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Re: [Xen-devel] Question about arch/x86/xen/mmu.c

On 12/04/2014 10:30 PM, Jan-Simon Moeller wrote:
Hi !

My name is Jan-Simon Moeller and I'm looking into compiling the kernel with
LLVM/Clang (see llvm.linuxfoundation.org) .

Right now we face this issue when compiling with clang:

  CC      arch/x86/xen/mmu.o
arch/x86/xen/mmu.c:1343:18: error: fields must have a constant size:
      'variable length array in structure' extension will never be
                DECLARE_BITMAP(mask, num_processors);
include/linux/types.h:10:16: note: expanded from macro 'DECLARE_BITMAP'
        unsigned long name[BITS_TO_LONGS(bits)]
1 error generated.

Question to the experts: why can't we just use NR_CPUS and be done with it ?
NR_CPUS will be setup by CONFIG_NR_CPUS and thus static.
( e.g. arch/x86/configs/x86_64_defconfig:CONFIG_NR_CPUS=64 )

This would expand the structure on kernels configured for many cpus
(e.g. 4096) but running on a smaller machine dramatically.


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