linux-kernel - Re: [PATCH] powerpc: allow cross-compilation of ppc64 kernel

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Date:	Fri, 6 Nov 2015 15:09:40 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Laurent Vivier <laurent@...ier.eu>
CC:	<benh@...nel.crashing.org>, <paulus@...ba.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc: allow cross-compilation of ppc64 kernel

On Thu, 2015-11-05 at 12:47 +0100, Laurent Vivier wrote:
> When I try to cross compile a ppc64 kernel, it generally
> fails on the VDSO stage. This is true for powerpc64 cross-
> compiler, but also when I try to build a ppc64le kernel
> on a ppc64 host.
> 
> VDSO64L fails:
> 
>   VDSO64L arch/powerpc/kernel/vdso64/vdso64.so.dbg
> /usr/bin/powerpc64-linux-gnu-ld: arch/powerpc/kernel/vdso64/sigtramp.o:
> file class ELFCLASS64 incompatible with ELFCLASS32
> /usr/bin/powerpc64-linux-gnu-ld: final link failed: File in wrong format
> 
> This fails because gcc calls "collect2" with
> "--oformat elf32-powerpcle" with ppc64 objects, without the
> "--oformat" ld works well because it use the format of the
> first object as output format.
> 
> As this case is correctly managed to build the other kernel
> objects, this patch replaces $(GCC) by $(LD) to generate the
> VDSO objects.

I cross-compile ppc64 kernels and have not seen this problem.  I do need to 
pass in -m64 as part of $(CC) if it's not the toolchain default, which is not 
nice, but the proper fix for that is to add -m64 in the makefiles -- and if I 
don't it fails way before VDSO.

Why is GCC building ppc64 object files but telling the linker --oformat elf32-
powerpcle?  Are different options somehow being passed to GCC in one case 
versus the other?

-Scott

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