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