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

From: Scott Wood
Date: Fri Nov 06 2015 - 16:10:09 EST

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/
> /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?


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